What modelling program are you using? If I were using Blender for example I would make sure my root bone is somewhere around the “spine” of the backpack centered and make sure no bones are parented to it. That “parent to last bone” default setting most 3d apps always gets people, wondering why their root bone is moving. Make sure nothing is parented to it (except the mesh of course)
If your asking how to have that mechanic done dynamically? Thats an IK/controller setup thats pretty advanced and you might wanna do some research cause I’m not aware of any tutorials on that for ue4 yet.
Hope this helps
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