SPX: Simulated Explosions and Air Mortars

Post questions and info about pneumatic (compressed gas) powered launchers here. This includes discussion about valves, ratios, compressors, and anything else relevant to launchers powered by compressed gas.

Postby Detigr » Thu Feb 22, 2007 12:32 am

Hi all,

It's me again, the Canadian pyrotechnician who wanted to know how to build Tim's staff (from Monty Python) a few months back. That thread eventually got locked, understandably, but I eventually puzzled out a design that I'm currently building thanks to a couple forum members.

Anyhow, fast forward to last Friday in Lake Havasu City, AZ; home to Western Winterblast. For those outside the pyro community, it's essentially a big convention where pyrotech's from across North America gather to share info and blow stuff up in the desert. While there, I met up with a gentleman who runs a small movie studio in California and who has been a customer of Joel's. Being a member of the forum and something of an amateur spud gunner myself, I was intrigued and talked to him for a while as well as took a few photos of his "gun".

http://i104.photobucket.com/albums/m176/Detigr/Gun1.jpg
(Link goes to a photo of his gun)

http://i104.photobucket.com/albums/m176 ... rSmall.jpg
(Link goes to a photo of his gun in action)

As you can see, it's a pretty spectacular little device. The gentleman who owns it uses naphtha (white gas), pressurizes the chamber shown in the first photo to 100-110psi using a portable compressor and switches it remotely through a simply flick switch attached to the valve.

Now, I don't want to take business from Joel, as that's a pretty low thing to do, but we're all hobbyists here and I want to build one of these things on my own at the lowest possible price.

Specifically, I need a <i>smaller</i> version, and 10-12 of them for special effects usage. I am a certified special effects technician in Canada, so I do have sufficient experience with explosives and such. In addition, I have experience with taps/die, solvent welding, 24 vac sprinkler valves from 3/4 inch through 5 inch and pvc pipe (I run an irrigation company as my day job).

I can see quite a few parts that are easy to obtain and relatively cheap (except the copper), such as:

- A Schraeder Valve (would a valve-stem from a car tire work as a substitute to eliminate the tapping of threads?)
- a pressure gauge
- a 1 inch 24 vac solenoid sprinkler valve
- 1 inch copper piping (and assorted fittings)
- 2 inch copper piping
- Some sort of safety blow-out valve for the air resevoir. What kind?

What I need <i>your</i> expertise is how to shrink everything down to a smaller size, in order to create much smaller explosions as well as to cheapen the production of multiple units. I figure a 2 inch resevoir and 1 inch copper pipe may work, but don't know.

Any opinions? Joel, I hope you don't mind, but I can't afford 300 bucks and the (necessary!) wait for 12 individual units! If you want to use that image above, please just let me know and I will let you have full release.

Thanks everyone; this forum hasn't let me down yet!

- Nathan Wood
Detigr
 
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Postby BewareOfDog » Thu Feb 22, 2007 1:34 am

There are many of us who would probably love to help you, Detigr, but the discussion of such a device would be classified as a flamethrower, or an "Incendiary projectile".
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Postby Sardaukar » Thu Feb 22, 2007 1:04 pm

Seriously, man, this is simple stuff. Just look at the picture.

If you can't figure it out and build it by yourself you probably better not build it at all...
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Postby Detigr » Thu Feb 22, 2007 1:59 pm

DR:

I never seem to have much luck with these "incendiary projectiles". I do believe it was you who gave me such detailed help on my last project. Would you mind answering a few questions over e-mail again?

Sardaukar:

It may be simple to someone who has built pneumatic launchers before, but I've only had the experience with building combustion launchers.

Where is the harm in asking expert opinions on something that could potentially injure myself or someone else if I make an error in construction that could be easily avoided?
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Postby spuzi14 » Thu Feb 22, 2007 4:04 pm

The harm is 12 year olds who know everything. It's too bad the old BCPneumatics forum isn't still around...
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Postby Mr.Plow » Thu Feb 22, 2007 6:31 pm

Detigr-

Check your email
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Postby Sardaukar » Thu Feb 22, 2007 11:26 pm

The harm is that you ask advice on how to build some illegal device...building it yourself is part of the learning process of being safe with the thing.
If you want to build a flamethrower, look at the picture, build the same thing, be safe.

BTW, is that an ABS pneumatic?... not good.
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Postby Detigr » Fri Feb 23, 2007 3:16 am

Mr.Plow:

I received your e-mail, and have replied. Thanks for such a prompt response.

Sardaukar:

I understand the concern, but the device is certainly not illegal if handled by a person specifically licensed to deal with such devices. In my line of work, I deal with concussion mortars, movie effect air mortars and gas (or "ghost") mines all the time, but have been <i>actively</i> trained to do so safely.

I'm not looking to build a flamethrower. If that were the case, I would not ask for "expert" opinion, nor would I make my name obviously known along with contact information. What I am asking for help with is the construction of a specialty device that <i>can</i> be operated safely.

I'm not looking to start a flame war, no pun intended, and thank you for being vigilant about safety; it's something I'm strict about on an site I work at.
Detigr
 
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Postby BewareOfDog » Sat Feb 24, 2007 7:29 am

Detigr,
It's not a question as to whether or not <b>you</b> can build/operate such a device. It's just that we cannot openly <b>how</b> to build/operate it. ;)


~Sardaukar:
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">
BTW, is that an ABS pneumatic?... not good.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

YES! - There is no way that it's SCH40 pipe painted black!- That would make no sense! :mrgreen:
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Postby Detigr » Sat Feb 24, 2007 1:26 pm

DR:

I totally understand, and have gotten some help from another of the forum members already. It makes sense to mention this device wasn't actually intended to be a gas mine in the first place, but Joel was asked to make something closer to a classic air mortar (fill it with dirt, dirt goes in the air to simulate bullet shots or shell hits or whatever).

Now I just need to figure out if the solenoid valves I have are going to work.
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