GEARMOTORS

  A gearmotor,  consists of a motor and speed reducer in an integral assembly. The motor portion of the assembly can be either dc or acpowered. The speed reducer portion can use spur, helical, or worm gears. Gearmotor sizes range from fractional to above 200 hp. The main advantage of a gearmotor is that the driving shaft can couple directly to the driven shaft, thus in many situations making belts, chains, or separate speed reducers unnecessary. Also, because the motor and speed reducer are aligned during manufacture, field installation is simpler. Starting and running torque must be considered separately because starting characteristics of the motor and gearing differ. Applications needing high breakaway torque require careful selection of the motor—splitphase polyphase, capacitor-start, and brush types have high starting torque.

  The gearmotor manufacturer should analyze any application with high inertia. This problem is especially important with self-locking right-angle gearmotors. Because the rotor and load are rigidly connected by the gear train, both must stop in the same time. In severe cases, momentary power failure may be all that is necessary for a high-inertia load to destroy the gear train. Overhung loads are applied to the output shaft of the gearmotor whenever the gearmotor is connected to the application by belts, chains, or gearing. Applications requiring cams, hoisting drums, or switches at the output shaft can also cause very high overhung loads on gearhead bearings. It is inherent in gearmotors that overhung load capacity decreases as delivered torque increases.