Videos | Donations | Imprint | Contact

The Constant Velocity Joint

Fullsphere! Now my new model is ready! And now I can realize angles much above 90°. Mathematically up to 180° but there are no infinite thin sticks.

There are two axles perpendicular to each other at the classical cardan joint. Therewith you can transmit a turning moment around a corner. But the known cardan joint has got the so called "cardan mistake". The turning moment is not transmitted 1:1 but it goes a bit ahead and then back. The more the joint is folded, the bigger is this effect.

The classical cardan-joint
Bild "Inventions:Kardan.gif"
with the axles


If you are sitting upon a tractor with a machine on a clinger and this machine is connected with the motor of the tractor, you will feel the vibes, if you drive a curve. Most farmers do not like this kind of music.


cardan mistake
Bild "Inventions:Kardanfehler.png"

On the blue circle moves the drawing axle of the cardan joint and on the green circle the axle, that is to this axle perpendicular. This axle is humped. At the time t = 0 stands at A a man on the equator, his dog is at B (or the North Pole). Now the man goes one latitude circle to the south until he reaches point A'. Now he draws the dog on the green circle in the direction C. The dog lands not at B' but at B". And B" lays not on the same latitude circle like B', as you can see on the picture. The more the joint is folded, the more southern the dog runs. If the man reaches the South Pole the dog stands on the equator at point C. So between the dog has to slow down. And this faster and slower causes the pulsing of the turning moment => the cardan mistake.
It is called mistake, because this effect is mostly unwanted.


There a some attempts to get rid of the cardan mistake.
The easiest is the Double Cardan Joint.

Bild "Inventions:Doppelkardan.png"
two combined cardan joints
(source of the picture: Wikipedia)

At this method a second cardan-joint is behind the first one. And so both cardan mistakes neutralizes each other. But the great disadvantage: the web in the middle must have the same angle towards both joints and if you fold the joint the distance of the axles move towards each other. All this is not so good.

The next attempt is the Rzeppa-Joint. Here the turning moment is transmitted by balls.

Bild "Inventions:Rzeppa_constant_velocity_joint.png"
(source of the picture: Wikipedia)

The balls roll within grooves parallel towards the axles of the turning. They can accommodate towards changing angles. But there are some disadvantages: the range of angles is small, the balls need much lubrication and there is a problem-position. It is possible, that when both axles lay on a straight line, the balls can get out of place. If that happens and you fold the joint at the one wrong position, the joint can break. That is not so good.

The next attempt is the Thompson coupling.

Bild "Inventions:Thompson_coupling.png"
Thompson coupling
(source of the picture: Wikipedia)

This joint is a bit complicated. The turning moment is transmitted on a 45° delayed cardan joint and this cardan joint is re-transmitted upon the next 45° delayed cardan joint. Therewith the inner cardan joints do not run away they are held. But this joint has a disadvantage: it cannot angles of 0°±2°. Therefore you must take care that it is always folded. At the Thompson coupling all axles are perpendicular. Obviously Mr. Thompson does not have the generic intersection formula.

The Soltuuli company has got the generic intersection formula.

I tinkered two models of joints out of wood, that have not the cardan mistake and not the disadvantages of the joints mentioned above. I made two videos. One of it I put on YouTube. The new constant velocity joint can fold up to 95°. Actual this all is obvious. You just have to use the thought of the Double Dogs here. Master and mistress travel on the 2-dimensional surface of a ball in circles with the same radius. They both hold a dog lead of the same length in their hands. So the dog has to run on a great circle in the middle. If master and mistress meet at a point the curve of the dog becomes indifferent. To avoid an outbreak you just have to run more couples with dogs around the globe. It is quite simple. The couples are not forced to run around the same globe with the same radius. The radius of the globe is equally whether for the angles of the movement.

If the video could not displayed, try the Firefox browser!

The new Constant Velocity Joint
from 0° to 90°

Bild "Videos:Constant_Velocity_Joint.png"
... and as a video for the YouTube customers.

On the homepage somebody has made himself his own mind towards the constant velocity joints, too. But he forgot to make the arms of the dogs-hold-dog device turnable on both sides. And so it cannot function. If you would build it as shown, it would break immediately, when you fold it. The other pictures are even more complicated Thompson couplings. Curtly over is besides, too.