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A place to ask general spud cannon related questions.
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Unread postAuthor: Technician1002 » Thu May 28, 2009 11:22 pm

jook13 wrote:If money is no option and you want a challenge, I say go for a large bore pnuematic with high pressure. I could only imagine a steel cannon with a 4 inch barrel and 500 psi. It would be more awesome then a one legged waitress working at the IHOP.


I'm working up to that a step at a time. I gotta finish the 3 inch 200 PSI one first. The 100 PSI 2 inch is working flawlessly. From what I found on the DOT regulations on my tank, the 2 inch should be good for up to about 300 PSI. I don't trust my brazing job that far.
:shock:
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Unread postAuthor: inonickname » Fri May 29, 2009 3:25 am

Mike_Hunt0420 wrote:
inonickname wrote:I challenge you to beat me

If you can go smaller, I'll be impressed. I'm up for competition.


I might be up for that, a few questions first. What kind of power you looking at on that little guy? And I might be inclined to make one smaller just to try it but really, are they even worth it that tiny? No offence I still think mini's rock but I just have big doubts as to their power is all...


Well, you're pretty much correct. While you don't sacrifice velocity you lose muzzle velocity in smaller calibers, but with the benefit of a higher penetration co-efficient.

The power on propane or butane is better than ye old pill bottle gun, and much better with a burst disk. Making an electrolysis unit and using oxy-hydrogen makes VERY high velocities, and if you're an ex RC car racer and have some stick nicad or nickel metal hydride packs they make a great portable power supply. Lots of current.

Though making a mini 'advanced' on this scale has little point. You'll notice the biggest performance boost from using the absolute coirrect amount of fuel.

If you're up for competition, I'll give you one hint. Make the chamber shorter and fatter if you can.

Btw: I found an even smaller motor with a diameter of 3.5 mm. So there you have it, if you can go smaller than 3mm chamber I.D. I'll have to start winding my own coils to beat you :P
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Unread postAuthor: Mike_Hunt0420 » Fri May 29, 2009 1:31 pm

I'll probably stick to making the hybrid next, I might build a bbmg right after my current project just to have it, but the hybrid looks the most fun. As for building a smaller gun, i bow to you ino I just can't get mats that small lol.
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Unread postAuthor: Moonbogg » Fri May 29, 2009 3:15 pm

@inonickname

Its crazy you mentioned the electrolysis cannon. I was thinking about that recently actually. Fuel would be cheap lol...but I don't know how fast your batteries would die, so that might get expensive. Immagine going camping and fueling your hybrid down by the lake?
So the 2:1 ratio of hydrogen to oxygen...is it optimal for combustion? I haven't really researched to be honest.
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Unread postAuthor: Ragnarok » Fri May 29, 2009 3:24 pm

Moonbogg wrote:So the 2:1 ratio of hydrogen to oxygen...is it optimal for combustion? I haven't really researched to be honest.

Well, given that your combustion product is water, which has two hydrogens to one oxygen, and the aim with fuel mixtures is to have a stoichiometric mix...

... in other words, yes.
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Unread postAuthor: Moonbogg » Fri May 29, 2009 4:40 pm

Ragnarok wrote:
Moonbogg wrote:So the 2:1 ratio of hydrogen to oxygen...is it optimal for combustion? I haven't really researched to be honest.

Well, given that your combustion product is water, which has two hydrogens to one oxygen, and the aim with fuel mixtures is to have a stoichiometric mix...

... in other words, yes.


Brilliant! Has it been tried? And is it supposed to be more powerful than mapp/propane?
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Unread postAuthor: Ragnarok » Fri May 29, 2009 5:10 pm

There are a couple of hydrogen powered launchers on the site, mostly minis, because of the convenience of using the stoichiometric "Brown's gas".

Theoretically, you can get more energy shoved into the chamber, because it's using a purer oxidiser than air. It's also got a faster burn rate, but it's also implosive after it's cooled, because it takes three moles of gas, and makes two moles of liquid.

Power therefore depends.
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Unread postAuthor: inonickname » Fri May 29, 2009 7:12 pm

When I finally got my electrolysis unit working for the hydra it could be run off rechargeable NiMh or NiCd RC car stick packs. (I have about 5 ones that I don't use, I just buy new ones when the performance drops) so when your inside on a rainy day I charge them all up for it. A car battery is another good source, but the stick packs are much more compact.

Image
(hydra and adv. combustion)

I'm planning on building a better electrolysis unit and remaking the hydra. The mix that comes straight out of the unit is stoichometric, so you can just purge your chamber with it. That said, you don't get more energy out than you put in so it's more suited to small cannons.

If you wanted to make an oxy-hydrogen cannon I'd recommend at least fair aluminum or brass.

The power is MUCH better, the mixtures burns MUCH faster. But you need a much stronger cannon. The mixture also ignites so much easier due to oxygen and the massive flammability range of hydrogen (around 4-75%, compared to 4-9% ish for propane/butane).
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Unread postAuthor: Moonbogg » Tue Jun 02, 2009 7:51 pm

Any progress on those designs? I have overcome one of two hurdles for the hybrid for this particular design.
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