1

1. INTRODUCTION

This chapter provides the motivation for the research presented in this thesis by

describing some of the difficulties inherent in the sport of RC (Remote Control) car racing.

Based upon the problems certain goals were established. Next, the objectives and approach

to achieve them are explained. The chapter ends with an outline of the thesis.

1.1. Motivation

For as long as products have been in development engineers have struggled to trade off

between research and development time and quality or performance of the product under

development. This is especially true for the RC motorsport industries. Let us take an example

from Automotive engineering history to highlight that necessity to continuously improve the

efficiency of research and development was due to changing market demands [1]. In the RC

motorsport industry this market demand was replaced by the performance of one’s

competition.

The RC hobby industry is now riding a wave of enthusiasts and has become a sport

and in some formats has specific rules and regulations. The cars itself are a testament to the

detailing and over engineering of such small components, that they show some likeness to

formula one cars. However the people preparing them are not necessarily well trained and

hence they lack the engineering to prepare their cars based upon numbers and stats, instead

they choose to buy special parts labelled with superlatives. This thesis hopes to annihilate

such misconceptions by offering the novice a chance to learn and use test results to make his

2

car to race specifications without spending. By repeated tests he can find out the accurate

damping, spring stiffness and sprung weight to use. Thus they can self fabricate.

The indoor lab based nature of the product allows the experiments to be documented

properly and also the time taken for successive experiments is lesser. Also the repeatability

and accuracy of the rig are other pillars for this thesis.

Also this thesis is to provide a platform to develop the software and electronic

know how to be able to fabricate a full size test rig for BAJA as well as FSAE team of SRM

University

1.3. Approach

Figure 1.1 The Process flow chart of the thesis.

To achieve the goals the following approach is taken. The state of current full scale

quarter car test rigs is analysed. Then the requirements of the RC car enthusiast was

analysed. Then the rig that is to be built was foreseen to be able to fulfil these rigorous

demands of the customer. Once the conception was complete the CAD modelling and

analysis was started. Once a base frame was finalised, the fabrication process was initiated.

3

Later on the electronics and pneumatic systems were prototyped around the completed

mechanical setup and the final prototype was assembled. Rigorous testing was done to

ensure the repeatability and safety of the test bench.

1.4. Outline

The following is a brief outline of the chapters to come. Chapter two provides the

background for such a study which includes complete literary review of the current state of

RC motorsport and the void that this product wishes to bridge. Also the salient features of full

scale quarter car rigs are studied and reviewed. These salient features are to be integrated as

the rig is scaled down. The mechanical design and development aspects are discussed in

chapter 3 with illustrations from CAD modelling and analysis.

In later chapters control aspects are discussed along with the automation and

electronics working and assembly discussed in detail. Once the construction details are

established the theory behind the model are shared and the mathematical models are

presented.

In the final chapter the test results are compared to theoretical models and the

inference is stated. This inference is aimed at establishing the product as an effective tool for

any RC enthusiast.

4

2. LITERATURE REVIEW

The literature review aids in providing perspective before pursuing the task at hand.

In the first half of this chapter the problems with existing test rigs are studied. The second

part of this chapter deals with how the electronics are adapted to serve the function of control

as well as interface with the PC.

2.1. Vehicle Test Rigs

It is clear that the main purposes of a shaker rigs regardless of the number of posts is

that they are used to measure noise, vibration and harshness (NVH), to perform durability

tests and to improve handling[1,2,3]. These goals vary depending upon the nature of the

industry they are applicable. The Automotive manufacturing segment would primarily be

interested in the NVH and durability but on some occasions may want to improve their

vehicle’s handling without spending countless hours in the proving grounds. The RC racing

industry is slightly different. They are not interested in the NVH aspects; however durability

and handling are critical.

2.1.1 Complex Shakers

Among the most complex test equipments are complex shakers. Complex shakers can

be of 4-post, 7-post or 8 post variety. In a 4-post shaker each wheel of the car is supported by

a servo actuator. If tyre is not to be tested then the servos are directly coupled to the spindles.

Thus test rig can input various disturbances onto the chassis and the vehicle response can be

measured. The 7-post rig works in a similar manner with the exception of three additional

actuators and in 8-post there are four additional actuators. These extra actuators allow

5

increased capability in the form of simulating vehicle response from inputs like acceleration,

braking and aerodynamic loads.

Figure 2.1 Image of Servo Test 7-post Test Rig

Figure 2-1 represents a Servo Test tire-coupled 7-post rig with a Formula 1 race car.

