Idea from Omni-Ball robot in video: http://www.youtube.com/watch?v=AmWJ6gcP9Lc
The OpenSCAD Parts Library (http://www.thingiverse.com/thing:6021) is needed. (not included) The Pin Connectors V2 (http://www.thingiverse.com/thing:10541) is needed. (not included)
v 0.5, 20 Nov 2013 : Changed license
v 0.4, 31 Jul 2013 : Using pins v2 library for connecting the 2 hemispheres to the main axle. Added pin_radius parameter
v 0.3, 30 Jul 2013 : Added print_mode parameter (rotates the hub ready for printing)
v 0.2, 29 Jul 2013 : First gamma print (by jinx) failed http://www.youtube.com/watch?v=NPs9qu7P9ec (Y braket broke upon cleaning of support and caster wheel stuck on the inner axle). Changed default hub_side_thickness from 1mm to 2mm and hub_extra_height from 0mm to 1mm
v 0.1, 26 Jul 2013 : Initial release