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The 7-11


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#1 KaneTheMediocre

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Posted 11 July 2013 - 11:39 PM

The 7-11 is a lever action blaster that primes like a springer and dumps like an airgun.
It needs a lot of ergonomic work (See bottom of post for current status) , but it reliably fires through a hopper, and has 3 firing modes.
The hopper fires in single and slam-fire mode, while the lever doubles as a catapult that fires stock ammo or
whatever farther than most of Nerf's pre-elite / pre-vortex line of blasters.
Ranges are unknown, but seem on par with my other blasters.

This is the 7-11 unprimed:

Posted Image

This is the 7-11 primed

Posted Image

The function of this blaster, if we ignore the lever / air cylinder for a time, is very similar to 3dBBQ's
airguns. When the tank has air, the positive pressure holds a PVC check valve closed until a stick pushes it open.
The only difference there is that 3dBBQs used O-rings to seal, and mine uses an oilite bushing.
Really this is a matter of taste. Everything past from the check valve, including trigger, to the end of the barrel only needs
to seal as well as a springer, as it's only exposed to pressurized air at the moment of firing.
Other than that everything past the check valve is conceptually the same (although the plumbing is in a different shape).

Posted Image

The size of the "pump", for which I used a 1.5" x 6" Bimba air cylinder from McMaster, gives enough volume to fire with
one stroke, but the traditional airgun analogy breaks down here, because there is no check-valve between the pump and
the tank-the remaining stroke in the air cylinder merely adds to the size of the tank. If you tried to prime / pump this
blaster directly with the air cylinder (no lever), you would not only find that it requires a great deal of strength, but it
also wouldn't stay "pumped", as the air would just push the cylinder piston back. The lever is the magical piece that
sets the 7-11 apart from traditional airguns, because it uses the pushback force from the air cylinder to lock it in place.
Furthermore, the lack of checkvalve ensures that IT IS IMPOSSIBLE TO PUT MORE THAN 1 "PUMP"'s WORTH OF AIR INTO THE TANK.
Unlike an airgun with an OPRV, the intrinsic safety of this blaster is that it cannot be overpumped by speed or by sabotage.

The basic mechanism of the lever and how it pumps the cylinder should be clear from the primed and unprimed pictures at the start,
but the locking mechanism may need some explanation. Basically, the direction the lever is pushed by the force from the
air in the cylinder depends on the orientation of the lever linkage. In one direction, it travels about 60 degrees, but in
the other, only a few degrees. The latter, smaller travel is the lock zone, because the lever is being pushed against a stop
(in this case, the 1.5" PVC frame of the blaster). The diagram below should give you an idea of how this works:

Posted Image

These are the measurements of the plates I used for the aforementioned lever mechanism. I planned to use 2 of the triangle pieces, but wound up with just one. The triangle piece is triangular to that I can attach a long lever arm to it more easily.
Posted Image

My ergonomic intent with this is to get something like the buzzbee rapid-fire-rifle, pictured below with my current tape-job / replumbing.
The priming-hand is the trigger hand, which can work because the trigger is at the end of the priming stroke. The other hand
just goes in front of the lever linkage, which is farther away than I'd like. With cleverly shaped linkages, I could change
this so that there is a place for the hand underneath the lever mechanism without getting pinched.

Posted Image


Materials:
1.5" x 6" Air Cylinder
1/8" NPT to 3/8" Barb adapter
8" 3/8" x 5/8" Hose
5/8" Hose Clamps
3/8" Barb to 1/2" NPT adapter
1/2" NPT to 3/4" NPT adapter
3/4" NPT to 1/2" socket adapter
1/2" PVC Check valve
2x PVC Wye
1/4" x 3/8" Flanged Oilite Bronze Bushing
3d printed bushing holder / dead space reducer
2x 3d printed hingepiece
3/8" HDPE Sheet

TODO:
Trigger pad
Trigger return spring
Trigger out limit
Front handle for non priming hand
Rear handrest for priming hand / priming rod
Hole in frame tube to allow a farther past-center prime.
Graph of linear prime force vs linear displacement
Graph of linear displacement vs angular displacement
Graph of linear prime force vs angular prime force
Graph of angular prime force vs displacement
Design more elegant plumbing for future models
Learn how to make plungers that seal perfectly and not buy any more air cylinders
Actual instructions

Edited by KaneTheMediocre, 13 July 2013 - 10:27 PM.

