Continuous rotation transmission part 2: Universal joints

Universal joint 1 

Axles of the two shafts may be:

1. Parallel and coincident

2. Parallel and distinct (with eccentricity)

3. Intersecting

4. Skew

Universal joint 2 

This low torque joint allows axial shaft movement. The angle between shafts must be small.

Output velocity is not constant.

  

 Universal joint 3 

This pump type coupling has the reciprocating action of sliding rods in cylinders.

Centers of spherical joints are always in the plane that bisects the angle α between the two shafts even when α changes so it is a constant velocity joint.

Pin universal joint 

It is a constant velocity joint.

There is a spherical joint between pink shaft and green one.

For each shaft the opposite contact straight lines must be symmetric about the rotary axis and have a common intersection point with it. Angle between the two shafts reaches up to 30 deg. in this video. The mechanism cannot be used for reversing rotation because of large backlash.

Study of Cardan universal joint 1 

Universal joints allow to adjust an angle between input and output shafts even during rotary transmission. This case shows +/- 45 degrees regulation. It is clear that single Cardan joint is not of constant velocity when A differs from 0 deg.

Study of double cardan universal joint 1a 

Double Cardan drives allow to adjust relative linear positions between the input and output shafts even during rotary transmission. The output velocity is always equal to the input one (constant velocity joint) because their shafts are kept parallel each other.

The pin axles on the intermediate half shafts (in yellow and in violet) must be parallel each other.