RMax's right upper and lower arm.  Bicycle wheel hubs allow both upper and lower
arms to spin.  This models the human arm's ability to spin.  Servos have yet to be
attached to control the spinning.  That is scheduled next.  The elbow is a u-joint
which has been constrained to spin in only one direction.  The elbow servo is attached
and functional.  The elbow design is very similar to the shoulder u-joint/servo design.
The quick-release hub bolts will likely be replaced with allen-wrench quick-release
bolts because the quick-release flange handle protrudes too far and impedes motion.
Except for the flange getting in the way, I like the idea of a quick-release arm.  With
this design, it would be easier to attach such an arm to Marvin, the roving Hero Jr