Need help with my 12 gram nerf launcher!

Blitz18 · 03-30-2012, 09:35 PM

All the co2 in the 12 gram is not going into expansion chamber. I started with a 12" long 1" piece of steel and thought I had to much area to fill so I moved to a 3" long piece and having the same problem! Not sure what I'm doing wrong! Below is a picture and video of whats going on! Also what is the max pressure that can be put into this 1" galvanized steel if I hook a regulator and hpa talk to it? Thanks in advance!

http://youtu.be/ehbctrchKy4

Boom Master · 03-31-2012, 02:26 AM

The easy one first. Galvanized pipe is rated 300 psi according to the spec sheet at Ace Hardware. With that short of pipe and small volume, you might well be exceeding the 300 psi.

I would suggest you remove the Barrel fitting and temporarily install a 0-1000 or so psi pressure guage to see WHAT the pressure is and how the changes you attempt are affected pressure wise. It would give you a clue if you have any air leaks as well. Tell you what is going on inside there.

I haven't been inside a 12 gram adaptor but how big is the hole in the 12 gram cartridge when you remove it? Is is possible it is not pierceing it properly? You might want to try to back off the 12 gram screw a bit after you activate it so there is room for the CO2 to exit out of the hole. Check the hole in the piercer of the 12 gram unit for debris and gunk making sure it is open and air flowing through it. You should be able to see light through it.

CO2 is notoriously dirty and dirt seems to be the first thing to check for when you have air problems with paintball gear.. It should fill and 2-3 seconds and it sounds like you have very little pressure.

It wouldn't hurt to bubble it or put it in water and check for air leaks. The cheap Galvanized from china and elsewhere are notorious poor quality threads that leak like a sieve... That should keep you busy the weekend.

Haz-Mat · 03-31-2012, 10:58 AM

My understanding of 12grams is that it does take a while for the pressure to build up in the air chamber. Once you puncher the 12 grams you have to wait till the pressure builds up in the air chamber to get a good shot. What issue are you having? Is it the fill up time or your not getting enough pressure?

The ones I've see are 1" x 10"+ size for an air chamber on a 12gram with ball valve. The two guys that I talked to say they have to wait 30+ seconds to get the max pressure in the air chamber. You can still fire it in less time but won't get the speed.

fbkboe · 03-31-2012, 05:21 PM

This is my 12g launcher. You can see how big my expansion chamber is by comparing it to the Nerf. I've never had problems with air volume or lag time in filling it when I crack the 12g. I can't claim any grand building skills, this was my first attempt, I think I just got lucky. Your chamber is rather small and that may be a factor.

Greyknight Jazzious · 04-03-2012, 07:20 AM

I have built 4 "stick" launchers, and copied the spec from another player from events I have been too.

All parts for chamber and trigger are in 1/2" size pipe.
1. My expansion chamber was only 5.5" long, 6" is ok. I had no bends, fittings or nods to the chamber.
2. I connected my 12g cage to an electrical coupling (it had the best thread match). However it wasn't quite right. Ended up JB Welding the cage to the fitting.
3. Normal teflon tape work well for all other fittings.
4. Tape and threaded the coupling/cage onto pipe.
5. Tape and threaded valve (I use a gas valve for better closure)
6. Tape and thread nipple into valve.

From here I built a PVC barrel with a tube length of at least 18", but 24" to 30" is ideal.
This length is the most important part of the launcher I have found. Once released the pressure in the chamber will continue to expand and accelerate you round out the tube. Since the ball valve is not instantaneous, you need more tube to give the round more time for the back pressure to do its thing. To little barrel and you cannot actuate the valve quick enough and you have a limp launch. By giving the barrel at least 18", it gives you enough time to fully open the valve and get the most pressure behind the round you can, before it leaves the barrel.

My launchers easily lob a round a football field, and direct fire about 50 to 70 ft.

We call them M-Rex launchers after the guy we copied from, but they are also know as stick launchers

Boom Master · 04-08-2012, 08:07 AM

Hey, Blitz

You get your problem solved?

Blitz18 · 05-25-2012, 10:55 AM

No sadly I put the project down for a while cause I have been very busy! Now that school is out I have more time to mess with it! I'm thinking of putting a gauge on the 12" expansion chamber and putting one of my regs on it and pump it up to 200 psi with hpa! Still using the ball valve! Think this will work?

Boom Master · 05-25-2012, 08:27 PM

They have worked for years but ball valve is old technology. It is hard to keep your point of aim while jerking on a lever... However if you are going 200 psi or higher, a ball valve is about the only affordable valve rated for that pressure. Everything else tops out at 125-150 psi.

12 inch long by what diameter? The pic looks like 3/4"-1" pipe. You will need much higher psi or a much larger volume chamber to run at 200 psi.

