SUPRA SAEINDIA 2019

DESIGN REPORT

Team ID : 115

Team Name : XLR8

College Name : Osmania University

City : Hyderabad, Telangana

location within this space only)

Report Author : ARPITA.L

Report Co-Author : A. ANUSHA

Introduction :

Our team consists of 25 members comprising of students from first to fourth years and we have aimed to develop this
student formula vehicle in accordance to the rulebook provided by SAE INDIA, including driver ergonomics and safety
. This report includes all the design considerations, calculations and Finite Element Analysis of all the various
components used in vehicle. Vehicle systems are designed considering all safety parameters, performance, ease in
manufacturability, various technical requirements and affordability. This is a one man driven racing vehicle which
includes design of various systems and sub systems to work as a single unit to deliver high performance .Based on the
rulebook, the chassis and various components which are to be manufactured were designed and analyzed using 3d
models and computer softwares. Later the assembly of all the components was carried out according to the design plan.

1. Basic Dimensions 2.Wheels:

Tyre size 175/50 R13
Length 93in
Tyre type All weather
Width 67in
Rim size R 13
Height 170cm
Front track width 56in 3. Braking:
Rear track width 52in
Type Hydraulic system
Wheelbase 64in Circuit X circuit
Ground clearance 3.5in Disc diameter 220mm
Weight 270kg Caliper Honda 25mm
Weight distribution 45:55 Master cylinder : 2 independent reservoirs
4. Chassis material

Material 1 AISI 4130

Cross sections : 25.4 X 3 mm
25.4 X 2 mm
Material 2 AISI 1018
Cross sections: 25.4 x 3mm
25.4 x 1.65 mm

Chassis:

Introduction and considerations: The primary chassis of the vehicle was designed according the rulebook . The
possible tolerances were assumed and the structure was constructed.

All the components and their assembly were taken into consideration after which all the static calculations were
done. The load distribution and centre of gravity were identified and further optimizations were done. The shear force
and bending moment diagram were drawn to identify the best lateral load transfer. The procedure was repeated for
different wheel bases and track width and subsequently the optimum wheelbase and track width were noted.
Upon identifying the suspension geometry and suspension points, nodes and triangulations were designed and
analyzed. A prototype of the chassis was constructed using PVC pipes. The chassis was verified with Percy template,
cockpit template and cross-section template as per the rulebook. All the clearances with the driver seated were observed
to be in compliance with the rulebook. The model was then manufactured and MIG welding was used.

Material selection:
Both AISI 1018 and 4130 were chosen upon taking care of the cost aspect and strength of the chassis and striking a
proper balance between these two, AISI 4130 tubes were majorly used for the Roll Hoops and the Base because of its
better strength to weight ratio. The side impact structure and support members being properly triangulated, AISI 1018
was selected keeping in view the cost aspect. Other properties like availability, weld-ability, cost and machinability
were considered for selecting AISI 1018, AISI 4130.
S.No Members Material Dimensions
1 Main hoop, front hoop. AISI 4130 25.4 X 3 mm
2 Base of the chassis , front bulkhead AISI 4130 25.4 X 2 mm
3 Main roll hoop bracings, side impact structure. AISI 1018 25.4 X 3mm
4 Front bulkhead support, main hoop bracing AISI 1018 25.4 X 1.65 mm
support.

Finite Element Analysis:

The frame structure was analyzed using “ANSYS (Version 19.2) software” and the safety factors were calculated.

Element Type: BEAM 189 element type is used for all roll cage FEA. It is a quadratic, 3 node elements with 6 DOFs at
each node. It is based Timoshenko beam theory which also takes into account shear deformation effects and is used to
analyze slender to moderately stubby, thick beam structures.

1. FRONT IMPACT – full width 2.FRONT OFFSET

Assumptions were made such that the vehicle crashes into a In this scenario the obstacle or the other vehicle
Wall and comes to a complete stop in 0.220s .Application of impact was assumed to hit the front of the car with an
load on the front part of the roll cage. The rear wishbone mounting offset (50%) so that the load is distributed on 2
points were constrained points on one side of the front part of the vehicle.
Stress developed = 111MPa Constraints same as taken in front impact-full
FOS=4.144 width
Stress developed = 220MPa
FOS=2.09

3. Side Impact :
The impact loads were applied to one side of the chassis on
the side impact structure as described in the rule book.
The constraints were the wishbone mounting points on the
other side of the chassis.
Stress Developed = 173MPa
FOS=2.65
4.Rear Impact :- full width 5. Rear Offset :
For the rear impact test a worst case scenario of In this scenario the obstacle or the other vehicle was
constraining the front and applying force on the assumed to hit the rear part of the chassis at an offset.
rear was considered. (50%) so that the load is distributed to only 2 points
Stress Developed = 80.3MPa on rear part of the chassis.Similar constraints as in rear
FOS=5.72 impact – full width.

