[UPDATE 1: Sorry, I just realized, that I accidentally used 80034 ball bearings, not 624 ball bearings for this design. I'm already working on a updated, new, better, nicer and prettier design, using "real 624" ball bearings. I'll publish this new design on thingiverse shortly. For more information on this, see http://pleasantsoftware.com/developer/3d/2010/04/22/the-power-of-reading/.][UPDATE 2: The new design is now available: http://www.thingiverse.com/thing:2473 ]Ok, RustySpoon1121 beat me on this one ( http://www.thingiverse.com/thing:2318 ), but since my design is different (only 8 rollers, centrally mounted) and already finished anyway, I publish it as an alternative approach.I use 624 80034 ball bearings to mount the 8 rollers on the center wheel.For more information on the project (and more detailed build instructions), please see my blog post at http://pleasantsoftware.com/developer/3d/2010/04/18/the-power-of-vacuum/For one Mecanum wheel, you need to print: