After reading Neal Stephenson's Snow Crash a friend and I looked into how hard it would be to make something like the smart wheels on YT's board or on Hiro's bike. It really just came down to having a really accurate map of what was in front of you. So low power cheap accurate radar would be ideal. Of course you still need something that can pulse one of the spokes like 18/sec at just 60 miles an hour but hey why not...