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Basic Nerf Cannon Help

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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Unread postAuthor: RabidDuck » Mon May 13, 2013 6:14 pm

I guess I did. I asked that question when I didn't have the CPVC in front of me. So it would work to use the CPVC?
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Unread postAuthor: RabidDuck » Mon May 13, 2013 7:29 pm

Just got all my parts together and I'm sorry for the double post but I have a quick question. I feel dumb for asking it but I don't want to mess it up. Which way should the slide valve be facing or which end screwed into the QEV?

Thanks guy!
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Unread postAuthor: dewey-1 » Mon May 13, 2013 8:15 pm

Use Google and learn to do some research!

http://www.legris.com/Legris_ecom/Reche ... ngue=en_GB
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Unread postAuthor: PVC Arsenal 17 » Mon May 13, 2013 8:53 pm

RabidDuck wrote:Just got all my parts together and I'm sorry for the double post but I have a quick question. I feel dumb for asking it but I don't want to mess it up. Which way should the slide valve be facing or which end screwed into the QEV?

Thanks guy!



Before you ask us the question, consider the nature of a QEV. How do we use them? First we supply air to the "inlet" port. This air travels through and accumulates in the "cylinder" port (where the air reservoir is attached). At this point, our QEV is ready to fire. To fire it, then, we vent the air from the inlet port. Consult the wiki or perform a search if you don't understand how a QEV works.


So, which steps are we (the users) directly involved with? We do the following in order to operate the QEV:
-Supply air to inlet port
-Vent air from the inlet port

You know already that the slide valve you purchased it designed to do this job... somehow. But how exactly?

Try taking the slide valve to your mouth and blowing air through either end while manipulating the slide. You should be able to observe how the air flows through the valve in each condition. (Hint: there are 4 possible conditions)

Remember, our goal is to first supply air to the QEV with the slide in one position. Then, with the slide in the other position, we want to vent the air. Dedicate some time to studying how the parts work before you try to assemble them. The knowledge you'll acquire along the way will serve you throughout the rest of your time partaking in this hobby.
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Unread postAuthor: RabidDuck » Mon May 13, 2013 11:01 pm

Got it right on my first guess after playing around with it for a little bit! Fired a few and had fun with it.

Would load the chamber with around 60 to 80 PSI each time. Found a few leaks but took care of them right away. I have some trouble getting the female and male quick connects to lock in right away so I lose some pressure. Also the slide valve is very easy to manipulate and sometimes slides when i'm trying to connect the air supply.

The 48 inch long chambers are very long and hard to maneuver with. I did make a 24 inch chamber today but i'm waiting for the cement to cure 24 hours. With 60 to 80 psi in the longer chambers I would get around 4 to 5 shots.

Once the PSI dropped around 20 or 30 the barrel would start to leak and then the rest of the air would come out. Is this because there's not enough pressure for the QEV to seal?

I did a little chrony testing but not in depth or many times. I hit 182 fps once but otherwise most were around 80 to 90 fps.

Would it be bad or would there be any reason to create a much larger diameter chamber that's quite a bit shorter? This would make the cannon much easier to use.

I tried some dart modification too however I doubt that it works. I melted wax and poured them in the darts to give them more weight. I'll test these out tomorrow night. Any other ideas to give the darts more weight or anything?

While the semi auto for the 4 to 5 shots is pretty awesome it's not at full potential till I can find a better way to load darts besides muzzle loading. Any ideas on dart clips or bolts? I was told to look into a blow forward bolt and I did however I still have no idea how exactly I would incorporate that in my cannon.

Can't think of much more to ask or point out now but thanks for all the help and input guys! Big help!

http://imageshack.us/photo/my-images/71 ... 02736.jpg/
http://imageshack.us/photo/my-images/71 ... 12822.jpg/
http://imageshack.us/photo/my-images/22 ... 12915.jpg/
http://imageshack.us/photo/my-images/70 ... 13001.jpg/
http://videobam.com/jpnoJ
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Unread postAuthor: jackssmirkingrevenge » Mon May 13, 2013 11:58 pm

dewey-1 wrote:Use Google and learn to do some research!


Nice find, they have a cool little animation :)

The 48 inch long chambers are very long and hard to maneuver with. I did make a 24 inch chamber today but i'm waiting for the cement to cure 24 hours. With 60 to 80 psi in the longer chambers I would get around 4 to 5 shots.


You definitely want something short and fat, honestly a soda bottle will do just fine.

Once the PSI dropped around 20 or 30 the barrel would start to leak and then the rest of the air would come out. Is this because there's not enough pressure for the QEV to seal?


Probably.

I tried some dart modification too however I doubt that it works. I melted wax and poured them in the darts to give them more weight. I'll test these out tomorrow night. Any other ideas to give the darts more weight or anything?


