rmi golf cart report

Rolling Motion Industries Drive Golf Cart

Gregory LattariMichael Penso

Eric Wahl

1

Table of Contents

Abstract................................................................................................................................................1

1. Introduction................................................................................................................................................2 1.1 Objective................................................................................................................................................2 1.2 Background................................................................................................................................................2 1.3 Technology................................................................................................................................................5 1.4 Societal Contributions................................................................................................................................................6 1.5 Member Responsibilities................................................................................................................................................6 1.6 Initial Estimated Time Table................................................................................................................................................7

2. Market Research................................................................................................................................................8 2.1 Patent Research................................................................................................................................................12 2.1.1 Two-Speed transmission for electric vehicles................................................................................................................................................12 2.1.2 Motor-drive axle for a motor vehicle................................................................................................................................................14 2.1.3 Transmission unit for axles for vehicles with electric drive................................................................................................................................................15 2.1.4 Summary................................................................................................................................................16

2

3. Product Design................................................................................................................................................17 3.1 Project Design Specifications................................................................................................................................................17 3.1.1 Has to fit 2009 and newer club car golf carts................................................................................................................................................17 3.1.2 Must Handle Weight of Golfers and Accessories................................................................................................................................................17 3.1.3 Must be a Quiet and Smooth Operation................................................................................................................................................17 3.1.4 Must be More Energy Efficient................................................................................................................................................17 3.1.5 Maintain standard 12:1 Gear Ratio................................................................................................................................................17 3.1.6 Must be Comparable in Price Within 20%................................................................................................................................................18 3.1.7 Must have Recordable Data (Volts, Amps, Torque, Decibels)................................................................................................................................................18 3.2 Product Design Criteria................................................................................................................................................18

4. Conceptual Product Design................................................................................................................................................20 4.1 Concept Components................................................................................................................................................20 4.1.1 Concept Component 1 – Mounting ................................................................................................................................................20 4.1.2 Concept Component 2 – Internal Component Restrictions................................................................................................................................................21 4.1.3 Concept Component 3 – Data Monitoring................................................................................................................................................

3

23 4.2 Concept Generation Designs................................................................................................................................................25 4.2.1 Design B – “Total Enclosure”................................................................................................................................................25 4.2.2 Design A – “Separate Enclosures”................................................................................................................................................27 4.3 Concept Design Evaluation ................................................................................................................................................29 4.3.1Weight Factor 5................................................................................................................................................29 4.3.1.1 Affordability................................................................................................................................................29 4.3.2 Weight Factor 4................................................................................................................................................29 4.3.2.1 Assembly................................................................................................................................................29 4.3.2.2 Durability................................................................................................................................................29 4.3.2.3 Quality................................................................................................................................................29 4.3.3Weight Factor 3................................................................................................................................................30 4.3.3.1 Fabricatability................................................................................................................................................30 4.3.4 Weight Factor 2................................................................................................................................................30 4.3.4.1 Serviceability................................................................................................................................................30 4.4 RMI Drive Golf Cart Final Concept................................................................................................................................................31

4

5. Detail Design................................................................................................................................................37 5.1 System Design................................................................................................................................................37 5.1.1 System Overview................................................................................................................................................37 5.2 Subsystems and Components................................................................................................................................................39 5.2.1 Electric Motor Mount................................................................................................................................................39 5.2.2 Traction Drive Input / Output................................................................................................................................................40 5.2.3 Bearings................................................................................................................................................42 5.2.4 Traction Drive Covers................................................................................................................................................43 5.2.5 Transmission Mount................................................................................................................................................46 5.2.6 Differential/Spacer................................................................................................................................................46 5.2.7 Transmission Casing................................................................................................................................................48 5.2.8 Axles ................................................................................................................................................51

5.2.9 Monitoring .......................................................................................................................................52

5.2.9.1 Accuenergy Meter.................................................................................................................................525.2.9.2 Volt Meter.................................................................................................................................52

5

5.2.9.3 Amp Meter.................................................................................................................................53

5.3 Stress Analysis................................................................................................................................................54

5.3.1 Casing.....................................................................................................................................54

5.3.2 Traction Drive Mount Block (TDM)................................................................................................................................................60 5.3.3 Motor Mount (MM)................................................................................................................................................64 5.4 Component Measurement................................................................................................................................................70

5.4.1 Casing, Gear Shafts & Differential Dimension.....................................................................................................................................70

5.5 Component Summary................................................................................................................................................72

6. Prototype: Fabrication, Assembly and Standards................................................................................................................................................74 6.1 Prototype................................................................................................................................................74 6.2 Component Fabrication................................................................................................................................................75 6.2.1 Modified Gear................................................................................................................................................75 6.2.2 Differential Spacer................................................................................................................................................76 6.2.3 Mount Clamp................................................................................................................................................77 6.2.4 Bottom Cover................................................................................................................................................77

6

6.2.5 Side Covers: Left/Right................................................................................................................................................78 6.2.6 Driver Side Case................................................................................................................................................79 6.2.7 Output Shaft................................................................................................................................................80 6.2.8 Input Shaft................................................................................................................................................81 6.2.9 Passenger Side Case................................................................................................................................................82 6.2.10 Motor Mount................................................................................................................................................83 6.2.11 Traction Drive Mount................................................................................................................................................84 6.2.12 Top Cover................................................................................................................................................85 6.2.13 Front Plate................................................................................................................................................86 6.3 Assembly................................................................................................................................................87 6.3.1 Transmission Case................................................................................................................................................87 6.3.2 Traction Drive and Motor Assembly................................................................................................................................................87 6.3.3 Complete Assembly................................................................................................................................................88 6.4 Failures................................................................................................................................................88

7. Assembly................................................................................................................................................93

7

7.1 Testing Procedures................................................................................................................................................93 7.2 Results................................................................................................................................................94 7.2.1 Test 1 – Constant Pedal Position................................................................................................................................................94 7.2.2 Test 2 – Constant Tire Speed................................................................................................................................................94 7.2.3 Results Discussion................................................................................................................................................95

8. Conclusion................................................................................................................................................96 8.1 Future Work................................................................................................................................................96

8

List of Figures

Figure 1: Six Deep Cycle 8V Batteries................................................................................................................................................3Figure 2: Graziano Transmission................................................................................................................................................3Figure 3: Existing Transmission................................................................................................................................................4Figure 4: RMI Traction Drive................................................................................................................................................5Figure 5: Input Shaft and Output Cup Detail................................................................................................................................................5Figure 6: 10-Degree Angle Detail (cm)................................................................................................................................................6Figure 7: Assembled Golf Cart Transmission................................................................................................................................................9Figure 8: (A) from [Figure 7] Outside of Transmission Case................................................................................................................................................10Figure 9: (C) from [Figure 7] Outside of Transmission Case................................................................................................................................................10............................................................................................................................................Figure 10: Two-Speed Transmission for Electric Vehicles................................................................................................................................................13Figure 11: Motor-Drive Axle for a Motor Vehicle................................................................................................................................................14Figure 12: Transmission Unit for Axles for Vehicles with Electric Drive................................................................................................................................................15

9

Figure 13: Rear End Exploded View................................................................................................................................................21Figure 14: Open Differential from Original Transmission................................................................................................................................................22Figure 15: 3.3 hp Golf Cart Motor................................................................................................................................................22Figure 16: Amp Meter................................................................................................................................................24Figure 17: Volt Meter................................................................................................................................................24Figure 18: Installed Sensors................................................................................................................................................24Figure 19: Accuenergy Sensor................................................................................................................................................24Figure 20: Total Enclosure Concept................................................................................................................................................26Figure 21: Traction Drive Inside Passenger Side of Transmission Case................................................................................................................................................26Figure 22: Total Enclosure with Gears................................................................................................................................................27Figure 23: Separate Enclosure Concept ................................................................................................................................................28Figure 24: RMI Final Concept Drawing................................................................................................................................................32Figure 25: Passenger Side Case................................................................................................................................................32Figure 26: Motor Mount Resting on Axle Tube................................................................................................................................................33Figure 27: Motor Mount with Existing Bolt Pattern................................................................................................................................................34

10

Figure 28: Modified Graziano Gear................................................................................................................................................35Figure 29: Inside Components of Transmission................................................................................................................................................36Figure 30: Exploded View 1................................................................................................................................................38Figure 31: Exploded View 2................................................................................................................................................38Figure 32A: Electric Motor Mount to Traction Drive................................................................................................................................................39Figure 32B: Electric Motor Mount to Traction Drive................................................................................................................................................40Figure 33: Female 10-Tooth Spline................................................................................................................................................40Figure 34: Male 10-Tooth Spline................................................................................................................................................41Figure 35: Modified Input Shaft................................................................................................................................................41Figure 36: Output Shaft of RMI Traction Drive................................................................................................................................................41Figure 37: Modified Gear................................................................................................................................................42Figure 38: Radial Bearing................................................................................................................................................42Figure 39: Modified Left Side of Traction Drive................................................................................................................................................43Figure 40: Modified Right Side of Traction Drive................................................................................................................................................43Figure 41: Bottom Side of Traction Drive................................................................................................................................................44

11

Figure 42: Top Cover of Traction Drive................................................................................................................................................44Figure 43: Traction Drive Mount Block................................................................................................................................................45Figure 44: Combined Modified Traction Drive................................................................................................................................................45Figure 45: Mounting Bracket from Traction Drive to Transmission Casing................................................................................................................................................46Figure 46: Graziano Differential................................................................................................................................................47Figure 47: Differential and Modified Output Shaft in Casing................................................................................................................................................47Figure 48: Passenger Side Custom Housing................................................................................................................................................48Figure 49: Driver Side Custom Housing................................................................................................................................................49Figure 50: Full Assembly of Transmission Casing................................................................................................................................................50Figure 51: Passenger Side Axle................................................................................................................................................51Figure 52: Driver Side Axle................................................................................................................................................51Figure 53: Accuenergy Meter................................................................................................................................................52Figure 54: DC-DC Converter................................................................................................................................................53Figure 55: Voltage Reducer................................................................................................................................................53Figure 56: Force Vectors on Driver Casing................................................................................................................................................55