These complex test rigs offer an immense amount of capability, however they are very

expensive to build and maintain. They also present other difficulties. These rigs are very

sophisticated multi-input/multi-output (MIMO) systems which require a high degree of

control knowledge and understanding to use properly. Often, the complex nature of these

multivariable problems requires multi-step iteration to obtain a suitable drive file for

commanding each of the actuators. Once converged data is extracted from tests run on these

6

systems, it is often very difficult to interpret and correlate to the real world counterpart. Some

reasons for these issues with more complex test rigs are the lack of literature and other

available documentation [5, 6]. To the authors knowledge only a handful of papers that

discuss multi-post test to any detail exist [2, 4, 7, 8]. It is likely that the lack of available

information is partially due to race teams and automotive companies trying to protect their

competitive advantage.

2.1.2 Current Quarter-Car Rigs

As an answer to the high complexity and expense of these systems, simpler test beds

such as the quarter-car test rig are used. A rig such as this reduces the complexity greatly by

only focusing on one corner or quarter of the vehicle. These may b considered one post or

two-post systems. Often, these systems can be viewed as a single input/single-output (SISO).

This greatly reduces computational time and complexity and often closed form solution may

be reached. This allows for much better understanding of both the problem and results.

Problems with existing quarter car test rigs are mentioned in the following illustration.

Often the suspension components are simplified; hence the suspension is not tested as a single

unit, but in the form of a simple linear spring. The analysis is made simpler at the expense of

correlation of the results with the actual vehicle test data. This point is illustrated in Figure 2.2

which shows a simplified quarter car test rig which has elastomeric mounts in the place of

tyres and air-springs make up for the suspension compliance. The theory is correct but the

execution is wrong.

7

Figure 2.2 Simplified Quarter-car Test Rig (VT AVDL)

2.1.3. Functional Requirements

After reviewing the operational functions offered by the current state-of-the-art test rigs,

the following requirements were proposed for a new quarter-car test rig:

• Design for a large range of vehicle corner weights (buggy to truggy).

• Design for sprung mass external forces such as aerodynamic loading and/or weight

transfer

• Design in flexibility to add future functionality such as vehicle roll or rotating and/or

steering the tire.

8

These functional requirements are made such that a new state-of-the-art test rig would

be as flexible as possible, allow for more accurate and realistic representation of the test

vehicle, and achieve these goals as inexpensively as possible.

9

3. HARDWARE DEVELOPEMENT

This chapter discusses the engineering approach to the design and construction of the

quarter-car test rig used in this research. It begins with a general discussion of the quarter-

car rig’s design. Following, are detailed discussions of how each major component was

developed and or specified. Included is discussion of the implementation of the first

suspension tested with the new rig (Thunder Tiger XXT). The chapter closes by

summarizing the functionality of the new quarter-car rig and presents some future

developments being planned.

3.1. General Description

The Quarter Car is used to represent one corner of the test RC car. The schematic of

the first design is shown in figure 3.1 in this diagram the suspension type shown is Mc

Pherson strut type in the later stages this was changed to double wishbone type due to

availability of parts. However there was no change in the layout and functioning of all other

components.

10

Figure 3.1 Schematic of the Quarter-Car test rig.

The above representation shows the critical components of the rig as the sprung mass,

sprung mass adapter plate, tire, tire pan, actuator, load cell and accelerometer. The sprung

mass and adapter plate are constrained to move in a single axis. The actual suspension of the

vehicle is attached to the sprung mass adapter plate via an industrial grade adhesive.

The actuator is fixed to the base plate via a threaded sleeve which in turn is welded

onto the base plate. The actuator is excited by the switching of the pneumatic direction

control solenoid valve or DCV. The solenoid valves are switched via an electrical pulse

width which is decided by the frequency at which the suspension is to be oscillated.

11

The amplitude of the oscillation is controlled by the supply pressure which can be

adjusted in two steps via the regulator at the main pressure supply line (Coarse adjustment)

and via flow control valve located just before the DCV. The input vibration is fed into the

suspension system and then the RC vehicle response is noted via an accelerometer located at

the sprung mass plate. The amplitudes of both the wheel and the sprung mass are compared

to understand the suspension efficiency.

Figure 3.2 CAD Model of the test rig.

The above illustration Figure 3.2 shows the initial CAD model done in PRO-E. The

suspension components are shown as in the full assembly. The actuator position and length

were decided after checking the dimensions in this model.

