Frame tubing wall thickness

[sanddrag]

Recently I am finding myself constantly trying to push the limits of robot design and get away with less material in critical areas. So, this is another one of my "how thin is too thin" threads.

Traditionally we have used 1/8" wall 6063 aluminum box tubing for our frame rails. But now I'm wondering if we can get away with .090 wall 6063 (2.5"x2.5") for the main frame side rails.

The way we like to play, the robot is often subjected to heavy contact. So, can the .090 wall 6063 2.5"x2.5" handle it? There would be a 1.5" wide slot centered in each of the four sides. The wheel would stick through the top and bottom slots and pillow blocks would reside/slide in the side slots. Sort of like this. I'm thinking where the slots are, it would not be strong enough. Since the .090 wall thickness would most likely be achieved by surfacing down .125 wall tube, what if we just left it .125 in the slotted areas? Would it be strong enough then? Or would we need to add a doubler plate?