Wall-ter

Views:6431Difficulty: 3 Status: Development
Screen_shot_2013-02-03_at_3.16.26_pm

Wall-ter is a wall following robot.

Using 3 proximity sensors Wall-ter senses walls. Then he follows them! A few simple rules for how wall-ter moves combine into a complex emergent behavior. Corners are always tricky as you may see in the video below. The three proximity sensors are available at pololu , they cost $6.95 and give a 0 signal when something is near them and 1 if not. Hook them up to any general purpose I/O pin set for reading.
Images
1

Heads-Up Wallter

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Wall-ters 3 proximity sensors are strategically located so that walls will be found and followed.
Video
0

Video

Watch wall-ter roll! He finds walls and follows them. He tries not to crash into them. Corners can be tricky as the video shows.
Code
2

Arduino Code for Wall Following

This code assumes there are 3 digital (binary) proximity sensors arranged with two pointing to the left but a different distances and one sensor pointing forward with a slight inclination towards the left side. So 3 sensors with 2 possible values for each sensor, how many distinct readings can we have? 2 to the 3 or 8 . So here is the code that dictates what to do in each of the 8 possible situations: 
if (fwdIn == LOW && midIn == LOW && leftIn == LOW) {    go_backward();  }   else if (fwdIn == LOW && midIn == LOW && leftIn == HIGH ) {    turn_right();  }  else if (fwdIn == LOW && midIn == HIGH && leftIn == LOW ) {    stay(); }  else if (fwdIn == LOW && midIn == HIGH && leftIn == HIGH ) {   turn_right(); }  else if (fwdIn == HIGH && midIn == LOW && leftIn == LOW ) {   turn_right(); }  else if (fwdIn == HIGH && midIn == LOW && leftIn == HIGH ) {   go_forward();   wall_timer = millis(); }  else if (fwdIn == HIGH && midIn == HIGH && leftIn == LOW ) {   go_forward();    wall_timer = millis(); }  else if (fwdIn == HIGH && midIn == HIGH && leftIn == HIGH ) {   if( millis() - wall_timer > 1500 ) go_forward();    else turn_left();  } }
Each of those simple instructions carried out when the sensors are activated in a certain way adds up to a more simple elegant behavior. This robot seems to follow walls. This is a small example of emergence , here's a little example of emergence from MIT exploring emergence .
Download File 
/* LucidTronix Wall Follower * autonomous robot * 3 proximity sensors  * Details pictures, explanation at: * http://www.lucidtronix.com/tutorials/5 */#include   Servo right;Servo left;int fwdSensor = 0;int midSensor = 1;int leftSensor = 2;int high_pwm = 110;int low_pwm = 75;boolean wall_near = false;unsigned int wall_timer = 0;void setup() {    right.attach(6);  left.attach(5);    pinMode(fwdSensor, INPUT);  pinMode(leftSensor, INPUT);  pinMode(midSensor,INPUT);}void loop() {  int leftIn = digitalRead(leftSensor);  int midIn = digitalRead(midSensor);  int fwdIn = digitalRead(fwdSensor);  if (fwdIn == LOW && midIn == LOW && leftIn == LOW) {    go_backward();  }   else if (fwdIn == LOW && midIn == LOW && leftIn == HIGH ) {    turn_right();  }  else if (fwdIn == LOW && midIn == HIGH && leftIn == LOW ) {    stay(); }  else if (fwdIn == LOW && midIn == HIGH && leftIn == HIGH ) {   turn_right(); }  else if (fwdIn == HIGH && midIn == LOW && leftIn == LOW ) {   turn_right(); }  else if (fwdIn == HIGH && midIn == LOW && leftIn == HIGH ) {   go_forward();   wall_timer = millis(); }  else if (fwdIn == HIGH && midIn == HIGH && leftIn == LOW ) {   go_forward();    wall_timer = millis(); }  else if (fwdIn == HIGH && midIn == HIGH && leftIn == HIGH ) {   if( millis() - wall_timer > 1500 ) go_forward();    else turn_left();  } }void turn_left(){  left.write( high_pwm);     right.write( high_pwm );  }void turn_right(){  left.write( low_pwm );  right.write (low_pwm );}void go_forward(){  left.write(high_pwm);     right.write( low_pwm );}void go_backward(){  left.write(low_pwm);     right.write( high_pwm );}void stay(){  left.write( 90 );     right.write( 90 ); }
Parts
parts

Parts

Title Description # Cost Link Picture
Servo Motor Continuous rotation servo motor. 2 $13.95 Link 09347-1
Proximity Sensor Digital proximity sensor. 5vValue:5v 3 $6.95 Link 0j1178.600
Servo Wheel Wheel that attaches easily to servo motors. 2 $4.0 Link Servowheel_lrg
ATMEGA168A-AU IC MCU AVR 16K FLASH 32TQFPValue:1.8 V ~ 5.5 V 20MHz 1 $2.43 Link Screen_shot_2012-12-28_at_7.31.53_pm

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Permalink: http://lucidtronix.com/tutorials/5
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