Micro Mouse Seminar

P.Raghaven .Raghavendra dra Prasa Prasad d

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INTRODUCTION

Micromouse is an autonomous robot designed to reach Micromouse reac h the center of an unkno unknown wn maze in shortest ossible time and distance .

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INTRODUCTION

Micromouse is an autonomous robot designed to reach Micromouse reac h the center of an unkno unknown wn maze in shortest ossible time and distance .

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M I 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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Basi Ba sicc com com one nent ntss of of Mi Micr crom omou ouse se:: 

Sensors



Microcontroller



Batteries

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SENSORS

its environment. These

are used to detect the presence or absence of walls and to verify your position in the maze. The They y

will also be important impor tant in ensuring that the mouse maintains

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Commonly used sensors in the field of robotics igita sensors

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IR Digital sensors Transmitter



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:

Res onds to IR ra s resent in ambient li ht.  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 ra s to avoid Ambient li ht effect :

Transmitter IR led

frequency greater than 1KHz

of Microcontroller

Peak Detector

High pass er , u -o freq more than 300Hz

Receiver IR Photodiode

obstacle

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Hi h-Pass filter :

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Peak Detector:

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Errors involved in mouse movement :

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 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 is known as pointing at walls

rather than down the middle of the cell

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:



Top Down



Side Looking

SENSORS

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Side lookin sensors :

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Initialize ADC

Select ADC channel

Start ADC

N0

ADC conversio n complete

Yes

Read ADC value

Sto

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Side looking Unsigned int left_adc; left_adc = adc(0xE0); unsigned int adc(unsigned int temp) { ADMUX = temp; //selects ADC channel = x ; s ar s while(conversion_not_over()); //waits till ADC conversion completes ADCSRA |= 0x10; // clears ADIF flag ; }  _

_ 

{ unsigned int temp; tem = ADCSRA temp = temp & 0x10; // checks for ADIF flag return(!temp); }

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Reducing error using PD controller :

Error

PD

Motors

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Error calculating: If wall is on both sides _ – _ ; 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; + 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. 

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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Choosin a DC Motor o or w ear ea  Operating voltage 12V Depends on our application Some available speeds in market  30 RPM  60 RPM 

150 RPM  350 RPM  1000 RPM

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Red wire

Black wire

Positive

Negative

Clock wise

Negative

Positive

Anti clock wise

1

0

Clock

0

1

Anti clock

Direction of rotation

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i- irection contro o

otor bidirectional driving of DC motor

Direction

Pulse to

Clock wise

A and C

n

oc w se

an

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-

’

The most commonly used H-Bridges are L293D and L298  L293D has maximum current rating of 600ma  L298 has maximum current ratin of 2A  Both has 2 H-Bridges in them  These are desi ned to drive inductive loads such as relays, solenoids Can be used to drive 2 DC motors or 1 ste er motor 

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PWM

STEPPER MOTOR 

STEPPER MOTOR is a brushless DC motor whose rotor rotates in discrete an ular increments when its stator windin s 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 .

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4 – Lead stepper

6 – Lead stepper

5 – Lead stepper

8 – Lead stepper

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Full Ste drivin of Ste

er 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 Ste drivin of Ste

er Motor

Full step 2 phases active

4

3

2

1

1

1

0

0

0

1

1

0

0

0

1

1

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Half Step driving of stepper motor

4

3

2

1

1

0

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 o eratin volta e 1.8 degree step 6 Lead 250 to 500 ma of current or



Size and shape depends on application  In most of the robotics cube sha ed motors are preferred with frame size of 3.9 to 4 cm

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Commonl used IC’s for drivin Ste 

er motor

ULN2803 It has 8 channels It channel has maximum current rating of 500ma can be used to drive 2 unipolar stepper motors • •

•



L297 & L298

UDN2916

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Bi – Polar drivin of Ste

er 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); = x ; delay(65); = 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 tar et reached

Update Output compare register No Wait et

Yes Stop timer

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Chopper Driving: 

For better erformance of Ste and current should be limited .

ers the should be over driven

For example a 5 V 500ma motor can be driven at more than 15V but current in the coil should be limited to approximately . 

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Methods of current limiting : 

Traditional method of usin a resistor of a series with common terminal.



ro riate ower in

This method is not recommended as there will be huge power .

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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

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 ou ave curren capac y more an ma

Can provides high current at 1.2 V Can be charged by Constant Current or Constant Voltage chargers



Li – Ion Should be charged using CCCV charger .

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