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.
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.