Back to the pyramid model. I'm making a few more changes to the design. Initially I had the centre section lifting and dropping under the power of a Geneva drive. I wanted to add a little more to the mechanism so I'm now working on a design where the centre section lifts, turns a quarter turn then lowers back into place. I think I have most of this worked out. It is going to feature the tour toothed ratchet gear shown above left in a mechanism sometimes features in retractable ball point pens.