12

Figure 57: Force Vectors on Passenger Casing................................................................................................................................................56Figure 58: Von Mises Stress Analysis Driver Side................................................................................................................................................57Figure 59: Von Mises Stress Analysis Passenger Side................................................................................................................................................58Figure 60: TDM Force Vectors Front................................................................................................................................................60Figure 61: TDM Force Vectors Back................................................................................................................................................61Figure 62: TDM Von Mises Stress Analysis Front................................................................................................................................................61Figure 63: TDM Von Mises Stress Analysis Back................................................................................................................................................61Figure 64: MM Force Vectors Front................................................................................................................................................64Figure 65: MM Force Vectors Back................................................................................................................................................65Figure 66: MM Von Mises Stress Analysis Front................................................................................................................................................65Figure 67: MM Von Mises Stress Analysis Back................................................................................................................................................66Figure 68: Full Prototype of Final Design................................................................................................................................................74Figure 69: Prototype Modified Gear................................................................................................................................................75Figure 70: Prototype Differential Spacer................................................................................................................................................76Figure 71: Prototype Mount Clamp................................................................................................................................................77

13

Figure 72: Prototype Bottom Cover................................................................................................................................................77Figure 73: Prototype Side Covers................................................................................................................................................78Figure 74: Prototype Driver Side Case................................................................................................................................................79Figure 75: Prototype Output Shaft................................................................................................................................................80Figure 76: Prototype Input Shaft................................................................................................................................................81Figure 77: Prototype Passenger Side Case................................................................................................................................................82Figure 78: Prototype Motor Mount................................................................................................................................................83Figure 79: Prototype Traction Drive Mount................................................................................................................................................84Figure 80: Prototype Top Cover................................................................................................................................................85Figure 81: Prototype Front Plate................................................................................................................................................86Figure 82: Broken Output Shaft................................................................................................................................................88Figure 83: Wrong Hole Locations................................................................................................................................................89Figure 84: Cart Mounted on Jack Stand................................................................................................................................................93

List of Tables

14

Table 1: Time Table................................................................................................................................................................................7Table 2: User Needs Survey................................................................................................................................................................................11Table 3: Percentage Graph of Owned Carts................................................................................................................................................................................11Table 4: Patent Matrix Evaluation................................................................................................................................................................................16Table 5: Concept Design Evaluation Matrix................................................................................................................................................................................30Table 6: Material Summary................................................................................................................................................................................54Table 7: Casing Physical Attributes................................................................................................................................................................................55Table 8:Casing Force Vectors 1................................................................................................................................................................................56Table 9: Casing Force Vectors 2................................................................................................................................................................................56Table 10: Casing Force Vectors 3................................................................................................................................................................................57Table 11: Casing Force and Momentum on Constraints................................................................................................................................................................................58Table 12:Casing Results................................................................................................................................................................................59Table 13: TDM Physical Attributes................................................................................................................................................................................60Table 14: TDM Force Vectors 1................................................................................................................................................................................62Table 15: TDM Force Vectors 2................................................................................................................................................................................62

15

Table 16: TDM Force Vectors 3................................................................................................................................................................................62Table 17: TDM Pressure 1................................................................................................................................................................................62Table 18 TDM Pressure 2................................................................................................................................................................................62Table 19: TDM Force and Moment on Constraints................................................................................................................................................................................63Table 20: TDM Results................................................................................................................................................................................63Table 21: MM Physical Attributes................................................................................................................................................................................64Table 22: MM Force Vectors 1................................................................................................................................................................................66Table 23: MM Force Vectors 2................................................................................................................................................................................66Table 24: MM Force Vectors 3................................................................................................................................................................................67Table 25: MM Force Vectors 4................................................................................................................................................................................67Table 26: MM Pressure 1................................................................................................................................................................................67Table 27: MM Pressure 2................................................................................................................................................................................67Table 28: MM Pressure 3................................................................................................................................................................................67Table 29: MM Force and Moment on Constraints................................................................................................................................................................................68Table 30: MM Results................................................................................................................................................................................68

16

Table 31: Final Design Physical Properties................................................................................................................................................................................69Table 32: PCdmis Housing Measurements................................................................................................................................................................................71Table 33: PCdmis Differential Measurements................................................................................................................................................................................71Table 34: PCdmis Gear Shaft Measurements................................................................................................................................................................................72Table 35: Component Summary................................................................................................................................................................................73Table 36: Group Assessment................................................................................................................................................................................92Table 37: Testing Data................................................................................................................................................................................94

17

Abstract

The RMI Drive Project is the implementation of a newly designed traction drive system for integration into 2009 and newer club car golf carts that are used every day by millions of people. This report includes data that will represent everything including, user needs, existing product data, design specifications, conceptual designs and final concept description, design and data analysis. All relevant figure and tables are included within the report.

Golf carts are used in many every day applications and extensively used in the golf industry. This large use of golf carts comes with a large use of energy and we want to design a transmission that will reduce the overall energy consumption of every golf cart the unit is installed into. The standard golf cart transmission has two gear sets – four gears total - and loses most of its efficiency through heat, vibration, and sliding friction. Through data analysis it’s possible to compare the efficiency of two different transmissions. By replacing the standard golf cart transmission with a new RMI transmission we were able to prove an increase in efficiency greater than 10%. These results come from swapping one set of gears with a RMI traction drive. The design is a complete retrofit with no modification to the existing golf cart.

Based on the extraordinary volume of golf carts used, we believe that even slight increases in efficiency will potentially have a significant effect on reducing carbon emissions. This project also can lead into the development of many other electric vehicle applications.

1

1. Introduction

RMI LLC has developed a new traction drive system that has been proven to reduce operating costs over v-belt and gearbox driven systems. With the approval of RMI LLC and the guidance of Stony brook University we will be seeking to integrate the design so that it can be installed into a Golf Cart. This design will reduce the overall energy consumption compared to the existing Graziano transmission currently installed [Figure 2]. Removing one set of gears and replacing it with a RMI traction drive will increase the efficiency; this will require us to design a completely new transmission case and new mounting interfaces for the traction drive. We will also be gathering data such as, volts, amps and time for both new and old transmissions. With these values we can compare the efficiencies of both styles of transmission.

1.1. Objective

The objective of our design is to reduce the electricity used in a golf cart by increasing the efficiency of the drivetrain. We are seeking to modify the power train while remaining within the mounting space of the current transmission. This reduction in electricity used would save money, increase battery life, possibly reduce weight - if a smaller motor can be used - and reduce the total amount of energy consumed. Since this is brand new technology, it has not been tested in any type of transportation vehicle to date. This will contribute to the continued efforts of making our planet a greener place. With the commercial and residential golf cart market being as large as it is, we hope to create a design that can easily be installed into any 2009 and newer Club Car electric golf cart. It is important that the transmission can be retro fit into existing models with minimal mechanical knowledge and ability. The end product would be able to be purchased and installed by anyone from a skilled technician to an amateur mechanic.

1.2. Background

In traditional golf carts, the energy supplied is typically from six deep-cycle 8V batteries. Seen in [Figure 1]. These batteries are wired in series to achieve a total of 48V DC. Electric carts are designed for 36 holes of golf between charging, which is about 12 miles. The power from the electric motor is transferred through a transmission that houses double reduction helical gears. The output of a Graziano Transmission [Figure 2] in a Club Car Golf Cart offers a 12:1 ratio. This is achieved by the first stage of double reduction helical gears producing a 3:1 ratio and a second set of gears producing a 4:1 ratio [Figure 3]. This 12:1 ratio matched with the 3.3 HP motor at 4000 rpm allows for the golf cart to operate at a max speed of 12 to 15 miles per hour. According to the manufacturers specifications, the golf cart currently emits 68.5 dBA of noise and 0.6 m/s2 of vibration at the operator’s position. The current golf cart transmission needs to have its oil changed annually or after every 100 hours of operation. The oil capacity is 22 ounces of SAE 30 WT. API Class SE, SF or SG

2

oil (or higher). [1]

Figure 1: Six Deep Cycle 8V Batteries [2]

Figure 2: Graziano Transmission [3]

3

Figure 3: Existing Transmission [2]

4

1.3. Technology

The technology being used in our golf cart conversion is called the RMI Traction Drive [Figure 4]. We have been supplied a traction drive (Model MD-2) which is currently rated for 3hp. The manufacturer specifications state it has a ratio of 1:3, a max input speed of 5000 rpm and an efficiency of 97%.

Figure 4: RMI Traction Drive

The RMI Traction drive is set on a 10-degree angle from input to output shafts. This angle is required in order to allow the two ceramic balls (C) to engage on the input shaft (A) and the output cup (B). An example of this can be seen in [Figure 5].

Figure 5: Input Shaft and Output Cup Detail

There are many design challenges that are going to be faced while designing the RMI Drive Golf Cart. The biggest challenge being faced is fitting the RMI Drive into the existing case or redesigning the case entirely if it does not fit. The size limitation along with the angle at which the RMI Drive is designed comes into play when trying to retrofit this unit into golf carts. The 10-degree angle is best seen in [Figure 6].

(A)

(B)

(C)

5

Figure 6: 10-Degree Angle Detail (cm)

1.4. Societal Contributions

‘Going green’ has been a big selling point for many new technologies; a greener world is a large part of our future. The main contribution achieved from a more efficient drive system is the reduction of energy used in thousands of golf carts all throughout the world. With a lower cost of operation and a lower power consumption rate, the RMI Drive will contribute to having greener technology globally. This transmission can reduce the carbon footprint of golf carts employing the technology.

2. Market Research

Θ = 10o

Output

Input

6

Aside from the benefits for the golfer, the golf cart is extremely desirable to the golf course owners from a business perspective. Golf courses provide golf carts as a perk for golfers and the course benefits from the higher volume they can achieve due to the decrease in time between rounds. Along with the increased volume of golfers, they also increase their revenue by renting these carts to their patrons. Aside from lawn maintenance, a golf cart fleet is one of the highest expenses a golf course owner can incur. Implementing a way to save energy, increase lifespan, and better the performance of the cart would greatly reduce the operating cost of golf carts. Your typical electric golf cart under extensive use will require new batteries every two to three years and under minimal use about six years. [1] The average cost of each replacement battery is about $100, and each golf cart requires a total of six batteries. The average golf cart fleet size in the United States is 60 carts, which can result in a $36,000 expense in batteries alone. The “golf channel” did a survey and found that on average each course plays about 30,000 rounds of golf per year [6]. If we assume no one walked the course, but each cart was full every time it went out, we can say that a golf cart went 18 holes 15,000 times. If each cart is designed to last 36 holes between re-charge, it would require a full charge 7,500 times. A golf cart with new batteries requires 2.5kWh to charge, and 10 KWh with old batteries. If we average this, a cart requires 6.25 kWh to charge, at 7,500 re-charges, that’s 46875 kWh. In New York the average price per kWh is $0.20, which means each year, golf course owners pay approximately $9,375 in electricity to recharge their fleet. Other than cost, golf is a sport that requires a lot of focus and distractions are extremely frowned upon meaning the quieter a golf environment can be the better. This is where the RMI Traction Drive also benefits golfers because it is quieter than your traditional geared transmission, making this vehicle even more desirable to the golfing community, and recreational user. Outfitting a golf cart with the energy efficient RMI Traction Drive would not only significantly reduce the energy required to propel the golf cart, but reduce the frequency that the golf cart needs to be charged. Lengthening the lifetime of these expensive batteries will dramatically cut costs when it comes to charging and replacement.

