U-joint, CV-joint, Thompson coupling

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.

 

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?

 

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.

 

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.

 

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?

 

I think this is a newer video on that Thompson Constant Velocity Joint

https://www.youtube.com/watch?v=UEvaOg7glKk

 

Retractable, steerable shaft drives have always been possible and efficient with twin U/V`s and a sliding spline and a thrust bearing on the propeller shaft.
Shaft drives have been used forever in boats like this but only in a fixed position.
I would just love to see some one give solid evidence that this is not good engineering practice.With this set up you can have 30 degrees of steering and rise and fall on a retractable shaft.
Taking a wild guess about anything mechanical is a bit useless, you need an observable experiment with mathematical proof thrown in.
https://www.youtube.com/channel/UCWplXLumAtHxb-0LEMJmoIg

http://www.4xshaft.com/bamf.asp

 

ttp://www.fourwheeler.com/how-to/1006or-universal-joint-cv-joint-transferring-torgue/h

CV Joints
Constant velocity (CV) joints behave just as their name implies. The joint is often comprised of a double U-joint (double-cardan) assembly that allows the joint to articulate through angles while always providing a constant, smooth transfer of rotational energy.
http://www.fourwheeler.com/how-to/1006or-universal-joint-cv-joint-transferring-torgue/h

Or try www.fourwheeler.com/
and search transferring torque.

 

"I am still looking for an inexpensive thrust bearing, the CV joints aren't the problem."

Rather than inexpensive , why not one that can be replaced with out pulling the boat?

The first haul not required will pay for the cost difference.

 

U-joint,

Why is a thrust bearing expensive? it should be cheap.
If you had a retractable shaft drive fitted in your boat you could remove a thrust bearing, a propeller shaft or propeller on water.

Just disconnect the TWIN U/V joints with the sliding spline from the g/box,
and slide the prop shaft to the rear to clear the thrust bearing and replace the thrust bearing from it`s cage, or replace the cage too. Easy peezy.
I could easily replace a propeller from my boat on the water.

 

U

Why would you need a Thompson C/V joint when you can use any of the tried and easily available joints now available to build a retractable, or steerable propulsion or a conventional shaft drive.

 

U-joint,

A DOUBLE cardan shaft is what makes a constant velocity joint.

 

The big problem with cardan shaft couplings is that they are not constant velocity, so they exhibit vibration from the constant acceleration and deceleration in the system. This also uses up energy.

The Thompson coupling reduces vibration and energy loss and as a result has proved to last longer in use.

I've played with the Thompson system and it is being evaluated in some interesting and very tough applications.

I've worked with Cardan shaft couplings in the past and seen the failure results, when comparing a boat to a car you also have to understand that in a boat the load is continuous, it's like driving a car up hill for it's whole life. In practice automotive joints have an easier time. Other joints I've worked with in the past include The Marine Joint from PowerTrain in Norway a nice CV design that takes thrust. Now most of my work is bearings rather than the couplings.

 

http://www.boatdesign.net/forums/at...able-inboard-outboard-why-not-diagram-i_o.jpg

The two back to back U/V joints ( shown no 3 in diagram)as used universally in machinery everywhere do the same job as cardan shafts and C/V joints.Where is the problem? well proven in service. No trouble fitting thrust bearings to prop shafts.