19 replies to this topic

[Doom]

Normally I don't post things until they're completed here but there will be little opportunity for me to make progress in the next week or two so I'm going to post what I have done now. Not much more work is necessary aside from construction of the shell, magazine, handle, and some trigger components, which sounds like more than it would be.

The FANG will be a semi-automatic nerf gun. Right now I have all of the moving parts aside from the magazine complete. I might redo some of them if it'll improve the function later but it essentially functions as it should. The only problem at the moment is that my bolt returns slowly, which was likely due to some gunk on the outside of it from it's construction.

This gun uses the same DCV actuated QEV that I've mentioned before and that CaptainSlug intends to use in ARR. This makes the gun very efficient, too efficient in fact. I've reduced the pressure chamber volume since describing the valve assembly and my stefans are still falling apart on impact. I'll definitely lower the pressure from 40 PSI but if more change is needed I could add more pilot volume or reduce the pressure chamber volume more.

Let me state that this is just a prototype using parts I could easily source and tools I had available at my home (a drill press, a rotary tool, and some saws). This is far from the best way to build this design, in fact, I think it's a hack job. I wholeheartedly intend to replicate the basic design with aluminum using the machine shop at my university sometime in the next few years, but until then I'm sure this will serve me fine.

Pictures follow.



An overview of the current system. The moving parts aside from the magazine are complete so I can test the system under pressure.



The bolt is open. My finger is on the button on the directional control valve.



The bolt is closed.

There's obviously a good deal of work to be done, and some of it's not very obvious. I'll post more later. Right now I have other things I need to do. I've already spent too much time on this project.

Any questions, comments, suggestions, etc. are welcome.

One last thing. FANG stands for FANG automatic nerf gun. It's a recursive acronym.

Edited by Doom, 06 December 2008 - 04:26 PM.

[Lt Stefan]

That looks really cool. When you say semi-auto it doesn't include loading the darts, right?

[Doom]

No, true semi-auto. As I said, the magazine hasn't been constructed yet. Anything involving cutting plastic sheet hasn't been constructed yet.

Edit:

To get a sense of what the gun will actually look like take a look at this earlier photo with some parts on top of some graph paper I used to help with positioning. The darker outlined parts are gun parts to be cut from polycarbonate sheet. The lighter pencil drawings show the handle, magazine, and a few other things.



Note that not everything in that picture is final and it only served to help with positioning. I have the templates made for all the pieces I need to cut. The gun and magazine are very simple and requires 2 sets of 5 parts plus the follower. 4 of those parts are rectangles. The handle will be made of wood. Some of the other parts, like the trigger system, will be a little more complicated but not much more. I'm trying to keep this as simple as possible so that others can duplicate it.

If you're confused by the location of the magazine in relation to the other parts, note that the magazine will not be easily removed. Darts can be loaded through a hole like one of boltsniper's guns.

Edited by Doom, 28 August 2008 - 03:32 PM.

[Lt Stefan]

Can you please elaborate on how the magazine functions? I don't understand how it could work.

[Doom]

If you're confused by the internal magazine concept, check out boltsniper's NTS: http://www.boltsniper.com/BS-9/BS9.htm

The NTS uses an internal magazine. To load it you basically pull the follower down and push the darts through a hole. I think it's simpler than making something removable because you don't have to worry about any locking mechanisms.

Edit: I've improved the motion of the bolt to the point where it returns quickly in over 90% of shots after taking steel wool to the bolt and adding a vent hole at one point (it was pulling a vacuum on the up stroke and then compressing air a bit on the down stroke). Lubrication and taking steel wool to the assembly could help more, but I suspect it's bent slightly so I plan on redoing it.

I'm running out of air in my HPA tank so further tests will have to be done with my air compressor. That and I have to return to college tomorrow so I better get packing...

Edit again: I'm interested in anyone's thoughts on this, especially if they have an idea or suggestion to improve it.

Edited by Doom, 28 August 2008 - 10:38 AM.

[Lt Stefan]

Oh you mean that the pressure from the air pushes the bolt forward and back? That's really cool. And I am familiar with that magazine, I didn't know that's what you were using.

