Gear Train is any combination of gear wheels by which motion is transmitted from one shaft to another shaft. In epicyclic gear trains, the axes of shafts on which the gears are mounted may move relative to a fixed axis.It is a motorized unit consisting of a SUN gear mounted on input shaft. Planet gears meshes with the annular gear. These planet gears are mounted on a common arm to which output shaft is fitted. Loading arrangement is provided for loading the system and to measure holding torque.