R V College Of Engineering
Bangalore
Project
Garuda
2011
Design Report
2011
Project Garuda
1.Mission Statement:
The overall goal of this project is to design and fabricate a single-person, fuel efficient
vehicle powered by a modified, iso-octane burning Honda four-cycle 2.1 hp motor. The
objective of the Supermileage Team is to apply our engineering knowledge and
experience to design and build a vehicle that will achieve in excess of 1000 miles per
gallon while satisfying all of the Shell Eco Marathon Competition rules and
requirements. This target will be met by designing and constructing a lightweight,
aerodynamic shell that will house a modified Honda 50cc engine.
2.Introduction:
RVCE Supermileage team consists of student from various engineering backgrounds
working on a common objective of building a highly fuel efficient vehicle making this
project truly interdisciplinary. Over the last few months the project has made significant
progress and is now currently working on the 2011 prototype to take part in the Shell
Eco Marathon Event.
2.1.Our Aims and Targets:
Build on existing platform and optimize the Design efficiencies
Target to obtain a mileage of more than 1000mpg
Use the Supermileage energy efficient platform, to test out alternate energy options
and optimize automobile energy requirements
To improvise existing design and develop expertise in the field of
1) Automobile Design and Manufacturing
2) Computational Fluid Dynamics (CFD)
3) Engine Design
4) Electronic Fuel Injection (EFI) Systems
The main intent of this project however, is to collaborate with various minds across the
industry and build on technical knowhow.
R V College of Engineering
Dept of Mechanical Engineering
Page 2
2011
Project Garuda
3.Vehicle Configurations:
Our vehicle is a single seater and has three wheels. The driver sits in a reclined position
with his/her legs directed towards the front of the vehicle.
The two independent wheels are mounted on the front and the drive is sent to the rear
wheel.
The Engine, transmission and its associated components are mounted in the rear
section of the vehicle, that is, just behind the firewall and the roll-cage.
The steering system controlling the front two wheels is based on the Ackermann
Steering System, taken from a go-kart.
Our Chassis is made of tubular aluminum and the shell is made out of Fiber Reinforced
Plastic, a patented plastic generously donated by General Electric (GE).
Overall length of the car is 2400mm, maximum width being 600mm and maximum
height above the ground being 700 mm. the minimum ground clearance is 100mm.
R V College of Engineering
Dept of Mechanical Engineering
Page 3
2011
Project Garuda
VEHICLE SYSTEMS:
4.Engine:
The engine of the Shell Eco-Marathon car is power source for the vehicle, converting
chemical energy stored in the fuel to rotational mechanical energy output by the
driveshaft. Three different base engines were considered for the Eco Marathon vehicle
including: a modified SAE Briggs and Stratton engine, a Honda GX35 used by the 2010
Eco-Marathon team, and a Honda GX50.
4.1. SAE Briggs and Stratton:
Teams entering the society of Automobile Engineers (SAE) Supermileage competition
are required to use a 148cc Briggs and Stratton engine as the basis of their
design.Garuda team in the past have experimented with this engine and made
progressive modifications to the base engine including converting a side head valve
engine to over head valve engine and reducing the displacement by altering the bore
and stroke. The engine has not run for several years and is less efficient than some of
the stock engines because its design is not optimized to run at the lower displacement it
has been modified to. We are not planning to compete at the SAE Supermileage,
therefore the use of Briggs and Stratton engine will not be required. Using a small
displacement base engine will have the advantage of a more optimized design and a
significant weight reduction over the Briggs and Stratton engine, giving us an advantage
over teams planning to compete at the SAE event.
4.2. Honda GX35:
The 2010 RVCE Supermileage team used a 35cc Honda engine.The Honda engine is
small and light but produces its maximum power and torque at high engine speeds
where fuel consumption is also high. As well, the vehicle as currently designed has been
proven underpowered for initial acceleration, partly due to the insufficient torque
R V College of Engineering
Dept of Mechanical Engineering
Page 4
2011
Project Garuda
available from the engine. Further the engine is designed for use with carburetor and
would require significant modifications to convert to a fuel injection system. These
limitations warranted research into stock fuel injected engines suitable for the
application and the decision to pursue a new base engine for the 2011 Eco-Marathon
vehicle.
4.3.Bajaj Kristal Engine:
The 95cc Bajaj Kristal engine is designed for fuel economy and comes with a stock auto
clutch system. The engine is compact and light weight, while incorporating many of the
advanced technologies used on larger displacement engines. We plan to incorporate an
electronic fuel injection system to this engine to have greater control over the air to fuel
ratio. With these few additions the Bajaj Kristal engine should provide an excellent base
engine for our design and for future Eco-Marathon teams to improve on. Based on the
discussion presented above the Bajaj Kristal engine was selected as the base engine for
the 2011 Eco-Marathon vehicle.