4. Front Torsional Analysis : 5. Rear torsional analysis

A 3G load in the form of a couple is applied to the front A 3G load in the form of a couple is applied to the rear
Wishbone mounting points in opposite directions on either wishbone mounting points in opposite directions on
Side of chassis.Constraints were applied on the rear either Side of chassis.Constraints were applied on the
Wishbone mounting points. front Wishbone mounting points.
Stress Developed = 81.7MPa Stress Developed = 95.2MPa
FOS=5.63 FOS=4.831

Design Validation: The roll cage was designed in accordance to the rules of the rule book.
The analysis results were satisfactory and Factor Of Safety (FOS) was found within the good and hence the cross
sections for various members were finalized.
STEERING DESIGN:
Steering system is the system used for controlling the direction of the vehicle while in motion .All intentional turns are
initiated and are controlled by the turning of the front
Geometry and selection:
The intention of selection of Ackermann geometry is to avoid the need for tyres to slip sideways when following the
path around a curve. The rack and pinion steering gear is considered to be the most suitable gear system for Formula
SAE race cars. This type of steering system was selected as it provides good geometry, compact design, accurate and
light weight.
Track parameters

Parameter Value
Track width(b) 1422.4mm
Wheel base(l) 1625.6mm
Steering arm length 76.2mm
Ackerman angle 20˚

Table 2-Basic steering parameters :

Geometry Validation: The geometry validation was done by performing the analytic treatment. The concept of reverse
engineering was applied in order to validate the designed geometry.

Parameters Value
Angle of inside lock(ϴ) 40˚
Angle of outside lock(Ф) 25.82˚
Turning radius of front inner wheel 2.53m
Turning radius of front outer wheel 3.73m
Turning radius 3.73m
Rack travel 7in
Rack length 14in
Steering ratio 8:1

The following calculations were performed in order to validate the geometry.

Angle of inside lock (ϴ)= 40˚
According to Ackermann geometry perfect steering is given by:
Cot (Ф) – Cot(ϴ) = (b/l)
Cot(Ф)=(1422.4/1625.6)+cot(40˚)=2.066
Ф=25.82˚
Inner wheel turning radius=l/sin(ϴ)=1625.6/sin40=2.53m
Outer wheel turning radius=l/sin(Ф)=1625.6/sin25.82=3.73m

POWER TRAIN

The main aim of this power train design is to get an increased overall performance with balanced torque and power in
compliance with SAE rules

Engine selection criteria:

KTM DUKE RC 390

 High Power to weight ratio

 Less engine vibrations
 Precise throttle response
 Flexible to changes
 Affordable
Engine Details:

The engine used is KTM 390CC.It is a single cylinder 4-valve 4-stroke petrol engine. The Bore and stroke length of this
engine is 89mmx60mm and displacement is 373.27cc. The compression ratio is 12.88:1. The main differences which
made us to choose KTM 390 over RE 500 are as follows-

Characteristics KTM 390 RE500

Max power 43.5 BHP @9000rpm 27.2 BHP @5250
rpm
Max torque 37 NM @7250 rpm 41.3 Nm @4000 rpm
Gear box 6 speed 5 speed
Top speed 170kmph 130kmph
Mileage 25kmpl 30kmpl
Cooling Liquid Air
Weight 36kg 58kg
Power to weight ratio 271.76 BHP per tonne 135.23 BHP per tonne
Torque to weight ratio 221.20nm per tonne 211.91nm per tonne

AIR INTAKE SYSTEM :

The main aim of designing the air intake system is to minimize the pressure loss caused due to the introduction of a
20mm air restrictor.

