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Old 09-06-2008, 09:15 PM   #1
Ben
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Default FANG automatic Nerf gun

Judging by the lack of interest at Nerf forums in my new Nerf gun and the recent inactivity here, I thought it would be a good idea to post something about a recent project of mine. Check out the link in the first sentence.

The FANG will be a semi-automatic Nerf gun. And I mean it. The pneumatic components work and everything else will be easy at this point.

I left for college before I could finish the gun so I'm going to finish it here. I'll have to figure out which machine shops are available to me though... I think the one I used in a few classes last year can be used by any engineering student though I'm not sure because it might be specific for some courses.

I'll post more later. Right now I'm going to take a shower.
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Old 09-07-2008, 06:27 AM   #2
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Default Re: FANG automatic Nerf gun

So I'm not quite sure how this works, being unfamiliar with NERF in general. Do you propel the dart by the air directly, or does the air move a piston or something, that then propels the dart.

And how does it load the next dart? It doesn't look like a gravity-fed magazine or a revolver design.

Also the key questions: how big's the magazine, and what's the expected rate of fire?
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Old 09-07-2008, 09:35 AM   #3
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Default Re: FANG automatic Nerf gun

How long does it take for nerfhaven to validate your account? I made mine in July and I am still waiting. I made the plusbow but i have been having some problems with it and I want to ask captainslug some questions as well as some other people but I need my account validated. Just roughly in months or years how long does it take?
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Old 09-07-2008, 10:44 AM   #4
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Default Re: FANG automatic Nerf gun

I should have explained the cycle in the first post. Basically, when the trigger is pressed, the QEV is actuated and the bolt moves back. A dart moves into the area previously taken up by the bolt. When the trigger is not pressed, the bolt moves forward, pushing the dart into the chamber and keeping others out. It's a simple cycle.

The magazine is fed by a small constant force spring. The problem with Nerf darts is that they can be squished, so a normal spring isn't always a good idea because the force depends on the displacement. A constant force spring prevents darts from being squished.

I'm going for a 10 to 12 inch long magazine, which should mean it'll have a capacity of 20 or more darts.

I had some problems with the bolt returning slowly as a result of my use of easily bent brass tubes, but it has improved now. I plan to redo some of those parts to ensure they perform optimally. Judging by what I've experimented with, a rate of fire of 1 shot per second would be the realistic. I could see two shots per second if the return problems are solved and some lubrication is used. Higher than that would probably require a higher flow directional control valve.

Of course, the rate of fire depends on whether or not the system would shred darts. I used a low force air cylinder so there shouldn't be any problems with that, but if there are I'd have to change the design slightly.

@swirlycurly: I've read that it could take 6 months or more for them to validate your account. I'd suggest writing an email to VACC about it. Be short, polite, write well and he'll probably validate your account soon.
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Old 09-07-2008, 11:28 AM   #5
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Default Re: FANG automatic Nerf gun

cantab, Nerf guns can use either springs or compressed air to fire darts. The springs push on pistons to push air anyway. Spring require fewer pumps but usually get less range, plus you can't store energy for more than one shot.

On a side note, my account is still being validated too. It seems they do validation in short sprints and then forget about it for a while.
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Old 12-06-2008, 12:07 PM   #6
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Default Re: FANG automatic Nerf gun

Last week I put some more work into FANG and it's about 80% complete so far. The cycle works--the gun is a semi-automatic--and it has great range of about 115 feet at only 30 PSI. This is the first homemade semi-automatic Nerf gun I know of to get more than 80 feet of range. And it's a rarity simply because of the semi-automatic cycle. This is the third working homemade semi-automatic Nerf gun I know of. This is the forth if you count something I made back in 2004, which operated on one pull of a lever, but that wasn't highly reliable or convenient.

Oddly, barely anyone at NerfHaven was interested. I suppose they like concepts more than finished products, judging by how some of the most replied to threads in their forum are nothing more than concepts that never say the light of day. Spudfiles seemed more receptive and offered some good suggestions.

