Assorted spinning shafts.  The bicycle hub on the left was the first attempt at
providing spin to the upper and lower arms.  The design was sound except for
the excessive weight.  The servos were barely able to move the arms in all
dimensions.  An old device [code-named the Flux-Capacitor] at the upper
right was brought out of mothballs.  It was developed years ago as a proto-
typical U-Joint.  The bearing hubs spin freely.  Except for the mini-bearing
hubs (4 in black), the rest of the construction is Aluminum (2 nuts, 2 bolts,
1 head of a bolt into which all the hubs screw into.  A penny is present for
relative size comparisons.  However, the mini-bearings don't provide free
spin in the perpendicular direction.  Thus, the device at bottom center is the
latest design.  Off-the-shelf at a cost of $5.00, it provides bearing rotation,
and no resistance along the axis of the bolt.  It's much lighter than the bicycle
hub, so it should provide the weight savings the arms need.