After converting the Clacks Tower on Angst-Lespork to Arduino control, the obvious next step was to apply the same idea to the working model Popham semaphore tower (which has taken a rather back seat over the years, because it's too big for the layout and the existing control system was too slow and cumbersome).
Originally, I used stepper motors to drive the arms, because they both have to swing through 270 dgrees, which is outside the range of "normal" servos. Quite why I didn't work out how to do it until a couple of months ago, I'll never know. The answer, of course, is to use a larger chain sprocket at the lower end to the one at the top!
So: just find a couple of 20-tooth sprockets compatible with the "0.1227" chain and 10-tooth sprockets up at the arms. The supplier I used orignally is no longer stocking these items. I found that the sprockets and chain are all made in the USA and I found a supplier that covers the UK - based in Canada and using a distribution centre in the Netherlands. No worries, then!
The sprockets duly arrived after a few weeks, and I have been scheduling time on the kitchen table to do the upgrade. I finished the work to day:
Here is a video of it in action
A brief update. for the technically minded, here's a video of the mechanism inside the tower...