[Daryl]

I kind-of stuck it in the arm because there are some rotary alignments to maintain.

The Path of an orbit is three dimensional. The Orbit can exist on a two dimensional Plane. Hinge Action and keeping the peas on a spoon are two different vegetables.

What off plane forces/motion do you have in mind that will make the third, off plane, dimension?

There are rotations of the Left arm. But those rotations are the Start-up Swivel and Release Swivel. They're independent of Hinge Action.

3 dimensional path = down-out-forward. No off-plane motion because the 3 dimensional path is within the 2 dimensional Plane.