A permanent magnet rotor of a generator is used to excite a electromagnet stator to generate electric power for the generator and to control a disengagement mechanism whereby the generator can disengage from an accessory, such as a gear box drive shaft, when the generator is not working properly. The permanent magnet is affixed to an outer ball screw which normally rotates with an inner ball screw that is operatively engaged to the accessory. An increased load to the electromagnet stator slows or stops rotation of the permanent magnet rotor and outer ball screw, causing the inner ball screw to move axially from the outer ball screw and away from an accessory and toward a re-settable lock.