Michael Curry's Turtle Shell Racer - High Powered Edition Thingiverse blog post / instruction manual is now live! LInk to page!
His turtle shell racers where the talk of Maker Faire Detroit!
Link to the instruction pdf.
I must warn you that you need a 3-d printer or some other way to make the shells for the racers. The project is open sourced so I can not wait to see what mods people come up with.