1:1: IntroductionIntroductionREV, the Racing Electric Vehicle, comes out of a strong tradition of Motor Sports at Florida Tech. For years now, Florida Tech has been competing in the Formula SAE and Mini Baja competitions. This year the team hopes to begin a new tradition at Florida Tech as we introduce Florida Tech to the growing field of electric racing.

The REV Team has built an electrically driven, open-wheel, single-seat, purpose-built vehicle optimized for Autocross racing. In Autocross, the drivers race through a flat road course that is often setup in a large parking lot. It takes only a few minutes to race through the tight, winding course in which the car must accelerate, decelerate, and corner very quickly. To help keep the weight and cost down, we will design the battery setup and gearing for the short, high acceleration races, where the speeds are usually between 20 and 40 mph. To decrease the cost and time of development, we plan to utilize legacy components from the 2001-2002 Florida Tech Formula SAE car. This should help decrease the overall cost for the project and reduce the design and fabrication time.

The REV team is composed of 12 members from various disciplines and is actively working to overcome the design, management, and communication challenges of the project.

1.1: Purpose1.1: PurposeThe ability to be powered by electricity generated from all types of alternative energy sources has drawn much attention towards electric vehicles. The significant efficiency advantage that electric motors have over internal combustion engines has determined their place in the future of automotive engineering. With the rise of electric motor systems in all design applications, an electric drive race car is exceedingly relevant.

The Racing Electric Vehicle (REV) project is a remarkable opportunity for students to become a management, design, and production team. Every student is learning in a whole new way as they must apply all their knowledge to this demanding practical challenge. Together, the students will learn to manage themselves and communicate in ways much closer to the industry than any other experience during college. Invaluable experience and knowledge will be gained by every student through this challenge, and with it one more piece to the developing array of electric powered vehicle knowledge.

This project also serves to highlight electric drive technologies on and off the Florida Tech campus in a visible, personally dramatic way. The team looks to draw the public and the campus community into the excitement of the project and the potential of electric power systems for the future. In that,

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they seek to further school spirit, Florida Tech’s relations with the community, and public interest in electric vehicle technology.

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1.2: Team Goals1.2: Team GoalsThe goals of the REV project are:

To design and build an electric vehicle for Autocross style racing which is competitive with Formula SAE and Formula Hybrid style cars.To diminish the challenges commonly associated with electric vehicles including Power to Weight Ratio and total cost. To build effective management, communication, and teamwork skills amongst the student team, mentors, sponsors, and the community.To allow time for thorough testing and optimization of the completed vehicle.To advance Electric Vehicle knowledge and public education/support.

1.3: Background1.3: BackgroundIn the 1830’s the first electric vehicle was invented by Robert Anderson in Scotland. This was a crude vehicle that was basically an electric carriage. Electric vehicles, or EVs, began to gain notice in America in the 1890’s and after this interest increased in vehicles such as the one in Figure 1 below.

This is the is the 1902 Wood's Phaeton it is a typical electric vehicle of the time, and had a cost of $2,000, a max speed of 14 miles per hour, and a range of 18 miles [1]. These vehicles were widely used because they lacked the noise and hand cranks of the gasoline vehicles, and most people only went around town so the small range was ideal for them.

As gasoline vehicles made advances, a decline began in electric vehicles. Electric vehicles made a return in the 1960’s and 1970’s when there was a push for environmentally friendly automobiles. Between this time and 1990 there were several companies that accomplished making vehicles that fit certain needs and most had ranges from 50-60 miles at around 40 miles per hour. These vehicles ranged from service trucks to city cars, and while these vehicles may not be widely known, they laid the ground work for the more modern electric vehicles. During the 1990’s there was another push for electric vehicles because of new regulations in pollution control. The US Department of Energy and several other companies began creating new vehicles from the ground up and converting existing vehicles to run on electricity. These new and converted vehicles, like in Figure 2, were trucks, vans, and even sports cars that could run at highway speeds with larger ranges than any of the previous electric vehicles. The downside to these vehicles was that they

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Figure 1. Historical EV

Figure 2. EV Pick-Up Truck

cost up to $40,000, but improvements in production are making these vehicles have prices on the same lines as gasoline vehicles.

Electrical vehicles are used in various applications: working in industrial plants, on golf courses, and on college campuses. Today these quiet, pollution-free vehicles are no longer overgrown golf carts. There has been a recent emergence of high performance open-wheeled electric race vehicles. These vehicles compete at well known race venues across the USA and demonstrate that electric vehicles are no longer slow lumbering vehicles. In the past there have been specific races catering to electric race cars. One of the more widely spread races among colleges was the Formula Lightning competition. Numerous universities across the country made serious entries into this competition every year it was held. In this race, most cars ran between 350 and 400 V at about 240 amps.

Also, other organizations, such as the National Electric Drag Racing Association (NEDRA), promote the sport of EV drag racing. For this vehicle however, the best competitions are the Formula Hybrid Competition, FLEAA (Florida Electric Auto Association) Autocross, and the Sports Car Club of America (SCCA) Solo Autocross competition. Autocross is made up of short (under 2 minute) races involving obstacles and straight track runs. Drivers race through a flat road course that is often setup in a large parking lot. The drivers run one at a time though the tight, winding course in which acceleration, deceleration, and cornering are most important. The electric vehicle design would race in a modified category and would run against all types of vehicles.

2: Design 2: Design ObjectivesObjectives For our electric vehicle, we have decided on specific design objectives we intend to reach. These objectives include:

Acceleration from 0 to 60 mph in under 5 secondsTop speed of 85 mphMaximum power available between 20 and 40 mph. Lightweight (under 650lb without driver)15 minute battery life running at high performance speeds

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3: Design3: Design3.0: Design Concept3.0: Design Concept3.0.1: Design EvolutionFrom the beginning of this project the car was always intended as an electric car. Based on the increased look toward the future and ways to divert from fossil fuels, electric cars have moved into the spot light. Designing and building an electric race car brings with it unique hurdles to overcome and requires more integration of electrical engineering work in the design process than for an internal combustion race car the same size.

To start the design functional specification where needed. To set those we had to know what competitions we would take part in. The first competition that was looked at was the formula lightning competition which is based on a longer race with battery exchange stops, but the competition no longer exists. The other competitions we looked at involved autocross style races (at least as part of the competition). The most prestigious one of them being the Formula Hybrid Competition by SAE and IEEE (All electric vehicles are allowed to enter for one year as “Hybrids in Progress”). This competition is constituted of an endurance race of 22km, an autocross style course, and an acceleration run (along with design judging). The vehicle needed to be designed to excel in all three races without any modifications. SCCA (Sports Car Club of America) racing and EV Rally are two other competitions, but their races involve just autocross and acceleration which are already encompassed in Formula Hybrid.

With these competitions in mind the functional specification for the car were set. The car needed to be as light as possible, run for at least a two and a half minute autocross race or a half hour endurance race, and accelerate and decelerate as quickly as possible, while keeping costs down and retaining reliability. The races give more specific rules related to safety which cover a multitude of areas from frame construction to wiring methods. The goals were simple, build a car to win at these competitions and advance Electric Vehicle technology in terms of Engineering and public knowledge/opinion.

Out of the goals came the functional requirements: accelerate from 0 to 60 mph in less then 5 seconds, have a top speed greater than 60 mph, have maximum drive train power available between 20 and 40 mph, weigh less then 650 pounds, and be able to run for 15 min.

There are many different components that have an influence on the cars performance and specifications. Only the main components such as motor configuration/power train, chassis design, and battery system will be covered in depth. All other components had less involved iterative design and will only be mentioned for the sake of brevity.

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The chassis design began with knowledge of common Formula SAE and other race car space frame design, the SAE chassis requirements, and the need to accommodate the motor, batteries, and differential. As seen in Figure DE01 the chassis first only incorporated one compartment in the rear to house either a dual motor configured setup or a single motor configuration with a chain and sprockets. (Figure DE02) For a dual motor configuration gear reduction is still needed for each motor and control algorithms to simulate the function of a differential. This type of system would involve a precise and integrated control system that would need significant development. The second major option was to use a single rear facing motor with a standard rear differential or a laterally mounted motor with a chain, sprocket, and center differential. The chain and sprocket method was avoided primarily because of the challenges of maintaining chain tension and integrity, as well as the size of sprocket needed for the large reduction required. Though electric motors generally have high torque, the lack of a transmission required a significant reduction (for further detail see the Motor and power train section). The other option for a single motor was chosen for its simplicity (just link the output from the motor to the drive shaft of the differential), and reliability (internal lubricated commercial helical gears). The decision between a single motor and multiple motors was incorporated into the overall motor choice. DC motors were chosen for their lower cost, greater simplicity, and the availability of knowledge in the EV (Electric Vehicle) community.

A spread sheet that incorporates motor speed-torque curves, battery specifications, gear ratios, and component weights was used to evaluate the different configurations against the functional specifications. Component availability, ease of construction, cost, and versatility (in light of unforeseen design changes) were also considered. As further information was gained this processes was applied in several iterations. The motor initially chosen was the Advanced DC FB-01 which was later replaced with the Warp 9 motor (a nearly identical motor, manufactured specifically for EV’s).

Other sources of power where considered, such as fuel cell and capacitors. Current Fuel Cells do not have a sufficient power to weight ratio for a race car. Capacitors on the other hand can provide large amounts of power in a very short time but don’t have the energy density needed to provide enough power for an entire race (without adding too much weight). The chosen battery setup was 500 A123 Li-Ion cells. The team did not acquire the funding to buy these batteries and there were complexities producing a working battery management system. The Li-Ion battery pack would have cost four times what the replacement pack of 16 Odyssey PC680’s cost, not including charging and battery management systems. The PC680 battery has the highest power to weight ratio of any Lead Acid battery that could be obtained in a configuration that would work in the car. The final motor,

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battery and controller configuration is a Warp 9” motor with 16 Odyssey PC680 batteries controlled by a Zilla 1K-HV motor controller. (Figure DE03)

The detailed evolution of the chassis can be found in the chassis section, and the both the calculations and logical process for selecting the motor setup, gear ratio, and differential are all listed in the motor and power train section.

From the beginning the vehicle was supposed to have extensive monitoring and control. To ensure this could be done a PLC system was designed to monitored multitude of heat, speed and voltage sensors. With the Lead acid batteries, the monitoring system became far simpler, only the speed, battery voltages, and a few other sources of data (which can be read about in the electrical section) are monitored. It outputs the data onto a student programmed touch screen that was mounted into the steering wheel. (Figure DE05). The process of redesigning the duties of the PLC primarily evolved with the battery monitoring and control system (which is at the heart of the Electrical Engineering Team’s design and research work).

Rims for the tires came off of another car and where adapted to fit the calculated optimal tires. The brakes where also taken from another car and only received new master cylinders because of a leak. The suspension was adapted to the weight it had to suspend repositioned during construction due to interference with the frame. Other components such as the swing arms and the differential mount where designed fairly quickly (as all the real design choices had been made beforehand).

3.0.2: Weight DistributionOne of the considerations important to all handling characteristics is weight distribution. Weight is needed in the front to provide sufficient traction for the steering wheels, while more weight in the rear increases the traction for acceleration. All wheels need weight on them for cornering, and the distribution onto the different wheels, and it’s height of the ground all effect the handling significantly. Keeping the center of graving as low to the ground as possible prevents body roll which can either cause roll over, or just reduce stability and the ability to track a corner. To keep it low, the car is designed with low ground clearance with all the heavy components (batteries, motor, and driver) fixed right on the lower frame.

The front to rear weight distribution is optimally for race cars is generally around 45/55 front/rear. After positioning the batteries as far forward as possible (the batteries provide and excellent adjustable counterweight) we were able to get the weight distribution to 47 / 53. The frame is assumed to be uniform and the heavy components were simply placed on a line and a simple moment calculation was done to determine the weight on the front vs. the rear.

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3.1: Chassis and Body3.1: Chassis and Body3.1.1: Frame3.1.1.1: Engineering Specifications

The specifications for the chassis are based on ideal characteristics for space frame design. A list of optimal values for this frame is provided in Table 3.1 below. The Formula SAE rules [15] regulate length, main hoop, driver clearance, and vehicle track. Deflection and maximum stresses are based on the material used in the frame. As stated in Material Study, 3.1.1.4, AISI 4130, Chromoly, is used. According to the American Society for Nondestructive Testing [5], a factor of safety for vehicles in this size is 3. This factor of safety is applied to all the stresses acting on the vehicle. Stress on the weld points is important factor because these areas may be a weaker point on the frame. We determined a maximum stress these welds handle to be sure our frame does not buckle at these weaker points. Torsional rigidity is based on data from other similar frame designs, see reference [19]. If the frame is too flexible (i.e. below 1600 ft-lbs/deg) the vehicle will not handle well.

Table 3.1: Engineering SpecificationsLabel ValueLength Minimum (front-to-rear wheels) 60 inch

Main Hoop Angle 10 º from vertical

Driver Head Clearance 2.00 inchVehicle Track (S = Small Track, L = Large Track) S>.75L

Deflection .333 inch

Torsional Rigidity >1600 ft-lbs/deg

Maximum Stress from Static Loading 21,300 psiMaximum Stress on Weld Points 26,600 psiMaximum Stress from Dynamic Loading 21,300 psi

Chassis also needs to follow some basic specifications. Because we reused part of the body from the 2001-2002 Formula SAE car, the chassis is designed to fit within that body envelope. The chassis accommodates the dimensions of a 95th percentile person, as defined by Formula SAE rules [15]. The chassis is designed and sized to support a motor and differential in the rear. The side pods need to follow certain envelope restrictions too. Side

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pods need to be designed as to not interfere with driver and be reasonable in size. The sidepod width should not extend past the mid-plane of the front wheels. The side pods should also be capable of supporting the size and weight of the battery packs.

3.1.1.2: Design ConceptsThe chassis went through a set of iterations of conceptual design then another set of iterations of optimization. The conceptual design utilized basic geometric patterns to construct the support on the chassis. Triangulation inherently creates rigid bodies instead of mechanisms being held still by the joints, so many of the developments of our chassis increased triangulation in the final conceptual design. The first design concept is shown in Figure 3. This concept represented the initial size of the vehicle, but would not adequately support the different weights. This design would not support the weight of the heavy components and the rear is not sized to support a motor, differential and a rear suspension setup.

Figure 3. First Conceptual Chassis Design

In the next conceptual revisions we added more triangulation for support and a better structure for supporting the various components. We took into consideration a two motor setup in this chassis, as shown in Figure 4a. This idea was eliminated due to the complexity of a dual-motor setup (especially the need for 2 gearboxes). A single motor inline with a geared differential became our final setup. For this idea we redesigned the rear section of the frame shown in Figure 4b for a differential mounting box. This design was changed due to manufacturability.

Figure 4. (a) Chassis Two Motor Setup, (b) Chassis with Differential Mounting Box

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(a) (b)

The next revision was developed with changes to the rear end. The chassis has more triangulation on the bottom surface and the rear differential support is now constructed with square tubing, as shown in Figure 5. This is lighter than the metal box and adequately supports the differential. This design is also easier to manufacture because it only involves welding steel tubing.

Figure 5. (a) Side view, (b) Top view

Now that the chassis has been developed, the side pods have to attach following the set specifications. The first concept of the side pod (Figure 6) was a general layout of columns of batteries and the general sidepod footprint. The idea was to have the side pod open to the outside to allow air to pass through the pod over staggered columns of batteries for cooling. This design rejected in favor of battery cooling which involved freezing packs of batteries during charging and then putting them in an insulated sidepod. Later it was learned that the batteries put out their best power between 70-100 oC. The final design provided for enclosed, but not insulated sidepods. The strength of the sidepods

was tested with excessive loads and passed with large safety factors, so they did not have to be redesigned to accommodate the 16 Lead acid batteries which were the final choice.Figure 6. Top view of side pod (First concept)

The second side pod conceptual design is shown in Figure 7. The changes allowed the side pod to have a side profile similar to that of the existing frame. This eases the construction and analysis of the side pods. The side pod shown in Figure 7 is mirrored to the other side. It fits within the envelope and adequately supports the battery packs. The side pod is built to be larger than needed for the batteries to accommodate any future 3

changes or additions.

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(a) (b)

Open to air flow

Front

Release air

Figure 6. Top view of side pod (First concept)

Release air

Figure 7: Top view of side pod

The final conceptual design of the chassis includes the side pods and some small changes from the previous layout. The variation of placement of the square tubing for the differential, bending of roll hoops for ease of manufacturability, and measurement changes to support the components are some changes made to this final chassis layout. Also, the chassis was evaluated and modified to incorporate the rules set by Formula SAE [15]. This latest version can be seen in Figure 8.

Figure 8. Final Chassis Concept

Next, the final conceptual frame design was optimized for handling and support. Cross members were added and variable wall thicknesses were changed for better support with reduced weight. Table 3.2 lists the optimization iterations the frame underwent from finite element analysis.

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(a) Isometric

(b) Side (c) Front

Table 3.2: Optimization IterationsIteratio

nDeflecti

on(inch)

Stresses

(psi)Cause of Change

1 .0068 8493 No change, conceptual chassis2 .0054 4341 Add cross member in chassis, see Figure 93 .0070 5706 Some member wall thicknesses changed

to .049”4 .0020 8934 Driver side support changed angle, see Figure

115 .0055 4348 Suspension perches wall thickness changed to

.095”6 .0054 4342 Suspension perches wall thickness changed to

.049”7 .0099 4929 Added Battery weight, increased overall

weight, and added side impact member

For the side pod, the second cross member was added to decrease the overall deflection (see Figure 9). This added support also stiffened the frame, increasing the torsional rigidity.

