Jim Zondag posted up a very good write-up of our process:
http://www.chiefdelphi.com/media/papers/2493?
It most closely follows the V-model for the main robot. In reality, there is a little bit of spiral model at the start during the prototype phase, and at the end as well, but the bulk of the design, build, and testing follows V.
Minibot was totally spiral model (and often felt like it was spiraling out of control). If I ever get our minibot development paper written up, it should showcase the good and bad of the spiral model as well as a decent amount of requirement and scope creep. Monday we boxed up approximately 15 different chassis with different designs. That was enough trips around the spiral model, that I was pretty sick of minibots by week 6.