Explorer robot without sensors

Usually the first robot you make when you get the NXT is the wheelbase with a bumper, you know, make it run into a wall, turn back and repeat.

To really get my point about saving sensors across, I made a robot like that without any sensors.

It works by turning the motors in regulated mode(constant speed, varying power) and measuring the actual power applied. If the robot runs into a wall, the firmware will apply extra power to the motors to keep them turning. With some tweaking, you can even detect which wheel hit the wall.

The commented code:

// define 2 variables for containing the actual speed
dseg segment
  aaspeed byte
  caspeed byte
dseg ends

thread main
Start:
  // turn the motors on, regulated
  OnFwdReg(OUT_AC, 50, OUT_REGMODE_SPEED)
  // wait for the robot to accelerate
  // it will apply full power here
  wait 1000
Forever:
  // get the actual power used
  getout aaspeed OUT_A ActualSpeedField
  getout caspeed OUT_C ActualSpeedField

  // print the power to the screen
  NumOut(0, LCD_LINE1, aaspeed)
  NumOut(0, LCD_LINE2, caspeed)

  // if one of the motors uses more than 75 power
  // jump to either LResistance or RResistance
  brcmp GT LResistance aaspeed 75
  brcmp GT RResistance caspeed 75

  // repeat forever
  jmp Forever

LResistance:
  // reverse, turn right, jump to start
  OnRevReg(OUT_AC, 50, OUT_REGMODE_SPEED)
  wait 2000
  OnFwdReg(OUT_A, 50, OUT_REGMODE_SPEED)
  wait 500
  jmp Start

RResistance:
  // reverse, turn left, jump to start
  OnRevReg(OUT_AC, 50, OUT_REGMODE_SPEED)
  wait 2000
  OnFwdReg(OUT_C, 50, OUT_REGMODE_SPEED)
  wait 500
  jmp Start
endt
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