This piece marks my third by-line in Popular Science. It opens the “Manual” section of the October 2015 issue. Besides designing the circuit, writing the copy, and building the solder-free breadboard-based device shown in the photo, I also carved the pumpkin. Fun fact: Halloween magazine content has to be in bed in the summer, when nobody is selling pumpkins. There is, however, a high quality brand of carve-able fake pumpkin, called a Funkin, which is apparently the industry standard for this sort of thing. It carves easily with a special tool which is somewhere between a paring knife and a fine-tooth hacksaw.
I’m indebted to Lenore and Windell at Evil Mad Scientist Laboratories for the two circuits on which the electronics are based. My breadboard is really just a simple mash-up of their dark detecting jack-o’-lantern and solderless flickery flame designs. Their online store remains the best place to buy candle-flicker and other specialty LEDs in the known universe, as well as tons of other cool open-source electronics you can’t get anywhere else.
Here’s Popular Science Projects Editor Sophie Bushwick building the project on camera:
Of course I knew for months in advance that this was coming, but what I did not know, until I actually received my copy of the March 2015 print issue, was that I also got a coverline.
This project actually started as one of six ideas I sent to littleBits when I began negotiating to develop projects for their Explorer Series kits in late 2014. It was inspired by the well-known “Kelvin” hovercraft activity developed for primary-school STEM educators. There was a lengthy prototyping process in which I tried to produce a workable styrofoam-plate hovercraft using littleBits components; when it became clear that the single 5V case fan bundled with their Premium Kit was not going to be able to lift its own weight, I pushed forward anyway, adding fans and stripping away other components as needed until I got to a reliable power-to-weight ratio. The 5V fans that I used in the final build (Sunon #MB50100V2-000U-A99) are exactly the same part used in the littleBits Fan Bit (though they are deliberately overdriven at 9V).
Here is some heretofore unpublished video of the finished prototype in action. On a fully-charged 150mAH NiMH 9V, it will float for about 5 minutes. You can see that it tends to precess in the same rotational direction as the fans themselves; I would like someday to try a similar build using counter-rotating fans to cancel the net torque, but it will have to use bare motors rather than all-in-one case fans, because case fans all turn the same direction and are not, to my knowledge, ever available in the opposite handedness.
If the torques could be made to cancel, the next logical question is whether they could be modulated to provide steering. It seems likely to me that a four-fan configuration using impellers counter-rotating across the centerline and controlled by a “Herbie” type BEAM circuit with two photo-diode sensors could in fact be arranged, fairly easily, to both float the vehicle and steer it towards the brightest light source in the environment using a “net torque” steering mechanism.