We've been kicking around the idea of making the robot frame this year out of steel, or a combination of steel and plywood. Thinwall (1/16") square steel tubing is a bit heavier per unit length than thickwall (1/8") square aluminum tubing, but it offers several advantages that might make the few extra pounds well worth it.
Like plywood, steel tubing is easy to get locally, and also like plywood, it's relatively easy to work with. Welding it together with the MIG process does not require as much skill as welding aluminum, and the equipment for welding steel is more commonly available (I have a 140 amp gas MIG welder in my home shop, as do many of my friends).
To mount brackets, axles, and such just requires welding on a piece of steel. Cantilevered axles can be made by simply welding a bolt to the lower edge of the tubing. Brackets for mounting transmissions can be steel strap with holes or slots cut in them.
If you see some weird steel chassis prototypes showing up in the next week or two, don't be surprised!
(I did search for other posts on the subject, the previous one that seems to be most applicable
http://www.chiefdelphi.com/forums/sh...ad.php?t=60165 is locked)
The holiday season is formally known as "kick-off rendering season" - dlavery [more] 
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