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New Combustion Ignition?

A place to ask general spud cannon related questions.
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Unread postAuthor: daccel » Tue Jan 06, 2009 9:45 am

Nothing wrong with spark gaps, but it would make a more compact ignition system and could more easily ignite very high mixes.

However, I'm not suggesting anyone run out and put one in their existing hybrid. It would only make sense in a very high pressure cannon like Larda's, and if you're making one like that you would have the means to incorporate it safely.

For the rest of us with mere mortal cannons, the benefits do not outweigh the risks.

I'll add more of a disclaimer next time :wink:.
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Unread postAuthor: john bunsenburner » Tue Jan 06, 2009 10:06 am

how about this, you go out and make the strinking mech not the gun(i dont want to be responsible for your legs being on two seperate sides of the you country) and show it to us, really it should be some kind of cap gun mounted into a screw on cap, that would then be mounted onto the chamber, and shot it to us, or just draw a good diagram, but to come here and ask us if a cap gun would work as an ignition is some what dumb, due to the fact that chances are it will, thats like asking us if you could use c4 to power a gun of coarse you can, but god only know how it will turn out therefore we cannot comment much. But if you make a concrete idea as to using the cap gun then we can comment, and together we can elaborate on the idea and MAYBE make it work.
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Unread postAuthor: daccel » Fri Jan 09, 2009 1:08 am

Well this concept has been floating around upstairs for the past few days so I decided to put something together.

It's a 1/4" acorn nut with a 3/64" (smallest drill bit I had) hole drilled in the end, and a 1/4" set screw with an 1/8" hole drilled through. Couldn't find paper caps so I dug out the contents of a plastic one, and sandwiched it between tape and aluminum can. This allows it to seal the chamber but still be struck from outside.

The nut is cracked because I turned the screw in too far, not from the cap.

I used a drill bit turned backwards for a firing pin. It wouldn't work just holding it in my hand, but when I set it on the table and gave it a light tap it fired.

I'm not sure if it's something I'll pursue in my next cartridge cannon, but thought I'd throw it up as a reference.

Anyone know the temperature this might burn (detonate?) at? All I could find was that it's similar to 'armstrong's mixture', but couldn't find any data on that.

I'll try building a rig to photograph it with low light/long exposure and see what kind of flame jet is coming out of the hole.
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Unread postAuthor: john bunsenburner » Fri Jan 09, 2009 10:52 am

It is pretty much arm strongs mixture. I can tell you it will ignite your gasses if done correctly. 10grams will DESTROY a piece of paper, but be careful, 10grams will also DESTROY your hands from the wrist down wards... :twisted: The idea os ok but how will you fire fom out side the chamber and how will you prevent the alli from going right through you, i would try a little harder, explosives are serious things and not something you can just play around with toi see if it works, chances are you wont be there to make it work after you first failure, even a cap gun could become dangerous...!
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Unread postAuthor: daccel » Fri Jan 09, 2009 8:27 pm

And that's why I'm using a single cap. Which if the package is accurate is .01 grams. Seeing as how they are still sold today to be fired in plastic toys by children, I'll take may chances playing around with it encased in steel :roll:.

It is fired from outside the chamber via a simple spring loaded firing pin. How this and the cap holder are integrated would obviously vary depending on your cannon design. The tape/aluminum sandwich seal the chamber so that it works for a hybrid (like a mini burst disk, minus the bursting). The combination of a small hole and firing pin backing would hopefully keep the aluminum intact, but if it fails you could move to a steel disk instead.

Edit: file comment. Also, do you think gluing it into the neck of a pop bottle for trials would cut down on the sound level, or is there going to be too much coming out the back to matter? Caps are louder than I remember them being, and I need to be able to test this inside :?.
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Unread postAuthor: GalFisk » Sat Jan 10, 2009 6:36 am

A few summers ago I used paper caps for igniting my coke-bottle combustion, before I had made a portable electric ignition. I ignited them by focusing sunlight through the chamber wall with a magnifying glass.
Not very practical, just a fun thing to have done.
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