16 replies to this topic

[Flaming Hilt]

IT'S... ALIVE!!!
I mean... it works. See post #11.

- - -

So, I hope this doesn't fall under the "Concept and Ideas" thread category, because theoretically, it should work. It's not a concept or an idea, it's a finished design. The reason I don't just go and do it is because -- long story short -- I can't use my workbench right now.

Anyways. I've been working on a squirt gun design. In my boredom I was paging through howstuffworks.com (always a fun site to "page through") when I can across this page, about the invention of the modern squirt gun.

What does this have to do with Nerf? Well, obviously, Nerf pump guns and Super Soakers are closely related. They're practically the same thing, except that Super Soakers shoot water and have an extra reserver for the pressurized water. And if you modify this trigger:



...with some hardware store-friendly materials, you get:





You could even make it more simple and instead of constructing your own pivot, just use a clothespin:



- - -

So, as I said, this should theoretically work. The only potential problem I foresee is the ratio retained air pressure:spring strength. In other words, unless you can find an extremely strong clothespin, this trigger will only work for weaker guns. Experiment is the only way to determine max PSI.

There should probably be some kind of flat pad on the end of the clothespin because clothespin pads are grooved and could let air out.

Hopefully by saying this it won't go back to a "concept/idea," but: I'll be constructing this as soon as my workbench is accessible. I have tubing, clothespins, and an air tank... all that has to be done is it getting put together. It is indeed so simple one could do it in a matter of minutes.

Assuming it works, it should probably be called the Pinch Trigger. : o) [u]

Edited by Flaming Hilt, 25 June 2007 - 09:32 PM.

[Prometheus]

You'd want a fairly thin walled tubing, so it'd deform from the clothespin easier...

[Flaming Hilt]

Oh yea, sorry I wasn't clearer. Something flexible; ie acrylic or... well actually I don't know what it's called... but the air tubing one finds inside an At2k or another stock nerf gun.

Surgical tubing (the only other kind of flex tubing I can think of the name of) would also work, though you might have expansion problems in between the air tank and the clothespin.

[watkins]

Surgical tubing could be good for the pinched part of the tube if it was spliced into a less flexible tube for the main air lines. I suppose you could always try to nest it or wrap it in something too.

[Carbon]

Those small-ish nylon spring clamps (like for gluing woodwork) would be nice, since their jaws have a large, flat surface area (unlike a clothespin) and a lot of strength. That would seal the surgical tubing very well.

I just wonder if a tubing large enough to provide decent airflow would still seal properly.

Edited by Carbon, 24 June 2007 - 06:43 PM.

[Jangadance]

Hey Hilt, what's up.

Well, if you've opened up a Super Soaker or two you know how the triggers work. Let me see if I can summarize.

The original Super Soaker models (SS 50, SS100, etc) DID use this low-tech pinch "valve" which you illustrate.

The XP and CPS models use Supermaxx/Airtech-esque pull valves. Faster action, better pressure capabilities, more reliable.

(The new Max-D models use a fancy quick-release ball valve which is actually pretty neat and has been used for Nerf homemades before.)

Unfortunately, the easiest and most old-school Super Soaker trigger (and therefore valve) style won't make an easy transition to Nerf. To experiment, pick up an old working Super Soaker at a garage sale, hot glue some 1/2" PVC on there and fire a few stock darts. It may take a few pumps, but you'll understand how slow the release is on this system and how it wouldn't be very air efficient or practical for Nerf. Nice idea though... always good to keep an open mind. If it works, you can punch me in the kidney at the next Minnesota War.

[Flaming Hilt]

Woah dang. Well thanks Janga.

...I feel like such a noob. : o(

I'm still going to go ahead with it. Because you know, I really want to punch you in the kidney. ; o) When did you become such an expert on squirt guns?

Thanks for the suggestion, Carbon. I'll look around and see what I can find.

I will probably just dig up the stuff and try this, regardless of the accessibility of my workbench. I mean, it doesn't really require any tools.... The best test will be connecting it to a gun. That I can't do yet. But I promise to keep ya'll updated.