The intake design consists of the following parts in sequence

1. Air filter
2. Throttle body( throttle actuation )
3. Restrictor
4. Plenum
5. Runner
6. Throttle body(fuel injection )

Our restrictor was designed as converging and diverging nozzle. Flow analysis was done and we obtained the best
results for 12 degrees converging and 6 degrees diverging with inlet and outlet diameter of 48mm .Plenum is designed
cylindrical in shape and its main function is to equalise the pressure.It has a volume of 0.996 litres(2.5 times of engine
capacity).
KTM 390 throttle bodies were used with one upstream of air restrictor and other downstream of air restrictor. First one
is used for throttle actuation and the second one is for fuel injection and Map sensor. The model was designed and
analysed (flow analysis) on solid works software and fabricated using aluminium for weight reduction.

FUEL SYSTEM:

The fuel tank of KTM 390 is used. Fuel used is petrol and all fuel lines are connected with barbed fittings to avoid
leakages at the connections. The fuel system was installed in accordance to the rule book and the height of the filler
neck was decided to be 210 mm to accommodate the sight tube.
The electrical system majorly consists of ECU, battery, fuses, sensors and relays. The whole electrical system is
powered by 12V DC, 9Ah Lead-Acid EXIDE battery. The whole electrical system is designed and installed keeping in
mind all adverse engine conditions.
The cooling system of KTM 390 is used with water acting as the coolant,
Type of transmission: Chain drive and a chain differential with a final drive ratio is 15:66.

BRAKING SYSTEM

A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. Brakes are thereby used
for stopping a moving vehicle, or slowing so as to control the speed of the vehicle in motion. As per the rule book of
SUPRA SAE 2019, it is compulsory for the system to consist of two independently operated hydraulic circuits. Also, all
the four wheels must lock simultaneously. A brake pedal over-travel switch is installed on the car as a shutdown system
in the unlikely event of brake system failure.

BRAKE SYSTEM CALCULATIONS:

Firstly, Initial Weight Distribution of the car is considered and CG is calculated. Based on this data, Dynamic Weight
Distribution during hard braking is calculated. Simultaneous the force required to move the master cylinder is calculated
by using mechanical advantage. Then the pressure on the master cylinder and the calliper can be found by carrying a
number of iterations while selecting the components that best suit our requirement.

Total weight of the vehicle 270kg

Pedal ratio 4.5:1
Front axle static load 135.64 g-N
Rear axle static load 134.325 g-N
Weight transfer 64.462 g-N
Front axle dynamic load : w1 + g L) 200.137 g-N
Rear axle dynamic load : w2–((α W H)/g L) 69.862 g-N
Torque required ( Tfront) 297.68 N-m
Torque required ( Trear ) 103.91 N-m
Force applied on pedal (Fp) 250 N
Pressure on master cylinder (Fmc/Amc) 3949052 N/m2
Force on calliper 3873.31 N
Force on disc 3098.65 N
Torque generated 341 N-m
Where,
g = Acceleration due to gravity.
H=Height of center of the gravity= 9.55in from ground
L= Length of the wheel base= 64 in
α=Deceleration of the vehicle

Specifications:

PARAMETER OEM VALUE

Master Cylinder TVS Girling Bore=19.05mm
Stroke length=25mm
Calliper Honda Dazzler Dia=25mm
Disc Honda Dazzler Disc dia=220mm
OEM Selected

Disc and caliper specifications:

PARAMETER FRONT REAR

ROTOR
TYPE Disc Disc
MAKE Honda dazzler Honda dazzler
CALLIPER
TYPE Dual piston Floating Dual piston floating
MAKE Honda Dazzler Honda Dazzler

SUSPENSION:

We are selecting double wishbone suspension system for both Front and Rear suspension because of the following
reasons:-

* Double wishbone designs allow us to carefully control the motion of the wheel throughout the suspension travel, and
better control of parameters such as camber angle, caster angle, toe pattern and scrub radius.

* In a double wishbone suspension it is fairly easy to work out the effect of moving each joint, so you can tune the
kinematics of the suspension easily and optimize wheel motion.

* Double wishbones are usually considered to have superior dynamic characteristics, load handling capability and are
still found on higher performance vehicles.

Double wishbone suspension has been design based on swing arm geometry by placing the lower arm approximately
parallel to the ground for optimum performance.

