Making Of Micromouse

MAKING OF MICROMOUSE

Amit Raj 2nd Yr ECE SASTRA 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 .

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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 ELECTRONI CS

SESNSO RS

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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 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 Microcontrol ler

Peak Detector

Transmitter IR led

High pass filter , Cutoff 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 convers ion comple te

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 www.amitraj.webs.com

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 . www.amitraj.webs.com

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 www.amitraj.webs.com torque

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

Negative

Logic 1 0

Positive

Logic 0 1

Direction of rotation Clock wise Anti clock wise

Directio n Clock Anti clock

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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 www.amitraj.webs.com stepper motor

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

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Full Step driving of Stepper Motor Full step 2 phases active

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Half Step driving of stepper motor

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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

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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); }  With this SW Steppers can’t

void delay(unsigned int m) { unsigned int n; while(m--) for(n=0;n<=100;n++); }

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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Initialize timer

Interrupt routine Give Pulse to stepper

Start Timer

Is Stepp er target reach ed

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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You can download this presentation at www.amitraj.webs.com

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