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Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: DR » Wed Jan 14, 2009 12:47 am

I absolutely live for questions like these! Well, not really- but they DO get my attention more than most other things.

Large explosion / Minimum Cost / Minimum Effort :

A company sells HDPE drums, such as Yankee Containers, would be your best bet. The drums that they list have specs as to what the UN Ratings are on each container. These UN Rating numbers, are listed in kpa (kilopascals)

If you were to bury a 55 gallon HDPE drum and pressurize it through the 2" threaded bung, it would give you a pretty damn big special effect.

They also carry smaller ones, such as a 15 Gallon, but the pressure rating (UN Rating) is 2.5 times higher.

The 55 gallon ones are mostly rated at 100kpa ( 14.5 psi )
One of the 15 gallon ones is rated at 250kpa ( 36.26psi )

Here are some links:

<a href="http://www.yankeecontainers.com/QandA.php?action=show_answer&id=174">What are UN Ratings???</a>


<a href="http://www.yankeecontainers.com/Items/SPP055CN00UL1.html">55 gallon</a>


<a href="http://www.yankeecontainers.com/Items/SPP15DDBK55.html">15 gallon</a>
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Unread postAuthor: kissass78 » Wed Jan 14, 2009 4:32 pm

What about a large reservoir going into a 2" sprinkler valve, which is attached to a large barrel. On the end of the barrel is a burst disk. So I can pressurize the reservoir and (remotely) release the valve forcing the air into the barrel and thus making the explosion through the bust material.

Has this been done?

This would allow me to remotely discharge the air, and get the size explosion I want.

Is this correct or am I missing something? (I am so sleepy).
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Unread postAuthor: SP00K » Wed Jan 14, 2009 5:02 pm

If you're making a movie, then just go to [url]detonationfilms.com[/url]

It's funny because as mentioned before, they used the thunderpipe from spudtech.
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Unread postAuthor: Tidbit77 » Wed Jan 14, 2009 5:13 pm

just an idea but, what if instead of using one big cannon, you could use several smaller ones all piloted by the same blowgun/sprinkler valve/or whatever, this would allow you to use higher pressures than 1 big cannon and would make the explosion wider ( if you wanted to make it wider)
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Unread postAuthor: Pilgrimman » Wed Jan 14, 2009 5:43 pm

Someone linked earlier too the mythbusters' dairy creamer cannon. I think this is your best option, due to the sheer simplicity, and of course, the result. The design is not too complex (to my knowledge) and shouldn't set you back too badly. Glad to see our hobby is making it's way into the film industry some more :D Good luck with the movie! Hope to see it in theaters :D
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Unread postAuthor: MrCrowley » Wed Jan 14, 2009 6:10 pm

BTW, I take it this is pretty much exactly what you want to build:
[youtube]http://www.youtube.com/watch?v=Qaiut9O50MU[/youtube]
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Unread postAuthor: kissass78 » Wed Jan 14, 2009 7:16 pm

Yup that's it.

How's it work though? That's the question.
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Unread postAuthor: Fnord » Wed Jan 14, 2009 7:50 pm

Just looks like cone full of debris with a valve at the bottom.

I'd actually try what DR suggested. If you don't want to buy those containers, you could even epoxy a 5 gallon water jug shut with a 1" port left for pressurization. They burst at about 60-80 psi, so I'd pre-pressurize them to 40, then dump unreggulated co2 from a bulk storage tank or fire extinguisher into it when you want to trigger it.
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Unread postAuthor: kissass78 » Wed Jan 14, 2009 8:04 pm

Ok.....so I'm not understanding the idea there.

The 55 gallon drum comes with a cap and a 2" threaded opening on the bottom? And I just pump it up until it blows? Is it reusable?
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Unread postAuthor: Hotwired » Wed Jan 14, 2009 8:21 pm

After a bit of rummaging about I think some ideas are way more powerful than you're after.

I mean this is what I'm seeing people selling as air mortars ex. 1, ex. 2. Just large air tanks with standard albeit large sprinkler style valves on them which are triggered electrically.

An 8" burst disk could possibly flip a car let alone a funnel of lightweight debris.

I have found a 12" air cannon however and I do think it does use a burst disk
Image.
Also that it probably IS used for launching car sized objects.


I believe what they're meaning with the drums is that you pressurise them until they physically explode. Not at all reusable.
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Unread postAuthor: kissass78 » Wed Jan 14, 2009 8:40 pm

Oh....

Well a $55 drum is too much for something I can only use once.

Thanks for the input though! This is awesome.

I went to Lowes and priced all the parts (larger PVC is no longer being sold after inventory is gone). It will be well over $300 to build it out of PVC.

I'm willing to do that if it works....the problem is I can't know if it works until I do it. Sucks.

What are people using as burst disk material...a few layers of foil?
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Unread postAuthor: FishBoy » Wed Jan 14, 2009 8:59 pm

starman wrote:You could also build yourself some movie "dirt" by using something called vermiculite. It's not anywhere near as heavy as real dirt clods and you should be able to blow it quite a good distance. They sell it at garden stores and use it to make a very light potting soil. They also sell it for use as packing material. It's very light so you can blow it around very easily but when mixed with some real dirt, maybe some peat moss, and tree bark chunks, should look just like dirt on film.

You could try cutting out a cardboard "piston" to fit in the bottom of a 5 gallon bucket that's had a hole cut in it for your spudgun barrel, fill it with it the movie dirt and attach your spud gun....fire away. Should easily blow it 30-40'. You may be able to scale it up to bigger 55 gallon barrels as well. You'll need a bigger cannon of course.... :wink:


So far I'm thinking this sounds the best, this could also be used pneumatic or combustion. The only caveat of the pneumatic option is that you will need a fast valve
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Unread postAuthor: MrCrowley » Wed Jan 14, 2009 9:56 pm

a few layers of foil?

For 1.5", 2" and smaller diameters. You will need several hundred layers for 8" i'd imagine. That's why very thing sheet metal may be best. Some members might know of some very thin and flexible sheet metal that would work.
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Unread postAuthor: kissass78 » Wed Jan 14, 2009 10:06 pm

Should work provided it doesn't send shards out on release. That would be bad.
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Unread postAuthor: MrCrowley » Wed Jan 14, 2009 10:22 pm

It should only tear, but if it does send shards a grill between the burst disk and funnel might help. The dirt should stop it from doing any damage anyway.
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