FINAL DESIGN REPORT- STUDENT FORMULA 2014

MAHARASHTRA INSTITUTE OF TECHNOLOGY, PUNE

TEAM ACCELERACERS

TEAM ID - M13191

For the 2014 event, we, Team Acceleracers, present our third car which is an open wheel,

rear wheel drive vehicle powered by a single cylinder naturally aspirated engine with a six

speed sequential gearbox. We aim at making the lightest car without any compromises in

strength and performance. We have followed the KISS (Keep It Simple Silly) principle to

every possible extent. Simplicity in design is our main aim. Based on Newton's law, force

equals mass times acceleration, thus a lower mass will produce greater acceleration from the

same force. A lighter car accelerates faster, brakes harder and turns quicker, the advantages

can be felt throughout the lap. Light weight gives us more freedom in design as well. We can

compromise with a smaller engine with lesser power, use economical materials as the loads

are smaller and also make use of smaller bearings at various places. The major subsystems

used are explained in detail as follows:

TYRES AND WHEELS: - We will be using MRF soft compound racing tyres of

specification 175/60 R13. The rim size gives us ample tyre choices and permits us to mount

the large brake rotors outboard along with the upright and hub assembly at the front. The rim

size also gives us the necessary space for multiple options in suspension geometry and tie rod

mountings. We are using Keizer Kosmo series Aluminium rims with magnesium centers to

have a low weight to benefit from the low rotational inertia.

SUSPENSION: - The suspension of our car was designed to provide maximum contact with

the track surface during all dynamic conditions. We are using a double wishbone setup at all

corners with the front springs being pull rod actuated while the rear springs are pushrod

actuated. The front shocks are mounted vertically outside the frame in accordance with other

systems for the best possible packaging of all components and maximum space available for

the drivers legs in the smallest frame. The rear springs are mounted diagonally above the

differential. This position was chosen to leave enough clearance for the driveshaft to move

about during suspension travel. The pushrod and pull rod systems are designed to be coplanar

with the shock absorbers and bell cranks to prevent any off planar forces. Better adjustability

was achieved by providing the bell cranks with multiple mounting points. The shock

absorbers themselves are custom built as per our requirements so that the springs have

different stiffness to cater to the different ride characteristics at the front and rear due to the

weight distribution and other dynamic requirements. Soft compound racing tyres are used to

provide maximum traction while braking, accelerating and cornering.The uprights are made

from 7series aluminium alloy to keep the weight down whilst not compromising on any

structural strength. The wishbone joints at the upright are plain spherical in nature to avoid

any rod ends in bending. Aluminium live spindles with rotor and wheel mounts are used in

the front while alloy steel spindles are employed in the rear to transfer torque from the

differential to the wheels.

STEERING: - Our steering system is designed with a lock to lock angle of 360 degrees with

a low steering-ratio to facilitate quick steering response and a good drivability from the

vehicle. Ackerman geometry was implemented to obtain accurate steer angles and to help

manoeuvre the vehicle during tight turns on the track. The steering assembly is kept as planar

as possible for its even force distribution. Pinion pitch circle diameter is reduced to lower

steering effort required from the driver and lesser rack displacement thereby increasing

steering sensitivity. Lower rack position is chosen to ensure adequate space for the drivers

legs. Our rack is designed for simple mounting and minimum compliance at the steering

wheel to ensure consistent feel and feedback. The entire assembly requires only two

mountings on the chassis thereby making the assembly of the system simple and light weight.

CHASSIS: - Our requirements from the current chassis are high safety levels, rule book

compliance, good torsional rigidity, light weight, compact packaging and essentially easy to

fabricate. After debating the use of a steel space frame against a CFRP (Carbon Fibre

Reinforced Plastic) monocoque and discussing the advantages and drawbacks of each, a steel

space frame won our votes. The raw material was readily available in the various sizes and

thicknesses required. The analysis is relatively much simpler and is a much better fit for our

manufacturing abilities, ease of modification and the ability to repair any damages in case of

accidents. The chassis is designed keeping in mind the suspension hard points. It is adjusted

such that the wishbone mounting points, bell crank pivots and the shock absorber were

positioned at rigid nodes for minimum deflection under high loads. Compliance is restricted

to a minimum allowing the suspension to perform its job as designed more efficiently. Next

the driver compartment is designed incorporating the drivers space requirements defined by

the side impact structure and roll hoops. The position of all the controls was chosen with

ergonomic considerations and then adjustments to the chassis mounting points were made

accordingly. The engine is mounted using specially designed brackets to evenly distribute the

load on the frame members. Low displacement rubber bushings will be used for engine

mounts to constraint the movement but prevent the transmission of vibrations into the frame.

The mountings are designed with serviceability in mind so as to cater to the easy removal of

the engine for any maintenance purposes. Finally other frame members and triangulations are

added as per the requirements to complete the chassis. Finite Element Analysis is performed

on the chassis to evaluate its performance in case of front and side impacts and also during

rollover conditions. Based on the results, areas of large stress concentration are modified and

revaluated.

ENGINE: - This year our car houses a single cylinder, naturally aspirated engine with a

displacement volume of 373.2 cc. The stock engine produces a maximum power of 44HP

@9000 RPM and a maximum torque of 35Nm @ 7250 RPM and is lighter as compared to

other similar displacement engines, providing us with a better power to weight ratio. We are

also using a custom programmable ECU that allows us to tune the air-fuel ratio, ignition

timing and some other parameters. It gives us a notable performance gain of about 10%

increase in torque graph area and peak power of about 46.5 HP @ 8200 RPM. Even the rev

limit is increased to 11,300 RPM from 10,500 RPM while maintaining the improved

performance curves.

