After the first weekend of building automata kits at the Sunday Streets SF, I decided to make another that was larger and more eye catching.

This version builds on the windmill which used a rubber band to transfer the motion of the crank to the axel. In this case there are two bands and two axels. By twisting the bands in opposite directions as they are connected to the axels, they spin in opposite directions.

At this size, the elasticity of the rubber bands and friction in the axels lead to varying speeds. It seems that the bands can stretch for a bit, building up enough energy to spin the axel, then they spin for a while before losing momentum. At first I was frustrated by this effect, but I could not solve it by using different sized bands. As I showed it around, folks seemed to like the variety… so there you go. It’s a feature, not a bug.

Detail of crank with one band on each side of the middle support.
The axel holding the inner disk is a 4mm pipe. Is goes from the front to the middle support and is driven by the orange band. The axel driving the outer disk is a 2mm rod that goes from front to back, passing through the pipe. Twisting the blue band in opposite direction as the orange reverses the motion of this axel.

Automata kits

In addition to helping to update digital exhibits at the Exploratorium, I have been volunteering with them at the Sunday Streets SF fairs.

To provide something for kids to construct and take home, I designed two automata kits inspired by some examples I found online.

For variety, I used a rubber band to make a belt drive for the windmill kit. This had an added advantage of simplifying and speeding up the kit’s assembly. Glueing the wheel to the crank shaft (as is done in the rabbit kit) requires the maker to wait for the glue to dry before they can enjoy their toy.

All-in-all, the windmill was easier to assemble, primarily due to the coordination needed to fit all the tabs of the hat into the box for the rabbit kit.

Production of the kits involved a good deal of laser cutting and glueing as many pieces together ahead of time. I decided to assemble all the crank handles, turbine shafts, and rabbit plungers to minimize the amount of gluing at the fair. The image below shows all the pieces prepared for the first fair.

Make your own

If you have access to a laser cutter you can use the Illustrator files below to cut out most of the pieces, or you can cut your own by hand. If you are cutting your own, there is no need to follow the templates exactly, just use them as a rough guide and make simplifications and embellishments as you wish.

Aside from cardboard, you will need some rubber bands (I used size 64 from Office Depot) and some bamboo skewers (I got mine at Safeway).