MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
Used my own larger wheel: http://www.thingiverse.com/thing:906457 and a cheap 1" ball caster from amazon.
Also went with an ESP8266 + atmega328p instead of a raspberry pi. A 5x7cm board can be made to fit pretty easily.
Fun project to do with the kids. Thanks for the design!