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Developing District 9 style cannon, chamber help.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Developing District 9 style cannon, chamber help.

Unread postAuthor: Sparrow » Wed Nov 24, 2010 2:31 pm

I saw that the D9 weapons have a nice canister on them similar to a small propane tank, and I designed a cannon with an automatic fuel meter and "push forward" reloader.

I am extremely happy with everything so far and I will post designs and pics of everything.

My question to the experienced combustion spud gunners is that I did not want the tennis ball to come out of the 0.75m barrel at lethal velocities and so opted to make the chamber a little less than a third of the barrel volume.

Rules.

Forum Rules wrote:2.Discussion of shooting anything at any person and/or animal is prohibited, and may result in a permanent banning of your account.
A.The exception to this rule is for proper use of legal airsoft and/or paintball markers.


I want to know how hard the ball would be shot with this barrel camber ratio

Thanks!

Edited by jrrdw.
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Unread postAuthor: kjjohn » Wed Nov 24, 2010 3:21 pm

District 9 is my favorite movie, I would like to see a cannon modeled after one of the alien guns.

You want to shoot at someone? I would not recommend that.

However, I would download HGDT. It's a combustion gun simulator that should let you figure out an optimal chamber size, etc.
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Unread postAuthor: Sparrow » Wed Nov 24, 2010 3:30 pm

No No!! LOL I would never hit someone! I was just using something for a reference to the power. I could have used newtons, but that means I need to get my calculator.

all I am really asking, is will it come out of the barrel at a reasonable speed?

I will use that sim, thanks!
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Unread postAuthor: Gaderelguitarist » Wed Nov 24, 2010 3:48 pm

It should come out reasonably fast. I feel like this project would be aimed more towards aesthetics than performance.
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Unread postAuthor: saefroch » Wed Nov 24, 2010 4:08 pm

Sparrow wrote:I did not want the tennis ball to come out of the 0.75m barrel at lethal velocities
Sparrow wrote:I want the ball to come out at a speed much faster than you can throw, but that would only cause a red mark when it hits someone.
If it is indeed true that you're not intending to shoot tennis balls at a person, please at least try to come up with a better reference. We're all a bit touchy about shooting people here...

If you set your build up as an advanced (metered) combustion, it will probably be substantially faster than a person can throw, but just looking through a few D9 weapon designs, I don't think many of them are suited to adapting into a tennis ball-size cannon. Have you considered a smaller bore for a more optimal C:B ratio (and thus moar powa!)?

Would this be it?
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Unread postAuthor: kjjohn » Wed Nov 24, 2010 5:41 pm

I remember from the movie there were several distinct types of alien guns. The one pictured is the one the shoots green fire. There was also the lightning gun, the gun that shot grenade-type things, and the sonic blaster.
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Unread postAuthor: omniscient » Wed Nov 24, 2010 8:05 pm

Many may protest against the idea, but you could actually make a pneumatic, out of a disposable propane tank design.

With a 1" sprinkler valve, you could either trigger the valve electrically (low-performance) or modify it for increased performance.

The propane tank would still put out approximately 40psi, even if the temperature (where you're at) drops to 18 degrees F. - Which is too cold to be using a PVC cannon, anyway.
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Unread postAuthor: saefroch » Wed Nov 24, 2010 8:59 pm

omniscient wrote:Many may protest against the idea, but you could actually make a pneumatic, out of a disposable propane tank design.
Do you mean use one entire tank of propane for every shot, then replace the tank for the next?
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Unread postAuthor: kjjohn » Wed Nov 24, 2010 9:10 pm

I believe he means using the propane tank as a sort of reserve tank to fill the chamber. This has been done before, and seems to work fairly well.
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Unread postAuthor: Sparrow » Thu Nov 25, 2010 6:39 am

saefroch wrote:Would this be it?
Image


:D Exactly it.

Here's a quick sketch of the design (painting not done):

Image


I ran some tests on The HGDT and it showed that with one grill igniter I can get 270fps, which seems a little much. But what I was really interested in was that when I increased it to 2 igniters, the chamber pressure and speed of projectile doubled! Does it really make that much of a difference?

I appreciate the help very much. It's really nice to have a community like this.
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Unread postAuthor: saefroch » Thu Nov 25, 2010 10:43 am

Yup, it does. You can greatly lower burn time with multiple ignition points, which as I understand it, is like putting a faster valve on a pneumatic. The effect of this faster burn was probably magnified by your design's 1:3 C:B ratio, but that's just a guess.

HGDT and GGDT are very reliable, unless you're modeling extreme circumstances, like this.
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Unread postAuthor: Mountain Storm » Mon Dec 13, 2010 2:48 pm

The D9 weapon is so chunky you could almost have a completely coaxial design and multiple ignition points along the rather long and skinny chamber. That would be a reason to have all those tubes down the length of it.
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Unread postAuthor: Technician1002 » Mon Dec 13, 2010 7:52 pm

The basic small volume chamber and large volume barrel would work well. Starting with a configuration like this air cannon, but combustion should work well as combustion produces about the same pressure as this air cannon.

With a metal chamber, the power of the launch can be regulated by using flow restriction plates between the chamber and barrel to limit the muzzle energy if desired. Using an air cannon, the power can be regulated by reducing pressure.

The little launcher shown below can toss tennis balls a hundred yards on 100 PSI with it's 1 inch piston valve. A proper fuel/air mix should be able to toss tennis balls about the same distance.
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