NOTE: This has been upgraded to a much more flexible version that incorporates all previous designs and adds lots of new features.

The new version is here: http://www.thingiverse.com/thing:21486

This is a flexible parametric robot wheel with a "circles" pattern. It's a variation of the biohazard wheel code here thingiverse.com/thing:21010 -- but it's tweaked a bit to support the circles design specifically.

There's a slot for a captive nut and hole for a set screw that are a little difficult to see in the renderings.

You can modify a number of properties in the OpenSCAD file to suit your needs, including tire size, wheel width, rim height, number of spokes, hub height/diameter, shaft size, set screw diameter/thickness, number of set screws, and fillets/chamfers. Or, if you need an STL for a specific size o-ring, just let me know and I'll try to accommodate.

Wheel Designs using the same foundation: Biohazard: http://www.thingiverse.com/thing:21010 Circles: http://www.thingiverse.com/thing:21065 Spoked: http://www.thingiverse.com/thing:21064 Spiral: http://www.thingiverse.com/thing:21277 ...and more in the works!

For detailed instructions, including how to work with these printed STLs and how to modify all the parameters in the OpenSCAD file, see the instructions for the biohazard wheel here: thingiverse.com/thing:21010

The STLs here are based on a 93mm ID (100mm OD), 3.5mm CS o-ring that I found on ebay for $3.50 for five, and also a set of 45mm ID o-rings that was selling for $3 for two. I haven't actually tried these, but it looks like it's probably a common size, so I thought they'd make a good example rendering. For complete control, edit the OpenSCAD file. If you're not comfortable with that, let me know and I can try to get an STL uploaded for you.