When you turn one end either way the other end always turns clockwise - could be used for example in a pendulum clock.
About this creation
This device is built in two separate parts, and each sort of functions without the other. Originally there was just a bottom half, and I didn't originally intend to build a top half bacause I seemed complete. But with the two tegether it is definitely better.
What the bottom half did was that when the lever was turned anticlockwise (counterclockwise), the output gear turned anticlockwise. However, when the lever was turned clockwise, the output gear didn't move. Thus if the lever happened to be a pendulum the output gear would turn every 1/2 oscillation, and always anticlockwise.
With the top half added it ensured that it wasn't stationary when the input was clockwise - it went anticlockwise whichever way the lever turned (every 1/4 pendulum oscillation). I'll explain the whole lot below.
NOTE: When the input turns anticlockwise, the output turns in the opposite direction. However, in the description above I said the output went anticlockwise. This is because that's when you look at it from the opposite end. Looking from the input end, with the lever, the output actually goes clockwise. But looking at it from that end, you can't actually see the output turning, so you turn it round and it looks like it's going clockwise. You know, like right becomes left when you look the other way.
The top half works in exactly the same way, and turns when the bottom isn't turning. But since the output can always be turned clockwise by an external force the two complement each other and ensure it turns whichever way you turn the lever.
I'm afraid to edit this page in case I lose my Brickshelf photo links - the edit page doesn't seem to let you keep them any more and it seems like a lot of effort to add the photos again manually... Anyway check out http://www.mocpages.com/moc.php/102616 for an improved version. I'm really flattered that this guy took the time to redesign this thing (which is completely inappropriately named by the way - now I'm a qualified but non-practising engineer, I know this has nothing to do with cranks). It's probably the MOC I'm most proud of - it feels like an invention more than a model, even though I'm sure many better versions of it have existed since the start of the industrial revolution!