Posted: 12/08/2007 15:45 PM Post subject: SCTBDCv1.5 - 450psi 50mm steel cannon (updated with new vid)
Rear Brigadier
Joined: 07 Jul 2007 Posts: 2308 1164.60 Spud Bux
I knew that a lot of you didn't want to wait until spring to see this, so I dragged it out, along with a heater light for the barrel, to take one full power shot before giving it a rest for the winter. I've been advertising this thing constantly since September sometime, so you probably know most of the specs already. For those who don't, here they are. For those of you who do, the pictures and a video are at the bottom.
I now wear hearing protection when I fire this, as well as eye protection, as it is rather loud. The response to pulling the trigger is instantaneous, and extremely violent, with anything touching the stand being thrown to the ground, and the entire stand recoiling several inches. Effects on the target are becoming kind of scary, as you will see in the video. A hint as to the power is that the plywood and steel target on the last clip (the only full power shot) weighs over 15 kg (30lbs), and has 4' long legs to prevent it being knocked over.
SCTBDCv1.5 specifications:
Valve
Type: pressure differential triggered cascade failure burst diaphragm
Porting: 40.9mm (1.61")
Exhaust: 1/4" (nominal size) brass ball valve
Standard burst diaphragms: 32 layers of standard aluminum foil
Operating pressures: 5.5 bar (80psi) - 34.5 bar (500psi)
Notes: alu. foil diaphragms seal extremely well in unions, even at higher pressures. Their burst pressures seem to range from 400 - 450 psi.
Chamber
Size: 2.067 ID x ~50" long
Material: Schedule 40 2" galvanised welded steel pipe, theoretical burst pressure ~2300 psi (159 bar)
Fill valve: 1/4" (nominal size) hydraulic quick connect (male), rated for 3000 psi (207 bar)
Filling system
Storage vessel: Type 16 industrial nitrogen tank, operating pressure ~2400 psi (165 bar)
Regulator: 50 - 500 psi Praxair purging regulator (which doesn't like the cold), output is 1/4" flare fitting
Hose: 1/4" PVC hydraulic hose, rated for 5800 psi (400 bar)
Outlet: 1/4" hydraulic quick connect (female) rated for 3000 psi (207 bar)
Since I posted the original SCTBDC, there have been several improvements. The chamber volume has been doubled, the operating pressure has been tripled, there are now 3 different barrels (all 12' long), and the reliability is 100%, with no failures of even the more dubious parts. The stand is a hefty, two piece construction with a carriage made of 2x4s and plywood, and a stand made from 4x4s and 2x8s, along with other pieces that were lying around. The stand is wearing out from the recoil already, and a steel base with wheels may be built in the spring. There is a piece of 3/4" threaded rod being used as a bolt through what used to be the balance point.
The pictures that I have of it assembled are all of with the shorter (80ci) chamber, but other than that are accurate. I do have a picture of the newly extended chamber however.
And now the video. Please don't request more, because I'm not bringing it back out until spring.
I can take it to 500 psi, which just happens to be the limits of the disks and of the regulator. Worries of exploding barrels stalled the big video until spring though.
After watching the video, I have an inexplicable urge to quote the Simpsons:
Researcher: "The surgery could greatly increase your brain power - or it could possibly kill you"
Homer: "Increase my killing power eh? Lets do it!"
I'm impressed - I wasn't expecting the target to fly quite that far.
@VH_man: .50 AE is closer to 1400 ft-lbs - and that's from a barrel half an inch across and 6 inches long.
3100 ft-lbs is quite possible in a barrel 2" across and 12' long, even if the pressure is only about 1 or 2% of the firearm cartridge.
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.
I wasn't expecting the target to fly at all, considering how light the projectile was. Something got forked up, and the dart hit the target sideways (how a 12" long dart tumbled 90 degrees before it had even left the barrel escapes me). We never did find the dart though, just the imprint on the steel plate.
"Increase my killing power, eh?" That one's a classic.
Last edited by DYI on 12/08/2007 16:23 PM; edited 1 time in total
Wow, kind of reminds me of a mini version of those Pumpkin chuckers.
Pity that the burst setup can take "only" 500 psi, it seems as though the rest of the launcher could handle much higher pressures.
I await spring with anticipation
Very nice job DYI.
The problem with the burst disk setup is that I need to use aluminum foil for the disks. 8 layers bursts at around 70-80 psi. 16 layers bursts at 140-170 psi. 32 layers bursts somewhere between 350 and 450 psi. Judging by that, 64 layers (which would be difficult to cut, and use loads more foil) would burst anywhere from 800-1100 psi (or maybe more), which is far too close to the burst pressure of the pipe for my liking, and I'd need to build a new high pressure pump for the main chamber, since the nitrogen reg will only go to 500.
The damage pic was a low power shot with 1/2 pound of steel ball bearings wrapped up in aluminum foil.
That's a slightly different number to what I got when I was looking up muzzle energies of typical 12 gauge slugs a while back. (because I was wondering how HEAL compared). I got about 1500 ft-lbs for a 1 oz. buckshot load from a 2.5" shell.
I get a fifth of that currently, but could easily reach a quarter, possibly a third if I get round to using more pressure. Obviously I use a slightly larger bore (actually, within 0.1mm of the size 9 gauge would be) and longer barrel but it's still quite cool that spudguns are starting to blur the line of power that used to define them from firearms.
Being able to claim that a homemade trombone look alike is within an order of magnitude of what most people have down as an uber-weapon is quite enjoyable.
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It really is a nice cannon.
- you wouldn't shoot that in the direction of your shed now eh?