Team Registration ID: 49983

College Name: Sri Sai Ram Engineering

College

Author: K.V.Vidya Shankar

Co author: S.Vignesh

Email id: vidyashankar1389@gmail.com

INTRODUCTION:

This report is aimed at explaining the

performance achieved and design

methodology adopted by team “The Most

Wanted” for SAE BAJA 2011. The design

methodologies we have used for our vehicle is

modelling using CATIA, Solid Works, AutoCAD

etc to generate intricate features of the model.

Once the design was over, it was then

analysed using the ANSYS, COSMOS

EXPRESS software to check for the stresses,

displacements acting at different points in the

roll cage. The expected performance of our

vehicle is a max speed of 60 km/hr, having a

gradability of 40 degrees, turning radius of

3.5m, a stopping distance of 3m. The outcome

of our vehicle is a max speed of 55 km/hr,

having a gradability of 38 degrees, turning

radius of 3.17m, a stopping distance of

3.04m.Thus in the following detailed report, we

are going to elucidate the ways in which these

performances have been achieved in our

vehicle with calculations pertaining their

support.

TECHNICAL SPECIFICATION:

S.No Technical descriptor Specification

1. Engine Maximum Torque

Lombardini LGA 340, air cooled engine 19 N-m @ 3000 rpm

2. Drive Top gear ratio

Mahindra Alfa Transmission. 7.35:1

3. Suspension Front travel Rear travel

Mcpherson strut. 127mm 101.6mm

4. Wheels 25*8*12 ATV tubeless tires.

5. Brake 228.6mm dia disc

6. Steering 12:1 rack and pinion.

7. Dimensions Overall Length Overall height Wheel Base

2311.4mm 1574.8mm 1524mm

8. Weight

350 kg

TARGET PERFORMANCE:

Maximum speed:

The max speed of the vehicle is calculated as

follows:

Thus v = (3.14*D*N)/60.

But N is the maximum rpm wherein the drive

ratio is 7.35:1 and considering an efficiency of

0.85, v = (3.14*25*25.4*4000*0.85)/ (60*

1000*7.35), v= 55.36 km/hr, v= 15.38 m/s,

where D- diameter of tire.

Maximum acceleration:

The max acceleration of the vehicle is

calculated as:

Thus a= (550*g*HP)/ (v*w)

= (550*32.2*11)/( 16.67*3.28*420*2.205)

Therefore the maximum acceleration is

3.847 ft/s2 = 1.172 m/s

2 where,

g- ft/s2, HP- ftlb/s, w- lb, v- ft/s.

Gradability:

First, the tractive force is calculated, which is

the force available at the wheels, which is

equated with the grade component:

Tractive force= (TNtf)/r- inertia losses, where

Ntf is the final transmission ratio, r- radius of

wheel.

Substituting the values, we get the tractive

force to be 2845 N.

Now equating the tractive force to the grade

component,

2845= mgsinө,

2845=4200*sinө,

Ө= 31.48 degrees.

But this is inclusive of an inertial loss of 15%

assumed.

Turning radius and angle of steering

system:

The calculations for all these parameters have

been done in the latter section (Steering

system). The values are as follows:

Outer Akermann angle- 18.17 degrees

Inner Akermann angle- 30 degrees

Turning radius- 3.17m.

Deceleration:

The deceleration of the vehicle on application

of brakes is found to be 35.45 m/s2 .

Stopping distance:

The calculation of the stopping distance is

done in the brake systems. The value of

stopping distance is 3.04m

Ground clearance: 12 inches.

3D VIEW OF VEHICLE:

CAD diagram:

Fig 1. CAD model of the vehicle.

We used the CAD modelling software CATIA

to design the vehicle’s roll cage and other

parts. The 3D view of our vehicle with the

sheet metal, seat, engine mounted etc is

shown using the CATIA software.

Fig 2. Actual view of vehicle

The actual (uncompleted) view of the vehicle is

shown above. As it can be seen, the vehicle

has been fabricated in accordance to the

design, keeping in mind the safety,

ergonomics, performance etc.

ROLL CAGE DESIGN AND ERGONOMICS:

Roll Cage Design Considerations:

Safety: Safety was one of our important

considerations in design of our roll cage. The

design is such that the driver avoids injury due

to the frame even under unavoidable

circumstances. Our design enables the driver

to exit the vehicle within 5 seconds.