5. Fuel System:
Bajaj Kristal Engine
The fuel system is responsible for supplying the correct air/fuel mixture to the engine
for combustion, balancing power output and fuel consumption. Our design
requirements specifically state that the 2011 Shell Eco-Marathon car will use a fuel
injection system (for improved fuel delivery), so a carbureted system was not
considered as an option. As well, Shell does not permit the use of electric fuel pumps for
the Eco-Marathon competition. The remaining two options were: manifold injection
with a mechanical fuel pump and throttle body injection with pressurized fuel.
5.1. Direct Injection (MI) with a Mechanical Fuel Pump:
Direct Injection is the most efficient form of fuel injection where high pressure fuel is
delivered to the cylinder during compression stroke (figure 3). A mechanical fuel pump,
driven by the engine’s crankshaft, would provide the power to pressurize fuel. Direct
Injection offers precise control of fuel metering and excellent fuel distribution to the
engine. As well, direct injection requires precise control of injection timing and is
uncommon in small engines.
R V College of Engineering
Dept of Mechanical Engineering
Page 5
2011
Project Garuda
5.2. Throttle Body Injection with a Pressurized Fuel System:
Throttle body injection delivers fuel to intake air instead of directly into the cylinder.
Throttle body injection requires lower fuel pressures than direct injection systems
because the injection point is at lower pressure. As a result, it is possible to pressurize
the fuel with a compressed gas and eliminate the need for a mechanical fuel pump,
requiring no energy from the engine. Throttle body injection offers comparable fuel
metering precision to direct injection and also requires less precise injection timing.
Based on these advantages, throttle body injection was selected for 2011 Eco-Marathon
vehicle.
Fig: Throttle Body Injection
R V College of Engineering
Dept of Mechanical Engineering
Page 6
2011
Project Garuda
6. Electronic Control Unit (ECU) and Sensors:
Having the EFI (Electronic Fuel Injection) system gives a computer controlled injection
rather than a mechanically controlled one. The ECU (Engine Control Unit) is
incorporated and is designed as an embedded microcontroller system with inputs and
outputs connected to the ADCs (Analog to Digital Converters) and DACs (Digital to
Analog Converters) respectively.
The reasons for using an ECU instead of the traditional carburetor system are as
follows:
1. Highly Accurate Air/Fuel Ratio Control Throughout all Engine Operating Conditions.
2. Atomization of fuel occurs due to the injectors, creating better mixing of air and fuel.
3. eliminates the head losses (pump losses) through the venture of the carburetor.
4. And most importantly, Electronic Fuel Injection (EFI) is considered to be superior to
carburetion because it allows more precise fuel metering for easier starting, lower
emissions, better fuel economy, and performance.
In addition, the EMS controls other subsidiary functions, which are as follows:
1) The spark timing, discussed in the section on the ignition system.
2) Limiting the speed to which the engine can rev.
The layout of the EMS used in ‘Garuda’ is shown below:
The Engine Management for our car is carried out by a simple and easy-to-install ECU
system. The RD0601 ready to use ECU kit implements the above functions. The RD0601
is essentially a 32 bit, RISC (Reduced Instruction Set Computer) microprocessor.
A generic block diagram of our Engine Management System is shown below:
R V College of Engineering
Dept of Mechanical Engineering
Page 7
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Project Garuda
Sensors used include a Throttle Position Sensor (TPS), a Camshaft Position Sensor and a
Temperature Sensor. Details of each sensor used are given below:
6.1. Throttle Position Sensor:
A DELPHI throttle position sensor
(Essentially a Hall Effect sensor) has
Been attached to a mechanical throttle
Body as shown in the picture.
Advantages of using this sensor:
*Non-contact sensor provides increased
Durability and reliability compared
To contact sensor designs.
*Contact sensor is physically separated
From the gearbox to avoid gear dust
Contamination of sensor and reduce shaft
Position variation for improved warranty performance
6.2. Camshaft Position Sensor:
A Suzuki Camshaft Position Sensor (a Hall
Effect sensor) is being used by us for accurate
Detection of the camshaft position.
Specifications:
a. RPM Range: 10 to 36000 RPM
b. Output Voltage: 0.4V dc max.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
6.3. Temperature Sensor:
A DELPHI temperature sensor is used in our
Engine to measure temperature variations while
Engine runs. Mode of operation of such sensors
is a change in resistance of a thermistor inside
the sensor with variations in temperature.