[Doom]

There are several reasons why Larami stopped using this valve. The only reason they used it originally was because it was cheap. They found out fast however that it doesn't have very high flow and can leak. While flow might not be as important for Nerf as it is for water guns, folding tubing still is a bad idea for a firing valve. I've done a TON of research for my water gun website's new history section and that's the only thing I have heard about the "pinch trigger."

"Surgical tubing," AKA latex tubing would not be a good idea here. The tubing expands when put under a certain amount of pressure. Usually those pressures aren't very high even on the highest end tubes. Folding them isn't a good idea at the point because they could pop from the increased pressure (they keep the same pressure and increase in volume when more air comes in). And the highest end tubes expand at like 35 PSI... which isn't very high. Folding those tubes would be difficult anyway because they're often 1/4-inch thich!

You can build this, but I think you will be quickly disappointed in the poor performance and unreliability. I think homemade pull valves are the future of pressurized Nerf homemades.

[Jangadance]

There's a reason Doom and I both have the Lorax as our avatar; we both dole out indispensable advice.

flow might not be as important for Nerf as it is for water guns...

True, Doom- "flow" is not as important, but it is significant nonetheless. Typically, the best way to get alot of pressure behind a dart is to let all the pressure out as fast as possible. A pinch valve would inhibit that. This is why people who make homemade Nerf rifles use faster-flowing valves such as solenoid valves instead of slow-flowing ball valves, etc. Once the dart starts moving, there is pressure lost in the space behind the dart. People (starting with cxwq) have corrected that by using nested brass barrels to keep the dart in place while pressure builds up behind it, and then less friction by using graduated brass tubes.

Also, Hilt - make note of the fact that in Super Soakers, it isn't just the regular plastic tube that gets pinched, there is a thinner, more rigid section of the tube where the pinch action occurs.

• provides less resistance against the pinching mechanism
• seal opens/closes faster for quicker "flow" and cut-off

I'm sure there's a pinch valve in there somewhere...


<edit> Finished response, forgot to add some stuff before </edit>

Edited by Jangadance, 25 June 2007 - 05:48 PM.

[Doom]

True, Doom- "flow" is not as important, but it is significant nonetheless. Typically, the best way to get alot of pressure behind a dart is to let all the pressure out as fast as possible. A pinch valve would inhibit that. This is why people who make homemade Nerf rifles use faster-flowing valves such as solenoid valves instead of slow-flowing ball valves, etc. Once the dart starts moving, there is pressure lost in the space behind the dart. People (starting with cxwq) have corrected that by using nested brass barrels to keep the dart in place while pressure builds up behind it, and then less friction by using graduated brass tubes.

I don't think you understand the context I wrote under. I understand the entire physics behind Nerf guns better than most anyone here. Flow is air output in this case. Comparatively, you won't need as much flow to get good ranges in Nerf. For example, to get over 70 feet of range in a water gun, I had to create over 3.5 liters per second of water flow. 70 feet I would say is equivalent to about 200 to 250 feet in Nerf. I was saying that lower flow is appropriate for Nerf.

Your explanation also isn't completely correct. You want a fast opening valve to accelerate the dart to a higher velocity. To put it in layman's terms, If the valve opens slowly, the dart moves down the barrel slower initially but picks up speed. Eventually, full flow is achieved, but the dart has less distance to travel to accelerate even more being pushed by the force of pressure. If the barrel is too long, the force of friction between the dart and the barrel becomes greater than the force of pressure due to the pressure drop, and the dart starts decelerating. If you wanted to do all the math, you could find the ideal barrel length with friction and pressure, but I prefer the simple empirical method myself.

You also could, as you noted, reduce the friction, but I think we're pretty close to as low as we could get. Lower is possible however. One thing most people don't know is that you can get PTFE (trade name Teflon) pipe to use for barrels. The only problem I have noted is that the tolerances of such a pipe make it unfeasible for a barrel. The pipe's inner diameter has a relatively high tolerance making the diameter smaller... a dart will not fit well. For this reason I am using aluminum tubing for a barrel because it has low friction, is light, is cheap, and also comes in any length wanted (nested brass can cause dart catching issues).

