In the commercial cars, the generally conventional gearbox is used, but in an all-terrain vehicle and military combat vehicle automatic transmission is used, where continuous variable transmission (CVT) is coupled with the epicyclic gearbox or generally recognized by the planetary gearbox. In this type of gearbox, we are establishing a gear train with high torque in a compact and light package. Here we are designing single stage planetary gearbox with co-axial alignment. Epicyclic gearing arrangements are comprised of four different elements that produce a wide range of speed ratios in a compact layout. These elements are: (1) Sun gear, an externally toothed ring gear co-axial with the gear train; (2) Annulus, an internally toothed ring gear co-axial with the gear train; (3) Planets, externally toothed gears which mesh with the sun and annulus; and (4) Planet Carrier, a support structure for the planets, co-axial with the train. The name "epicyclic" is derived from the curve traced by a point on the circumference of a circle as it rolls on the circumference of a second fixed circle.