Bone always facing down

Support Animation and Rigging
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1

Hi.

‘A’ is parent of ‘C’ and ‘C’ parent of ‘B’

Captura
Captura1213×532 60.5 KB

I need the bone ‘B’ always facing down independently ‘A’ rotates and ‘C’ moves back and forward. I tried an empty with ‘Copy location’ to ‘C’ on Y local but when rotating ‘A’ it moves. Any idea how to solve it?

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‘B’ is inheriting its rotation from its parents. There are a couple of possible ways to get around that:

  • Parent ‘B’ to a root bone that is a parent to everything, then use ‘Copy Location’ to move it to where you want it to be, under ‘C’.
  • Create another bone not parented to ‘A’ or ‘C’ which is rotated to point down. Keep ‘B’ as a child of ‘C’, and give it a ‘Copy Rotation’ in World Space constraint to match this ‘gravity’ bone.

I would lean towards the ‘gravity bone’ option, as that keeps ‘B’ in its logical place in the heirarchy.

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Ok ,that gravity bone solution is so easy that it hurts :sweat_smile: I am ashamed: I’ve been trying complicated combinations of hierarchies and that’s an elegant and simple way. Thanks a lot!

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You might also want a ‘Locked Track’ constraint to keep it aligned with ‘C’, so you can turn corners without it twisting on its Y axis. Or make sure that the gravity bone is parented to main truck body.

This file has two versions, one with and without a Locked Track. The gravity bone is parented to the base on one, and ‘free’ in the other. Where it’s parented to the base, it will follow the general rotation, but going up hills would be a problem. The ‘free’ one with a locked track behaves more like what you’d probably want.

GravityArm.blend (116.5 KB)

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