The next illustration Figure 3.3 shows the suspension components much more clearly

as seen the upper and lower control arms as well as the wheel hub and tyre.

12

Figure 3.3 The suspension components of and RC car (Thunder Tiger XXT)

3.2. Base Plate and Support Frame

The base plate and frame form the skeleton over which the entire assembly is built

such that it can withstand the vibrations and shocks that will be subjected on it over a period

of time. The base was a 350mm x 400mm x 6mm mild steel plate. The frame consisted of

two long L-sections each 400mm long and 50mm x 50mm cross-section. The L-sections

were placed with their length along the vertical axis and welded on to the base plate.

13

3.2.1 Frame Modal Analysis

The vibrations from the actuator could undergo resonance with the frame and base

plate causing damage to rig as well as error in the readings. Before the frame was fabricated,

it was tested in ANSYS to determine the modal frequencies of the frame. The test was

performed on two separate designs namely Design I and Design II. The frame designs are

described below along with their modal analysis results.

Analysis of Frame Design I

Frame Design I consisted of two L-sections welded on to the base plate, the two L-

sections would each have a linear guide way to allow the suspension adapter plate to translate

along the vertical axis. The modal analysis however revealed that the first modal frequency

was quite low. This posed a safety issue, if the frame were to undergo resonance with the

actuators frequency at any point of time the rig would be damaged.

Figure 3.4 Meshing of the frame done in ANSYS

14

Figure 3.5 Total displacement of Frame Design I at its modal frequency.

Figure 3.6 First six modal frequencies of frame Design I

119.7

204.66

399.36

766.54

Frame modal analysis of frame I

first modal second modal third modal fourth modal

15

ANALYSIS OF FRAME DESIGN II

Figure 3.7 Meshing of Frame II

Figure 3.8 Total displacement of frame II

16

Figure 3.9 First six modal frequencies of frame II

Hence it was concluded that the frame design II would be used in the final model.

This design ensured that the rig was dynamically safe. Also this new design minimised the

weight of the rig by 1.445 kg and the centre of mass of the rig as a whole was brought nearer

to the geometric centre.

3.3. Linear Guide

The Figure 3.10 shows the linear guide which is a readymade component available in

the market. It is used in heavy cabinet drawers; it consists of three U-sections separated by

balls which allow each section to slide out one by one. The component was chosen mainly

1

192.4212.48

373.98

474.23

Frame modal analysis of frame II

first modal second modal third modal fourth modal

17

for its smooth motion as well as the large travel available. The large travel allows a large

range of suspension to be tested on the rig.

3.4. Moving Masses

The moving masses are a critical part of the experiment. The experiment requires a

minimum load of 556gm to be added as minimum sprung mass of the RC car(RC-Radio

Controlled). The RC car weighs a total of 3.125kg the weight distribution was 50-50. The

minimum weight was used to serve as a control setup for the experiment, upon addition of

the remaining 235gm the car would reach its actual weight. For the purpose of fixing and

removing weights an aluminium block was drilled and threaded such that weights could be

added and taken off at will. The minimum weight was secured to the slider directly such

that the load was finally transferred from the slider to the wheel. The weights were secure

and immune to any movement during testing.

3.5. Suspension Adapter Plate

The sprung mass plate is the part to which the suspension components are fastened

securely. This plate has to be light such that it doesn’t disturb the sprung mass. The

material for the sprung mass plate was chosen as Aluminium Composite Polymer (ACP)

the durability combined with the light weight and the excellent machine-ability led to this

choice. The plate itself was 100mm x 100mm x 8mm square piece. The differential of an

RC car was cut and bonded with the ACP using industrial strength Anabond 201. This

ensured the plastics remained together under all loading conditions. The differential

provided the perfect mounting points for the suspension.

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Figure 3.10 Fabricated Test rig

3.6. First Application

The first suspension to be tested on this rig was a Thunder Tiger XXT model left front

suspension assembly; there are three reasons why this particular model was chosen for the

test bench. Firstly, the Thunder Tiger XXT 1:10 scale car is the most common type of RC

car found in India, this fact was supported by SRM WiRL members, many of whom owned

the same model. Secondly, the suspension layout of car had a lot of flexibility and has plenty

of room for adjustment; this would do away with complex movable fixtures for varying

caster, camber toe etc. Thirdly, the easy availability of spares for this model also added in

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the favour of this model; as for all other model cars the spares had to be ordered from

overseas manufactures and the time taken for the shipment would have made it impossible

for completing the project within the deadline.