Golf carts are not just designed for 36 holes but have grown very popular as an alternate form of transportation. A great example of this can be seen in The Villages, Florida. This is a seniors-only community of around 83,000 residents that was developed in the late 1980’s. There are about 100 miles of golf cart trails and it was developed so that all traveling can be done by golf cart. There are about 50,000 privately owned golf carts located in The Villages. This adds up to be more golf carts than Manhattan has taxis. In many warm weather retirement communities the golf cart is the primary form of transportation. When the primary source of transportation is a golf cart, it means that you cannot go very far or fast. [7] The RMI Traction Drive Golf Cart Transmission will seek to improve the distance one can travel on a normal battery charge.

All electric golf carts are currently being driven by standard geared transmissions as

7

shown in [Figure 7]. This transmission is capable of handling a 3.3 HP motor and produces a 12:1 gear ratio that is broken down into two stages. Stage one produces a 3:1 ratio between gears (A2) and (C1) as shown in [Figure 8] and [Figure 9]. Stage two produces a 4:1 ratio between gears (A1) and (B). The RMI Traction drive will seek to replace gears (C1) and (A2) but produce the same 1:3 ratio. This would leave gear (A1) and gear (B). Gear (A1) will be relocated to the output shaft as seen on [Figure 6] and the shaft spline (C2) will be machined onto the input shaft in [Figure 6]. These alterations will require the design of a new transmission housing to properly fit all modified components. We will also seek to redesign the mounting ability of the traction drive if necessary.

Figure 7: Assembled Golf Cart Transmission

(A)

(B)

(C)

8

Figure 8: (A) from [Figure 7] Outside of Transmission Case

Figure 9: (C) from [Figure 7] Outside of Transmission Case.

In order to be successful in the sales of the new traction drive, we plan on inventing a cost effective system in which a typical golf cart can be retrofitted with the new power transmission device. The main goal is to create a kit that can convert older models to use this new technology. Anyone from a private owner to a large business can buy this product and have it installed in their vehicles. A future goal will be to replace the old technology completely and have the drive installed right from the manufacturer. The cost to produce a prototype that will meet the specifications necessary to propel the golf cart without failure will be kept relatively low due to our collaboration with RMI Drive and their experience with producing these units. The majority of our budget will be spent on the custom design and fabrication of the housings and pieces needed to make the drive compatible.

(A1)

(A2)

(C1)

(C2)

9

2.1.1. Summary

After reviewing the patents that are available we made a comprehensive list of what the three patents had in common and compared them accordingly. The data can be seen in [Table 4].

Table 4: Patent Matrix Evaluation

As can be seen in the table above there is many criteria that are important when creating a design that will work. The fact the transmission can accept an electric motor is the one of the highest scoring features. Equally as important is the fact all the transmissions utilize multiple gears. This feature does not appeal to us because we are effectively trying to reduce the amount of gears in the design. Using the traction drive we will be able to remove one set of gears while still maintaining the 12:1 ratio needed at a higher efficiency. The less gears we can have the more efficient our design will be. With this information we can now begin to create realistic conceptual designs.

3. Product Design

10

3.1. Project Design Specifications

This report contains the PDS for the RMI traction drive golf cart conversion. The purpose is to outfit a golf cart with an energy efficient transmission that has the RMI Drive installed. This would mean removing a gear set in order to increase efficiency. The new design shall be capable of being retrofitted into older models and also have the ability to be installed in newer applications. Our team of three senior year engineering students will be taking on the challenge ahead.

3.1.1. Has to fit 2009 and newer club car golf carts

The transmission that will be outfitted with the RMI Drive must be a direct bolt-on option for both 2009 and newer club car golf carts. It is important that the drive is cost effective and easily installed.

3.1.2. Must Handle Weight of Golfers and Accessories

The transmission must be designed to handle all forces that are loaded on to the golf cart. The force of the golfers, their bags and the strain put on by the terrain are all going to be taken into account. The average male golfer weighs 196 pounds and the average set of clubs is approximately 35 pounds. In total the cart will have to handle about 500 pounds of weight – on top of the 855 pounds the cart weighs itself - while still maintaining its top speed of around 12 to 15 miles per hour and its ability to go up and down hills.

3.1.3. Must be a Quiet and Smooth Operation

The transmission should not be any louder or rougher than the existing alternative. It is to be designed as a quiet and smoothly operating transmission. Helical gears are used in golf carts in order to keep noise down; our goal is to remove a set of these gears completely in order to further quiet the ride.

3.1.4. Must be More Energy Efficient

The transmission should be able to reduce the overall operating cost of a golf cart. With a higher efficiency rating we should see longer battery life, which should allow the golf cart to go further on a single charge.

3.1.5. Maintain standard 12:1 Gear Ratio

The transmission should maintain the same gear ratio as the existing alternative, which is known to be 12:1. Maintaining the same ratio will allow our design to be comparable to the existing design performance.

3.1.6. Must be Comparable in Price Within 20%

11

The transmission should be priced within 20% of the existing alternative in order to be competitive in the market place. The price can be altered based on how efficient the final design is.

3.1.7. Must have Recordable Data (Volts, Amps and Time)

The transmission must be tested and recorded before, after and during use. The parameters for both data sets will be equivalent in every way for more consistent results. All Amps, Voltage and time readings will come directly from the motor and batteries measured by volt and amp meters. By placing the recording devices on the golf cart itself we can compare our values directly with no moving or switching of the sensors.

These specifications will be used to guide us through the design and testing of the product. Some specifications will prove to be more valuable than others as the design comes to maturity.

Meeting specification one, two and three is critical to the success of this product and project. Since this is not an existing product these specifications will not be completely analyzed until the first concept is created. As each design is completed and tested we will have a broader knowledge base on how we can more closely create a design that meets these specifications.

3.2. Product Design Criteria

With the product design specifications listed in section 3.1 we will be able to create a quantifiable table that will assist us in choosing the best design throughout the report. Each criterion chosen is assigned a weight based on how it will affect the final design, the more important the criterion is found to be, and the higher the weight it will be assigned. These topics will be elaborated upon in section 4.3 of this report.

3.2.1. The combined cost of the product including the manufacturing, raw material, installation and sale cost should be as low as possible. This is to stay competitive in the current market.

3.2.2. The design must be easily retrofitted to 2009 and newer club car golf carts and should maintain a similar profile as the existing alternative. We have a working area where the existing transmission is of 24” x 15” x 12”. All designs will have to maintain a size that is within these parameters.

3.2.3. The final design should maintain or be within 20% of the weight of the existing product. The existing product currently weighs 29 lbs. This would give us a range of 29-35 lbs.

12

3.2.4. The final design should be more energy efficient than the existing alternative. The projected efficiency increase is currently 10%. The average golf cart can travel about 12 miles on a single charge. (Refer to Section 1.2)

3.2.5. The final design will seek to decrease the amount of total gears inside the transmission case. The existing alternative has two sets of helical gears and we will be reducing that to one.

Both the product design specifications and criteria will create a straightforward approach that we can use to create the best possible final design. With every new design and alteration there will be a reevaluation; the reevaluation will be necessary in order to keep track of the potential designs that can be taken to the final design process.

4. Conceptual Product Design

13

The conceptual product design process is an integral part of bringing an idea to life. There are a total of three possible design concepts being compared for the RMI Drive Golf Cart. Each design will be rated comparatively and the best selection will be the product with the highest cumulative total. Since this is a totally new product, concepts can vary greatly which means choosing the best possible design is integral to the success of the project. The design criteria have been previously stated in section 3.1 of this report and will be used as our basis for our conceptual design as well.

4.1. Concept Components

Concept components are what we are using to help us create better working concept generation designs. These components are an integral part of our thought process when coming up with the designs that will be seen in section 4.2 of this report. Section 4.1.1, 4.1.2 and 4.1.3 below clearly state our results when coming up with working concept generation designs.

4.1.1. Concept Component 1 – Mounting

The first concept component consists of how golf cart transmissions are mounted to a golf cart. Golf cart transmissions are most commonly mounted in-between two axles on the lower portion of the transmission case. The driver side axle, which measures in at 25.3 cm (9.96”), is shorter than the passenger side axle of 50.4 cm (19.84”) as seen in [Figure 3]. The reason behind this design is that the electric motor, which is bolted directly to the upper half of the transmission case, overhangs on the passenger side. The leaf springs that the axles are mounted to support the weight of the electric motor and the transmission; the axles are designed to be a certain distance apart. Locating-pins are mounted on the leaf springs while the mounting brackets, that have holes to accept the pins, are welded to the axle tubes. The mounting bolt pattern for the axles have to be properly oriented to ensure proper alignment of the locating-pins. These components will ensure proper orientation of the drive assembly when complete and all of these specifications can be seen in [Figure 13]. It is important when generating concepts to be able to easily retrofit the new design into older products. With all this information in mind we must maintain the same width as the original transmission case, which is 6.3014” wide. Inside the rear of the golf cart, where the transmission is mounted, there is a volume of 13.75” x 21” x 12” that we have to keep our design specifications within. As long as we stay within the specified volume there will be no other modifications that will need to be done to the golf cart to accept the new transmission. These are major factors that dictate an easy retrofit design.

14

Figure 13: Rear End Exploded View [2]

4.1.2. Concept Component 2 – Internal Component Restrictions

With the design of the new transmission there will be some regulating factors that cannot be changed. Since we don’t plan on making every component, pieces from the original transmission will be used in the new design. The open differential, as seen in [Figure 14], will be removed from the original transmission and installed into our new design. This adds a degree of difficulty because there are constraints that we cannot break. The width of the differential from bearing to bearing is 5.032” wide. The bearing width is 0.591” and has a diameter of 2.677”. This means our design concepts will have to accommodate the width of the original differential and the case must have mounting holes for the bearing to be seated inside. We will also be using the same spline as in [Figure 9] and the same smaller gear as seen in [Figure 8 (A1)]. The spline will have to be machined onto the existing input shaft and the gear will have to be installed onto the output shaft of the RMI traction drive. These splines will provide the male component when mounting the electric motor to the traction drive. The electric motor is already outfitted with the female component as seen in figure [Figure 15]. The splines on the input of the traction drive will slide into the electric motor and this will allow for power transmission from the electric motor to the first stage of the transmission. The traction drive will produce the first gear ratio of 3:1 without the use of any gears and provide power to the second stage of the transmission. The second stage of the transmission will be provided when gear (A1) seen in [Figure 8] is driving the open differential seen in [Figure 14]. Gear (A1) will be mounted the output shaft of the traction drive. Using an interference fit or the use of setscrews between gear (A1) and the output shaft of the traction drive can accomplish this. This is to prevent the gear from free spinning on the output shaft of the traction drive as seen in [Figure 6]. Once mounted, the output gear to the differential will prove a 4:1 ratio and complete the overall desired ratio of 12:1.

