The big Bike hub and the custom Mini-Hub side by side for comparison.  If you take a bicycle hub and
remove all the extraneous outer shell stuff, and then shorten the bolt, you'll end up with the Mini-Hub.
The Mini-Hub bearings are from a bike hub.  These cost $9.00 each.  The total cost of the Mini-Hub
is about $22.00.  The weight, space, and cost savings are very significant.   If your bike hub isn't
cutting it, just build your own.  :-)