Question on using co2 cartridges as power source

[drmoreau]

Greetings all! I'm new to the forum and want to jump right in.

I am the commanding officer of a Stargate fan group and we are working on a pneumatic Nerf launcher in the form of a Jaffa Staff for use at our booth at conventions.

If you'd like to see my progress then check out our website: www.sg-21.com , it is the first post, a video. Currently the staff is powered by a bicycle tire valve that allows me to compress air into a small chamber at the back, but this is extremely time consuming to re-pressurize after every shot so I'm looking to go co2 power.

I've already tested the barrel with a Nerf dart in it and some co2 from a co2 cartridge-powered air duster and it fires just fine. (mind you not as hard as with the bicycle pump, but enough to shoot at targets).

Now what I'm wanting to do is source a co2 cartridge assembly/housing/holder? (whatever it's called). Kinda hard to explain, but I just want the part with the valve and the part that holds the co2 cartridge to attach to my staff. Let me put it another way:

I would like my staff to be composed of two 3 foot lengths of pipe, I want it to unscrew in the middle and allow me to put in a fresh co2 cartridge (and also so it's not 6 feet long when I transport it) and it also needs a trigger to release a blast of co2.

Does anyone know of the availability of a part like that (just the co2 cartridge valve and holder) that I could source? If not then I'll be stuck with a duster unit strapped to the side of my staff. I tried searching Google and Amazon but couldn't come up with anything that would do what I need. Thanks![/u]

[Brian the brain]

What you are looking for is called a 12 gram quick change adapter.



Depending on temperature a 12gram CO2 bulb could contain 1000psi of pressure.

Make sure you know what you're doing.

Pressure this high is dangerous.
Either have a pressurecontainer large enough to allow the pressure to drop to a safe pressure or build the entire launcher to withstand the high pressure without failing.

info found on 12 gram bulbs and the pressure/volume relations are found here:
http://www.spudfiles.com/forums/how-muc ... t7133.html

[drmoreau]

In that case I may decide to stick with my schrader valve and bike pump idea. it's only reaching about 80psi (absolute max). I may just get a bicycle frame pump and mount it to the staff so that it's a little easier to pump it up for the next shot.

That or I may just adapt my little co2 duster unit into the side of my PVC launcher. I know co2 and pvc don't typically mix and I know co2 can have high pressures and I'd never try to fire anything heavy or that creates a ton of back-pressure. With Nerf darts though (at least in my early tests) there isn't enough back-pressure to damage anything. Just a quick release of co2 from the duster and the Nerf dart goes PLUNK out of the barrel.

[jackssmirkingrevenge]

You could use a CO₂ inflator like this:



I used one for BBs here, obviously with Nerf darts it would not be as dangerous: http://www.spudfiles.com/forums/co2-inf ... 20236.html

[drmoreau]

The problem is that I'm making a staff weapon and that would add a "grip" to the staff making it a gun. Now I COULD use something like that to quickly fill the pressure chamber on my current "staff"....I'm just afraid that it'd be too much pressure and my pressure chamber would blow up in my face.

[jackssmirkingrevenge]

The problem is that I'm making a staff weapon and that would add a "grip" to the staff making it a gun. Now I COULD use something like that to quickly fill the pressure chamber on my current "staff"....

You could mount it in line with the staff and feed the pressure though an elbow. The beauty of this is that it also gives you a handy trigger, so all you have to worry about is piping the outlet to a barrel

I'm just afraid that it'd be too much pressure and my pressure chamber would blow up in my face.

No risk of that with the system outlined above.

[drmoreau]

I see what you're saying, mount it along the barrel and pipe it in using elbows, then when you depress the trigger co2 rushes into the barrel and once it overcomes the resistance of the Nerf dart's rubber edge lodged in the barrel it just "pops" the dart out.

That solves 90% of the problems, except me trying to figure out how to physically mount the inflation device to the barrel while still being able to easily take it apart and change the cartridge. I'll have to do some thinking on that one.

[drmoreau]

I did a little test and it seems to work. I removed the nozzle from my current co2 duster (looks just like the co2 air pump except a different outlet) and mated a black pressure hose to it then piped that hose into my barrel.

On a fresh cartridge it shot very hard and performed very well, but I was only able to get 20 shots from a single cartridge before needing to replace it. Obviously I will need to get 50 or more per charge to make this viable.

I think the issue is that the cartridge is having to pressurize a barrel that is 1/2" in diameter by 2 feet long, that's a lot of wasted co2.

I'm thinking about running a smaller barrel down the main barrel that's very narrow (whatever the inside diameter of a Nerf dart is) and only pressurizing that. That would still propel the dart and should at very least double the capacity.

[jackssmirkingrevenge]

Definitely go with a very short barrel, I would think even 6 inches should suffice - and learn to "tap" the valve lightly, just enough to shoot the dart. Also, the amount of tubing between valve and barrel should be kept to the bare minimum.



*phooomph..... plink!*

hehe

[biged]

Calc chamber size into cubic inches:

Radius * Radius * PI * Length

All 12 Grams of CO2 @ 70 degrees

6 Cubic inches 700 psi
7 Cubic inches 600 psi
8 Cubic inches 525 psi
9 Cubic inches 466.666667 psi
10 Cubic inches 420 psi
11 Cubic inches 381.818182 psi
12 Cubic inches 350 psi
13 Cubic inches 323.076923 psi
14 Cubic inches 300 psi
15 Cubic inches 280 psi
16 Cubic inches 262.5 psi
17 Cubic inches 247.058824 psi
18 Cubic inches 233.333333 psi
19 Cubic inches 221.052632 psi
20 Cubic inches 210 psi
21 Cubic inches 200 psi
22 Cubic inches 190.909091 psi
23 Cubic inches 182.608696 psi
24 Cubic inches 175 psi
25 Cubic inches 168 psi
26 Cubic inches 161.538462 psi
27 Cubic inches 155.555556 psi
28 Cubic inches 150 psi
29 Cubic inches 144.827586 psi
30 Cubic inches 140 psi
31 Cubic inches 135.483871 psi
32 Cubic inches 131.25 psi
33 Cubic inches 127.272727 psi
34 Cubic inches 123.529412 psi
35 Cubic inches 120 psi
36 Cubic inches 116.666667 psi
37 Cubic inches 113.513514 psi
38 Cubic inches 110.526316 psi
39 Cubic inches 107.692308 psi
40 Cubic inches 105 psi
41 Cubic inches 102.439024 psi
42 Cubic inches 100 psi
43 Cubic inches 97.6744186 psi
44 Cubic inches 95.4545455 psi
45 Cubic inches 93.3333333 psi
46 Cubic inches 91.3043478 psi
47 Cubic inches 89.3617021 psi
48 Cubic inches 87.5 psi
49 Cubic inches 85.7142857 psi
50 Cubic inches 84 psi