VEGATAS.pdf

8/18/2019 VEGATAS.pdf

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BIRLA INSTITUTE OF TECHNOLOGY EXTENSION CAMPUS

DEOGHAR

TEAM VEGATAS

Chiradeep, Vineet, Amit , Murtaza ,Vinay

ABSTRACT

BAJA SAE is an inter college design competition run by the Society of Automobile

Engineers (SAE). Teams of students participating in the BAJA event has to design, build

and race a single seated off-road vehicle run by a small gasoline engine intended for sale

to the non-professional, weekend, off road enthusiast which can withstand the harshest

elements of rough terrains. Using a combination of Microsoft Excel and CATIA V5

software the design of the BAJA Vehicle was completed. Microsoft Excel was utilized to

optimize the material usage as well as to calculate the proper loading forces seen on the

vehicle. CATIA V5 was used for the design and analysis of the frame. Due efforts have

been put to validate our design by theoretical calculations, simulations and known facts.The vehicle should meet the necessary requirements of performance which is

manifested in terms of

Manoeuvrability, driver comfort, acceleration, hill climb, braking and endurance tests.


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ROLL CAGE

PRIMARY OBJECTIVE: 3D Space around driver for

protection during eventuality, light weight as engine

power is limited, rigid and safe for driver.

MATERIAL SELECTION

According to rule no. 31.5 of the rule book: (A) Circular

steel tubing with an outside diameter of 25mm (1 in)and a wall thickness of 3 mm (0.120 in) and a carbon

content of at least 0.18%. Materials available for

selection under the specified guidelines are as follows:

MATERIAL SPECIFICATION COMPARISON [1]

4130 Chromoly is the lightest; however it’s very

expensive and requires TIG welding which is again

costly. So a compromise was reached between costs,

weight, strength and weldability and we selected ASTM

A106 GradeB.

THEORIES OF FAILURE:

In reliability analysis failure is when the part o

assembly is unable to perform its intended purpose

satisfactorily. In this context failure is used for fracture

or permanent deformation beyond operational range

due to yielding of the material i.e. when elastic limit is

reached.

Approx. stopping time= 0.18 seconds

Front Impact: Collision with stationary object

Side impact: vehicle hit by another Baja vehicle

Neither vehicle would be a fixed object

Roll over: Secondary impact or a glancing blow, sustain

a force equivalent to its own weight.

Shock Mount Loading: To make sure the roll cage

would be able to sustain the forces generated during

and sharp and sudden inclines.

Calculation for maximum working stress:

V = U – a * tTaking initial velocity U= 50kmph and V=0

t = 0.18sec

a = 13.89/0.18

= 77.17 m/s2

F = M*a = 350*77.17

F = 27,000N

FRONT IMPACT


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SHOCK MOUNT IMPACT

REAR IMPACT

SIDE IMPACT

ROLL OVER IMPACT

Constraints - farthest end from the impact zone to get

the maximum lever arm

Mesh Size - 10cm

POST PROCESSING

Target FOS – 2 (achieved in all the impact cases)

Change in design – Gussets were applied at the junction

of over head roll hoop and front roll hoop. Engine

compartment reinforced with 2 additional tubes

Vehicle length was increased by 12 inches to fit drive

more comfortably.


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ERGONOMICS

The blue region shows reach of driver’s hand. All

essential and emergency controls are within easy reach.

Seat inclination at 20 degrees for supreme comfort,

steering at an 20 inches from lower frame and 19.5

inches from fire wall. Enabling comfortable drive for at

least 2hours

Pedals distance at 4.5inches, sufficient for driver

wearing shoes.

Steering system

Aim-To align the wheels in the desired direction and

provide a feel to the driver about what is happening at

the wheels and how the vehicle is behaving at corners.

Design Methodology:

After acquiring prerequisite knowledge through

exhaustive reading of books and different vehicle

design reports and performing extensive market

research catering to local and foreign markets the

following targets were set keeping in mind the

constraints and design specifications mentioned in the

SAE baja Rulebook 2013:

1.

Following comparison matrix was formed for

selecting the steering system.

