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a couple questions about my first shoulderfired pneumatic

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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a couple questions about my first shoulderfired pneumatic

Unread postAuthor: Jaygnar » Sat Sep 19, 2009 2:09 pm

This is my first post, so let me start off by saying hello to everyone. I'm very happy that I found this site and have been pouring over a lot of the information that is available here. Previously, I have made a basic combustion cannon with a grill piezoelectric ignition from PVC. And a large wheeled pneumatic cannon that was all metal and simply a scuba tank, ball valve, filler valve and barrel.

Now I want to try my hand at a portable pneumatic shoulder fired golf ball launcher. I'm using the tried and true over-under design, a sprinkler valve modded for blowgun firing and that's pretty much it. I'm not ready to start fooling with custom valves and just want a quick build with as much power as I can get in a small portable package.

As far as available pressure goes, I'm currently stuck at about 90psi max due to compressor limitations, but that should be plenty.

The overall design will be very similar to this cannon
http://www.antennalaunchers.com/csv19/index.html

However, I will be launching golf balls instead of tennis balls. I want to make the barrel about 3 feet (36 inches) max.

Now, for my questions.

First, I need to know what type of pipe that I need to sleeve into itself for the barrel. I know 2 inch and I'm assuming schedule 40 but I don't want to make a stupid mistake and have to drive back to Home Depot to get more materials so I will ask and hopefully benefit from your combined experiences.

Second Question:
I plan to use 3 inch schedule 40 PVC pipe for the pressure chamber. I know that there are ideal chamber to barrel ratios and I do plan on learning more as I go but for now, time is a factor and I need to have this thing built by the middle of next week if possible, so I want to know how long a pressure chamber I need to launch my golf balls the max distance possible with my 2.5 to 3 foot barrel.

I know that there is software available to provide the calculations but I don't have the capabilities to download it right now.

Finally, (I promise, last one{for now})
Anyone have experience with this valve?(It's probably the one I will end up using)
http://www.homedepot.com/webapp/wcs/sto ... =100098062


Thank You in advance.
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Unread postAuthor: pizlo » Sat Sep 19, 2009 2:38 pm

Well If you have a 3 inch chamber and you are launching golf balls any chamber size around or below the length or your barrel would be fine.

and that's the most common valve I believe, make sure you have very viscous epoxy to plug the hole left by the solenoid.
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Unread postAuthor: auxiliary » Sat Sep 19, 2009 2:45 pm

If you have a plumbing supply company around you that does commercial sales, it is possible that they have a will call center that you can just walk into. This is that kind of place where you might be able to find SDR-21 (perfect fit for golf balls) and sleeve it into 2" Sch 80 PVC. You probably already know that, but I think your best chance is with large plumbing supply companies and not home depot because the one around me doesn't even carry pressure rated 3"PVC.

As for C:B ratio, I think is is 1:1 so just calculate the volume of the barrel and set it equal to the chamber volume and solve.

I would get the 1" Rainbird sprinkler valve because it is rated to a higher pressure and it has a convenient valve on the top that you can remove and tap with 1/8" NPT tap.

http://ecx.images-amazon.com/images/I/41lGBpzbrJL._SL500_AA280_.jpg

Home Depot carries this valve
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Unread postAuthor: covey12 » Sat Sep 19, 2009 3:06 pm

yea, basically what they said, try ace hardware if you have it they almost always have pressure rated parts ( all the way up to 6" at the ones near my house), and btw how do you plan on firing an over-under from your shoulder, most use plain in-line designs for that


as always, the biggest thing to get yelled at here for is, DON'T USE DWV PIPE ( not to be rude against you, just helping)
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Unread postAuthor: Jaygnar » Sat Sep 19, 2009 3:44 pm

Thank you for the fast replies.
I will not be using any Non pressure rated parts, so don't worry about that.
I cant find the SDR-21 anywhere nearby but will call around again on Monday before gathering materials just to be sure. :happy7:

Also, Just to make sure, I do need to use two layers of schedule 40 pipe right? Not schedule 80?
Unless I find the SDR-21 in which case I will need the 2 inch schedule 80 sleeve.
Is this correct?

