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Attempting to build a "net shooter"

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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Attempting to build a "net shooter"

Unread postAuthor: Mike_D202 » Fri May 18, 2007 4:28 pm

Hey fellas, I'm new here. Ever since I saw this product:

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http://www.ajoka.com/Shooting_Net/shootingnet1.htm

I've been trying to build one. I read on the website that it uses compressed air and is refillable, so I know it can be done. I just started learning about air cannons a week ago and built a small design (like the ajoka version):

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Heres my problem: I cant seem to build enough pressure (I even stuck a potatoe in there air-tight and then farthest it went was 3 feet). I was recommended a bike pump, but I can only get about 2 pumps maximum before it wont let me pump anymore. I'm about ready to go to the gas station and just use the air compressor there to fill it up, but I dont know how long I should let the air in for (before I get a plastic shard stuck in my neck). The pipe can handle 450 psi, but the valve only 150 psi.
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Unread postAuthor: paaiyan » Fri May 18, 2007 4:38 pm

Well, 150 PSI should be plenty depending on the size of your chamber and everything. As for fill time, that all depends on the amount of volume in your chamber, and the speed at which the compressor puts out air. Your best bet is to install a pressure gauge and go by that.
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Unread postAuthor: sjog » Fri May 18, 2007 5:03 pm

Reducer is the muzzle, I'm assuming. The chamber could be bigger, it looks to be 1 1/2. You could cut and add a bigger chamber. Ball valves are not very " fast ". Sprinkler or QEV valves can give better ' speed "
The idea is to let the air out all at once, that is the speed I'm talking about.
Why did you cut your assistant's head off?
A small fishing Cast Net might be easy to set up for your idea.
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Unread postAuthor: paaiyan » Fri May 18, 2007 5:07 pm

Decapitition! Oh em gee! Haha, so I'm assuming that you just pack the net into the reducer and fire it right? part of the reason the potato didn't go very far might also be that it doesn't have any room to accelerate. The barrel on a cannon serves to alow the gasses behind the projectile to expand, and since the projectile is in the way, they are forced to push it out. With just that reducer there, the gasses will expand till the potato comes out, but you won't get the full force as the potato is released before the gasses are fuly expanded.
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Unread postAuthor: Mike_D202 » Fri May 18, 2007 5:15 pm

sjog wrote:Reducer is the muzzle, I'm assuming. The chamber could be bigger, it looks to be 1 1/2. You could cut and add a bigger chamber. Ball valves are not very " fast ". Sprinkler or QEV valves can give better ' speed "
The idea is to let the air out all at once, that is the speed I'm talking about.
Why did you cut your assistant's head off?
A small fishing Cast Net might be easy to set up for your idea.


Gah! I was hoping I wouldnt have to do that...but then again, at this point I just want this puppy to work. How much bigger would you say it would have to be? About the size of the "muzzle" at the barrel or wider? And if it were to go wider, could I shorten the length of the tank by 5 inches so its just 1 foot?

Hah, I took off her head so this thread wouldnt be filled with "wow whose the chick?!" replies :D
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Unread postAuthor: paaiyan » Fri May 18, 2007 5:20 pm

Haha, that's what I figured you did it for. Well you can use the search feature on the site and look up chamber:barrel ratios for a pneumatic cannon. For a pneumatic I'm not sure what the ratio is right off the top of my head. Basically what the ratio does is to give you the optimum amount of space for the gasses to expand. If you have the barrel too short, you don't get all the power, if it's too long, then after a certain point, the gasses expandign aren't enough to overcome the friction between projectile and barrel and it starts to slow down considerably.
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Unread postAuthor: sjog » Fri May 18, 2007 5:34 pm

Big chamber - big projectiles
Paaiyan brings up a good point. The barrel is where the projectile accelerates.
Mike- you could turn the thing around and mount chamber on reducer,IF it is pressure rated. Ball valves are slow any way. Look up sprinkler valves they are easy to get. Do a little research before cutting or adding to present
configuration.
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Unread postAuthor: boilingleadbath » Fri May 18, 2007 5:36 pm

A larger chamber will not help very much. Check it with the GGDT if you don't believe me.

Other than that, I'm fairly speculative.
For starters, I'm rather surprised that the potato only went 3 feet.
Was this cut to size and rammed to the rear of your (stubby) barrel?

2) The GGDT is leading me to believe that a sprinkler valve, or similar, would be a good choice.

3) It may be best for the spread of the net and the muzzle velocity if you accelerate it using multiple small barrels, pointed slightly outwards, along the perimeter. Each of these might contain a small, tight fitting, weight.

4) Otherwise, I'd recommend using a longer barrel - you won't get much speed from the 4" (or so) long thing you have on it right now.
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Unread postAuthor: Mike_D202 » Fri May 18, 2007 5:45 pm

So probably something like this, eh?

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For the net, I have 4 rubber plugs that will fit into some clear 1" tubbing I bought. Would it help if this were to happen:

Image

That would focus the compressed air into the four tubes.
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Unread postAuthor: paaiyan » Fri May 18, 2007 6:06 pm

That would help, yes.
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Unread postAuthor: veginator » Fri May 18, 2007 7:31 pm

u should definetly get a metal ballvalve they are sooooo much easier to operate and over time the longer you use it, it will be even harder to operate. one of my plastic ballvalves was impossible to close after a while. other wise i am very impressed by such a clean gun. you did a good job for someone new to pneumatics.
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Unread postAuthor: integral » Fri May 18, 2007 8:09 pm

Can't really determine how cleanly you frankinstien'ed those bits of clear tubing, but I'm suspecting that you won't get enough flow from that one bit of tubing in the barrel to all four. That would mean you will lose ALOT of power. However, if each one of those rubber plugs have the same ID all the way into the 1in tubing, then you would be fine. Of course a longer barrel and sprinkler would dramatically increase your performance.
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Unread postAuthor: sjog » Fri May 18, 2007 9:43 pm

Mike- Your moving right along!!
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Unread postAuthor: turbohacker » Fri May 18, 2007 9:58 pm

the barrels on that four way connector will be spaced out to far causing the net to over expand in mid air ind then snap closed and get tangled up. Make the four way barrels straiter
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Unread postAuthor: sharpshooter » Fri May 18, 2007 10:49 pm

it looks as if the weights on the end of the net are in separate barrels, and the net just sits in the middle.

What pressure are you using? 100psi in chamber half the size of one at 50psi will be much better. I would go with upping the psi first before a bigger chamber. I wouldn't worry terribly much bout goin to 150... maybe even 300 with a ball valve. They have a high safety factor built in.

i would suggest putting pieces of 1/2" pvc around the edge of the reducer, then epoxying them in. This way the weights will have their own barrel, which should result in a more powerful shot.
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