I'm trying to simulate a rope (ultimately for hair physics) by making rig A copy rotation of rig B. I'm using world space and the effect makes the mesh on the left jitter all around (it jitters faster than how you see it on the gif below). Not only that but the mesh is a bit screwed (literally). Why is this happening? The axis are all aligned.
Here is my blend file. Use W and S for movement.
OK, now the mesh doesn't twist. What I did was to remove 2 of the bones for the display mesh. Then pulled the only bone left to the height of the rope, then subdivide it. Subdivide. Not extrude it. Then parenting with automatic weights works without twisting the mesh. Why? I don't know. The axis are all aligned perfectly.
I'll tinker with this more. I'm leaving these files for anyone who's having difficulties with these matters. I don't completely understand them myself.
To sum it up:
1/ Why did the mesh jiggle? I did some more tests and bone bigger than the mesh didn't case problems. Was it my laptop? HP Elitebook 2530p. It's not that powerful really.
2/ Why did extruding bones and then parenting a mesh with automatic weights twist the mesh?