Abnmp78 · 05-27-2012, 07:48 AM

I checked psi on a 12g and a 6"x 1" pipe runs around 300 psi and a 8"x 1" with a t connector ( approx 9" pipe) is down to 225 PSI. Normally for a 12g use a 6-8"x 1" pipe will keep the fps under 220. Barrel 18-24". Yes a 3/4" pipe works just adjust cu in.
As boom said ball valves are the easiest to work with( good starting point) but least accurate since it's hard to keep on target as the lever moves also consist opening. But I started with ball valves and learned a lot from my first builds.

CNCRouterman · 05-27-2012, 09:56 AM

Not to knock sprinkler valves, but pneumatic pulse valves like those made by Asco LIKE a bit of back pressure, and from my limited experience tend to honk of they don't get it. They will "dry fire" a Nerf cannon (as in, without Nerf), but if you have no barrel, or too short a barrel, then it honks. The advantages to a pneumatic pulse valve include being able to use an electric (12 to 24v DC) solenoid on the pilot, yielding consistent opening times, and no (or very little) operator induced jerk when firing. Using a timer, or maybe cannibalizing a PB Marker's trigger board, can allow you to set the open time as well, to reduce wasted air. The current requirements for operating the electric solenoid are minimal, so a couple of nine volt batteries work fine. My solenoid is a 24v, and I use 3 each 9V batteries in series (27 volts DC) and it works quite well. As the trigger impulse is momentary, the combination works great, and yields good battery life.
The down side to these valves is operating pressure, mine is only rated for 150 psi.
However, as the valve opens increadibly fast, I don't need much pressure, something around 40 to 60 psi is more than enough to reach or exceed 230 fps.

With a very short barrel, it is less about pressure and more about how fast you open the valve.

If a pulsed valve is out of the budget, then a home made shuttle valve may be the next best choice.

Boom Master · 05-27-2012, 10:20 AM

Got a link for those ASCO pulse valves? They make a LOT of stuff. Not sure I've looked at them. Different that the quick exhaust I gather? Are the the pneumatically piloted valves?

CNCRouterman · 05-28-2012, 09:21 PM

Yes:
When the page opens, look in the right side column under "Special Service Valves" for "Dust Collector".
These valves are used in what is called reverse flow pulse cleaning, basically, you shoot a blast of air to back flush the dust collector bags to blow the fine stuff off the bag so it drops down into the lower part of the cyclone or bag house.
http://www.ascovalve.com/Application...o_catalog.aspx
When you click on the "Dust Collector" it will pull up a PDF file.

Blitz18 · 05-29-2012, 09:23 AM

Quote:

Originally Posted by Boom Master

They have worked for years but ball valve is old technology. It is hard to keep your point of aim while jerking on a lever... However if you are going 200 psi or higher, a ball valve is about the only affordable valve rated for that pressure. Everything else tops out at 125-150 psi.

12 inch long by what diameter? The pic looks like 3/4"-1" pipe. You will need much higher psi or a much larger volume chamber to run at 200 psi.

It is a 1" diameter pipe! For 200 psi what diameter and length do you recommend for the ball valve design? Also what barrel length would be good! This was ment to be more of a light bunker buster than anything!

CNCRouterman · 05-29-2012, 02:35 PM

A shuttle valve might work for your application, they can handle 200 psi, some go as high as 500 psi.
http://www.mrostop.com/shuttle-valves-c-515_611.html
the SV-5 series is 1/2" ports, should do pretty well compared to a ball valve.
There are other versions out there, this is just the first one I found in a search.

Haz-Mat · 05-29-2012, 03:18 PM

Which one do you use CNCRouterman? do you have a photo of your setup?

CNCRouterman · 05-29-2012, 03:50 PM

This is strictly a test rig, the PB Combat version will have steel or aluminum reservoir. I experimented with a PVC cartridge breech loader I machined out of MDF. Worked pretty well, but was heavy. At the time I only had my CNC Router, so the breech loader was designed around machining everything from one side, and stacking parts. The two pieces of MDF on the white PVC are some of those components. The 4 through holes were for stacking up a bunch of those parts, some with an air plenum machined in. The dadoes were for cross bolting on the plenum cap and valve body receiver. Rate of fire was roughly 3 seconds, pretty much as fast as you could pluck the empty cartridge out, and stuff another in. Neat, but sufferers from the typical downfalls of MDF, not weather proof by any stretch, and subject to dimensional changes with humidity variations. Functional, but not durable. Next gen version will be both.

Seems to me that even with this short barrel, and around 45 psi, I had trouble keeping the velocity below 260 fps. That was another reason I experimented with the MDF breech, MDF breaths, and I could introduce controlled air flow restrictions. These 1.5" valves are just too bloody efficient. Something like a 3/4" or 1" version would probably be easier to dial in. It has been suggested, and I intend to test, that reducing my reservoir size will help me tame the hot FPS issues. Current reservoir on the test rig is around 84 cu. inches I think. Probably need to cut that in half. This valve is only rated to 150 psi, but again, opening time plays a bigger roll than pressure, and electric firing improves consistency.