Figure 3.11 Thunder tiger XXT

3.6.1. Adjustments

The suspension assembly had to be adjusted to ensure the hard point locations were

all consistent with the original RC car. The information for setting up the suspension is

available online at www.thundetiger.com this website provides working ranges for caster,

camber, toe, KPI (King Pin Axis Inclination), Axle loads and cornering weights. The table

below illustrates the ranges defined by the manufacturer and the actual values used in the

test rig.

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SETTING RANGE SETUP ON RIG

CASTER 5 deg to 15 deg 5 deg

CAMBER -5 deg to +5 deg +2 deg

TOE 6mm toe out to 6mm toe

in

Neutral

AXLE LOAD 900gm to 1200gm 1112gm

CORNERING WEIGHT 100gm -200gm 150gm

Table 3.1 Default suspension setup values

Figure 3.12 Thunder Tiger XXT disassembled

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3.7. Actuation

The actuation assembly was composed of a pneumatic double action cylinder which

was controlled by means of a 3/5 way valve. The valve is solenoid actuated; the solenoid is

switched on at 12V supply voltage and remains off at anything below that voltage. The

valve is controlled by an Arduino UNO which is a Programmable Interface Device (PID).

The details of Arduino controls are discussed later on. The Arduino undertakes the function

of switching the solenoid on or off; but what advantage it provides is that the delay period

i.e. the period that the 12V supply is given to the valve, is controlled as per our

requirements.

Figure 3.13 Double action pneumatic cylinder.

The cylinder has a bore of 25.4 mm and has a stroke of 100 mm. The cylinder can

withstand a maximum pressure of 9.8 bars which is well above the working pressure of the

rig itself. The pressure or air supply was adjusted by controlling the pressure via a

FRL(Filter Regulator Lubricator) unit at the supply line as well as a flow control valve

located before the DCV(Direction Control Valve). The actuator is held in place by a

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threaded sleeve which is welded to the base plate. The base itself was lined with smoked

creep rubber to ensure that the base was well damped.

Figure 3.14 Actuator system is high-lighted.

Figure 3.15 FRL unit

23

Figure 3.16 Pneumatic circuit Diagram.

3.8. Control

The system was controlled by an Arduino Uno PID device which connected to the

solenoid valve via a switching circuit which was built around an IC L293D which allowed

the single 12V signal to be routed in between two solenoid valves (although it is possible to

route it between up to 4 outputs). The solenoid valve delay period was adjusted via the

Arduino program.

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3.8.1 Arduino Uno

The Arduino Uno is a microcontroller board based on the ATmega328. It has 14

digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16

MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button.

It contains everything needed to support the microcontroller; simply connect it to a computer

with a USB cable or power it with a AC-to-DC adapter or battery to get started.

The Uno differs from all preceding boards in that it does not use the FTDI USB-to-

serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2)

programmed as a USB-to-serial converter.

Figure 3.17 Arduino UNO exploded view

SALIENT FEATURES:

14 digital I/O ports

6 analogue I/O ports

5V and 3.3V output

Serial Port

25

Figure 3.18 Data sheet of the Arduino UNO

3.8.2. Accelerometers

The ADXL193 is a low power, complete single-axis accelerometer with signal

conditioned voltage outputs that are all on a single monolithic IC. This product measures

acceleration with a full-scale range of ±120 g or ±250 g (minimum). It can also measure

both dynamic acceleration (vibration) and static acceleration (gravity).

26

The ADXL193 is a fourth-generation surface micro machined iMEMS®(intelligent Micro

Electro-Mechanical Systems) accelerometer from ADI with enhanced performance and lower

cost. Designed for use in front and side impact airbag applications, this product also provides

a complete cost-effective solution useful for a wide variety of other applications.

The ADXL193 is temperature stable and accurate over the automotive temperature range,

with a self-test feature that fully exercises all the mechanical and electrical elements of the

sensor with a digital signal applied to a single pin. The ADXL193 is available in a 5 mm × 5

mm × 2 mm, 8-terminal ceramic LCC package.

Figure 3.19 Functional block diagram of ADXL 193

27

Figure 3-17 Data Sheet of ADLX 193

28

Figure 3.20 Working principle of an accelerometer.

