Description: A planetary gear train, made using a planet and ring gear rotating on the same two shafts as the base chain, with an outer ring gear. Planetary gear trains are widely used in automotive machinery as well as in servo-motor speed reducers found in robotic machines. Specifically, it has been used in the transmissions of helicopters, automobiles, wind turbines, aircraft engines. This gear, specifically, is number G3 in the Releaux Collection.
 

There are 220 models in Cornell University’s Reuleaux Collection, which were built in the late 19th century to demonstrate the elements of machine motion, as theorized by the German engineer Franz Reuleaux.