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Going out of my mind, thought you guys could help.

A place to ask general spud cannon related questions.
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Going out of my mind, thought you guys could help.

Unread postAuthor: Drake78 » Wed Nov 12, 2008 10:20 am

I'm a special effects artist and i'm doing a job where I need to blow up a fake head. I've built a pneumatic system, but it's not working the way I want. What I need is a radial blast, similar to an explosion. If I use the spudgun design, the blast(projectile) takes a linear path. Does anybody have any idea how I would make the cannon "explode" instead of "shoot"?
Please help, time is of the essence. Thanks.
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Unread postAuthor: Carlman » Wed Nov 12, 2008 11:19 am

dwv...







jokes man dont really do that...

probobly have to go pyrotechnics for that one mate of which you cannot discuss here.
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Unread postAuthor: jimmy101 » Wed Nov 12, 2008 12:44 pm

Build the head with a balloon inside. Plumb a large pressure tank into the head / balloon via an electrically operated sprinkler valve. Fill the balloon with pink glop. When the balloon bursts you'll get a radial blast.
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Unread postAuthor: jrrdw » Wed Nov 12, 2008 12:58 pm

jimmy101 wrote:Build the head with a balloon inside. Plumb a large pressure tank into the head / balloon via an electrically operated sprinkler valve. Fill the balloon with pink glop. When the balloon bursts you'll get a radial blast.


10/4 on that. A nice size storage chamber pumped up to 100psi getting dumped all at once will bust any ballon that I know of.
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Unread postAuthor: Hotwired » Wed Nov 12, 2008 1:50 pm

It may still have a linear blast despite using a balloon.

Although Carlman was joking about DWV, actually pressurising a "hard" chamber to destruction as opposed to a soft balloon would mean a much more radial blast as the chamber itself could hold the full pressure you were after before bursting and not require the blast to be directed in by a cannon. Also, a soft balloon might cause distortion before bursting (good or bad?).

It wouldn't have to fill the entire head of course as the blast would do the rest. I'm thinking of a small drinks bottle pressurised til it blows (could be up to 300psi to do that) or pressurised to 100psi or so and burst with a puncturing device.
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Unread postAuthor: Biopyro » Wed Nov 12, 2008 2:40 pm

Try using a muzzle brake, except no point for the projectile to exit.
A little like this,
http://www.septicsolutions.net/store/Images/VentFilter4inch_LG.jpg
the air would not be able to go up, but would instead be forced to spread out in a 2D radial shape.

My ideal solution would be a "sun" or hedgehog shaped pipe arrangement, but there aren't any conventional fittings which allow this.
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Last edited by Biopyro on Wed Nov 12, 2008 2:46 pm, edited 2 times in total.
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Unread postAuthor: brogdenlaxmiddie » Wed Nov 12, 2008 2:42 pm

I'm with Biopyro. Just add a piece on top of your barrel that goes into the head to stop the blast and push it towards the sides. Should be exactly what you need.
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Unread postAuthor: Hotwired » Wed Nov 12, 2008 2:59 pm

Bear in mind that if using a multi-directional blast spreader inside the head you will end up with it still being there after the "head" gets blown off.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 12, 2008 4:05 pm

I would go with something tougher than a balloon, perhaps a PET bottle - made for water, not carbonated soft drinks though, as they blow at lower pressures.

The issue would be getting it to fail consistently as opposed to teraing in one location.
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Unread postAuthor: Biopyro » Wed Nov 12, 2008 4:23 pm

PET bottles would be good, but I have tested a 2l bottle (lower burst pressure) up to 100psi, and it only burst when I gave it a good tap.
It mostly destroyed itself in small pieces on one side (the whacked side) but the other side was left fairly intact.
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Unread postAuthor: Fnord » Wed Nov 12, 2008 6:01 pm

I'd go with the combustion route for this. Preferably a small bag or one of those plastic juice bottles filled with an acetylene or oxy/propane mix. It's perfectly safe so long as you keep static away by working in a semi-wet environment and use hearing/eye protection.

It'll give you a much better *pop* than a pneumatic system would as well as no debris or water vapor flying around. The most you'll have to worry about is doing some post production on 1 or 2 frames to remove the flash.
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Unread postAuthor: rp181 » Wed Nov 12, 2008 9:03 pm

just put a flat plate about a inch away from the barrel, perpendicular to the barrel, so when looked at sideways, it looks like a "T"
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Unread postAuthor: jook13 » Wed Nov 12, 2008 9:28 pm

you could try putting an end-cap over the barrel and drilling a bunch of holes facing all different directions... Just trying to come up with a simple solution.

Or you could just make the head itself a combustion chamber. You know, fill the head with propane and then ignite.
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Unread postAuthor: Biopyro » Thu Nov 13, 2008 3:34 am

_Fnord wrote:I'd go with the combustion route for this. Preferably a small bag or one of those plastic juice bottles filled with an acetylene or oxy/propane mix. It's perfectly safe so long as you keep static away by working in a semi-wet environment and use hearing/eye protection.

It'll give you a much better *pop* than a pneumatic system would as well as no debris or water vapor flying around. The most you'll have to worry about is doing some post production on 1 or 2 frames to remove the flash.


That would probably work really well, especially as you'd have the advantage of it being near instant. Using a PET bottle should work well too because any shrapnel is extremely light.

I thought about the endcap method too, but you'd need pretty good flow or it really wouldn't work.
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