A busy summer meant that not much got done, however we were able to get some of the frame assembled. The ends are attached to the beams that hold the motors (that are mounted now). I used some angle aluminum to join the pieces instead of welding. It feels like it will be a very sturdy frame! Some sheet aluminum covering the bottom of the main area will stiffen things up further.
The wheels we purchased are probably going to be too small, and difficult to attach a sprocket to. I saw this option which would really simplify the drive train construction. By combining a sprocket and wheel, it removes one challenging bit of construction. I wish I had my own lathe! Still, $200 for wheels is a little more than I wanted to spend. I also wanted to see if I could run with a live axle (where the axle is mounted on bearings and the wheel and sprocket get mounted directly to the shaft). For example, using a sprocket like this and a flange bearing like this, the robot could run a live axle.
I'm itching to order something new... drive train... electronics... hmm.