The ADXL193 provides a fully differential sensor structure and circuit path, resulting

in the industry’s highest resistance to EMI/RFI effects. This latest generation uses electrical

feedback with zero-force feedback for improved accuracy and stability. The sensor resonant

frequency is significantly higher than the signal bandwidth set by the on-chip filter, avoiding

the signal analysis problems caused by resonant peaks near the signal bandwidth. Figure 3-18

is a simplified view of one of the differential sensor elements. Each sensor includes several

differential capacitor unit cells. Each cell is composed of fixed plates attached to the substrate

and movable plates attached to the frame. Displacement of the frame changes the differential

capacitance, which is measured by the on-chip circuitry.

29

Complementary 400 kHz square waves drive the fixed plates. Electrical feedback

adjusts the amplitudes of the square waves such that the ac signal on the moving plates is 0.

The feedback signal is linearly proportional to the applied acceleration. This unique feedback

technique ensures that there is no net electrostatic force applied to the sensor. The differential

feedback control signal is also applied to the input of the filter, where it is filtered and

converted to a single-ended signal.

3.8.3. Switching circuit

The Arduino Uno and the pneumatic switching circuit had to be connected via a

switching system which would allow the 12V supply to be switched in between two solenoids

thus allowing us to run the application with a single Arduino board and thus saving on cost of

the product. The switching system was to be built around an L293D IC, which is generally

used to control multiple servo motors with a single supply. The details of the circuit are as

follows.

30

Figure 3.21 Switching circuit in detail.

31

Figure 3.22 The complete hardware setup.

32

4. SOFTWARE DEVELOPEMENT

4.1 Arduino Programming

The Arduino interface is the best platform for use in control systems. This fact can be

attributed to two main factors. Firstly, the Arduino is an open source software which means

that all Arduino users around the globe can upload their codes for less experienced users to

use in their own projects, everything is free and any plain user can simply log into

www.arduino.cc and download the codes for signal processing, sensor control; the list goes

on and on. Secondly the Arduino programming language borrows its words extensively

from C and C++ as well as MATLAB. Arduino simply burns the program into its

RAM(Random Access Memory) and execute it.

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4.1.1 Code for Pneumatic circuit control

The code written initiates the switching circuit and is used to switch the solenoid

valve on and off according to the delay time. The delay time is analogous to the pulse width

given to the solenoid valve injector by the ECU (Electronic Control Unit).

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4.1.2 Code for Receiving Accelerometer Reading

The above code is used to read the analogue values received from the accelerometer.

The Arduino takes a sample (or reading) every 100 milliseconds and transfers it to the PC.

35

4.2. MATLAB Program for Data Processing.

The values obtained from Arduino show variation in voltage whenever the device is

displaced. The values in milli-volts need to be converted into displacement values. The next

step is to use unitary method fo find out how many milli-volts are generated per millimetre

of displacement. The information will allow us to obtain the displacement of the sprung

mass in milli-meter from the milli-volts generated by the motion. the process is called offset

calibration. The accelerometer is placed beside a scale and the values in milli-volts are taken

for a known displacement i.e. 1cm, 2cm, 3cm etc. The values were plotted on a graph and

the slope of the graph will show the conversion factor.

Figure 4.1 Calibration graph for ADXL193

y = 3.0976x + 296.08

R² = 0.9941

0

100

200

300

400

500

600

0 20 40 60 80

Accele

rom

ete

r r

ea

din

g (

mv)

Displacement (mm)

Accelerometer reading vs Diplacement

Accelerometer reading

Linear (Accelerometer

reading)

36

Once the conversion factor was obtained the MATLAB program for instantaneous

data acquisition was made into a loop to receive and convert the accelerometer values into

legible data and plot the displacement with time.

37

5. SUSPENSION THEORY

5.1 Quarter-Car Model

To prove the concept purely in simulation, a plant was required. Though the theory is

completely known for this simulation study; it is useful to know the theory because this

allows a direct measure of how consistent the system is with the theory that gave rise to it.

For this study a simple linear two-mass quarter-car model was chosen. This was an obvious

choice because it has the same types of input and outputs that the real quarter car test rig has.

In this case one velocity input and two acceleration outputs. The use of a quarter-car model as

the plant was not required to demonstrate the concept. The quarter car model was chosen

simply to allow for a chance at being able to compare data from the test rig later in the study.

Its use also aids in making physical sense of the results given.

