This is the wheel collection I've developed for the miniFloppyBots and SquattyBots kits ...
Best MCU board and chip for this is the RoboGuts™ circuit board with a PICAXE 28X2 module and SpeakJet chip. Build your own $50 talking and singing (in any language) robot toy! http://www.r2pv1.com/
The fastest and cheapest way to get all my .STL files FREE is to donate $5 to help fund school materials ... once I have $3,500 I'll convert all these files to FREE downloads. https://www.gofundme.com/roboguts-kits-lessons