Starter Motor: Description and Operation

These planetary gear reduction starters consist of an armature, a frame with permanent magnet poles, a planetary drive mechanism, a solenoid and a housing.
The starters use a planetary gear drive between the armature and motor pinion. The gear drive allows the use of permanent magnets eliminating heat that normally would be produced by coil fields, and also simplifies motor construction since there are no internal field coils and connections.