[Jim Giacchi]

We've used aluminum angle , extrusion, and angle iron.
We stoped using the aluminum angle because our welding teacher retired and we have no idea how to mig or tig weld(tried it once the results were not pretty) so we switched to angle iron which was much easier to weld, but weighed a ton. This year we used 80/20 extrusion which was nice and modular but was heavy also.
So out of my expieriance the best framing material is some sort of aluminum structural material like box or angle that you weld together because you just can't get a stronger lighter frame that actually allows you to put other mechanisms for the other part of the game on the robot.