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 the crashes of the helicopter, the motor current draw will significantly increased because of the sudden stop of the rotor. The speed controller may be damaged if the user forget to pull down the throttle stick immediately after a crash.

This fuse will open the circuit if a high current  pass through, but the fuse is reset-able in few minutes after cool down.