I'm no rocket scientist so it's hardly surprising that I hadn't heard of paradoxical gears. They aren't some crazy future tech invention apparently, but an elegant engineering solution that is seeing something of a comeback courtesy of the 3D printing craze.
Watching these gears turn is pretty amazing — they are fluid and graceful so naturally I had to find out what makes them so different from traditional gears. Simply put, paradoxical gears all turn in the same direction. (Yeah, think about that for a moment.)
In traditional gears the tooth from one gear must go in between two teeth in the second gear — in order to work the two gears must spin in opposite directions. In paradoxical gears the tooth of one gear must pass in front of the second gear without meeting any of the second gear's teeth or this mechanism will lock.
Paradoxical gears were apparently patented back in 1988 by a "Mr. Mercier," who worked for Renault. The purpose of the gears then was for a special differential using "torque transfer." Or in other words, equalizing the torque on all the wheels of a car in cases where one wheel might have low torque adherence — such as on ice — and the other wheels don't. The gears on the low torque wheels are essentially slipping and can't move the car.
Because paradoxical gears start with low efficiency gearing where there is little contact between the gears in the first place, they offer a simple solution to the differences encountered in torque presented by things like snow and ice.
Though differences in torque are now generally adjusted by electronics in cars, we still have to say, nice job Mr. Mercier!
Speaking of nice jobs, the buzz about paradoxical gears is courtesy of a new post on Thingiverse with detailed instructions on how to make your own set with the MakerBot Replicator. You know, just in case you needed a party trick.