Musings

By: Spatula Tzar

This page holds my incomplete and unsorted thoughts pertaining to my research. If you have any ideas or suggestions, feel free to contact me.

Igniters

I think I found the secret of a good igniter: low resistance and a short thin bridgewire. I previously thought resistance was needed, but this foolishly ignores Ohm's law. The lower the resistance, the greater the amperage for a given voltage. The greater the amperage, the greater the wattage. If the bridgewire is small, it heats up much faster while consuming less power.

With 120v, my #32 copper filament igniters glow red and break within half a second. But using a short 5mm segment of the same wire yields a much more spectacular result. It explodes, sending hot globes of flaming copper into the air. It burned the insulation on my connecting wires, and lightly welded my alligator clamps shut. It also tripped the breakers, but my igniters are meant to consume very high peak amperages.

I must test how short bridgewires perform with 330v from a 120uF capacitor. Magnesium wire from old flashbulbs may prove to be a perfect filament, especially if used with an oxidizer. Perhaps dip it in a KNO₃ solution and let it dry?

Bridgeless igniters may prove to be better than bridged. They work very well with the capacitor, and can be made in large quantities with little effort. So far acrylic based lacquers seem the most durable. Astonishingly, they can be fired dozens of times with little degradation. They even fire underwater, though this destroys them quite quickly. They are capable of lighting visco fuse. The only downside is the acrylic doesn't burn when firing. Nitrocellulose does, but it is brittle, dries porous with many air bubbles, and crumbles from the wire with little force. Adding an oxidizer to the acrylic will help.

Bridgeless igniters may be the idea blasting cap as well. Mix in some AP with the lacquer, and pour it into a microtiter plate like a tray of muffins. Stick the wires in while wet. When dry, pop them out, and you have dozens of small waterproof AP primaries.

More success with copper bridgewires. I found some #40 magnet wire, and so far my theory is holding. It explodes just as well as the thicker wire, while consuming less power. It even works with the capacitor.

The flashbulbs didn't work out how I expected. Sure the Mg wire is extremely thin (and very difficult to work with), but it cannot be soldered. Because of it's reactivity, magnesium always has a bit of oxide on its surface, which cannot be penetrated with low voltages. If I could find a way to make a reliable connection, it would certainly be the best so far. It ignites with a brilliantly hot white light.

I made some bridgeless igniters with a bit of AP in the solution. Surprisingly, they don't work at all. It shows the same resistance when dry, but they do nothing when fired. They just become an open circuit. I'll have to keep trying different mixes.

I also moulded some nitrocellulose in the microtiter plate. It didn't work all that well. Nitrocellulose dries with lots of open air gaps, and the shape of the mould inhibited evaporation of the acetone. It took a week to dry. With a bit of coaxing, they popped out nicely. Unfortunately I forgot to place the igniters inside, so I'm left with a bunch of cone-shaped plastic slugs. I think a better way is to simply dip the igniter with a blob of lacquer, then let it dry in the open.

Success with lacquer blobs. I coated my #40 igniters in a thick layer of acrylic/AP paste, and they detonated with a small crisp *pop*. I am getting closer to the ideal blasting cap. Oddly the nitrocellulose version was weak in comparison. It barely fizzled, leaving the lacquer intact. I'll have to test if my igniters can directly detonate a secondary like nitroglycerine or nitrostarch.

I'm getting closer to a final electrical ignition design. It will be based off a camera flash unit. If the igniter is placed in series with the flash tube, it will go off when the flash is triggered. In essence it is a spark gap switch to control the high voltage high current pulse. If it were switched directly with a relay, the contacts would arc weld themselves shut.

Direct detonation of nitroglycerine was a failure. I used the #40 igniters with 120v AC. The nitroglycerine deflagrated with an anemic fizzle, barely enough to breach the container. There were however two potential points of failure. First, the nitroglycerine sample was of low quality. I spilled some water in the nitration bath, reducing the yield to a few drops, just enough for a single test. Second, a 330v capacitor will likely deliver a more energetic pulse than household AC. I'll have to conduct more tests.

Website

My homepage is in need of a redesign. As the number of my articles continues to grow, the more cluttered it becomes. Sorting them by subject will help, but this means breaking links from external websites. Then again, moving to a new domain will break them just the same. That would be the ideal time for the change.

I need an icon for this musings page. Maybe something with gears and a hamster wheel to comically portray my thought process.

Everyone likes the simple and elegant layout of my site, but I can't help but think there's something missing. Something unobtrusive, but greatly adds to the look.

In regards to the layout code, maybe the text to the right of my images should wrap underneath it instead of stretching the table cell with narrow browser windows. But does it need a <hr /> tag to differentiate from the next block of text?

Misc

I once heard someone mention launching bottle rockets from a mini RC helicopter. Naturally I must steal the idea. My 330 V capacitor ignition system is ideal for this setup. I inserted an igniter directly into a bottle rocket, the same way as my squibs. It didn't work very well. It shot off the igniter in an uncontrolled manner, and exploded a few seconds later. I suspect all the propellant burned at once instead of normally. The solution is to connect the igniter to the base of the fuse. It will create a small delay, but it should work reliably.

Salutes and other firecrackers are trivial to implement. Simply connect the igniter to the end of the fuse from which it is suspended. It will drop as soon as the fuse lights, and should explode a fairly reliable distance below the chopper.

~~Spatula Tzar
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