This relation is inversely proportional in nature.
Specifications include:
Thermal and Electrical Properties
Typical voltage supply: 5 V DC
 Operating temperature: -40°C to +135°C
 Resistance at 25°C: 2795 ohms
 Thermal time constant: 60 seconds in dry air stream
 Accuracy (±°C) -40°C to +100°C: 0.56 to 0.77
 Accuracy (±°C) +100°C to +150°C: 0.77 to 1.24
A single actuator is being used presently, that being the fuel injector:
A DELPHI fuel injector is used for our purpose as it
Satisfies our requirements for spray pattern, linear range, working
flow range and operating voltage.
Specifications include:
*Injector quality performance...<1ppm
*IPTV at 12 months (4-cylinder applications)...<.7
*Plugging test cycles with <5% flow shift...>300 (Delphi test cycles)
*Dynamic durability, % at billion (1,000 million) cycles...+/-3%
*Tip leakage (mean cc/min) air at 420 kPa...<0.02 cc/min
*Spray SMD, μm at 400 kPa, 3.0 g/s...<50 μm
*Linear range with 5 V minimum...>16
*Minimum operating voltage at 400 kPa...<5.0 V
Picture shows the Multi Point Fuel Injection (MPFI)
Injector being used in our car. MPFI ensures better quality of fuel injection and hence a
complete optimized usage of fuel.
6.4.ECU MAPPING:
The RD0601 EMS system being used in our car utilizes a visual basic (VB) software
interface And hence provides us with the facility of fuel injection and ignition timing
control.
R V College of Engineering
Dept of Mechanical Engineering
Page 9
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Project Garuda
We use a 20*16 tuning map for fuel and ignition and a 10*1 tuning table for injection
opening time and ignition dwell based on battery voltage.
An added accessory is a 10*1 tuning map for fuel and ignition correction based on the
following factors :*) Air temperature.*) Engine temperature.*) Battery voltage.*)
Altitude. A rev limiter and a VTEC (Variable valve Timing and lift Electronic Control).
The ecu maps are lockable and the injection sequence can be programmed for fully
sequential, semi-sequential or of batched operation.
A 20*16 map allows us to specify the injector nozzle open time for a wide range of
RPMS at particular engine load value. Real time mode of operation shows us enigne
rpm, temperature, air to fuel ratio in real time. We then set the injector open time values
in the map and 'Send to the ECU'. 'Burn to ECU' stores the map values permanently in
the ECU RAM.
The typical 20*16 injection map used by us is shown above.
All signals from sensors are fed to the microprocessor chip through a simple data bus
system. A serial bus / Bafo (a serial to USB adapter) system connects the ECU system to
our computers. The microprocessor board runs on the same 12V battery source (1.4
Ah) being used for all other systems onboard the car. Detailed studies on the ignition
curves and rpm v/s load curves gives us an idea about the optimum fuel amount to be
injected at the rpm level range at which our car will run.
The RD0601 ecu system has proven itself robust, reliable and easy to use. Using the
RD0601 we can display up to four of the available ECU parameters and have the values
updated in real-time as we drive. It also decodes the internal ECU error codes as they
occur and displays them in real time.
Having the EFI (Electronic Fuel Injection) system gives a computer controlled injection
rather than a mechanically controlled one. Electronic fuel injection is considered to be
superior to carburetion because it allows more precise fuel metering for easier starting,
lower emissions, better fuel economy and performance.
R V College of Engineering
Dept of Mechanical Engineering
Page 10
2011
Project Garuda
7.Drive mechanism:
The drive mechanism transfers the power generated by the engine to the clutch,
transmission and finally the rear wheel to propel the vehicle. Three concepts for the
drive mechanism were considered: belt drive, gear drive and chain drive.
7.1.Belt Drive:
Belt drive systems use pulleys that grip the belt on either end while they rotate
transmitting the angular rotation of the input pulley to that of the output pulley Friction
belts, such as flat or v-belts, are unstable because of inherent power loss when slippage
occurs as high torque overcomes the friction generated by the tension in the belt. A
notched synchronized belt is more efficient because it uses grooves cut into the belt, low
in cost, and do not require lubrication; however a belt drive is not as robust as a chain
or gear drive because belts tend to wear and stretch with extended use. As well,
synchronized belts are not compatible with belt drive transmissions (such as variable
diameter sheaves); therefore a secondary drive mechanism would be required if a belt
drive is used .The disadvantages of a synchronized belt drive outweigh the benefits,
eliminates it as an option.
7.2.Gear Drive:
In a gear drive, power is transmitted through the teeth of meshing spur or helical gears.
