4pcs Emax 20a Blheli ESC 2a 5v Bec Speed Controller for Rc 250 Qav250 Quadcopter Multicopters Rotation direction of the motor is programmable: normal, reverse or bidirectional All parameters can be programmed via using a program card or a transmitter, including default settings Multiple protection features including low voltage cut-off protection/over-heat protection/throttlesignal loss protection Alarm to help you find the devices: keep the throttle on FULL ON position for a while, the ESC will help Throttle range can be configured and is fully compatible with all receivers, providing smooth, linear and precise throttle response