A-Arm design:

 Front Roll centre Height : 1.63in

 Rear Roll centre Height : 2.42in
 Front Static Camber : -1 degree
 Rear Static Camber : -1 degree
 Front kingpin Inclination : 7 degree
 Rear kingpin Inclination: 0 degree
 Front Caster: 7 degree
 Rear Caster: 0 degree

FEA on wishbone:
Load applied was 1788N and the spring mounting points were fixed. Frictionless supports were given to the
mounting points on the chassis. The maximum stress obtained was 214MPa with a factor safety 2.15 and the fatigue
life was found to be 20005 Cycles.

Fatigue analysis Stress analysis

We have calculated the angle between the A arms to be 80 degrees for the stability of the vehicle in accelerating and
braking conditions.
Now according to design, 45% of the total weight will be distributed at the front portion and the remaining 55% of the
weight will be at the rear end as the major components of the total mass (in terms of weight) like engine, transmission,
driver etc. are located at the rear side.
From the above estimations, we find that the weight distribution at one side of front end will be approximately 74.25 kg
and at one side of rear end will be approximately 60.75 kg. So, all the calculations are done considering this weight
distribution only.
And longitudinal weight distribution during braking was observed as 80% of weight is distributed in the front while
20% is distributed at the rear.
Lateral load transfer during cornering: 1527.76249 N
The front wheels bear the maximum load on application of brakes which is 1058.4 N.
Considering the above static and dynamic loads, springs have been selected with the following specifications

SPRING CONSIDERATIONS:

Vehicle Weight with driver 270kg

Longitudinal weight distribution 45:55
Static load on front wheels 121.5 Kg
Static load on rear wheels 148.5 Kg
Maximum load transfer ( during braking ) 216

Spring calculations:
Step 1: To calculate wire diameter and mean coil diameter of spring

ζ = k [ 8PC / πd2 ]
D is the mean diameter of spring, d is wire diameter, k is Wahl’s factor.
K =( 4C-1/4C-4 ) + 0.615/4
Step 2:- Finding active number of coils N
Using formula ∂ = 8PD3N/Gd4
Step 3:- Finding stiffness of the spring K
K = Gd4/8D3N
Step 4:- Finding the free length of the spring
Lf = maximum compression + solid length + clash allowance

Spring Specifications Front Rear

Coil diameter 6.4mm 7.8mm
mean coil diameter 54.74mm 48.9mm
Spring index 8.5 7
No of active coils 12 16
Free length 205mm 215mm
Motion Ratio 1.54 1.54
Installation ratio 0.65 0.65
Spring Rate 10.6N/mm 27.4N/mm

UPRIGHTS:

The design considerations and constraints of our upright assembly are:

1. A arm geometry
2. Roll center height (1.63in (front), 2.42in(rear))
3. Loads on the upright ( axial , radial , cornering loads )
 4. Rim dimensions (R13 rim)
5. King pin inclination (7 degrees)
6. Caster angle (7 degrees)
7. Size of shaft ( 20mm dia )
8. Size of the bolt
9. Brake caliper dimensions
10. Steering mount
11. Less weight ( to reduce un-sprung mass )

Based on the load calculations, a suitable spherical roller bearing was selected. According to the design
considerations, the locations of the mounts on the upright were found. The upright was designed enveloping the
bearing and the upper & lower A-arm mounts by considering optimum material thickness. Analysis was done in
ANSYS 19.2 software and excess material was removed. The optimized design was then given for manufacturing
and the material AL6063 T6 was selected. The actual design was however not manufactured as the complexity was
high and machining was difficult. Hence the components were re-analyzed and have been put here.

Analysis result of Front and Rear knuckle:

REAR UPRIGHT FRONT UPRIGHT

HUB

Design considerations:

1. 4-stud 100mm PCD R13 Rim

2. Brake disc of 100 mm PCD
3. Loads on hub
4. Shaft dimension
5. Space available in wheel assembly

The material used for the hub is AL7075 T7 and designed based on the constraints and proper fitting of all parts was
ensured. The design was then analyzed for the stress and fatigue life, optimized and manufactured.
CONCLUSION:

The design and analysis were done for all the in-house manufactured parts and optimisations were done. Easy
manufacturability, better drivability, better performance, safety and cost were the major areas of focus. We have worked
towards building a safe and stable formula car which stands in compliance with the rule book and our design
considerations, hoping to deliver good performance, thrill and comfort to its drivers.

VEHICLE VIEWS:

1. FRONT VIEW:
2. SIDE VIEW:

3. TOP VIEW: