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Constraining bone to twist opposite it's parent (for upperarm_twist_01_r)

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    Constraining bone to twist opposite it's parent (for upperarm_twist_01_r)

    I'm trying to get proper twist with an IK rig I cam creating. upperarm_twist_01_l and upperarm_twist_01_r are supposed to rotate opposite their parent (based on this: https://answers.unrealengine.com/que...earm-roll.html)

    I want to get the delta rotation of the upper arm R bone from the ref pose along the bone axis, and apply the opposite of it to the upperarm_twist_01_r bone.

    I tried with a bone driven controller, using a -1.0 multiplier to try and reverse the X rotation:





    but it doesn't seem to work correctly:



    From reading the code, copying X copies from a Euler rotation, so I think I might be getting Euler angle related errors, since I think UE4 applies X last.

    Is there a different approach I can take to solve this? I haven't been able to find the right nodes to do what I need.

    #2
    I was able to fix it by switching to the Apply A Percentage of Rotation node; commented out code in its C++ impl refers to DEBUG_TWISTBONECONTROLLER, which may be related to a node that used for twist correctives in UDK: https://api.unrealengine.com/udk/Thr...trol_TwistBone .

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