Driver ergonomics: A large cockpit space has

been incorporated in our design to ensure

driver’s comfort. The roll cage has been

designed to enhance the driver’s visibility. All

the essential controls in vehicle have been

placed such a way that it can be accessed with

ease.

Production: Our design has not been made

complex to facilitate the fabrication process.

Our design ensures mass production.

Roll Cage material and properties:

The RHO, FBM, RRC, LC members of the roll

cage are made of ASTM A106 Grade A steel

with OD of 26.7mm and a wall thickness of

3.91 mm. The structure of these members is

tubular in section. The other members of the

roll cage are also made of ASTM A106 Grade

A steel with a OD of 26.7mm, but a wall

thickness of 2.87 mm.

Properties of the roll cage material:

Material – ASTM A106 Grade A Steel

Yield Strength – 327.4 N/mm2

Ultimate Strength– 475 N/mm2

Carbon composition–0.2%C(>0.18% C)

Total weight of the roll cage : 80 kg

Selection criteria for roll cage:

The main reason for choosing this material is

because of the strength offered by this steel

for the estimated weight. Since the strength

was high enough to withstand the weight of the

roll cage without breakdown, we preferred this

material. Another reason to choose the

material was its cost effectiveness. Since cost

is an important factor in determining the

material, we chose an economic, cheap

material. The reason behind using pipes of two

different thicknesses is to minimise the weight

of roll cage, to improve the vehicle

performance which we managed to achieve.

Front Impact:

For a perfectly inelastic collision, energy transferred is DE = ½ (m1m2/m1+m2)(u2-u1)

2

where m1 and m2 are masses of two vehicles and u1 and u2 are corresponding velocities. Assuming m1=m2=420 kg and u2=0 (vehicle at rest), DE = 1/4 m1u1

2 & work done = DE/t,

where t=time=1 sec. Hence WD= 29.17*10^3 Nm. Now consider the work done over 1m. Then the force applied is equal to 29.17*10^3 N.

Hence a frontal impact force of 7292 N is

obtained at 4 points in the frame. The back of

the frame is constrained completely. The

displacement as a result of frontal impact is

11.7 mm. But the above figure shows the

stress values for a force of 10,000N to be

174.72 N/mm2.

Thus for this value the frame

doesn’t collapse since stress is less than 327.4

N/mm2 .

This shows that our design is safe.

Rear impact:

The rear impact is obtained by completely

constraining the front of the frame and

applying the forces at 4 points in its rear end.

As shown above the stress obtained for a load

of 10,000N is less than 327 MPa, and hence

the design is safe.

Side impact:

Similar to the front and rear impacts in the side

impact of the ATV, the wheels opposite to side

of impact are constrained and load is applied

on the face along which impact takes place.

Even in this case the stress is within

permissible limits concluding that the design is

safe.

Roll Over test:

For the roll over test a force equivalent of twice

the weight of the vehicle (8500N) was applied

on the top corner of the frame, while the base

was constrained and the results were

obtained.

As shown the stress obtained is 188MPa,

which is below the permissible value of 327

MPa. Thus design is safe from roll over. So the

vehicle is prevented from toppling in cases

where the ATV tends to fall apart.

Bump test:

In the bump test the upper portion of the frame

is constrained and load is distributed along the

base of the frame. The resultant stress

obtained was:

SUSPENSION DESIGN AND WHEELS:

To enhance the stability and to provide better

handling for driver we have chosen double

wishbone for rear and front .The suspension

we are using is Maruthi Alto (OEM parts)

suspension. So as to improve the action of the

spring on rugged terrain the stiffness of the

spring has been altered. Modifications with the

damper have also been made to suit our

vehicle.

Wheels:

We are using 25*8*12 tyres for both rear and

front. This is to enable the vehicle with more

stability in rugged terrains and allow for easy

turning, smooth ride, and comfortable steering

for the driver.

Wishbone:

The wishbone used in our vehicle is the

Double wishbone type. The material of the

wishbone is the same as roll cage material.

This double wishbone type is chosen because

of its lightweight and ability to avoid deflection

and remain stable in corners and bumps. Thus

it prevents any chances of wheel misalignment

while driving, thereby reducing any danger of

breakdown.

