Universal Joint
The universal joint mechanism (Hooke's coupling) transmits rotary motion while allowing for various relative angles and displacements between the driver and follower.
The universal joint consists of four forks, pin-jointed to an intermediate member. at right-angles. The follower makes one revolution for one revolution of the driver but the velocity of the follower will vary from the driver when the axis are not collinear. With the driver at a uniform angular velocity, the angular velocity of the follower varies between cos a and 1 / cos a where a is the angle between the shafts. These variations in velocity must be considered in terms of inertia forces, torque, noise and vibration.
This hand crafted decorative model of the universal joint is made and sold by Pierre Olivier.
A double universal joint, shown, eliminates the variation of angular motion between driver and
follower by using two universal joints that cancel out the non-linearity. A common application of the double universal joint is in the drive shaft connecting an automobile engine to an axle.