A gear drive is efficient and has low maintenance, but weighs significantly more than a
belt drive or chain drive and is more costly. As well, a gear drive is not practical for
transmitting power over distances that require idler gears to connect the driven and
driving gears because of the increased weight of the additional components. The layout
of the Eco-Marathon car’s power train will require a distance between the engines and
drive wheel that would make a gear drive impractical, thus a gear drive impractical,
thus a gear drive is also unsuitable.
7.3.Roller Chain Drive:
The idea of a roller chain drive is much the same as a synchronized belt system in that
both the drive and driven pulleys or sprocket have teeth that grip the notched roller
chain as they rotate, transmitting power. Roller chains are durable and offer high
transmission efficiency at a reasonable cost compared to a belt or gear drive.
8.Clutch:
A clutch is necessary to engage and disengage the engine to control movement. As well,
a clutch to disengage the engine while starting is a requirement for the Shell EcoMarathon. Three different clutch designs were designs were considered: centrifugal
clutch and cone clutch.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
8.1. Centrifugal clutch:
A centrifugal clutch (Figure 4) uses the angular velocity of the engine’s driveshaft to
Extend a rotating mass, creating pressure between two friction surfaces to transmit
Power to an output shaft. At low engine speed, the clutch is disengaged because the
Centrifugal force is not large enough to cause the rotating mass to move the friction
Plate outward and lock onto the output mechanism. However, as the engine speed
Increases the centrifugal force generated by the rotating mass pushes the friction
Plate to the outer drum, allowing power to be transmitted. Centrifugal clutches allow
The motor to develop high torque before engaging and operate at high efficiencies
once engaged. Thus the centrifugal clutch is suitable for the Eco-Marathon vehicle.
Figure 4: Centrifugal Clutch
8.2. Cone Clutch:
Friction cone clutches offer superior transmission of high torque because the design
provides a wedging action that helps the frictional surfaces to bond together (Figure
5). As a result of the wedging action, more force is required to disengage the clutch
compared to a plate clutch. A cone clutch was eliminated because of its additional
size, weight, and design complexity compared to a plate clutch described below.
Figure 5: Cone Clutch
R V College of Engineering
Dept of Mechanical Engineering
Page 12
2011
Project Garuda
9. TRANSMISSION:
A transmission is required to provide a variety of gear ratios to optimize fuel
efficiency throughout the range of operating speeds encountered during the course of
the competition circuit. Three transmission designs were considered: continuously
variable, planetary hub, and sprocket and chain.
9.1. Continuously Variable Transmission (CVT):
A CVT transmission (Figure 6) uses a mechanism to open and close both the input
and output pulleys, changing the input to output gear ratio. A CVT transmission
offers a large range of gear ratios and smooth shifting between gears. As well, a CVT
can be designed to disengage at low speed, eliminating the need for a separate clutch
mechanism. The major drawback of a CVT is inherently lower efficiency due to belt
slippage and the weight of all the required components (sheaves, clutch arms and
weights, springs, etc.). These disadvantages eliminated the CVT as an option for the
Eco-Marathon transmission.
Figure 6: Continuously Variable Transmission
9.2. Planetary Hub Transmission:
A planetary hub transmission (Figure 7) uses a series of planetary gear sets enclosed
in a bicycle wheel hub to offer a range of gear ratios. This design is compact and
requires low maintenance. The drawbacks of a planetary hub transmission are its
higher cost and weight compared to a simple chain derailleur system, as well as its
lack of availability at power ratings required for the engine of the Eco-Marathon
vehicle. Planetary hub transmissions are typically designed for bicyclists and are not
able to take the higher torque and speed of a gasoline engine, therefore hub
transmission is unsuitable for the Eco-Marathon vehicle.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
Figure 7: Hub Transmission
9.3. Direct Transmission:
A sprocket and chain transmission (Figure 8) similar to
that of a bicycle to move a roller chain from a large sprocket to a smaller sprocket,
effectively increasing the output-to-input gear ratio of the transmission. The larger
gear would be used to provide the high torque needed to accelerate the vehicle from
the starting line, while a smaller gear(s) would be used to provide acceleration to top
speed. Advantages of a sprocket and chain transmission are its light weight,
high efficiency, and low cost. A disadvantage of the sprocket and chain
transmission is its limited gear ratios compared to a CVT or planetary hub. Overall,
the sprocket and chain is the best alternative for the Eco-Marathon vehicle’s
transmission.
(fig 8:Direct Drive)
R V College of Engineering
Dept of Mechanical Engineering
Page 14
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Project Garuda
10. Final Design
The final design selection is based on an assembly made up of the five components
discussed above. Table 1 summarizes the alternative chosen for each of the five
components. Each of the components and its design will be discussed in more detail
in the following section.
