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mythbusters air cannon

A place to ask general spud cannon related questions.
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Unread postAuthor: SpudBlaster15 » Thu Jan 18, 2007 4:06 pm

I watched the Palm tree/hay episode last night, and I am not impressed to say the least. They built a HUGE pnuematic cannon in an attempt to fire a piece of hay exactly 320mph, or 470fps. The cannon had a 24 foot long barrel, and a chamber that appeared to be about 6 feet long and several inches in diameter. Based on the extremely small mass of the projectile, speeds such as this could have been acheived using a cannon 1/4 of the size, using the same pressure (80psi). They needed a better valve. A diaphram valve actuated by a solenoid just doesnt work well.
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Unread postAuthor: MrCrowley » Thu Jan 18, 2007 4:32 pm

I saw that on youtube, hard to see exactly what was going on but the barrel looked the length of their M5 studio. The piano wire went clean through though :P
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Unread postAuthor: squeaks » Thu Jan 18, 2007 5:28 pm

Yes, the barrel was overdone on the straw myth. So what if it was an 80ft long barrel(yes 80ft, not 24), they still got what they wanted and it looked really funny.
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Unread postAuthor: pyrogeek » Thu Jan 18, 2007 5:42 pm

Yeah, they could have made a better cannon pretty easy. But, they weren't necessarily going for the top speed possible, they just wanted to reach speeds like those in a hurricane. So, having a supersonic cannon wouldn't necessarily be important.

The exploding pants episode was cool. But, the idea of nitrating a pair of pants is pretty dumb. Due to the large quantity, there is too much risk of a runaway nitration from it overheating, and nitrogen oxides being released (like what happened when the red gas was billowing out in that episode). Smaller bits of cellulose would have worked better. Anyway, single base nitrocellulose is pretty lame stuff. Thats what ping pong balls are made of. And even double base sucks, it still requires quite a bit of confinement to explode.

They show is cool, but they definitely don't know that much about a lot of things they are doing.
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Unread postAuthor: MrCrowley » Thu Jan 18, 2007 5:46 pm

Someone on their forum should give them a link to spudfiles and tell them to revisit the myth and come to use for help on valves and C:B ratios :P :wink:
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Unread postAuthor: Brian the brain » Thu Jan 18, 2007 5:51 pm

I'm getting the idea they don't want to teach people how it could be done better.
They don't want to get sued.

a chicken gun with a giant ballvalve?

Come on!!!

Try again with 4 supahvalves baby!!
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Unread postAuthor: frankrede » Thu Jan 18, 2007 6:23 pm

Not a ball valve Brian. It was a butterfly valve. Butterfly valve>ballvalve.
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Unread postAuthor: MrCrowley » Thu Jan 18, 2007 6:46 pm

Yeah butterfly valves have alot more flow then a ball valve and if you got it to open in a split second well that would be some valve. Some guy is selling a 8" butterfly valve for $250NZD($180US)
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Unread postAuthor: judgment_arms » Thu Jan 18, 2007 7:22 pm

SpudBlaster15 wrote:I watched the Palm tree/hay episode last night, and I am not impressed to say the least. They built a HUGE pnuematic cannon in an attempt to fire a piece of hay exactly 320mph, or 470fps...


470fps??? If that’s all the velocity they needed why the heck did they make the huge air cannon? Just get a medium powered BB gun, you can get a BB gun at china-mart that shoots 625fps, for about $30u.s., and that’s with a 5gr. BB!
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Unread postAuthor: StealthSpud » Thu Jan 18, 2007 7:35 pm

Well that wasn't really the point though...
They couldnt have concluded anything from a BB gun

But either way you put it the Mythbusters rock!!
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Unread postAuthor: judgment_arms » Thu Jan 18, 2007 8:44 pm

Why not? The myth was that a piece of straw could shoot clean through a palm tree when blow by hurricane force winds, about 470fps, and the Crosman model 760 shoots at 625fps, more than enough velocity. So what’s the difference between a 470fps and 625fps? Why couldn’t they use a BB gun? Oh I know, that would be too easy and it wouldn’t make a good show. Not saying I don’t like Mythbusters, just they tend to over complicate things.
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Unread postAuthor: StealthSpud » Thu Jan 18, 2007 8:52 pm

Yeah that is a very good point...
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Unread postAuthor: SpudBlaster15 » Fri Jan 19, 2007 3:02 am

pyrogeek wrote:The exploding pants episode was cool. But, the idea of nitrating a pair of pants is pretty dumb. Due to the large quantity, there is too much risk of a runaway nitration from it overheating, and nitrogen oxides being released (like what happened when the red gas was billowing out in that episode). Smaller bits of cellulose would have worked better. Anyway, single base nitrocellulose is pretty lame stuff. Thats what ping pong balls are made of. And even double base sucks, it still requires quite a bit of confinement to explode.


The nitration reaction did not run away due to the quantity of nitrocellulose they were attempting to produce, it did so because they didnt cool it. The reaction is very exothermic, and once it reaches approximately 100*C, you have reached the point of no return. Nitrogen Dioxide is bad stuff.
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Unread postAuthor: Pyrodogg » Fri Jan 19, 2007 8:50 pm

Just a general comment about the Mythbusters, after all they are an American TV show, first and foremost they are going for Entertainment/Shock value, not necessarily correctness and perfection. To anyone who doesn't know anything about airguns aka the majority of the population, I would think that a bigger barrel would look more impressive and intimidating.

Besides their screw-ups are sometimes better than the actual myth.
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Unread postAuthor: schmanman » Fri Jan 19, 2007 8:59 pm

I like it when the myth is impossible, then they try to replicate it.
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