15

Figure 14: Open Differential from Original Transmission

Figure 15: 3.3 hp Golf Cart Motor

Female Output

16

4.1.3. Concept Component 3 – Data Monitoring

The third concept component will consist of a monitoring system. This will provide all the data to properly compare the original transmission against the newly designed traction drive transmission. To have results worth comparing, careful selection in instrumentation is crucial. Golf carts do not have sensors and gauges installed to acquire any information, this task is entirely new and will be specific to our project only. This provides a challenge, since retrofitting a data-recording gauge set is imperative to properly documenting a standard golf cart transmission. Aspects to be recorded will include volts amps and distance. All sensor components will be mounted on the golf cart itself. This provides a unique way of measuring both transmissions without compromising the recorded data. Installing the equipment on the old and new transmissions would require double the amount of sensors. If everything is mounted on the cart itself all constants will remain equal and there will be no disputing the data. This will make it easier than having to design two sensor subsystems for the transmission. We will install an amp meter on the last battery, in series, on the negative side in-between the electric motor and the battery. This will provide us with the amps drawn from the electric motor needed to move the golf cart. Amp readings can be used to calculate torque and horsepower provided from the motor. A voltmeter will be installed on the positive side on the first battery in series and the negative side of the last. This will provide us with a full 48v reading across all the batteries. [Figure 16], [Figure 17], [Figure 18], [Figure 19] show an example of the type of gauges that will be seen in our design.

17

Figure 16: Amp Meter [8]

Figure 17: Volt Meter [9]

Figure 18: Installed Sensors

Figure 19: Accuenergy Sensor [13]

18

4.2. Concept Generation Designs

In conceptual component 1, where and how to mount the unit will be discussed in each conceptual design. Component 2 will require us to design a transmission, which can accept existing parts from the original transmission such as the open differential. Concept component 3 will be installed on the golf cart itself and won’t play into the designing of the new transmission case. We have generated two different design concepts, which can meet the previously discussed requirements in section 3. We will evaluate these designs in a matrix against each other and choose the highest scoring concept as our final product design.

4.2.1. Design B – “Total Enclosure”

The total enclosure concept is based off of the idea that the transmission housing will encompass the traction drive and the differential. This design will replace a set of helical gears currently in the golf cart transmission. The gears being replaced are (A2) in [Figure 8] and (C1) in [Figure 9], with a RMI Traction Drive. Replacing the current helical gears will prove to be very quiet since all components, besides the electric motor, are enclosed in the housing. The conceptual housing will be constructed of two aluminum pieces. The driver side will be a flat rectangular piece, while the passenger side will have a spot to mount the traction drive and electric motor as seen in [Figure 20]. The electric motor will mount to the outside of the passenger side housing with the original three bolt mounting design. The drive side case will measure 12” x 8” x 3.3” overall and the passenger side case will measure 12” x 8” x 12”. The traction drive will mount to the inside of the passenger side case with four bolts as seen in [Figure 21]. These bolts will go though the case and screw directly into threaded holes on the bottom of the traction drive. These bolt holes will have to be sealed so oil does not leak out. The traction drive will mount inside the case and a gear will be connected to the output shaft. This gear will then rotate the open differential, which is supplied from the original transmission, which is simply drawn in [Figure 22]. The output gear will send rotational energy through the traction drive and convey it to the differential and the axles. The axles will slide into the differential and mount to the outside of the casing, just like the original golf cart transmission. The traction drive is capable of producing a 3:1 ratio for the first stage and the transmission will still produce a 12:1 ratio overall. This will allow the golf cart to travel at the same speeds and produce the same torque as the original transmission. This design will mean that the gears and the traction drive will share the same lubrication. The lubrication used in the traction drive is a proprietary blend and does not have the same properties as oil used for gears. This means either the traction drive or gears will not have the proper lubrication and can cause problems in the future. The passenger side casing will be large in comparison to standard transmission casing so aspects such as raw materials, machining time, and cost will increase. This design is shown in [Figure 20].

19

Figure 20: Total Enclosure Concept

Figure 21: Traction Drive Inside Passenger Side of Transmission Case

3.3 HP Motor Input

20

Figure 22: Total Enclosure with Gears

4.2.2. Design A – “Separate Enclosures”

The separate enclosure concept will require that the traction drive, (B) in [Figure 23], be mounted on the outside of a custom-made transmission case, (A) in [Figure 23]. This design will provide a simple way to mate all major components of the drivetrain and allow servicing to be done on each component separately. The input side of the traction drive will have to be modified to accept the electric motor, (C) in [Figure 23]. The original 3.3 hp motor used on the old style transmission will be the same motor used on the new traction drive transmission. The motor comes with a standard 10-tooth female spline shaft that accepts a male counterpart with the same spline design as seen in [Figure 9]. The required spline configuration will be machined onto the input shaft of the traction drive, which will allow the electric motor to transmit power to the input side of the traction drive. The outer housing on the input side of the traction drive will have to be modified to allow the 54lb electric motor to face mount directly to it. The housing must be designed with the original 3-bolt mounting configuration that the electric motor is currently using; the motor will be mounted on an upward angle of 10° which is naturally produced by the traction drive. The output side of the traction drive will be required to face mount directly to the transmission. This will require the use of a new mounting bracket for the traction drive, which will be co-designed by RMI LLC and our design team. There will have to be a way to seal the traction drive and transmission case mounting point; this can be accomplished with a gasket or an O-ring mounted between the traction drive and transmission case. The O-ring or gasket seal will prevent oil from leaking out of the transmission and putting the golf cart at risk of major issues. The traction drive itself is a sealed system in this application and will not leak regardless of mounting

Open Differential (To Axle)

Output Gear (From Traction Drive to Differential)

21

configurations. This setup will allow the use of separate lubrications between the traction drive and differential gears. Standard gear oil in the original transmission is SAE30 and the traction drive uses a proprietary blend only offered by RMI. Separated cases will allow for separate fluid changes, maintenance, and repair. In this design a 3:1-ratio-traction-drive will be installed. This will allow the overall transmission ratio to remain 12:1 when completed by the 4:1 ratio gear set that is mounted to the output of the traction drive mating with the differential gear ring. With this design the only restraints are to maintain the same axle-to-axle width profile as the original case and stay within the 13.75” x 21” x 12” space in the rear of the golf cart. With this being achieved it can easily be retrofit in 2009 and newer Club Car golf carts by anyone who is slightly mechanical. This concept will prove to be quieter than standard transmissions due to the removal of a set of gears. Since the drive train components are separate and the transmission case will be a smaller design, the raw material and machining time could be kept to a minimum. This design is shown in [Figure 23].

Figure 23: Separate Enclosure Concept

4.3. Concept Design Evaluation

22

In order to effectively compare both of the designs above we have to create a set of criteria to evaluate each design semi-quantitatively. The two designs are being compared to the criteria, not each other. The evaluation has multiple criteria that have a weight set from one to five (5 = most important, 1 = least important); each design can score up to five points per category, which is then multiplied by the weight. The reasoning and comparisons can be reviewed below and the final results can be seen in [Table 2].

4.3.1. Weight Factor 5

4.3.1.1. AffordabilityAffordability is the number one concern when dealing with production of an item that is going to be marketed for sale. Not only do we want our production cost low, but the consumer wants their purchasing cost low too. When it comes to the two designs, design A beats out design B by a considerable margin. The shear amount of material needed for design B in order to encase both the differential and traction drives brings its cost way up. Since Design A has separate housings it can use less material, bringing the cost way down.


4.3.2.1. AssemblyAssembly has a large importance to our designs. A main factor in our designs is that we want it to fit into 2009 and newer club cars with little effort. We want to build a stand-alone unit that can be installed by any mechanic or hobbyist there is. Both designs encompass this so they both received the same score.

4.3.2.2. DurabilityDurability is a main concern when it comes to products that a company puts its name on. A product that lasts is one way to ensure you have a loyal following when the product becomes more popular. Design B rates higher than design A because it is made with more material and has less parts that are open to the environment; even though design A will be about as reliable, it still scores lower due to this fact.

4.3.2.3. QualityQuality and Durability are very closely related but differ only at the fabrication side. It is important that the product being marketed is consistently sold at the highest standards available. Since both designs are going to be manufactured by the same company using the same techniques and machines, both designs score the same.

23


4.3.3.1. FabricatabilityFabricatability scores a little lower than most of the others because all though it is important, it does not have very much to do with the product when it reaches the consumer. Design A beats out design B because design B needs more material and bigger machines to produce. Since there is more effort being put in it scores lower in this category.


4.3.4.1. ServiceabilityThe lowest on the importance scale for these designs is serviceability. It is assumed that the people who use golf carts just drop them off at the end of their round or have their privately owned carts serviced at a shop. Design A scores very highly in this category because of the ability to change the oil and service the transmission and traction drive separately. Since design B has only one case you would have to take apart the entire thing if one small part of the traction drive broke.

Table 5: Concept Design Evaluation Matrix

It can be seen that design A scored the best overall beating design B by 13 points. This matrix proves that design A is the superior concept and should be the design we focus our attention on. It won in almost every category and with good justification. Design A is going to be the focus in order to get our final design as good as it can be.

24

4.4. RMI Drive Golf Cart Final Concept

After comparing all data and conceptual designs throughout the design process RMI Drive Transmission is going to most closely represent the separate enclosure concept seen in [Figure 23] with a few added design details in order to make it applicable in a real life situation.

The separate enclosure concept will require that the traction drive be mounted on the outside of a custom machined transmission case. This design will provide a simple way to mate all major components of the drivetrain, while keeping them separately serviceable. The input side of the traction drive will have to be modified to accept the electric motor. The original 3.3hp motor used on the old style transmission will be used on the traction drive transmission. It comes standard with a 10-tooth female spline shaft that accepts a male counterpart with the same spline configuration. These splines will be machined onto the input shaft of the traction drive. This configuration will allow the electric motor to transmit power to the input side of the traction drive. The outer housing on the input side of the traction drive will have to be modified to allow the 54lb electric motor to face mount directly to it.

