[kken]

And yet another perpetuum mobile. Does not work, is scam.

[mrmagooey]

Indeed, why people upvote these things is beyond me.

[officialjunk]

Don't have the links handy right now, but there are patents for these types of physics hocus pocus "inventions."

Also, why does the title of this submission have quotes around "cheapest?"

[Cogito]

It seemed to claim to draw power from the Earth's gravitational field.

I highly doubt it would be very effective, but it's not quite the same as a perpetuum mobile.

[EDIT] Though, after a little reading, it seems most supposed perpetuum mobiles tend to claim they harvest gravitational energy. That correlation makes your statement much more understandable.