I'm not very experienced with homemade air guns so I have no suggestions for you.

Edited by Lt. Stefan, 28 August 2008 - 10:53 AM.

[Doom]

Perhaps I should have posted a more detailed explanation of the system. It works basically the same way that ABP5K did. The cycle is similar but not exactly the same. My design pushes the darts instead of using the barrel as a breech. My use of a DCV and QEV make mine a little more complicated (in the physics of it) but much easier to build too.

I've tried to make the gun something more people could build by intentionally not doing machining when it's not necessary or work work well. The two gray PVC parts are the most machined parts of the system and they were pretty straightforward, though it did take me a few screwups to make them satisfactorily. Most of the screwups involved mistakes and/or not being exactly sure how to do this. I'll be honest in that I winged a good deal of this too. I had a basic idea and I just went with it in my spare time.

Edit: I'm surprised that there's not too many replies to this. I guess people are more interested in concept threads than finished or partially finished projects.

Edited by Doom, 29 August 2008 - 09:11 AM.

[Doom]

The first prototype is 80% complete and works. Aside from occasional jamming caused by a poorly made magazine (which is easily corrected as I'll show in a future post), the gun works great.

Many other things need changing but the majority of the changes are small, like cutting the plastic around the handle to be more comfortable, lubricating the bolt, adding grip tape, cutting the tubing to the air cylinder shorter, etc. The biggest change remaining is the addition of a trigger. Currently the valve must be depressed manually.

Range at about 30 psi is about 115 feet measured with the stride method. I could get three shots off in less than 15 seconds including some jamming. Those shots were true semi-auto as well.





More information and photos will come soon.

Prototype 1 will serve primarily as a test bed for design data for prototype 2. Prototype 2 I intend to do less sloppily and more efficiently through engineering.

Any comments, questions, suggestions, criticisms, etc. are welcome.

Edited by Doom, 29 November 2008 - 05:27 PM.

[zadjii]

I dunno about you guys, but i want to be the first one to say it

Oh hot dam. this is just, well, to say the least, gun porn.

From what i can see, other than the clear need for a trigger, maybe some sort of stock would be needed. Oh, and a write-up, because I WANT one.
Oh, and can we hope to see it anytime at a war?

[firstblood]

Is it uncomfortable to hold?

[Gyrvalcon]

This looks really excellent. It's nice to see a semi-auto homemade that's so simple, with mainly off-the-shelf parts.

[Doom]

If anyone's wondering what the piece of wire on the gun is for, I used it to pull the spring that pushes the follower down. It's not part of the gun.

Thanks for the comments.

Is the pressure tank shown (looks like about 3" of 1.5" PVC) expended for just one round?

And you need a constant source at the supply hose near the butt of the grip, right?

The long silver tube at the back (far right) ... that's a linear actuator for the breech?

The pressure tank works as you've described it. It is rather large, so I plan to experiment with smaller sizes.

The air source is attached to the hose, correct. Ideally it would be attached to an HPA tank. My HPA tank is empty at the moment so I used an air compressor.

The silver tube is an air-cylinder/linear-actuator/whatever you want to call it. It pushes the bolt.

I dunno about you guys, but i want to be the first one to say it

Oh hot dam. this is just, well, to say the least, gun porn.

From what i can see, other than the clear need for a trigger, maybe some sort of stock would be needed. Oh, and a write-up, because I WANT one.
Oh, and can we hope to see it anytime at a war?

A stock was in the original plan but I decided to wait before adding one because I wanted to experiment with padding. Adding one would not be difficult.

I do plan on making writing instructions eventually. However, let me note that as a work in progress, it'd be exceedingly difficult to make useful plans for this specific gun. I didn't even bother taking photos as I worked today because I knew I would make so many changes from the initial design. Prototype 2 would be a good opportunity to work on a writeup as I would be much more deliberate.

I can and do plan on posting a rough guide of what I've done sometime after this specific gun (prototype 1) is completed. Remind me if I take exceedingly long after the gun is complete.

