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Design And Fabrication Of Robotic Systems :
Converting A Conventional Car To A Driverless Car
Amrithanandha Babu G, Guruvayoorappan K, Sajith Variyar V.V, Dr K.P Soman
Centre for Computational
Engineering and Networking (CEN),
Amrita School of Engineering, Coimbatore,
Amrita Vishwa Vidyapeetham, Amrita University, India
Email : amrithanandhababu@gmail.com, k guru@cb.amrita.edu,vv sajithvariyar@cb.amrita.edu,kp soman@amrita.edu
Abstract—Drastic changes in the robotics and intelligent
controls brought a radical change in Automotive engineering
sector that leads to the driverless vehicles in this new era.
For these vehicles to safely run in today’s traffic and in harsh
environments, a number of problems in vision, navigation, and
control have to be solved. Driverless cars use sensors to detect
the environment, computers to process the data and actuators
for mechanical systems. To adopt the self driving car technology
to current academic and research , we need a cost efficient and
affordable mechanisms. In this scenario we need a system that
can incorporate existing vehicles and convert that driverless cars
which will reach to academicians and research fields. Considering
the possibilities and implementation of driverless vehicles in
Indian scenario we need an agile mechanical design to be included
on existing vehicles. This paper proposes a portable mechanical
design that can be fabricated and fit into existing vehicles and
can be used as a platform to develop an autonomous car.
Conventional cars can be altered to be a driverless car by using
different actuators. Popularly motors are used as actuators in
the automation of the vehicle. A pneumatic system is designed
to automate the intended platform apart from the motors. The
mechanical structure is an essential part of an autonomous car
and is to be altered and designed in such a way that it is
dynamically unwavering. Further improvements will make the
system capable of being commercially produced.
I. INTRODUCTION
Majority of car crashes in the US are caused by the errors
of the driver . There won’t be any need of skilled drivers and
there won’t be any mistakes on the road, if all vehicles became
autonomous. Sensors could possibly perceive the health of
the people or the surrounding conditions effective than the
senses a man has, to see farther distances, effective in low
visibility, detect minor and more difficult to notice, obstruct-
ing or stopping things, more reasons for no car accidents
[1]. Speed of the vehicle can be increased to enhance the
safe driving, shortening trip time. Guided vehicles are used
in manufacturing industries widely and can be routed and
controlled [2] Parking the vehicle and very heavy navigation
would be less upsetting and require no unique abilities. The
automobile could even simply take you to your destiny and
then park independently. People who already face problems
or delays with driving, such as handicapped people or older
people as well as the very younger generation, would be able
to experience the advantage of using a car. Driving license
and driving test will not be needed after this innovation [1].
Autonomous vehicles have the conceivable capacity to give
expanded capacity to move around for the old, the impaired
and the visually impaired [3]. The wastage connected with
traffic jam could be reduced because riders could do other
tasks travelling. The innovation additionally may decrease
automobile proprietorship and help increment ride-sharing [1].
Producing a lot with very little squander travel additionally
implies fuel funds, cutting expenses. Diminished requirements
for safety measures implies that the roads ability to hold or do
something for vehicles would be expanded to a considerable
measure. Travellers ought to encounter a smoother riding
experience, driverless cars would prompt a diminishment in
auto robbery. The wireless sensor networks can also be im-
plemented to monitor the speed of the vehicle and to route
the traffic. [4] Autonomous car projects are carried out by
many leading company’s and universities, we at our university
are developing an autonomous platform with a conventional
car. A car which has got only manual systems and less
electronics in it. Automation of the mechanical systems like
steering,accelerator,clutch and brakes are done as an initial
phase. The designs and a simulation of the actuators are
depicted in this work. Automatic transmission system will also
be developed once the whole system with the vision module
is tested and the errors are eliminated.
II. AUTONOMOUS CAR
A self-driving car is an automotive that can explore itself
without human mediation. The project of driving this kind
of conveyance has become an authenticity and will pave the
fashion for future systems where the computers can supersede
[5]. The prototype which we developed can move through a
known environment with inputs from vision module through a
computational platform and control system to the steering and
other mechanical systems like accelerator, clutch and brakes.