Hub and Stub Axle Assembly:

The hub and stub axle used in our vehicle is the one used in Maruti Alto. The hub assembly is made of cast iron. Analysis is performed on the assembly such that the point attached to wheel is constrained and the point where suspension is attached, load acts. The max stress acting for a load of 4000N is shown. FRONT SUSPENSION The only set rule for Baja suspension is that the track width cannot exceed 64 inch. The car

was designed to have a front width of about 58 inches at ride height. Through design refinement, it has been proven that 10 inches of wheel travel is enough to dissipate the energy from the track and smooth out the ride enough to traverse standard track terrains. Dynamic analysis has been carried out using the Lotus Suspension analyzer to check the bump, roll and steer reactions on the vehicle. The parameters have been tuned to obtain desired specifications. Bump:

Front end travel ranges

The three graphs show the effect of toe, camber and castor angle against X-axis bump and rebound (suspension travel). It can be concluded from the graph that for a 100mm bump the toe angle is within 0.5 degree and castor, camber is within 2 degrees, thus reducing forces on ball joints and improving stability. Roll:

The above figure shows the effect of roll on the vehicle. From the above graph one can conclude that the camber angle adjusts itself as per the roll angle thus ensuring better handling and improved comfort is obtained while driving. Steer:

fig 1 fig 2 Ackermann steering is normally achieved by levering the steering point off the front knuckle. The figure 1 shows the location of this point. It is concluded that the car achieves a 82 percent change in Ackermann Computing from the equations for Ackermann and using max toe angles, the Ackermann percentage is close to 60%. The figure 2 shows camber gain versus steer rack travel. The graph is meant to show that the inside tire gains almost 6 degrees of positive camber while the outside tire remains negative at 3.5 degrees camber. If one were to view this car from the front while it was steered, it would appear that the inside tire is laying down more than the outside tire, and both tires would be leaning away from the turn. This provides more force on the tires so that they can better push the car into turning. REAR SUSPENSION: In a vehicle approx. 65% of the total weight acts on the rear side. So the stiffness of the rear suspension should be comparatively greater than the front suspension. Dynamic

analysis of rear suspension is carried out to meet the desired specifications.

Shown above are the characteristic curves of the rear suspension. As can be seen from the graph, as the bump increases the camber angle too increases but not linearly. From the other graph it is evident that initially the camber angle is around 7.5 degrees, but as the roll angle increases the camber angle decreases linearly. Full Car Shark Model

Shown above is the image of how the suspensions of the 4 wheels act during a drive. The front wheels as seen have a greater turn radius than the rear wheels, while the suspension travel is equal in the front as well as the rear.

STEERING SYSTEM:

The steering system used in our vehicle is rack

and pinion type steering system. The

Ackermann angle of this type of steering

system is calculated as follows:

(1/ tanα1) – (1/tanα2) = L/B.

Where,

α1- outer Ackermann angle

α2- inner Ackermann angle

L- Wheel base

B- Track width

Steering system has a lock-to lock of 2.5 turns and the steering ratio is 12:1. The inner Ackermann angle is found to be 30 degrees .Also the values of L and B are 60 inches and 52 inches respectively. Substituting these values we obtain the value of α1 as 18.97 degrees. Thus the Ackermann angles are 30 and 18.97 degrees. Let us now calculate the turning radius of the wheel: Rl = (B/tan α2) + (L/2)

Substituting the required values the value of Rl

is obtained as 118.33 inches.

Now the turning radius is calculated as,

R= (Rl2 + b

2)^1/2.

Thus the turning radius is obtained as 3.17m.

Fig.1 Steering system setup using AutoCAD.

BRAKING SYSTEM: The brake pedal force can be found out by,

Fbp = Fd* (L2/L1). Substituting the values of

force applied on pedal by driver, Fbp =

386*1.30= 501.8N.

The force on pedal equals the force on the

master cylinder.

Thus the pressure on master cylinder equals,

Pmc= 501.8N/(3.14*22^2/4)= 1.32N/mm2.

The force on calliper is given by, Fcal=

Pcal*Acal=Pmc*Acal= 1.32* 3.14 *

42^2=455.71N.

The clamp force of the calliper pad is twice the

force on calliper= 911.425N.

The frictional force = Clamp force* µ=

911.425* 0.3= 273.4275N

Torque on the rotor is Frictional force* Reff=

273.4275*100= 27342.75Nmm

Ftire= Tr/ Rt= 27342.75/317.5= 86.11N

For four tires, Ftotal=344.47N

Ftotal=m*a, a- deceleration,

Thus a= 3.5m/s2.

But deceleration = g*a=34.335 m/s2.

