Complex U-Joint Problem

Questions & Answers
1

Hello. I’ve got a couple u-joints that I’m trying to model. The set up is a triangular yoke connected to two hanging arms with u-joints at the bottom and top of the arms. I’m using two hinge-joints at each u-joint connector.

The problem is that the right hinge comes apart at the axis of rotation slightly. It’s always the same hinge, but only happens when both left and right sides are active. If I deactivate the left hinge and let the system fall apart, the right one actually sticks together like it’s supposed to. As soon as I activate the left hinge again, the right one gets “loose” again.

Is there some priority things going on here? The settings are exactly the same for left and right sides. Can someone explain what’s going on here?

System setup:

199722-system.jpg
199722-system.jpg896×716 25 KB

Hinge that fails:
199723-hinge-fail.png

Hinge that always works:

2

So I couldn’t figure out how to fix the “loose hinge” problem. I did observe that it only happens, or gets worse when the mass is high. When mass is very low, it does not happen, or happen nearly as bad.

So the solution is to reduce the mass a lot. In my case, my objects in real life weight on the order of hundreds or thousands of tons. However, I was always just keeping the default mass = 1 and still having problems. So now I have scaled down the mass significantly, like to 0.001 by default. When I start going back to modify the mass of the objects, I will focus only on the relative difference, and keep the numbers very low.

Now all my hinges are tight!