A funny detail about this is that Feynman hadn't bothered to budget the $1000 for the prize. He thought someone would have to invent new tech to build the motor which would take years. If he had just gone a little smaller, say 1/100th of an inch instead of 1/64th, he might have gotten his wish.

Despite his disappointment he did keep his word and pay the prize. His wife was not happy.