Mechanum wheel, 0.2" flat-shaft.

thingiverse

I made some tweaks to Joakim's original designs, giving the wheels a hub and set-screw, and implementing tiny pressure pads to secure the roller shafts in place, instead of requiring glue. This lets you swap out rollers if one breaks. I'm currently printing my set, so be on the lookout for finished product pics when they're done! EDIT: For those who grabbed the first version, I accidentally swapped core designs - now it's fixed, so give downloading another shot. Instructions: You'll need 2 cores of each kind to make a simple 4-wheeled robot work. Each core needs 11 rollers and 11 pin clips, which translates to 44 rollers and 44 pin clips for a full set. You'll also require screws to hold the pin clips and set screw in place. You can craft the shafts from pieces of 3mm filament, but I don't have that handy, so think outside the box! PROTIP: Avoid trying to print all 44 pin clips at once - I made that mistake and ended up with a 43-piece catastrophe on my first layer, while the last one failed to stick... kill the print and remove those 43 partially-printed parts to avoid a bigger mess later. It was chaos - tiny pieces fell like snow when I scraped them off!