I designed one!
It was magnetic induction drive.

Stressman & I were in a hotel last Summer.
"I said, "Peter, I want to show you something"
and then pulled-up the design on my laptop.

Peter looked at it, looked closer, pondered a bit,
looked at me and said, "NO...!"

(Aw man, that was my Magnum Opus!)

"It won't???"

"No, and besides, you're out of phase."

"Oh, well I can fix that! Will it work then?"

"No... well, not long-term."

(Whew, I'm off & running!) "Well, that's good, I didn't
need it long-term, just say... eighteen months or so."

"No... more like five hours."

(DANG!)

-G'pa