design & make » flash paper

Crushtoberfest promo video!

joel — Thu, 29 Oct 2009 15:46:46 +0000

everything’s better with fireballs, part II

joel — Tue, 27 Oct 2009 11:47:31 +0000

Three days left till Crushtoberfest, and I prepared a total of ten fireball launchers for the Hi-Striker. They’re used in pairs, so that gives us five “wins” worth of awesomeness. Here they are:

First I cut the copper tubes to length, drilled each end cap and JB-Welded 1/4″ phono plugs into each one. Then I soldered model rocket ignitors to the phono plugs’ contacts inside the caps. The gray boxes are aluminum project boxes with phono jacks installed in one side. These will be mounted to the back of the Selleck head, but for now they were a good way to hold each cap as I was soldering. I then assembled the tubes to the caps and used a little electrical tape to hold them together.

I cut each 8″ x 9″ sheet of flash paper into strips (across the short length),

folded all the strips in half together and twisted them loosely,

then stuffed the whole thing into the end of the tube.

Done!

everything’s better with fireballs

joel — Fri, 02 Oct 2009 04:42:49 +0000

I never intended for the Selleck Striker to include fireballs. But this time last year we started thinking about fireballs for something else and got all the pieces together, so they were really just waiting around for something awesome like this. Here’s how it’ll work.

The fire itself is created by igniting “flash paper”, which is a nitrocellulose paper used by magicians to create relatively safe indoor fire effects in their act. Basically the stuff flares up and it’s gone… no burning embers, hardly any ash at all. It is fire, but you can basically hold it in your hand, it’s there and gone that fast.

The flash paper is ignited by a model rocket engine ignitor, which is essentially a tiny incandescent filament with some flammable paste packed around it. You apply 6-12 volts with enough current and it flares up breifly, but plenty long enough to light the flash paper. The Arduino can’t supply nearly enough current to light it, so I’ll end up using a transistor to switch a higher-current (and slightly higher voltage) power supply to the ignitor.

For now I’m just concerned with the hardware. I’d like to have a replaceable “charge” that can be unplugged once it goes off, and replaced with a fresh one. So the sketch below shows a small metal tube with a 1/4″ phono plug on one end that plugs into a matching jack behind the Tom Selleck head.

The tube is copper and the end fitting just slips on snugly, but everything else turned out just like the sketch:

For now I’m using a 9V battery touched across the plug’s contacts. The trick, it turns out, is packing the right amount of flash paper in the right way. It took a few tries, but I think the third attempt got it right: