In my on-going survey of simple mechanical devices, including toys, one repeating form that comes up often is that of the jumping jack toy, where you can pull on a string or stick on the bottom of the toy, and it articulates usually the legs and arms of the toy figure to move up and down.

I don’t pretend to be an expert in any of this, which is precisely why I am experimenting with making my own working versions of these simple forms and mechanisms: so that I can learn first-hand how they function, and gain experience combining different components into novel configurations. I sort of consider things like this to be very basic precursors to robots…

Here are two Humpty Dumpty themed jumping jacks that I made with my kid, where the limbs are attached via brass fasteners, which I had completely forgotten about as even existing, and turns out are a lot of fun to play with.

Front:

Back:

This site has some nice clear diagrams of how these mechanisms ought to be arranged. Mine is a little messy with the twine and hot glue, so these might be easier to understand.

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