I built this little fella in a matter of minutes, and it cost me nothing. I built it from scrap metal I had on hand and 2 motors I extracted from old Xbox controllers. I would love for this site to be a guide, but rather than list out all the steps as I normally would, they are already here: http://letsmakerobots.com/node/728. I have already written out detailed instructions there, and it was a fun little project to do.

Brennon