A Tutorial on Robotics

Deepak Kumar

CSE(evening shift)

Section: N2

Roll no: 115343

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

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 Sensory devices for feedback Sensor Data processing unit Control system End actuators Power supply 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

Locomotion System

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

The issue is to control these motors to give the required speed and torque

Power, Torque and Speed

A simple equation: Power is the product of Torque and Angular velocity

P = ζ X ω This implies that if we want more torque

(pulling capacity) from the same motor we may have to sacrifice speed and vice versa

Another Simple Relation

The dc motors (tape motors) available have very high speed of rotation which is generally not needed. But what they lack is torque output

For reduction in speed and increase in pulling capacity we use pulley or gear systems

These are governed by: ω1 X r1 = ω2 X r2

The above concept will be discussed shortly

Using Pulleys

r1

r2

ω1 ω2

MotorWheel

ω1r1 = ω2r2 => ω2 = ω1r1 / r2

τ1ω1 = τ2ω2 => τ2 = τ1ω1 / ω2 => τ2 = τ1r2 / r1

Thus we get reduction in speed and increased torque. Hence our machine is able to cross over obstacles easily and also pull more load

Belt

Belt

Multi Pulley Systems

Motor WheelIntermediate Pulley

ω1

ω2

ω3

ω1r1 = ω3r2 => ω3 = ω1r1 / r2

τ1ω1 = τ3ω3 => τ3 = τ1ω1 / ω3 => τ3 = τ1r2 / r1

ω3r1 = ω2r2 => ω2 = ω3r1 / r2

τ2ω2 = τ3ω3 => τ2 = τ3ω3 / ω2 => τ2 = τ3r2 / r1 => τ2 = τ1r22

/ r12

Hence for n pulley system => τ2 = τ1r2n

/ r1n

r1

r2

r2

r1

Features of Pulley System

Simple and easy to use Flexible rubber belts make the job easier Maximum torque restricted by friction limits Very high torque system cannot be achieved

Geared Systems

Gears are the most common form of torque increment devices, found in almost all mechanical machines

The concept of reducing the rotation speed to increase torque is known as ‘Gear Reduction’

A high speed motor with low torque is used to drive heavier loads at lower speeds

They have much more efficiency than pulleys The maximum torque capability is not limited

by friction but material strength

Uses of Gear Systems

‘Gear Reduction’ to increase torque / decrease speed of rotation

Alter the direction of rotation axis Synchronization to two axes Reversal of direction of rotation

Types of Gears

Spur Gears Helical Gears Bevel Gears Worm Gears Rack and Pinion Gears

Spur Gears

Very common kind of Gear

Used primarily for gear reduction

Reduction ratio is the ratio of teeth in the driver gear and the driven gear

Helical Gears

These gears have better grip on each other than the spur gears

Can also be used for changing the axis direction

Bevel Gears

Mostly used for altering the direction of the rotation axis

The gear reduction can be achieved by different number of teeth in the gears

Worm Wheel Mechanism

Used for very high gear reduction

The wheel is driven by the worm screw.One rotation of the worm causes the wheel to advance one tooth

Rack & Pinion Mechanism

Used for converting rotational motion into linear motion

Power Supply System

Suitable power supply is needed to run the motors and associated circuitry

Typical power requirement ranges from 3V to 24V DC

220V AC supply must be modified to suit the needs of our machine

Batteries can also be used to run robots

DC Power Supply

D8D1N4007

Step Down Transformer

D10D1N4007

Ground

C11000uF

230 V AC

+ V

D9D1N4007

TX1 D7D1N4007

Simple Current Direction Reversal

S1

V3

V DC

A- +

MG3 DC MOTOR

12

U5

Relay_DPDT_nb

COM1

A

B

NC1

NO1

COM2NC2

NO2