I'm planning prototype 2 at the moment. The current gun--prototype 1--will serve as a test bed for experimental data to help make a computer model of similar Nerf guns. I hope to use the model to minimize the air spent per shot to achieve a certain range. This'll be a little challenging but I'm always up for a challenge. Luckily I'm good with differential equations and fudging a theoretical equation to work more like reality.

My goal with the computer model is to accurately model the internal and external ballistics of the gun. Due to the relatively low speeds of the Nerf dart and the fact that it's front weighted I should be able to neglect many things that normally would be taken into account in more powerful spud guns and firearms. I'll still have to use numeric approximations for my differential equations but that's fine because we have computers for that.

One thing I'd like to reiterate is that building FANG was significantly easier than I had originally anticipated, mostly due to good planning. The design minimized the number of machined components and required as little precision as possible. Prototype 2 should be even better in that respect.
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Old 12-06-2008, 12:42 PM   #7
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Default Re: FANG automatic Nerf gun

I've held this thing and it is awesome. It's not large at all and is very light. It didn't seem fragile either. The gun's a giant leap in the right direction. My bolt-action gun was quite large and probably helped push some people to pursue creative valve assemblies, but Ben really perfected the semi-auto valve system. I can't see any real improvements, but he has proven me wrong in the past so I'll wait for his other prototypes.

Quote:
Oddly, barely anyone at NerfHaven was interested. I suppose they like concepts more than finished products, judging by how some of the most replied to threads in their forum are nothing more than concepts that never say the light of day.
I'd imagine the average NerfHaven user would think "What's there to discuss? It's already built and works." Plus, ever since Boltsniper came around, members at NerfHaven really only discuss stuff about fully automatic guns or spring-piston guns; anything in the middle seems to be left out.
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Old 12-06-2008, 01:49 PM   #8
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Default Re: FANG automatic Nerf gun

Quote:
I'd imagine the average NerfHaven user would think "What's there to discuss? It's already built and works." Plus, ever since Boltsniper came around, members at NerfHaven really only discuss stuff about fully automatic guns or spring-piston guns; anything in the middle seems to be left out.

Good point. I'm into well designed finished products and I'm very satisfied with this one so there really isn't much to discuss.

The bias towards spring guns exists too. There's so much bias that I was reading a thread where people were talking about how air pressure guns are worthless and are banned from most wars. The sheer ignorance left me scratching my head. They were talking about banning an air pressure gun with less than 90 feet of range while at the same time allowing a spring gun with 140 feet of range... does that seem inconsistent to anyone else?

Maybe if I built a gun around the basic dart cycle that used springs I'd get a trillion replies. That wouldn't be difficult.

The thread has been getting many views at least--it is my most recent thread but it also is my first thread to get more than 2000 views there.

I've listed some tentative plans for changes at Spudfiles and NerfHaven, so if you can't think of anything that needs changing, I can, have, and wrote about it.
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Old 12-06-2008, 06:09 PM   #9
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Default Re: FANG automatic Nerf gun

That's a pretty clean build.

Heh, I had to go back and re-read the earlier discussion to remember how FANG worked. I'm still wondering what you're using to control the bolt though - maybe I haven't read it too carefully. It looks like you've got a vinyl tube connected to the pressure chamber for the return motion, using a piston in the rear. And I'm guessing a spring makes the piston "return" the bolt to the open position. That's a neat way of linking the pressure chamber to the bolt, although you might want to shorten the hose.

Then again, the hose could just be a shoulder strap.

In one of your later Spudfiles comments you mentioned a smaller chamber at higher pressure. I'm pretty sure the massive initial acceleration will tear apart the darts, though.
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Old 12-06-2008, 08:15 PM   #10
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Default Re: FANG automatic Nerf gun

You have the right idea. The bolt is pushed forward by the air cylinder. The pressure chamber and air cylinder are linked so that when pressure is stored in the pressure chamber some is also stored in the air cylinder, which pushes the dart. The air cylinder does have a return spring so that when the pressure chamber is empty, the bolt retracts so a new dart can be advanced.

The hose was cut just to see if the air cylinder would work. I hadn't even noticed it was too long. That's definitely something to shorten.

As for the high initial acceleration, I haven't run into that myself but I could see it happening. I suppose the only way to know is through testing.
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