Further experiments with the hippo head I made the other day. I’d like to have the bird on the hippo’s back hop and and down a little making small quick movements. Meanwhile, I’d like the hippo’s mouth to open and close slowly.

Ideally, two or three turns of the handle would be needed for full movement of the head, this would require a little but of gearing down.

I’ve made various different paper gear designs in the past, this is my latest version. The mix of wide and flat gears makes the larger gear easier to construct, it is simply a piece of double thickness card. The triangular teeth on the smaller gear are more stable that four sided teeth which can easily be squished over.

Here’s how everything is fitted into the box.

I’ll fit a cam to the large wheel to drive the hippo mouth open. A second cam on the small gear shaft can be used to drive the bird.
I’ll be publishing the gear-in-a-box shown here as a kit in the next few days.