The designed transmission will have to be able to maintain its integrity while going over unavoidable road imperfections. The transmission casing and traction drive will have to be designed sturdier in certain areas to prevent flexing or even breaking. Major areas of concern are the holes for the mounting bolts. These holes are located on the mounting brackets of the electric motor to the traction drive and the traction drive to the transmission casing. The biggest area of concern is the mounting of the traction drive to the transmission case. At this location the weight of the electric motor and traction drive are cantilevered off the transmission casing and will produce severe stress concentrations around the mounting holes, especially on the upper mounting area. The bolts located on the upper half of the traction drive mounting bracket will be more susceptible to failure since they are holding most of the weight.

25

Figure 24: RMI Final Concept Drawing

The traction drive to transmission case face will consist of four equally spaced grade 5 mounting bolts approximately 3.5” deep by 3/8” in diameter (Using SAE J429 ASTM A449). The transmission casing will have the appropriate mounting holes and thread pattern machined into it during production. This is to distribute the weight of the traction drive equally along the transmission case. The passenger side case is designed to have steps in it to decrease the weight of the case and overall length of the design. This configuration can be seen in [Figure 25].

Figure 25: Passenger Side Case

During prototyping we plan to deal with the forces coming from the weight of the motor by machining the motor mount so that it goes from the electric motor to the passenger side axle. This will remove the moment caused by the

26

unsupported weight on the case and transfer it to the steel tube housing of the passenger side axle [Figure 26]. The axle tubing is strong enough to compensate for the weight and moves simultaneously with the transmission. The housing must be designed with the original three bolt-mounting configuration the electric motor is outfitted with. The bolt pattern being used can be seen in [Figure 27].

Figure 26: Motor Mount Resting on Axle Tube

27

Figure 27: Motor Mount with Existing Bolt Pattern

The input shaft on the traction drive must slide into the electric motor a minimum of 0.5” but not more than 1.2”. These dimensions will prevent the shaft from being too long and bottoming out inside the motor. If the input shaft bottomed out on the motors female output, it would not allow the motor and traction drive to properly mate and will cause major problems. At the same time having an input shaft longer than 0.5” will provide enough length to prevent shearing or any deformation of the input shaft under high stress. The input and output shafts on the traction drive will be machined out of 52100 steel. RMI chose this steel because it has high resistance to deformation, cracking, and heating, while offering superior hardness and is cost effective [12]. The electric motor will be mounted on an upward angle of 10°, which is naturally produced by the traction drive. The rest of the components in the traction drive are machined out of 6061-T6 aluminum, which is also what the transmission case will be machined out of. This is a good metal that is easier to machine than steel and it’s available in large block sizes at a low cost, which will be required to produce the transmission case.

The output shaft of the traction drive will extend into the new transmission case

28

attaching to shaft housing gear (A1) from [Figure 8] by use of a double keyway. Since the gear is proprietary to Graziano we had to customize our own gear out of the pre-existing gear that was already installed in the golf cart. This process consisted of grinding the gear shaft down to size, drilling a through hole and creating a keyway using a Wire EDM Machine. The finished part can be seen in [Figure 28]. The output gears purpose is to transfer energy from the electric motor to the differential.

Figure 28: Modified Graziano Gear

The standard gear oil in the original transmission is SAE30 while the traction drive uses a proprietary blend only available through RMI LLC. This design will allow for separate fluid changes, maintenance, and repair. The new transmission will have a magnetic drain plug installed on the drivers side. This will allow for easy servicing and the drain plug will collect any metal that is deposited into the oil through hours of use. There will be a fill plug at a predetermined height on the side on the transmission case, which will only allow the proper amount of oil to be installed inside the casing. This will prevent over filling the transmission when being serviced.

To reinforce the traction drive output shaft a radial bearing will be mounted on the end of it. This bearing will then slide into a precision-machined hole internally on the driver’s side transmission case. This bearing to hole coupling will occur naturally when the traction drive is mounted externally on the passenger side. The shaft will slide through the hole on passenger side inserting it into the modified gear shaft and it will rest in the bearing mounted on the driver side case. This design will keep the concentricity of all parts within a very low tolerance. It is important to maintain alignment to the best of our ability because unaligned components can produce unwanted forces that increase wear on all parts. In order to save room we mounted a spacer on the differential. This allows

29

us to set the unit further into the case footprint allowing us to shorten the overall length of our design. A spaced differential along with the custom gear can be seen in [Figure 29].

Figure 29: Inside Components of Transmission

Although the new transmission case will be smaller than the original design, it will produce a bigger drivetrain footprint in the golf cart. The traction drive eliminates one set of gears but will extend further on the passenger side. This will make the motor stick out approximately 1.789” more than the original transmission. With the use of a 3:1 ratio traction drive, the overall transmission ratio would remain the same as the one produced by the original. This is completed by the 4:1 ratio produced by the gear mounted to the output of the traction drive mating with the differential ring gear. Through gear multiplication this equals the desired original ratio of 12:1.

5. Detail Design

30

This section is comprised of the detailed designs of components and the overall system. The overall system is explained in detail in section 5.1. Section 5.2 described the individual component designs used in section 5.1. This will serve as a parts list of needed components to complete a prototype. A summary is located at the end of section 5.

5.1. System Design

This section will describe in detail the overall design, which was chosen in section 4. This will outline the whole system and how each component will work together. CAD drawings of the system will be included as a visual aid to see how all the components will work together and create a functioning golf cart transmission.

5.1.1. System Overview

When all the components in the system are assembled it provides a new way to transmit power from an electric motor to a wheel. [Figure 30] shows an assembled drawing of what the new transmission will look like. The first component needed to build a complete system is the electric motor mount, as seen in [Figure 30], (Part A). This allows the electric motor, which is supplied with the golf cart, to mount to our new transmission design. This electric motor mount was designed to bolt to the input side of the modified traction drive. The electric motor mount was designed to support the weight of the electric motor and distribute it to the steel axle housing. The modified traction drive, (Part B), is designed to have a spline on the input shaft, which mates the to electric motor and allows power to be transmitted without slip between components. The output side of the traction drive is also modified to allow it to work in the transmission system. The output side has an extended shaft, which slides through a completely assembled transmission case. The output side has an extended shaft with one 3/16” keyway slot. This will mate with the gear shaft, which has a hole in the center with one internal keyway slot. The traction drive has a modified mount to allow it to attach directly to the passenger side of the transmission case. The two-piece transmission case design will allow the internal components to be easily installed and serviced. This casing will house five bearings, one gear mounted on a shaft, a differential, a seal and an O-ring. The case will have spots for the axle tubes and traction drive to mount. Once mounted, the modified gear shaft, as seen in [Figure 28], mates to the ring gear on the differential. The bearings on the output shaft are to prevent unwanted movement and provide stability under heavy loads. The differential, seen in [Figure 29], is mounted in-between the two-piece transmission case and rides on two radial contact bearings. The differential has two female spline inputs, which allow the axle splines to engage with the differential and transfer the rotational energy from the differential to the axles. The axle

31

tubes mount to the transmission case and house the axles, which slide into the differential. These are all the components needed to assemble a complete transmission system utilizing a traction drive.

Figure 30: Exploded View 1

Figure 31: Exploded View 2

5.2. Subsystems and Components

32

Described in the sections below is a detailed description of the entirety of our design seen in [Figure 31]. Each section has a detailed concept drawing along with a detailed description, which describes the component and explains the reason for its design.

5.2.1. Electric Motor Mount

Figure 32A: Electric Motor Mount to Traction Drive

This part plays a major role in our design concept. This part of the transmission allows the motor to be mounted to the RMI Traction Drive. The electric motor will be mounted on an upward angle of 10°, which is naturally produced by the traction drive. This has the mounting bolt pattern of the electric motor so they can be bolted together. This component will be machined out of 6061-T6 Aluminum. This Motor Mount sits directly on the axle tube in conjunction with the motor clamp [Figure 32B] in order to support the weight of the motor and all the stresses it encounters.

33

Figure 32B: Motor Mount Clamp

This part was designed to create a more rigid connection between the axle tube and motor mount. The axle that the transmission is attached to slides into the rounded part of the motor mount clamp and two 3” grade 5 3/8” bolts are then attached from the motor clamp to the motor mount (Using SAE J429 ASTM A449).

5.2.2. Traction Drive Input/Output

The modified input shaft is 4.21” long and can be seen in [Figure 35]. The shaft will have a 10-tooth spline machined into it so that it can mate with the output of the electric motor as seen in [Figure 33] and [Figure 34]. This shaft will be machined to accommodate two 1.1811” inner diameter by .472” width taper roller bearings. The smaller flat spot contacting the input spline will be machined to accommodate a bearing with an inside diameter of .787” and a width of .27”. This configuration will allow the modified shaft [Figure 35] to transmit its energy through the traction drive and along to the Traction Drive Output.

Figure 33: Female 10-Tooth Spline

34

Figure 34: Male 10-Tooth Spline

Figure 35: Modified Input Shaft

The modified output shaft as seen in [Figure 36] will have our modified gear mounted on its shaft with a 3/16” key way to prevent free spinning on the shaft. The output of the drive extends through the passenger side transmission case, slides through the gear shaft and sits in a .59” inner diameter by .354” wide radial bearing in order to drive the differential. The gear can be seen in [Figure 37].

Figure 36: Output Shaft of RMI Traction Drive

35

Figure 37: Modified Gear

5.2.3. Bearings

To reinforce the traction drive output shaft tapered roller bearings will be installed to handle the forces. This will provide greater rigidity for the output shaft instead of the standard angular contact bearings. 0.984” inner diameter radial bearings will be used to hold the gear shaft in place. These Bearings provide great support under heavily loaded shafts and offer minimal wear and resistance.

Figure 38: Radial Bearing

36

5.2.4. Traction Drive Covers

The RMI Traction Drive original design did not fit into our new transmission design. The traction drive requires modification in order to handle the extra stress from all of the components and fit properly within the constraints of the golf cart. The side and top covers were designed to be .75” wide. This will increase the carrying capacity of the drive and should be able to withstand face mounting it to the transmission case and the weight of the electric motor mounted to it as well. The bottom cover was designed to be .21” thick because it needed to clear the axle housing. The bottom cover also has a small recess in it so the axle still fits without any modifications. This 1” x 1” x .18” recess can be seen in [Figure 42]. The cases got more mounting bolts to reinforce the rigidity of the drive as well.

Figure 39: Modified Left Side of Traction Drive

Figure 40: Modified Right Side of Traction Drive

37

Figure 41: Bottom Side of Traction Drive

Figure 42: Top Cover of Traction Drive

38

Figure 43: Traction Drive Mount Block

When all parts ([Figure 37, 39, 40, 41,42 and 43]) are combined the end result is a completely assembled traction drive as seen in [Figure 44].

