Introduction to Robotics

Electronics and Robotics Club

What Is “Robotics” ?

• The word robotics is used to collectively define a field in engineering that covers the mimicking of various human characteristics

• Sound concepts in many engineering disciplines is needed for working in this particular field

• It finds it’s uses in all aspects of our life

What A Robot Can Mean ?

• An automatic industrial machine replacing the human in hazardous work environment

• An automatic mobile sweeper machine at a modern home

• An automatic toy car for a child to play with

• A machine removing mines in a war field all by itself and many more…

What Do We Mean Here ?

• Here we are aiming at design and prototyping of mobile robots capable of controlled locomotion

• It may be human controlled or automatic

• It must be able to perform certain tasks we set for it

• The task must be achieved within some given limitations

Basic Parts Of Our Mobile Robot

• Locomotion system• Power supply system• Actuators• Sensory devices for feedback• Sensor Data processing unit• Control system

Locomotion System

• As the name suggests a mobile robot must have a system to make it move

• This system gives our machine the ability to move forward, backward and take turns

• It may also provide for climbing up and down• The concept of locomotion invariably needs rotational

motion e.g. a wheel driven by some power source• This involves conversion of electrical energy into

mechanical energy, which we can easily achieve using electrical motors

Wheeled Locomotion Systems

• Differential drive• Car type drive• Skid steer drive• Articulated drive• Synchronous drive• Pivot drive• Dual differential drive

Power Systems

• Suitable power source is needed to run the robots• Mobile robots are most suitably powered by

batteries• The weight and energy capacity of the batteries may

become the determinative factor of its performance

Motors

• AC Motors : Not used much in robotics• Stepper Motors : For controlled rotation• DC Motors : Finds extensive general use• Servo Motors : DC motor with in built

feedback & error compensation

Stepper Motor

• Used for measured rotation

• Can be held at a particular position of the shaft

• Ideal for many autonomous robots requiring higher precision

Working-Single Excitation

Double Point Excitation

DC Motors

• As the name suggests, a motor which uses a DC (Direct Current) power

• Can run in both directions

• Speed Controllable

DC Motor Working

• Direction of rotation controlled by polarity of current / voltage

• Speed of rotation controlled by average energy (power) fed to the motor

A-

+

DC MOTOR12

A-

+

DC MOTOR12

V DC

V DC

DC Motor Drivers

• These are current amplifying circuits• A low current control signal is converted into a

proportionally higher current signal that can drive the motor

• Power Transistors can switch high currents. The ICmax is usually of the order of Amps as compared to small signal transistors which have ICmax in mA

DC Motor Speed Control Circuit

• Input is the operating voltage & control signal• Output is a part of the operating voltage

depending upon the control signal

A-

+

DC MOTOR12

OPERATINGVOLTAGE

VOLTAGECONTROLCIRCUIT

CONTROL SIGNAL

Pulse Width Modulation

• PWM is a technique using which we can modify the duty cycle of a waveform depending upon an input control voltage

• This forms the backbone of our speed control circuit

• It can be easily implemented using the popular multipurpose IC 555, used widely for hobby electronics

Servo Motors

• Used to obtain discrete angles• Used extensively in robotic

arm, humanoid to mimic limb movements

• Used in environments where dynamic load changes take place.

• Require PWM, angle of rotation depends on the duty cycle of the pulse.

Sensors

• Sensors are the are the sensory organs of the robot

• Integral in order to achieve automation

• Widely used in mobile robots for achieving various tasks

• Output can be digital or analog

• Multi-purpose

Infra Red Sensor

• Detects light in infra red region• Gives output depending on the

amount of light received by its receiver component

• Comes in digital and analog variety

• Used for proximity sensation, line following obstacle detection

Ultrasonic Sensor

• Operates in Ultrasonic range• Detects reflected wave and sends

signal to MCU for distance calculation

• Used extensively in navigation• Also used for mapping and

obstacle avoidance.

LDR - Light Dependent Resistor

• Made of cadmium sulphide

• Resistance between two terminals vary depending on the intensity of light

• Can be used to differentiate contrast colours

Microcontroller

• It is the brain of the robot• Responsible for all control decision, check

conditions and control outputs.• Can perform various calculations to aid

various tasks.• Can be easily interfaced with sensors,motors

and other multi purpose devices and I/O devices

Other IC’s

• Besides the microcontroller robots need other IC’s for various tasks.

• Current amplification• Voltage regulation• Control • Pulse generation

Motor driver

• MCU control signals insufficient to drive motor

• Motor driver helps MCU maintain control signal and uses External Power to drive motor.

• Implements H-Bridge circuit to allow for digital control for direction variance

DC Motor Direction Control

• H – Bridge Circuit Diagram

S1

S3

M1 2

VCC

S2

S4

H – Bridge Working

S1 S2 S3 S4 Current Direction

Effect

1 0 0 1 1 to 2 Motor spins forward

0 1 1 0 2 to 1 Motor spins backward

1 1 0 0 - Braking Occurs

0 0 0 0 - Free running

555 timer

• Application as timers and pulse generators

• Multiple modes• Cheap and widespread• Used to make various

allied circuits like the TSOP obstacle detector.

Voltage Regulator

• LM-78XX series• Used to step down voltage

to certain value• Control fluctuations in circuit

and prevents damage to IC’s.• Helps increase flexibility in

circuit.

Communication

• Sometimes your bot needs a PC for performing complex calculations

• Effective com devices are required to send data to off board computer

• RF modules, bluetooth models are used for wireless transfer

• For wired transfer we have Serial cables and USB

Build a Bot

Exploring

practical

methods

Brain

storming

STEPS INBUILDING A

ROBOT

Testing

and

debugging

Copyright © ERC, BITS Pilani-Goa Campus

Designing

Building

and

Fabrication

51

Problem Statement 1

• Design a line following robot that autonously follows the black line on the following map.