Rack and pinion operated Ackermann steering

geometry is used as it is simpler and employ pivots and

not sliding constraints due to which maintenance is easy

Component

characteristic

Optimum

value/range

Reason

Camber +2-4 deg. Helps in cornering

nullifying –camber due

to weight transfer

Caster +3-7 deg. Provides directional

stability but higher

values may lead to

oversteerSAI 10-15 deg. Straight head recovery

by raising the vehicle

at corners

Toe in 0-3mm Helps maintaining

steering geometry

during cornering

Turning angle 25 - 40 deg. More this angle lesser

will be the turning

radius

Turning radius 2-4 meters Lesser the radius more

will be the handling

Scrub radius 0-12mm Smaller this value

more handing lesser

risk of traction loss

Steering ratio Low(upto

20:1)

lesser this, more

sensitive is the

steering action

Lock to lock Low(upto 3) Lesser this ,lesser be

the driver efforts ,

improved handling

Wheel base Low Shorter wheel base

Criteria|/gear

type-

Rack &

pinion

Worm &

wheel

Re-circulatin

ball

cost low medium high

Mechanical

complexity

simple medium high

weight Light

heavy medium

availability high low low

Sensitivity good poor fine

backlash high low medium

feedback high poor medium

Mechanical

advantage

poor good fine

Efficiency

Good Poor Very good


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shorter the turning

radius for same

steering ratio

Wheel track Low Affects the weight

transfer during

cornering

Tie rod

location

- Minimising bump steer

locating in plane of

both A-arms

Design approach:

The turning radius was found using the formula

Rof =b/sin A + (a-c)/2 ; Rof =62/sin A +5

cot A- cot B =c/b ; cot A – cot B = 21/31

Rof: turning radius of outer front wheela:wheel track

A: turning angle of outer front wheel.

c: distance between steering knuckle joints.

Turning angle vs. Steering wheel angle

Turning angle(deg) vs. Turning radius(inch)

The rack and tie rod orientations are decided using catia

v5 and LSA.

Our calculations approximated the below mentioned

results:

Steering ratio 12:1

Lock to lock 1.5 rotations of steering wheelTurning angle 32 deg.

Turning radius 3.5m

Rack travel 4 inch

Rack length 9 inch

Tie rod length 16 inches0

5

10

1520

25

30

35

40

0 200 400 600

STEERING WHEEL ANGLE

steering wheel…


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SUSPENSION:

Goals:

Minimize roll center movement.

To keep the roll center near the center of

gravity.

To ensure the independency of suspension

system, so that upset of one wheel does not

affect others.

To obtain a ground clearance of 8 inches

[approx.].

For achieving these goals, we are working on softwares

like LOTUS SUSPENSION ANALYSIS & CATIA.

The suspension is to be designed for the total weight of

310 kgs.. From the weight transfer calculations it is

found that weight is 60 kgs. (approx.) on eachsuspension in front & 95 kgs. on each suspension at

rear.

FRONT SUSPENSIONS:

Double wishbone having unequal a-arms with coil over

system.

The reason why?

Double wishbone suspensions minimise camber

change.

Roll center adjustments are easy.

Design methodology:

The roll center is so adjusted to keep it near the

COG which will minimize the turning couple.

The length of a-arms is kept as long as possible

to minimise camber change.

The spring damper system would be mounted

at lower wishbone.

REAR SUSPENSIONS:

Mac person strut with single a-arm is to be used at rear.

The reason why?

As ours is a rear wheel drive & engine is mounted at the

back the load concentration is more at the back.

Design methodology:

Roll center is adjusted to keep it near COG &

near the front roll center.

Change in wheel toe is to be restricted. So ball

joint is not used at a-arm.

WEIGHT SPECIFICATIONS

Weight of driver[with accessories] 113 kgs. (max.)

Total weight

[vehicle +driver]

350 kgs. (approx.)

Unsprung mass 40 kgs. (approx.)

Sprung mass 310 kgs. (approx.)

