Design of Transmission Shafts

The design specifications required for a transmission shaft are the power transmitted by the shaft and its rotation speed.

Based on these specifications, the material and cross-sectional dimensions of the shaft are chosen by ensuring that the maximum shearing stress allowed by the material remains within the elastic limit while transmitting the required power at the specified speed.

Now, the power associated with a system depends on the torque applied. Rearranging the terms, the torque applied to the shaft can be calculated. This equation accounts for both power requirements and rotational frequency of the shaft.

The calculated torque and the maximum allowable stress are then applied in the elastic torsion formula to determine the minimum allowable value for the shaft radius.

For a solid circular shaft, this ratio of the polar moment of inertia to the radius of the shaft varies as the cube of the shaft radius. Substituting it gives the minimum required value for the shaft radius.

For a hollow cylinder, the minimum allowed value of the outer radius of the shaft is calculated.