Figure 9. Side Pod cross members, iteration 2

To optimize deflections and stresses, the driver side support angle was changed as shown in Figure 10. The increase in stresses was too great to justify the decrease in deflection.

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(a)

Figure 10. (a) Driver side support, iteration 4, (b) Final design choice

3.1.1.3: Engineering AnalysisAll of the design modifications were taken into consideration in the analysis performed on the chassis. The chassis was evaluated using the ANSYS finite element analysis and ADAMS CAR simulation software. Beam 189 element type with sections was used in ANSYS for the analysis and the stress was compared using Von Mises stess criteria. All the calculations were originally done with a 550 pound car, but were redone with the new actual weight of the car of 945 pounds.

For static loading, the frame was generated in ANSYS and all heavy weight components were applied to the frame. These components include the motor, differential, driver, controller, and batteries. The frame is constrained at the attachment points of the suspension to accurately represent the actual model. Figure 11 shows a layout of the loads and constraints applied to the chassis for analysis. The batteries are applied as several loads to approximate their distribution of weight; as such the maximum load is placed at the back of the frame at the motor’s location. Figure 12 shows the max stress in the frame of 5361 psi. Figure 13 Shows the deflection in the frame which occurs at the side pods of the chassis because that is where all the batteries are being concentrated at.

Figure 11. Constraints and Loads applied for finite element analysis

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(b)

Figure 12. ANSYS Static Loading Stress Results

Figure 13. ANSYS Static deflection

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Figure 14. ADAMS Model of Vehicle

Figure 14 shows the ADAMS model that was used for dynamic analysis. In ADAMS, we used braking, cornering and lane change analysis. In doing so, the forces at each A-Arm attachment point were acquired. These forces, seen in Figures 15 and 16, were then applied to the ANSYS model at the attachment point locations to see the stress that occurred in the frame. Because we are evaluating the stresses applied at the A-Arms we needed to re-constrain the frame. For this we constrained the center of the frame at the front and rear of the chassis. With this constraint, the static loading is still taken into account in the dynamic loading. For braking in figure 17, the analysis was done for a 60mph to 0mph maneuver in 3 seconds. The lane change was done at 60mph and the cornering analysis, shown in figure 18, was done for a radius of 328 feet at a constant speed of 60mph. The analysis is conservative because the max loads applied in ANSYS from each ADAMS tests were applied to each point, even though they did not necessarily happen at the same time during the given ADAMS test. Therefore, a larger total load is applied to the frame for each dynamic force stress analysis scenario. Table 3.3 shows the results of each case.

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Figure 15. Loads applied on front A-Arm geometry

Figure 16. Loads applied on rear A-Arm geometry

The resultant stresses of cornering and braking yield higher values than those seen in a lane change. Since the frame can handle the loads of cornering and braking, the frame is obviously able to handle the loads from a lane change.

Table 3.3: Results of Forces from ADAMS  Cornering Breaking Lange change

point:Magnitude(Poun

d force)Magnitude(Poun

d force)Magnitude(Poun

d force)1 120.4975934 -275.9529775 135.0429207

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2 371.3843738 517.6900339 509.69234363 -164.7849552 -257.1814308 -312.02441564 112.6292804 419.1035129 139.04463555 -100.7144065 308.2180566 -146.22492216 243.0184674 -520.4889053 -164.45304637 -472.3235892 294.1479496 244.77496828 227.9562682 -300.7910758 188.61385969 -184.1185243 -420 -299.097589610 -72.61328859 183.0022764 155.153121911 -128.8155243 -294.9799285 75.3316421912 -30.12439836 229.4581833 56.2869837213 -106.1098211 286.5432614 -40.3358525814 -86.55144306 -143.3814472 67.4366973315 223.6848983 339.5376344 -126.257814416 176.2502113 -212.9197184 66.94110284

stress(psi) 16159 22126 NA

The expected max Von Mises stress that we experienced is 22126 psi with a factor of safety of 3, which is not below our engineering specification of 21300 psi, but is acceptable because this breaking condition is a worst case scenario. Under normal conditions, the max stress is below our specification with a value of 16159 psi.

Figure 17. Braking stress Figure 18. Cornering system

To prove that ADAMS analysis is correct, hand calculations for the lateral acceleration and lateral tire forces are calculated and then compared to the ADAMS output.

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Where a is radial (lateral) acceleration, v is velocity, r is the radius of turn, F is the force, and m is the mass of car.

The data output from ADAMS:a= F= 1555 N

Percent difference between ADAMS analysis and hand calculations:

The ADAMS analysis is obviously in agreement with the hand calculations.

Figure 19. Torsional Rigidity, (a) Loads and Constraints, (b) Stress Results

The torsional rigidity was calculated in ANSYS by constraining the back of the frame and one center point at the forward most hoop (see Figure 19). An upward force was applied on the left side of the hoop and a downward force was applied at the right side.

Using the displacements each node encountered, the torsional rigidity was calculated as:

Where k is the torsional rigidity, L is half the length of the hoop, y1 and y2 are the displacements of the nodes, and F is the force applied. Based on

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(a) (b)

other studies, 100 pounds of force is a reasonable amount of force to determine a rigid structure.

The welds at each intersection are another point that must be analyzed. We considered the weld as 1/8” fillet at the point of intersection. The weld material, type S70-2, is placed as 1/8” bead around the attachment points of the chromoly. This material has yield strength of 70,000 psi. Dynamic analysis showed the forces that each beam holds. These forces were then applied to a small section of the chassis. Then the stresses were observed just at the area of the weld material. Figure 20 shows the analysis results of the weld analysis. According to Finite Element Analysis, the highest stress the weld material will see is 14,608 psi. From this data, the welds will easily endure the stresses that the vehicle encounters.

Figure 20. Weld Analysis Stress Results

Table 3.4: Dynamic Stress and DeflectionMax Stress (psi) Max deflection (in.)

Dynamic Braking 22126 NADynamic Cornering 16159 NAStatic Loading 5361 .009

3.1.1.4: Material StudyAccording to Formula Hybrid/Formula SAE Competition Rules, the main assembly of the vehicle is to be made of round, mild or alloy, steel tubing (minimum 0.1% carbon). Other alternative materials may be used, like aluminum or composite materials, but need to follow these requirements listed in Formula SAE rules, section 3.3.3.2.1 [15] –

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(A) The material must have equivalent (or greater) Buckling Modulus EI (where, E = modulus of Elasticity, and I = area moment of inertia about the weakest axis)(B) Tubing cannot be of thinner wall thickness than listed in 3.3.3.2.2 or 3.3.3.2.3.(C) A “Structural Equivalency Form” must be submitted per Section 3.3.2. The teams must submit calculations for the material they have chosen, demonstrating equivalence to the minimum requirements found in Section 3.3.3.1 for yield and ultimate strengths in bending, buckling and tension, for buckling modulus and for energy dissipation.

Based on the rules, we studied the material properties of carbon steel, alloy steel, aluminum, and carbon fiber. For the materials under consideration, we compared strengths, corrosion resistances, machinability, weldability, availability, and costs of each of the materials.

Material Strength and Corrosion Resistance:For material strength we looked at the yield strength of the material and the modulus of elasticity. Table 3.4 shows a list of strengths of the various materials.

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Table 3.5: Material PropertiesMaterial Tensile Yield

StrengthModulus of Elasticity

Carbon Steel, ie AISI 1010 [3] 44200 psi 29700 ksiAlloy Steel, ie AISI 4130 [3] 64000 psi 29700 ksiAluminum, ie 6061-T6 [3] 40000 psi 10000 ksiCarbon Fiber [23] 34800 psi 10700 ksi

Machinability and Weldability:For alloy steel, specifically AISI 4130, the low carbon, about .30%, within the content of tubing makes for easy welding. This material can be machined by conventional methods. Machining is best under normal conditions. Welding can easily be done by all commercial methods [2].

For carbon steel, like AISI 1010, this alloy material is easily machined, welded, and fabricated. It can be machined very well in cold worked condition. It can be welded using any standard welding technique [2].

Machining and welding Aluminum 6061-T6 is an easy process. For this structure to adequately hold the stresses with this type of material, the frame would undergo a heat treatment process to restore it to T6 condition after being welded together. This process returns the material to a uniform hardness to eliminate stress concentration and return lost strength.

Since carbon fiber material is a layered composite it is treated differently than metals. The possible variations in layering can cause the material properties to change. Carbon fiber is not flexible and is often pre-manufactured for custom sizes because cutting is not recommended due to fibrous debris. Material is not welded; however, it is bonded together with itself or other materials.

Availability and Cost:The availability and cost of the each material played a big factor in our decision of frame material. Carbon Fiber is costly and not easily accessible. We also do not have the resources to handle this type of material for space frame tubing. Aluminum and steels are commonly available materials. However, Formula SAE rules state a thickness requirement of the tubing. This limits availability because not all materials under consideration are available in the required tube thicknesses. Cost of aluminum and steel are seen in Table 3.5.

Table 3.6: Material Cost [4]Material $ - .049” wall $ - .065” wall $ - .095” wall

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thick thick thickAISI 1010 $3.24/ft $2.52/ft $4.68/ftAISI 4130 $3.24/ft $2.52/ft $4.68/ftAluminum 6061-T6

- $3.24/ft $3.72/ft

Although carbon fiber material is very lightweight, it is expensive and not widely available. Aluminum becomes a much stronger alloy after heat-treating but a heat treatment process is expensive in time and money. Carbon steel is strong steel, but is not commonly used for tubing structure. This type of steel is used for bolts and fasteners. Alloy steel is a strong material which is harder to weld than aluminum but has material properties to support our frame. AISI 4130 chromoly is a readily available material that, with our resources, we hoped would be donated or discounted by local vendors. Based on all these facts, we decided to use an alloy steel, AISI 4130 chromoly steel tubing. It’s readily attainable, strong, and fairly easy to machine and weld.

3.1.2: Body3.1.2.1: Engineering SpecificationsThe design of the vehicle shell is constrained by several factors. First it must fit over the frame and various components outside the frame. Also, the shell needs to be removable for easy access to the internal components. It also needs to be somewhat aerodynamic (though is a minimal factor at most autocross speeds), and add as little weight as possible. The body is generally the most prominent feature for conveying the beauty of the vehicle. Therefore it was important to choose a body design and layout that will grab attention, respect, and appreciation.

To accommodate these requirements the rear of the car is open and the side pods will have hinged Lexan covers. The sidepods are simply boxed in with curved aluminum pieces. The front end of the body has been taken from the 2001-2002 Formula SAE car and modified to fit our components. The overall aesthetic impact of the body must be seen in of itself (currently not finished).

3.1.2.2: Design ConceptsThe shell of the car is designed around the frame and any externally mounted components. Figure 21 shows several artists’ renderings of original concepts of the shell of the body. The shape of the front body is that of the 2001-2002 Formula SAE car. The rest of the shell was created to accommodate any future changes in the frame.

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Figure 21. (a) Top View of Conceptual Body, (b) Isometric view of Body Design, (c) Top view of Body Design, (d) Side view of Body Design

A later revision of the body takes into consideration air vents for cooling the motor and controller, side pods to accommodate the batteries, and options for paint. These are shown in Figure 22. The final body is slightly different in shape, and does not include a rear section due to time constraints.

Figure 22. Optimal body with paint design

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(b) (d

)

(c)

(a) Single color

(a)

(b) Lightning design

3.1.2.3: Material StudyFor the shell of the vehicle, there were two types of materials that were considered: sheet metal, and fiberglass with resin. The sheet metal was considered because it would be easy to manufacture. The sheet metal is bent to the shape of the frame and then painted. Fiberglass involves more time and steps. Fiberglass first needs a form, or mold, and then several layers of fiberglass would be applied. We have the facilities and resources to work with both materials, and have used a combination of both. The front body from the 2001-2002 Formula SAE vehicle is utilized in combination with some fiber glass additions and several aluminum components. The fiberglass meshes with the current body shape while the aluminum is simply easier to form into clean shapes without good molds.

3.2: Vehicle Dynamics3.2: Vehicle Dynamics3.2.1: Suspension and Steering Geometry3.2.1.1: IntroductionWhen designing a suspension for a high performance vehicle such as this, many different parameters must be taken into consideration: wheelbase, track width, ground clearance, suspension geometry, and spring rates are just part of the equation. Unfortunately, not all of these variables can be optimized at the same time. The design of a suspension system is made into an iterative process in which decisions are made with certain parameters in mind and check to ensure other parameters are not greatly compromised. Finally, the designer must choose what is most important and make compromises accordingly.

3.2.1.2: Geometry AnalysisThe definition of track width is the distance of the centerlines of the tires when viewed from the front, see Figure 23. This dimension greatly influences the amount of resistance the vehicle has to the moment caused by the inertia forces acting at the center of gravity of the car. Looking at previous years’ cars, as well as other highly competitive schools vehicles, the track width is set to 52 inches front and 50 inches in the rear.

Figure 23. Track width

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Once the track width is decided upon, the geometry of the suspension can now be addressed. The first is the amount of caster. Caster is the angle of the steering axis when viewed from the side, shown in Figure 24. Positive caster is defined by the top of the steering axis being tilted back towards the rear of the car. By implementing positive caster, the outer wheel in a corner will camber negatively and thereby offset the positive camber induced by the body roll experienced in a corner. A moderate amount of caster also proves to be beneficial in providing the driver with feedback and good steering feel. The initial baseline value of caster in the front suspension is a positive 5° degrees.

Figure 24. Caster Angle

The next parameters to be considered are Kingpin Inclination (KPI) and Kingpin Offset (KPO). Kingpin offset (also know as Scrub Radius) is defined by the amount of distance between the centerline of the tire and the point of intersection between the steering axis and the ground plane (see Figure 25). This distance affects the amount of steering force required by the driver. Small amounts of KPO are beneficial for steering feedback, but need to be kept minimal to reduce any excessive steering forces. Kingpin inclination (defined as the angle between the steering axis and the wheel centerline seen in Figure 26) is used to help control the

25

Figure 25. Scrub Radius [26]

amount of KPO. Because packaging constraints often forces the KPO to be too great; in this scenario KPI can be used to offset this and bring the steering axis closer to the mid plane point on the ground plane. However, KPI has the negative drawback of adding positive camber to the outside wheel in a corner. We are utilizing the wheel centers and uprights from the 2001-2002 Formula SAE car which provides us with values of KPO and KPI. The wheel centers have an appropriate amount of backspacing to allow the uprights to

sit deep enough inside the wheel without the need of any KPI.

Next, the amount of static camber that will be built into the front suspension geometry is considered. Camber is defined by the angle that the wheel is offset from vertical when viewed from the front (see Figure 26). It is considered negative when the top of the wheel is inclined closer toward the center of the vehicle. By implementing negative static camber the positive camber induced by the vehicle rolling in a corner will be counteracted. The amount of static camber in our vehicle will be 1.5° negative but will be easily adjustable with shims between the chassis and the suspension pickup points. By using unequal length a-arms and manipulating the geometry, the amount of camber gain during suspension

travel can be controlled and utilized to ensure that the tire remains as flat as possible on the ground during suspension travel. Therefore, this ensures the contact patch of the tire is a maximum at all times and thereby supplies the maximum amount of grip in corners.

Locating the Roll Center of the geometry can be argued by some designers to be the corner stone of suspension design. The roll axis (the imaginary axis the vehicle rolls about in a corner) is defined by the front and rear roll center points. The roll center point is more clearly defined in illustration than in words (see Figure 27). After investigation of the illustration, the point is clearly defined by the geometry of the a-arms. By choosing proper pick up points on both the uprights and the chassis the roll centers, can be located according to the designer’s choice. Based on empirical data, the location of the roll center is historically located in a range just above or just below the ground plane. For our vehicle, the front roll center is as close to the ground plane as possible. However, the roll center is an instant center and moves as the suspension travels. So, our goal is to keep this roll center in as fixed a position as possible. A final layout of the front suspension geometry is shown in Figure 28.

26

Figure 26. Camber and Kingpin Inclination

Kingpin Inclination

Camber

Figure 27. Roll Center [26]

Figure 28. Front View showing Roll CenterIn Figure 29, the kingpin offset is seen in the

distance between the red line and the gray line just to the left of it. Note that these two lines are parallel showing the lack of kingpin inclination. Also seen in the figure is the amount of static camber that is built into the suspension. Figure 30 shows the amount of caster built into the suspension. The first iteration contains 5° of negative caster.

27

Kingpin Offset

Roll Center

Figure 30. Side View with caster

Figure 29. Front View with Kingpin Offset and CamberNow that the static geometry has been setup in the first iteration of the front suspension design, geometric analysis can take place. The substantial variables are the Static Roll Center, Roll center migration, and Camber Gain through suspension travel. Table 3.7 shows the break down of the suspension design and geometric analysis.

Camber gain is also an important value in suspension design. Because the A-arms are not equal in length, non-parallel, the amount of camber seen at the wheel will change as the suspension travels. The A-Arm geometry setup can be designed and analyzed as a simple four-bar mechanism. As the tire travels upwards relative to the chassis (known as Jounce) it experiences negative camber in the order of 1.035˚ for every inch of travel. Similarly, as the tire moves down relative to the chassis (known as Rebound) it experiences positive camber in the order of 0.954˚ for every inch of travel.