Figure 44: Combined Modified Traction Drive

39

5.2.5. Traction Drive Mount – Modified cover

The traction drive to transmission case mounting face will consist of four equally spaced grade 5 engineering standard SAE J429 ASTM A449 mounting bolts approximately 3.5” deep by 3/8” in diameter. The casing is going to be drilled in order to accept this piece with the traction drive mounted to it. This piece will distribute weight of both the traction drive and motor along the transmission casing. The mounting bracket will have more material around the mounting holes to increase the capacity it can hold. In order to save additional space the plate was notched 1” inward to allow the unit to sit further into the transmission casing, reducing the overall footprint. The RMI Traction Drive is a sealed system also will not leak regardless of mounting configuration; this setup will allow the use of separate lubrication between the traction drive and differential gears. Standard gear oil in the original transmission is SAE 30 while the traction drive uses a proprietary blend only available through RMI LLC. This design will allow for separate fluid changes, maintenance, and repair.

Figure 45: Mounting Bracket from Traction Drive to Transmission Casing

5.2.6. Differential/Spacer

The differential being used is also a proprietary Graziano design that can be seen in [Figure 46]. The casing was designed in order to accept this differential along with all of the other parts in order to transfer the energy to the wheels. The ring gear of the differential matches up with the small Graziano helical gear. This small gear was modified to attach to the output shaft of the RMI Drive. Along with the modified gear, a spacer was incorporated in order to set the ring gear back 1.681” in order to reduce the overall footprint of the design. The bolt pattern on the ring gear will be matched on the spacer and will allow the use of 2.75” bolts in order to mate the ring gear with the differential. [Figure 47] shows the mating of the spaced differential and the modified output shaft.

40

Figure 46: Graziano Differential

Figure 47: Differential and Modified Output Shaft in Casing

41

5.2.7. Transmission Casing

The transmission casing is a crucial part of the RMI Transmission design. The casing is designed to accept both newly fabricated parts and existing parts from the old transmission. The inside of the casing accepts the differential, bearings, output shaft and the small Graziano helical gear. The design also incorporates an o-ring and a seal to restrict the mixing of oil between the gear and traction drive. [Figure 48] shows the side of the outside of the transmission casing that will accept the modified RMI Traction Drive. The four 3/8” holes near the top are where the front cover is bolted in to firmly attach the drive to the casing. The lower hole accepts the existing axle in order to mate them with the new modified parts.

Figure 48: Passenger Side Custom Housing

42

Figure 49: Driver Side Custom Housing

The inside of the transmission casing is where the small helical gear and the differential are combined. [Figure 50] shows how all of this is designed to that old and new can come together smoothly. This casing is designed to be relatively the same size as existing transmissions so it can replace them with ease.

43

Figure 50: Full Assembly of Transmission Casing

44

5.2.8. Axles

The axles we are using are part of the existing design. The passenger side (side with motor above it) measure in at 50.4 cm (19.84”) long and the drivers side axle measures in at 25.3 cm (9.96”) long. From the case to the leaf spring perch on the axle is 13.75”. The perch is located directly in line with the frame so this constrains our design to 13.75” passed the axle flange. These components are not modified because they need to maintain the same length and total width in order to fit into 2009 and newer club cars. The two axles still mount into the existing differential the same as they did in the current design. The two axles are shown in [Figure 51] and [Figure 52].

Figure 51: Passenger Side Axle

Figure 52: Driver Side Axle

45

5.2.9. Monitoring

With the implementation of the RMI Traction Drive technology in our design information regarding the efficiency is needed. With the use of a Accuenergy monitoring devices we will be able to record all of the information needed to prove the efficiency gains of our design. All of the monitoring equipment will be installed on the golf cart itself; rather than have it individually on each transmission. Installing the equipment on the old and new transmissions would require double the amount of sensors, with our design we will have one set of sensors that can be easily recorded from a laptop.

5.2.9.1. Accuenergy Meter

The distance can be recorded using the device seen in [Figure 53]. The distance will allow us to see how far we have traveled, which will show us our true efficiency values when comparing the two different transmissions.

Figure 53: Accuenergy Meter [13]

5.2.9.2. Volt Meter

A voltmeter, as seen in [Figure 17], will be installed on to the batteries to display the existing voltage. Since the batteries are wired in series we will connect the positive and negative cables on the first and last battery in series to monitor the full 48-volt system.

46

5.2.9.3. Amp Meter

The amp-meter, as seen in [Figure 16], will be installed on the last battery, in series, on the negative side in-between the electric motor and the battery. This will provide us with the amps drawn from the electric motor needed to move the golf cart. Amp readings can be used to calculate torque and horsepower provided from the motor. A DC-DC isolated converter - as seen in [Figure 56] - isolates the ground of the 12-V side of the system so that the current does not back-feed into the 48-V side. If back feeding were to occur, the amp meter display could burn out. A transformer 48 volt to 12 volt, as seen in [Figure 57], converts the 48-volt battery supply from the golf cart into 12-volts. This is needed because the amp display runs off of 12-volts and would fail if it was given the full 48-volts.

Figure 54: DC-DC Converter [14] Figure 55: Voltage Reducer [15]

47

5.3. Stress Analysis

Using Autodesk Inventor Professional 2016 we were able to do a Von-Mises stress and displacement analysis using simulated forces associated with what we are expecting the golf cart to encounter. With the design of new parts we need to make sure that the shape and placement of all components will have all necessary requirements to do everything that it was designed to do. The material for all parts used can be seen in [Table 6].

Table 6: Material Summary

5.3.1. Casing

Our transmission casing housing will be machined out of T6-6061-Aluminum. With the use of Autodesk Inventor we were able to do a Von-Mises stress analysis using assumed forces. The figures below displays arrows in the direction at which the forces are working. With the results produced for the case we can see that it has been built ruggedly enough to withstand the forces of holding the electric motor, traction drive and mount. It was strong enough so minimum stress concentrations were produced around the boltholes of the axle tubes which, holds the transmission in place. The displacement was minimal and not of concern. All the calculated results can be seen [Table 11].

48

Table 7: Casing Physical Attributes

Figure 56: Force Vectors on Driver Casing

49

Figure 57: Force Vectors on Passenger Casing

Table 8: Casing Force Vectors 1


50


Figure 58: Von Mises Stress Analysis Driver Side

51

Figure 59: Von Mises Stress Analysis Passenger Side

Table 11: Casing Force and Moment on Constraints

52

Table 12: Casing Results

53

5.3.2. Traction Drive Mount Block (TDM)

Our traction drive mount block will be machined out of T6-6061-Aluminum. With the use of Autodesk Inventor we were able to do a Von-Mises stress analysis using assumed forces. The figures below displays arrows in the direction at which the forces are working. With the results produced for the mount block we can see that it has been built ruggedly enough to withstand the forces of holding the traction drive, motor mount and motor to the transmission casing. It was strong enough so minimum stress concentrations were produced around where the unit enters the mount. The displacement was minimal and will not affect how the unit functions. All the calculated results can be seen [Table 20]

Table 13: TDM Physical Attributes

Figure 60: TDM Force Vectors Front

54

Figure 61: TDM Force Vectors Back

Figure 62: TDM Von Mises Stress Analysis Front

Figure 63: TDM Von Mises Stress Analysis Back

55

Table 14: TDM Force Vectors 1



Table 17: TDM Pressure 1

Table 18: TDM Pressure 2

56

Table 19: TDM Force and Moment on Constraints

Table 20: TDM Results

57

5.3.3. Motor Mount (MM)

Our motor mount will be machined out of T6-6061-Aluminum. With the use of Autodesk Inventor we were able to do a Von-Mises stress analysis using assumed forces. The figures below displays arrows in the direction at which the forces are working. With the results produced for the motor mount we can see that it has been built ruggedly enough to withstand the forces of motor to the traction drive. It was strong enough so minimum stress concentrations were produced around where motor mounts to the motor mount. The displacement was minimal and will not negatively affect the design. All the calculated results can be seen [Table 30]

Table 21: MM Physical Attributes

Figure 64: MM Force Vectors Front

58

Figure 65: MM Force Vectors Back

Figure 66: MM Von Mises Stress Analysis Front

59

Figure 67: MM Von Mises Stress Analysis Back

Table 22: MM Force Vectors 1


60



Table 26: MM Pressure 1



61

Table 29: MM Force and Moment on Constraints

Table 30: MM Results

62

5.3.4. Physical Properties of Total Design

Displayed in [Table 31] are the overall physical properties of the complete design. This table was produced using Autodesk Inventor 2016 and helped us obtain a total weight of 45.643 lbm.

Table 31: Final Design Physical Properties

63

5.4. Component Measurement

Utilizing a Brown & Sharpe 4.5.4 CMM machine we were able to retrieve critical dimensions needed for our project. Through the use of software PC-dmis we were able to make visual drawings and record dimensions. This allowed us to accurately produce our parts to within tolerances of 0.0001” within factory specifications. The gear was sent out to Precipart to be analyzed and the results can be seen below.

5.4.1. Casing, Gear Shaft, & Differential Dimensions

The differential case had to be analyzed to get the distance from center to center of the differential to the shaft containing the smaller gear. This distance is critical because it needs to be exact in order to have proper meshing between the gear teeth. We also retrieved dimensions for proper bolt hole locations on the axles and electric motor. The diameter of the electric motor was measured off the case as well as the overall distance from axle to axle to learn what our restrictions were pertaining to the width of the new casing. The width has to be the same and is very critical in making an easily retrofit-able design. [Table 31] shows some dimensions and the drawing created by PC-dmis from analyzing the casing. The differential width and gear shaft dimensions were also retrieved from the CMM machines. These dimensions can be seen in [Table 32] and [Table 33].

64

Table 32: PCdmis Housing Measurements

Table 33: PCdmis Differential Measurements

65

Table 34: PCdmis Gear Shaft Measurements

66

6. Prototype: Fabrication, Assembly and Standards

This section is composed of details pertaining to the fabrication, assembly, and final prototype of the RMI Traction Drive Golf Cart Transmission. Problems encountered throughout the prototyping process and the steps taken to fix them are discussed along with the steps needed to assemble the final prototype. This section also highlights failures, solutions and engineering standards used throughout the project.

6.1. Prototype

The final prototype is a fully operational golf cart transmission, which can be seen in [Figure 68]. This traction drive transmission is used in testing to prove the efficiency gains over standard gear golf cart transmissions. The material needed to complete a working prototype can be seen in [Table 35]. This outlines all costs including building a traction drive, sensory equipment, and transmission components.

