Download Making of Micromouse - India Electronics and Robotics Components

MAKING OF MICROMOUSE
P.Raghavendra Prasad
Final Yr EEE
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INTRODUCTION
Micromouse is an autonomous robot designed to reach
the center of an unknown maze in shortest possible time
and distance .
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M
I
C
R
O
LEFT
MOTOR
MOTOR
DRIVER
RIGHT
MOTOR
C
O
N
T
R
O
L
L
E
R
SENSOR
ELECTRONICS
SESNSORS
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Basic components of Micromouse:
 Sensors
 Motors
 Microcontroller
 Batteries
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SENSORS
 Your mouse is going to need sensors to tell it about itself and
its environment.
These are used to detect the presence or absence of walls and
to verify your position in the maze.
They will also be important in ensuring that the mouse maintains
an appropriate path without hitting any walls
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Sensors
Commonly used sensors in the field of robotics
 IR Digital sensors
 IR analog sensors
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IR Digital sensors
Transmitter
 IR led connected to 38KHz oscillator
Receiver
 TSOP1738
Advantages
 Detects an obstacle at a distance more than 1meter if tuned
perfectly.
 No ambient light effect.
 Easy to use.
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Designing a transmitter :
 Use IC 555 in Astable mode
 For approximate 50% duty cycle take Ra = 1 k ohm
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Receiver :
IR Analog sensors
Transmitter
 IR LED
Receiver
 IR Photodiode
Advantages:
 Can measure distance up to 15 cm.
Disadvantages:
 Responds to IR rays present in ambient light.
 Intensity of reflected rays is non-linear with respect to distance of
obstacle
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IR Analog sensor
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 Modulate IR rays to avoid Ambient light effect :
Astable oscillator at
frequency greater than
1KHz
ADC
of Microcontroller
Peak
Detector
Transmitter
IR led
High pass
filter , Cut-off
freq more
than 300Hz
Receiver
IR Photodiode
obstacle
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High-Pass filter :
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Peak Detector:
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Errors involved in mouse movement :
Forward error:
Forward errors begins when a
mouse is either too close or too
far from the wall ahead
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Errors involved in mouse movement :
Offset error :
Offset errors, which happens often, is
caused by being too far to the left or
to the right as you pass through a cell
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Errors involved in mouse movement :
Heading error:
Heading error is known as pointing at walls
rather than down the middle of the cell
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Commonly used Sensor arrangement :
 Top Down
 Side Looking
SENSORS
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Top Down
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Side looking sensors :
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Initialize ADC
Select ADC channel
Start ADC
N0
ADC
conversio
n
complete
Yes
Read ADC value
Stop
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Side looking
Sample code for ADC conversion in AVR controllers :
Unsigned int left_adc;
left_adc = adc(0xE0);
unsigned int adc(unsigned int temp)
{
ADMUX = temp;
//selects ADC channel
ADCSRA |= 0x40;
//starts ADC
while(conversion_not_over()); //waits till ADC conversion completes
ADCSRA |= 0x10;
// clears ADIF flag
return(ADCH);
// returns ADC result
}
int conversion_not_over(void)
{
unsigned int temp;
temp = ADCSRA;
temp = temp & 0x10; // checks for ADIF flag
return(!temp);
}
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Reducing error using PD controller :
Error
PD
controller
Motors
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Error calculating:
If wall is on both sides
err = left_adc – right_adc;
If err is +ve
• Mouse is near to left wall and as a correction it has to move towards right wall
If wall is only on leftside
err = left_adc – reff_value;
If err is +ve
• Mouse is near to left wall and as a correction it has to move towards right wall
If wall is only on rightside
err = right_adc – reff_value;
If err is +ve
• Mouse is near to right wall and as a correction it has to move towards left wall
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Implementing PD controller:
err_d = err – err_past;
adj = err * kp + err_d * kd ;
 kp is proportional controller constant
 kd is derivative controller constant
 The value of adj is used to either speed up or
speed down one of the wheel .
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DC Motor
 DC
Motors are small, inexpensive and powerful motors used widely.
 These are widely used in robotics for their small size and high
energy out.
 A typical DC motor operates at speeds that are far too high speed
to be useful, and torque that are far too low.
 Gear reduction is the standard method by which a motor is made
useful .
