There are two kinds of electro-modulation for multi-rotor UAV, one is electro-modulation with BEC and the other is OPTO electro-optic-modulation without BEC. BEC is the meaning of battery-free circuit in English. It has shunt power supply capability. It can change the power battery voltage to 5V voltage to supply power to flight control. But if all four electrical adjustments of a Four-rotor supply power to flight control, it is easy to be confused, so we usually only keep one electric adjusting power supply. Flight control needs to be provided if the flight control uses an electrical control without BEC.