To get back on topic, pinch valves would be somewhat hard to implement now that I think about it. Clothespins won't work well, so you'd have to use clamps or fold the tubing. You could do what I call a "double fold" valve that no water gun had done if you're set on trying it though, Flaming Hilt. I would consider this valve to be the most reliable form of the pinch valve. I'll have to make a drawing of it.

[Flaming Hilt]

Janga, I'm going to punch you so hard in the kidney you won't be able to pee for a week.
...or something like that.

No, I'm not going to punch you in the kidney. Happy Birthday though. : oD

IT WORKS!!!

Here's my prototype. It's crap for a gun but the point was to test the valve. With no further ado:

Left, glue drying. Right, pumped and ready to go.

Obviously the surgical tubing was... interesting to work with. But it worked. In future tests I will probably put acrylic tubing over the non-pinched part to keep it from doing that.

Here it is set up to fire:


Ranges are to the end of that wall, which I would say is 25 feet. Obviously a bigger tank would provide longer range. The point is, though... it works.



Also, something important to note is that (as you will see in the picture) the tubing is held relatively close to the spring, or pivot point, on the clothespin. Therefore, putting a flat pad on the end or using another lever that would hold it out farther would provide a faster opening and perhaps more range.

I can't do much with it now. I think I'm going to wipe my workbench though, regardless of the fact that I have nowhere to put it all. And then we'll have FH's 1st 100% homemade pump gun. WoOt yeyah.

(I still encourage ya'll to criticize/offer suggestions for improvement. IE a diagram of this "double fold" valve, maybe.... I'll get around to testing it all eventually)

Edited by Flaming Hilt, 25 June 2007 - 09:56 PM.

[Prometheus]

Use it in conjunction with some type of pull valve, so the pinch valve fills the air tank, and the pull valve fires. That way, a slight leak will have no effect on it all all (assuming the air leaks through the valve, and not right out the tubing), and it also removes the slow air flow factor. Just an idea.

[Flaming Hilt]

...why wouldn't you use just a pull valve then?

The point of this valve was to make a simple, cheap, well-working valve.

And that's just what it is. I haven't put it into a gun yet but I don't get why everybody condones it so much.

[Prometheus]

...why wouldn't you use just a pull valve then?

The point of this valve was to make a simple, cheap, well-working valve.

And that's just what it is. I haven't put it into a gun yet but I don't get why everybody condones it so much.

Because with a large air tank, the pull valve can use excessive amounts of air. Look at CS's d-chap design that utilizes the 2 valves, which allows it to be hooked up to his air tank, and still conserve air.

[Flaming Hilt]

...so what you're saying is that you can build a pull valve as large as you want to, thus meaning it has infinite potential for the speed at which it releases air? "...excessive" amounts of air?

With two of any kind of valve, you can conserve air... although a ball valve would probably be best, because of the way it opens. Pulling something back like a a trigger (and having it only be open when you pull) doesn't seem like a good way to switch pressure between tanks.

[Brass]

God... I'm amazed you actually got that to work.
Props.

[Prometheus]

...so what you're saying is that you can build a pull valve as large as you want to, thus meaning it has infinite potential for the speed at which it releases air? "...excessive" amounts of air?

With two of any kind of valve, you can conserve air... although a ball valve would probably be best, because of the way it opens. Pulling something back like a a trigger (and having it only be open when you pull) doesn't seem like a good way to switch pressure between tanks.

I was using the d-chap as an example as I find it easy to orient for a trigger. But two of these would work well with an external tank. If you have a breech system, you could pull back to pump, and a rod presses the first pin. That pressurizes the air tank. Then you close the breech, which closes the first valve. Pull the trigger, the second valve, to fire.

CaptainSlug said that hooking a gun such as an AT2/3/4K up to his external air tank would consume larger volumes of air due to the valve type. I just used that valve type in my example as I'm familiar with it. But two of these would work good.