Epicyclic Gear Train:

In planetory gear train or epicyclic gear train, the axis of at least one of the gears also moves associated to the frame. Given figure shows an epicyclic gear train. This consists of two gears S & P. The axes of these gears are linked with each other through an arm a. If arm is fixed, these two gears comprise a simple gear train. If gear S is fixed and arm rotates around axis of gear S, this constitute an epicyclic gear train. However it is not essential that S is fixed, it can have some known rotational speed. As gear P moves around gear S as a planet moving around sun, it is also known as planetary gear and gear S is known as sun gear.

Since the arm rotates, planetory gear P moves around gear S. Epicyclic gear trains are utilized in automotive transmission, vehicle differential, computing devices, etc. An epicyclic gear train may be designed to provide large gear ratio, also that is not possible in other gear trains in shorter space.

              Epicyclic Gear Train

As the operation of an epicyclic gear train is different from other gear trains, there are particular methods to analyse this gear train. The methods are following:

 (a) Algebraic Method, and

 (b) Tabular Method.