SUSPENSIONS USED

Front Double wishbone unequal a-arm

Rear Macpherson strut

SPECIFICATIONS

(FRONT SUSPENSION)

Wire diameter 9 mm

Mean coil diameter 70 mm

Spring stiffness 19.13 N/mm

Number of turns 10

Suspension travel Bump - 3 inches

Rebound - 2 inches


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BRAKES

The objective of the braking system is to safely stop the

vehicle. It is required by the client for the vehicle to

statically and dynamically lock all four wheels on both

hard and loose surfaces as per the SAE rule book.

For designing the braking system we have calculatedthe weight of our vehicle in static as well as dynamic

conditions as per deceleration (0.7g).in static condition

it is around 60kg on each front and 95kg each on rea

tire.

We have calculated dynamic weight using the formulae

given below:

Approx. total weight (Including driver) = 310 kgs

W = 3040.0615 N

Location of center of gravity is 24 inches from rearwheel and 38 inches from wheel axle line.

Weight applied in rear = 3040.06*38/62=1863.2635N

Weight applied in front = 3040.0615*24/32= 1176.798

α = 0.7g

Stopping distance

S = v2 /2α V = 50km/hS = 14.08m

DYNAMIC WEIGHT TRANSFER:

(1) Due to Braking

FRONT AXLE (FA)

= W1 + ∆w

=1465.11351N

REAR AXLE (RA) =W2- ∆w

= 1574.94799N

Where ‘∆w’= M * α * h / b

(2) Due to Acceleration

FRONT AXLE (FA)

SPECIFICATIONS

(REAR SUSPENSION)

Wire diameter 9.9 mm

Mean coil diameter 80 mm

Spring stiffness 31.27 N/mm

Number of turns 6

Suspension travel Bump - 3 inches

Rebound – 2 inches

CHARACTERISTICS EXPECTED VALUE

WHEEL BASE 62 inches

TRACK WIDTH

FRONT 52 inches

REAR 50 inches

CENTER OF GRAVITY

HEIGHT

8.44 inches

FRONT SUSPENSION

UPPER A-ARM LENGTH 14 inches (approx.)

LOWER A-ARM LENGTH 15 inches (approx.)

REAR SUSPENSION

ARM LENGTH 11 inches (approx.)


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= W1 - ∆w

=927.396 N

REAR AXLE (RA)

=W2+ ∆w

= 2112.665 N

Where ‘∆w’= M * α * h / b

W1= front weight of vehicle in static condition

W2= rear weight of vehicle in static condition

∆w= weight transferred

M= total weight (W1+W2)

α =maximum deceleration/acceleration

h= height of centre of gravity

b= length of wheel base

We planned to use disc brake in front and drum brake

in rear. Initially we thought of using disc brake for all

four wheels, but disc with parking brake have highercost and we found it necessary to use parking brake to

increase all terrain capabilities of vehicle.

Following are formulas used for designing our brakes:

TFRONT = (FA/2) *(R/2) * α = 1577.6119N-m

TREAR = (RA/2) *(R/2) * α = 1510.818N-m

T(Disc) + T(Drum)= m * α * R

T(Disc)= µ * R1 * (P * A) * 2

Where

T(Disc)= frictional torque on the disc

T(Drum)= fritional torque on the drum

m= mass of the vehicle

R= radius of tires

µ= coefficient of friction between rotor and pads(0.45

approx)

P= pressure applied by TMC

A= area of calliper for disc brake and wheel cylinder for

drum brake

R1= radius of disc

We will be using proportioning valve so that greater

braking force is applied at rear which bears majority of

load ,this will be also important for driver’s comfort.

BRAKING PARAMETERS VALUES

FRONT DISC O.D (in mm) 210

REAR DRUM (in mm) 180

PEDAL RATIO 4:1

WEIGHT OF VEHICLE PLUS

DRIVER (in kgs )

350(approx)

Brake lines O.D (in inches) 3/16

CIRCUIT FOR BRAKING SYSTEM:

DRIVE TRAIN

ENGINE

The source of power to the drive train begins at the

engine which is a stock four, air cooled, Briggs &

Stratton OHV Intake Model by Briggs and Stratton. The

Model 20, weighs 52 pounds with 305 cubic centimetre

engine produces a mere 10 horsepower at 3800 rpm

and 13.5 pound feet of torque at 2400 rpm. This engine

serves as a common governing agent between all teams

in competition.

