void backOff(int distance, int speed){
  float time;

  reset_encoder(SHAFT_LEFT);
  reset_encoder(SHAFT_RIGHT);
  time=seconds();
  wheelLeft(-speed);
  wheelRight(-speed);
  while((read_encoder(SHAFT_LEFT)+read_encoder(SHAFT_RIGHT)<distance)
	&& (seconds()-time < BACK_OFF_TIMEOUT)){ sleep(0.02);}
  ao();
}