Now the stopping distance is,

S.D=v2/2*a=3.04m.

The weight transfer can be found out using the

formula,

Weight transfer= ( wheel thrust/ weight of

vehicle)= g force.

Brake G- force = (501.8*4)/4200= 0.4779 g

Weight transfer = (weight of vehicle* COG

height* g force)/ wheel base

Weight transfer= (4200*18.37*0.4779)/60=

614.531N

POWER TRAIN DESIGN:

Mahindra Alfa transmission is used and

coupled to wheels. Engine is mounted on

rubber bushes which are in turn mounted on

wooden boards. These bushes help absorb

vibrations, thereby reducing the noise

produced. NVH considerations include the use

of bushings, card board to minimise noise,

vibrations, and harshness. The overall

transmission ratio is 31.48:1 for 1st gear,

18.7:1 for 2nd

gear, 11.40:1 for 3rd

gear, 7.35:1

for 4th gear and 55.08:1 for reverse gear. The

inlet system comprises the fuel tank, fuel filter

and carburettor, air filter. The exhaust system

includes the silencer which is mounted such

that one end is on engine out and the other

end is attached to the frame by rubber pads. A

catalytic converter too is used to reduce the

smoke emitted. The fuel tank used is a 5.5L

tank (<6L) made of plastic in compliance with

the rules, which is mounted at a good height to

enable smooth flow of fuel to the engine.

S.No Component with mountings

Weight

1. Engine 35 kg

2. Transmission 20 kg

3. Fuel Tank with max petrol 6 kg

4. Exhaust 2 kg

5. Axle 2 kg

Calculation of Centre of Gravity (COG):

For calculation of COG we have taken the X

axis as front of the vehicle, Y axis as outside of

the right of the wheels and Z axis as base of

the frame.

Sub-system

X(mm)

Y(mm)

Z(mm)

Mass(kg)

Engine 1950 893 280 40

Differential

1850 560 200 20

Battery 1450 500 500 10

Seating 1000 790 200 8

Rack & pinion

1300 790 50 8

Frame 1168 790 366 90

Tyres (inclusive of hubs)

Front-right

150 100 75 22

Front-left 150 1410 75 22

Rear-right 1775 1410 75 22

Rear-left 1775 100 75 22

Wishbone & suspension

Front-right

150 350 75 12

Front-left 150 1160 75 12

Rear-right 1775 350 75 12

Rear-left 1775 1160 75 12

The centre of gravity of the entire vehicle is

calculated to be (1230.51, 763.91, 209.42).

Gradability at each gear:

Gear 1 2 3 4

Gear Ratio

31.8 18.7 11.4 7.35

Engine Horse Power

10.72

10.72

10.72

10.72

Tractive Force(N)

2845 1395 850.95

548.64

Torque at wheels (Nm)

903.28

442.91

270.17

174.19

Gradablity (degrees)

38 15 10.5 6.8

BODY PANEL:

Body panel in the ATV mainly includes the

sheet metal used to cover the frame.

According to the rule 32.4, the body panel

must be sheet metal which covers the Lower

Frame Side Member (LFS) and the SIM. We

have ensured that this has been implemented

in our ATV as per specifications. Also,

according to rule 31.6, roll cage padding has to

be used in the ATV. So, we have included

Etho foam material of 1.5 cm thickness (>1.2

cm) along all the members surrounding the

driver to avoid any injury to the driver. The

dashboard shall also be included as part of the

body panel. The dashboard will include an

ignition switch to initiate the ignition, a kill

switch, speedometer and digital fuel indicator.

SAFETY EQUIPMENT:

The safety equipments are those which play a

vital role in ensuring safety to driver in case of

accidents and other emergency. These are

very critical and mandatory in any car and

these have been installed in our vehicle in

compliance with those prescribed in the rule

book. The safety equipments include a fire

extinguisher (min 1L), a 5 point restrain

harness seat belt, an arm restraint with SFI

3.3, helmet for driver which is of motor-cross

type, neck braces with SFI 3.3

COST AND BILL OF MATERIAL:

S.No COMPONENTS COST

1. Materials 7400/-

2. Brake 8500/-

3. Steering 4125/-

4. Suspension 20000/-

5. Fire extinguisher, neck brace, fire suit

9000/-

6. Seat 7000/-

7. Tyres 23,000/-

8. Miscellaneous 10000/-

9. Total 89,025/- INNOVATION Our intended proposal is energy scavenging using Flexible capacitive film that has long strain capability. We intend to convert Vibration into useful energy that can be boosted by a converter and used for electronics. Poly Power film is a capacitor and as such it can store electrical energy. When the capacitance of a DEAP element is changed, as a result of mechanical force on the element, the amount of stored energy changes. This feature of the material can be used to convert mechanical energy directly into electrical energy. Electro Active Polymers are polymers that exhibit a change in size or shape when stimulated by an electric field.