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#2 LinkMT

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Posted 12 July 2013 - 08:53 AM

Very nice day to post this, Kane :). This design looks fairly interesting, especially because you incorporated "slam fire" into it. Nice job!
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#3 andtheherois

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Posted 12 July 2013 - 09:55 AM

Looks good. Could we get an explained view of the lever? Also could you replace the hose with PVC fittings?
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#4 Darkdragon

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Posted 12 July 2013 - 12:08 PM

It took me a while to understand how this works... But now that I do, Kane, I've gotta say youve got another great homemade in the works here. Pretty quirky!
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#5 Langley

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Posted 12 July 2013 - 02:35 PM

How about some mcmaster numbers? don't forget to use the mcm tags.
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#6 DartSlinger

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Posted 12 July 2013 - 05:25 PM

How exactly does the locking mechanism work, and how does it shoot stock ammo with the lever? Also, could we get a video of it operating, or some clear pictures with a contrasting background? And how long is it?
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#7 KaneTheMediocre

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Posted 12 July 2013 - 05:41 PM

Very nice day to post this, Kane :). This design looks fairly interesting, especially because you incorporated "slam fire" into it. Nice job!


Slam fire was more of an accident than a deliberate design choice. So was catapult mode. I still love them both.

Looks good. Could we get an explained view of the lever? Also could you replace the hose with PVC fittings?


The following parts:

1/8" NPT to 3/8" Barb adapter
8" 3/8" x 5/8" Hose
5/8" Hose Clamps
3/8" Barb to 1/2" NPT adapter
1/2" NPT to 3/4" NPT adapter
3/4" NPT to 1/2" socket adapter

were chosen because they were the most direct option to adapt between the 1/8" NPT port on the air cylinder to the 1/2" socket using the parts available at the Ace by me. I do not recommend or otherwise endorse them. It is super-important that they seal well, and "well" does mean "better than a bunch of socket PVC connections with screws through them". Glue wasn't a good option because as a first prototype, nothing can be permanent, so any connection that I want to take apart later has to be a threaded pipe connection.

As for the lever, I'll try to do a better diagram. See below. But as far as how to actually put together the lever, it's a lot like the plumbing described above--I did what I had to to get it working NOW, and substantially deviated from my more elegant plans for the lever.

How about some mcmaster numbers? don't forget to use the mcm tags.


Yeah, I did rush this out a bit to make a deadline. I'll get those in ASAP. I am, however, unfamiliar with these "mcm tags". They sound like something I should familiarize myself with.


How exactly does the locking mechanism work, and how does it shoot stock ammo with the lever? Also, could we get a video of it operating, or some clear pictures with a contrasting background? And how long is it?


1. The locking mechanism was sufficiently described in the OP, but I'll have a prettier diagram ASAP.
2. Turn the blaster upside down, prime it, put a tagger in tip of the PVC priming handle, then push the priming handle up an inch or so to get it to snap out of the lock-zone.
3. A video of it operating is something you should get. But I might wait until I get the ergonomics worked out a little better. Even then, I can't hold a camera (phone) and fire it at the same time, and if I set my camera down it randomly stops recording between 2 and 20 seconds after letting go.
4. I don't do clear pictures. See all my other posts / writeups. I don't know why I'm even allowed to hold cameras.
5. Too long / about 3 feet.

Edited by KaneTheMediocre, 13 July 2013 - 10:20 PM.

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#8 Langley

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Posted 12 July 2013 - 06:20 PM

Yeah, I did rush this out a bit to make a deadline. I'll get those in ASAP. I am, however, unfamiliar with these "mcm tags". They sound like something I should familiarize myself with.

