Pneumatic Minnow

So this project followed an improvisational demo of buoyancy vs. pressure after noticing a “toy” pipette in a chemistry set D had received and weighing it down a bit with a coil of solder. I rememer a cereal toy tony the tiger that worked the same way except that you’d squeeze a plastic liter bottle to watch him drop and float. I always thought there was a missed opportuntiy there to observe the captured air pocket within change size so I was happy to leverage that in this clear pipette. We used a syringe to pressurize/vacuum the air within these bottles and cause them to react.

So, with that quickie experiment out of the way, we got to thinking it would be pretty cool to try to build a little fishy that could be animated using air pressure. To get started there, I just sketched up a quick fish body and tail. For some reason I thought it should have a flexible diaphragm oriented parallel to the swim direction and only got smart in the 2nd version which is the most featured in the video. The diaphragm is just a little round disc cut from a disposable rubber glove and pressed into a .25″ hole with a rounded pencil eraser while the contact edge with the resin is superglued/sealed in place. I did find this was a bit tricky for the arc shaped tail connecting rod to bond to. I think we just ended up using super glue again but I can’t quite remember since we tried a few things.

Overall this worked out pretty well. The bonding and materials was prbably the hardest, but the end result is there. I’m mulling over a v3 where we just get even smarter and use a thread knot or two to establish a more defined tail hinge. As it stands there is just a little polymer mesh joining the two but it’s not as defined as I’d like. Anyway, I think we’ve achieved our goal here so we’ll probably move on. Fish are one of D’s favorite animals though so we might go ahead with another just for bonus fun.