Most electric bikes and scooters include four primary parts: the battery pack, the motor, the throttle and the controller.  The controller stands "between" the throttle and the motor and controls the motor.  On small, low-power drive systems, a simple on/off switch or relay may be the only controller.  But for systems using motors rated above 250 watts, a controller generally limits how quickly the motor accelerates and its maximum speed.  The manufacturers set the controllers on all its motors (300, 350, 400, and 600 watts) to limit the LEV maximum speed to 16 mph.