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Coin Gun?

A place to ask general spud cannon related questions.
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Unread postAuthor: elitesniper » Sun May 10, 2009 5:55 pm

I t wont be very good beacuse there is not much surface area for the air to push.. correct me if im wrong though somebody :)
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Unread postAuthor: Gaderelguitarist » Sun May 10, 2009 5:58 pm

Small bore cannons do fine with a small surface area...
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Unread postAuthor: MountainousDew » Sun May 10, 2009 6:02 pm

Surface area would not be a problem, if you would follow a design like I proposed... It would fly straight and very fast!
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Unread postAuthor: psycix » Sun May 10, 2009 6:49 pm

Even though I like your idea, it will NOT fly straight. Sorry.
It will be fired straight, but it will tumble over and spin wildly as this projectile is not stabilized.

Just throw the coin into any barrel it fits in, and put some wadding behind it.
It will tumble over anyways unless you give it a tail.
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Unread postAuthor: MountainousDew » Sun May 10, 2009 7:42 pm

This reminds me, the other day at my school some firefighters came in to give a demonstration of the tools they use, and they had some scissors that could cut coins in half... So what if you cut into two pennies, half way though and fit them together to make a ball. It would fit into a 3/4 sch 40 piece of pipe, and would probably do good damage and they would in most cases be reusable...

What do you think?
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Unread postAuthor: mikemurph » Sun May 10, 2009 8:23 pm

Just remember that flat surfaces are very weak for holding pressure. It wants to unfold itself really bad and you'll need much thicker wall than if using round tube.

I have taken that into account, but thank's anyway

I think you can shoot a penny from a circular barrel as well. Just get the penny in flat, and wadding behind it. It will tumble in the air anyways, so it doesnt matter if you fire it straight or not.

Yea I know that, but im wondering if it would stay on its side like a frisbee. This would increase accuracy and range. I'm not an expert on this, but if it spins, its will work a whole lot better


And one last thing, would a magazine work if this was going to be semi-auto.

http://www.prezziesplus.co.uk/user/products/lg-disc-shooter.jpg

I want to try this with a spring and compressed air.
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Unread postAuthor: jook13 » Sun May 10, 2009 8:24 pm

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Unread postAuthor: daberno123 » Sun May 10, 2009 8:25 pm

Take a look at JSR's coin launcher.

Edit: Jook read my mind!
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Unread postAuthor: mikemurph » Sun May 10, 2009 9:15 pm

thank's, but im looking for a higher PSI, one that is capable of penetrating more than paper. I'm first going to build a gun with detachable barrel, then I'll work on the modified barrel with a magazine. Thanks for that link though daberno123, its a great proof of concept project. I'll post the gun later than get back with you on the barrel. What metals should i use for the chamber/barrel. And what valve should i use?
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Unread postAuthor: boom_o_matic_2.0 » Sun May 10, 2009 9:21 pm

if I were to make one, it would be of this nature:
http://www.spudfiles.com/forums/6mm-sem ... 10075.html
just put a flat barrel on that. I think it would totally work
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Unread postAuthor: jackssmirkingrevenge » Sun May 10, 2009 11:41 pm

Some useful points are also made here, particularly if one takes the "flat barrel" idea into consideration:

me wrote:The problem is one of surface area when it comes to firing them on their side. Say a coin is 20mm in diameter and 1.5mm and weighs about 3.5 grams.

A typical steel BB weighs 0.35 grams and has a surface area of 0.159 square cm.

The coin will have almost double the area, but weighs ten times more. This means that velocity will be severely limited, even if using shock pump pressures. Ideally you'd have your air pressure driving a large diameter piston that then pushes the coin out between guide rods (or just make a 1" cannon and load them sideways in a sabot)
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Unread postAuthor: psycix » Mon May 11, 2009 5:15 am

Jack, with your coin launcher you launched the coins "flat". Did they tumble or fly straight?
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Unread postAuthor: jackssmirkingrevenge » Mon May 11, 2009 6:51 am

psycix wrote:Jack, with your coin launcher you launched the coins "flat". Did they tumble or fly straight?


As you can see from the different impacts in the videos, they tend to tumble. For stable flight I think ideally you want the striker to hit the coin off-centre in order to generate spin.
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Unread postAuthor: jimmy101 » Mon May 11, 2009 10:21 am

psycix wrote:I think you can shoot a penny from a circular barrel as well. Just get the penny in flat, and wadding behind it. It will tumble in the air anyways, so it doesnt matter if you fire it straight or not.

Exactly. If the gun is going to be air (or combustion) powered with the air acting directly on the ammo (no piston+pusher like most disk firing guns use) then you might as well use a barrel ID = coin diameter + wading.

The gun will be a heck of a lot more efficient since you'll have a decent amount of surface area to actually push on.

If you go to all the trouble to make a flat barrel then try to push the ammo with high pressure gas you are going to be very disappointed in the performance. The sectional density is way to high for decent performance. Fire the penny from a round barrel+wadding and get the sectional density down by an order of magnitude or so.

The only advantage to a flat barrel would be that you might be able to get the penny to spin about an axis perpendicular to the line of flight. A spin stabilized penny would carry much better than one that is tumbling (think Frisbee). But, you're back to the problem of how to effectively accelerate something with such a small cross section.
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