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Looking for beginner tutorials on properly setting up twist bones

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    Looking for beginner tutorials on properly setting up twist bones

    Dear all,
    [Context: I have this humanoid skeletal mesh freshly imported from Blender (using Auto-Rig Pro, I use the default UE4 mannequin skeleton, twist bones are here, so this part is ok and is not the object of my question), mesh that I'm using in VR.
    When I rotate my motion controller / hand, I have this visible 'candy paper-wrap' effect at the wrist. My twist bones are here, but not used yet.
    So as I'm a total beginner on twist bones, I tried to find the relevant documentation, but the documentation I found so far is extremely light and assumes some preliminary knowledge in UE4 twist bones set up.
    ]

    -> Could you please point me towards some tutorials related to the principles of setting up twist bones in UE4? (ideally in the context of a hand IK chain, but any simpler example would be welcome, as a starting point).
    I thank you in advance

    #2
    Twist bones are parented to the actual bone of the joint and aren't considered altered or moved by the IK systems. You would have to implement a custom solver to achieve that.


    If you are referring to the rig, then the twist bones allow you to fix up the orientation of the shoulder muscle and the forearm muscle.
    They are useful for making poses more anatomically correct - along with morph targets to correct the elbow folds and such.

    This has nothing to do with UE4 and is just general animation stuff, hence why the first answer.

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      #3
      Hi, in case someone ever stumbles on the same issue as I did, I solved my problem with the use of the node "Apply a Percentage of Rotation", it allows defining a source bone (e.g. here the left/right hand bones), a target bone (the considered twist bone) and a multiplier for the rotation. I just used it in my animation blueprint > Anim Graph, can be used after some FABRIK or whatever IK solver you use (if any), it works.
      Note: It may not be the best performance friendly approach (I don't know, with 4 twist bones on each lower arm, I suspect it may take its toll, especially like in my case, in a VR scene), but the result is ok for me!
      Originally posted by MostHost LA View Post
      This has nothing to do with UE4 and is just general animation stuff, hence why the first answer.
      In my specific case, it had everything to do with UE4 though, since as I suspected, the twist bones were there, but inactive (and not parented) and therefore in need for the setting up of additional explicit constraints. "Apply a Percentage of Rotation" does the job.
      Regards.

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        #4
        FYI, you can also use a Post Process AnimBP for things like this. I use them for twist bones and corrective morphs (driven by Pose Readers). You assign it as a property of the skeletal mesh, so it will be applied to any animation the skeletal mesh plays.

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          #5
          I will look for the benefits of the approach you suggest, in my case. Thanks!

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