This is a wheel that is able to drive in all direction in a plane without having to turn (with som limitations). The idea for the design isn't mine, I stumbled across this [ http://www.youtube.com/watch?v=BTp2UAaihaI ] video a couple of years ago and thought, I want one of those!

And now I have a 3d printer. I've made a model in openscad and printed a version of it that seems to work to some extent. I wanted to make it all printable but was unable to manage the gears (I'll have to spend some more time on them as of now I use some I got of ebay ( http://www.ebay.com/itm/BEVEL-GEARS-PAIR-2mm-BORE-12mm-DIAMETER-BLACK-NYLON-66-/290844724436 )), the bearings was another part I were unable to print. I tried making a bearing using cylinders instead of printed balls but it didn't work well (seen some designs here using BBs I want to try though).

The problems I've thought of this far are mostly ones concerning how to drive the wheel and control the motion. As long as you only turn the thick axis (the one that makes it turn around the y-axis in the picture) there isn't really any problems. The thing that is hard to control is the behaviour when you turn the thin axis (which makes it turn aroun the z-axis). This motion depends on how the other axis is turn.

I will update this when I have time to work on it. Hopefully I'll get a working design and some control circuit for it.