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Robotics
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MAKING OF MICROMOUSE
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Amit Raj2nd Yr ECESASTRA University
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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 .
MICRO
CONTROLLER
SESNSORS
SENSORELECTRONI
CSMOTORDRIVER
LEFTMOTOR
RIGHTMOTOR
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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 :
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IR Analog sensors
Transmitter IR LEDReceiver 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
TransmitterIR led
ReceiverIR Photodiode
High pass filter , Cut-
off freq more than
300Hz
Peak Detector
ADC of
Micro-control
lerobstacle
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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 :
SENSORS
Top Down
Side Looking
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Top Down
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Side looking sensors :
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Initialize ADC
Start ADC
ADC convers
ion comple
te
Select ADC channel
Read ADC value
Stop
YesN0
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Side looking
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); }
Sample code for ADC conversion in AVR controllers :Unsigned int left_adc;left_adc = adc(0xE0);
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Reducing error using PD controller :
Error MotorsPDcontroller
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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 leftsideerr = 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 rightsideerr = 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 .
Gears 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 applicationSome 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 Direction of rotation
Positive Negative Clock wise
Negative Positive Anti clock wise
Logic Logic Direction 1 0 Clock
0 1 Anti clock
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Direction Pulse toClock wise A and CAnti Clock wise B and D
Bi-Direction control of DC Motor
H-Bridge Ckt using transistors for bidirectional driving of DC motor
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H-Bridges in ICs 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
PWM
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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 5 Lead stepper
6 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 ICs 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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A B C D
1 1 0 0
0 1 1 0
0 0 1 1
1 0 0 1
Bi Polar driving of Stepper Motor
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4 Lead stepper 5 Lead stepper
6 Lead stepper 8 Lead stepper
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Sample program
for(p=0;p
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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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Initialize timer
Start Timer
Is Stepp
er target reach
ed
Wait
Stop timer
Give Pulse to stepper
Update Output compare register
Reti
No
Yes
Interrupt routine
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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 ICs 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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You can download this presentation at www.amitraj.webs.com