Attached objects rotate at different pivot point on rig?

Question

So this question is fairly hard to word but I hope it attracts the attention of the knowledgeable...

I have a model of a person, a viking to be specific. This viking has a mustache and a rig. His mustache pivots along the head bone as intended but it rotates on the wrong point so it doesn't exactly stay attached to his head. It's a little complicated since the Mustache is a separate model but joined with this one. It uses separate vertices and stuff if that's relevant. The mustache has full weight influence but it doesn't help since the problem is with the pivot point it's following.

Here's a vid to explain it -

https://imgur.com/a/8oj6V

Thanks!

Answer 1

It's not a pivot point problem but a weight problem. This is a common beginners mistake: to think that if some vertices have 1.0 weight relatively to a bone they will follow exactly that bone.

This is not true: if a vertex has 1.0 to head bone and 1.0 to neck bone, if you move the head the vertex will follow at 50% of strenght only.

In your video the moustache have 1.0 weight relatively to the head, but it's easy to see that they are not following exacltiy head bone movements: this means that they have some weight assigned relatively to some others (not moving) bones.

In edit mode select a vertex and open the "N" properties panel: you will be able to read all its vertex weight assignements. By removing all unintended assignements you will see that moustaches will follow head bone movements exacltly, with pivot point on the Head bone head.

Answer 2

It looks like it has some weight on the neck/shoulder bone. Double check it's only weighted to the head in weight paint.

Answer 3

There are two solutions that I can think of.

Solution 1:

Make the head and the mustache one mesh. You can do that by selecting both and pressing Ctrl+J. Now you have to make sure that the pivot point is stil right. If not select the point where the head connects with the body and move your 3D-Cursor to it by pressing Shift+S and selecting "Cursor to selected". Now press Ctrl+Shift+Alt+C and select "Origin to 3D Cursor".

Solution 2:

If you want to move the head/mustache only once or twice you can move your 3D Cursor to the point where the head connects with the body as described above. Then just change the pivot center to "3D Cursor" (see screenshot). You don't need to make the head and the mustache one mesh in this option.