5.1.1. Mathematical Model

The quarter-car model is the usual two degree-of-freedom vibration model of a single

corner of a vehicle. Figure 5.1 is a diagram of the quarter-car model. This model is a two

mass model which only concentrates on the vertical motion of the vehicle on one corner. The

model contains a sprung mass and un sprung mass denoted by ms and mu respectively. The

coordinate associated with the motion of the sprung mass is called z and the coordinate

associated with the un sprung mass is y. The suspension is modelled with a simple linear

spring, ks , and damper, cs . The tire is modelled as a linear spring denoted by ku . The road

input to the tire is modelled as a velocity input called xin.

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Figure 5.1 Showing the two degree of freedom Quarter-Car model.

The schematic defined above was modelled using Lagrangian dynamics. In

modelling, energy functions are defined for kinetic, T, and potential energies, V, as well as a

pseudo-energy damping function, D. These functions are defined for this model as:

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Figure 5.2 Schematic of the quarter car test rig.

The sprung mass resting on the suspension and tyre springs is capable of motion only in

vertical direction. The effective stiffness of suspension and tire springs is called the “ride

rate” the ride rate can be represented as given in the following equation.

(4)

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In the absence of tyre damping the equation the bounce frequency at each corner of the

car can be determined by the following equations.

When the damping is present as it is in a suspension the frequency at which resonance

occurs can be given by the following equation.

For good ride suspension damping ratios in RC cars falls between 0.2 and 0.4. Because

of the way damping influences the resonant frequency in the equation above (i.e. under the

square root sign); it is usually quite close to the natural frequency. With the damping ratio of

0.2 the damped natural frequency is 98% of the un damped natural frequency and even at

0.4 damping, the ratio is about 92%. Because there is so little difference, wn is commonly

used to characterise the vehicle.

The ratio of W/Ks represents the static deflection of the suspension due to the weight of

the RC car. Because the “static deflection” predominates in the determination of the natural

(5)

(6)

(7)

41

frequency, it is a straight forward and simple parameter indicative of the lower bound in the

isolation of a system. Figure 5-3 provides a monograph relating the natural frequency to the

static deflection.

Figure 5.2 Un damped natural frequency verses static deflection of a suspension.

The dynamic behaviour of the complete quarter car model in steady state vibration can

be obtained by writing Newton’s Second Law For the sprung and un-sprung masses. By

considering a free body diagram for each, the following equations are obtained for sprung

and un-sprung masses respectively.

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While the two equations make solving more complicated, closed form solutions can be

obtained for the steady state harmonic motion by means found in classical texts. The

solutions of primary interest are those for the sprung mass motion in response to the road

displacement inputs, forces at the axle and the forces applied onto the sprung mass, The

amplitude ratios of these three cases are as follows.

The equations above are in complex form consisting of real and imaginary

components, the latter denoted by the j operator. To obtain the amplitude ratios, the real and

(8)

(9)

(10)

(11)

(12)

43

imaginary parts of the numerators and denominators must be evaluated at the frequency of

interest. The magnitude of the numerator is determined by taking the square root of the sum

of their squares of their real and imaginary parts. The denominator magnitude is determined

similarly and then the ratio of the two may be taken. With appropriate manipulation, the

phase angle of the equations may also be determined.

The quarter car model is limited to the study of the dynamic behaviour in the vertical

direction only. Yet, using equations such as those developed above, it can be used to

examine vibrations produced on the sprung mass as a result of inputs fro road roughness,

radial forces arising from tyre/wheel, non-uniformities, or vertical forces applied directly to

the sprung mass from on board sources. The response properties can be presented by

examining the response gain as a function of frequency, as shown in figure 5-4. The gain is

defined differently for each type excitation input.

Figure 5.3 Theoretical quarter-car response to road, tyre/wheel, and body parts.

44

6. SIMULATION AND RESULTS

This chapter aims to summarize the practical aspects of the project as well cement the

fact that the product is consistent with the theoretical model. It also communicates the

algorithm of operation for testing and perfecting the suspension of the RC car.

6.1 Experiment Setup and Execution

The process begins by identifying the ride frequency range to be tested. The following

table shows the relative ride frequencies of different types of terrain. This is essential

as the ride frequency is the target frequency that we are trying to isolate from our RC

car. Also the ride frequency changes depending upon the speed of the RC car itself.

The faster it goes the higher the frequency.

TERRAIN 70 km/h 80 km/h 90km/h

SAND 2 Hz 3-4 Hz 5Hz

TARMAC 8-9 Hz 10-12 Hz 15-25 Hz

DIRT 4Hz 5Hz 6Hz

MUD 2Hz 3-5 Hz 6-9 Hz

GRAVEL 5Hz 9Hz 12Hz

The next step is to fine the weight of each wheel of the suspension. This can be done

by using basic mechanics.

