7 replies to this topic

[pwnchu]

http://www.amazon.co...n/dp/B000GL1NR2



The pump and spring ball valve are taken from the max d 2000. It works well enough, although the pump is kind of slow, and one of the ball valves had its expansion springs break (but i had gotten 2 for $5 a long time ago from target. I saw 1 for $5 there recently). The bladder is from another gun.


This picture kind of sucks, it's supposed to be a segment of pvc with some tape covering the end. You poke a hole (needle size is fine; high pressure stretches the hole larger) in it, which serves to keep air from going in too fast. The pvc segment goes between the compression couplings, with the taped side closer to the bladder/pump to allow an air reservoir.

It does well at high pressure, judging from the hiss, although it takes a bit longer to refill at low pressure. It refills fast enough for hand reloading, although i think at high pressure you can use it with a clip as a crude semi auto weapon (unfortunately i have neither the tools, supplies, nor the competence to build a clip).

I made the barrel short because i nerf indoors, and plus people i play with would get mad if it were more powerful anyways. It's not straight because i suck at gluing.

edit: I guess i should follow the example of not posting ranges.

Has anyone tried something like this before? I would assume yes because it's so simple, but I havent seen anything about it.

Edited by pwnchu, 10 April 2008 - 06:40 PM.

[Bomberman]

Um.. Just a hair fugly, but it looks like it sort of works. Where is the trigger? And in the last pic, for pictures up close, at least turn your flash off. But 80 or 90 foot ranges don't lie. I guess whatever floats your boat man. It's all about how you use it, so props that is works well for you.

~Bomberman

Edited by Bomberman, 10 April 2008 - 01:07 PM.

[jwasko]

It depends on what you mean by "this before"

If you mean using a bladder for semi-auto fire, I believe the semi-auto 2k was one of the first.

If you mean using the Max D 2k: I haven't seen anyone else using one, but I experimented with one. It got pretty good range, If I remember correctly. I made the air tank too big, though, because it took about 30 pumps (using the stock pump) to fill it. I wish I could find some more of the epoxy that I used to put everything together back then...that was some darn good epoxy.

Bomberman: I'm sure Pwnchu can explain this better (and, more particularly, provide pics), but I'll just mention that the Max D 2k uses a rather ingenious spring-operated ball valve.

Edited by jwasko, 10 April 2008 - 02:46 PM.

[Doom]

I made a gun that used latex tubing (the same material as in "bladders") about a month and a half before the semi-auto 2K project and posted about it here, but few noticed (read about it here and go here and here to view some pictures). I recommended buying latex tubing instead of cannibalizing other guns in the semi auto 2K thread, but from what I remember people didn't take kindly to my suggestions for some reason so I never really talked about that again. Bladders are nothing new, but they're uncommon, and that's a shame because they're a perfectly fine material for Nerf. Because there is little to no pressure drop given the entire bladder is emptied, there is no ideal barrel length, which simplifies things somewhat. However, the bladders can get very large because they only compress the air to 50 PSI at most.

You can buy latex tubing at http://www.mcmaster.com/ if you want some. You also can go directly to the manufacturer of the tubing if you want more variety, but the minimum order often is 50 feet or more. That can make these tubes very expensive. One tube I was looking at had a minimum order of something like 200 feet, which put the total price over $1000.

Other rubber tubings do not exhibit the unique properties of latex from what I've read. They wouldn't expand as much or return as closely to the original shape as latex does, so latex tubing is ideal. I also don't know if the lack of expansion would affect how constant the pressure is. The force and internal surface area of latex tubing grow approximately proportionally, so the pressure is relatively constant.

There's no reason to use a Max-D Super Soaker valve in this gun, in my opinion. Those valves have low flow and they're ball valves, so they open relatively slow. That's not an ideal design, but if it works for you, great. They are spring loaded ball valves however, so they're definitely better than plain ball valves. The reduced flow would be the main problem with them.

As for the Max-D spring ball valve design, it's patented and exists mainly to make the water flow more laminar. You can pull part of it and it will open the valve. However, in the current implementation it also reduces flow, which reduces performance in water guns significantly more than having very laminar flow would, so it's a pointless design.

Edited by Doom, 10 April 2008 - 04:12 PM.

[puggy]

Those valves may be ballvalves but are highly lubricated and have a nice sring action so their damn good.

[pwnchu]

jwasko: I meant the concept of using a small hole for air to refill the reservoir instead of using a more sophisticated mechanical system to close off the flow for a true semi auto gun.

Dont feel like resizing, and i figure it might be easier to see if i dont.

http://i217.photobuc...chu/trigger.jpg
You press on the corner of the triangle that doesn't have any screws.

http://i217.photobuc.../springless.jpg
Same thing, but the spring broke off.

http://i217.photobuc...hu/actuated.jpg
Trigger depressed, not returning because there is no spring

http://i217.photobuc...nchu/closed.jpg
Ball valve closed

http://i217.photobuc...pwnchu/open.jpg
Ball valve open. about a .5 cm diameter (about the same as a straw).

The way you press it will affect it; ie it will open a slight bit before the spring snaps it open, but it's generally not a problem.

Edited by pwnchu, 10 April 2008 - 06:59 PM.

[Doom]

Those valves may be ballvalves but are highly lubricated and have a nice sring action so their damn good.

I don't think you understood what I was saying. The smaller internal diameter reduces potential flow. That makes them far from "damn good." Because they are ball valves they are inherently slower than other valves, which is true even if they're spring loaded, but that's not the real problem with these valves. The real problem is the reduced flow.

[pwnchu]

So, the main reason I made this topic was about the pinhole mechanism. What do you guys think about it?