<div class="section abstract"><div class="htmlview paragraph">THE usefulness of planetary gear trains and the engineering techniques necessary for optimum design are discussed in this paper. A simple method for calculating planetary gear ratios is described which can be used to determine quickly the potential usefulness of any planetary configurations.</div><div class="htmlview paragraph">The author lists criteria which help to evaluate the potential of a planetary gear train schematic from the standpoints of gear noise and structural viewpoint.</div><div class="htmlview paragraph">Detailed design of individual members include spacing of the pinions, mounting considerations, thrust direction, lubrication, and stress evaluation.</div></div>