[EricH]

Originally Posted by gburlison

We have used C channel for a couple of reasons.
Two 1x1 box extrusions used on the side of a frame is heavier than a 4x1 C channel.
We have had good results bolting together a C channel frame and do not have the ability to weld aluminum.

In that case, I'd take squirrel's suggestion about pultruded fiberglass. Talk to 842 and 1726 about their frames. (And you don't need a 4" tall frame, do you? 2" should be fine...) Or go to 80/20, which several teams have used in the past. Steel is not a nice thing to have on a robot frame for weight reasons.