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My First Pneumatic (Help Me) (With Pictures)

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: pyromaniac » Sat May 12, 2007 11:14 am

Yes you could make every thing inch. you really should modify the puck maybe drill a 1/2 hole and stick about 6 inched of an oak dowel inside and glue it. This will at least make your puck not flip in the barrel.
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 11:25 am

Hey Everybody, I'm also in Hotrock's Science group for making the puck spud gun, but I have a few questions about measurements. See, the puck is almost exactly 3 inches in diameter, so if we were to use a three inch barrel, it would be an incredibly tight fit right? Even with lubing down the barrel and puck, there would be a huge amount of friction, which would drastically reduce the distance our puck will travel. In addition this, any modification made to the puck must be additions, not subtractions, meaning the fit will be even tighter, or not even fit at all. Should our barrel then be 4 inches? How does this affect everything else? Maybe I'm misunderstanding something.
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Unread postAuthor: pyromaniac » Sat May 12, 2007 11:29 am

My puck slider easily down 3 inch. if you want just put soem grease on it.

do not make a 4 inch barrel you will be fine. truth be told my puck is a prefect fit in 3 inch. if anything just shave down the puck with a knife.
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Unread postAuthor: hotrocks » Sat May 12, 2007 1:58 pm

yeah and im thinkin of makin an addition to make it more missle like so it wont flip biaccident and be more aerodynamic
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 3:29 pm

Hotrocks, i think the missle idea is bad. The only reason a bullet doesn't flip is because it is rotating, and since the puck won't be rotating, it can flip just as easily, making even less aerodynamic than its original form of a puck.
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Unread postAuthor: pyromaniac » Sat May 12, 2007 3:31 pm

The missile idea will work. just make sure the weight is more towards the back. why are you shooting a hockey puck anyway?
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 3:33 pm

Oh yeah, just a reminder, we can't shave down the puck, we can only add to it.
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 3:37 pm

The actual assignment is just to propel a hockey puck as far as we possibly can, any way we want, without using our hands. we decided on the spud gun idea, which is why we have to use a hockey puck. Any way, I don't fully understand the missle cone idea, but we were thinking we could maybe mold some non-drying clay around the puck to make it more sphrerical and spud-like, but would that be better than missle idea? If not could you please explain a little bit more in depth what you think we should do with the missle idea? Thanks a lot by the way.
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Unread postAuthor: pyromaniac » Sat May 12, 2007 3:37 pm

Why cant you shave down the puck? Why are you even shooting a puck?

atleast give it a nose cone and make a tail using a dowel and come contrustion paper fins.

makeing its sperical would work pretty good. sorry i didn't see your last post, o and there is an edit button.
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 5:28 pm

I think that we're going to end up shooting the puck without any modifications at this point, shooting it with the flat side sideways, so we can get the most air pressure to our surface area. I'm only a little bit concerned about whether or not the puck will flip inside the barrel. Pyro, i didn't quite understand your explanation as to how to prevent flipping in the barrel, but i am also concerned about it flipping in the air. I was hoping to somehow rifle the barrel, but I'm assuming that's way to complicated or hard. Unless anyone has a secret maybe. Anyway, if a rifled barrel is out of the question should we just forget about air resistance and leave the puck unmodified. Please keep in mind that whatever modifications you're thinking about must not exceed 3 inches, otherwise it won't fit in the barrel. Sorry to be so repetitive. By the way Intel, why wouldn't i shoot it with more than 15 psi? Isn't that not very powerful? How far would 15 psi get the puck?
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Unread postAuthor: Intel Xeon » Sat May 12, 2007 5:30 pm

Just to answer the questions,

You don't put the pump in the chamber, you either need a screw in, or a pop in schrader valve. these are available at practically all auto stores. Due to the increase in tubeless tires, pop-in valves are common.

The C:B ratio is dependent on the pressure used. You generally want the projectile to exit when the pressure in the barrel has reached 15psia (or slightly above normal atmospheric pressure.) for maximum performance. I suggest you use GGDT's simulation software.

The missile idea will increase weight and possibly drag on the puck. Foam pieces to make a sphere maybe? I still think the hop-up is a fun idea :D . Then again, I am not considering the fact that a group of mid-teens might not have the means to cut through thick metal pipe and then mold it all the way through to fit a cylindrical projectile...

EDIT: What? I never said anything about shootng at 15psi. I just mentioned 15 psi right now. I said that the pressure inside the barrel should be slightly over 1 bar
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Unread postAuthor: stupidandcontagious » Sat May 12, 2007 5:56 pm

Sorry, misunderstanding.
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Unread postAuthor: jrrdw » Sat May 12, 2007 6:49 pm

You could find some plastic or paper cups to use as sabets. That would stop the puck from tumbling in the barrel.
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Unread postAuthor: hotrocks » Sat May 12, 2007 8:23 pm

I was thinking, mabye we could use a wad (paper or cardboard) so even if the puck does turn, it won't be too big of a problem. Or, we could load the barrel from the breech and then screw it on and tape it. We will only be doing three trials for the contest, I believe.

what about trajectory?
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Unread postAuthor: jrrdw » Sat May 12, 2007 8:27 pm

Ever think of building a really big sling shot?
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