Geneva Drive – Laser-cut

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The automata in the Archive Project use all kinds of different mechanisms to make all kinds of different movements. The one I’m working on at the moment uses a particularly interesting mechanism. There is a little window in the background of the model. Through the window you can see a portrait of a woman. As the mechanism runs I need the picture in the window to change to another portrait, then another, then another… and so on. I need the picture to be stay still for a set amount of time then flip quickly to the next picture as the mechanism runs.

geneva-a01This is the perfect tesk for a Geneva drive.. In my test version I went for an eight step drive.

The mathematics of the parts layout is fairly straightforward. I wrote a blog post about it a while back here. The key centres for an eight step drive are based around a right-angle triangle with a 22.5° angle. The angle is worked out by dividing 360° by eight, for the eight steps, then halving it.

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Having designed the parts in Illustrator, I’ve cut out the resulting mechanism from 3mm plywood and used 12mm and 9mm hardwood dowel for the axles. The drive pin is then fitted onto a 26 tooth gear which will be driven direct from the automata mechanism. This prototype works a treat!

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