4in coaxial cannon UPDATE:Stand!!!

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deathbyDWV
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Sat May 16, 2009 4:50 pm

Hi guys this is my first post on spudfiles. I have been looking at this website for a while now and finally got to post something. This is the the bigger one of the two cannons i built. It is a basic coax and the first piston gun i have built. I haven't searched much yet but i haven't found another one this big any where on the website.

Specs:
chamber- 4" by 6'
barrel- 2" by 5' (9 feet with extension)
piston- 3" cap with washer on top
pilot- modified 1" sprinkler valve
operating pressure- between 50 and 70 psi usually
length- 8' (12' with extended barrel)

The barrel disconnects at the two inch union at the front of the chamber.

At 60 psi it shoots a mini nerf around 1/4 mile, a full tube of caulk 150 yards, and a bouncy ball 3/8 mile, through 2 sheets of 1/2 inch osb, or up into a blue sky until it disappears.

We estimate it shoots a bouncy ball between 500 and 700 fps.
I need to get my dads chronograph out to see how fast it really shoots.

I am now working on a stand for it and will have pics up soon.

Damage pics and video are coming.

PS: i don't have a name for it yet, any suggestions?

EDIT:
This is a video of shooting a full milk jug. My dad is shooting so that i can record it. The first part is shooting it, the second shows the milk jug, and the third shows the 2" ball sized piece that it cut out of the milk jug. Notice how it got the whole backstop wet. :D

[youtube][/youtube]

Edit: I finally got pics of the stand up. I know the size in kinda over kill but i don't want it to fall over. It has a full range of motion so i can shoot straight up if i want to. The stand comes apart so it's easier to store. both pics are without the extended barrel.
Attachments
Pilot valve, air in, and pressure gauge
Pilot valve, air in, and pressure gauge
Stood up on saw horse to shoot
Stood up on saw horse to shoot
Full view with extended barrel
Full view with extended barrel
at an angle
at an angle
aimed horizontally
aimed horizontally
Last edited by deathbyDWV on Sun Jun 14, 2009 3:42 pm, edited 4 times in total.
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MountainousDew
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Sat May 16, 2009 4:58 pm

Congrats on making a successful piston cannon! (Something I have yet to master...)
But I doubt you are getting a quarter-mile at only 60 psi.
Can't wait until the video and stand.
Welcome to SpudFiles.

Edit: I was looking at your pictures again, and I noticed you are using a quick connect to fill your cannon... Doesn't that get uncomfortable to have the pump still attached when you are shooting the gun?

I searched, too and I think you do have the largest coax. Congrats, again!
Last edited by MountainousDew on Sat May 16, 2009 5:08 pm, edited 1 time in total.
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mark.f
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Sat May 16, 2009 5:06 pm

Very nice. What sealing face do you use on the front of your piston, or do you have something on the back of your barrel?

I don't doubt you're getting very good distances with nerfs out of this cannon.
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MountainousDew
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Sat May 16, 2009 5:11 pm

mark.f wrote:I don't doubt you're getting very good distances with nerfs out of this cannon.
Unless I did something wrong, GGDT isn't predicting anywhere near a 1/4 mile at 60 psi... But none the less, it is still a very good cannon.
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Lentamentalisk
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Sat May 16, 2009 5:13 pm

Mind explaining how the barrel is only 5' long, when the chamber is 6' long? Your pictures clearly show otherwise, with the barrel being 3-4ft longer than the chamber.

You do realize that you can push your ammo all the way back down the inside pipe, right up to the piston, right?

I would hate to think that you had been shooting with deadspace 1-2x the volume of your barrel...
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mark.f
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Sat May 16, 2009 5:13 pm

What CD did you use for the projectile?
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deathbyDWV
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Sat May 16, 2009 7:03 pm

having the hose still connected really doesn't bother me

the sealing face is a 2" union connected to the barrel and the piston has a big washer on it

the barrel inside the chamber is five feet long, with the extention it's nine feet long

what do you mean about cd i used for a projectile
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mark.f
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Sat May 16, 2009 7:10 pm

deathbyDWV wrote:having the hose still connected really doesn't bother me

the sealing face is a 2" union connected to the barrel and the piston has a big washer on it

the barrel inside the chamber is five feet long, with the extention it's nine feet long

what do you mean about cd i used for a projectile
Pretty unique way of making a sealing face there. What's better, it should seal extremely well, depending on how well you attached the washer to the piston. Even better than that, it decreases the opening speed of the piston by bringing the diameter of it and the sealing face closer together. Only thing I would worry about is how much clearance there is between the edge of the union and the inside of the chamber, but I'm sure it's not enough to harm flow too much.

I was talking to MountainousDew about the CD he used in GGDT to model your cannon's performance. 0.5 is typical of spherical projectiles, but a nerf should be a tad lower than that.
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deathbyDWV
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Sat May 16, 2009 7:27 pm

i'm kinda new so can you tell me what CD is and what GGDT is? :oops:
by 0.5 for spherical projectiles do you mean .5 mile?

nevermind about the GGDT i found it on the wiki but i still couldn't find CD
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Lentamentalisk
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Sat May 16, 2009 7:34 pm

CD is the coefficient of drag, ie: how streamlined an object is.
GGDT is the Gas Gun Design Tool, written by D_Hall, which is a pneumatic spudgun simulator, that helps predict how a cannon will preform before actually going out and making it. It can be found here: http://thehalls-in-bfe.com/GGDT/
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deathbyDWV
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Sat May 16, 2009 7:42 pm

OK thanks alot i do think the nerfs go around 1/4 mile but that is just an estimate by sight.
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deathbyDWV
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Sat May 16, 2009 7:50 pm

Also, could someone tell me how many feet per second a bouncy ball goes? I would just download GGDT but it won't work for me. :cry:
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MountainousDew
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Sat May 16, 2009 9:31 pm

deathbyDWV wrote:Also, could someone tell me how many feet per second a bouncy ball goes? I would just download GGDT but it won't work for me. :cry:
First, we need to know the approximate weight of the bouncy ball....
Second, there is a FAQ section on his site, it didn't work for me at first either, just check it out. You will be glad you did when you are using GGDT, it is pretty sick-nasty!

Edit: @Mark: I most likely didn't change the CD, either because I didn't think to, or because I didn't know what it was before this topic...
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deathbyDWV
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Sun May 17, 2009 10:25 am

Ok i'll try the GGDT again. Also i bought some cheap knock-off brand foam rockets and the tail and fins just get ripped off as soon as it leaves the barrel. :D
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