U-joint, CV-joint, Thompson coupling

[DCockey]

Originally Posted by brian eiland

I'm not saying that Cardan joints don't accept axial loads, but when you are directing pushing maybe 200-400 hp thru them to push your vessel, i don't believe they would hold up for long

And my point was the Thompson joint, which is the subject of this thread, would not be any better handling thrust than a Carden joint.

Here is that dwg. I'm not so sure you could place the trust bearing in the rotating member and have it do its job properly. I suspect the trust bearing is after the 'pivotable joint' where the shaft enters the hull??
[ATTACH]67033[/ATTACH]

That's the same drawing I looked at. My guess is the thrust bearing is in the cylinder on the propeller side of the swivel joint. The thrust would then go through the pivots for the swivel joint.

Understood. One must also consider extracting the prop shaft for servicing, particularly in the case of bending the shaft upon striking an object

The setup I looked at was designed to be serviced, and may be easier to service than a conventional single piece long prop shaft.

[Stumble]

Dcockey,

I can only go by their sales pitch, but the Thompson joint is supposed to be designed to accept high axial loads. In fact it is part of their sales pitch if you review their materials.

[DCockey]

Originally Posted by Stumble

Dcockey,

I can only go by their sales pitch, but the Thompson joint is supposed to be designed to accept high axial loads. In fact it is part of their sales pitch if you review their materials.

Understand, but is it any better than a simple Carden joint? If so why?

[philSweet]

I didn't see anything in the videos that showed it, but if the joint has true point centricity as claimed, it should be possible to add a separate thrust bearing with spherical geometry connecting the shafts that only does thrust, and let the gimbals transmit the torque. You can see that the knuckling is prevented by caging one shaft in the gimbal of the other. Ought to be able to put a thrust bearing there.

[Petros]

DCocky,

the cardan joint is not constant velocity, so if you want smooth power transmission AND the ability to take thrust, the Thomson joint is the only one that can provide both.

As the cardan joint rotates the speed changes slightly up and down, this will add a vibration to the drive train that either has to be dampened or just tolerated. this also puts strain on the drive train and could reduce the fatigue life of the drive train, including transmission gears, input/out shafts, etc.

That is why this joint is so much better. If you actually watched the video demonstrations you might have realized this issue.

[DCockey]

I already knew a Cardan joint is not constant velocity. Perhaps if you read the thread you would realize my references to Cardan joints were in response to Brian who brought up the Cardan joint as one which does not like axial thrust.

Whether a CV joint is needed over a Cardan joint depends on the angle difference between the shafts and how much speed variation is acceptable in the particular application. The drawing of the Amartech RPS system shows a small shaft angle change when deployed and operating. A system with Cardan joints or most CV joints should be designed so that the joints do not operate for sustained periods at zero angle to minimize wear in the joints.

Petros, have you surveyed all available CV joints to know that the Thompson joint is the only one with axial thrust capabilities?