INTAKE AND EXHAUST: - Extracting more power and improving the drivability of the

car was the foremost objective while designing the intake and Exhaust system. Extensive

CFD testing was carried out to obtain minimum pressure drop across the complete intake

system. This was achieved by iterating different restrictor, plenum and runner configuration.

The exhaust setup is done so for least backpressure and maximum scavenging. An absorptive

type, straight perforated muffler is employed since it achieves appropriate noise attenuation

with least back pressure. By studying the performance curves of the stock engine setup, we

decided to tune the intake and exhaust for 8600 RPM and 5500 RPM respectively to obtain a

near flat torque curve.

POWER TRAIN: - Our drive train is designed by applying a constraint to the top speed of

the vehicle @110Kmph. The reason behind limiting the top speed of the vehicle is to achieve

a better acceleration which is must for the tight twist and turns coupled with the short

straights of the competition track. Torque is sent to the rear wheels by means of a Quaife

ATB(Auto Torque Biasing) limited slip differential which is capable of providing a torque

bias ratio between 2.6:1 to 4:1. The differential weighs about 7kgs along with the casing and

has a readymade mount for the sprocket, thereby providing a optimized cost effective design.

Another consideration is the mounting distances between the engine and the differential

which is kept to a minimum feasible distance to have the chain as short as possible to reduce

any unnecessary losses.

BRAKES: - We have opted for a three rotor brake system to achieve a comparatively lower

system weight without compromising on the braking efficiency. To get maximum braking

force, keeping in mind the rim size available, we have decided to mount two outboard rotors

of 220mm diameter each on the front wheels and a rear rotor of 270mm diameter on the

differential. The above mentioned sizes are easily found in the local market and hence are

cost effective. A brake bias bar is utilized for precise distribution of force to the front and rear

ends. The difference in forces is due to the weight distribution and the dynamic weight

transfer. At the front, the braking force will be provided by two dual piston single acting

calipers, one on each wheel while at the rear, we are mounting a Brembo dual piston double

acting caliper. The fluid is passed through steel braided hoses to minimize any expansion

losses while still having the flexibility of a rubber hose.

IMPACT ATTENUATOR: - The rulebook clearly states that the impact attenuator must be

able to effectively absorb the impact forces of a car travelling at 7m/s and weighing 300kgs,

while maintaining an average deceleration not exceeding 20g's. The most common design

opted for the impact attenuator amongst FSAE teams consisted of a honeycomb structure

made out of aluminium encased in a sheet of metal. While this design proved to be highly

efficient, it was complex and laborious to manufacture while being relatively expensive. We

began to look for other options which might better suit our needs. We decided on using

aluminium soda cans for our impact attenuator. It would consist of two layers of cans

mounted on each other and then encased by a 1mm thick sheet of aluminium. This design

proved to be highly efficient in absorbing the forces, easier to manufacture and cost effective

and at the same time has less impact on the environment as recycled materials are used.

BODY PANELS AND AESTHETICS: - Considerable effort has been put into the design of

the vehicle's body panels. The design was influenced by factors like aesthetic appearance,

aerodynamic drag, manufacturing cost and easy accessibility to components below for

service. An exposed frame design was chosen for the lower half to portray toughness and

masculinity while a single large floating panel was designed as a top covering which is curvy

and feminine. The upper half is mounted on few bolts and is designed to come off easily. The

combination of the two design philosophies leads to an outcome that is truly unique and

innovative.

The paint scheme is also given its due regard. A navy blue hue is chosen for the lower half

while white dominates the upper half, which gives a stunning background for the sponsor

logos. And finally the exposed frame is painted in a contrasting colour to showcase the

unique frame design. The innovative panel design along with a spectacular paintjob is

guaranteed to make our car stand out at the competition.

SAFETY AND ERGONOMICS: - We have designed our car in accordance with the rules

stated in Rule book. The chassis was designed keeping in mind the 95th percentile male

template dimensions. We have strived to achieve maximum safety and operative conditions

by working on a few techniques as mentioned below:

1. In case the drivers harness is unbuckled, the engine can turn on only in neutral, and

power off if put in gear without first buckling up. Likewise, the engine will turn off

automatically if the harness comes off while the vehicle is in motion. These functions

are incorporated to ensure maximum safety of the driver.

2. The seats are fixed with a mechanism to provide increased adjustability according to

the driver body type and comfort whilst holding him securely.

3. A lock to lock of 360 degrees on the steering wheel ensures that the driver doesnt

have to let go off the steering at any point of time allowing better driver control and

quick response.

4. We are using an instrument cluster which includes gear shift and position indicator,

speedometer, odometer, fuel indicator with low fuel warning, ideal driving rpm band,

average speed and average fuel consumption displays. They offer valuable

information to the driver regarding the vehicles condition and performance figures.

ELECTRICALS: - Our vehicle has minimal electric requirements other than the stock

electrical connections. We are using a 12V lead acid battery to provide power for ignition,

brake over travel switch in case of brake system failure, a kill switch to stop the vehicle at

any instant and an auxiliary fan that we are using to cool the radiator.