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chamber size?

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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chamber size?

Unread postAuthor: brettdotcom14 » Wed May 13, 2009 1:47 am

im going to be using 4" pvc for the chamber

my barrels are all 5' long and 3/4,1 1/2, 2, and 2 1/2

i read that 1:1 ratio is good and i think 24" chamber would work correct? want to make sure before i cut it
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Unread postAuthor: jackssmirkingrevenge » Wed May 13, 2009 2:11 am

It depends on many factors, operating pressure, valve type, you can go lower than 1:1 and still have decent power for reduced noise and pressurising effort. I suggest you download GGDT and model your launcher virtually, it will give you an idea of how variations in chamber volume will affect power.
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Unread postAuthor: brettdotcom14 » Wed May 13, 2009 12:48 pm

i did that but im not sure how to translate the results.

btw id be using a 1" sprinkler valve

at 50psi

muzzle energy=4.5 ft*lb
muzzle velocity =48 ft/s

not sure if thats a lot or not a lot
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Unread postAuthor: Technician1002 » Wed May 13, 2009 12:52 pm

brettdotcom14 wrote:i did that but im not sure how to translate the results.

btw id be using a 1" sprinkler valve

at 50psi

muzzle energy=4.5 ft*lb
muzzle velocity =48 ft/s

not sure if thats a lot or not a lot


88 fps is 60 MPH. Many pitchers can easily exceed this. It's not a lot as it's only about 30 MPH. :( A larger valve will make a world of difference. Remember that doubling the valve size provides 4 times the area for flow. With that in mind you can see a 1.5 inch valve is about DOUBLE the size of a 1 inch. :D Toss that at GGDT.

For fun, here is a graph of a 2 inch valve with a little larger tank and barrel, just to show the flow you can get through a larger valve. The projectile is a 4 inch foam Poof brand ball.
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Attachments
GGDT.jpg
GGDT for 2 inch valve cannon tossing a 4 inch foam ball at 60 PSI.
Tree.JPG
Damage to a tree after 2 cans of root beer was launched at 60 PSI. A 30 MPH shot doesn't do this.
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Unread postAuthor: brettdotcom14 » Wed May 13, 2009 3:58 pm

i would love to find a 2" sprinkler valve where can i get one?
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Unread postAuthor: MountainousDew » Wed May 13, 2009 4:01 pm

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Just some of them...
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Unread postAuthor: jackssmirkingrevenge » Thu May 14, 2009 1:38 am

brettdotcom14 wrote:muzzle energy=4.5 ft*lb
muzzle velocity =48 ft/s

not sure if thats a lot or not a lot


That's not a lot for a launcher that size, can you post a screen cap of what you've modelled?
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Unread postAuthor: Technician1002 » Thu May 14, 2009 2:11 pm

jackssmirkingrevenge wrote:
brettdotcom14 wrote:muzzle energy=4.5 ft*lb
muzzle velocity =48 ft/s

not sure if thats a lot or not a lot


That's not a lot for a launcher that size, can you post a screen cap of what you've modelled?


I do see form his original post he wants to use barrels up to 2.5 inch in size.

my barrels are all 5' long and 3/4,1 1/2, 2, and 2 1/2


The soda can into a tree is with the 2.5 inch thin wall barrel.
From here; http://wiki.answers.com/Q/How_much_does_a_can_of_soda_pop_weight I find Which means the average can of pop weigh 240.7962 grams or .5552 pounds.

I just ran GGDT on the soda can launch that hit the tree. I used 60 PIS, chamber dia 8 inch length 15 inch, inner diam (coaxial QDV) 2.3 in, Barrel seal valve, seat diam 2.08 in (actual measured), left flow coef at default 45%, dead volume at 3.05 cu in (2 inch valve outlet to screw on barrel) piston diam at 2.1 (had to lie to GGDT as it won't take the QDV dimension of 2.08.) etc.. Barrel is 2.6 inch 72 inches long.

With these values I have a muzzle energy of 890.5 Ft Lb and a velocity of 329 FPS for the can that hit the tree.

If I use the valve effeciency I am seeing for the QDV in this configuration and change the coef to 75% the values are 1052.8 muzzle energy and 358 for the muzzle velocity. Since one of the shots knocked over one guy, I believe the recoil we were feeling. It was insane at only 60 PSI.

If I screwed the 36 inch barrel on the marshmallow launcher with the 54 cu in chamber at 80 PSI I should be able to launch a can of pop with 193 ft lb energy at 153 ft/sec with a 45% coef valve or 250 ft lb force with a velocity of 175 ft/sec with a coef of 75%.
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Unread postAuthor: brettdotcom14 » Fri May 15, 2009 5:14 pm

how do you have a 2.3 inner diam and a 8 outter diam?

this is what i get..its better but still not sure if i should have a 24" chamber or 32" chamber

its only about 15 ft*b more and 50 ft/s more with the 32" worth it?

1" valve gb
Image
1" valve tb
Image
2" valve gb
Image
2" valve tb
Image
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Unread postAuthor: CpTn_lAw » Fri May 15, 2009 5:28 pm

your gun is a co-axial?if not, inner diamter must be set to 0....gues that'll change some results...
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Unread postAuthor: brettdotcom14 » Fri May 15, 2009 5:32 pm

i plan on making it a over under

im now thinking i might want to make a piston valve..is a piston valve cheaper then a 2" sprinkler valve and reliable?
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