45

The next step is to find the ideal wheel stiffness that can produce the ideal ride rate of

1.2 Hz which is the most sustainable. This can be done by using the following

equation which relates suspension frequency with wheel stiffness and sprung mass on

each wheel.

s

wheel

nm

kf 2

Where,

fn –Suspension frequency(1.2Hz)

Kwheel – wheel stiffnesss

ms- sprung mass on each wheel

Once the target road frequency is fixed then the target suspension frequency is fixed.

The suspension frequency should be ideally 1.2 Hz for front suspension now to

achieve this ideal frequency we need to fix such a ride rate such that this is possible.

This is shown by this equation:

springwheel kMRk 2)(

Where,

Kwheel - wheel stiffness.

Kspring- spring stiffness

MR- motion ratio (Mechanical advantage of spring over wheel)

Now that we know the ideal wheel rate we can control the spring rate as well as the

motion ratio to achieve the ideal wheel rate or at least something nearby. If we can’t

do both then we have the option of changing the weight on each wheel.

(13)

46

6.2. Experiment Readings

The results of the experiment are interpreted in simple to show the graphs starting with the

graph showing the signal given to the solenoid valve 1 by Arduino pin 13 , then the wheel

displacement plotted for the sinusoidal disturbance caused by the piston on the wheel, and

then finally the superimposition of the disturbance and the response on the RC car.

Figure 6.1 Arduino pin voltage(y axis) with respect to time(x axis).

47

Figure 6.2 Displacement time graph of the wheel.

Figure 6.3 Road input at 1.87Hz and 15mm amplitude (yellow) and vehicle response (purple)

48

Figure 6.4 Road input 4Hz and 5mm amplitude (yellow) vehicle response(purple)

49

7. CONCLUSION AND DISCUSSION

The last chapter of this thesis aims to seek out the future prospects of the product as well

as to form a conjunction between the theoretical analysis and the experimental results.

7.1. Results Interpretation.

The quarter car model results were imported into MATLAB and the results plotted to

show the displacement time curve of the RC chassis. The afterwards based on the

mathematical model another simulation was run with same parameter variables to compare

the real and experimental data. The results showed the effectiveness of the suspension over

various load cases as well as road input cases.

7.1.1.Variations in Suspension performance due to change in axle

load.

The suspension test rig was oscillated at 4Hz frequency and 8mm amplitude. The load

on the wheel was varied from 1162 grams up to 1262 grams in steps of 50 grams. The

results were as follows.

50

Figure 7.1 Road Input 4Hz and 8mm amplitude (yellow) and vehicle response at axle load

1162 grams (purple)

Figure 7.2 Road Input 4Hz and 8mm amplitude (yellow) and vehicle response at axle load

1212 grams (purple)

51

Figure 7.3 Road Input 4Hz and 8mm amplitude (yellow) and vehicle response at axle load

1262 grams (purple)

From the experiment it is clear that the ideal axle load for the car is closer to 1262

grams rather than 1162 grams. The amplitude at the chassis is much lesser compared to the

initial readings. The maximum chassis displacement is noted as 2 mm in response to the 8mm

road disturbance.

52

8.2 Future Scope of Work.

The product can be mass manufactured and made cheaper to aid as a tool for RC car

enthusiasts to tune their vehicle according to the race.

The product can be used as a tool to educate students about the functioning of a

suspension system.

The product was initially to fabricate a full scale test rig to suit a wide range of

vehicles, but due to cost constraints the project was made smaller for a smaller car (an

RC car)

Based upon the suggestion of Assistant Professor Siluvaimuthu the rig underwent a

slight modification to measure the suspension adhesion. This was executed in the later

stage of the project and hence did not feature in the report. The results of the adhesion

tests could not be obtained in time for the submission of this report. However a simple

load cell was placed under the wheel and used in the measurement of disturbances

caused by the wheel. Whenever the wheel loses contact with the road the load cell

will register a null reading hence we can gather the percentage of tie that the load cell

53

registered a null reading and hence we can put an idea on the suspension adhesion and

hence the efficiency.

The electronic components and sensors can be utilised in the larger size test rig, the

only modification required is the multiplication of a correction scale factor, and

recalibration of the accelerometer accordingly.

