For use between the motor and 4-in-1 control unit, to protect your expensive speed controller with the over-current protection PTC resettable fuse devices.

During a crash, the motors current draw will significantly increased because of the sudden stop of the rotor. The speed controller may be damaged if the user forgets to pull down on the throttle stick immediately after a crash.

This fuse will open the circuit if a high current  passes through. The fuse is reset-able in a few minutes after cooling down.