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SCTBDCv1.5 - 450psi 50mm steel cannon (updated with new vid)

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: elitesniper » Sat Dec 29, 2007 7:03 pm

DYI you do like burst disk alot dont you? :D
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Unread postAuthor: SpudBlaster15 » Sun Dec 30, 2007 1:26 am

DYI wrote:Updated original post with new damage video (SB15, this is for you).


YES!!!!!!!!!!!!:D:D:D That was awesome! Much more impressive than I expected, I had no idea that the door would completely shatter into dozens of fragments. But I guess when you deliver nearly 6000ft/lbs of energy to almost anything made of wood, it is going to suffer some pretty immense damage.

Also, this cannon has inspired me to build a monstrous (2" bore, 13,000+ft/lbs) hybrid launcher over the next few months.
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Unread postAuthor: Carlman » Sun Dec 30, 2007 4:33 am

hmm local cops might want that to bust into some house one day...

well at least you can get in if you get locked out lol
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Unread postAuthor: Billy Bob » Sun Dec 30, 2007 1:28 pm

What are your neighbours say about the. "Huge Weapontestings " :D

The gun is excellent !!! simple and usefull AND POWERFULL dont forget.
8)
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Unread postAuthor: DYI » Sun Dec 30, 2007 2:13 pm

Well, the neighbours are either indifferent, or actually like it. Kind of strange, but it isn't that loud because of its high efficiency.

SB15, I'm assuming that this must either be using 10x+ mixes, or be impractically long, because that's almost half the muzzle energy of FEAR.
But I'm building a 20x, 2" bore hybrid in the summer, so that should be pretty impressive too.

But my next main project is the massive backstop I'm building for the SCTBDC so I can safely fire it in my backyard. Probably 1/2" plate steel of something, with 4x4s for supports. That, and the recoil absorbing stand for the launcher, to avoid another mishap like yesterday's.
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Unread postAuthor: SpudBlaster15 » Sun Dec 30, 2007 2:38 pm

The launcher will likely use a 3" x 36" Sch 40 steel chamber, a 2" x 144" ABS barrel, and 8x mixes. GGDT estimates a muzzle energy output of ~13,600ft/lbs. My backyard is ~5 acres, so I should have lots of room for such a huge cannon.
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Unread postAuthor: DYI » Sun Dec 30, 2007 2:52 pm

Where do you live Spudblaster?

My plan is a 3" x 24" steel chamber, and a 2" copper barrel, with 10x - 20x mixes. EVBEC forecasts a hell of a lot of muzzle energy, about half what FEAR generates.
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Unread postAuthor: mark.f » Sun Dec 30, 2007 3:15 pm

DYI, have you considered bungees and a sliding platform for a stand? I'm not talking just one or two cords, either. Depending on your max projectile weight, several bungee cords and a platform allowed to slide "freely", (minus the friction from wood on wood), backwards, but not side to side, should allow enough flex to avoid future failures of your stand due to "quick" loads. Your stand will still have to be pretty beefy, however, if you plan to fire heavy rounds. Perhaps you could try reinforcement with 1/2" or 3/4" threaded rod? Or maybe rebar if you've got the tools to work with it...

SpudBlaster, do you think a larger (3") chamber would survive many 8x mixes? I know you and others have lit off these kinds of mixes in smaller chambers, like 1-1/2" or 1-1/4" SCH-40 steel, but with the larger pipe, I think your "safe" pressure would be reduced. I definitely forsee some sort of remote ignition in your future. :wink: Probably the RC servo again, no? I've just been using a pull-string tied off to the toggle switch on my new ignition box, playing around with my old hybrid.
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Unread postAuthor: DYI » Sun Dec 30, 2007 3:32 pm

I'd be using SCH 160 steel in my design. The purpose of wider chambers is to reduce the chance of DDT at higher mixes (or at least that's the purpose of the wider chamber on my design).

My plan was to make a stand out of 4x4s, and instead of a single support in the middle of the carriage, I would use one on either side. Then I would make a rectangular-prism shaped base, with 4 wheels, so that the whole thing would slide backwards, and use chains and various clamps to secure the cannon to the stand.
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Unread postAuthor: SpudBlaster15 » Sun Dec 30, 2007 4:04 pm

DYI: I live on the other side of Canada in BC.

Mark: Remote ignition will be a must. No way will I be standing anywhere near a 3" diameter steel chamber filled with a mixture that can potentially generate internal pressures on the order of 800psi. The servo setup will likely be used.
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Last edited by SpudBlaster15 on Thu Oct 20, 2011 5:06 pm, edited 1 time in total.
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Unread postAuthor: mark.f » Tue Jan 01, 2008 12:41 pm

DYI wrote:If you can show me how to post GGDT files, I'll show you the GGDT output for it. I don't actually have any close up pictures of the valve area.


You don't have the option to export GGDT files in a format convenient for this forum, but most people just take screen-shots. This is from the steel ice-slug shot...
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Unread postAuthor: WOW!! » Tue Jan 01, 2008 12:50 pm

For ammo you could take 2 1 1/4" end caps and make a little section of pipe with them at the ends and then fill it with concrete, Pykrete, or something to that extent and shoot that. Since the 1 1/4" end caps give a good seal in 2" pipe.
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Unread postAuthor: DYI » Tue Jan 01, 2008 10:35 pm

Mark, that GGDT is close, but not quite;
The pressure used was 470, not 450, the dead space is more like 10+ cubic inches, and the flow coefficient of a burst disk valve is at least 50, possibly 55.

The most significant problems however, are the bore and the valve:
I used a 3" barrel for this shot, and you entered a 2" barrel. The use of a 3" barrel significantly increased muzzle energy for this shot.
Also, you entered 2" porting, while the porting on my valve system is only 1.61". This slightly reduces performance. (the union is ~1.9" ID, but the rest of the valve is only 1.61, and the flow is determined by the place with the least flow)
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