The autonomous car has generally three sub systems as in
Fig.(1)
A. Application
There are many applications in an autonomous system such
as camera or the vision system, the feedback system etc These
applications are done as to detect the environments and thereby
move the car in a safe manner. The fundamental drivers
Fig. 1: Autonomous Car [5]
for accomplishing self-sufficient driving is the diminishment
of auto collisions by dispensing human blunder, increasing
street limit and movement stream by decreasing separation
amongst cars and making use of traffic Administration data,
concealing the auto tenants from driving and navigating tasks
and authorising them to participate in different works or rest
B. Computational Platform
The computational platform is an extremely important part
of an autonomous car to integrate and control the whole sys-
tem. The applications are controlled by the processing platform
by the inputs given by the sensors and feedback data from the
actuators. The platform should be computationally potent to do
the tasks and processing in no time. The sudden reflex actions
are to be sensed and implemented by the platform. Video and
Image processing are done by the computational platform, the
inputs from the camera are directed to the platform. The inputs
to the actuators and the pneumatic systems are sent from the
computational platform
C. Mechanical Control
The mechanical control is done by using pneumatic actu-
ators in this system. Feedback systems are attached to the
systems so as to get a continuous feedback to the computa-
tional platform. The mechanisms in the conventional systems
are attached with different sensors and encoders, they are also
used to make this system work. There is a continuous feedback
to the computational platform. Our system has basically two
systems to control the mechanical systems that is a pneumatic
system or framework to actuate the accelerator, clutch and
brakes and a stepper motor drive to actuate the steering. The
conversion of the gear system into an automatic one will be
done in our second phase of the project where we need to test
the vehicle at higher speeds. Currently it is not necessary as
we run the vehicle in the 1st gear at a minimum speed below
20km/hr
D. Implementation Platform
The platform which we have is a 2002 model daewood matiz
car with limited electronics, manual transmission, mechanical
clutch and brake , mechanical steering. The technical specifi-
cations and the car is shown in Fig.(2)
Fig. 2: Implementation Platform
III. MECHANICAL SYS TE M
The mechanical framework of the vehicle is divided into
the following parts as depicted in the Fig.(3)
Fig. 3: Mechanical system
A. Gear
Gears are used for transmitting power from one part of a
machine to another [6].In this conventional car there is a five
speed manual transaxle transmission system.
The five-speed assembly has a synchronized mesh type 5 speed
forward transmission. The reverse gear is driven by sliding
gear without synchronizer [7].
B. Clutch
An instrument for engaging and disengaging an engine and
the transmission system in a vehicle to transmit power, or
to the working parts of any machine. The clutch engaging
mechanism consists of the clutch pedal, a clutch release shaft,
a clutch cable, a release arm and a release bearing. Pressure
is applied to the clutch pedal and the clutch release shaft by
rotating pushes against the release bearing. The diaphragm
spring in the pressure plate assembly is pushed by the bearing,
and it releases the clutch
C. Brake
Brake is a device or a mechanism to stop a moving vehicle
by applying friction or pressure on the wheels, when the
brake lever is pressed the pressure will be transmitted to the
master cylinder through a push rod enhancing the brake fluid
from the fluid sump to flow to a pressure chamber through
a compensating port. This results in the increase in pressure
of the whole hydraulic system, forcing the liquid through
the tubes to the wheels where the callipers are present. The
callipers then apply force directly to the turning wheel, the
friction between the drum and the rotor creates a barrier to
the torque produced and stops the vehicle. Heat produced by
the friction will be dissipated to the vents in the wheel or
goes through the brake pads which is usually made of heat
and friction resistant materials
D. Steering
It is used to steer an automobile to the desired direction
during the motion. We have a mechanical steering system used
in the conventional car. It consists of a steering wheel, trans-
mission systems and the axles for the operation. A reduction
gear is used by the steering box to achieve a higher torque on
the steering linkage by applying only a low force. Along with
it the extend of the axle movement will be decreased for the
steering wheel’s angular movement so that the reactiveness of
the steering on account with the driver’s force on the wheel
is minimized
E. Accelerator
It is a device also called as throttle, a foot pedal, which
controls the speed of a vehicle’s engine. The foot pedal is
connected to the engine via a cable, the throttle valve is
controlled by the pedal which allows the amount of air intake
to the engine manifold. There are various sensors in the system
to determine the amount of fuel to be supplied to the engine
when the pedal is pressed. The position of the pedal is given
as a feedback for the operation
IV. PNE UM ATIC SYSTEM
Pneumatics is a branch of mechanics which uses com-
pressed gases and the utilization of such gases to deliver
movement [8].It is used in many industrial applications which
needs to be automated. The pneumatic system basically has
pressure vessel to store the inert gas or air, a control valve,
and an actuator to do the specified job. Different types of
valves and actuators are added depending upon the purpose
and needs of operation. The basic pneumatic system consists
of a reservoir to store the air, a regulator and filter to control
the air flow and to filter the dust particles, direction control
valves to control the flow to the actuators and thereby control
their motion.