Table 1: Components Selected for Final Design
Component
Engine
Fuel System
Drive Mechanism
Clutch
Selected
Honda GXH50
TBI with Pressurised Fuel System
Roller chain
Centrifugal clutch
10.1.Engineering Design:
Intermidiate drive:
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
A direct chain drive from the engine to the wheel sprocket will be incorporated. An
automatic clutch assembly will be used to increase efficiency.
The Honda GXH 50 cc engine comes with a power of 2.1 bhp (@7000rpm) and a max
torque of 2.8Nm (@4000rpm).
10.2. Calculations:
1. Sepang circuit distance (single lap) =2.8km
only 30% of this distance is done by running the
engine=0.84km
2. Number of laps to be done=4
3. Max time=28min (for 4 laps)=7min/lap
30% of this value=2.1min/lap=0.035hr/lap
4. V= dist/time
0.84*1000 = 6.67m/s
0.035
5. V=W*r
6.67=W*0.127
(W)wheel=52.51rad/sec
Speed of wheel=60*33.35 = 501.46rpm
2*3.142
6. Speed of engine=4000rpm
(W)engine=2*3.142*4000 = 418.93rad/sec
60
7. (W)wheel = no. of teeth on engine shaft
(W)engine
no. of teeth on wheel sprocket
Assuming no. of teeth on engine shaft=12
418.93
=
12 teeth
no. of teeth on wheel sprocket
No. of teeth on wheel sprocket=100
8. Gear reduction=96/12=8
Intermediate Drive:
An intermediate drive will be included to change the direction of rotation and also to
change reduction since we need a reduction of 1:20.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
So the number of teeth on the intermediate drive will be 48 and 20.
Acceleration:
1. T/r = F
2.8/0.0075 = 373N
2. F/20 = (F)wheel
373/20 = 18.65N
3. (F)wheel+mmg = ma
18.65+0.3*9.81*100 = 100*a
a=3.1295m/s
4. For 45kmph,
v = u+at
45*10^3 = 0+3.1295t
3600
t=4 sec
For 65kmph, t=5.32sec
11. CHASSIS:
The material selected for construction of the chassis is aluminum 6063, T6 age
hardened. This was our material of choice because of its relatively high specific strength
for its weight, ease of machinability and its corrosion resistance.
We specifically chose 6063, T6 grade due to its availability in Bangalore and due to its
widespread use in structural applications.
Wheel base:
Wheel Track:
Maximum height:
Ground Clearance:
Chassis Material:
78 inches
18 inches
11 inches
6 inches
Tubular Aluminum, 6063, T6.
Tubular cross-sections employed: Square cross-section 1’’ X 2” and circular crosssection of 1” diameter. Rectangular cross-sections were preferred over Circular ones
because they have a higher Moment of Inertia (MI) and hence are stronger.
Tubing Specifications:
Al 6063, T6 properties:
Density: 2700 kg/m^3
Elastic Modulus: 70 - 80 GPA
Tensile Strength: 310 Mpa
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
Yield Strength: 275 Mpa
Tubing Dimensions:
Circular Tubing:
Outer Diameter: 1 inch
Tubing Thickness: 2.54mm
Rectangular Tubing:
External Dimensions: 1 inch X 2 inch
Tubing Thickness: 2.54mm
11.1.Chassis Design Methodology:
The Shell Eco-Marathon Chassis components undergo a variety of loads during
operation. To assess the strength of chassis under different loading conditions, we have
used Inventor to validate our designs.
The various loads considered during the design of the chassis were:
A 75 kg load on the roll cage with varying force components.
Driver weight along with vehicle components.
Road reactions at the location where running gear is mounted.
Vibrations due to reciprocating parts in the engine.
Gyroscopic forces associated with the drive train.
Dynamic forces during turning, braking and acceleration.
The priorities taken into account while designing the chassis are:
To provide safety to by suitably designing the roll cage to protect the driver in case of a
rollover.
Ensuring that the chassis remains stable and copes with the dynamic forces involved
during operation.
To minimize weight and to optimize the space frame to accommodate the necessary
components that constitutes the other systems.
The driver position was selected as semi-reclining to strike a balance between good
visibility and an aerodynamic shape. The weight distribution in the chassis had to be
managed so that, after mounting the engine components, the drive train, the engine
accessories and the safety equipment, the weight balance is acceptable.
To achieve the above goal we made use of two different cross sections of tubing, circular
cross-section tubing in reinforcing members and the roll cage and rectangular crosssection tubing in the load bearing members. This greatly improved not only the weight
distribution but even the rigidity of the chassis.