4. I don't do clear pictures. See all my other posts / writeups.


We usually discourage work-in-progress threads. I get that this is sort of a proof of concept thing, but as such, the thread is pretty lacking in information, and it would be fairly difficult for anyone else to try and reproduce what you're working on based on what you've posted. I'm not going to take any moderator action, I'm just throwing that out there.

See the list of BBCode Tags. I've added some non-standard ones, including the gmap tag for posting maps of your war site and the mcmaster/mcm tag which turns a mcmaster part number into a link to that part.

Example (quote to see the code): 9637K26
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#9 snickers

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Posted 12 July 2013 - 06:33 PM

How exactly does the locking mechanism work, and how does it shoot stock ammo with the lever? Also, could we get a video of it operating, or some clear pictures with a contrasting background? And how long is it?

Are you having trouble viewing pictures on the device you are using? Kane took a picture of the blaster next to the lever action buzzbee shotgun. Purely based on my perception, the blaster looks 4 1/2in longer than the buzz-bee rapid fire rifle.


Work in progress? Job well DONE! This is a great new blaster. Your post IS filled with enough information that I am going to replicate one myself. I guess this sort of blaster is a complicated build for non homeade builders. I also have to conclude that first time homeade builders shouldn't attempt it if they have trouble understanding simple schematics and pictures.

Edited by snickers, 13 July 2013 - 11:34 PM.

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#10 Langley

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Posted 12 July 2013 - 07:50 PM

I guess this sort of blaster is a complicated build for non homeade builders. I also have to conclude that first time homeade builders shouldn't attempt it if they have trouble understanding simple schematics and pictures.


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Yes, Snickers. It's very impressive how awesome you are at building homemades, especially with Kane's balls resting on your chin.

You are generally expected to post a writeup or at least a finished project (ie something you would use at a war). I don't think I'm completely out of line thinking this isn't done yet, since there is an actual to-do list in the first post. But as usual, Kane's photo of a polar bear in front of a sheet holding some pipe in a blizzard gets a pass because.....kane. I guess. I just don't want anyone else to start throwing their half-baked ideas around like they own the place. One Kane is more than we need already.
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#11 KaneTheMediocre

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Posted 13 July 2013 - 08:35 PM

You are generally expected to post a writeup or at least a finished project (ie something you would use at a war). I don't think I'm completely out of line thinking this isn't done yet, since there is an actual to-do list in the first post. But as usual, Kane's photo of a polar bear in front of a sheet holding some pipe in a blizzard gets a pass because.....kane. I guess. I just don't want anyone else to start throwing their half-baked ideas around like they own the place. One Kane is more than we need already.


Definitely not out of line thinking it's not done yet. It's not. It's not even particularly close--Handles are not a trivial matter that I can just slap on, especially when most of the places I want to attach them are off limits. I just thought that this unique concept for a blaster was worth posting now that I've proved (to myself) it can consistently fires out of a hopper.

Although I'm not a fan of having forums be for finished projects only, I have had a lot of half-baked writeups lately. Generally, I justify them to myself by
1. Telling myself that I'll totally finish the blaster,
2. Telling myself that I'll totally finish the writeup when 1 happens,
3. Believing that posting a super vague, super incomplete writeup is better than posting nothing at all,
4. Believing that it's better to post something incomplete than to post something that doesnt work and lie about it, and
5. Believing that the pain I get when using a computer is an excuse for half-assing this sort of thing.

I do intend to make incremental improvements to the post and the blaster until it's an instruction writeup for a polished blaster. But it's not a finished blaster or a finished blaster, and the number of posts under my belt that remain indefinitely under construction is large enough to lend legitimacy to Langley's complaints. I also think that whining about it and not doing anything was the correct decision. So everyone just relax, and check back here in a couple weeks if you're looking for a full writeup.

edit:
For a full writeup to be of much use, I need to not use a $50 air cylinder, which means need to learn how to make plunger heads and plumbing that seal perfectly under possibly higher than normal springer pressure. I know a lot of nerfers can do this, and do this regularly, but so far I'm not one of them. So help with that would be nice, and help lead to a more reproducible blaster

Edited by KaneTheMediocre, 13 July 2013 - 10:23 PM.