I'd love to attend some wars. Despite the fact that I've been around for 5+ years, I've never attended a major war. I attend the University of Maryland and hope to do some of their smaller wars so if you want to see it I can have it there. If I have the time I could show up to the next DCNO too.

Is it uncomfortable to hold?

The plastic right above the grip is annoying, but that problem is easily fixed. Once the extra plastic is removed, I stain the grip, and add some grip tape, the handle should be very comfortable. I think wood is a much better handle material than plastic.

This looks really excellent. It's nice to see a semi-auto homemade that's so simple, with mainly off-the-shelf parts.

Simplicity is something I've strived for in this design. I've intentionally avoided machining parts and have require very little precision. This required using off-the-shelf parts as much as possible. The main problem was designing a valve that used off-the-shelf parts, and I achieved that with the combination of a QEV and a directional control valve.

The most machined parts are the two grey PVC pieces the brass tubes slide in. It took me 2 or 3 attempts to get those parts machined to acceptable precision. If I had a lathe it would have been easy but I was working with a rather bad drill press.

Edited by Doom, 29 November 2008 - 09:09 PM.

[rork]

This is no less than 11 kinds of awesome. It's nice to see this sort of thing going on in the Homemades forum. I'd been wondering what had happened to this thing, and I'm looking forward to seeing it completed. Good luck.

[TheNerfLoki]

I am confused. Is that magzine manually operated? I don't see a spring in the magazine. Or is it a gravity clip?

Edited by TheNerfLoki, 30 November 2008 - 12:45 PM.

[death by cheez]

I am confused. Is that magzine manually operated? I don't see a spring in the magazine. Or is it a gravity clip?

Unless gravity started to work in the opposite direction, then no. If you looked at the pictures above you would see the clip is on the bottom of the gun, same side as the handle.

[Doom]

This is no less than 11 kinds of awesome. It's nice to see this sort of thing going on in the Homemades forum. I'd been wondering what had happened to this thing, and I'm looking forward to seeing it completed. Good luck.

Glad to hear you like it.

The project had to go on hold for a while because of life. That's sadly true of the majority of the projects. I made sure to spent some time on it when I could.

I am confused. Is that magzine manually operated? I don't see a spring in the magazine. Or is it a gravity clip?

The magazine is advanced with a constant force spring. The small cylinder you see under the follower is the spring. If I had shown the other side you would have seen the spring much easier because it runs up that side.

I chose a constant force spring because there would be no limits to how long the clip could be. Helical springs apply more force as you add more darts. Making something with torsion springs isn't the most straightforward.

Later after deciding to use a constant force spring I noticed boltsniper had the same idea in one of his pistols a few years back. They're a good idea.

I've answered many more questions at Spudfiles too so check them out.

Edited by Doom, 30 November 2008 - 11:18 PM.

[Doom]

After some discussion at Spudfiles, I've already decided on one major change from prototype 1 to 2. I used a spring-return air cylinder here. The air cylinder seems to be designed to move the rod at once rather than gradually, so the spring is prestressed. To keep the force increase small, the spring doesn't travel much and has a low spring constant. And to keep the force sufficiently high to return, the spring must be rather long. All that combines to make a long air cylinder. My cylinder was about 8 or 9 inches long when it only had a 4 inch stroke.

The solution is to use a dual action air cylinder and make one side contain compressed air, with a small air chamber attached to the opening. This will still allow the spring to return all at once, but the energy can be stored in a dimension other than length.

Also, earlier I had said there was some jamming that is easily fixed. The problem is that I did not put plastic in an area I should have. You can easily see the problem in the image below.



When the bolt pushes the active dart into the firing chamber, friction between the active dart and the next dart push the next dart forward too. Because there was nothing stopping that dart from moving forward, it can and did get caught. The solution is obvious--remake the magazine so it doesn't have that empty spot.

Interestingly, the jamming wasn't too major of a problem. All I had to do was cycle another shot and the dart was unjammed. The friction between the dart and the bolt pulled it back. It took me a few seconds to figure this out. I think after I get the magazine fixed prototype 1 should easily be able to get off a shot every second or two.

