The other day I was watching the beautiful series of videos on the Michelson Fourier Analyser, (Yes, I couldn’t resist buying the coffee table book) and I started thinking about cams.

They’re a beautiful tool when you’re doing mechanical design. They can be used for very sophisticated calculations in a mechanical computer. Another use is  ‘programming’ extremely sophisticated systems using them.

If you haven’t seen things like the ‘Bow Shooting Boy‘ from 1850, or the ‘Letter Writing Automaton‘ from 1774, check them out.

It occurred to me that every cam I’d seen was limited by 360* symmetry. That is, for every revolution of the input shaft, the output point was back in the same position again. If your cam was outputting a sine wave, you could make a continuous cam that output sin(1f), or sin(2f), etc. but you couldn’t make one that outputted sin(1.5f)

It seemed to me that there was room to make the cam a bit more ‘stateful’ and have something with only 720* symmetry or better.

I did some sketching and laser cutting, and soon had a very quick and dirty prototype put together:

The yellow ‘boat’ shape is the rounded follower that can slide through the track and avoid getting stuck in the wrong turn.

It can run scarily fast

I watched and timed it for  a bit, and a quick back of the envelope calculation says that as it’s making 20 right hand moves in 15 seconds, that’s 80RPM.

It’s not too fragile a system, either. My quick and dirty prototype has been running next to me for the last fifteen minutes at full speed and shows no signs of breaking.

Obviously this isn’t a terribly sophisticated cam, both tracks are only outputting a single static value, but it demonstrates how you can have a cam with 720* symmetry.