Chain reactions, crickets, and pie
by Luigi Anzivino
I built my first chain-reaction machine! It’s hard to explain why, but it gave me one of the most intense feelings of accomplishments I have ever experienced.
Let’s start from the beginning: the Exploratorium is part of the PIE Network, an NSF grant aimed at promoting and developing science education and concepts through Playful Invention and Exploration (PIE, get it?). Karen and Mike, who work on the PIE initiative, held a workshop a few weeks ago, which lasted several days. After participating to that, our manager Anne decided that the experience was so exceptional that the explainers should get a taste. So she managed to schedule a special mini workshop for us (thanks Anne!), over the course of two days. We had to do it that way because the museum was open during those days, and some of us had to man the floor!
Here is what we did: Karen and Mike introduced the idea, which was to develop an activity using very basic and cheap materials. So they went to Home Depot and bought some pegboards, dowels, bits of molding, plastic tubes, funnels, etc. Everyday materials, nothing fancy. Now our job was to build a pathway for a ball to travel from the top to the bottom of the pegboard in the longest time possible. Anything was allowed.
Half-way through, they introduced crickets! Crickets are mini-computers that are programmable through a very simple interface, and can control a variety of devices. We had switches that we could have the ball hit, thus triggering a cricket, and pretty much have them do whatever we wanted.
Well, after three long hours (which flew by!) of toil, here’s my baby (click on the picture for the chance of seeing a larger version, and for notes labeling the various parts):
The first thing I decided was that in order to maximize descent time I should try to make the ball go around the back. This proved more difficult than I thought, because the blue plastic tubing was really hard to bend to the right angle, and also the ball had to have quite a lot of speed going through or it would get stuck. So most of the contraption actually ended up taking place in the back. Oh well. However, Mike challenged me at the end to make the ball go back to the original side, so I eventually figured out that I could use a length of spring as a tube, and did just that.
So the ball starts at the top (left panel), goes down a couple of ramps, jumps into a funnel, takes the tunnel (middle panel) to the other side (right panel), where it goes uphill for a while, falls into a closed tunnel, then into a funnel, then through a series of swinging doors (to slow the ball down even more), hits an upside-down swing, which triggers the cricket as it falls. Meanwhile, the ball continues its descent, jumps into the spring functioning as a tube, shoots back to the other side and heads for the yellow bucket.
Now here’s the part I am absolutely the most proud of: the bucket, you might notice, is tilted the wrong way to receive the ball. That’s on purpose. What the cricket does when activated back on the other side is: it waits an appropriate delay (which took a bit of trial and error to figure out), then activates a motor which swings the bucket counter-clockwise to receive the ball, waits a beat, then swings it clockwise to dump the ball on top of three chimes, for a final, ever-so-satisfying “ping”!
The whole experience was incredibly satisfying, we all felt so accomplished at the end, and it was really great to work with simple materials, yet achieve some sort of vision that you had in your mind. The worst part was having to take them apart at the end! I felt I needed a week of time to work on it and really make it into what I wanted it to be.
Of course, there were a few snags along the way: for example, all of us started building without testing, and we all had a moment of disappointment when we first let the ball go down the first ramp and it just jumped off instead of smoothly flowing into the next segment as we had imagined. But that’s when the problem-solving demon kicked in, and we all became adjustment freaks, using tape and whatever else was available to keep things just at the right angle.
Also, I originally had a different idea for the ending, much more ambitious: I wanted the ball to fall into the bucket off the side of the board, and have the bucket connected to an elevator (activated by the cricket) that would raise it back up to the second ramp, and there dump it out, so that the whole process could start again and ideally keep going indefinitely. That proved much more difficult to accomplish within our time limit, and so I had to abandon the idea after experimenting with it just long enough to understand how complicated it would be to build. Ultimately, though, I was absolutely thrilled at the finale.
So there you go, just a little slice of one of the best aspects of being an Exploratorium explainer!