Techleads ESC (electronic speed controller) ESC 30 amp 30A Brushless Motor Speed Controller RC BEC ESC for Quadcopter Plane Helicopter | Drone Quadcopter Science Project Interconnect Electronic Hobby Kit

An electronic speed control(ESC) follows a speed reference signal (derived from a throttle lever, joystick, or other manual input) and varies the switching rate of a network of field effect transistors (FETs) .By adjusting the duty cycle or switching frequency of the transistors, the speed of the motor is changed. The rapid switching of the transistors is what causes the motor itself to emit its characteristic high-pitched whine, especially noticeable at lower speeds.