I think your barrel is a bit long to be honest, I would chop it in half. There really isn't much air in the firing chamber and you're most likely losing performance because the air has too much space to expand in.

While the semi auto for the 4 to 5 shots is pretty awesome it's not at full potential till I can find a better way to load darts besides muzzle loading. Any ideas on dart clips or bolts? I was told to look into a blow forward bolt and I did however I still have no idea how exactly I would incorporate that in my cannon.


If you want a blow forward bolt, you're going to need a bit more air to make it work. Have a look through this thread: http://www.spudfiles.com/forums/6mm-sem ... 10075.html
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Unread postAuthor: RabidDuck » Tue May 14, 2013 7:39 am

I want a cleaner look so i'll grab some PVC and throw together a 4 inch x 12 inch chamber. About 5 times the size of the 48 inch long ones.

I'll chop the barrel down today and see how that works.

And if a blow forward bolt isn't exactly ideal without changing too much what could I do for easier and quicker loading? Just a breach load maybe? Still not sure how i'd do that.

Thanks a ton guys!
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Unread postAuthor: jackssmirkingrevenge » Tue May 14, 2013 8:12 am

RabidDuck wrote:And if a blow forward bolt isn't exactly ideal without changing too much what could I do for easier and quicker loading? Just a breach load maybe? Still not sure how i'd do that.


This method is simple and with minimal air loss or dead volume, make a hole in the barrel covered with a sleeve, something likethis golf ball launcher:

Image

Image
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Unread postAuthor: RabidDuck » Tue May 14, 2013 9:46 am

I'm limited on tools so making a hole maybe a challenge but I'll try and find a way. And just find a sleeve that fits snuggly over the barrel and slide it over the breech hole? No o rings or anything are needed?

Thanks!
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Unread postAuthor: jackssmirkingrevenge » Tue May 14, 2013 10:36 am

RabidDuck wrote:I'm limited on tools so making a hole maybe a challenge but I'll try and find a way. And just find a sleeve that fits snuggly over the barrel and slide it over the breech hole? No o rings or anything are needed?


Hacksaw and patience :)

A tight enough fit should do nicely.
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Unread postAuthor: RabidDuck » Tue May 14, 2013 10:43 pm

Went ahead and made a few changes including:

- Cut the barrel down by half. So it's right around 12 inches now.
- Made a larger chamber/ air supply. (4 inch in diameter, 14 inch in length)
- Created a breech in the barrel with a dremel tool.
- Tried to find/make a sleeve for the breech.

So everything worked great except for the last part. I'm having trouble finding a piece that fits snugly over the 1/2 inch CPVC barrel. Interestingly a 1/2 inch PVC pipe is very close to fitting over it. I took sandpaper (lots) and other ideas to grind down the inside of the 1/2 half inch PVC hence making it able to go on the CPVC. However I finally got it to work but the ends were too large while the middle was just perfect.

I would slide it on and it would be very snug but also able to move with ease until it hit the breech. Then it was very loose and it would slide back and forth. I tried firing it like this and it didn't work.

So i'm stuck with finding something to use as a sleeve. Ideas? Suggestions?

Here are some pictures:

New Air Supply:
http://cdn.imghack.se/images/7bfa2a4a9f ... 2be57b.jpg

Short barrel with New Air Supply:
http://cdn.imghack.se/images/783a8fee95 ... 155c5c.jpg

Breech:
http://cdn.imghack.se/images/abdbbe63fc ... 1a6032.jpg

Breech w/ Dart:
http://cdn.imghack.se/images/cf6eb47d8a ... 4ab1b0.jpg

Sleeve (Didn't work):
http://cdn.imghack.se/images/5224cb1ad6 ... d5aab7.jpg
http://cdn.imghack.se/images/b98c05bebb ... 50d13e.jpg

Sleeve over Breech:
http://cdn.imghack.se/images/76ec0f7804 ... 667012.jpg

Thanks much guys!
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Unread postAuthor: jackssmirkingrevenge » Wed May 15, 2013 12:06 am

That's more like it :)

For a sleeve, you could consider casting one out of epoxy for that perfect fit...
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Unread postAuthor: RabidDuck » Wed May 15, 2013 7:42 am

I could try that. But rather find something easier to do! Does something like clear hosing work just as well?
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Unread postAuthor: jackssmirkingrevenge » Wed May 15, 2013 7:50 am

RabidDuck wrote:Does something like clear hosing work just as well?


If its tight enough to seal properly, then it will be a bítch to slide.
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Unread postAuthor: jhalek90 » Fri May 24, 2013 7:46 pm

Cut a slit in a length of 1/2'' PVC, then that will open slightly larger, side it over the cpvc and keep the cut side of the pvp opposite of the breech.

always works for me.

Nerf darts require so little air, this will work just fine.
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POLAND_SPUD wrote:Anything is possible with the proper 3-way valve.
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