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Need help with a Halloween concussion air cannon design

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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Need help with a Halloween concussion air cannon design

Unread postAuthor: OpenTrackRacer » Mon Sep 22, 2008 10:47 pm

I'm working on a concussion air cannon for Halloween. The idea is to generate a loud report to scare visitors and to set off sound activated props.

I've build a few prototypes (one using the chamber and barrel from my propane combustion spud gun) and have not had good results.

I'm using an electrically activated 1" sprinkler valve and I get an awful honking sound. It sounds as if I'm killing a goose.

Any suggestions on how to achieve the desired effect without the outlay for a special valve?

Thanks!
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Unread postAuthor: Lentamentalisk » Mon Sep 22, 2008 11:04 pm

why dont you read the sticky at the top of the section that you just posted in, that explains exactly what the problems are?
http://www.spudfiles.com/forums/sprinkl ... t8780.html
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Unread postAuthor: MrCrowley » Mon Sep 22, 2008 11:20 pm

Unless you are using a burst disk valve instead of a sprinkler valve, I would use a combustion. (Search the SpudWiki if you are unsure of Burst disk valves).

Pneumatics limited to 125psi with such a small valve are generally not loud at all.
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Unread postAuthor: starman » Mon Sep 22, 2008 11:37 pm

Take a look at my noise cannons. They are combustion and burst disk based and are very effective....not sure if you need this level of boom or not. They could be designed on a smaller scale if you like.

The key is the burst disk and no barrel to speak of. The bigger the breech opening the louder and lower the frequency.
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Unread postAuthor: OpenTrackRacer » Mon Sep 22, 2008 11:49 pm

Thanks Captain Obvious. I read the troubleshooting guide and the Wiki before I posted. Care to point me to the section of the guide that talks about curing honking in electricaly activated sprinkler valves?

Lentamentalisk wrote:why dont you read the sticky at the top of the section that you just posted in, that explains exactly what the problems are?
http://www.spudfiles.com/forums/sprinkl ... t8780.html


To everyone else, thanks for the feedback. Since this is a Halloween prop, it must be electrically activated and repeatable. It will be triggered via a motion sensor and single shot timer circuit. It will fire at a maximum rate of one every ten to fifteen seconds.

Thanks!
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Unread postAuthor: Lentamentalisk » Mon Sep 22, 2008 11:57 pm

What voltage are you using? If you don't have enough voltage running through, it won't open fast enough, and will honk. You should probably have somewhere around 18v going through it.
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Unread postAuthor: OpenTrackRacer » Tue Sep 23, 2008 12:08 am

The solenoid is being actuated by 22 volts DC (from a regulated power supply).

I should add that the honking occurs when the cannon is fired, even very short blasts (1/10 of a second).
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Unread postAuthor: Lentamentalisk » Tue Sep 23, 2008 12:10 am

That is very odd... I am sorry that I can't help beyond that, sorry that I sounded so mean at first, I could have sworn there was some trouble shooting in there for honking, modded or no.
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Unread postAuthor: psycix » Tue Sep 23, 2008 10:55 am

A sprinkler will not likely make much of a concussion blast at all, especially when its not modded.
For a big blast you need 5 things:
-Big chamber
-Big diameter valve
-Bust disk (this makes the blast significantly louder
-No barrel
-High pressure

A 3" or 4" burst disk will make a big blast, probably combustion.
A big piston valve can also do the job.
For the loudest blasts of all, use a hybrid cannon.
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Unread postAuthor: OpenTrackRacer » Tue Sep 23, 2008 12:40 pm

Anything that isn't auto-resetting and able to fire every ten to fifteen seconds is a non-starter.

I've seen some info on a coaxial design that fires a ball into a diaphragm to release all the air at once. I'm trying to get more detailed information.
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Unread postAuthor: grumpy » Tue Sep 23, 2008 12:59 pm

here is a site with some holloween projects that could be fun, including a concussion cannon. i have no idea if it works as claimed, but have done a few of the other projects that worked very well.
http://www.deathlord.net/sprojectp.htm
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Unread postAuthor: OpenTrackRacer » Tue Sep 23, 2008 1:09 pm

Thanks for the link. I've been on that site. My prototypes are pretty much identical to their concussion cannon except I have a honking goose instead!
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Unread postAuthor: OpenTrackRacer » Tue Sep 23, 2008 10:08 pm

Got a new valve and I'm all set. I'm now using a Lawn Genie 1" anti-siphon 180 degree valve and it sounds very good. It has a much better solenoid design compared to the Rain Bird with bigger ports. I bet you could open them up even more but I'm not going to bother.

Best sound seems to be with a slight reducer at the end of the output pipe. My spudgun barrel sounded good too but sort of hollow.

One interesting thing I noticed... the sprinkler valve end of the steel pipe chamber (2" x 12" with reducers to 1" at each end) is getting warm after repeated firings. It's about 20 degrees warmer than the inlet side. This is an in-line chamber with the air entering at one end at exiting at the other. The plastic valve body itself isn't warming up at all (that I can tell).

Any thoughts on that?
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Unread postAuthor: FishBoy » Wed Sep 24, 2008 6:00 am

air gets warmer when it's compressed, also, metal conducts heat better than plastic. I've noticed that after a few 120 psi charges with my bike pump(metal), it get kinda hot near the bottom, where most of the compression occurs.
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Unread postAuthor: psycix » Thu Sep 25, 2008 10:58 am

True, and when the air gets released, it becomes cold.
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