At the very least, I think you need to reconsider using 1x1x1/8" angle as cross members. Even in pairs, they're not going to give you the rigidity you're looking for and you stand a good chance of knocking the chassis out of square, if not, worse, the first time you clip your corner on something at a reasonable speed. You can probably stand to use lighter stock on the side rails and move some of the weight and strength to the cross members.
I looked into using 80/20 extrusion as the basis of a drive train about a month and a half ago as we iterated our existing design and tried to eliminate as much manufacturing time from it as possible. Ultimately, I decided to do things a different way, but here's a look at what I'd come up with:
We do all of our machining work and so I design for our skill set -- and that means no multi-op milling. If you're expecting to have a shop do some work for you, you could easily have them create bearing blocks from blocks of aluminum that replace the function of the individual plates depicted here.
We have the axles sitting above (or below, really) the 80/20 in an effort to eliminate milling operations on our side rails. If you're planning on milling slots into the 80/20 to allow axle clearance for tension
and you're expecting to machine bearing blocks for your axles, why use 80/20 at all? The advantage in 80/20 is that it allows for tensioning easily, but since you're milling the side rails anyway, it'd be pretty easy to add some slots for tensioning.
I'll wait for someone else to do it, then disagree with whatever they say. :p - Jcarbon [more] 
31-12-2007, 11:14
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