Post on 16-Jul-2015
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
LED
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.
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
DC Motors
As the name
suggests, a motor which
uses a DC (Direct
Current) power
Can run in both
directions
Speed Controllable
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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%
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
DC Motor Direction Control
H – Bridge Circuit Diagram
S1
S3
S2
S4
M1 2
VCC
Power
Transistor
Switches
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
Electronic Direction Control
H – Bridge Circuit Diagram
GND
VCC
NOT GATE
12Q1 Q3
A- +
DC MOTOR
12
LQ4Q2
R
NOT GATE
12
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
Copyright © Robotix Team, IIT Kharagpur
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
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