This fall, I’m running the Autumnal Maker School (AMS). What’s required to be in the school, and to graduate? Make ten things between September 21 and December 21. Preferably useful things, but artistic things work too. I have made a 1) Volvelle, a 2) computer program that calculates the area of a hexagon, a 3) graphic design sample that shows how to make an Egyptian god, a 4) braiding disk, and 5) picture IDs for my school; there was also an 6) art exhibit in there, and guiding a group of students into 7) designing a manufacturing process. Yesterday was 8) The Pulley Spinner. And shortly there’s likely to be a 10) game to teach Latin translation skills, and 11) a wind-powered toy car. But today is for the unexpected 9) the Pulley and Counterweight.
Pulley and Counterweight
//embedr.flickr.com/assets/client-code.jsHere’s an unexpected project. A pulley and counterweight system. This wasn’t one I was expecting to build until next week, and yet here it is. Because of the distance between the two pieces, it’s hard to make out in a single photo. So I’ve taken a photograph of the relevant elements, and you can draw your own conclusions. The pulley mechanism is a wooden frame made of 1/2″ square doweling. It’s had simple dado joints cut into the three blocks of wood that make up the frame, and a second piece of easy balsa wood has been hot-glued to the underside of the wooden frame, to act as the attachment point with pins into a cork board. It seems pretty stable. The cord wraps around the pulley a couple of times; the pulley itself is a wooden spool mounted on a piece of 1/4″ round doweling. 
At the other end is the ornament, in this case a rocket ship with a watery tail (in celebration of our water-bottle rocket project earlier this year. Behind the rocket are two plastic straw tubes holding the strings up to the pulley and keeping them untangled. One of those strings, the left string, leads down to the counterweight, which here is a group of washers tied to the end of the string. The other end of the string has a single bead attached to it, which is poking out from behind the right-hand side of the rocket-sploosh. Without a cleat (in this case, a couple of pins mounted to the side of the cork-board), the rocket would fall back to earth like Earth was a gravity well or something (hey, it is!), at a speed much greater than just letting the rocket ride down its strings on its own. The right string, that is, the pull-string, thus ‘stores up’ potential energy in the rocket; and the left string, that is, the counterweight string, releases it.
Why I built it
//embedr.flickr.com/assets/client-code.jsAs is often the case, I built this thing partly for my boss, and partly for myself. The “for my boss” thing was that she wanted a “Design Thinking thing” to be part of a given display in the hallways. This rocket poster was part of the original design; she wanted something more … mechanical… more operative. I worry that it’s too operative. That kids will want to play with what she wants to be a static display. But that’s a problem for another day.
The other reason was that I wanted to build a model that built on what I learned from this one, at left. That’s the pulley spinner, that I built as a toy on Monday for part of my Automata class on Monday afternoons. When you pull the right string, the disk with the round chessboard pattern turns right; when you pull the left-hand string, the disk with the chessboard spins left.
Now I’ve moved up a little bit from that.
I have a device which loads up the disk with potential energy, and then gradually releases that potential through the falling counterweight, as kinetic energy. Motion. I think I understand this better, now. At least I think I do.
My eventual goal is to build a two-string, two pulley and counterweight system, with some sort of ratchet mechanism, such that pulling two strings down ‘charges’ or lifts the counterweight, and then lets it fall, gradually. But first I had to make a counterweight and see how it behaved. Here was a chance to do that.
What I gained
And now I have a model for what I want the students in my Automata class to build over the next six-ish weeks:
- Simple string mechanism
- pulley spinner
- pulley and counterweight (with or without spinner)
- horizontal and vertical cam system
- cam controlling a lever
- ratchet system
Six mechanisms in six weeks. Ambitious. I got two to work in two days. But they’re two of the simplest. All the others are much more complicated. Yet there’s an advantage here too: The tools and skills which built the first one, the simple string toy, are applied to the second model, the pulley spinner. The pulley-spinner, plus some weight in the right place, makes the counterweight system. The use of the axles in the first two models helps bring about the idea of a horizontal cam, which helps bring about the idea of a horizontal cam interfacing a vertical cam. And from there to a lever, or to a cam that controls a pulley, isn’t that big a leap. From there to a ratchet that regulates it? Maybe more of a leap. And a lot more careful cutting and sawing and making for all of us.
But there’s a curriculum here, for those who know how to follow it.