Table 3.7: Initial Front Suspension Geometry

Static Camber -1.5˚Camber Gain in Jounce -1.0353˚/

1"Camber Gain in

Rebound .954˚/1"Caster 5˚

Kingpin Offset .915"

28

Caster

Camber

Roll Center

Kingpin Inclination 0˚Toe In 0˚

Ground Clearance 1.5"Static Roll Center -.17"

Roll Center @ 1" Jounce -1.56"Roll Center @ 1"

Rebound 1.25"

Suspension design is an iterative process. With the front suspension geometry values determined, the data is evaluated to determine if values are in an acceptable range or need to be modified. The amount of migration the roll center undergoes and crossing the ground plane during migration is a concern. The first modification of the front suspension geometry analysis was to raise the ground clearance height to 2” (which ensures the chassis never bottoms out in full rebound). The rise in ground clearance will alter the location of all three listed Roll Centers (RC) and change the equivalent four-bar location. Thus this alters the amount of camber gain and loss through suspension travel.

Figure 31 shows an equivalent four-bar mechanism (red lines) of the suspension and the geometric layout. The two circles are the path that the upper and lower a-arms (the top and bottom red lines) travel on. The left red line is the chassis and the right red line is the upright. Using this geometry, the roll center migration and camber gain were analyzed. Figure 31 more clearly presents the equivalent four-bars that represent the front suspension. Figure 32 shows the suspension at equilibrium (in blue), at 1” of Jounce (in red), and at 1” of rebound (in green).

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Figure 31. Suspension Geometric Layout

Figure 32. Suspension at Equilibrium, Jounce, and Rebound

Before a complete geometric analysis of the rear suspension, several iterations of the static Roll Center (RC) were evaluated to determine a satisfactory static RC. The static RC for the rear is slightly higher than the front RC to allow the weight to transfer forward onto the front wheels and thereby increasing the load of the front tires to slightly improve traction. The only alteration made to the front was to increase the ground clearance to 2”. This allows the enough clearance for the amount of suspension travel desired while still allowing the cars Center of Gravity (CG) to remain low to improve vehicle dynamics. Tables 3.8 and 3.9 show the new suspension geometry and geometric analysis of the front and rear suspension.

Table 3.8: Current Front Suspension Geometry

Static Camber -1.5˚Camber Gain in Jounce -.95˚/1"

Camber Gain in Rebound .89˚/1"

Caster 5˚Kingpin Offset .915"

Kingpin Inclination 0˚Toe In 0˚

Ground Clearance 2"Static Roll Center 1.23"

Roll Center @ 1" Jounce -.18"Roll Center @ 1"

Rebound 2.65"Front Track Width 52"

Table 3.9: Current Rear Suspension Geometry

Static Camber 0˚Camber Gain in Jounce -1.05˚/

1"Camber Gain in

Rebound 1.02˚/1"Caster 3˚

Kingpin Offset 0.02"Kingpin Inclination 0˚

Toe In 1˚Ground Clearance 2"Static Roll Center 1.34"

Roll Center @ 1" Jounce 0.4"Roll Center @ 1"

Rebound 2.75"Rear Track Width 50"

Using ADAMS the vertical migration of the roll center during suspension travel can be determined for the full range of motion. Figure 33 shows the suspension through its motion by moving the platforms that the tires rest on.

30

ReboundJounce

Equilibrium

The graph is a plot of the position of the roll center (in mm) through the entire range of motion. The maximum vertical displacement of the roll center is just over a half an inch. Note that this value differs from the previous roll center displacement value because the analysis done using the equivalent four-bars was for symmetric suspension motion where this analysis was for the motion of the A-arms in opposite directions. Therefore, the equivalent four-bar analysis is more relevant for pure acceleration and braking where the ADAMS analysis is more relevant for cornering. With that said, the roll center location for cornering is more important because the vehicle is rolling while turning a corner. Minimizing the migration of the roll center to maintain predictable and near constant handling is important and it becomes clear that a small value of roll center movement is ideal.

Figure 33. ADAMS Analysis of Suspension

The Rear Suspension geometry layout can be seen in Figure 34 and Figure 35. Notice clearance was created for the suspension clevises to move up and down on the chassis rail to allow easy manipulation of the geometry and therefore the ability to ideally locate the Roll Center. Figure 35 shows the amount of Toe In visible in red. When designing a suspension, the analysis is based on theoretical values and the actual layout will differ from these values. With this in mind, it is wise to build in a certain amount of adjustability whenever possible. For our vehicle we used suspension pickup clevis, seen in Figure 36, that are bolted to allow shimming between the clevis and the chassis which adjusts the amount of camber built into the suspension and the static roll center. Furthermore, in the rear the clevises are placed on the vertical rails (which is made of square tubing for ease of adjustability). In this way, the clevises may be shimmed, and moved up or down along the rails to adjust the roll center, camber gain, and static geometry (see Figure 36).

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Figure 24. ADAMS Analysis of Suspension

By analyzing the lateral weight transfer of the vehicle based on the parameters listed below the amount of load on each wheel can be calculated. Because the most weight transfer occurs during hard cornering this will be the time in which there is the most load on the tires and therefore the time of maximum suspension travel. As mandated by the SAE rules the car must have 1 inch of travel in both directions. Therefore if we find the maximum load during cornering and want the suspension to travel one inch during that load we have found our spring rate. The following calculations assume a 1g corner. This assumption is reasonable in light of researching high performance vehicles with maximum cornering capabilities of around 1g.

The idea of calculating the weight transfer in suspension is that the spring rates must be assumed in order to calculate the lateral roll resistance of the vehicle. Therefore an excel spreadsheet is produced to make easier iterative calculations. Because the spring rates are given by the maximum load divided by one inch, the numerical value of the maximum load becomes the numerical value of the spring rate. Table 3.10 lays out the iterative process of the spring rate calculations. The terminology and calculations can be found in the Appendix, section 7.1.

Table 3.10: Suspension Spring Rate CalculationsTOTAL

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Figure 35. Top View of Rear Suspension

Clevis

Bearing

Figure 36. Shimmed Clevises

Suspension Rail

Figure 34. Rear View of Rear Suspension

SW WDR TM CM GM LM St Wt850 0.51117

650.97765

1.286229

14.53353

13.2473

220.8851

256.0887

850 0.511176

50.97765

1.286229

14.53353

13.2473

220.8851

256.0887

850 0.511176

50.97765

1.286229

14.53353

13.2473

220.8851

256.0887

The spring rates derived from the calculations were approximately 350 lb/in for the front and 375 lb/in for the rear. Do to availability of coil over springs made for the dampers we are running we are using 300 lb/in springs up front and 372 lb/in in the rear. After some testing theses spring rates having proven to work well.

The dampers chosen for the vehicle are Jupiter 5 coil over dampers made by Risse Racing. These dampers are originally designed for mountain bikes but are very commonly used in Formula SAE vehicles. These dampers were chosen due to there adjustability in jounce, rebound, spring preload and overall damping by changing the nitrogen charged pressure

3.2.1.3: Material StudyFollowing the logic behind our material use for the chassis, the suspension components are primarily be made of chromoly tubing. The tube diameter is 5/8 inch based on data from previous years’ vehicles. This diameter and wall thickness of the tubing is verified using FEA analysis on the suspension components. Before FEA can take place, the suspension is placed in an ADAMS simulation to determine the forces acting on the suspension components and where they are acting.

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(b)

(a)

The manufacturing of the a-arms will include flattening them at the ends to join to the bearing rings where the bearings mount shown in Figure 37. The spherical bearings are mounted to the A-Arms by press fitting them into the rings welded to the ends of the tubes. Aurora Bearing [20] recommends using this process. The bearings allow 24˚ of misalignment which is sufficient for our design.

3.2.1.4: SteeringMuch of the design strategy behind the suspension is directly related to the steering of the vehicle since it is the suspension’s primary job, in a race car, to provide maximum grip and optimum handling. What remains is what actually turns the wheels. Our vehicle employs rack and pinion steering mounted just above the lower A-arm and just behind the front axle. This configuration offers the most clearance for the driver’s legs and more importantly enables full Ackermann geometry to be achieved easily. Ackermann geometry allows the inner wheel to turn a tighter radius during cornering and eliminates slip angle which is ideal for this style vehicle.

3.2.2: Braking3.2.2.1: Engineering SpecificationsAccording to the SAE rules [15], the brake system must act on all four wheels and operate by a single control. It must have two independent hydraulic circuits in case of a leak or failure the braking power is maintained. We will dynamically test the brake system to show the brakes lock all four wheels and stop the vehicle in a straight line at the end of an acceleration run. A brake pedal over-travel switch is required on the car. In the event of the brake pedal extending beyond its range, this switch will be activated and will stop the vehicle. This switch will cut the power to all electrical devices. The switch is executed with analog components, and not through the programmable logic controller. The car will have a red brake light which is clearly visible from the rear. This light is mounted between the wheel centerline and driver’s shoulder level on the vehicle centerline laterally.

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Figure 37. (a) A-arm with flattened ends at bearing rings (above), (b) pressed bearing welded to the a-arm (below).

The original components of the brake system were taken from the 2001-2002 Formula SAE car. The caliper and rotor are built into the upright, as seen in the Figures above. This brake system includes a Wilwood combination “remote” tandem master cylinder, which meets the Formula SAE specifications [15], calipers with brake pads, rotors, brake lights, and steel braided Teflon hoses.

3.2.2.2: Design ConceptsThe brake systems was collected and inspected to verify all the parts we present and still in working order. It was determined that the only parts that needed to be purchased were steel hard brake lines and brake fluid. However, after some actual usage, the original master cylinders were replaced with newer cylinders due to severe leaks. The new cylinders also have the advantage of screw on caps which are much easier to work with. 3.2.2.3: Engineering AnalysisCalculations were done to verify that the brakes could provide adequate stopping distance for the vehicle. It was found that, with assuming a no slip condition for the wheels, the brakes could bring the car from 60 mph to a stop in 124.73 feet (a very reasonable number in comparison with modern sports cars). Using the coefficient of friction of 1.7 (estimated for warm, broken in tires) the car could theoretically be stopped in 70.73ft, this however is not possible due to the power of the brakes. It is would also be unlikely for the tires to actually achieve their 1.7 coefficient of friction in most situations and in emergency braking there would likely be a combination of slipping (kinetic friction) and rolling (static friction) which would also increase the stopping distance . Detailed brake calculations can be found in the Appendix, section 7.1.

3.2.2.4: Material StudyThe rotors are made from hardened steel and meet the specifications for handling the forces applied during braking.

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Figure 38. Brake and upright Assembly

Figure 40. Brake Pedal and Master Cylinder

Figure 39. Brake and upright Assembly

Because our vehicle is designed to run primarily in autocross competitions it will need to be able to accelerate very quickly and stop very quickly to achieve fast times through the tight and winding course. Therefore, we will use disc brakes with cross drilled rotors (reduces heat buildup during repeated breaking) on all four wheels of the vehicle.

3.2.3: Wheels, Tires, and Uprights3.2.3.1: Engineering SpecificationsAccording Formula SAE rules [15], 10” and a 13” wheels can be used. To reduce the budget, wheels from the 2001-2002 Formula SAE car are being reused. The wheel shells are 13” three piece all aluminum shells, from Keizer Company [21]. The shell consists of two pieces that are bolted together along with the magnesium centers shown in Figure 41 and 42.

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Figure 41. Front view, Wheel shell and center

The uprights were also taken from the 2001-2002 Formula SAE car. The uprights, in Figure 43, are made from 6061-T6 aluminum and were manufactured to fit inside the shells, as shown in Figure 44. The suspension was designed to accommodate these uprights so that they provide correct amounts of inclination. The uprights’ unique design includes the calipers and rotors for the braking system.

Figure 43. Front Upright brake assembly

Tires selection is based on a number of different factors. The diameter of the tire is chosen based on the selected wheel size. Since the wheel shells are reused, the tires are constrained to 13” tires. However, this is an optimal size for the vehicle because of the overall weight of the car. Another factor is the width of the tire. The width of the tire is dependent on operating temperatures. Once the tires are at operating temperature, the tires will reach its full handling potential. The wider the tire, the more mass it has, thus the longer it will take for the tire temperature to rise. Since power conservation is a concern with limiting battery run time, “warming” the tires before a race will not be an option. To compensate, a thinner tire is used to reduce the time it would take the tire the reach its operating temperature (while still maintaining a good width for a contact patch). These are Goodyear 13” by 6.5” (D1383, R065 - 18.0x6.5-10) racing tires (Figure 45).

Figure 44. Rear Upright, brake, wheel, tire assembly

Figure 42. Rear View, Wheel shell and center

This tire has an operating temperature of approximately 60-70 degrees Celsius.

Figure 45. Goodyear D1385, R065 - 20.0x6.5-13 [7]

3.2.3.2: Design ConceptsOriginally two tire widths had been chosen – 7.5” and 6.5”. The 7.5” tire was a possibility because it is readily available. The 6.5” tire is also an option because it weighs less and can reach its operating temperature faster than the 7.5” tire. Both tires are compatible with our chosen wheel shells (which can accommodate some variation in tire size and still maintain pressure). In this case the Keizer wheel shells can handle both 6.5” and 7.5” tire width.

3.2.3.3: Engineering AnalysisThe following calculation is a simple design calculation to determine the distance it takes a tire to reach its operating temperature. Some assumptions are made based on values for tires and vehicle. The following data and assumptions are used in our calculation.

Tires:Mass of 7.5” wide tire: 13 lb = 5.896 7 kgMass of 6.5” wide tire: 9 lb = 4.082 3 kg

Temperature:Ambient Tire Temperature: 25ْ C = 298.15 KelvinDesired Final Tire Temperature: 70ْ C = 343.15 Kelvin

Assumptions:Full slippageOverall Car weight with 150lb driver: 945 lb = 428.64 kgConstant Specific heat is equal to rubber (Cv): 1600 J/kg-K Assuming a coefficient of friction: 1.7

Where mtire is the mass of the tire, Cv is the specific heat of the tire, Tdesired is the desired tire temperature, Tamb is the ambient tire temperature, m is the coefficient of friction, mcar is the mass of the entire vehicle, and g is gravity.

It was found that the 7.5” tire will take 1115.98 feet and the 6.5” tire only 772.54 feet. These calculations prove that the 6.5” width tires can reach full potential at a shorter distance than the 7.5” width tires. Based on these conditions, the 6.5” width tires are preferred.

3.2.3.4: Material Study Tires selection is based on weather, dry or wet, compound, and size. For our application, tires will be dry slicks. The tire material is made on only one type of compound – R065 compound. Sizes of the tires vary, but for our application a best fit tire is a 13” rim with a 6.5” tire width as proven in the engineering analysis. These types of tires are not commonly used and only sold from two companies, Goodyear and Hoosier. The prices for these tires are comparable, $153 from Goodyear [7] and $133 from Hoosier [6]. Since these types of tires are the same in material and close fit in size, the performances between Goodyear and Hoosier tires are comparable. With good contacts and the possibility of tire donations, the Goodyear tires have been chosen.

3.3: Drive System3.3: Drive System3.3.1: Motor and Power Train3.3.1.1: Engineering SpecificationsBased on race records of autocross events [24], the vehicle will most often race in the range of 30-40 mph with peak speeds not much higher than 60mph. A calculation of time needed to accelerate from 0 to 60mph for a given motor configuration is taken as a representative estimate of the performance of that configuration in autocross (since it covers the full range of speeds likely to be encountered). This calculation also gives the added bonus of giving the average person a common point of comparison with the quickness of REV. On courses with longer straight-aways, speeds of as much as 85mph may be achieved. To take advantage of these courses, the car also needs to be able to reach 85mph. Our requirement for a 0-60mph time was set at 5 seconds; however, as a race car, the faster it is capable of, the better.

The motor is the heaviest component of the vehicle. Therefore we carefully analyzed the motor, its placement, and mounting. There are several standards that the motor mount must conform to. The first is that the mount must be designed to fit within the frame and fit the specifications of the motor (i.e. set attachment points). Secondly, the mount must be designed to hold the engine weight so if the rear (rear refers to the side of the motor, not the direction in the car) motor mount were to fail, the front motor would hold as shown in Figure 46. Next, the mount must be able to withstand the maximum torque that the engine outputs. Finally, the rear motor mount must be sized to create a restraint at the rear of the motor so that it is not acting as a cantilever beam off of the front mount.

Figure 46. Motor Diagram without Rear Motor Mount

Motor

Weight of Motor

Front Motor Mount

Attachment Points

Another important mounting bracket is the bracket for the differential. This bracket is required to hold the differential and its unusual shape. It also needs to mount the differential and align the input shaft directly with the motor shaft. This is an important tolerance design to ensure the direct drive of the motor.

3.3.1.2: Design ConceptsThe motor and power train as a system is absolutely crucial to the design of the car. The motor selection process began with evaluating the motors by their power, torque, and efficiencies in comparison with the weight, battery, and power train tradeoffs. After some basic research into light weight, powerful motors four were given serious consideration. They were three sizes of motors by Advanced DC (from smallest to largest - the A00, the 203-06-4001, and the FB01) and one motor by Netgain Technologies (the Warp 9). Qualitative factors such as durability, ease of drive train implementation, and configuration flexibility were considered, but quantitative comparisons needed to be made. To do so a performance calculator was created. These performance calculations are found in the Engineering Analysis, section 3.3.1.3.

