You follow @mechamechanisms on twitter right? So you'll have seen this mechanism pop up on their stream of amazing mechanical animations.
Although it is labeled as a sheet metal gear it looked to me like a perfect candidate for a paper version. Time to crack out the coloured card!
My first step was to work out the geometry. I opted to 9mm teeth and plugged the numbers into Matthias Wandel's super useful Gear Template Generator (You follow Matthias on YouTube right? Of course you do.)
The smaller gear, I've translated into a ring with 17 slots. This wraps round a central core.
Here's the 17 tooth gear.
For the 23 tooth gear I make each tooth smaller than the original to that they would fit easily into the slot. I've make it from double thickness card for extra strength.
The two gears mesh together nicely. Next step, mount them in a box and make sure they work smoothly in situ.
There'll be a downloadable version for you r to try oput in the next day or so.