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#12 Langley

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Posted 15 July 2013 - 10:26 AM

edit:
For a full writeup to be of much use, I need to not use a $50 air cylinder, which means need to learn how to make plunger heads and plumbing that seal perfectly under possibly higher than normal springer pressure. I know a lot of nerfers can do this, and do this regularly, but so far I'm not one of them. So help with that would be nice, and help lead to a more reproducible blaster


Someone who's better with Physics than I am can probably put this more clearly, but it seems like the air seal is not your only problem. Unlike a spring, that lever doesn't apply force neatly in a direction parallel to your plunger. The cylinder that you are using is probably very tolerant of that because it is built to constrain the motion of the plunger along one axis even when there are very strong forces acting upon it in different directions. If you were to substitute--for example--a plunger and plunger tube from a plusbow, I think the plunger rod is likely to flex away from the center line of the plunger tube, or bind up in the bushing, or the plunger head would be compressed against one side of the plunger tube.

You might actually want to take a look at screen door closers as a cheap alternative. I've tried using them in springers before, but the plunger head couldn't stand up to being slammed into the inside of the cylinder at high speed. I don't know if they would be ideal for this application, but they're cheap and made mostly of metal, and may not require a lot of work to get a drop-in replacement for your air cylinder.
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#13 Doom

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Posted 15 July 2013 - 08:13 PM

Kane, this is an interesting concept that you have executed well for a first pass. I have a few suggestions.

The main reason springers can be primed in one action but that most air guns can not is because springers are much more energy efficient. This is not obvious. I recall calculating the energy efficiency of a modified Crossbow at about 35%. For comparison, none of the air guns I've tested have done better than 15% (most are less than 10% efficient), though computer simulations suggest much more is possible. So, you need about 4 times as much energy for a typical air gun as a typical springer to get the same performance. (I'm not quite sure why this is, but I suspect it's because the plunger volume decreases so that relatively more of air moves to the barrel and accelerates the dart.)

One of your primary goals should be improving the energy efficiency to reduce the required amount of input energy. This means you'll have to ditch 3DBBQ style valves because they open slowly and leak (you might be able to fix the latter problem). As a replacement I would suggest an air piloted valve like a QEV or one of their homemade equivalents (look at Spudfiles for "piston valves"). If you don't improve the valve (and keep the same basic design) you should at least use larger diameter tubing to feed the valve area to improve the flow rate. You also should try a bunch of different barrel lengths to see what works best. Use the highest pressure you can safely and ergonomically; higher pressures usually lead to higher efficiency. If you do all of this, my hope is that your gun would have an energy efficiency comparable to that of a springer.

I have thought of a one-pump air gun before, and I intended to use essentially the same design I use for my other air guns, just with a highly optimized setup. Levers aren't really necessary, and just make the system more complicated. I would suggest looking into this option.

If you don't want to go that route, I suggest looking at piston cups on McMaster-Carr as an alternative to air cylinders. If you can manage to get PVC pipe that has a diameter fairly close to 1.5 inches (1.5 inch sch. 40 is larger; schedule 80 might be okay) then you can use 1.5 inch piston cups and pipe instead of an air cylinder.


Someone who's better with Physics than I am can probably put this more clearly, but it seems like the air seal is not your only problem. Unlike a spring, that lever doesn't apply force neatly in a direction parallel to your plunger. The cylinder that you are using is probably very tolerant of that because it is built to constrain the motion of the plunger along one axis even when there are very strong forces acting upon it in different directions. If you were to substitute--for example--a plunger and plunger tube from a plusbow, I think the plunger rod is likely to flex away from the center line of the plunger tube, or bind up in the bushing, or the plunger head would be compressed against one side of the plunger tube.