The design of the motor mount originated from a combination of several different electric motor mounts that were found during research on the subject. A more complex idea was first presented to create a thick plate to mount the motor. This design was simplified to vertically mounted motor and a damper system to reduce vibrations of the motor. The vertical mounting allows us to adjust the height of the motor thereby moving the center of gravity of the car. The motor mounting, shown in Figure 45, attaches directly to the skeleton of the car. Calculations were applied to this mount and it was found have a factor of safety of over 10. So, the forces that are applied to these bars were determined (shown in Engineering Analysis, Section 3.3.1.3). This configuration was found to support the loading. So, the two bars were added as the front motor mount, and two straps were placed as the rear mounting (as shown in Figures 47 and 48).

Figure 47. Front Motor Mount Shown With Partial Frame

Figure 48. Rear Motor Mount Shown With Partial Frame

The differential mount has been developed for the Kawasaki Prairie 700 front differential. The differential is mounted to the rear of the car directly facing the motor. Mounting the differential directly aligned to the axle of the motor, is a manufacturability concern. The mounts were made to align with the three holes in the diff and attach to the frame with mount brackets as seen in Figure 49. This design allows for easy adjustability while being manufactured by first tacking the mounting brackets to the chassis and checking the alignment until the differential lies inline with motor. Space is left between the brackets and the differential mounts to allow for finer

adjustments with washers. The mounts were manufactured using the CNC mill machine.

3.3.1.3: Engineering AnalysisPerformance CalculationsBelow is an example of the performance calculations used to evaluate the motors with the FB01 9” DC motor at 144V and a maximum current of 550 amps. Weights, distances, and torques are originally known in lbs, feet or inches, and ft-lbs and are later converted to SI units for the actual acceleration calculations. The Warp 9” motor which was eventually chosen has less data available for it, but is a nearly identical in design other then small improvements.

First, the average torque is found over the rpm range needed to achieve 60mph. The plot of the speed torque data (for 144V with 550max amps) used can be seen below This is a plot of the data points taken from the supplier’s speed-torque curve, with lines connecting the points to visualize the area over which the torque is averaged.

Figure 49. Differential and Mount

MountingBracket

DifferentialMount

Differential

TopBracket

FB01 motor, 0-60mph Speed Torque curve

0

20

40

60

80

100

120

140

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

RPM

Torq

ue (f

t-lbs

)

The area under the curve is found by finding the average torque for each line segment (the height) and then multiplying by the rpm range (the width) which gives the area of that section. The sections are then summed and divided by the rpm range (the total width) to get the average torque, or the average height.

Ti (i=1-6) represents the torque (in ftlbs) at each rpm starting at 0 rpm and going to 4300 rpm (4300rpm is approximately the rpm that coincides with 60mph). Tavg is the average torque at the motor shaft.

Using GR (the gear reduction in the differential) the average torque at the wheels, Tw, is obtained. Then using Өw, the tire outer diameter, the average force at the wheel tread, Fw, is obtained.

Before further performance calculations can be done, drag, weight, and rolling resistance need to be calculated.

Cd is the coefficient of drag, AF is the frontal Area, and U is the speed in miles per hour. The integral of the drag from 0 to 60mph is found and then divided by the speed range to get the average drag force, Davg,.

Ns is the number of battery cells in series, Np is the number of series sets in parallel, and Wc is the weight of each cell. The weights are WD for driver, WM for motor, WB for all the batteries, WRC for the rolling chassis, WCN for the controller, WO for all other, and WT for the total. MT is the total mass. Both the weight and mass will be used in further calculations.

FR is the rolling resistance at 50mph and rolling resistance is estimated as a linear function of speed, thus the average rolling resistance (FRavg) for the 0-60mph acceleration is approximated as ½ of FR.

Knowing the force at the wheels and the losses the net force (the force that provides acceleration) can be found. Using this net force and the mass the acceleration and then the time from 0 – 60mph can be easily found. A comparison between peak force and traction is found at the end of these

calculations. The net force is just slightly higher than the traction, which will cause some wheel spin. However, this excess torque may be canceled out by the rotational inertia of motor and other components which have not been taken into account in this calculation.

Aavg is the average acceleration, VF is the final velocity (60mph), and t is the time to that final velocity. Thus the time needed to achieve 60mph from a standing start is calculated at 3.246 seconds.

Friction Force vs. Motor Force Comparison

Rwd is the rear weight distribution, FNR is the rear normal force (for both wheels together), and CoF is the coefficient of friction (estimated number from users in the Formula SAE forums for broken in Hoosier slicks, which has been assumed to be the value for the Goodyear slicks as well). FFR is the rear friction force and FP is the peak force which is provided by the motor.

These calculations neglect the efficiency of the differential (which provides the gear reduction, but should be around 97% or better for spiral bevel gears), efficiency of the CV joints, and the effects of rotational inertia, all of which increase the 0-60mph times by between .25 and .5 seconds.

For the analysis of the front motor mount, several hand calculations and a weight calculation are performed in Pro-Engineer Wildfire 2.0. First, a free body diagram is created to show the forces that the motor will apply to the bars of the mounting. This is shown below in Figure 50, and after these forces were found they were resolved into X and Y components. These forces were used to find the shear stress in the bolts, the bearing stress on the bars, and the stress in the bar. The equations for these calculations are found in appendix 7.1.

Figure 50. Left hand image shows the forces the motor causes, torsional and weight. Right hand image is the free body diagram with the reaction forces.

Analysis was done on the differential mounts to ensure that it could withstand the torques applied to from the motor. The analysis was done in Ansys due to its odd shape. The mounts were imported into Ansys as a volume and a solid45 element type was used. The material properties for the aluminum were obtained from matweb and are as follows: density of 0.1 lb/in3, tensile yield strength of 47,000 psi, modulus of elasticity of 10600 ksi and a Poisson’s Ratio 0.33. The mounts were analyzed under an extreme loading case where the full torque of 127 lbs*ft is being applied through differential, while the tires are full locked. An assumption was made that the torque is being evenly applied to all 6 mounting holes of the differential. The x and y forces at each mounting points were then calculated form that torque by considering the distances from the axis of rotation. A sample calculation is provided below.

Maximum torque (lbs*in):

Torque applied at each mounting hole (lbs*in):

Example of a x and y force calculations:

The results from Ansys were a maximum Von Mises stress of 33,665 psi. With a tensile yield stress of 47,000 psi we had a factor of safety of 1.3. This factor of safety is not great enough due to the fact that the differential mount is a main driving component. The following figure 51 shows the stress as it is applied to the mounts under loading.

Figure 51. Differential ANSYS Analysis

To increase the factor of safety an additional mount was added to the top of the differential. The above calculations were redone except that the torque at each mounting hole was found by dividing the total torque by 8 due to 2 additional mounting points. The ansys analysis was redone using the same process and the maximum Von Mises stress was found to be 25,994 psi. This increased our factor of safety to 1.8. This factor of safety does not need to

Figure 53. Warp 9 motor

meet the overall factor of safety of the chassis due to the fact that this analysis was the most extreme condition that will be seen by the by the mounts. The following figure 52 shows the stress as it is applied to the mounts under loading.

Figure 52. Differential ANSYS Analysis

3.3.1.4: Material StudyMotor SelectionThe performance calculations accounted for the variations in motor and battery weight along with the variations in torque speed curves. Each motor package option was compared with a gear ratio that made the peak force at the wheels just higher than the rear friction force so as go get the best possible accelerating force, while still allowing the ability for slight wheel spin.

The motor design analysis included two options. One option used A00 motors. Two were hooked up with one to each wheel with electronic differentiation. The other option was analyzed with three different motors where a single motor runs to a differential. The A00 setup was the lightest, but the drop off of in torque at higher RPMs, due to the small motor size, caused poor 0-60mph times. The 203-06-4001 motor did well, but not as well as the FB01 and Warp 9. These two 9” motors did the best in the performance comparison, and also provided the greatest efficiency, the ease of a single motor configuration (which requires a single gearbox for reduction), the greatest flexibility for gear

Figure 54. Kawasaki Prairie 700 Front Differential

ratios (being larger they could provide more torque easily if a differential with a high enough gear ratio could not be found), and the greatest continuous horsepower (the amount of horsepower they are able to provide indefinitely without overheating).

The Warp 9 (in Figure 53) did not have data available for it at high currents and voltages, but conservative extrapolations showed that it provides better performance than the FB01 with greater efficiency. This level of performance was confirmed by the experiences of various sources in the electric vehicle community. The Warp 9 also had larger commutators and advanced timing (which reduces arcing at higher rpms). NetGain Technologies, LLC [11] designed the Warp 9 with these advantages specifically for electric vehicles, while Advanced DC builds motors only for general applications. Thus the Warp 9 was selected for REV.

The Warp 9 motor weighs 156lbs and is rated for 32.3 continuous hp. It has an estimated 85hp peak in our configuration, and an estimated 140ftlbs at 600amps (controller limited maximum) from 0 to 3000 rpm. The estimated 0-60mph time for the REV with the Warp 9 motor and a 4.375:1 gear reduction (and 16 lead acid batteries) is 4.5 seconds. This calculation takes into account 97% efficient spiral bevel gear reduction in the differential, some CV joint losses, and the estimated rotational inertia of the components. This significantly exceeds our acceleration requirements.

The ability to change gear ratio would help REV obtain a higher top speed, but would have negligible advantages during an autocross race. A transmission would also add significant weight (an obvious disadvantage). Thus the REV has no transmission. Based on comparing the rear friction force to the peak motor force it was determined that a gear reduction between 4 and 5 to 1 is needed in a differential. A differential with this gear ratio provides the necessary gear reduction without the addition of another gear box. For the sake of racing performance a differential with limited slip is preferred. When one wheel on a car with a regular (open) differential slips all the torque goes to the slipping wheel and none goes to the wheel with traction. In racing conditions some wheel slippage can be expected in heavy acceleration and cornering. A limited slip differential causes more of the torque to go to the wheel with traction, thus increases acceleration and control.

The front differential in Kawasaki 4x4 ATV’s (Bruteforce or Prairie of any size) 2002 or newer has a 4.375:1 spiral bevel gear reduction and limited slip

capabilities as shown in Figure 54 [22]. It is also lockable which allows full torque to be given to both wheels regardless of whether one is slipping or not. If activated, this will increase friction in corners, but increase control and acceleration in drag race conditions, or 0-60mph time tests. This differential was the only one to meet the above criteria for gear ratio and limited slip capacity. After inputting this 4.375:1 reduction into the performance calculations it provided just enough peak force over rear friction force to allow the desired the ability for some wheel spin at peak force while maximizing acceleration (in the lithium ion scenario, however with the 16 lead acid batteries and 600mps there is more friction than torque if the tires are achieving an actual coefficient of friction of 1.7). This small margin of peak force over rear frictional force also provides for some efficiency and rotational inertia losses while sill maintaining peak, or near peak acceleration. The limiting factor for acceleration is the rear friction force, and thus peak acceleration is when the peak force matches the rear friction force. In the 16 battery lead acid battery scenario the torque is the limiting factor, but it is not far below optimal. Using a safe maximum motor speed of 6000 rpm (series wound motors do not have a fixed no load speed, but their lifespan exponentially decreases with higher speeds) and the 4.375:1 reduction the top speed of the REV would be approximately 84mph. This also exceeds our design requirements.

For the motor mount the materials chosen were limited by how they are going to be attached to the frame. Since the motor mount design is welded to the frame, this material will be the same material as the frame for ease of weldability. To keep the material consistent throughout the frame of the car the motor mount will be made of AISI 4130. Manufacturing of these pieces is going to be relatively simple because it is simply drilling four holes, but they also need to be done with high tolerances so that they will match up with the mounting points that exist on the engine.

3.3.2: Power Source3.3.2.1: Engineering SpecificationsBatteries are the biggest component of the car. With today’s technology, there are many different batteries we can choose for this application. However, we need to compromise and chose the best battery for this vehicle by comparing efficiency, power, cost, and weight. Optimally, we want these batteries to include the following specifications:

- Battery Temperature Rangeo -30°C to +60°C

- Battery Temperature Rangeo Total battery pack voltage: 144 Voltso Total battery pack amperage: 550 Ampso Total battery pack amp-hours: 25 Ah

- Number of Batterieso Based on voltage and amperage of each

- Battery Pack Containero completely isolate batteries and connections from the chassis

and bodyo hold half of the complete set of batterieso batteries easily accessibleo reduce movement and vibration of batteries during usage of

vehicle to keep batteries in contacto Container easily removable from side-pods

- Battery Connectiono Highly safe, no chance of electrocutiono connection between battery pack container and controllero easy to connect and disconnect battery packs for faster battery

pack switching

3.3.2.2: Design Concepts

Figure 55. Current Side pod and battery layout

The figure above shows the battery packs which are isolated from the chassis and the rest of the car. This will done using a box made of a non-conducting material (i.e. plastic). The box will be easily removed from the side-pods per engineering specifications. This container was never designed in detail.Within each column of batteries, there would be three (3) battery cells. Between the batteries, there would be disc connectors made from a copper disc surrounded by a non-conducting (plastic) annulus. The annuluses hold the copper connector in position. The columns of batteries are held in place by a tube of PVC with a slot cut out to allow for thermocouples to be placed on the batteries. This setup is shown in Figure 56.

The concept for the battery layout has changed because we need to ensure continuous connectivity. Since these cells were originally taken from DeWalt battery packs, we decided to use the same concept from the DeWalt setup to ensure connectivity. The configuration used by the Dewalt batteries is shown in Figure 57.

Side Pods (Frame support)

Battery packsFront

of car

Batteries (3)

Connector

PVC

The following is the third design concept for the battery packs.Side-pods contain battery packs that are 7 columns of batteries wide, 15 columns deep, and 3 tall. This will get a total of 315 batteries per battery pack. This configuration will give 30

Figure 56. Single Battery Layout

Figure 57. Battery pack layout

Figure 57 shows two columns of five batteries each. These packs will be connected together to make up the battery packs in each side pod. The number of batteries needed decreased to 400 according to our electrical engineers. This layout includes space for 480 batteries to allow for flexibility in the number of batteries in the future; batteries would be able to be removed from the design if necessary.

There is a box that the battery blocks would be placed into make up one battery pack (see Figure 58). The box would be used for two purposes, one to hold the batteries in place and the other is to safely isolate the batteries as described in the design objectives. The box will be completely enclosed with the exception of two power leads connected to the batteries, a small opening for sensor wiring exiting the box. The current design doesn’t include ventilation, though a fan would be required for Formula Hybrid Eligibility.

Figure 58. Battery Pack in side pod Figure 59. Batteries and Box layout

Further information on the Lithium Ion Battery Pack and management designs can be obtained from the Electrical Engineering Report.

SL

SLSd

V, Ti

Figure 60. Staggered Tube Arrangement

Unfortunately the Lithium Ion pack could not be purchased or built, so the final battery packs are 8 Odyssey PC680 batteries each (16 total batteries). The nominal voltage is 192 volts which compensates for the large voltage drop under high current and allows for extended runtime. The Lead Acid Batteries add approximately 140lbs to the car, but can provide sufficient energy for an endurance race, and the 550 amps required by the design specifications. They should actually be outputting as much as 600 amps at peak. Their 192 V compensates for the voltage drop caused by pulling the 600 amps though the 16 batteries in series (the internal resistance of the batteries acts like 16 resistors in series). These batteries should also be capable of powering REV though the Formula Hybrid Endurance Race. Maintaining a speed of 35mph should only take 115amps at 72 volts, resulting in a power draw of only 8.4Ah for each 6.8mile section. At 80% discharge the batteries should be able to output 13.6Ah, which leaves approximately 5Ah to account for the acceleration during the race. If the course proves to need unexpectedly large amounts of slowing and speeding back up gain, then the overall speed can be reduced to ensure the car will still finish (75% of points are given in the endurance race simply for completion) These high performance Lead Acid batteries are capable of being charged in approximately 20min (at 50amp). Between the first 6.8mile section and the second there is a 30 minute driver change out period in which the batteries will then be fully recharged.

3.3.2.3: Engineering AnalysisThe following Heat Transfer calculations were used for an excel sheet that helped determine whether or not the current battery configuration would meet heat transfer specifications. These requirements are needed for extended high current use. However, the cars requirements are either for show runs, acceleration runs, short autocross races, or long slow runs. Also, the batteries provide more output at higher temperatures (though with less cycle life). As a result this study was not used in the final stage of Li-Ion battery pack design.

As of right now the specification is that the rate of heat generated by the batteries must be less than the rate of heat transfer. All equations are taken from Fundamentals of Heat and Mass Transfer [17]. The layout of the batteries, shown in figure 60, are staggered cells to help improve the flow of air through the set of batteries.

The governing equation for rate of heat transfer from a liquid flowing through the bank of tubes is as following:

Where N is the total number of tubes, h is the convection coefficient, D is the diameter of the tubes, ΔTlm is the log mean temperature, and L is the length of the tubes.

The Reynolds number is calculated using the maximum fluid velocity. It is used in calculating the convection coefficient, h.

Vmax is the maximum fluid velocity, in our case air, within the tube bank. V is the velocity of the air flowing into the tube bank, in our case it would be approximately the speed of the car. The constant Pr is the Prandlt number for air at the inlet temperature Prs is the Prandlt number at the highest possible temperature, the surface temperature of the tubes. C and m are constants given in a table in Fundamentals of Heat and Mass Transfer [17].

Now all that is needed to find is the log mean temperature, T lm, to find the rate of heat transfer. To find log mean temperature the outlet temperature must be estimated by the following equation:

The final step is to compare the heat generated by the batteries and the rate of heat transfer of the flow of air through the side pod.

