Hi
I am using the metahuman templace to build a rig and I noticed that the shoulder joint “upperarm_r” and “upperarm_l” are flipping. Is this a bug?
I saw that many people don’t use the rotation on that joint and rather skin the arm to the first twist joint. I am connecting the rig to metahuman joints directly so I can’t change the skinning.
Flipping when and how? Can you show an example with screenshot or gif?
If you are rotating the arm greater than 180º, then it might make sense it is flipping. You might have to compensate with added shoulder rotation, so the arm isn’t doing all the work.
Or possibly you can find a way to fix the flipping by changing the rotation order of the nodes that read the twist. It might be arm_L0_0_bone, but I’m, not sure.
I think you are right, skipping the skin on a joint doesn’t seem like the right solution. 
It is exactly as you describe - it’s more than 180 degrees and after digging deeper into it it is only a ‘sense’ of flipping.
This was made ‘worse’ as I was using the Epic UE5 Manny without their RBF ( so driving the correctives straight from the shoulder ).