code: def left_motor(self, speed, durationS=-1.0):
          
          if speed > 0:
              self.left_rev(min(abs(speed), 255))
          else:
              self.left_fwd(min(abs(speed), 255))
          if durationS > 0:
              self.board.sleep(durationS)
              self.left_stop()
docs: Basically the same as drive(), but omitting the right motor.