I've created a car chassis! If you print it as is to scale, it is about 5 inches long, and a little less than that in width. It will work for whatever servos you want, and it was made for standard little motors (whose axles are about 2mm in width). Of course, all parts are made to accommodate the slight expansion that occurs during printing with a MakerBot Replicator 2X and an unheated bed (since this is what I have access to).