How to animate the parent bone moving without moving the child bone?

Question

For my animation I need to move character's right arm without moving it's child - the gun. I cant just unparent it or do anything with the rig, because I'm making for a mod for a game, and its all hardcoded, so I have to keep the rig as it is.

Usually when I had to make it so that the right hand moves, but the gun doesnt, I just tried to return it to it's position and rotation, but it still moves slightly and just doesnt look right.

How can I fix the child bone in global space so that it doesnt move along with the parent bone?

Answer 1

1. Create a dummy object. It will be your "anchor" for your gun bone.
2. Add a "copy transforms" constraint on your gun bone, pointing to the dummy object in world space. This will make the gun bone follow the dummy object without any regard to whether it's also a child of some other bone. When you first constrain it, the position and rotation of the gun bone will get screwed up, so you'll have to move the dummy around to move the gun back where it belongs.
3. Now animate your character. Since the gun moves with the dummy now, you're free to animate the hand and the gun independently.
4. (This is an important step after which you won't be able to edit the animation anymore, so make sure you're 100% done with it) You have to bake the action now. In pose mode, go to Pose > Animation > Bake action or just type Bake action in the search bar. The bake window appears. Specify the time frame and make sure to check "clear constraints" and "visual keying" (you may also want to check other boxes depending on the situation). Note: if you have other constraints that you DON'T want cleared, just don't select those bones and tick "selected bones only". Click OK.
5. Now all the bones are back to their hierarchy, no constraints, but the gun moves the way you animated it as if it's not parented.