Figure 68: Full Prototype of Final Design

67

6.2. Component Fabrication

Individual components needed to complete a transmission are discussed in this section. A description accompanied by figures describes the manufacturing process used to bring to life each component needed for the project. Problems encountered are touched upon as well as possible solutions. All the engineering drawings were completed on Autodesk Inventor 2016 and can be viewed in Appendix A. These drawings were used to complete the manufacturing of most components on a HAAS VF2SS milling machine. Parts were analyzed on a Brown and Sharpe 4.5.4 CMM for accuracy of up to +/- 0.0001” in order to achieve maximum quality of the finished compnonents.

6.2.1. Modified Gear

The modified gear was ground down from the original gear in [Figure 8] in order to produce the modified gear seen in [Figure 69]. The first process was to bring down the larger gear to a manageable size using a Drake CNC thread-grinding machine. Grinding was the only feasible option in bringing the gear down to size since it was hardened steel. Once completed on the CNC we brought the outside diameter down on a manual-grinding machine. We were able to bring it down to accept a 30mm inner diameter bearing, which is used on the opposite side of the gear. Once the grinding was complete we used an ANCO lathe to drill a 0.6250” hole in the center of the gear using a carbide drill bit. A 3/16” keyway slot was completed using a wire electrical discharge machine (WEDM). In the future it would be easier to make this gear along with the ring gear it mates to instead of machining a premade component. Since this will be used for testing it was critical to keep all standard components as similar to the original transmission as possible.

Figure 69: Prototype Modified Gear

68

6.2.2. Differential Spacer

The differential spacer was machined from a 5.500” x 2.750” round piece of 6061-T6511 aluminum. It was completed using the HAAS milling machine. The spacer was designed to be concentric over the differential and the machined 3.8610” x 0.170” lip was to allow the ring gear to sit concentric in the spacer. The bolt hole pattern was matched from measurements pulled from the ring gear using the CMM machine. The concentricity of the piece would have been better if completed on a lathe but due to restrictions a milling machine was used.

Figure 70: Prototype Differential Spacer

69

6.2.3. Mount Clamp

The mount clamp was milled out of a 2.500” x 7.500” x 8.625” piece of 6061- T651 aluminum. A radius with the same dimensions of the axle tube (1.1353”) was milled in the center of the clamp. This radius insures the motor mount will be kept in place under the loads it will see. The mount clamp was one of the simpler pieces to machine and no problems were encountered with this piece.

Figure 71: Prototype Mount Clamp

6.2.4. Bottom Cover

The bottom cover for the traction drive was milled out of a 0.3750” x 5.500” x 3.750” block of 6061-T6511 aluminum. This piece has four 5/16” holes with 0.1800” depth countersink bores to allow the 5/16”-24 socket button head bolts to rest inside the bottom covers foot print. The cover also has a 1.000” x 1.000” x 0.1800” void milled out to allow the axle flange to mount in place without any further modifications.

Figure 72: Prototype Bottom Cover

70

6.2.5. Side Covers: Left/Right

The left and right covers are both milled out of 1.000” x 4.000” x 4.250” blocks of 6061-T6511 aluminum. The covers have two standard 3/8” holes and two countersink 0.470” holes drilled into them. The countersink holes are there to allow the 5/16”– 24 socket button head bolts to sit within the covers overall footprint. This was necessary due to the interference of the traction drive mount bolts and cover bolts. With the cover bolts recessed it is possible to mount the traction drive to the transmission casing. Separating the bolt holes before machining would alleviate this situation. The covers are notched out on the bottom to allow the unit to sit as far into the transmission case footprint as possible without compromising the integrity. There is also two 3/8”-16 bolt holes in the angled side of each cover to allow the motor mount to bolt onto the traction drive unit.

Figure 73: Prototype Side Covers

71

6.2.6. Driver Side Case

The driver side case was milled out of a 2.5”x 9.5”x 11.625” block of 6061-T651 aluminum. The outside of the case is designed to accept the original axles so the bolt holes needed to be measured and put in the right place. It was one of the more difficult pieces to mill due to the tolerances had to be upheld in order for a perfect fit. Center to center of the bearings had to be 4.016” so the gears would mesh correctly. The case is heavy and over built but with more refinements it could weigh less than the original. Threaded holes were included on the bottom and side of the case to allow magnetic drain and fill plugs to be inserted. The placement of the drain and fill plug will allow for easy access when maintaining the unit.

Figure 74: Prototype Driver Side Case

72

6.2.7. Output Shaft

The output shaft of the traction drive was turned out of a 6.5” x 3.75” round piece of 52100 Steel. The shaft is longer than a normal traction drive shaft in order for it to be held rigidly in place on both ends. There is a 3/16” keyway slot machined into the shaft to transmit power to the modified gear. One section of the shaft is ground down to the proper size to allow the use of 0.984” inside-diameter tapered roller bearings. M25-1.50 threads are ground onto the shaft right after the bearing section to allow a nut to properly seat the bearings. The other section is ground down to 0.625” to allow the shaft to slide through the modified gear. The shaft slides in and out of position in the transmission case very easily to allow quick assembly and disassembly.

Figure 75: Output Shaft

73

6.2.8. Input Shaft

The input shaft of the traction drive was turned out of a 4.5” x 2.0” round piece of 52100 steel. The shaft has a section ground down to accept 1.1811” inside-diameter tapered roller bearings. The shaft end has the same 10-tooth spline milled into it that the original transmission shaft has. This allows the motor to slide over the input shaft and transmit power. The shaft was shortened due to space constraints on the overall design. M30-1.50 threads are ground onto the shaft right after the bearing section to allow a nut to properly seat the bearings.

Figure 76: Input Shaft

74

6.2.9. Passenger Side Case

The passenger side case is milled out of a 4.5” x 9.5”x 11.625” block of 6061-T651 aluminum. This piece was the largest and most intricate to machine because the outside is composed of three layers. The lower most layer has to be 4.077” to maintain the original overall thickness of the transmission where the axles are mounted. We are limited to the 1.775” step depth because any further and it would hit the differential. The last and final section steps down another 1.00” for a total difference of 2.775”. These depths are done to allow the unit to sit as far into the transmission casing footprint as possible in order to stay inside the space constraints of the existing cart. All of the dimensions taken are within the accuracy of the HAAS milling machine of +/- 0.001”. The correct five-bolt hole pattern was machined onto the transmission casing and threaded with a 3/8”-16 form tap. There was also 10 3/8” through holes machined around the outside of the casing to allow bolts to slide trough and thread into the driver side case. The inside of the case had to be milled out to allow the differential and modified gear to sit correctly. The bearings for the modified gear sit in a 2.047” hole and the bearings for the differential seat into a 2.678” hole. The same 4.016” distance from the center of the differential to center of them modified gears had to be maintained for proper gear meshing. One inner void around the differential bearing hole was unable to be machined due to the lack of proper tools. This did not interfere with use but was slightly heavier due to not being able to remove unneeded material.

Figure 77: Prototype Passenger Side Case

75

6.2.10. Motor Mount

The motor mount was milled out of a 2.5” x 9.5” x 11.625” block of 6061- T651 aluminum. This piece was tricky to machine properly because it has a 10-degree angle on the bottom with a 3.389” radius going through it. This radius allows it to sit around the axle tube and distribute the weight of the motor. We also precisely milled the bolt pattern for the electric motor to mount onto the piece. We were able to accurately record the dimensions within .0001” from using a CMM and recreate them on this mount using a CNC milling machine. The electric motor has a circular lip, which seated it concentric into the old transmission. We reproduced the same 6.106” diameter by 0.350” depth to hold proper concentricity of the motor on our mount. This is important since the face of the motor is not supported by bearings. If concentricity were off it would put extra stress on the traction drive bearings along with possible destruction of the motor. On the backside of the motor mount it houses a 1.26” sealed outside diameter bearing along with a 2.512” diameter groove which houses a -228, AS568/ ISO3601 standards, O-ring.

Figure 78: Prototype Motor Mount

76

6.2.11. Traction Drive Mount

The motor mount was milled out of a 1.50” x 7.00” x 4.25” block of 6061- T651 aluminum. The Traction drive mount has two 3/8” holes on each side in order for bolts to slide all the way through into the passenger side casing. The top of the mount has two 3/8” – 16 threaded holes for the top cover to mount and two 5/16” – 24 holes per side for the side covers to mount. The larger center hole is milled out to a 1.85” outer diameter in order to allow two tapered roller bearings to seat inside the mount. In order to keep the center hole concentric we put in four 0.25” by 0.50” deep dowel pins. The mount is notched 0.775” down in order to save room and allow a flush fit to the transmission casing.

Figure 79: Prototype Traction Drive Mount

77

6.2.12. Top Cover

The top cover was milled out of a 1.00” x 4.00” x 5.5” block of 6061-T6511 aluminum. This block was one of the easier pieces to fabricate. It was milled down to size and had four 3/8” through holes drilled into it. These holes are used to fasten it to the traction drive. There was a 1/8”-27 NPT hole in the cover to allow a vent to be mounted on the top of the traction drive. On the side that meets with the motor mount it was milled on a 10-degree angle. This allows the motor mount to sit flush up against the traction drive. This allows the mount to distribute the pressure of the electric motor to all the pieces it comes in contact with.

Figure 80: Prototype Top Cover

78

6.2.13. Front Plate

The front plate is milled out of a 1.375”x4.00”x4.250” 6061- T6511 aluminum block. The hole in middle is a 1.85” diameter by 0.709” deep to allow the two tapered roller bearings races to seat inside the block face to face. The top and bottom of the block are milled on 10-degree angles to allow the unit to be assembled properly. On the top it has two 0.75” deep 3/8”-16 threaded holes to allow the top cover to be fastened in place. On the left and right sides there are two 3/8”-16 threaded holes and two 0.25” holes. The threaded holes allow the side covers to be bolted to the traction drive. The two 0.25” holes are for dowel pins. These pins allow for accurate assembly for repeated assembly. This was necessary for possible issue encountered during the trail of the complete prototype. Once refined the dowel pin-holes will not be needed.

Figure 81: Prototype Front Plate

79

6.3. Assembly

The final assembly of the prototype will require a bearing press, 5/8” socket, 9/16” sockets and wrench, 11/16” wrench, a brass hammer and a 6mm Allen key. This section will include instructions for the assembly of each individual component.

6.3.1. Transmission Case Assembly

1. Remove the six bolts holding the ring gear on to the differential and install spacer and ring gear using six M10-1.5 x 70mm bolts.