A. Advantages
•Air is used by pneumatic systems for their operation
which is available in abundant and is free of cost, so
we can easily refill the cylinders
Fig. 4: Basic pneumatic system
•Fast reflex actions can be made and large amount of thrust
can be achieved
•The pneumatic system design cost is very less as the
materials used in the system are reasonably low
•Apart from hydraulic systems where oil is used as the
pressurised medium which may lead to fire during leak-
ages, the air system is not at all harmful
•The system does not require large plumbing activities as
in hydraulic system and thus make the circuit simple
V. PNEUMATIC CYLINDER
Pneumatic cylinders are used in various industries and in
machineries to enhance motion and also generate sufficient
amount of force. They can easily move the components by
applying force through actuators and also can stop them from
moving by their ability to clamp the component in place
with pressure. There are thousands of varieties of pneumatic
actuators depending on the type of use, the place of use etc.
The best system can be made from them as they are in different
styles. Selecting the apt cylinder is a time consuming process
due to the variety, some of the factors are :
•Actuation time
•Double acting or single acting [9]
•Standardisation for dimensions
•Detection of position
•Thrust to be achieved (Bore dia)
•Length of actuation (stroke)
•Environment (type of fittings or the use of special mate-
rials)
•Pressure to be produced
•Need for cushioning
•Type of construction required
•Temperature
•Mounting
•Tube required
VI. SE LE CT IO N OFPNE UM ATIC CYLINDERS
These are the important specifications to be taken into
account while choosing a cylinder [9].
•Type of mountings.
•Couplings
•Air consumption.
•Cylinder Thrust.
•Piston velocity.
A. Cylinder Thrust
Thrust is the most important factor to be considered while
selecting the type of cylinder. The value of the force is the
product of the area of the piston and the air pressure in the
cylinder
d = Diameter of the piston rod in cm
P = Air pressure in bar
F = Thrust of the cylinder in KG
D = Diameter of the piston in cm
Double acting in forward stroke :-
F=π
4×D2×P(1)
Double acting in return stroke :-
F=π
4×D2−d2×P(2)
B. Air Consumption
The air consumption data for a cylinder is required to
estimate the compressor capacity. The calculations include air
consumption during forward as well as return stroke. The free
air consumption for forward stroke is calculated as follows:
Free air consumption = piston area x (operating pressure +
1.013) x stroke
let,
D = Dia of piston in cm.
d = piston rod dia.
L = stroke in cm.
P = Air pressure in bar
Free air consumed in forward stroke (litres):-
C1 = π
4×D2×L×(1 + P)
103(3)
Free air consumed in return stroke (litres):-
C2 = π
4×D2−d2×L×(1 + P)
103(4)
C. Piston Velocity
The piston velocity is determined by the factors like the
length of the tube between the control valves and the cylinder
, the pressure during operation , the control valve size and the
inner diameter . The velocity can be increased or decreased
by using a flow control valve or a exhaust valve in the airline.
The piston speed is about 100 and 500 mm/sec at no load
conditions on an average. The exact size and type of the valve
is selected depending upon the operational frequency and the
response time.
D. Type of Mountings
•Pivot mounts.
•Centerline mounts.
•Double Trunnion mounts.
•Centre Trunnion mounts.
•Clevis mounts.
•Hinge mounts.
E. Couplings
•Plain
•Rod end fork.
