The foam is a good idea. I had to make this in short order out of supplies around the house and tried using some springy stuff for the wrist but it was hard to get a consistent movement, so just made it rigid. Not a new idea, I know, but had fun with it.
I saw a fun one a few years ago for the 4th of July. It was a battery operated fan that would display animation of fireworks when the fan was running. The fan blades were a flex circuit with RGB LEDs that produced the animation. I wanted to say that it was a very cool toy, but that would be an awful pun even if it wasn't intended.
My kids had such a toy MANY years ago. You swung this paddle shaped object back-and-forth and it displayed your keyed in text using LED's. In the dark your eyes provided the persistence to make a stable image.
(My youngest is about to turn 39 years old... so this was quite a long time ago.)
Instead of pine, it might be better to use styrofoam. Seams the weight would waer on your wrist after a while. Another improment would be to use a spring steel joint between the handle and the "hand". That way, a little motion would set the hand into action with less strain on the wrist. Just a though for anyone concidering to build this.
New versions of BASF's Ecovio line are both compostable and designed for either injection molding or thermoforming. These combinations are becoming more common for the single-use bioplastics used in food service and food packaging applications, but are still not widely available.
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