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basic design report of baja vehicle
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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
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