•Universal couplings
•Claw couplings
VII. SEL EC TE D CYLINDER
On the basis of various data and the requirements of our
design the following cylinders are selected:-
•Cylinder Type 1:- Janatics A75 050 080 O (For brake
and clutch)
•Cylinder Type 2:- Janatics A75 032 080 O ( For Accel-
erator)
The brake and clutch pedal is actuated normally by applying
a thrust of about 40-50 Kg by a human being and hence the
following cylinders are selected [10] The cylinders selected for
accelerator and brakes are the same, the accelerator cylinder
is having less bore as it requires only less thrust as compared
to the other two. The specifications of the cylinders are shown
in the Table I
TABLE I: Cylinder Specification
Diameter of
piston
(D) cm
Piston rod
Diameter
(d)cm
Stroke
(L)cm
Air pressure
(P) bar
Min Max
Cylinder 1 5 2 8 2 10
Cylinder 2 3.5 1.2 8 2 10
A. Calculations
The thrust obtained from each cylinder is calculated and
tabulated in Table II.Two cases are taken in account for the
calculation i.e. forward stroke and return stroke of the cylinder,
they are again divided into two i.e. maximum pressure and
minimum pressure. The maximum pressure for the cylinders
are 10 bar and the minimum is 2 bar.
TABLE II: Cylinder Thrust
Forward Stroke
(Kg)
Return Stroke
(Kg)
Max Min Max Min
Cylinder 1 192.25 39.25 164.85 32.97
Cylinder 2 80.384 16.078 69.08 13.816
The air consumption is calculated so as to determine the
amount of air to be stored in the cylinder for the operation.
The cylinder should be filled by the compressor according to
the air consumption. The mountings are required to position
the cylinders in the right position without any disturbances.
Couplings are used in the cylinders to transmit power or to
change the direction of the force acting. The calculated values
and the selected coupling and mountings are shown in Table
III
TABLE III: Air Consumption, Type of Mountings, Coupling
Air Consumption
(litre) Type
Of
Mounting
Type
Of
Coupling
Max
Pressure
Min
Pressure
Cylinder 1 1.727 0.471 Clevis
Foot
Bracket
Rod
End
ForkCylinder 2 0.707 0.192
The air consumed by the system is only about 2 litres of
air for an operation and hence we select a cylinder of 100
litre capacity for the uninterrupted actuation of the cylinders.
The response time is adjusted by the flow control valves and
it changes during different operation.
VIII. DESIGN
A. Pneumatic Circuit
Pneumatic circuit consists of 3 cylinders for clutch, brake
and accelerator respectively as shown in Fig.(5). Cylinders
are controlled by a 5/3 direction control valve. The valves can
be controlled using a microcontroller. By actuating the valves
the cylinders will move to and fro and also can be made
still at desired positions. These cylinders may be actuated
separately or together depending upon the need of the vehicle.
Solenoid valves are used and the input is given through a micro
controller [11]
Fig. 5: Pneumatic Circuit
B. Cad Model
The cad drawing is made to design the position of the
cylinders, the mountings on the frame and the structure of
the frame. There are three cylinders in the model each for
Fig. 6: Cad drawing
accelerator, brake and clutch respectively. A frame is made and
fixed on the vehicle and the cylinders are mounted onto it as
shown in Fig.(6). The pneumatic cylinders are connected to the
direction control valves through tubes and are then connected
to the air reservoir . The proposed cad model is fabricated on
the vehicle and is tested with pneumatic inputs as in Fig.(7)
Fig. 7: Fabricated Parts
IX. STEERING SY ST EM
The steering system has a significant aspect in the dynamics
of the vehicle which deals with the navigation and guidance of
the vehicle. There are mainly three types of steering systems
namely hydraulic, mechanical and electrical systems. Most of
the cars are using hydraulic steering system leaving the old
mechanical system and some of the cars have started using
electric power steering. The electric power steering system is
having a number of advantages like less maintenance, easily
adjustable, easy to test , conserves energy, and is friendly to
the environment. New technologies like automatic parking and
automatic driving requires the use of electric steering system
[12]. The automation of the steering wheel is an essential part
in the control of a driverless car.
A. Cad model
The cad model is made in order to design and place the
stepper motor with the gear drive on the steering assembly.
The stepper motor is connected to the steering assembly with
the help of a gear drive. The driven gear is fixed to the steering
wheel hub, and the driving gear is attached to the motor shaft.