These calculations are only rough estimates. Due to minimal information on the thermal characteristics of the batteries, further testing will need to be done to find the surface temperatures of the batteries under a full load. This will be done using the motor that will be used on the project. With this testing and limited to the battery layout, the above calculations will be used to space the individual battery packs and determine if air vents will be helpful.

Voltage drop Calculations:Below is a sample of the voltage drop spread sheet which was used to help analyze the performance impact of decreased voltages due to high current though batteries in series. 600 amps is the maximum amperage draw. 12.8 is the voltage of an average, fully charged, 12V Lead Acid battery.

137.6V under maximum load causes a minimal impact on performance by causing the motor torque to decrease a few RPMs earlier. If the vehicle were to only have 12 batteries in series the voltage would have dropped to 103V, which would have significantly lowered the speed torque curve.

Run time Calculations:These calculations are an extension of the excel performance calculator. The amps needed is based on the motor torque curve, and the drag and rolling resistance calculations as seen in motor selection section above and a 95% drive train efficiency.

3.3.2.4: Material StudyThe choice of power source was critical to this vehicle, and in many ways the greatest challenge to EVs. The power source had to be able to handle the high current and voltage pulls that was required for a large enough motor to meet the functional specifications. We looked all major electrical power sources, but in the end the decision came down to two types of batteries, Pb-acid and Li-ion.

Though lead acids are the most basic, they can sustain a high current draw per given weight. Many other battery types would have been more expensive, provided greater range, but not had the current we wanted in the weight we sought. The prices were also significantly higher.

The Pb-acid would be suitable because they were dependable and easily available. They were also the cheapest of the batteries that were looked out. The draw back to them is the weight of the Pb-acid batteries. To have enough current and voltage the electrical engineers deemed that upwards of 12 batteries would be needed, with each weighing at least 14.5 lbs.

With further searching into the possibility of lithium-ion batteries, a relatively new battery that had been used in other high current and voltage

Figure 61. A123Systems Lithium-Ion ANR26650M1 cell

applications was found. The A123Systems lithium-ion rechargeable ANR26650M1 cell (in Figure 61) was light weight and had high amperage. Each cell only weighs 70 grams and only approximately 400-500 cells would be needed. The draw back to these batteries was the high price and need for an extensive battery management system (every cell must be regulated and monitored individually). The cells costs approximately $18-$20 each depending on where they are purchased. The power to weight ratio of the batteries was considered great enough to warrant the price and so these batteries were selected as optimal choice.

The Odyssey batteries have an excellent current out put for their weight (superior even to more expensive technologies such as NiMH and NiCd). They are made with pure lead (instead of lead alloy) which makes them harder to manufacture, but allows extremely high charge and discharge rates and longer cycle life.

The top of the battery boxes have been made out of Lexan, which allows the batteries to be safely (and non-conductively) contained and easily viewed. The Lexan was also donated, making it an easy and excellent choice for the battery covers.

The battery area is wrapped in Nomex, a fireproof, electrically insulating fabric. This in conjunction with the Lexan, and rubberized conduit housing all high voltage wires outside the battery area, fully contains the high voltage system.

3.3.3: Cooling3.3.3.1: Design ConceptsIn the initial design phase the idea was to air cool the controller. This decision was revised after further investigation of the manual of the controller. Since the controller is initially designed for water-cooling the decision was made to investigate the possibility of water-cooling. Below are the results of this study. Our application does not tax the 1000amp ability of the controller, nor is the car being used for long distances (such as a commuter car). Furthermore, our tests show minimal temperature increase in the controller in real world testing. Thus, at this point, the controller is being air cooled with the water cooling design ready in reserve.

The system would have to be small, light weighted, simple and cheap. It had to be able to provide 2 gallons per minute (120 Gal/hr) flow rate across the component. Also the pump has to run low voltage (12-36V). The cooling for this system will be provided by a small radiator. The internal component ideally is to be kept at below 55 C due to manufacturers specifications. The heat dissipated is about 2 watts per amp of current.

3.3.3.2: Material Study

The components found suitable for this project are mostly based off of computer processor water-cooling systems. These meet the specifications given and provide adequate heat dissipation to cool the water. Also a closed overflow container with a pressure valve will be used to contain the extra water. The system will be closed to avoid contact of water with the electronic components in direct vicinity.

The pump system that we are using is a Alphacool AP700 12V Water pump, in figure 62, capable of pumping up to 190 GPH. With this pump we are assured to be able to move the water from any location with in the vicinity between the radiator, controller, and water supply. With this extra power the water supply can be mounted lower for safety incase of a leak.

The Radiator we are using is either a Swifttech Quiet power 3x120mm Radiator or a Black Ice extreme II 240mm Radiator. The choice is pending data for the heat transfer rate of one of the radiators. The smaller of the radiator has a heat reduction power of 6270 BTU/h (1837 watt). Given this value the controller produces around 2 watts of heat energy per amp. Assuming a 700 amp current draw the produced heat power is around 1400 watt.

The water overflow and storage system is still undetermined because it can be any coolant holding device which shape is unimportant. The container will fit in a location where it causes the least amount of problems, can be refilled easily, and causes the least amount of damage if it does leak, break or damaged in any other way.

Figure 62. Alphacool AP700 Water pump

3.4:3.4: ElectricalElectrical

The electrical system consists of the motor, controller, batteries, battery management, programmable logic controller, and touch screen. Our main purpose is to provide an efficient electrical drive train system with the capability of graphically display vital car information to the driver.

3.4.1: Technical Hardware Design3.4.1.1: System DesignThe block diagram below describes the general layout of our electrical system. The main components of our system include the batteries, motor, controller, programmable logic controller (PLC), battery management system, user interface, main contactor, and pot box.

We have two sets of batteries: the 192V main power supply and the 24V auxiliary batteries. The main battery set is made up of 16 lead acid batteries in series. Our auxiliary batteries are 2 lead acid batteries in series. Our DC series wound motor comes from NetGain Technologies WarP Series and is specifically designed for electric vehicles. The Zilla motor controller and Hairball interface controls the voltage and current delivered to the motor. The battery management system contains PIC microcontrollers to monitor the battery voltages and send the data to the PLC. The PLC then sends the data for display to the touch screen.

The main contactor is our system’s main switch. All the voltage and current go through this contactor. If this contactor is not on, the controller receives no power to deliver to the motor. The pot box is installed in the acceleration pedal and is connected to the controller’s Hairball interface. The controller varies the current delivered to the motor depending on the resistance from the pot box. The monitor is the display on the steering wheel showing the status of the system with warnings. The speed sensor measures the revolutions of the motor which enables the calculation of the speed by the PLC in real time.

Figure 63. Electrical Diagram

3.4.2: Electrical Drive Train3.4.2.1: MotorThis series wound DC motor with a double ended shaft is an important component in our system. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls.

3.4.2.2: Motor ComparisonThe Warp 9” motor has a number of specific advantages including an extra large commutator and brushes, and advanced timing. All of these allow power to be transferred more smoothly and effectively. The motor is also slightly larger than the competing Advanced DC 9” motor which allows for greater head absorption and dissipation.

3.4.2.2.1: Series Wound DC Motor AdvantagesSeries wound DC motors, such as the Warp 9” are widely used because of their significant advantages. They have a theoretically infinite stall torque, which would require infinite current. This allows low end torque to be increased by simply increasing current to the motor.

3.4.2.2.2: Warp9 SpecificationsOur system utilizes this motor for the 144V to 192V range. Figure 64 is a performance curve for when the motor is run with 72 Volts applied. As shown, at a current draw of 335 amps, the horsepower is 32.3, the torque is 70 ft. pounds, and the revolutions per minute (rpm) are 5,500.

Figure 64: WarP 9Motor Torque Curve

3.4.2.3: Controller3.4.2.3.1: Controller DesignThe controller delivers power to the motor and limits current depending on the resistance across the potentiometer in the acceleration pedal. The user

can also limit current and voltage from the battery and to the motor using the Hairball interface. It also has multiple microprocessors which cross check for security and safety. A future enhancement option is to water cool the controller, which is recommended to prolong the life of the controller (especially in longer run time situations).

3.4.2.3.2: Zilla Z1K-HV Controller Specifications Maximum nominal input voltage range: 72 to 300 volts Absolute maximum fully loaded input voltage range: 36 to 300 volts Maximum motor current at 50˚C heatsink temperature: 1000 Amps Maximum battery current at 200V: 950 Amps Continuous motor current at 50˚C coolant temperature and 100% duty

cycle: 350 Amps Peak power: 320.000 Watts Pulse Width Modulation (PWM) frequency: 15.7 kHz Voltage Drop: less than 1.9 volts at maximum current

3.4.2.3.3: Hairball interfaceThe Zilla Motor Controller Package comes with the Hairball 2 Interface. It is required to use the controller. It has added safety features and is programmable. Connecting the Hairball to a computer via serial port allows the user to view errors and change features, such as voltage and current limiting.

Figure 65: System Diagram of Hairball 2 Serial Connection Input Menus

SHAPE \* MERGEFORMAT

Figure 66: Hairball 2 Unit

Table 3.11: Hairball 2 Wire Connection ListPin # Function: Connects To:1 Chassis GND Ground of the vehicle2 SLI+14V in SLI battery (12V) through a 4 amp fuse. Always

on3 Key Input Run connection of the ignition switch with a

4amp fuse

4 Start Input Start connection of the ignition switch5 Main Contactor

CoilMain Contactor Coil plus connection

6 Pot In - 5k ohm Throttle Potentiometer one connection7 Pot In + 5k ohm Throttle Potentiometer other

connection9 Ck Eng Lt Out Check engine light on dash10 Battery Lt Out Battery Indicator light on dash12 Cruse Mode In Cruise Mode selected manually Valet mode19 ACC+14V Out Red Wire on speed sensor20 Mot Speed 1 In Green wire on speed sensor, 4 pulses per

revolution22 Signal GND Black Wire on Speed Sensor25 Controller + To main contactor terminal that connects to B+ 27 Battery + To main contactor terminal that connects to B+

3.4.2.3.4: Hairball Utilized Features Control connections to the Hairball are low voltage and referenced to

the vehicle 12V ground for safety. Controller precharge circuit is included with self resetting fuse and arc-

less main contactor control. Uses standard 5 K ohm potentiometer for pedal input. Custom "accelerator to amps" transfer function for smooth starts, even

in high voltage systems. Standard RS-232 serial port for adjusting controller parameters. Programmable motor and battery voltage and current limits. Valet mode allows on-car changes without additional programming Two motor speed inputs for overspeed limiting of one or two motors. Separate voltage, current and speed limit adjustment for reverse. Adjustable low battery voltage protection. Additional battery voltage indicator set point for operating a dash

warning light. Many status and error codes insure easy diagnostics in case of faults. Main contactor voltage drop and stuck contactor monitoring. Two dash light outputs a check engine light and low battery indicator. Stalled rotor protection to reduce the possibility of damaged

commutators. Hairball code with new features can be downloaded as it is developed

by means of the bootloader and flash memory.

3.4.2.4 System Design for Hairball 23.4.2.4.1: Accelerator Potentiometer (Pot)The Curtis Potbox uses a special 5K ohm, two wire potentiometer that has a 25% initial dead-zone(to ensure the car is off when the petal is released), a linear variation from 0 to 5k ohm in the middle 50% of travel, and a flat 5k ohm resistance for the last %25 (toe ensure the driver can reach full throttle with risking damaging the pot by pushing it too far). It is used to vary the voltage to the controller, and thus control the speed of the car. Our throttle

assembly has two return springs where either one is strong enough to return the pedal alone in case the other should break. On the input to the Hairball, below 150 ohms is off, and over 4.8K ohms is full on. Resistance over 7K ohms causes a fault condition.

3.4.2.4.2: Key and Start WiringThe key input informs the Hairball that the driver is about to start. It enables the battery light, check engine light, and turns on the motor contactors. The start input initiates a pre-charge sequence, and upon successful completion of safety tests it turns on the main contactor and allows the controller to drive.

The start input needs only a momentary activation to start the controller. It is possible to tie the key and start wires together for those applications desiring only one switch to activate the vehicle. The Key Input carries the current for the main contactor and is therefore fused with a 5 amp fuse rated to take the full coil current of the contactor.

3.4.2.4.3: Speed SensorThe Hairball needs a speed sensor connected to the motor in order to do rev limit and stall detect, as well as to drive the tachometer. The Hairball has been designed to use a four pulse per revolution sensor.

3.4.2.4.4: Endurance RaceFor the Formula Hybrid Competition, the endurance race involves traveling 13.6 miles in an hour. With the Hairball Interface, we can limit certain aspects such as the motor voltage and amp draw. This will ensure that the driver remains at a constant speed and extends the battery life of that race.

Figure 67: Controller and Hairball System Diagram

3.4.2.5: Energy Source3.4.2.5.1: Battery Pack ConfigurationIn addition to our 16 Odyssey lead acid batteries wired in series, we also have 2 auxiliary batteries to power accessories.

3.4.2.5.2: Wiring DesignThe high voltage system is wired using 00 wire. The crimps used in the high voltage system for the batteries, fuse, contactor, controller, and motor were custom made. We used copper pipe to make the crimps.

3.4.2.5.3: ChargingAfter draining the batteries we have a charging system to charge them up for the next use. The charger is a high voltage high current charger that can charge our high voltage battery pack in series. There are also individual car battery chargers that can be used for charging batteries individually.

3.4.3: Battery Management System3.4.3.1: RequirementsThe Battery Management System (BMS) must monitor the battery voltage for each individual battery for input to the Programmable Logic Controller (PLC) and Touch Screen to give the driver full awareness of the current status battery pack.

3.4.3.2: DesignThe BMS consists of 16 remote battery sensing boards containing the circuitry depicted on the following page. Each board monitors one battery. All the battery voltages are sent to a master PIC that sends the voltages to the PLC in timed intervals.

3.4.3.3: Remote Battery Sensor The remote battery sensor monitors the voltage level of a battery. There are 16 remote battery sensors all connected to each other and to a main PIC base. Each sensor sends its data to the PIC base which then sends the data to the PLC.

Figure 68: Remote Battery Layout

Figure 69: Remote Battery Monitor Schematic

PIC Program for Remote Battery Sensor

********************Battery Remotes "remote2"TRISC = %10000001TRISB = 0TRISA = 255DEFINE ADC_BITS 8DEFINE ADC_CLOCK 3DEFINE ADC_SAMPLEUS 50ch1 VAR WORD x VAR BYTEz VAR BYTE ' address x=1High PORTC.4  'on - Initial blink of Led when hooked up Pause 100

Low PORTC.4   'offPause 300Start:High PORTC.4 ' LED on --- Blinks off once Data received from base unit -- On while waiting for base Low PORTB.0                        ' output coupler disengaged                      

SerIn2 PORTC.7, 396,[wait ("*"),z] ' receive from base

IF z=12 Then GoTo finish            ' Set "Z" for each remote numberGoTo start

finish:High PORTB.0                       ' output coupler engagedFor x=1 TO 2Pause 10ADCIN 0, ch1SerOut2 PORTC.6, 396,["$",ch1]     ' response to baseNext xLow PORTC.4  ' LED off Pause 200GoTo start

3.4.3.3.2: PIC BaseThe PIC base is the main part of the battery management system. All the voltages measured by the remote battery sensing boards are sent to the PIC base. From there the PIC base and the PLC communicate to send and receive data effectively.

Figure 70: PIC Layout

PIC Base Program

'********************"Bases 1 to 12"'********************DEFINE ADC_BITS 8

DEFINE ADC_CLOCK 3DEFINE ADC_SAMPLEUS 50adcon1.7=1Pause 1000TRISB = 0TRISC = %10000001TRISA = 255ch1 VAR BYTE Value VAR BYTE t1 VAR BYTE:t2 VAR BYTE:t3 VAR BYTE:t4 VAR BYTE:t5 VAR BYTE:t6 VAR BYTE:t7 VAR BYTE:t8 VAR BYTE:t9 VAR BYTE:t10 VAR BYTE:t11 VAR BYTE:t12 VAR BYTEv1 VAR BYTE:v1a VAR BYTE:v1b VAR BYTEv2 VAR BYTE:v2a VAR BYTE:v2b VAR BYTE v3 VAR BYTE:v3a VAR BYTE:v3b VAR BYTE v4 VAR BYTE:v4a VAR BYTE:v4b VAR BYTE v5 VAR BYTE:v5a VAR BYTE:v5b VAR BYTE v6 VAR BYTE:v6a VAR BYTE:v6b VAR BYTE v7 VAR BYTE:v7a VAR BYTE:v7b VAR BYTE v8 VAR BYTE:v8a VAR BYTE:v8b VAR BYTE v9 VAR BYTE:v9a VAR BYTE:v9b VAR BYTE v10 VAR BYTE:v10a VAR BYTE:v10b VAR BYTE v11 VAR BYTE:v11a VAR BYTE:v11b VAR BYTE v12 VAR BYTE:v12a VAR BYTE:v12b VAR BYTE v13 VAR BYTE:v13a VAR BYTE:v13b VAR BYTE v14 VAR BYTE:v14a VAR BYTE:v14b VAR BYTE v15 VAR BYTE:v15a VAR BYTE:v15b VAR BYTE v16 VAR BYTE:v16a VAR BYTE:v16b VAR BYTE x VAR BYTEz VAR BYTE ' address of remotey VAR PORTC.1  ' output flag w VAR BIT      ' input flagx=0z=0ontime VAR WORDofftime VAR WORDOntime = 10offtime= 10Low PORTC.5 ' LED off

Start:z=z+1For x= 1 TO 2Pause 10

SerOut2 PORTC.6, 396,["*",z]Next xHigh PORTC.5 ' LED onSerIn2 PORTC.7, 396,[wait ("$"), value]

********************Simplified Code For Remote Iterations for 1 to 12 ********************

IF z=1 Then     t1 = value    v1 = value*30           ' compensate for resistor divider  v1a=v1/528                                 ' 1st two digits based on 15V max v1b=v1//528                                ' next digit after decimal point

EndIF      .

