The contrived idea of the project is "Maybe we don't need to automate everything", but it started out just as something I wanted to make. I was inspired by the breakfast machine that Dick van Dyke's character made in Chitty Chitty Bang Bang and a diagram I saw.
The original motor I began the project with was from a 1930s era video projector. That motor was really beautiful with centrifugal switches and polished wood and brass components but even geared down with the two bicycle hubs it was far too fast. Once I decided that I needed something slower the question became "Well, what speed would be ideal?"
So I timed myself dunking tea and my natural tea dunking speed is about 50 dunks per minute (0.83Hz) and the gearing I had already built slowed it down by a factor of 4 so I needed a 200 rpm motor. I found a motor on Surplus Center's website (which now appears to be sold out) in that range.
The motor is actually two "shaded pole" motors which sacrifice torque for simplicity and price. The two motors are connected by a shaft and each spin in a different direction when powered. I'm only using one of the motors in this setup because one of the bicycle hubs prevents spinning in one direction.
It was featured on Hackaday.
And New Atlas.
And A Japanese Website.
And A Russian Website.
And A British Website.
My coworker, Leigh Campbell, took some great shots of it.
Here are a few videos about making it.
And a video of it in action