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Mythbusters and Their Cannons

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Mythbusters and Their Cannons

Unread postAuthor: miskaman » Mon Oct 08, 2007 10:06 pm

Was watching a show one time and I saw a cannon Jamie whipped up to go shoot a net at the pigeons outside because they were getting on his nerves. It looks like this.

Image

Image

So did anyone else see it? Where would I buy a splitter to go to 4 barrels? Or at least 3? Because I really want to make a net gun.

Or could somone machine me a piece like this, but just in PVC?
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Last edited by miskaman on Tue Oct 09, 2007 5:28 pm, edited 3 times in total.

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Unread postAuthor: knappengineering » Mon Oct 08, 2007 10:20 pm

I have seen this episode and its very cool, but to get the spliter angled like that I suggest a large chain hardware store(home depot or lowes) or you could posible use a normal 4 way fitting (looks like +) with some combination of 90 degree or 45 degree fittings. Good luck, cant wait to see it when finished. :D
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 08, 2007 10:26 pm

see also here and here
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Unread postAuthor: ammosmoke » Mon Oct 08, 2007 10:26 pm

Um, there is no pressure rated 4 way fitting that I know of... Try a T connected to two other T's, with 45 degree fittings on each corner. I would imagine though, that this would create a big kick, and some high stress on joints that are at sharp angles. Just thought I would throw that in there.
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<img>http://www.speedtest.net/result/309559995.png</img>
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Unread postAuthor: knappengineering » Mon Oct 08, 2007 10:41 pm

I don't think that a non-pressure rated 4 way would be too much of a problem because its for the barrel and there is only a brief amount of pressure on it. It would be best to go for the pressure rated fitting though because safety is # 1(at least for me), but it probably wouldn't be too big of a deal if it wasn't pressure rated. but its up to u.
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Unread postAuthor: Brian the brain » Mon Oct 08, 2007 11:39 pm

plastic scrapnel is always a problem!

You obviously haven't blown up a cannon...it's not something to repeat!
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: c19o » Mon Oct 08, 2007 11:56 pm

Or you could get a fitting from here and attach some elbows or 45s on there.
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Unread postAuthor: silverdooty » Tue Oct 09, 2007 7:24 am

you should be able to get 2" crosses at lowes or homedepot that are NSF-pw.
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Unread postAuthor: paaiyan » Tue Oct 09, 2007 8:03 am

The thing about this is, in order to achieve the same range as a 30 psi cannon, you'd need about 120 psi due to teh fact that you're splitting it four times. You've also got to factor in the drag of the net, that'll reduce range. So in order to get any kind of range with this, you'll really need a lot of pressure in the chamber. Also, you wouldn't relly want those barrels angled out that far. The net would simply stretch to it's limit, then fold back in on itself.
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Unread postAuthor: flamerz14 » Tue Oct 09, 2007 10:54 am

or....you could weigh the edges of the net with tennis balls, put the whole thing in a sabot and fire.
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well, this isn't much isn't it?

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Unread postAuthor: williamfeldmann » Tue Oct 09, 2007 12:28 pm

I did something similar with golf balls. My brother and I were playing ladder golf, and it sort of hit me that the little golf ball bolos would be SWEET flying out an air cannon. I rammed the little bolo down the barrel with a bit of tissue around the golf balls and it worked perfectly, opened and swung through the air and wrapped itself around a tree branch about forty times. I see no reason this premise would not work with 3 or 4 balls on the ropes.

I agree with paaiyan's comment on barrel angles. With seperate barrels you would need them all pointing in the same direction, instead of splaying, or the balls would stretch the net and then bounce back collapsing the net on itself inflight. Also three barrels greatly increases the need for air chamber volume. Granted, range is not really a factor here so having relatively short barrels is no big deal.
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Unread postAuthor: jimmy101 » Tue Oct 09, 2007 1:55 pm

Just a thought but...

During the civil war cannoneers experimented with using two cannon balls connected by a length of chain fired from two canons. The ideas was to get the chain stretched between the two balls to mow down infantry.

After killing a couple cannon crews it was decided that the project would be abandoned. They couldn't get the two guns to fire at the same time. One gun always fire first, the round would spin about the second cannon and take out the crew.

You might have similar problems with multiple barrels even if they are operating from the same valve. If one tennis ball sticks, perhaps because of the very large barrel cross sectional area compared to the valve throat area, then you might get the same thing happening here. I would think you will want a fairly small amount of friction between the tennis balls and the barrels.
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Unread postAuthor: PVC Arsenal 17 » Tue Oct 09, 2007 2:18 pm

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Unread postAuthor: williamfeldmann » Tue Oct 09, 2007 2:56 pm

I think the best idea is to have the net and balls in one barrel. The entire system is launched at the same time that way.

I really don't think you would see much performance (of the net) difference because the flight pattern of each ball is going to be different anyway.

Another option is to use a sabot that the net and balls fit in so you can wrap the whole thing in such a way that it will fly apart, and you have a lot less friction in the barrels.

Ultimately, if the mulitple barrels are different lengths you will have different firing times as well as the barrel in line with the valve firing faster than the peripheral barrels.

EDIT: spelling
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Unread postAuthor: Redcoat » Tue Oct 09, 2007 3:56 pm

I agree with wiliamfeldmann, You should use juts one barrel with the nets and balls in it.
Did you notice how the net Jamie fire in the Episode went?
It wasn't all that far probably 50ft at max. Putting it all in the one barrel would work alot better.

Though if you gave each barrel it's own individual valve it might work better as well.Though you would still have to tackle the problem of synchronising them all at once, otherwise you'd run the risk of one valve opening before the others and releasing half of the air too soon.

Happy Spuddin'

Edit- I know It's Unnecessary, but I just got Google Sketchup and I was bored so I decided to do this off memory......
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Attachments
Jamie's Bird Cannon..jpg
I know it's really unnecessary but I just got Google Sketchup so I thought I'd just post a Picture. The chamber is way out of scale, I know.

It's one Godzilla of a cannon, look how many times it is taller than that guy.
Jamie's Bird Cannon..jpg (27.21 KiB) Viewed 801 times
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