.

.

IF z=12 Then    t12 = value    v12 = value*30           ' compensate for resistor divider v12a = v12/528                                 ' 1st two digits based on 15V max v12b = v12//528                                ' next digit after decimal point EndIF

******************* End Simplified Code For Remote Iterations for 1 to 12 ********************

I

Low PORTC.5 ' LED offIF z=12 Then         z=0        w= PORTC.0 ' input flag must go low for send        IF w=0 Then GoTo sendEndIF       

GoTo start

Send:      PORTB=t1   High PORTC.1      ' output flag   Pause ontime    Low PORTC.1   Pause offtime   PORTB=t2   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1    Pause offtime   PORTB=t3   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t4   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t5   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t6

   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t7   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t8   High PORTC.1      ' output flag   Pause ontime    Low PORTC.1   Pause offtime   PORTB=t9   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t10   High PORTC.1      ' output flag   Pause ontime    Low PORTC.1   Pause offtime   PORTB=t11   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1    Pause offtime   PORTB=t12   High PORTC.1      ' output flag   Pause ontime    Low PORTC.1   Pause offtime     PORTB=t9   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t10   High PORTC.1      ' output flag   Pause ontime    Low PORTC.1   Pause offtime   PORTB=t11   High PORTC.1      ' output flag   Pause ontime   Low PORTC.1   Pause offtime   PORTB=t12   High PORTC.1   Pause ontime   Low PORTC.1        ' output flag   Pause offtime  GoTo start

'NOTE on connector to PLC:'pin1= Output flag

'pin2= D0'pin3= D1'pin4= D2'pin5= D3'pin6= D4'pin7= D5'pin8= D6'pin9= D7'pin10= Receive flag

3.4.3: Programmable Logic Controller3.4.3.1: Design Concept3.4.3.1.1: Technical Software DesignThe REV software package is spread over 3 main parts – battery management PIC, PLC, and touch screen. Several PICs are used in the battery management system to monitor the voltages of the batteries and communicate with the PLC. The PLC performs ladder logic to take the data from the battery management and send it for display on the touch screen. Input/Output modules on the PLC enable it to send and receive data.

3.4.3.1.2: Power-up InitializationAt power-up, the CPU initializes the internal electronic hardware. It also checks if all the memories are intact and the system bus is operational. It sets up all the communication registers. It checks the status of the back up battery. If all registers are go, the CPU begins its cyclic scan activity as described below.

3.4.3.1.3: Read InputsThe CPU reads the status of all inputs, and stores them in an image table. IMAGE TABLE is EZPLC’s internal storage location where it stores all the values of inputs/outputs for ONE scan while it is executing ladder logic. The CPU uses this image table data when it solves the application logic program.

3.4.3.1.4: Execute Logic ProgramThis segment is also called Ladder Scan. The CPU evaluates and executes each instruction in the logic program during the ladder scan cycle. The rungs of a ladder program are made with instructions that define the relationship between system inputs and outputs. The CPU starts scanning the first rung of the ladder program, solving the instructions from left to right. It continues, rung by rung, until it solves the last rung in the Main logic. At this point, a new image table for the outputs is updated.

3.4.3.1.5: Write OutputsAfter the CPU has solved the entire logic program, it updates the output image table. The contents of this output image table are written to the corresponding output points in I/O Modules.

3.4.3.1.6: Subroutines

The CPU executes subroutines when called for in the ladder program.

3.4.3.1.7: Functionality TestTesting for the PLC consisted of testing the input and output logic of each module. A power supply was used to supply the input modules with 24 volts. This way we could test the program logic in a lab setting. To test the output modules we used a PIC to receive outputs from the PLC.

3.4.3.1.8: SensorsSpeed SensorThe Zolox speed sensor was designed specifically for the Zilla controller. It allows the controller to perform advanced features such as stall detect and over speed protection. The sensor produces 4 (active low) pulses per revolution. These pulses are then sent to the PLC which calculates the speed and sends this data for display on the touch screen.

3.4.4: User Interface3.4.4.1: Design conceptThe touch screen was designed to be a graphical user interface improving the way electric car stats are conveyed to the driver. The programmable logic controller communicates vital car information to the touch screen for display. A colorful display of interactive and dynamic figures enables a quick grasp of the status of the vehicle. There are several screens available that display different vehicle systems. By pressing certain figures on the main screen, the driver can view the other screens.

3.4.4.2: FeaturesAmong its various screens the touch screen displays the car speed, a timer, battery side pod voltage level, and individual battery voltages. The driver can press certain figures and buttons on the screen to view other screens.

3.4.4.2.1: Main ScreenOn the main screen is displayed the car speed, a timer, and each battery side pod voltage level. The timer has two buttons to control it – one to start and stop and the other to reset. The battery side pod bars represent the left side pod and the right side pod. The color of the bars changes in response to a lowering of the voltage level. The default color of the battery side pod bars are blue representing top voltage (see Figure 65). When the average voltage in each side pod decreases a preset amount, a segment of the battery side pod bar turns grey/black (see Figure 66). When half of the segments are grey/black, the rest turn yellow, representing half voltage (see Figure 67). The segments still turn grey/black when the voltage decreases, and when two segments are left they turn red to warn of low voltage (see Figure 68). The battery side pod bars are also buttons to other screens. When touched, the left side pod bar changes to a screen showing individual battery voltages

of the left side pod. Touching the right side pod bar changes the screen to show individual battery voltages of the right side pod.

Figure 71 Figure 72

Figure 73 Figure 74

3.4.4.2.2: Left Side Pod Screen and Right Side Pod ScreenThese screens (Figures 69 and 70) show the individual voltages of their respective side pod. There are also buttons on the screen to switch the screen to the main screen or change to the other side pod.

Figure 75 Figure 76

3.4.5: High Voltage Safety Design3.4.5.1: High Voltage (HV) RequirementsThere must be no connection between the frame of the vehicle (or any other conductive surface that might be inadvertently touched by a crew member or spectator), and any part of any HV circuits.

HV and low-voltage circuits must be physically segregated:• Not run through the same conduit.• Where both are present within an enclosure, separated by insulating barriers.• Both may be on the same circuit board.

3.4.5.2: Battery Pack SafetyAll insulation materials used in HV systems must be rated for the maximum temperatures expected. Insulated wires must be commercially marked with a temperature rating. Other insulation materials must be documented.

All HV wiring must be done to professional standards with appropriately sized conductors and terminals and with adequate strain relief and protection from loosening due to vibration etc.

All HV wiring that runs outside of electrical enclosures must be enclosed in orange non-conductive conduit. The conduit must be securely anchored at least at each end, and must be located out of the way of possible snagging or damage.

3.4.5.2.1: No Exposed Connections

No HV connections may be exposed. Non-conductive covers must prevent inadvertent human contact. This would include crew members working on or inside the vehicle. HV systems and containers must be protected from moisture in the form of rain or puddles for any car that is certified to run rain or wet conditions. There will be no HV connections behind the instrument panel or side switch panels. All controls, indicators and data acquisition connections must be isolated using optical isolation.

3.4.5.2.2: ContactorBoth contactors driven through the Hairball have 12V continuous rated coils. The main contactor is controlled by the Hairball for safety reasons, but the power to drive the contactor comes through the Key Input. The Hairball has internal contactor drivers which require suppression diodes on the contactor coils in order to absorb the inductive kick produced by the contactor coil when it turns off.

Formula Hybrid SpecificationsContactors shall be enclosed in a fireproof shield and shall not be located in the driver's compartment

3.4.5.2.3: FusesIt is important to have a fast semiconductor fuse in the battery circuit that feeds the controller. If there were to be some major problem with the Zilla or motor, a standard fuse or circuit breaker would not trip fast enough to protect the controller from excessive internal damage. The current rating for the fuse should be so that it can withstand full controller current for 20 seconds

Formula Hybrid SpecificationsAll electrical systems must be appropriately fused. Any wiring protected by a fuse must be adequately sized and rated for current equal to the fuse rating. A separate main fuse is placed in series with the Drive Battery output. The fuse rating does not exceed two hundred percent (200%) of the maximum drive current requirement. The fuse has an interrupt rating of at least 20,000 amps. Fuses are rated at a higher DC voltage than the nominal system voltage.

3.4.5.3: Switches3.4.5.3.1: Master Switches The vehicle is equipped with 3 master switches. Each switch can disrupt current to the contactors, thus isolating the batteries. These switches are round, red emergency stop buttons which are off when pushed in and must be pulled out manually to turn them on.All three switches must be pulled out to the on position to allow current to flow from the High Voltage Accumulators.

3.4.5.3.3: Cockpit-mounted Master SwitchThe cockpit-mounted master switch provides for easy actuation by the driver in an emergency or panic situation. It is located on the instrument panel within easy reach of the driver.

3.4.5.3.4: Instrument PanelThe instrument panel contains the emergency stop button (Cockpit-mounted Master Switch), 3 light switches, and 2 lights. One of the light switches is the Key Input to the controller Hairball interface. The second switch is the Start Input to the Hairball. The last switch activates the cruise control (aka. Valet mode, which limits various settings in the controller for slow driving) connected to the Hairball.

Formula Hybrid SpecificationsA brake pedal over-travel switch must be installed on the car. This switch must be installed so that in the event of brake system failure such that the brake pedals over travels, the switch will be activated and stop the motor. Repeated actuation of the switch must not restore power to these components, and it must be designed so that the driver cannot reset it. The switch must be implemented with analog components, and not through recourse to programmable logic controllers, engine control units, or similar functioning digital controllers.

3.4.5.4: Safety Tests3.4.5.4.1: Dielectric Withstand TestThe isolation between the HV circuit and other parts of the vehicle is repeatedly tested at an RMS ac voltage equal to 1000 V plus 1.5 times the maximum expected peak voltage in the HV circuit. The primary test is between the HV system and the frame. Additional tests are conducted between the HV system and any other ungrounded conductive surfaces or objects, unless they are protected from human contact. A current of more than 4 mA constitutes failure.

3.4.5.4.2: Leakage TestFor testing, a 10,000 Ω resistor is connected between points on the HV circuit and the grounded frame. A current of greater than 1 mA through the 10,000 Ω resistor is considered excessive.

3.4.5.4.3: Battery TestThe power output of each battery pack has been tested by demanding various and continuous loads. We tested our battery pack system for the optimal charging routine, as specified by the manufacturing company.

3.4.5.4.4: Battery Management System (BMS) TestThe voltage outputs displayed on the PLC touch screen from the BMS is compared to a manual voltage reading using a multimeter.

3.4.5.4.5: Motor/Motor Controller TestTo test the configuration of the controller, more than 600A is supplied at a voltage in excess of 144V to ensure that the controller limits the voltage to the range of 72-144V.

Through the PLC, we will run the motor in two scenarios, race scenario of high RPMs and a distance scenario of nearly continuous RPMs, while monitoring the temperature of the motor to ensure that it does not overheat and does not cause malfunction of other system components.

3.4.5.4.6: Emergency Switches TestBecause the contactors are essential to the safety of the system, we first isolate the components themselves to test for functionality. Two power sources supply power to the contactor leads and the field.

3.4.5.5: Reliability and Maintainability AssessmentsDue to the scale of our project, the reliability and maintainability is vital to ensure the car is kept in race condition. Most of the electronics used in our car have a life limit. To guarantee that all parts make it to their projected life time all safety precautions and guidelines are followed in the user manuals.

The integrity of the motor should be maintained if the motor is handled with care prior to installation and carefully limited voltages and currents are applied to ensure the motor does not reach 7000 rpm. The series wound motor is capable of overheating and damaging itself if proper care is not taken. All safety manuals will be carefully review before motor testing and followed during motor testing and racing.

3.5: Driver Interface/Ergonomics3.5: Driver Interface/Ergonomics3.5.1: Acceleration Pedal3.5.1.1: Engineering SpecificationsThe main design objective is to design an acceleration pedal around a given potentiometer (pot). The design has to incorporate the pot and protect it from exceeding its operational limits. Also for the ergonomics of the driver, it should not interfere with the driver’s foot movement, but it should imitate the feel and travel of a conventional accelerator pedal. It also has to fit within the dimensions of the vehicle and be mountable within the vehicle chassis.

3.5.1.2: Design History During the design process of designing the mount and foot pedal the design took drastic turns within the process. The first pot used was right-handed but the mounting plate was on the right hand side and would have interfered with the movement of the driver’s foot from the acceleration pedal to the brake pedal.

After switching to a left handed pot the spring that moves the foot pedal into its initial position had to be chosen. Initially the choice was a torsional spring applied directly at the pivot point of the foot pedal. Instead the choice was made to use a extension spring attached to the foot pedal and the base plate. This system is easier and a larger variety of springs with the same extension and spring constant.

Later the point of contact for the foot was changed from a bar sticking out of the right hand side of the pedal to a plate attached on the top of the pedal. This way the force on the pedal is more centralized and causes less torsion.

Figure 77. Acceleration Pedal

Finally, this pedal assembly was replaced with a simple pivot point attached to the frame, a short pedal, and the pot-box (shown in green) attached to an L-bracket bolted to the floor. Springs were attached to both the pot-box and the pedal pivot point.

3.5.1.3: Engineering AnalysisThe pot has given dimensions such as mounting holes and maximum travel distance of the lever. The lever moves a max of 45 degrees in total, 22.5 in each direction starting from the vertical upright. The potentiometer layout is shown in Figure 78.

Figure 78. Potentiometer with all given dimensions [8]

3.5.1.4: Material StudyThe materials chosen for this project are to accompany the design in its simplicity. The materials must have easily manufacturability and be readily available on the market and also inexpensive. The main material that will suit this need is aluminium. It is light weighted, strong, easy to machine, cheap and available within short time and distance. The bolts and the pin part used are made of steel for easier machining and availability from local hardware stores.

3.5.2: Steering Wheel3.5.2.1: Engineering SpecificationsThe steering wheel for this vehicle needs to meet with several specifications set by the group. The steering wheel needs to be easily removable so that the driver is able to enter and exit the car quickly. Also, the steering wheel needs to be designed to hold the touch screen that will be installed to monitor the car. This touch pad is going to be mounted below the handles but above the steering column. The steering wheel needs to be able to turn a full rotation without hitting the driver, because otherwise the driver will not be able to complete all of the maneuvers that the vehicle will be capable of.

3.5.2.2: Design HistorySteering wheel underwent a couple iterations of design review to best determine driver ergonomics and positioning. Initially, a standard 10” round steering wheel was determined along with an instrument panel for the electronics. As the research and development of the vehicle continued, a different approach to the steering wheel was considered. Figure 79 shows how the touch screen of the PLC is attached directly to the steering wheel. On the back, a quick release switch, as indicated by Formula SAE rules, is seen in Figure 79b.

In addition to the previous specifications the touch screen needs to have some form of protection so that glare from outside light sources does not obscure the driver’s ability to read the screen. Also, this screen must attach in such a way as to not interfere with the driver’s hands.

Figure 79. (a) Steering Wheel with touch screen, (b) rear view showing quick release

The latest revision incorporates the touch screen with a barrier around the edges to the wheel. The touch screen will not be polarized; therefore sunlight needs to be blocked from the screen as best as possible for the driver to clearly view. This rendition is shown in Figure 80.

Figure 80. (a) Steering Wheel with touch screen, (b) rear view showing quick release

3.5.2.3: Material StudyThe material selected for the steering wheel is 6061 aluminum. This was selected because the material needs to be light weight and durable. This is especially necessary for the steering wheel because it will be removed from the car most of the time, which means that a heavy piece will not only be

(a)

(b)

detrimental to the weight of the car but also will be difficult to handle for the people carrying it. Also, while the steering wheel is removed from the car it stands a greater chance of being abused. These reasons along with material availability lead to our choice of aluminum.

For the screen shielding there are two options. First option was to shield the screen with aluminum sheet metal. This metal would attach to the outside of the screen casing and would extend towards the driver for approximately four inches. This option does provide difficulties in manufacturing due to the shape of the shield, and restricts the space for a driver’s hand. The metal chosen was aluminum for its light weight and resistance to corrosion. The second option was to find an LCD screen protector that also provides an anti-glare protection. These screen protectors are commonly used on palm pilots or on laptop screens. These screen protectors will be an optimal choice for our vehicle.

3.5.3: Driver’s Seat3.5.3.1: Engineering SpecificationsA driver seat has to accommodate for the driver comfort and ergonomics. It also needs to lightweight to keep down weight of the vehicle.

3.5.3.4: Material StudyWe will purchase a lightweight seat to integrate into the vehicle. The Tillet T11 seat shown in Figure 75, only weighs 3.5 pounds and can fit the dimensions of the driver’s cockpit. Other models of the T11 seat are shown but cost raise with the padding or flexibility of the seat material. This data is shown in Table 3.10.

Table 3.12: Tillet Seat Variations [13]Model Weight CostT11 1/4 pad 4.0 lb $239.00T11 no pad 3.5 lb $138.00T11VG 2.5 lb $170.00

Figure 81. Tillet Racing Seat no pad, Item #T11 [13]

With the prices and weights of the various lightweight racing seats, the standard Tillet T11 with no pad is the best option for our application.