The chassis was designed based on the previous design was optimised for weight
reduction.the chassis now weighs 3 kgs lesser than the previous design.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
The application of load on the chassis.
The driver’s weight and engine’s weight are the major weight considerations.
The ladder frame provides more rigidity and provides a more stiffer platform for the
application of loads.
Now the frame is being analysed for stress:
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
According to the rules the roll hoop must be able to withstand 70kgf of load.
The roll hoop is required to protect the car during an accident when the
car overturns. Here the roll hoop is analysed to withstand 70kgf.the roll
hoop consist of 1” circular section profile over a path to protect the
driver.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
12. The Steering System:
This section will deal with the selection, design, and fabrication of the steering system to
be implemented in our ecomarathon vehicle, keeping in mind the various constraints
imposed by the competition rules as well as the economics of our project.
12.1 Classification of Steering Methods:
The very first decision to be made was whether to select a front wheel steering or a real
wheel system. Since our vehicle would have only three wheels, two in the front and one
at the rear (the rear wheel being the drive wheel), it was possible to incorporate either
front wheel or rear wheel steering.
Front Wheel Steering:
One of the benefits of using this method of steering is that it provides a staple steering
system. In a three wheeled vehicle with a single rear wheel such as our Supermileage
vehicle it is also advantageous in the respect that only the single rear wheel is effected
by frictional scrub.
This system ensures better road grip and reduced tire wear. There are some
disadvantages of the front wheel steering system as well. Having room in the front of
the vehicle for the two wheels to swivel requires a larger frontal area, which
corresponds to larger aerodynamic drag.
Rear Wheel Steering:
A major benefit is the simplistic design when only one wheel turns. With the two front
wheels stationary they can be brought in closer to the driver’s legs to decrease the
frontal area and corresponding aerodynamic drag. A major disadvantage of steering the
rear wheel is that two wheels become stationary and suffer from scrub losses.
After a comparative study of the two methods, it was decided to incorporate a front
wheel steering. The front wheel system would be easier to control for the driver. Hence
it was decided to design and fabricate a front wheel steering system for our vehicle.
We decided to go with the simple go kart geometry of steering.
steering column
tie rod
to chassis
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
12.2. Working of Ackermann Steering:
In the above sketch, PC and QD represents the stub axles of each wheel. PA and QB
represent the steering/pitman arms, and AB the track rod. The angle α represnts the
Ackermann angle.
Also it may be noted that the dotted lines intersect at a point between the front and rear
axles approximately 0.3L in front of the rear axle, where ‘L’ is the wheel base.
Hence our first step will be calculation of the Ackermann angle ‘α’.
Ackermann Angle (α):
The very first data required for this calculation is the wheel base and wheel track.
the wheel base was determined taking into account the driver’s measurements in the
seated position, space for the engine and gearbox, as well as mounting of the rear wheel.
After numerous iterations a wheel base of 1700 mm was obtained.
the wheel track was determined once again keeping in mind the driver’s overall width
and adequate space for the steering system. However the main criteria was tolerance
between the shell and the wheel in its fully turned position. Taking all this into account
we arrived at a wheel track of 600mm from centre to centre of each kingpin.
Next a triangle was constructed from the above sketch of the system. This is shown
below.
In the figure alongside,
Wheel track PQ = 600 mm
Wheel base L = 1700 mm
Hence DE = 600/2 = 300 mm
CD = L -0.3L = 1190 mm
Hence tan α = 300/1190
Or Ackermann angle α = 14.14 ≈ 15 degrees
R V College of Engineering
Dept of Mechanical Engineering
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15°
ackerman angle
tie rod
Turning Radius:
35°
minimumturning angle right wheel
20°
to chassis
minimumturning angle left wheel
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Dept of Mechanical Engineering
Page 23
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Project Garuda
1
120,8
35°
20°
07
56,
50
Outer radius =120.81 cm
Inner radius=56.07 cm
12.3. Kingpin Inclination (Steering Axis Inclination):
The inclination (usually an inward tilt) of the kingpin from the vertical is called the
kingpin inclination, or kingpin rake. The kingpin is the main pivot in the steering
mechanism. It is also a load bearing structure since all loads acting on the vehicle are
taken up by the kingpin thereby preventing any stress on the steering system.
The kingpin inclination helps in steering return ability, i.e. straight ahead recovery, thus
providing directional stability.
R V College of Engineering
Dept of Mechanical Engineering
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Project Garuda
front view
15°
4°
tie rod
60°
wheel
to chassis
top view
R V College of Engineering
Dept of Mechanical Engineering
to chassis
back view
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Project Garuda
12.4. Camber Angle:
Camber is the tilt of the wheels from the vertical. Camber is positive if the wheels tilt
outward at the top. Camber is also called wheel rake.