I will make sure to use a high viscosity epoxy on the solenoid holes and will try to find the rainbird valve for easier modding:)
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Unread postAuthor: Jaygnar » Mon Sep 21, 2009 7:34 pm

Update!
I got the barrel made.(had to use 2 layers of schedule40 sleeved inside one another)
Also got the chamber assembled. I was able to get some 4 inch pipe for this so I was able to cut down the chamber length.
I'll probably head to Home Depot tomorrow and get the few fittings and the sprinkler valve that I need to finish the gun. 8)

A few more questions though.

Is there any downside to modding the sprinkler valve with a male hose barb that is attached to the blowgun by a tube? I assume that in theory, the blowgun will take slightly longer to vent the pilot area and that would slow down the diaphragm. Am I correct? Anyway was just wanting to know if there would be any noticeable difference in performance as long as I didn't get too crazy with the length of the hose.
I'm just going to use the hose to allow for easy relocation of the trigger.
Anyway, thanks for all the help so far and I hope to get the gun finished by the weekend at the latest. Maybe I can get some pics and a vid up.

anyway, later.
Update!
I used some fittings designed for truck airbrakes for the remote tubing and hand built a wooden spacer for the area between the barrel and the pressure tank.
I also used a screw, some scrap steel, and a big ball-peen hammer to fabricate (read smash) a clamp to hold the trigger assembly in place. I tried to use hose clamps but that looked a bit bad in my opinion.
I have test fired some golf balls and was able to launch them so far that they went out of sight. I don't know the actual range, but since I'm launching them into an area that is cleared through the woods for power lines, I'm not gonna try to retrieve or find them. At the time of testing, I had no pressure gauge on the gun so I couldn't monitor the psi. I have installed one now and will retest (play) some more after the painting phase is complete.


UPDATE
Ready for finish sanding and paint!

UPDATE
First coat of flat black on!
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ready for paint
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first base coat
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Unread postAuthor: Jaygnar » Thu Sep 24, 2009 2:47 pm

All dry, tested, leak free and ready for fun!
Thanks for the help people!
Now..... to build a piston cannon :twisted:
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Unread postAuthor: Technician1002 » Thu Sep 24, 2009 5:16 pm

I expect that to honk. I recommend using elbows the size to fit the chamber instead of reducing size and then using small elbows. Please note that the one you patterned it off of has as short of a path as possible from the bulk of the chamber into the valve. The elbows don't allow high speed flow to the sprinkler valve so the drop in pressure on the valve is faster than the pilot vents so it may close early several times making a honking noise and cutting performance.

That will launch golf balls, but using a valve close to the bore size of the barrel makes a world of difference in power.

For my golf ball launcher I simply flared the end of an SDR21 tube and slid it inside a 2 inch barrel and screwed it on a 2 inch male pipe fitting. The sleeve insert is removable for launching larger stuff with the same launcher.
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Unread postAuthor: Jaygnar » Thu Sep 24, 2009 6:17 pm

I like the idea of the interchangeable sleeve! Seems like it would be faster than unscrewing and re-screwing barrels.
The canon doesn't honk unless I fire it at 30 psi or below. And I don't really ever do that, I just noticed it when I was trying low pressure dry fires to test the integrity of the areas that have to hold static pressure.
I agree that bigger fittings would give it more power, as would a faster or larger valve. But for now it works great and for me, the performance gain of enlarging the fittings wouldn't justify the work involved. It's just a personal preference:)

ps
I'm a bit confused. I was under the impression that the valve should be located as close to the barrel as possible to avoid "dead area" of uncompressed air. Also, I used a 1 inch sprinkler valve just cause that was the largest available readily.
Anyway, I'm happy with it and It doesn't honk :lol:
Thanks for the constructive criticism! I wont make the mistake of downsizing fittings again!
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Unread postAuthor: Technician1002 » Thu Sep 24, 2009 7:00 pm