3.5.4: Safety Equipment3.5.4.1: Engineering SpecificationsFor safety requirements, the driver must comply with the safety guidelines of Formula Hybrid [16] and Formula SAE rules [15]. The driver is required to have a helmet, fire suit, gloves, goggles or face shields, and shoes as required by these rules. Specifications for each are as follows:

Helmet- Snell M2000, SA2000, M2005, K2005, SA2005- SFI 31.2A, SFI 31.1/2005- FIA 8860-2204- British Standards Institution BS 6658-85 types A or A/FR rating

Fire Suit- SFI 3-2A/1 (or higher)- FIA Standard 8856-1986- FIA Standard 8856-2000

Fire resistant gloves with no holes, no leather gloves

Goggles or face shields made of impact resistant materials

Shoes of durable fire resistant material which have no holes

Also required by safety rules is the safety harness for the driver. This harness is a 5-point harness made of Nylon or Dacron polyester. These harnesses are typically found at stores selling racing components.

3.5.4.4: Material StudyFigure 82 shows a layout of the driver apparel that is required to wear. Prices for these required safety items are accounted for in our budget as miscellaneous expenses. For a complete set of safety apparel, the cost is approximately $500.

To meet safety requirements from Formula Hybrid and NEDRA, a 5-point harness is implemented into the design. 5-Point harnesses made of Nylon or Dacron polyester are widely available. They generally range in price from $100 to $200. Figure 83 shows a typical harness used for this application.

3.6: Design Validation3.6: Design ValidationAt this point the design cannot be fully verified. The Final assembly was recently completed, and a suitable test site has not been secured. Efforts have been focused on ensuring that the vehicle will be ready and eligible for Formula Hybrid. What testing has been done has validated much of the design. The braking system has safely stopped the car in all testing, and the battery system has powered the car up to a verified 57mph. The frame has shown itself to be very stiff. The suspension performed well until a recent clevis failure due to parking lot bumps. The clevises are currently being corrected. The motor mounts and differential mounts handled the torque without any issue or sign of fatigue.

Figure 83. RJS 5-Point Harness [14]

Figure 82. Driver Racing Apparel [14]

As far as the actual functional specifications, the only primary specification that can currently be verified is the weight, which the car does not pass. After adding the 16 PC680 lead acid batteries the weight has climbed to 795lbs without a driver, and 945 with a 150lb driver. This far exceeds the allowable weight. Lithium Ion batteries would be needed to meet the weight requirements, along with an overall redesign to save weight. Weight savings was neglected in favor of ensuring a complete, working vehicle in this first attempt at building an electric racecar. Based on the motor speed-torque curve and the gear ratio peak power is available throughout the 20-40mph range.

Initial endurance testing allowed the car to run for 20minutes (without running the batteries all the way down) at around 10mph. This exceeds the 15minute run time requirement, however the number of batteries was then increased from 12 to 16 to ensure sufficient run time to complete each of the 2 6.8 mile legs of the Formula Hybrid Endurance Event. Repeated acceleration runs were also performed on a single charge which is more than comparable to the power needed to complete an autocross race. All current testing was performed with a Curtis controller (not the more powerful Zilla) and with only 12 batteries instead of 16.

To fully verify the design we need to tweak the suspension and alignment, and then test out the full power of the system with the new batteries and controller. Initial test drives indicate that the performance requirements should be easily achieved with the final configuration.

To test the acceleration times, two methods will be used. On a sufficiently long course the vehicle will be timed as a radar (or laser) gun is used to monitor the speed up to 60mph. To verify this first approach the car will be timed going a set distance from a standing start. This distance (198ft) is the calculated distance needed to reach 60mph. Upon crossing this distance the driver will begin braking. A GPS receiver will be mounted on the car for this test (recording top speed). Using the distance and time acceleration and top speed can be calculated and compared with the GPS. To test the range of the vehicle we plan to run at a constant 35mph on fully charged batteries until the batteries are drained. These two tests will not only verify the success of the vehicle but also validate the calculations used to model the cars behavior. Further testing and data collection methods will be easily available with the completion of the wiring and programming of the PLC/Touch screen.

The autocross competitiveness will be verified at the Formula Hybrid Competition (which will also officially test the acceleration and endurance).

4:4: Detailed Drawings Detailed Drawings

4.1: Parts List4.1: Parts List

Chassis (C)QTY Part Number Description1 C-001-A Frame Assembly1 C-002-P Chassis1 C-003-P Floor Panel, Pedal Mount1 C-004-P Floor Panel, Mid1 C-005-P Floor Panel, Steering Mount1 C-006-P Floor Panel, Driver Seat1 C-007-P Floor Panel, Motor2 C-008-P Floor Panel, Sidepod2 C-009-P Side Top Panel, Motor Guard2 C-010-P Side Bottom Panel, Motor

Guard1 C-011-P Mount Plate, Impact

Attenuator1 C-012-A Impact Attenuator Assembly6 C-013-P Honeycomb section2 C-014-P Honeycomb section, small7 C-015-P Steel plate, impact1 C-016-P Steel plate, chassis mount

Drive System (DS)QTY Part Number Description1 DS-001-A Differential Assembly2 DS-002-P Differential Mounting Bracket1 DS-003-P Differential Top Mount1 DS-004-P Differential Engagement Pin1 DS-005-P Plate, Differential

Engagement Pin3 DS-006-P Spacer Left, Differential

Mount3 DS-007-P Spacer Right, Differential

Mount

Vehicle Dynamics (VD)QTY Part Number Description1 VD-001-A Front Suspension Assembly1 VD-002-A Rear Suspension Assembly

2 VD-003-A Front Top A-Arm Assembly2 VD-004-A Front Bottom A-Arm Assembly2 VD-005-A Rear Top A-Arm Assembly2 VD-006-A Rear Bottom A-Arm Assembly1 VD-007-P Steering Column Sleeve4 VD-008-P Rocker2 VD-009-A Steering Tie Rod2 VD-010-A Front Push Rod2 VD-011-A Rear Push Rod8 VD-012-P Clevis, Front8 VD-013-P Clevis, Rear8 VD-014-P Clevis mounts, suspension

front16 VD-015-P Clevis mounts, suspension

rear

Driver Interface (DI)QTY Part Number Description1 DI-001-P Mount, Headrest1 DI-002-P Steering Wheel1 DI-003-P Instrument Panel

Electrical (E)QTY Part Number Description1 E-001-P Mount, Rear Motor1 E-002-P Mount, Controller1 E-003-P Mount, Hairball1 E-004-P Mount, Pot Box

COTS (Components Off The Shelf)QTY Part Number Description1 WarP 9 DC Motor, 32.3 continuous HP1 Zilla Z1K-HV Controller, 72-300VDC, 1000A

max1 Hairball Zilla Controller Interface16 Odyssey

PC680Battery, Lead Acid 12V

1 EZ-PLC-D-64 Programmable Logic Controller

1 EZTCC-S6C-S Touch Panel1 PB-6 Pot Box2 Brake Master Cylinders6 Brake lines, hard4 Brake lines, flex

16 Brake fittings4 20.5 x 7.0 -

13Tire, slick, 21.0" OD

Custom (Used or Custom Made Parts)QTY Description1 Body1 Seat1 Headrest cushion4 Spring4 Shock1 Steering Column1 Acceleration Pedal1 Battery Management System2 Brake Caliper Assembly, Front2 Brake Caliper Assembly, Rear2 Brake Caliper, Front2 Brake Caliper, Rear8 Brake Pad2 Brake Disk, Front2 Brake Disk, Rear2 Steering Base Mount2 Wheel Upright Assembly, Front2 Wheel Upright Assembly, Rear4 Upright2 Front Wheel Hub2 Rear Wheel Hub2 Small Bearing, Front Wheel2 Large Bearing, Front Wheel2 Bearing, Rear Wheel2 Spindle, Front Wheel2 Spindle Spacer, Front Wheel2 Spacer, Front Wheel1 Steering Bracket, Left1 Steering Bracket, Right16 Bolt, Wheel4 Wheel Assembly

4.2: Drawings4.2: DrawingsDetail drawings to follow.

5:5: BudgetBudget5.1: Initial Budget5.1: Initial BudgetThis budget is an initial estimation to construct a running electric vehicle. If time and money permits, the budget will turn to the final budget. This breakdown allows us to develop an electric vehicle, and then improve the design and performance of the vehicle. This budget also includes a donation of controller and tires and a donation of half of the batteries (250 cells).

5.2: Final Budget5.2: Final BudgetThis is the overall budget. If time and money allow, all components will be implemented in the design to construct a better performing, more enhanced electric vehicle.

Costs of research and development of other ideas and components were also factored into the final cost of the vehicle design.

Therefore the total cost of the project would amount to approximately $13,100.

6: Organization and Capabilities6: Organization and Capabilities

Team Member Discipline Title

Elizabeth Diaz Mechanical Engineering Team Lead

Valerie Bastien Electrical Engineering Sensors Lead

Jared Doescher Mechanical Engineering Thermal Effects Analyst

Kristina Harrell Electrical Engineering Power Systems Lead

Jason Miner Mechanical Engineering Mechanical Lead

Audrey Moyers Electrical Engineering Programmable Logic Controller Lead

Kathleen Murray Aerospace/Mechanical Engineering Aerodynamics Specialist

AJ Nick Mechanical Engineering Manufacturing Lead

Matthew Reedy Electrical/Computer Engineering Electrical Lead

Joshua Wales Mechanical Engineering Systems Integration Lead

David Wickers Mechanical Engineering Frame AnalystOliver Zimmerman Mechanical Engineering Mechanical Designer

Team Lead

Design Teams

Development Group Procurement Group Manufacturing Group

Integration Team

Chassis & Body

Chassis RedesignBody RedesignMounting PointsAeros/Ground Effects

Drive System

MotorDrivetrainControl SystemBattery SystemCooling SystemShielding System

Electrical

Battery Management InstrumentationData Transfer SystemPower Management

Vehicle Dynamics

Suspension SystemSteering SystemBraking System

Driver Interface & Ergonomics

Cockpit DesignSafety EquipmentDriver Interface

2007 R.E.V. TEAM STRUCTURE

7: Scheduling7: Scheduling7.1: Gantt Chart7.1: Gantt Chart7.1.1: Mechanical Task Schedule

7.1.2: Electrical Task Schedule

7.2: Milestones and Deadlines7.2: Milestones and DeadlinesMarch 30, 2006 – Sponsorship Package complete Motor/Controller determined

April 28, 2006 – Team Initial Proposal Complete

May 15, 2006 – Finish Research (include pricing) Finish Frame Design Concept

July 15, 2006 – Finish Suspension Layout Organize Electrical COTS Parts

September 14, 2006 – Finalize Preliminary Vehicle Design Begin ordering Major Components

October 23, 2006 – PDR

November 1, 2006 – Finish Analysis

November 11, 2006 – Finish Written PDR

January 19, 2007 – Complete Mechanical Build

January 20-21, 2006 – Battery Beach Burnout, NEDRA Event

March 1, 2007 – Complete Vehicle Build

March 30, 2007 – Finish Optimization and Testing

April 2, 2007 – Present Completed Car

May 3-5 Formula Hybrid Competition

8: Conclusion8: ConclusionOverall the REV project has been very successful. Many business, public, and EV community contacts have been established. Many people have been extremely impressed with REV and the potential it shows for electric vehicles. The car accelerates powerfully and runs quickly, though the exact numbers have yet to be verified. With the completion of the assembly and dialing in the suspension/steering parameters the vehicle should be a true, successful racecar.

There are a number of drawbacks to REV and improvements for the future. The heavy batteries with their limited cycle life are the greatest drawback, but they would be expensive to upgrade. This battery limitation is really the fundamental limitation on electric vehicles at this point in history. With lighter, more powerful A123 Lithium Ion batteries its performance could be greatly improved. With the lithium batteries the extended battery management system could be added, along with more extensive sensors and data collection. Accelerometers on frame and suspension would provide excellent objective handling data. For the Electric Vehicle community, real time torque data would be invaluable. There is no solid data to verify the speed-torque curve for the Warp 9” motor at the voltages and amperages we are running; our performance calculations are based on the very similar Advanced DC 9” motor. Torque data recorded in real time with the rpm sensor data, voltage data, and current data would greatly help the modeling of these electric vehicles.

Another limitation of the design is the alignment between the motor and the differential which is imperfect, and does not include a universal joint or CV (Constant Velocity) joint linkage which would compensate for the misalignment. Either a joint of that sort or a mounting setup that allows precise positioning would take care of this issue. The current setup is functional, and induces minimal vibration into the system, but for long term reliability a redesign would be important. Also, the water cooling system should be implemented if the car is to be used frequently over a long period of time. To complete the vehicle a weight savings analysis should be implemented, along with redesigned aerodynamics, which could be greatly enhanced (including a rear body section).

The motor choice is excellent because of its durability, versatility and torque. The Warp 9 and the Zilla 1K-HV are the best DC motor/controller combination available on the market at this time. The choice of running a DC motor over an AC motor proved to be wise because of the cost, time, and the community knowledge we were supported with. The frame is also well designed, providing excellent strength and impressive rigidity to support the various weights it is saddled with. The only advisable change would be to do a thorough weight optimization study. Spherical bearings in the suspension

should be made small, reamed to size, and installed with Locktite to ensure a solid hold. The clevis design needs to be strengthened, and it may be advisable to use larger spherical bearings along with correspondingly larger bolts and clevises to ensure the durability of the suspension.

REV has been very successful; much of its full validation is still to come, but there are many lessons that have been learned and improvements that could be made with further time and resources.

9: Appendix9: Appendix9.1: Calculations9.1: CalculationsTo calculate the top speed, we factor in the top rpm the motor can handle and the gear ratio.

Suspension:The following is a set of variables and equations used in an iterative process to term the spring rates used on the suspension.

Key of TermsW = Total weight of car and driverWF = Total weight, frontWR = Total weight, rearUWF = Total unsprung weight, frontUWR = Total unsprung weight, rearUGF = Unsprung CoG height, frontUGR = Unsprung CoG height, rearTF = Track width, frontTR = Track width, rearCF = Height of front roll centerCR = Height of rear roll centerSGF = Sprung CoG height, frontSGR = Sprung CoG height, rearSF = Front spring rateSR = Rear spring rateWmF = Front wheel movementWmR = Rear wheel movementSmF = Relative front spring movementSmR = Relative rear spring movementSWF = Total sprung weight, frontSWR = Total sprung weight, rearSW = Total sprung weight

UtF = Unsprung weight transfer, frontUtR = Unsprung weight transfer, rearCtF = Weight transferred via front roll centerCtR = Weight transferred via rear roll centerTM = Mean track of sprung weightCM = Mean roll center of sprung weightGM = Mean CoG of sprung weightLM = Mean roll moment of unsprung weightSt = Weight transferred due to the sprung massWt = Total weight transferArF = Front roll resistance due to springsArR = Real roll resistance due to springsDrF = Front roll resistanceDrR = Real roll resistanceWtF = Total weight transfer, frontWtR = Total weight transfer, rear

Weight TransferSWF = WF- UWFSWR = WR – UWR

SW = SWF + SWR

Unsprung weight transfer

Weight TranferSWF = WF- UWFSWR = WR – UWRSW = SWF + SWR

Unsprung weight transfer

Weight transfer via roll centers

Weight transfer via sprung mass

Total weight transferWt = UtF + UtR + CtF + CtR + St

Roll Resistance

Tire Load

The following calculations are used to find the distance the tires will take to reach its optimum driving temperature assuming full slippage.

Using the Energy Equation:

90 lb

360 lb

Brake Force CalculationsBrake Pedal:Assume that the driver input force is approximately 85 lb. The distance from the pivot to the master cylinder piston attachment is 1.25”

Moment output from pedal:

The master cylinder:You can adjust pressure output of each master cylinder by increasing or decreasing length of the piston push rod in the master cylinder. This is allows for an adjustable rear and front braking force. To account for this difference in the front and rear braking a percent is applied to the pressure calculation.

Where:

D: the master cylinder diameterF: the force from the brake pedalP: the pressure from the mater cylinder

4 in

The caliper:The calipers have two pistons that actuate the brake pads so the force is doubled.

Where:

P: the pressure from the mater cylinderD: the diameter of the pistonFCaliper Force: the clamp loadA: area of the caliper

Front Calipers:

Rear Calipers:

The brake pads:There is a brake pad creating friction on each sides of the rotor at this force, so the force is multiplied by a factor of two.

Where: = coefficient of friction = 0.45 (good assumption for most race cars)

Front:

Rear:

The rotor:

Where:d: The distance between the center of the rotation and the force acting at a point midway across the rotor face.

Front:

Rear:

The wheels and tires:

Where:F: Force generated between the tires and roadr: Rolling radius of tire

Front:

Rear:

Acceleration calculation:

Where:a: decelerationF: Force generated between the tires and the road for the front and rear tires. Force is multiplied by a factor of 2 because there are 2 front and 2 rear tires.M= Total Mass of car with 150lb driver.

Stopping distance:

Where:Si: the initial speeda: deceleration

Calculations based on Equations from Wilwood Engineering [25]

Motor mounting calculations prove that these mounts will handle the amount of load from the motor. A free body diagram shows the forces and loads applied to the front motor brackets.

Though this is just one calculation, but it gives an example of how little stress is on the beam in comparison with the strength of the material.

