second workshop presentation

TECHNOLOGY ROBOTICS SOCIETY

Indian Institute of Technology, Kharagpur

A TUTORIAL ON

ROBOTICS

Part III : Motors & Motor Drivers

Copyright © Robotix Team, IIT Kharagpur

Basic Parts Of Our Mobile Robot

Locomotion system

Power supply system

Actuators

Sensory devices for feedback

Sensor Data processing unit

Control system

Potentiometer

Capacitors

IR LED

Diodes

Current Flow in a Diode

Multimeter

Transformer

POWER SUPPLY (RECTIFIER

CIRCUIT)

IC7805

1 - Input 2 - Ground 3 - Output

THE RECTIFIER CIRCUIT

USES OF RECTIFIER CIRCUIT

Rectifier circuit is used to convert Alternating

Current to Direct Current.

We get Alternating Current as Power Supply in

our homes, but electronic components in

robots use Direct Current.

STEPS OF CONVERTING AC

TO DC

First the Transformer, converts 220V AC to

12V AC.

The Diodes rectify the current in a single

direction.

The Capacitor then normalizes the current.

The little distortions are further rectified by the

IC7805.


End Actuators

They convert the electrical energy into

meaningful mechanical work

Mechanical output can be rotational or linear

(straight line)

Motors provide rotational motion

Electromagnets provide linear motion


Motors are of various kinds

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


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

A

-

+

DC MOTOR12

A

-

+

DC MOTOR12

V DC

V DC

Direction of rotation controlled by polarity of current / voltage

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


DC Motor Specifications

Operating Voltage : Recommended voltage for powering the motor

Operating Current : Current drawn at a certain load on the shaft

Stall Current : Maximum current drawn, when motor not allowed to rotate

Stall Torque : Rotation force needed to hold the motor in stall condition


DC Motor Characteristics

Free running torque & current are ideally zero

Increased load implies, increased

torque, current drawn & power consumption

Power supplied by a motor is the product of

output shaft’s rotational velocity & torque


DC Motor Characteristics Cont...

DC Motors are high–speed, low-torque

devices

Using gears, the high speed of the motor is

traded off into torque


DC Motor Characteristics Cont…

Zero speed at maximum load (stall torque)

Highest speed while free running (zero load)

Highest power at half speed & half load

50%

50%

20%

10%

40%

100%

80%

60%

90%

SPEED ------>

POWER

60%

90%

40%

70%

70%

30%

LOAD

20%

30%

100%

80%

10%


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 Direction Control

H – Bridge Circuit Diagram

S1

S3

S2

S4

M1 2

VCC

Power

Transistor

Switches


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


Electronic Direction Control

H – Bridge Circuit Diagram

GND

VCC

NOT GATE

12Q1 Q3

A- +

DC MOTOR

12

LQ4Q2

R

NOT GATE

12


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

VOLTAGE

CONTROL

CIRCUIT

CONTROL SIGNAL


DC Motor Speed Control Cont…

Controlling the current by passing it through a

variable resistor is not advisable as it is

extremely energy inefficient

A trick is done to achieve reduced average

power

Power is supplied to the motor in short

intermittent bursts, as explained further

Duty Cycle Fundamentals

8s5s

2s

9s

100%

80%

4s

10s

100% Duty Cycle

40%

60%

7s8s4s

VOLTAGE

------>

40%

40% Duty Cycle

80%

5s9s

20%

1s

80% Duty Cycle

2s 3s3s

20%

6s

TIME------>

4s

20% Duty Cycle

VOLTAGE

------>

8s

2s

100%

9s

VOLTAGE

------>

20%

10s7s

80%

60%

1s

80%

7s

100%

9s6s

1s

5s 5s

TIME------>

40%

60%

TIME------>

VOLTAGE

------>

6s3s 10s7s

6s10s

2s 1s

60%

40%

3s

20%

4s

100%

TIME------>

8s


Duty Cycle Cont…

The time period (τ) is the duration after the

voltage waveform repeats itself

Duty Cycle is the % time of τ, the voltage is

equal to the operating voltage

The average voltage is equal to the ‘Duty Cycle’ % of the Operating Voltage


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

Analogous to human sensory organs

Eyes, ears, nose, tongue, skin

Sensors help the robot knowing its surroundings better

Improves its actions and decision making ability

Provides feedback control

Sensors

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

Comparator

VX > VY Z = 1

VX < VY Z = 0

+

-

X

Y

Z

Sensor Interfacing

Light Sensing Module using LED-LDR combination

Sensor Interfacing

Bump Detector Module

Shaft Encoder

Shaft Encoders are used to measure the rotation of

motor shaft. The holes / sectors are counted

An Example - Line Follower

A line follower is a robot

capable of tracking a line

drawn on a surface

Optical sensors capture the

line position at the front end

of the robot

The robot is steered to keep

it always over the line

Block Layout of Line Follower

Optical Sensor Array

Steering Controller

Left Motor Right Motor

Line Following Algorithm

All the sensors are assigned

some weight such as

Sensor 1 = a1 = 3

Sensor 2 = a2 = 2

Sensor 3 = a3 = 1

Sensor 4 = a4 = -1

Sensor 5 = a5 = -2

Sensor 6 = a6 = -3

Monday (9th August 2010)

Section 1-4 5:30 PM – 8:30 PM

Section 5-7 8:30PM - 10:30PM

Tuesday(10th August 2010)

Section 8-11 5:30 PM – 8:30 PM

Section 11-14 8:30PM - 10:30PM

Wednesday(11th August 2010)

Free Slot 5:30PM onwards

ROBOTIX Interviews

second workshop presentation

Education

torque current

maximum current

alternating current

motoroperating current

shaftstall current

motorcopyright robotix

macopyright robotix

higher current signal