I see what you mean here. A piston cup along with the right guides for the plunger rods could also work.

Edited by Doom, 16 July 2013 - 10:10 PM.

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#14 KaneTheMediocre

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Posted 24 July 2013 - 11:48 PM

You should build a regular air gun, but make everything super efficient and perfect so that it can be fire well with 1 pump


I actually did make a conventional 1 pump air gun with a big blast and a long, homemade pump in a 3/4" or 1" (can't remember, but I think 1") PVC tube. The pump had a skirt seal and flap valve.

It did fire out of a hopper with 1 full length pump, but the draw was well over a foot, the pump force was quite high and the end of stroke, and it fired 30-40 feet. Compounding the awkwardness of requiring a 1 foot "prime" was the fact that placing this in a reasonably ergonomic position relative to the handle required the pump end to be well behind the back of the blaster, and more importantly well behind where the air goes in the tank. Thus, more tubing between the pump and the air tank.

So, a conventional 1 pump airgun is certainly possible, although not trivially easy. And if you did a great or expensive job, it MIGHT work well enough to almost be as good as a springer. But perfectly optimizing conventional designs isn't really my style. It's yours, and you SHOULD do it because it's a good idea.

Another concern is your reference to energy efficiency, which I'm assuming is just KE of the dart / energy input, but reaching the minimum volume of air output to operate a hopper is also a constraint to consider.

The original plunger head didn't seal because the lever was bending the rod and everything was all crooked and shit

The first one did have a bushing for the plunger rod to pass through that basically filtered out all of the radial force and flex, and only passed the forces in the axial direction. And it the seal noticeably failed towards the end of travel, where the flex/radial forces were at their least, while the pressure was the greatest. So I'm confident this wasn't the problem, although I'm sure it would have been without the aforementioned bushing.

The second (published) one didn't actually rely on the cylinder rod bushing to take the radial loads, as I was afraid this would damage the air cylinder. They're not really meant to take that sort of load, although they're built pretty tough overall. This had different sort of bushing, attached to the other end of the plunger rod, which slides inside the 1.5" PVC. It's conceivable that I could have gotten away with doing how Langley had thought though.

Both of these certainly added friction to the system, but in both cases the plunger head only sees the axial force that I want it to.

You might actually want to take a look at screen door closers as a cheap alternative. I've tried using them in springers before, but the plunger head couldn't stand up to being slammed into the inside of the cylinder at high speed. I don't know if they would be ideal for this application, but they're cheap and made mostly of metal, and may not require a lot of work to get a drop-in replacement for your air cylinder.


These could possibly work, but it might be very difficult to adapt air fittings to these that would seal perfectly. And since the door application actually relies on them to leak, there's no incentive for the manufacturer to make the seal perfectly at any pressure. I'll take a look at them next time I'm at ace anyways, because I'd love a cheap replacement for the air cylinder.

Edited by KaneTheMediocre, 25 July 2013 - 02:26 AM.

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#15 KaneTheMediocre

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Posted 23 August 2013 - 12:26 AM

The hose developed a fairly crippling kink shortly (~1 week) after it was built. This most effectively choked the air intake, making the blaster very difficult to prime at best. When successfully primed, it still fired through a hopper, but not as far as before.
Posted Image

New plumbing consists of a 1/8" nipple pipe, a 1/8" female x 1/2" male threaded bushing, 2x 90 degree 1/2" female thread x female socket elbows with a 1/2" PVC stub glued between them, a 1/2" male thread x 1/2" female socket adapter with another 1/2" PVC stub glued to the dump/check valve and to the aformentioned adapter.

Posted Image

It now works 95% of the time with a 6" CPVC barrel. Originally it fired out of a roughly 10" cpvc barrel 100% of the time, so this isn't an improvement. I'm guessing that the new plumbing has more volume than the old plumbing, so my tank pressure is lower. I may be able to compensate for this by increasing the draw of the cylinder, as I wasn't using the full 6" before. This will reduce the primed volume while keeping the unprimed volume the same, for greater pressure and air output.
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