Universal joints

[pontiacjack]

I need a "primer" on u-joints. I don't even know the nomenclature for a typical cross-type automotive u-joint (steel cross with four needle bearings)? And I've never seen (or tried to derive) the math (output angular position vs. input as a function of running-angles, etc.). For a two-joint drive (typical front & rear of a driveshaft), what orientation of the joints provides maximum cancellation of angular velocity disturbances? Is it true that equal-but-opposite run-angles of the two joints is most desirable?

 

[BrianPetersen]

You used a panhard or Watts link together with a leaf-sprung axle? That's an additional axle control device that can fight with the lateral location given by the leaf springs ...

 

[Tmoose]

http://www.ponysite.de/transam212777.htm

http://www.ponysite.de/212777_wattslinkage.jpg

page 16 here, allegedly

http://www.shelbytransam.com/walt/ShelbyTA/1970_TA_Mustang_Suspension.pdf

allegedly a 1969 trans am car with narrowde leafs and a watts linkage

http://1.photos.ebizautos.com/used-1969-shelby-trans_am_mustang-boss302-9423-5421166-21-640.jpg

http://1.photos.ebizautos.com/used-1969-shelby-trans_am_mustang-boss302-9423-5421166-25-640.jpg

 

[NormPeterson]

You used a panhard or Watts link together with a leaf-sprung axle? That's an additional axle control device that can fight with the lateral location given by the leaf springs ...

I think the trick is setting the PHB or WL at the proper height.


Norm

 

[evelrod]

Brian, in our current Lotus Cortina vintage racer the PHB works out well enough. If care is not taken in the location (with limited adjustability) some adverse axle movement can be expected. In roadracing, suspension movement is rather limited and lateral movement is also quite small. Yes, I have several competitors that think the way you do (some professional teams also agree with you). All I can say is that my way works for us. I have had quite a few drivers in the seat over the years and, so far, NO complaints about the handling and drivability of the suspension setup. PHB aside, the big bugaboo with the leaf spring/live axle was "roll oversteer" which was more difficult to overcome.

Tmoose, I've competed against Bud Moore cars in vintage racing, including one Palm Springs Grand Prix in the late 80's where they were driven by Parnelli Jones and George Follmer. PJ broke and at the checker I could see Follmer's Mustang coming up to lap me. Good stuff!

Rod

 

[evelrod]

Well, that did not work out all that well. I clicked on the wrong file. This is the one I wanted to show.

Sorry 'bout that.

Rod

 

[pontiacjack]

Well... thanks for the help understanding Cardan joints. I trust that my truck will work out just fine.

Internet searches let me down, however, on a description of ball-and-trunnion style joints, such as used in my '55 Plymouth (and I'm too lazy to work out the math myself). Anybody know (or direct me to) the expression for output velocity vs. run-angle for such a joint (at constant input velocity)?

 

[GregLocock]

Lokks like a tripod joint to me. For all practical purposes they are true CV joints (they aren't but it is not far off).

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

Ah, I see they only have two rollers. As such you will get a strong 2nd order component.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[pontiacjack]

Thanks, Greg. Is that "strong" component in the same ballpark as a Cardan joint? The output rotational velocity of a Cardan joint at a run-angle of five degrees has a maximum second-order variation from .996 to 1.003 of the constant input velocity. Is a ball-and-trunnion variation even "stronger" than this at five degrees?

 

[GregLocock]

Hmm, I think it would be the same strength (that is variation in angular velocity for a given offset). That doesn't feel right.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[pontiacjack]

What doesn't "feel right"?

 

[GregLocock]

The vector diagram in my head says that the ball and trunnion would have the same peak/average speed as a Hookes joint. But I think that may be wrong.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[FeX32]

Be careful with Cardan joints.

See the attached paper. It outlines possible instabilities.
Other than that you should be ok.




Fe

 

[pontiacjack]

Fex- thanks for the link. I won't pretend to having understood the whole paper. But unless I got it completely wrong, it appears that all those horrible instabilities occur at U-joint operating angles greater than fourteen degrees. My U-joints (as do most automotive applications) don't run at more than about five degrees.

 

[FeX32]

You're welcome.
Yes you should have no problem. It's more of something to look out for, and to gain some technical knowledge of the subject.




Fe