 Gear’s reduce the speed of motor and increases the torque
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Choosing a DC Motor
 DC Motor with Gear head
 Operating voltage 12V
 Speed
Depends on our application
Some available speeds in market
 30 RPM
 60 RPM
 100 RPM
 150 RPM
 350 RPM
 1000 RPM
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Drive basics of DC Motor
Red wire
Black wire
Positive
Negative
Clock wise
Negative
Positive
Anti clock wise
Logic
Logic
1
0
Clock
0
1
Anti clock
Direction of rotation
Direction
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Bi-Direction control of DC Motor
H-Bridge Ckt using transistors for
bidirectional driving of DC motor
Direction
Pulse to
Clock wise
A and C
Anti Clock wise
B and D
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H-Bridges in IC’s to reduce the drive circuit complexity
 The most commonly used H-Bridges are L293D and
L298
 L293D has maximum current rating of 600ma
 L298 has maximum current rating of 2A
 Both has 2 H-Bridges in them
 These are designed to drive inductive loads such as
relays, solenoids
Can be used to drive 2 DC motors or 1 stepper motor
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PWM
STEPPER MOTOR
 STEPPER MOTOR is a brushless DC motor whose rotor rotates
in discrete angular increments when its stator windings are
energized in a programmed manner.
 Rotation occurs because of magnetic interaction between rotor
poles and poles of sequentially energized stator windings.
 The rotor has no electrical windings, but has salient and/or
magnetized poles.
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4 – Lead stepper
6 – Lead stepper
5 – Lead stepper
8 – Lead stepper
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Full Step driving of Stepper Motor
Full step wave drive
4
3
2
1
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
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Full Step driving of Stepper Motor
Full step 2 phases active
4
3
2
1
1
1
0
0
0
1
1
0
0
0
1
1
1
0
0
1
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Half Step driving of stepper motor
4
3
2
1
1
0
0
0
1
1
0
0
0
1
0
0
0
1
1
0
0
0
1
0
0
0
1
1
0
0
0
1
1
0
0
1
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Choosing a Stepper motor




12 V or 5 V operating voltage
1.8 degree step
6 Lead
250 to 500 ma of current
or
Coil resistance of 20 ohms to 40 ohms
 Size and shape depends on application
 In most of the robotics cube shaped motors are
preferred with frame size of 3.9 to 4 cm
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Commonly used IC’s for driving Stepper motor
 ULN2803
• It has 8 channels
• It channel has maximum current rating of 500ma
• can be used to drive 2 unipolar stepper motors
 L293d
 L297 & L298
UDN2916
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ULN2803
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Bi – Polar driving of Stepper Motor
A
B
C
D
1
1
0
0
0
1
1
0
0
0
1
1
1
0
0
1
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4 – Lead stepper
6 – Lead stepper
5 – Lead stepper
8 – Lead stepper
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Sample program
for(p=0;p<=20;p++)
{
PORTD=0xA9;
delay(65);
PORTD=0x65;
delay(65);
PORTD=0x56;
delay(65);
PORTD=0x9A;
delay(65);
}
void delay(unsigned int m)
{
unsigned int n;
while(m--)
for(n=0;n<=100;n++);
}
 With this SW Steppers can’t be controlled individually
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SW for steppers :
 Use timers to create delay.
 Use Clear Timer on Compare match
or
Normal Mode
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Interrupt routine
Initialize timer
Give Pulse to stepper
Start Timer
Is
Stepper
target
reached
Update Output
compare register
No
Wait
Reti
Yes
Stop timer
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Chopper Driving:
 For better performance of Steppers they should be over driven
and current should be limited .
 For example a 5 V 500ma motor can be driven at more than
15V but current in the coil should be limited to approximately
500ma .
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Methods of current limiting :
 Traditional method of using a resistor of appropriate power in
series with common terminal.
 This method is not recommended as there will be huge power
wasted in the series resistor.
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Best method of current limiting :
 Pulse Width Modulation
 Motors should be driven at 3 to 4 times the rated voltage.
 Measure the current in the coil if it raises to 10% more than the
limit switch off the supply to motors .
 If it falls to 10% below the limit switch on the supply to motors .
 Few IC’s that can do the current chopping
1. L297 & L298
2. UDN 2916
3. UCN 5804
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Microcontroller:
Choose the controller that has sufficient
 Amount of FLASH memory to store your program
 Amount of RAM memory for variables
 Number of Timers
Min of TWO 16 bit timers or ONE 16 bit timer with TWO
output compare channels and ONE 8 bit timer
 Number of ADC channels
 Good operating speed
 ATMEGA32 of Amtel made is one that is suitable
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Batteries:
Choose batteries that can provide high voltage and high power with low weight
 Should have current capacity more than 700 mah
 Ni-MH & Ni-Cds
Can provides high current at 1.2 V
Can be charged by Constant Current or Constant Voltage chargers
 Li – Ion
Can provide high current at 3.6v
Should be charged using CCCV charger .
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