def _set_speed(self, motor, speed):
        """
        Change the speed of a motor on the controller.

        :param motor: The motor to change.
        :type motor: ``int``

        :param speed: Speed from -100 to +100, 0 is stop
        :type speed: ``int``

        """
        self._validate_motor(motor)
        en, in1, in2 = self._motors[motor-1]

        if speed == 0:
            en.pwm_stop()
            in1.set(False)
            in2.set(False)
        elif speed > 0:
            en.pwm_start(abs(speed))
            in1.set(True)
            in2.set(False)
        else:
            en.pwm_start(abs(speed))
            in1.set(False)
            in2.set(True)
Change the speed of a motor on the controller.

        :param motor: The motor to change.
        :type motor: ``int``

        :param speed: Speed from -100 to +100, 0 is stop
        :type speed: ``int``