Wall Following Examples (video and code)

Comments

• Martin_H Posts: 4,051

  2012-04-02 19:24 edited 2012-04-02 19:24

  This is the two sensor wall following example. It uses a front bumper coupled with a Ping))). The bumper prevents a collision with a wall in front while the robot looks sideways with the Ping))). It then uses that distance to determine if one or both wheels need to turn to maintain distance. When the front bumper triggers the robot turns to avoid the wall in front. Again the code is really simple and only requires a single variable.
  
  [video=youtube_share;AQK6b2CNTrg]
  
  Here's the code which is nearly identical to the previous sample except for a slightly altered main loop.
  

  ' ==================================================  ============================
  '
  '   File...... AdvancedWallFollow.BSE
  '   Purpose... The robot follows a wall using an ultrasonic sensor and front bumper
  '   Author.... Martin Heermance
  '   E-mail.... mheermance@gmail.com
  '   Started... 2012 April 2nd
  '   Updated... 2012 April 3rd
  '
  '   {$STAMP BS2e}
  '   {$PBASIC 2.5}
  ' ==================================================  ============================
  
  ' ------------------------------------------------------------------------------
  ' Program Description
  ' ------------------------------------------------------------------------------
  ' This program can be used with a CBA or Boe-bot to follow a wall using a Ping)))
  ' and a front bumper.  The Ping))) points to the right and keeps the robot away
  ' from the wall while the bumper prevents front collisions the basic concept used
  ' is from page 608 of "Robot Builder's Bonanza" by Gordon McComb
  
  ' ------------------------------------------------------------------------------
  ' Revision History
  ' ------------------------------------------------------------------------------
  
  ' Pin allocations.  You might need to tweak the Ping))) pin.
  Bumper         PIN   9  ' Pin for front bumper (tactile or IR)
  Ping           PIN  10  ' Pin for PING))) Sensor
  RMotor         PIN  12  ' Pin for right servo
  LMotor         PIN  13  ' Pin for left servo
  
  ' These values need tweaking for each robot's servos.
  Speed075L      CON 831  ' Fast left
  Speed075R      CON 658  ' Fast right
  Speed050R      CON 685  ' Slow right (to arc)
  
  ' These values control distance from the wall and sharpness of left turn
  MinWallDist    CON   6
  MaxWallDist    CON   8
  TurnCount      CON   40
  
  ' Standard values from Ping))) example
  Trigger        CON    5 ' trigger pulse = 10 uS
  Scale          CON $200 ' raw x 2.00 = uS
  RawToIn        CON  889 ' 1 / 73.746 (with **)
  RawToCm        CON 2257 ' 1 / 29.034 (with **)
  
  ' Trigger Ping)))
  IsHigh         CON   1
  IsLow          CON   0
  
  ' This program is so simple it only needs a single variable to
  ' compute and test the distance to the wall.
  X              VAR Word
  
  ' Execution starts here
  Main:
    ' Pause at start of program to let user set down robot.
    PAUSE 1000
  
    DO
      ' If we are not close to a wall in front
      IF (Bumper = 1)  THEN
        ' find out how close to a wall to our right.
        GOSUB PingDistance
  
        ' If we are too far from the wall pulse the left motor
        ' else if we are too close to the wall pulse only the right
        ' otherwise we are in the goldilocks zone and can do both
        IF (X > MaxWallDist) THEN
          PULSOUT LMotor, Speed075L
        ELSEIF (X < MinWallDist) THEN
          PULSOUT RMotor, Speed075R
        ELSE
          PULSOUT LMotor, Speed075L
          PULSOUT RMotor, Speed075R
        ENDIF
        PAUSE 15
      ELSE
        ' We're about to smack into a wall so turn sharply left!
        FOR X = 1 TO TurnCount
          PULSOUT RMotor, Speed050R
          PULSOUT LMotor, Speed050R
          PAUSE 15
        NEXT
      ENDIF
    LOOP
  
    ' We'll never get here, but it's nice coding style.
    END
  
  ' PingDistance - reads the distance at the current head angle.
  ' Inputs:
  ' Outputs:
  '   X - distance in inches.
  PingDistance:
    Ping = IsLow                                ' make trigger 0-1-0
    PULSOUT Ping, Trigger                       ' activate sensor
    PULSIN  Ping, IsHigh, X                     ' measure echo pulse
    X = X */ Scale                              ' convert to uS
    X = X / 2                                   ' remove return trip
    X = X ** RawToIn                            ' convert to inches
    RETURN
  

  
  Attached for easy downloading:
  AdvancedWallFollow.bse

  bse

  bse

  AdvancedWallFollow.bse

  4K

  AdvancedWallFollow.bse 3.6K
• Matt Gilliland Posts: 1,406

  2012-04-02 20:32 edited 2012-04-02 20:32

  Sweet Martin! Will you be coming to Expo and bringing that little guy with you?
  -MattG
• Martin_H Posts: 4,051

  2012-04-03 06:24 edited 2012-04-03 06:24

  Thanks Matt. Unfortunately I can't make it due to prior commitments and the long flight.
  
  I published the videos and code to the forum in the hopes that someone who goes might use them and have some fun with them. They should run on a Boe-bot with just a Ping))) as no servo is used, one of the whiskers would work as the bumper.