2. Take modified gear and press two 25mm x 52mm x 15mm bearings onto both ends until seated flush.

3. Slide 3/16” keyway into modified gear4. Take driver side case and press a 15mm x 32mm x 9mm bearing into top

hole.5. Slide differential and modified gear into driver side case simultaneously.6. Take passenger side case and install 5/8” x 1-1/8” x 1/4” nitrile seal on

outside top hole. 7. Apply RTV silicon gasket maker to the sealing face of the driver side

case.8. Slide passenger side casing over differential and modified gear bearings

and bolt down using six 3/8”-16 x 6” bolts in the lower six holes. 9. Apply RTV silicon gasket maker to axles and bolt both on using 3/8” –

16 x 1.5” bolts (Shorter axle is driver side.)10. Install two M14-1.50 magnetic plugs into bottom and side of driver side

case.11. Install original vent into the top of the driver side case.

6.3.2. Traction Drive and Motor Assembly

1. Press 25mm x 47mm x 17mm bearing races into the traction drive mount block.

2. Press 30mm x 47mm x 12mm bearing races into the front plate.3. Slide inner bearing around the input shaft and slide into place on the

front plate. Repeat process with output shaft and slide into the traction drive mount.

4. Fasten shafts to blocks with appropriate shaft nuts. 5. Attach top, side and bottom plates using 3/8” – 16 x 1” bolts and 5/16” –

24 x 0.625” bolts.6. Install vent in to top cover.7. Press 20mm x 30mm x 7mm bearing into motor mount.8. Install 2.234” O-ring into motor mount.9. Fasten motor mount to the front plate using four 3/8” – 16 x 2.5” bolts.10. Install original motor to motor mount using original hardware.

80

6.3.3. Complete Assembly

1. Apply RTV silicon gasket 1/2” away from bearing races on traction drive mount block.

2. Slide complete traction drive and motor assembly into place on transmission casing and bolt down using four 3/8” – 16 x 4” bolts.

3. Attach mount clamp to the motor mount using two 3/8” – 16 x 2” bolts.4. For reinstallation of completed unit follow Club Car Golf Cart Service

Manual.

6.4. Failures

Upon the first few tests failures were encountered. The biggest failure we saw in our design was the output shaft shearing [Figure 82]. The output shaft was hardened to 64 Rockwell leaving it extremely brittle and vulnerable to breaks under stress. To combat this problem we had the shaft annealed in order to reduce the hardness of the material to a standard shaft Rockwell of 40 - 50. The annealing process will allow the shaft more flexibility, which will reduce shearing due to stress. Another technique used on the new shaft was to install a radius where the two different shaft diameters meet. This will increase the strength of the joint instead of having a 90-degree mate.

Another design flaw we encountered was the unit fitting inside of the existing space in the golf cart. When the unit was lifted in it hit a bracket that holds the shock in place. In order to avoid this interference, we were able to simply rotate the bolt holes 30-degrees in order to miss the bracket completely. This can be seen in [Figure 83] the red circles show the original location on the axle bolts.

Figure 82: Broken Output Shaft

81

Figure 83: Wrong Hole Locations

82

7. Performance

This section discusses the performance results acquired using various testing procedures. These results were recorded using an Accuenergy AcuDC 240 series specialty DC meter. This meter was able to record the voltage, amperage and power used throughout the tests. The RPMs were measured using an Omega HHT13 non-contact pocket laser tachometer. We conducted two tests for each transmission type, which allowed us to compare the data.

7.1. Testing Procedures

All testing was performed with each transmission mounted into the golf cart. Due to local laws and regulations and the lack of a testing track we were unable to physically drive the golf cart to acquire our data. Alternatively, we lifted the golf cart by the rear axles and allowed the wheels to free spin [Figure 84]. There were two tests completed for both transmissions. Each test was administered for the same amount of time. Due to a lack of quality instrumentation to apply an equal load to both transmissions we relied on the natural forces encountered by the drivetrain. Thee forces from the wheels, brakes and axles will remain the same while the only variable is the transmissions themselves. This testing procedure allowed for the least amount of discrepancy within the results.

Figure 84: Cart Mounted on Jack Stand

83

7.2. Results

The calculated results can be seen in [Table 37]. These results were gathered using the procedures outlined in the sections below. Volts, amps and power were averaged from thousands of data points.

Table 37: Testing Data

7.2.1. Test 1 - Constant Pedal Position

For both transmissions we left the throttle in the same position and allowed them both to run for the same amount of time. We started the analysis of the data by comparing the average amperage. Being that the average voltage was within 0.5% of each other we treated is as a constant. As we can see the average amperage of the original Club Car transmission is lower by 0.27363 Amps, which would tell us that our design uses 9.21% more amps when the gas pedal is held at the same position. The RMI transmission uses an 8:1 ratio as opposed to the 12:1 ratio produced in the original transmission. With the difference in ratios, the amperage comparison is skewed in favor of the original transmission and this is due to the increase in mechanical advantage. The mechanical advantage for the original transmission is 33% more. This information is misleading because in the same amount of time our transmission traveled 2.326 miles further, which is an increase of 23.1%. Comparing the average power to the distance traveled we found that the RMI transmission uses 14.66 W/mi to the original transmission which uses 17.29 W/mi. This shows that we use 2.6297 less Watts per mile, which means we have increased the efficiency over the original transmission by 15.2%.

7.2.2. Test 2 – Constant Tire Speed

For test two the RPM’s were held constant for both transmissions. Each transmission was set to produce a constant 130-RPM at the wheel. As seen in test one, the voltage deviation was negligible so it was again treated as a constant. Since time, distance and volts were treated as constants the only variation in data was seen in the amps used. Directly comparing the amps we are able to see the difference in efficiency between the two transmissions. The RMI transmission showed an increase of efficiency by 4.03%. This

84

number is misleading due to the ratio difference between the transmissions, which gives the original transmission a 33% mechanical advantage. This data can be better analyzed if the efficiency curve of the motor was known. Letting the motor run under a higher torque could potentially move the motor into an optimal efficiency.

7.2.3. Results Discussion

After completing and analyzing the data found in both tests we can conclude that the RMI transmission is an ideal replacement for the original transmission. It has proven itself to be more efficient even with a mechanical disadvantage. After analyzing all the data we can average the increase in efficiency to be about 15%. This estimate does not include the hidden advantage of the traction drives ability to not back drive the motor. To understand the back driving advantage one can imagine a car that instantly switches from drive to neutral when the throttle is released. This allows the RMI drive to travel further while coasting with the occupant’s foot off of the throttle.

85

8. Conclusion

This project took two semesters to come from concept to reality. We have been able to successfully take an existing product that has ruled the market and prove that there is a better alternative available. Our group has completed the steps necessary to produce a fully functioning prototype. This product has shown that it has the potential to revolutionize the power transmission industry.

The biggest asset towards our project was having a team that enabled the development of our design from start to finish. The process of identifying a problem and creating a successful solution is no easy task but our group was able to take it in stride. As our research began we created a clear path to a solution using our product design specifications as our first stepping-stone. With a foundation to build off of we started to add and remove designs as we saw them fail in what we originally expected them to do. We had to perform research and analysis to focus on the issues faced every day by golf cart owners and users. This showed us that the biggest problem faced by electric golf carts, aside from reliability, was there inability to travel long distances. We had to develop a transmission, which was as reliable, quiet, smooth, and light as the original design, while increasing efficiency. Once we had a design that satisfied our criteria we began to outline the details that were needed in order to show that our design would work. Once all of the pros and cons of the design were realized we were able to begin the process of creating a full sized prototype. Weighing out the concepts proved that the “separate enclosure” design was our best option.

Since this is the first time that a RMI unit would be used in a moving vehicle concept we had to make sure that our design seamlessly took into account all limitations of both the golf cart and RMI unit. As the design went from idea to prototype we saw that the solution to our problem was going to work incredibly well. While keeping our design simpler then the original transmission we were successfully able to meet all specifications that were necessary to call our project a success.

8.1. Future Work

After the completion of this project RMI LLC will seek to continuously improve the unit and bring this product to market. A few steps are necessary before that can happen. An in depth analysis of the design should prove useful to the manufacturing of the components. The components used to build the prototype were over engineered to increase the safety factor by a large margin. The components can be downsized to reduce production costs. Further testing will be needed to compare the new transmission to the original transmission. Although it was tested indoors, the transmission needs to be tested on a track or golf course to prove the true viability of the project.

86

References

[1] 2009-2011 Precedent Golf Car Owner’s Manual Electric and Gasoline. https://xrtdealers.clubcar.com/ownersmanuals/103472529 1108u0411t.pdf. 2015

[2] 2009-2011 Precedent Illustrated Parts List Gasoline and Electric Vehicles. http://bennettgolfcars.ca/upfile/manufile/20121115065834.pdf. 2015

[3] http://www.plumquick.com/images/inventory/used-parts/39683221.jpg. 2015

[4] Golf Cart. In: Wikipedia. https://en.wikipedia.org/wiki/golf_cart. 2015

[5] Walking The Golf Course vs. Riding in a Golf Cart. In: Fitness By Andrew Scottsdale Personal Trainer RSS2. http://www.fitnessbyandrew.com/walking-the-golf-course-vs-riding-in-a-golf-cart/. 2015

[6] The Average Cost for a Round of Golf. In: Golf Tips. http://golftips.golfsmith.com/average-cost-round-golf-20670.html. 2015

[7] Yoffe E Golf carts and retirement: How the vehicles have made life better for seniors (PHOTOS). http://www.slate.com/articles/life/silver_lining/2011/02/slow_ride_take_it_easy.html. 2015

[8] https://cdn3.volusion.com/adets.qcfpr/v/vspfiles/photos/2337-2.jpg?1422022691. 2015.

[9]http://www.riorand.com/media/catalog/product/cache/1/thumbnail/9df78eab33525d08d6 e5fb8d27136e 95/r/i/riorand_dc_12_24v_waterproof_digital_volt_panel_meter_4.5-30v_blue_led_motorcycle_voltage_gauge-1.jpg. 2015

[10] http://image.dhgate.com/upload/spider/b/014/504/b_3rw5fd504014_1.jpg. 2015

[11] http://www.instrumentchoice.com.au/images/productimages/other_meters/ga2006h-hand-arm-vibration-meter.jpg. 2015

[12] http://www.ibsco.com/chrome-steel-bearings.php. 2015

[13] https://www.accuenergy.com/product/acudc-dc-power-energy-meter. 2016

[14] http://www.amazon.com/DC-DC-Converter-Isolated-Module-10-16V/dp/B008P880QU/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1459779639&sr=1-2-catcorr&keywords=dc-dc+isolated+power+module+in+10-16v. 2016

87

[15] http://www.amazon.com/voltage-reducer-converter-Input-range/dp/B00OGZ3OTE. 2016

88

rmi golf cart report

Documents