Steve,

Yeah, I'm currently (well it's all on hold due to imminent arrival of second baby) working on something called optic flow, it's a navagation idea, which is used by flys and bees and other insects with compound eyes.

The theory is that if you keep objects moving past your left and right eye at the same speed then you avoid hitting anything.

I am trying to mount two mice on a platform so I can use this idea to make a robot which can avoid obstacles without using untrasouce, whiskers or anything like that. I find that "instrusive" detection like that will only work for one robot, if you have 2 robots using ultrasound it means that they will confuse each other. Usig optic flow, they will avoid each other without even being aware of the other robot.

Chris.