MAXIMUM POWER

The following is a graph of the Briggs and Stratton

motors horse power at different rpms.


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DRIVE TRAIN SELECTION

From Previous research of past competitions

determined that the average speeds of a Baja during

the endurance race were between 30 to 35 km per hour

due to the fact that there isn’t enough straight track to

increase the speed. The majority of the time is spent

accelerating and decelerating to account for a multitude

of obstacles such as turns and other vehicles. It was also

discovered that the average top speeds for the Baja

vehicles are around 50 to 55 km per hour. For this

reason the drive train will need to provide the most

power to the wheels at the greatest efficiency within

that range.

Objectives to choose type of reduction needed:

The drive train must be light in weight and

compact due to the small size of the vehicle,

cheap, easily available. It must transfer the calculated amount of power

to the drive shaft allowing it to complete both

high and low gear applications that will be

necessary to complete all aspects of the

endurance portion of competition without

failure.

We are using MAHINDRA ALFA gear box (model

no.0703ACO590M) and clutch box (model no.

080BH0471N) i.e. multi plate wet system.

AIR RESISTANCE

Drag force=0.5*ρ*v2*A*Cd

ρ is the density of air at a temp of 450C i.e. 1.11 kg/m3.

v is the velocity of vehicle.

A is the frontal area of vehicle and our biggest cross

sectional area is firewall which is inclined at an angle o

10 degree with vertical axis so, effective area taken i1.08m2.

Cd is coefficient of drag was hinted at by the Bosch

Automotive Handbook for box-like autos at 0.8 and the

Mechanical Engineers Handbook states that a high drag

vehicle the coefficient of drag is 0.55. The graph has

three plot lines for 0.6, 0.7, 0.8 coefficients of drag

trying to estimate a close number.

Power required overcoming drag force (Pdf )

Pdf = drag force*velocity

ROLLING RESISTANCE

Rolling resistance=Crr*m*g.

Crr is the rolling coefficient is taken 0.1(the loose soil or

gravel)

m is the mass of the vehicle.

g is the acceleration due to gravity.

Rolling power consumption=rolling

resistance*velocity.

Gear First Second Third Fourth Reverse

Gearratios

31.45:1 18.70:1 11.40:1 7.35:1 55.08:1


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POWER LEFT OUT FOR THE VEHICLE ACCELERATION

Power left=Power o/p from engine –Power loss (in

drag force + rolling resistance)

Maximum possible acceleration

Power=Thrust force*velocity=m*a*v.

So, acceleration=power/m*v.

WHEELS:

Specification of the tire used for front and rear:

Size 22X8.00-10/4

Pattern MATV1319

Rim 6 inchesOutside diameter 530mm

Cross section width 184mm

Inflation pressure 5 psi

Tires were strictly subjected to availability.The treads

ensured grip on slippery and sandy BAJA tracks and

their optimum depth made it sure that the tires did not

dig up loose sand. Light weight rims to decrease

unsprung mass were selected only after ensuring

proper packaging of knuckles and brakes.


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PROJECT PLAN:


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ELECTRICALS:

Circuit diagram connecting battery to the alternator:

Circuit Diagram showing electrical connections in the

car.

INNOVATIONS:

1.Use of Solar panel placed at top of the vehicle to drive

a cooling fan .

2.Use of bumpers at front acting as shock absorbers

incorporated with sping and damper assembly to

reduce shock travel and hence preventing the battery

and steering rack assembly from bumps

Circuit diagram for solar panel

3.Use of specially designed pvc pipes and guide vanes

assembly having nozzles at on end guiding cooling air on

to the engine from the surrounding , thus, increasing

the cooling effect.

CONCLUSION:

Thus the design of the rollcage is made and analysed

assuming factor of safety , it is found by FEA analysis

that it is stable and can be used. Innovations for other

parts of the vehicle can improve the performance of the

vehicle, especially sharp turning, effective braking. Also

parts are designed and selected such that they can be

easily used and manufactured so that higher production

rate is possible. The cost of the vehicle will also be fixed

so that it affordable for a recreational vehicle.


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BILL OF MATERIAL:


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Documents

VEGATAS.pdf