Epicyclic gear drive illustrates motion of a gear train consisting of a
60-tooth sun gear and arm carrying a 24-tooth planet gear riding
extremely on the sun gear. Epicyclic motion is the path traced on a
fixed end plate by a scribing point attached to the planet gear. An epicyclic drive has its planet gears integrated into separately built planet assemblies. Each planet assembly includes a pin which extends through the planet gear and an antifriction bearing located between the gear and the pin. The bearing also has rolling elements organized in two rows between the inner and outer raceways. The pins have mounting ends which lie beyond the ends of the planet gear to anchor the planet assembly in a carrier. Seals fit into the planet gear and around the pin and retain grease within the bearing and prevent oil that lubricates the teeth from entering the bearing and deteriorating the grease. The bearing is set with considerable precision so the planet gear does not skew with respect to sun and ring gears with which it meshes during operation at the epicyclic drive.
They are useful in illustrating characteristics of important class compound motions. They are also used in automatic door operator.