DOUBLE U joint Rigging

[twetzel2]

I have seen and followed multiple single U joint rigs, but cannot seem to get the second half of a double cardan joint to work.  I get a lot of floating or incorrect rotation on the remaining side.  

has any one done this and be able to give me some help?

[lauri_barnhart]

Hello @twetzel2, thanks for posting in the community!

Did previous replies by @leeminardi help clarity your question?

If they helped, feel free to accept them as the solution.

This helps other users benefit from the shared solution.

If the issue persists, let us know with an update so we can assist further.

Thanks!

Lauri | Community Manager

[leeminardi]

@twetzel2   I have given this some more thought and think I now better understand the kinematic relationship between the various components. As I'm sure you understand, a single U-joint will yield an output shaft rotation that varies sinusoidally from an input of constant rotational velocity. If that non-constant rotation is appropriately fed into a second U-joint then the final output will have constant angular velocity.  Hence the CV (constant velocity) joint.

The attached file does a pretty good job in showing the action of the double U joint.  The two joints do show some distortion as the tube rotates.  I determined that this could be fixed by relating the rotation of the x vector of the tube to the y direction vector of the joint.  For example, if the angle of the rotation of the tube is 0° or 180° then the flange axis direction should be parallel to the Y direction vector of the joint.  However, if the angle of the rotation of the tube is 90° or 270° then the y  direction vector of the joint should be parallel to a vector that is the angle bisector of the flange axis and the tube axis.   If you think that you would use the results I will try to make that correlation.

Let me know what you think.   Just click PLAY in the attached file. 

It was not clear to me how to use the file you posted.  

Lee

[twetzel2]

Although this rig looks great if the vertices are static.. the rig does not work if they are animated.  

I appreciate your work on this, but will be using the rig that I created above.  

I am attaching your file with the vertex that controls the direction of the flange being animated.  you should be able to see the pops that it creates as it moves.  I do not get that with my IK rig. 

[leeminardi]

@twetzel2 

Thanks for the detailed response.  I am trveling and will not be able to look at the file from your last post until the end of the week.  I am curious to look at the issue you found.   Please note that I am not satisified with the incomplete solution I posted and was planning to fix it if not for your use then to satisfy my own curiosity. I'm glad that you have a rig that works for you.  I will put this project aside for now.

Good luck with your animation.

Lee

[in_human]

https://pogribniy.net.ua/LooksLikeFinished.mp4

[wetzelt6MTHZ]

In_human, do you have a max file or explanation of how the rig is set up?

[in_human]

I can't share the source scene as this is a commercial asset and I don't own it.
I'm just a freelancer who did rigging. But I can assure you that it is relatively
simple and does not go further than several lookAt constraints.
No complex scripted transform controllers.
https://pogribniy.net.ua/emptyRig.mp4