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I want to rotate hand bone when I rotate IK bone as well. So I decided to using Copy Rotation constraint. Here's how looks like:

enter image description here

Nothing special, important thing is that Hand Bone has Copy Rotation to IK Bone. I set the Target Space and Onwer Space both Local Space.

But when I rotate IK bone, hand rotates totally wrong axis:

enter image description here enter image description here

I think this happens because Copy rotation just copy the rotation values literally, my guess.

How do I make hand rotates properly? I think it needs to be change the rotation based on current rotation, but there's no option for that in Copy Rotation constraint.

Any advice will very appreciate it.

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  • $\begingroup$ There is a constraint called Transformation that, I think, could allow you to copy a rotation from an axis to another axis, but is there a reason why the hand is not child of the controller? That's what I usually do so when I move the controller it moves both the hand and the lower arm $\endgroup$
    – moonboots
    Aug 28 '18 at 9:09
  • $\begingroup$ @moonboots Because of Unity Humanoid type, it forces me to keep parenting each connected bones. I generally do parenting hand to IK bone in first person animation, but full human rig couldn't do that. I already tried with Transformation constraint but it didn't worked. $\endgroup$
    – modernator
    Aug 28 '18 at 9:38
  • $\begingroup$ Do you know for absolute sure that the local space axis orientations are the same for both your hand bone and your IK bone, particularly when at rest? You may think they are the same, but you may still want to check. Because if you have them both set to Local Space in the Copy Rotation constraint, and yet they are not turning the same way, this is the most likely culprit, I think. Your local x axis may not point in the same direction for each of these bones. $\endgroup$
    – R-800
    Apr 11 at 22:21
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Copy hand bone. Make the copy a little larger or a little smaller than the original hand bone, so it'll be easy to select. Parent it only to the root bone and make it an IK target. That's the easiest way to avoid Copy Rotation problems and have clean, easy to work with rig.

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  • $\begingroup$ IK bones are already parented to Root bone. $\endgroup$
    – modernator
    Aug 28 '18 at 14:49
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    $\begingroup$ That's not the main point. The main point is to have IK targets at exactly the same starting location and rotation as hand bones, then you'll have no troubles. $\endgroup$
    – Mzidare
    Aug 28 '18 at 14:56
  • $\begingroup$ You may want to check the axis of the bones themselves the bone roll I think, some time that gets messed up. $\endgroup$ Dec 12 '19 at 5:46

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