Calculations for the Impact AttenuatorData

Table of Specifications of the Impact AttenuatorParameter ValueSteel Plate AISI Type 304 Stainless Steel, .03” thick

RxTop

RyBottom

RyTop

W 2

W 2

F2y

F1y

F1x

F2x

RxBottom

Motor Mount Free Body Diagram

MaterialHoneycomb Material

HRH-10/OX – 3/16 – 4.0 HexWeb Honeycomb [27]

Steel Plate size 7.80” wide, 3.90” tallLength 5.90” long

(a) (b)Layout of the Impact Attenuator: (a) Pro/Engineer 3D Model, (b) Dimensional Layout

The layout of the 7th (front most) layer is slightly different wit the width being the full 7.8” and the height being 2 strips 1.65” in height 1 at the top edge of the metal plate and one at the bottom edge. This layer is more stable (because of the elimination of the overhanging edge and the larger area moment) and will help distribute incoming loads onto the other 6 layers.

CalculationsTo determine the amount of energy the impact attenuator will absorb, the kinetic energy of a mass at 850 lbs (weight of car with driver) moving at a velocity of 23 ft/s2 is determined. The kinetic energy absorption is

The maximum force that the honeycomb would withstand at a specified area is calculated to determine how much force the honeycomb will use against the required energy. The force of the crushing honeycomb is based on the typical stabilized strength of the material. (Hexcel p.21)

The force is then compared to the evaluated kinetic energy and a crushing distance at the required parameters is determined. The distance is

Our total height of honeycomb is 7.0in which results in a 72.4% crush which is approximately in line with the 70% rated crush from Hexcel. That 70% is rated for aluminum honeycomb, which becomes a solid member as it crushes, however the composite honeycomb powders and falls away which should allow a slightly greater crush percentage.

The acceleration is then determined to verify if the impact attenuator can withstand impacts below 20g’s. This is determined by the following…

ResultsAccording to hand calculations completed above, we can see that the acceleration does not reach 20 g nor does the impact attenuator impale the frame when running at a velocity of 23 ft/sec.

9.2: Statement of Ethics9.2: Statement of Ethics

REV, the Racing Electric Vehicle, team has made a significant effort on this project to uphold the ethics and integrity as engineers in a professional manner. The intent of this project is to inform the public of the advancments in technology in electric vehicles. We strive to serve our clients (the public) with professional competent engineering practices and to resolve the issues emphasized by this product thereby helping with improvement of human welfare.

Necessary precautions and safety factors have been taken into account to ensure the safety of the driver and others around the vehicle while the vehicle is powered. We had made our efforts to show our true engineering professionalism by designing and creating this vehicle with the proper training obtained throughout our schooling. We do not compete unfairly with others but rather show the outstanding merits we have accomplished through this design.

Throughout the design and development of this product, we continue to utilize and improve our professional and ethical skills. We also strive to help others understand and take part in the project, with intentions of improving his or her skills. We drive to make a point of showing this car as a new way of successfully designing a project by incorporating values of hard work, teamwork, communication and interdisplinary work. We intend to aid any interested party to understand what the project is and what it can accomplish. We utilize any and all resources to ensure the public and any person of interest gets correct and valid information about our electric vehicle and the topics it highlights.

We intend to prove the environmental and sustainability of concepts presented by this project through quality of engineering professionalism. As a team with many members of the American Society of Mechanical Engineers, we strive to uphold the ethics and policies of the society to ensure the quality and reliability of our electric car.

9.3: Safety Plan9.3: Safety Plan

The 2006-2007 Florida Tech Racing Electric Vehicle, R.E.V., an electrically driven, open-wheel, single-seat, purpose-built vehicle optimized for Autocross racing. This is a small 500lb vehicle, similar in style to the Formula SAE vehicles. To reduce costs to the project, we will be using components of the 2001-2002 Florida Tech Formula SAE car. This vehicle will be built to comply with the rules of Formula Hybrid, Formula SAE, and NEDRA (National Electric Drag Race Association).

1. Power System/Battery Packsa. High voltage application of Lithium Ion batteries. Caution needs to be

taken with the amount of voltage and current that will be supplied by the batteries. Do not touch the batteries or battery packs unless completely disconnected and cooled to room temperature.

b. Batteries shall never be tampered or altered with unless specified in the manufacture’s manual.

c. The batteries contain vent holes on the top and bottom of the battery which have to stay free or blockage at any time except during constant temperature storage.

d. Batteries cannot short or overheat. Ensure that the battery packs have no loose connections and wires are isolated from each other. Also, use monitoring system to carefully watch the temperature of the batteries. Vehicle will shut down if temperatures are above recommended operating temperatures. (If operating temperature is below -30 C and above 60 C the system has to be shut down )

e. When handling battery packs the battery packs have to be disconnected from any other sources (i.e. motor controller, battery charger etc).

f. Batteries will be placed in a non air tight container and therefore no pressure buildup should be possible. A visual inspection of the container is necessary before any handling of the container. If a visual inspection shows signs of pressure buildup proper PPE has to be worn before container can be opened and handled.

g. Before any handling or prior to operation of batteries visual inspection of batteries and container for damage is necessary. If any damage to container is found an assessment of the damage on the spot can determine further use or replacement of the container. If damage to any battery is found it has to be removed using proper procedures and wearing proper PPE. Also the surrounding batteries and container have to be inspected to ensure no contamination has occurred.

h. No work on battery packs is allowed when the battery pack mounted in the vehicle.

i. Extra caution has to be taken when working with disassembled or individual batteries or battery packs. If a battery gets damaged in the process of assembling or disassembling battery packs all actions should halt and a safety perimeter established. Before any person is allowed to enter the perimeter, proper PPE is to be worn to asses the damage and if necessary to clean up the contaminant.

j. Users need to carefully monitor battery temperatures using temperature sensors. If battery temperatures are above recommended operating range, vehicle will have to be shut down. (Automated system is in place to assist with monitoring temperatures, but manual monitoring shall still be in effect)

k. Battery packs may generate electromagnetic field. To reduce the electromagnetic fields, lengths and loops or curves in the wires have to be minimized.

l. If not in use the battery packs have to disconnected and locked or tagged out with appropriate equipment.

m. Further battery handling and processing requirements are pending MSDS of company.

2. Motora. Motor will produce high amounts of torque and power. Designers and

testers need to be aware and cautious of motor operation.b. If examining or handling motor, user needs to be sure motor is

completely disconnected from power source (i.e. Controller) and brought to a zero energy state. Also visually inspect if the motor is spinning. The connectors of the motor have to be properly locked or tagged out using appropriate LOTO (lock out/ tag out) equipment.

c. All locks and tags have to be removed before motor can be reinstated and powered up.

d. Handling the motor requires a secondary temperature measurement before any procedures or operations may take, (what type of sensor) or w adequate wait time to let the motor cool down. A simple proximity feel test is then adequate to ensure safe handling temperature.

e. When handling or moving the motor proper lifting equipment has to be used or proper procedures have to be observed. At no point should an individual move the motor by themselves.

f. Users need to carefully monitor motor temperatures using temperature sensors. If temperatures are above recommended operating range, vehicle will shut down.

g. Motor may generate an electromagnetic field. To reduce the electromagnetic fields, designer needs to minimize the lengths and loops or curves in the wires.

3. Controllera. User needs to take caution of high or low voltage electrocution. b. Ensure that the controller is completely disconnected and is brought to

a zero energy state before handling or examining the controller. Also the connections have to be properly locked or tagged out with proper LOTO equipment.

c. All locks and tags have to be removed before controller can be reinstated and powered up.

d. Users need to carefully monitor controller temperatures using temperature sensors. If temperatures are above recommended operating range, vehicle will shut down.

e. Controller will be managing high amounts of voltage and amperage which may cause high temperatures. User needs to be cautious of temperature and be sure the unit cooled before handling. To prevent overheating during operating, ensure the cooling system is properly running.

4. Differentiala. The differential contains oil. Ensure all bolts are properly secured and

housing is properly sealed to prevent leakage of any oil. If an oil leak occurs, clean up and properly dispose any oily materials.

b. When working on the differential the differential has to either be disconnected from any sources of power or movement or it has to be jacked off the wheels and the motor has to be properly tagged or locked out to prevent any movement.

c. In case of a oil spill, oil is to be picked up with available spill material (cat litter, oil spill material, etc) and disposed of according to local rules and regulations for disposal of oil and oil soaked materials.

5. Building and Constructiona. Welding – Welders need to be aware and trained of all standard

welding practices. Welder and anyone around the welding area need to

wear proper Personal Protective Equipment (PPE), including gloves and welding mask. In the event of injury, contact emergency personnel.

b. Machining – Fabricators need to be aware and trained of all standard machining practices. The machinist and anyone around the machines need to wear proper PPE, including proper eye protection. In the event of injury, contact emergency personnel.

c. Drilling – Fabricators need to be aware and trained of all standard drilling practices. The machinist and anyone around the machines need to wear proper PPE, including proper eye protection. In the event of injury, contact emergency personnel.

d. Use of hand tools – Fabricators need to be aware and trained of all standard hand tool practices. Anyone using hand tools need to wear proper PPE, including proper eye protection. In the event of injury, contact emergency personnel.

e. Soldering – Fabricators need to be aware and trained of all standard soldering practices. Anyone soldering needs to use the appropriate equipment and proper PPE. In the event of injury, contact emergency personnel.

f. Fiberglass Construction – When laying, cutting, or handling fiberglass, use proper PPE, including latex gloves and surgical dusk masks. When resin is not in use, store outside to cure/cool to prevent fire or explosion. If any fiberglass breaks, user needs be sure to use caution and remove with latex gloves.

g. Handling electronic components – Fabricators need to be aware and trained of all standard electronic handling practices. Fabricators will need to use proper equipment and PPE. Fabricators also need to be aware of the wiring and insulation of the vehicle. No electric wires are allowed to be worked on while electrified. All wire connections and wires need to be insulated and wire routing needs to be reduced to a minimum to help prevent the possibility of electromagnetic fields. Before vehicle is tested or driven for the first time, all electrical connections and wires need to examined and ensured of compliance.

h. The vehicle will need to be completely disconnected and discharged while working on or handling any component on the vehicle.

i. All team members need to be trained in the above specified areas. Any member not trained to do a task, will not be permitted to complete it.

j. 2-person requirement – No working, building, or testing will be allowed without at least two people present. Building in the shop will require at least one team member and one shop employee. Testing and any vehicle work will require at least two team members to be present.

6. Testing and driving a. While testing the vehicle without driver, place vehicle on secure

mounts, (i.e. cinder blocks, etc) to prevent the vehicle from moving. (exception see 6d)

b. The testers need to ensure they use the all necessary equipment for testing the vehicle and any components on the vehicle. This equipment many include the use of lab testing equipment for testing circuits, computer tools to monitor the system, and software required to monitor and program the Programmable Logic Controller (PLC).

c. Any tests in which the motor is connected to the batteries and potentially can make the vehicle move, a driver has to be sitting in the driver seat.

d. Exemption to rule 6a only exists when testing controller. At this point the motor and main drive batteries have to be disconnected and locked or tagged out properly.

e. Buddy system – No working, building, or testing will be allowed without at least two people present. Working in the shop will require at least one team member and one shop employee. Testing and any vehicle work will require at least two team members to be present.

7. Usage of Fluidsa. The vehicle will have several units requiring the use of fluid for

lubricating, cooling, etc. The differential will need to be properly sealed to contain oil.

b. The brakes system will be required to be properly sealed to contain brake fluid. Also brakes will require a release valve to adjust pressure in the system. If a leak in the brake system occurs, the pedal will over-extend resulting in shut down of the vehicle.

c. The controller cooling system will contain water flow and will be examined for any leakage. The cooling system will also contain a release valve to adjust the pressure in the system.

d. The battery cooling system may contain ice or dry ice to quickly cool the battery packs. The Battery packs have to be able to vent to decrease the risk of pressure build up.

e. Handling dry ice gloves and closed toed shoes are required.

8. Safety Requirementsa. A level ABC fire extinguisher will be readily available while driving,

building, and testing.b. In case of a battery fire flush battery packs with water to cool them

and prevent further ignition of surrounding batteries. c. Three Emergency stops within driver’s reach will be placed on the

vehicle.d. The vehicle will automatically stop when brakes extend beyond a

specified position. It will also be programmed to shut down when batteries, motor and controller go beyond operating temperature limits.

e. To prevent the risk of electrocution, no food or liquids will be allowed near the vehicle.

f. According to the safety requirements presented by Formula SAE, a driver is required to escape from the vehicle in less than four seconds in the event that the vehicle becomes a danger.

g. Regulatory agencies controlling the vehicle are Formula Hybrid, Formula SAE and NEDRA. Team will comply with the rules stated by all the regulatory agencies.

9. Other concernsa. Many of the components on the vehicle have very high dollar cost. To

ensure security of these components, we will be locking up all relevant components, including battery packs, controller, motor, and touch screen.

b. Team members and others working with the vehicle will endure some amount of physical activity. Once vehicle is complete, vehicle may be required to be pushed from a position. While building and testing, motor and other heavy components on the vehicle will need to be handled. Larger components will require two or more people to handle.

c. Vehicle will be driven by all team members. All team members are aware of the handling of the vehicle, especially while driving at high speeds. If the driver is unsure of his or her situation, they will use one of the three emergency stops located within driver’s reach on the vehicle. Driver needs to be aware of his or her surroundings and drive the vehicle in a safe manner, especially if driving area is not an open field. In the event of injury, contact emergency personnel.

10. Off-Campus venturesa. Fiberglass molding may have to be fabricated off-campus. We have

intentions of working with professionals in fiberglass to ensure the procedure and creation is done correctly.

b. Painting the vehicle will require us to send the fiberglass body off-campus. Currently we have Bob Steele Chevrolet sponsor us to paint the body of the vehicle.

c. For any traveling with the complete vehicle, it will be necessary to have a trailer.

d. We have been and will continue to collaborate with Steve Cunn of Grassroots to discuss motor and controller issues. We will also be collaborating with our industrial advisors, Larry Davis and Brian Wright of Harris. Any concerns we have with parts used from the 2001-2002 car, we will discuss with the team lead, Jason Powell. Any matters with the differential, we will consult House of Power. We will also be talking with professionals in the fiberglass business.

e. Before any traveling and operating off campus all appropriate documentation will be present or arranged for.

11. Proposal

a. Although Florida Tech students have developed several vehicle projects in the past, this is a very different, unique project. Since we have implemented the use of electric power in the design of our vehicle, we have brought a different aspect of vehicle projects to Florida Tech. Not only is this unique of an electric racecar design, but it requires strong support from very different majors. This project works on the strong support and teamwork of mechanical, electrical, and computer engineering majors.

b. To knowledge of the team, this project has never been proposed in the past. The idea and concept is very unique so no objections have been made to the proposed project.

c. Once the car is complete, we will be traveling to promote this project as well as the school. We plan to go to the Battery Beach Burnout, an electric vehicle conference and race that is held in West Palm Beach from January 26-27, 2007. Although, we will not have a completed car we would like to display the vehicle at this event with the intention of promotion for the school and project and the possibility of more sponsorship. We also intend to compete in the Formula Hybrid competition held in New Hampshire on May 1-3, 2007.

d. We should be covered by the school on all the safety issues we have for this vehicle. No other liability insurance coverage should be necessary.

e. Before any traveling the proper arrangements will be made with Florida tech to ensure appropriate travel documents are present or arranged for.

9.4: References9.4: References(1)“The History of Electric Vehicles.” 2006. New York Times Company. 20

Apr 2006. http://inventors.about.com/library/weekly/aacarselectrica.htm

(2)General Information of Metals, http://www.suppliersonline.com/

(3)MatWeb, http://www.matweb.com/index.asp?ckck=1

(4)Chassis Shop, http://www.chassisshop.com

(5)American Society of Nondestructive Testing, www.asnt.org/ndt/primer3.htm

(6)Hoosier Tires, http://www.hoosiertire.com/Fsaeinfo.htm

(7)Goodyear Tires, http://www.racegoodyear.com/sae.html

(8)Café Electric, http://www.cafeelectric.com/

(9)New Micros, Inc., http://www.newmicros.com

(10) Omega Thermocouples, http://www.omega.com/prodinfo/thermocouples.html

(11) NetGain Technologies, LLC, http://www.go-ev.com/motors-warp.html

(12) EZAutomation PLC, http://www.ezautomation.net

(13) Tillet Race Seats, http://www.tillett.co.uk/estore/shop/kartSeats.asp?seat=T5

(14) Thunder Racing Apparel, http://thunderracing.com/ (15) Formula SAE Competition,

http://students.sae.org/competitions/formulaseries/

(16) Formula Hybrid Competition, http://www.formula-hybrid.org

(17) Fundamentals of Heat and Mass Transfer , 5th Edition, By Incropera and DeWitt

(18) A123 Systems, http://www.a123systems.com

(19) Cornell Stress Analysis Paper,

(20) Aurora Bearing Company, http://www.aurorabearing.com/

(21) Keizer Aluminum Wheels Inc., http://www.keizerwheels.com/

(22) Kawasaki Motorcycles, http://www.kawasaki.com

(23) Carbon Fiber Tubing, http://www.carbonfibertubeshop.com/

(24) SCCA Autocross, http://www.scca.com/

(25) Wilwood Brakes, http://www.wilwood.com/

(26) Introduction to Formula SAE Suspension and Frame Design, http://campus.umr.edu/fsae/library/sae_paper/paper.html\

(27) HexWeb Honeycomb Material, Hexcel, http://www.hexcel.com/NR/rdonlyres/599A3453-316D-46D6-9AEE-C337D8B547CA/0/HexwebAttributesandProperties.pdf