When we couple one single joint with two shafts (of which the driving one is rotating at a constant speed) forming an angle, we cause a periodic variation of the driven shaft, exactly four fluctuations per revolution.

The difference between the maximum and the minimum speed of the driven shaft depends on the angle formed by the two shafts. The difference grows with the increasing of the angle °.

To have a homokinetic transmission, you have to fit either two opposite single joints (paying attention that the two central yokes lie on the same plane and the angles are equal) or a double joint.

The irregularity caused by the former articulation is cancelled by the latter. The overall lenght resulting from the coupling of the two single joints is even more reduced using a double joint. In other words,the double joint is to be considered as the shortest homokinetic transmission.

For low speed applications (Max 1000 R.P.M.) joints with plain bearings (rubbing bearings) are suggested: types S, G/GB. They are able to support shock loads,motion reversals, irregular runnings and relatively high torques. The working angles must be kept between 500 and 1000 R.P.M.

For high rotation speeds, relatively low torques or wide angles, joints with needle roller bearings (type H) are to be preferred. They can reach 4000 R.P.M. always relating to the angle.