I'm working on a project for client that has a decorative clockwork key on its side. I'd really like key to turn as the model operates. The character itself will be jumping up and down so I'm trying to harness this motion to turn the key. If I can get the mechanism to work well it would apply well to a clockwork robot model like the one in the sketch below which I can then make into a model for robives.com.

The striped tab at the back is the drive that turns the key.  This would be connected to the box.

Inside the body I have this small toothed wheel. Twenty teeth, eighteen degrees apart.

To match up with the toothed wheel I've made a kind of toothed belt. There is a base strip onto which I have attached a series of overlapping squares glued on like the tiles on a roof.

The wheel will now only turn anti-clockwise, try turning it the other way and the teeth catch on the square tiles.

I've fixed a set of tile teeth in the back of a box so that they just touch the toothed wheel. Friction of the wheel against the tiles is only minimal but the wheel is effectively stopped from rotating backwards.

With the box closed a second tiled strip, this time with the teeth facing the other way, is threaded into a groove in the box. This strip is free to move up and down. 

I've finished off the box with a clockwork key slotted onto the axle.

As the strip is pushed into the box the key turns, as they strip is withdrawn the key remains stationary. The result is a slowly unwinding clockwork key. I'm pretty sure that this will work for the client's project and will also make the basis for a nice clockwork robot model for the website. 
Win / Win!