Fig1. Flexible capacitive film

The material is shown above and it is cost effective to be implemented in vehicles for energy harvesting and can also be used as active vibration control technique. The circuit diagram for energy harvesting is shown below.

Fig2. Circuit Diagram for Energy Harvesting

The change in capacitance is converted to equivalent frequency and the resultant waveform is given below. The energy stored is ½ Cv

2. Testing of sensor was made using RC

Oscillator and we saw variation in capacitance as frequency changes and the frequency variation for 50mm*50mm patch was from 300-350Hz. Biasing the circuit with load will generate sufficient energy tap for vehicular electronics.

Fig3. Waveforms of capacitance-frequency conversion GO GREEN Negative ion generation is used for ionising the air molecules and purifying the de-ionized air. In nature negative ions are produced by waterfalls, seas shores and due to lightning strikes. Electro spray based negative ion air purification is proposed here. The negative ion circuit is given below:

Fig4. Negative Ion generator

This module is placed in the exhaust to neutralize the dust particles and smoke. Here 3-4KV HV is produced from a 24V DC battery and used to ionise air and it is hermetically sealed at the output. We have made this into a very compact module mounted in the exhaust system with a catalytic converter fitted in the previous stage. By this way we can achieve zero emission and maximum air purification. The circuit is basically a flyback transformer which produces high voltage and the negative supply is isolated and given to fabricated rotor.

Fig5. Push-pull type HV transformer Negative ion generators utilize electronic devices, which cause an electron to be added to oxygen molecules and trace gases. They transfer negative charges to particulates including dust, mould, cigarette smoke, bacteria and more, which then attract positively charged ions. Eventually the particles become heavy enough to drop from the air to the floor and other surfaces. RESULT: The generator produces up to 2, 50,000 µC/hr. There are 6.25*e18 neg charges per coloumb. Current is 200 µA. Therefore the unit can produce 6.25*e18*200*e-6 = 2.5*10e15 negative charges/sec. Good for a 20*20*7’ room. We are employing it in exhaust for complete air purification.

The above diagram displays the various

materials used in our All Terrain Vehicle. The

materials have been selected in such a way

that they are eco-friendly and can be reused in

the future. It has also been found that 95% of

the total materials used can be recycled and

can be reused. Apart from the material being

eco-friendly , they are also cost-effective and

user friendly.

Driver ergonomics:

The cockpit is commodious, which provides

rich comfort to the driver.

This therefore enables an easy egress for the

driver within 5 secs in case of an emergency ,

thus following the rule in section 32.2.

The space above the top of the driver’s

helmet up to the top of roll cage is 10” ,thus

pertaining to the rule in section 31.4.1 ( >6”).

The visibility of the driver is improved by

slightly lowering the front portion of the roll

cage.

The minimum distance of the sides of the roll

cage from the driver’s seat is 4” ,which is well

above the value given in section 31.4 (>3” )

and keeps varying along the length of the roll

cage.

The accelerator, brake pedals are positioned

such that the driver shall stretch his legs for a

long time without any stress.

In the above fig. , it is seen that there is

enough space for the person sitting in the

cockpit ,inspite of him being 6 ft. 3” tall .

Hence, the cockpit has been designed in such

a way that , it ensures maximum comfort for

all, particularly for the driver .

The accelerator, brake pedals are positioned

such that the driver shall stretch his legs for a

long time without any stress.

In the above fig. , it is seen that there is

enough space for the person sitting in the

cockpit ,inspite of him being 6 ft. 3” tall .

Hence, the cockpit has been designed in such

a way that , it ensures maximum comfort for

all, particularly for the driver .

Reference:

Fundamentals Of Vehicle Dynamics ---

Thomas D Gillespie

Vehicle dynamics --- Reza N.Jazar

Automotive Braking Systems --- Thomas W.

Birch

Automobile design Problems --- K.M.Aggarwal

Tables for the Automotive Trade --- G.Hamm

G.Burk