The weapon drives the arms, and the pelvis drives the weapon. I also used versions of this where the weapon was free or driven by the chest.
The large pieces are constraint-driven, but can be additively tweaked by the animator
Simple version for blockout animation.
Aim-based humanoid. Great for cleaning up mocap of walking/scanning
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Curly Strap Rig
Detailed accessory rig with animator-driven deformation
Automatic placement onto the inside of the knee.
The animator can move, rotate, and scale all of the box controllers individually, or with the main strap controller. And scaling it makes the strap curl!
Full video of editing the parts individually
(on an older version with a very thin strap)
Further explanation and updates on my blog post about this: