[JDNovak]

We (The Bomb Squad) have used extruded aluminum for all our frames since 2003. We have always used 20mm x 20mm ITEM brand material purchased from the US distributor in Ohio. They offer a discount to FIRST teams.

The material is amazingly strong for its size and weight. As someone already stated, joints tend to loosen from impact but a good design can minimize that. I believe a bare frame can be made as light as any other construction with some practice. ITEM also has a lot of neat fasteners like slides and rollers that make arms and elevators easy to design.

The major issue of this construction is fasteners. To take advantage of the material we use "T" nuts with M5 screws to fasten everything to the frame from gussets to gearboxes. The advantages are no reduction in strength and the ability to slide structures for alignment and chain tensioning etc. The disadvantages are weight and cost. The ITEM "T" nuts cost a dollar each before discount and the 80/20 distributor I checked recently charges $1.25. We usually use two hundred or more a year initially and probably twenty-five more fall out during competition.

I really can't guess how much material you need without knowing a lot more details. We usually use four rails extending from front to back internal of the wheels to support the upper manipulator/drives etc. and then build a frame that tapers at the back to take advantage of our three wheel drive system. U shaped frames for ball pickup are more difficult to strengthen but we have done it.

I would get some material and build a box first and get a feel for the weight and strength and then go from there. You can always use the box for storage if it doesn't suite your needs.

Oh, I think ITEM and 80/20 as well as some other brands I have seen are equivelant but not always compatible between them.