SpudFiles

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.

dwv...







jokes man dont really do that...

probobly have to go pyrotechnics for that one mate of which you cannot discuss here.

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.

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.

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.

Try using a muzzle brake, except no point for the projectile to exit.
A little like this,
http://www.septicsolutions.net/store/Im ... nch_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.

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.

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.

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.

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.

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.

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"

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.

_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.