Machining a frame takes longer than I remember. I'm not sure if I've slowed down with lack of practice, or if it was always time consuming and I've just forgotten what "normal" pace is like.
The good news is that I didn't make any major machining mistakes, and all tolerances came out OK. The chasis is heavy, over 20 pounds including the wheel. Fully loaded, I suspect the weight is between 35 and 40 pounds. I have a lot of material I could remove, but I"ll wait until I'm completely "done" (whatever that means) before I worry about lightening the frame.
I made a few design mistakes that became apparent after building and debugging the software:
I noticed after bolting things together is that I placed the wheel and motor in such a way that an odd number of #35 chain links was needed for the chain. Luckily they make a special chain link to resolve this issue called a "Connecting Link". I tried using such a link, which worked fine. However, I eventually ordered a larger sprocket that gave me an even number of links in the chain, and also gave me more reduction.
I made the bearing blocks symetrical, but this caused one side to be hard to remove. In hindsight, I should have through-bolted one block, and threaded the other. That way I could have removed all screws easily.
The Netduino was crammed in the main compartment which makes it hard to access. During debugging, I had to remove and attach the main Netduino board hundreds of times. Next time I'll make it easier to access, or leave a USB cable mounted to that I can upgrade the software easily.
The bullet connectors on the batteries are not fun to mess with. They're not protected well, so it's easy to accidentally short them out on the frame or a board. I ended up frying one MC1 due to this. Ouch!