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BASIC
DIFFERNTIAL
BOT

An Introductory Tutorial

SUMMARY:
The purpose of this document is to help you build a Two Wheel
Differential Bot.
Starting with an overview of the system the document would
cover implementation details like circuits and algorithms,
followed by some suggestions on improving the design.
These are guidelines as per our experience. You can use or
derive different methodologies for building robots.

Introduction:
• What is a basic differential bot?
It is the basic mechanism used for the locomotion purpose
which carries all assembly mounted on it.
• Why build a basic differential bot?
Basic differential bot is a basic building block of robots, which
you will make for your college level competitions.
• Prerequisites:
You must be armed with your basic knowledge of Applied
Mechanics and Electronics.
• Background:
We will teach you the process of building a robot, as you make
it.The very first step anyone would make would be to design
your robot. Interestingly this is where beginners fail. Beginners
spend 90% of their time building, and 10% designing. Experts
are the opposite - 90% designing and 10% building. Of course
when you are a beginner it’s hard to design - you don't always
know what works until you try it. But planning never hurts.

As the size of a robot increases linearly, the cost and difficulty
to make it increases exponentially. Make it as small and light as
possible. Most importantly, remember to KISS. “Keep it simple,
stupid!” You will get thousand ideas but you should choose an idea
that can be implemented.
We will recommend you to follow steps given below to
build any bot.
• PLANNING
• IDEAS N DESIGN
• TESTING
• FABRICATION
• DIAGNOSTICS AND FLAW CORRECTION

COMPONENT LIST:
• Chassis
• DC Motors
• Clamps
• Remote Control
• Batteries
• Electronic Components
• Wheels
• Screw divers
• Hand drill (a electric one if u can afford it) & hack saw.
• Wire stripper
• Hammer
• Scissors
• Soldering gun

DRIVING MECHANISM:

1. Differential Drive



CONTROL ALGORITHM:
• To drive straight both wheels move forward at same speed
• To drive reverse both wheels move back at same speed
• To turn left the left wheel moves in reverse and the right
wheel moves forward
• To turn right the right wheel moves in reverse and the left
wheel moves forward
The differential drive algorithm is useful for light robots.
This locomotion is the most basic of all types, and is highly
recommended for beginners. It is very easy to make and control. It is
also called the ‘skid steering’. Note that this algorithm doesn’t just
work for wheeled robots, but is also the same algorithm you must
use for tank tread type robots and biped robots.
You can also get interesting curved paths just by varying
speeds of both wheels. But for now, let’s just keep the algorithm
binary to make your first program easy.

2. Steering Mechanism:


This mechanism is generally used in cars. Its normally Rack & Pinion
arrangement or direct servo motors can be used. At the beginners
level no need to use steering mechanism.

POWER:

Your total current requirement is about 2 to 3 amp(0.6
A to 0.7 A for each motor). You will get a battery in market that
will give that much current but it will be slightly costly. You can
use power supply. With any power source, make sure you use a
good robot power regulation circuit to help control power to
your robot. Power can be calculated as,

Power = Voltage × Current

Use power supply with following specifications:
• 0-30 Volts
• 2-4 Amperes
The sum required power of all your robot components
needs to be below the amount your power circuit can supply. If
power drops even for a fraction of a second below what your
bot requires,motors wont work very well.Always keep energy
required by bot is less than energy battery can supply.

MOTORS:

For an optimal bot choosing motors would involve
calculations of weight, gearing ratios, desired terrain, desired
velocity and acceleration, voltage, power consumption,
controllability. While choosing motors calculate roughly the
rpm and torque you required e.g if you are using bot for race
take motors of 300-600 rpm while if you are using it for
robowar take motors of 6 kg-cm. It will be better to use motors
of 300 rpm and 2 kg-cm torque at the beginning for general
purpose.
There are two terminals at the backside of motor.
For sake of convenience marked them as +ve and –ve as per
direction in which shaft of motor rotates i.e clockwise or
anticlockwise. Connect the wires coming from remote to these
terminals (It will be discussed later). There are in all four ways
in which we can apply voltages at these two terminals.


You can mount the motor on chassis by using circular or square
clamps as per design of your motor

REMOTE CONTROL:

Once you finish building your machine, you will need a
mechanism to control its movements. A simple DPDT switch can
effectively be used to control the motion of a single DC motor.
A DC motor performs different operations according to
the voltages given at two of its terminals. This is discussed in the
section of MOTORS previously. A Remote Control is used to achieve
the proper biasing of motors. Following diagram shows a sample
connection of how a motor can be controlled using a DPDT switch.
This is a simple case of controlling in which motor can
only be rotated in clockwise and anticlockwise directions. When we

switch the DPDT switch to one side, poles B and E get connected to
throws A and D respectively. Left terminal of motor connects to +ve
voltage and the right terminal connects to 0 volts which drives the
motor in clockwise direction (say). On pressing the switch to the
other side, the poles B and E get connected to throws C and F
respectively. This time the left and right terminals of the motor go to
0 volts and +ve voltage respectively, i.e. polarities at motor terminals
get reversed. This drives the motor in the other sense, which is
anticlockwise in this case.
Thus we achieve clockwise and anticlockwise rotation of the motor
using a single switch. When the switch is not pressed to either of the
sides, both the terminals of the motor remain open. This condition is
as good as Stop mode. In this case, motor stops its rotations.