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small spud gun

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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small spud gun

Unread postAuthor: varun_2308 » Wed Sep 19, 2007 9:55 am

Is it possible to make a gun that can launch ammo (weighing 20gms and 2.5cms in diameter) keeping the dimensions within 30cm x30cm x 30cm???
Please reply........
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Unread postAuthor: jimmy101 » Wed Sep 19, 2007 10:19 am

Sure, but how fast do you want the ammo going when it leaves the gun?

An over and under with a 30cm barrel. Chamber volume two or three (or more) times the barrel volume. So, for a 2.5cm barrel use 5cm pipe for the chamber, that'll give you a ~4:1 ratio assuming the chamber and barrel are the same length.

To maximize the barrel length, put the valve on the chamber then a 180° bend to the barrel. Gives you more dead volume behind the ammo but avoids using up a significant amount of the 30cm length limit which is really needed for the barrel.

Fiddle with GGDT to see what appears to be more important; minimizing dead volume or maximizing barrel length. (I would guess that maximizing barrel length is more important.)

Could do a coaxial design but a barrel sealing valve will use up a fair amount of your 30cm length limit.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 19, 2007 10:42 am

You could make something like this design using a 3" pipe for the chamber and 1" pipe for the barrel, and use relatively high pressure (say close to 200 psi) and you'd get decent performance (and a LOT of noise ;) )

If you don't want the trouble of making your own piston and want to use standard parts, there's some good inspiration here.
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Unread postAuthor: DYI » Wed Sep 19, 2007 5:54 pm

Using those dimensions and atmospheric air at 120 psi, you could use an 8" long, 10" diameter chamber, followed by a 180 degree bend, a 4" burst disk valve, and an 8" long, 4" calibre barrel. That would give you over 800 ft/lbs of muzzle energy with a 450 gram projectile, which is fairly decent in my opinion, and it fits well within the given specs. You might need hearing protection to fire it though...
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Unread postAuthor: varun_2308 » Mon Sep 24, 2007 5:42 am

The speed should be sufficient enough to make the marble penetrate a model township made of cardboard from 2-3m away......
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 24, 2007 6:20 am

hehe are you planning on destroying someone's history project :D

all you need is some 1 inch internal diameter pipe for both barrel and chamber and a ball valve.
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Unread postAuthor: varun_2308 » Wed Sep 26, 2007 5:10 am

here's the problem statement for the competition-
Construct a mechanism to fire (project) the specified ball and cause as much destruction as possible to an artificially designed township.

Problem Description

* The built mechanism will be tested for its accuracy and range (power) in an arena made to resemble a small township.
* The dimension of the township will be 2 m × 1.5 m
* The township will have building of many kinds and sizes.
* Points will be awarded for striking the building erected in different parts of the township.
* The smaller and farther the target, higher will be the weightage.
* The ball will be a marble approximately weighing 20 grams.
* The ball will be of diameter 2.5 cm and will be provided to each team

Rules and Regulations

* Each team will consist of a maximum of 3 members.
* Each team will be given three rounds to fire both in the elimination and final round.
* The minimum distance from which the ball can be fired is 2 meters and is compulsory to start with. Thereafter the point of projection is completely the discretion of the participant.
* Extra points will be awarded for striking the target from a longer distance.
* A one touch release mechanism has to be devised for firing the ball.
* Use of hazardous chemicals and explosives will lead to disqualification of the team.
* The mechanism must fit into a box of 30 cm × 30 cm × 30 cm
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Unread postAuthor: varun_2308 » Wed Sep 26, 2007 5:11 am

so can anyone tell me what should be the dimensions of the piston????
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