Thanks for the tips on soldering, I am going to try these very soon.
This build is looking a lot more interesting since you added details about the micro controllers and the related circuits
I don't know much about the AVR controllers, so I went ahead and looked at their website. Those MLF packages with their 0.5mm pitch look extremely small. I am used to PICs, and the smallest that I can get is SOIC package and looks large compared to these! Are you writing all the programs by yourself? Looks like you are not using a dedicated PCB to put all the circuits together, that should help keep everything really small.
Those motors look really cool, are they bipolar? How many phases do they have and how many H bridges per motor? Looks like one can build really small fully proportional steering mechanism with these since no servo is required, that is really awesome.
The chassis looks really nice with all the screws etc. Sorry, a lot of question, hope you don't mind. But this build is getting really interesting. Please keep us informed.
Thanks.