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I'm currently trying to constrain the rotation of some hand-bones in my rig to an IK-bone.

However when using the rotation constraint my hand bones (Thumb.001, Index Finger.001 and Middle Finger.001) behave unpredictable. I would expect them to stay in their default position and rotate if I rotate the IK-bone. But as soon as I add the constraint the bones snap into seemingly random positions.

Before activating the constraint The anomaly occurs after activating the constraint

I uploaded a minimal working example demonstrating the problem.

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  • $\begingroup$ Use local space -> local space instead of world -> world. $\endgroup$
    – Nathan
    Nov 3, 2022 at 16:03
  • $\begingroup$ @Nathan But I want my bones to act as if they were attached to the IK-bone. In local space they would start rotating around their respective axes. $\endgroup$ Nov 4, 2022 at 1:24
  • $\begingroup$ Then parent them to the IK bone, or parent them to bones with the same local axes as the IK bone which also copy rotation from the IK bone. $\endgroup$
    – Nathan
    Nov 4, 2022 at 4:24
  • $\begingroup$ Thanks for the tip. While I knew of that workaround, I would like to understand what the problem is first before changing my hierarchy. That is something I am trying to avoid. $\endgroup$ Nov 4, 2022 at 17:54
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    $\begingroup$ The target has non-zero world space rotation even at rest, because its axes are not aligned with world axes. This rotation is then applied to the constrained bone. $\endgroup$
    – Nathan
    Nov 4, 2022 at 18:38

1 Answer 1

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Thanks to Nathan's comment below my initial question I figured out why my constraint behaved unlike I expected.

When setting the target coordinate system to World Space it's initial rotation relative to the world origin will be added to the constrained bone. This can be avoided by changing the Target value of the constraint to Local With Parent (or Local) and the Owner value to Custom Space. Then select the target bone as reference for that custom space.

enter image description here

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