Velocity Ratio of Epicyclic Gear Train

The following two methods may be used for finding out the velocity ratio of an epicyclic gear train.

1. Tabular method: Consider an epicyclic gear train as shown in fig:

Let, TA = Number of teeth on gear A and
TB = Number of teeth on gear B.

First of all, let us suppose that the arm is fixed. Therefore the axes of both the gears are also fixed relative to each other. When the gear A makes one revolution anticlock, the gear B will make TA / TB revolutions, clockwise.

Assuming the anticlockwise rotation as positive and clockwise as negative, we may say that when gear A makes +1 revolution, then the gear B will make (-TA / TB) revolutions. This statement of relative motion is entered in the first row of the table:

2. Algebraic method: In this method, the motion of each element of the epicyclic train relative to the arm is set down in the form of equations. The number of equations depends upon the number of elements in the gear train. But two conditions are usually supplied in any epicyclic train, some element is fixed and the other has specified motion. These two conditions are sufficient to solve all the equations and hence to determine the motion of any element in epicyclic gear train.