Jaygnar wrote:ps
I'm a bit confused. I was under the impression that the valve should be located as close to the barrel as possible to avoid "dead area" of uncompressed air. Also, I used a 1 inch sprinkler valve just cause that was the largest available readily.
Anyway, I'm happy with it and It doesn't honk :lol:
Thanks for the constructive criticism! I wont make the mistake of downsizing fittings again!


It's no faster than unscrewing and screwing the barrels. This sleeve is breech loaded so it doesn't slide out when on the cannon.

Small pipe and dead space is bad there too. It's why I recommended using chamber size elbows to the valve and not barrel size elbows to the barrel. Sorry I didn't clarify this point. I approached it from a causes for the honking. All restrictions all up. Its not as powerful as the greatest restriction, but restricted as much as all restrictions added together.
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 24, 2009 7:17 pm

Jaygnar wrote:I was under the impression that the valve should be located as close to the barrel as possible to avoid "dead area" of uncompressed air.


You'd be right, I'm a bit confused by Tech's statement too as after all the pipe feeding the sprinkler appears to be the same diameter as the valve itself, so it wouldn't "realise" if you fed it from a bigger pipe.

Anyway, excellent effort for a first cannon, some folks don't achieve this level of workmanship on their fifth one :roll:

My two criticisms would be that your valve is too small for your barrel, while your chamber is at least double what it "needs" to be. Nothing wrong with the latter in terms of performance, but you get extra noise and pumping effort (irrelevant if you have a compressor really) for relatively little return in terms of increased velocity and range.

Now..... to build a piston cannon


From what we've seen so far, it'll be a good 'un :D give it a go, you will be amazed at the difference in performance :)
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Unread postAuthor: Jaygnar » Thu Sep 24, 2009 7:37 pm

So ideally I should have put the valve where it is but have used larger elbow sand delivery piping. Right?

About the barrel sleeve, I thought you had it set up to go in from the muzzle and were using the male pipe fitting on the muzzle to lock it in place, which might work but you'd have to flare both ends.

Thanks for the clarification! What with the all the QEVs, QDVs ,Hammers, Pistons, there's a lot of new and exciting stuff here. I'll probably end up remaking this cannon. But not until I get a piston valve built for it. Anyway, I'll try to get a video of the cannon in action soon. It's not as good as it could be, but I still like it and I'm proud to have built it and look forward to learning and improving in understanding and design! :)
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 24, 2009 7:57 pm

Jaygnar wrote:So ideally I should have put the valve where it is but have used larger elbow sand delivery piping.


As long as the pipe is the same diameter as the valve outlet you should be fine. And yes, the valve should be as close to the projectile as possible to avoid dead space.
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Unread postAuthor: Jaygnar » Fri Sep 25, 2009 8:13 am

My two criticisms would be that your valve is too small for your barrel, while your chamber is at least double what it "needs" to be. Nothing wrong with the latter in terms of performance, but you get extra noise and pumping effort (irrelevant if you have a compressor really) for relatively little return in terms of increased velocity and range.


The valve is a 1 inch valve. It's the largest I could find :)
I originally planned to use 3 inch pipe for the tank and was gonna have it at the same length as the current one, but my friend who works with the stuff and got it at a great price showed up with 4 inch fittings and pipe instead. I couldn't resist! It is rediculous overkill though, then again I could screw on a longer barrel. I used brass nipples to connect the valve to the pipe and barrel for easy maintenance and barrel interchangeability.
:idea:
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 25, 2009 8:36 am

With those sort of pipe sizes available, and if you have a suitable range to shoot over, you should consider a large coaxialas your next project, clearly within your skill level and the power will be something else...
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