The motor is placed or attached to a frame which rests on
the vehicle body. The frame helps to keep the gears engaged
and won’t allow them to detach. A wheel encoder is also
used to get the feedback of the rotation of the wheel. It is
used as the rotation of the motor cannot be converted directly
during heavy loads and also to convert the system a closed
loop feedback framework. The cad model clearly depicts each
part of the assembly, drive and the frame in which the motor is
mounted as shown in Fig.(8) and Fig.(9) The designed frame
is fabricated and mounted on the frame as shown in Fig.(10),
it is tested by running the motor at different speeds. The frame
could hold the motor even at high speeds, the gears were also
engaged throughout.
Fig. 8: Cad Model
B. Motor and Gear selected
For manual turning of the steering wheel for our car is a
maximum of 20kg/cm(t1)
Radius of the wheel (r) = 20cm
Radius of driving gear (r1) = 10cm
Radius of driven gear (r2) = 5cm
Torque of the Motor (t2) = 46Kg/cm
Torque = Force * perpendicular distance
Fig. 9: Other Views
Fig. 10: Fabricated Parts
Torque at centre of steering = r * 20 = 20*20 = 400 kg/cm
Torque on the driven gear (t3) = t1 * 10 = 20*10 =200 kg/cm
Torque on the driving gear (t4) = t2 * 5 = 46*5 = 230 kg/cm
The Gear drive could easily bring down the torque to
its half of the original value The motor selected is Bholonath
Nema34 46kg/cm stepper motor, the calculated torque on the
driving gear (t4) is 230kg/cm,which is more than the required
torque (t3) on the driven gear. Since t4 greater than t3 , the
selected motor is sufficient to drive the steering.
C. Steering Angle Estimation
1) Gear Ratio Calculation
Steering wheel is connected to the stepper motor to
transmit power from the motor through a gear drive.
The driving gear is attached to the stepper motor and
the driven gear is attached to the steering.
N1=25;N2=92
where N1 is the number of teeth in Gear1
where N2 is the number of teeth in Gear2
ratio =N1
N2=25
92 = 1 : 3.68 (5)
2) Steering angle to wheel ratio
Steering wheel can complete two revolutions to
the left and two to the right from the centre position.
Our daewoo matiz wheel turns only 30 degrees to
the left and to the right from the center. The ratio is
calculated in order to determine the extent to which or
the angle to be rotated by the steering wheel when the
wheel turns.
Total angle of turn of wheel = 60 degrees
Total angle of rotation of steering wheel = 4 rotations
= 4 * 360 = 1440 degrees
ratio =W1
W2=60
1440 = 1 : 24 (6)
3) Mapping wheel to stepper motor
This mapping is done to calculate the ratio between the
wheel turn to the stepper motor rotation. The stepper
motor is connected to the steering wheel with a gear
drive, so the ratio of the gear drive and the steering wheel
has to be multiplied by the ratio between the wheel turn
and the steering rotation. The final ratio will determine
the extent to which the motor has to rotate the vehicle
takes a turn of 1 degree.
ratio =W1
W2∗N1
N2=1
24 ∗1
3.68 =1
88.32 (7)
4) Calculation of number of steps
The stepper rotates in a step wise manner, they have
to turn a number of steps to complete a revolution.
The motor we selected is having a step angle of 1.8
degree ,i.e. the motor will turn with a maximum step
of 1.8 degree. The motor has to turn 200 steps to
complete one revolution. The motor we selected is in
half stepping mode by default, so the motor has to turn
400 steps for a complete revolution. The angle to be
rotated by the motor is calculated from the angle to be
turned by the vehicle and the ratios by the equation 9
f = frequency(Hz)
Rpm = no: of revolutions per minute of the motor
step size = steps needed to complete one revolution
angle = input angle to be rotated
Frequency to stepper motor
f=RP M ∗S tepsize
60 (8)
No: of steps to be rotated
=angle ∗3.68 ∗24 ∗2∗f
1.8∗stepsize (9)
As the vehicle is running at lower speeds the rpm of the
motor is set as 120 and the corresponding frequency is
800hz and the step size is 400 steps per revolution.
X. CONCLUSION AND FUTURE WORK
A mechanical platform is designed and fabricated to control
the mechanical systems like accelerator, clutch ,brakes and
steering of the vehicle. The designed system could work based
on our inputs from the vision module in the car. The actuation
was done without any errors and delay ,the controlling of
the systems. The motor drive could easily rotate the steering
system with minimum delay. Automation of the gear system is
to be done in the future to run the vehicle at higher speeds, it
will be either done using stepper motors or by using pneumatic
cylinders.
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