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[smclean1969]

If you have a local aluminum supplier, just tell them that you'd like to purchase any 1"x2"x1/8" or 1/16" wall aluminum that they have as scrap. You can cut your costs from about $3.25 per foot to $.40 per foot. Work it year round and you'll have plenty of material come build season.

[Hawiian Cadder]

We used 3*1.5 inch tubing with .125 thick walls and a special hole pattern cut into it this year. 3/16 rivets and grade A 10-32 Button-heads are our fasteners of choice. This year the drive frame weighed 10lbs, and the entire frame weighed less than 16lbs. If you have the machining resources to do it, I would look at perforated tubes as a construction method, I cannot think of a way to make a lighter frame. For some examples check out team 40 or 111's robot from 2011