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Making of Micromouse. P.Raghavendra Prasad Final Yr EEE. INTRODUCTION. Micromouse is an autonomous robot designed to reach the center of an unknown maze in shortest possible time and distance . M I C R O C O N T R O L L E R. MOTOR DRIVER.

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Making of Micromouse

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    1. Making of Micromouse P.Raghavendra Prasad Final Yr EEE

    2. INTRODUCTION Micromouse is an autonomous robot designed to reach the center of an unknown maze in shortest possible time and distance .


    4. Basic components of Micromouse: • Sensors • Motors • Microcontroller • Batteries www.raghu.conr

    5. 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

    6. Sensors • Commonly used sensors in the field of robotics • IR Digital sensors • IR analog sensors

    7. 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.

    8. Designing a transmitter : • Use IC 555 in Astable mode • For approximate 50% duty cycle take Ra = 1 k ohm

    9. Receiver :

    10. 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

    11. IR Analog sensor

    12. Modulate IR rays to avoid Ambient light effect : Astable oscillator at frequency greater than 1KHz Transmitter IR led ADC of Micro-controller High pass filter , Cut-off freq more than 300Hz Peak Detector Receiver IR Photodiode obstacle

    13. High-Pass filter :

    14. Peak Detector:

    15. Errors involved in mouse movement : Forward error: Forward errors begins when a mouse is either too close or too far from the wall ahead

    16. 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

    17. Errors involved in mouse movement : Heading error: Heading error is known as pointing at walls rather than down the middle of the cell

    18. Commonly used Sensor arrangement : • Top Down • Side Looking SENSORS

    19. Top Down

    20. Side looking sensors :

    21. Initialize ADC Select ADC channel Start ADC ADC conversion complete N0 Yes Read ADC value Stop

    22. 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); }

    23. Reducing error using PD controller : Error PD controller Motors

    24. 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

    25. 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 .

    26. 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

    27. 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

    28. Drive basics of DC Motor

    29. Bi-Direction control of DC Motor H-Bridge Ckt using transistors for bidirectional driving of DC motor

    30. 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

    31. PWM

    32. 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.

    33. 5 – Lead stepper 4 – Lead stepper 6 – Lead stepper 8 – Lead stepper

    34. Full Step driving of Stepper Motor Full step wave drive

    35. Full Step driving of Stepper Motor Full step 2 phases active

    36. Half Step driving of stepper motor

    37. 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

    38. 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

    39. ULN2803

    40. Bi – Polar driving of Stepper Motor

    41. 5 – Lead stepper 4 – Lead stepper 6 – Lead stepper 8 – Lead stepper

    42. 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

    43. SW for steppers : • Use timers to create delay. • Use Clear Timer on Compare match • or • Normal Mode

    44. Initialize timer Interrupt routine Give Pulse to stepper Start Timer Is Stepper target reached Update Output compare register No Wait Reti Yes Stop timer

    45. 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 .

    46. 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.