It is always desirable that the tires should roll on the ground
vertically so that the wear is uniform. If while running, the wheels are inclined either
outwards or inwards, there will be more wear on one side than the other. Hence it is
ideal to maintain a zero camber.
In order to do this the wheels are initially given a slight positive camber, in the unloaded
condition. Thus when the driver sits inside the vehicle, or when the vehicle is loaded,
the positive cambered wheels will now achieve zero camber.
For an overall weight of 100 kgs(driver and components),the deflection produced was
very minute. Therefore small positive camber of 5 degrees.
front view
5°
12.5.Fabrication:
Aluminum sections will be used to build the steering sections.
Circular sections of 1 inch diameter and 2mm thickness will be fabricated to
make the steering system for our vehicle.
Tie rods will be 25 cm in length.
Bearings will be used at each joint to reduce friction between the moving parts.
R V College of Engineering
Dept of Mechanical Engineering
Page 26
2011
Project Garuda
13. SHELL:
The shell design and fabrication represents one of the most complex and challenging
aspects of our project.
13.1. Shell Design Considerations:
1) The shell geometry should have as low a drag co-efficient as possible, thereby
Reducing air resistance and improving mileage.
2) The Aero design must produce as low negative lift (down force) as possible.
3) The shell should be light weight.
4) It should be possible to mount the shell to the chassis.
5) Parts of the shell should be readily detachable to facilitate driver exit as well as
Servicing of vehicle components.
6) The shell surface should be as smooth as possible, so as to reduce friction drag.
7) The finalized shape should be easy to fabricate.
The drag force experienced by the shell can be divided into two components, namely
form drag and the frictional drag. Our goal is to determine the optimal shell design to
reduce both components.
The basic design factors that reduce the form drag are:
1) Reducing the frontal area of shell
2) Contouring of shell to provide optimal streamlining
3) Prevention of separation of flow, both through optimal contouring and using special
Techniques for boundary layer control
The friction drag is influenced by the surface roughness of the body, as well as the
surface area (particularly over which un-separated flow occurs).
Further, to reduce the negative lift experienced by the shell, we need to reduce the
upsweep at the rear of the shell as far as possible, preventing the formation of a large
low pressure region at the rear underside of the shell that would reduce down force at
the rear.
In order to design a contour that was relatively simple to analyze and fabricate, we
needed to settle upon a basic curve/function to define the various contouring of our
shell. In order to do so, we made many designs in Pro-E and then short listed a few
based on the simplicity of design and aerodynamic profiles.
This results in a shape similar to a symmetric airfoil, when viewed from the top.
13.2. Positioning of Vents:
Another important consideration in our shell design is the positioning of air-vents for
the intake of air for combustion and cooling of the engine. We hence located our air
vents at the front of the shell, near the nose. The reason for this is that the stagnation
points of flow are located in this area, contributing the maximum to form drag and
generating a high positive pressure gradient. Hence, by placing our vents here, our
vehicle literally funnels the air into the engine as it moves forward. The air is carried to
the engine at the rear via tubing. The drawback of this system is the high engine pump
R V College of Engineering
Dept of Mechanical Engineering
Page 27
2011
Project Garuda
work when the vehicle is stationary; however this will rarely be the case during our
performance run, and so will not hurt our mileage score in the competition.
13.3. Provision to cover the wheels:
If the shell is to cover the wheels, sufficient room must be left for the front wheels to
turn during steering. While the vehicle is in motion, there is continuous movement of air
around it. If the wheels are not covered, the air, by deviating from its laminar flow,
moves across the spokes of the wheel thereby obstructing its proper motion. This is
similar to the egg beater effect where this kind of movement of air causes resistance to
the rotation of the wheels and hence resists the vehicle movement. To prevent such
inefficiency, we decided to keep the wheels covered inside the shell, keeping in mind the
provision for the turning of the wheels while steering.
13.4. Shell Material and Fabrication:
The main factors that decided the selection the selection of the shell material were
Lightweight and robustness.
The ease with which it can be fabricated (flexibility).
Availability of the material locally.
Cost of the material.
13.5. Shell Material:
The shell will be made using Glass fibre and Polyvinyl Ester as this material is very light .
13.6 .Shell Models:
From paper to CAD:
R V College of Engineering
Dept of Mechanical Engineering
Page 28
2011
Project Garuda
This image shows the vehicle configuration with two wheels in the front and one wheel
at the rear.