ANNEXURE I

COST REPORT

The components required for manufacturing the product can be classified into three main

categories :-

Mechanical

Electronics

Pneumatics

All the processes from procurement to surface finishing will be mentioned

category-wise.

MECHANICAL COMPONENTS DETAILS QUANTITY RATE PRICE(Rs)

54

MILD STEEL BASE PLATE (35CMX40CM) Rs 4500/m2 63

L-SECTION (40CMX5CMX5CM) Rs 100/m 40

ROUND MILD STEEL CYLINDERICAL JOB 6CM DIA X 5 CM Rs 300/m 15

SLIDER 1 Rs 50 50

FASTENERS (M6) 10 Rs 0.2 2

WHEEL PAN ROUND METAL CYLINDRICAL JOB 8CM DIA X 5 CM Rs 500/m 25

RUBBER MAT 35 CM X 40 CM Rs 200/m2 28

ACP SHEET 30CM X 10 CM Rs 400/m2 150

SUB-TOTAL 373

ELECTRONIC COMPONENTS DETAILS QUANTITY RATE PRICE(Rs) SINGLE AXIS ADXL 193 ACCELEROMETER 2 Rs1350 2700

IC L293D 1 Rs 75 75

LED 5 Rs 5 25

ARDUINO BOARD 1 Rs 2800 2800

POWER SOCKET AND CABLE 1 Rs30 30

9V BATTERY 2 Rs 20 40

M/F CONNECTORSAND CONNECTOR PINS 2 Rs 10 20

WIRES Rs 10 10

PCB BOARD 1 Rs 20 20

CABLE TIES 1 Rs 10 10

SUB-TOTAL 5730

PNUEMATIC COMPONENTS DETAILS QUANTITY RATE PRICE(Rs) PNUEMATIC CYLINDER 1 Rs700 700

5/3 PNUEMATIC VALVE 1 Rs 900 900

HOSE PIPE 2 metres Rs 15 per metre 30

FLOW CONTROL VALVE 1 Rs 20 20

SUB-TOTAL 1650

MISCELLANEOUS COMPONENTS DETAILS QUANTITY RATE PRICE(Rs)

55

ANABOND 201 (INDUSTRIAL GRADE ADHESIVE) 1 Rs 150 150

DOUBLE SIDED TAPE 1 Rs 20 20

SPRAY PAINT (SILVER) 1 Rs190 190

PAINT BRUSH + THINNER 1 Rs 35 35

PAINT 1 Rs 40 40

SUB-TOTAL

435

TOTAL COST OF MATERIALS Rs 8188

Labour charges will be zero as all the operations are done by self.

Welding costs include the price of two electrodes (Rs 30)

Buffing and grinding done by self.

Drilling, Turning and Threading performed at Machine Shop (permission letter enclosed )

FRL unit and compressor are used in the Automation Lab with the prior permissions from

HOD (Auto) and Lab in-charge. Thus the total cost is Rs 8218.

56

REFERENCES

1. Bigliant U., Piccolo R., Vipiana C., “On Road Test vs. Bench Simulation Test: A Way to

Reduce Development Time and Increase Product Reliability,” SAE Technical Paper Series,

No. 905207, Warrendale, PA, 1990.

2. Kelly J., Kowalczyk H., Oral H. A., “Track Simulation and Vehicle Characterization with

7 Post Testing,” SAE Technical Paper Series, No. 2002-01- 3307, Warrendale, PA, 2002.

3. Mianzo L., Fricke D., Chabaan R., “Road Profile Control Methods for Laboratory

Vehicle Road Simulators,” Proceedings of the 1998 IEEE AUTOTESTCON, SaltLake City,

UT, p. 222-228, 1998.

57

4. Vetturi D, Magalini A, “Road Profile Excitation on a Vehicle Measurements and Indoor

Testing Using a Four-post Rig,” Dipartimento di Ingengeria Meccanica – Universita degli

Studi di Brescia, 2002.

5. Milliken W. F., Milliken D. L., Race Car Vehicle Dynamics, Society of Automotive

Engineers Inc., Warrendale, PA, 1995.

6. Thomas. D. Gillespie, Fundamentals of Vehicle Dynamics, Society of Automotive

Engineers Inc. Warrendale, PA , 1995

7. Design and Adaptive Control of a Lab-based, Tire-coupled, Quarter-car Suspension Test

Rig for the Accurate Re-creation of Vehicle Response, Thesis by Justin. D. Langdon to the

faculty of Virginia Institute of Technology.