You can also see how sloppy I was in some parts of the construction. This was a learning experience for me and you have to mess up sometimes to get something right.

In a future post I'll give a brief but comprehensive outline of how the gun works and how to build it, not necessarily how I built it, but ways that would work. What I like about this design is that very little precision is necessary, the number of cuts to be made is low, and it uses off-the-shelf components extensively.

To summarize my current thoughts for changes for prototype 2:
- use a dual action air cylinder with an air spring to reduce the length, and potentially use a shorter stroke air cylinder
- put a sleeve of plastic around the barrel to prevent dents
- use less sizes of brass (It is not obvious but I have 4 different sizes of telescoping brass in this system... 3 would be possible but I didn't have the right size drill bit to allow for that.)
- potentially use a different directional control valve, possibly with higher flow
- consider a smaller QEV to reduce weight (the Cv values are all extraordinarily high for Nerf so it may not make a significant difference in performance)
- make model of this gun to minimize the pressure chamber volume and pressure for maximum range
- make a higher capacity magazine
- add retractable/adjustable/removable stock
- stain the handle and add grip tape (I might go for a prettier wood instead of a stain too)
- add trigger of sorts (I'm still considering various options)
- add some sort of sight

Prototype 2 should not be made until next summer at earliest so this list is tentative at best. I want to do a lot of modeling to figure out optimal setups so that prototype 2 is significantly better than prototype 1. Then maybe if prototype 2 works out so well I won't call it a prototype any longer.

Again, any questions, comments, suggestions, etc., are welcome. I'm getting a good response at Spudfiles but a limited response here, which I've found odd, but at least I'm getting a response.

Edited by Doom, 04 December 2008 - 08:44 AM.

[Ner Commando]

Wow that gun is cool. I'd like to see how this gun turns out. I still don't understand how the magazine cycles though. I don't see any spring. Is it manually operated?

[rork]

I am confused. Is that magzine manually operated? I don't see a spring in the magazine. Or is it a gravity clip?

The magazine is advanced with a constant force spring. The small cylinder you see under the follower is the spring. If I had shown the other side you would have seen the spring much easier because it runs up that side.

I chose a constant force spring because there would be no limits to how long the clip could be. Helical springs apply more force as you add more darts. Making something with torsion springs isn't the most straightforward.

Later after deciding to use a constant force spring I noticed boltsniper had the same idea in one of his pistols a few years back. They're a good idea.

I've answered many more questions at Spudfiles too so check them out.

[Doom]

Thanks rork.

Here's a photo of the other side that shows the constant force spring:



Yes, there are 14 darts in the magazine. And don't think I'll stop there. I'll be testing a simple 40+ dart hopper inspired by a cigarette hopper I saw when browsing patents. I don't see why it wouldn't work here other than the sheer impracticality of 40+ darts.

I'm at my parents house for the next month so I'll be making much progress towards this gun and it's successor. I have many plans and a lot of ideas.

Tomorrow I'm hoping to make a video of the gun cycling. I would have made one today but it got late and I didn't want to wake up the neighbors by turning on the air compressor.

Edit: I am running into some jamming problems that prevent getting off more than 4 or 5 shots in a row. There are three problems. The bolt is a little sticky on the return--this probably could be remedied with lubrication alone but I'm going to replace the brass tube the bolt slides in because I've always felt I was too sloppy when making it. Sometimes the darts get caught on the brass and don't move where they should. That should be fixed by angling the plastic or brass a bit so they feed in correctly. Sometimes the darts aren't pushed in correctly because they're at the wrong angle. This causes part of the bolt to get caught on them when pulling back and it's a mess. Angling the plastic or brass should help and modifying the follower to only allow fairly straight angles should fix this problem.

Edit #2: The plan at the moment is to buy some replacement tubes off McMaster-Carr along with the remainder of the parts to give me a working trigger. This'll set my video back a few days at least but that's fine.

Edited by Doom, 21 December 2008 - 05:23 PM.