14. Wheels and Brakes:
The requirements for our wheels and tires are as follows:
1. Sufficient Mechanical Strength, especially considering cornering forces.
2. Light weight.
3. Low air-resistance, especially for the front wheels, as they are exposed to the air
stream
4. Low rolling resistance.
Wheel and tire dimensions:
The dimensions of our wheels settled upon are as follows:
Front Wheels: 17 inch, locally available wheels, as smaller sized wheels improve
handling, and cornering stability. In addition to this, small tires also provide less air
resistance. Smaller the tires, lower is the car and hence better are its aerodynamics.
However a smaller tire requires more number of rotations to cover the same linear
distance as that of a bigger wheel. Hence, optimization is required. The 17” tires will be
used for road testing purposes.
Rear Wheels: A 20 inch wheel, with a racing slick tire is used in the rear as large size
wheels at the rear improve traction, and also provide better grip at the rear during
braking. Further, lesser rotation of a bigger wheel covers a larger linear distance as
compared to a smaller wheel.
Based on these criteria, we will be purchasing our wheels and tires from Schwalbe
North America, as they have the correct tire specs and tire dimensions to suit our
purpose.
Wheel Selected: Stelvio HS 350, Folding Bead tires.
R V College of Engineering
Dept of Mechanical Engineering
Page 29
2011
Project Garuda
14.1. The Hub:
Dimensions:
 The hub will have a diameter of 25mm
 The spoke housing will have a diameter of 35mm
 The distance between them will be 1mm on either side
 The length of the hub will be 100mm
 The total length of the whole the assembly with the spoke mounting is 120mm
Material used:
 The material for the hub will be aluminium as it is light and is more rigid.
 The material of the spokes is stainless steel as it has to bear the total load and
effectively transfer it to the tyres through the rims.
14.2. Brakes:
In order to select an appropriate braking system for our vehicle, we had to consider
various brakes on the market that could easily be fitted onto our wheels. Further, the
brakes needed to be as light as possible. They should also be compact as the wheels are
covered.
The logical choice was to go in for three disc brakes, one on each wheel, as they provide
sufficient braking force, while satisfying the above mentioned requirements.
Configuration of brakes: We are using three sets of the aforementioned disc brakes,
with one set for each wheel. The brakes are readily adjustable, allowing us to set an
optimal brake balance. The discs will be mounted (coupled) on the hub shaft of the
wheels and the calipers that will hold the disc and thereby stop the wheel from moving
will be mounted onto the chassis.
Braking force: We estimate a braking force of approximately 0.7g. Our method of
calculating this is as follows (for locking of wheels):
Nr = mg (0.47 – µh/l), Nf = mg (0.53 + µh/l)….. Normal forces at front and rear
respectively
F = µ (Nr + Nf)…… Total Breaking Force
Our tires on dry asphalt have µ = 0.7 approx.
h = 6” (height of centre of gravity), l = 78” (wheel base)
m = 100 kg, fully loaded.
Hence, Nr = 41.61 kgf at the rear wheel and Nf = 59 kgf at the front wheels, combined.
Therefore, F = 71 kgf.
Estimated Stopping distance from a speed of 10m/s (36 kmph) = 7.28 m.
Estimated Stopping distance from a speed of 4.44 m/s (10 mph) = 1.438 m.
R V College of Engineering
Dept of Mechanical Engineering
Page 30
2011
Project Garuda
15. Auto Electricals:
The Eco-Marathon car has certain electrical components like starter motor, rear light,
engine kill switch etc. This circuit diagram shows the flow of current from the battery to
various components.
16. SAFETY EQUIPMENT:
In a vehicle, it is very important to ensure driver safety. The following measures have
been taken:
The chassis of the car has been designed to withstand high impact forces in case of the
vehicle tipping over. The roll cage has been designed to prevent the driver’s head from
coming in direct contact with the ground in case the vehicle topples while at
considerably high speeds.Shatterproof materials have been used throughout the body of
the vehicle, thus ensuring no harm to the driver from small flying fragments.
A 3 point safety harness system is used to hold the driver tightly in his seat. This
ensures that in case of impact, the driver stays within the confines of the roll cage.
Three kill switches, one inside and two outside the car; ensure fuel cut-off to the engine
so as to prevent it from catching fire. Driver wears a helmet and riding glasses for
extended safety. A fire extinguisher is also installed within the reach of the driver.
A fire wall made of a thick aluminum plate is placed such that it separates the driver
from the engine. This prevents overheating of the driver cabin.
All the rules, as specified by Shell for the Eco-Marathon competition, have been taken
care of.
R V College of Engineering
Dept of Mechanical Engineering
Page 31