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Semi auto mag fed (air powered) revisited

semi-auto mag-fed Big salvo longstrike bladder panther

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#1 shmmee

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Posted 01 March 2017 - 03:22 PM

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Hi, sorry - long time, no content. I've found a local, well established nerfing group so I've been able to pick up my favorite hobby again! And as such, I've decided to start chasing my unicorn - the project I've been trying to make for years. A reasonably simple and efficient pneumatic clip fed semi auto blaster. Some of you might remember my previous attempt involving a salvo tank plumbed in line to a secret shot pump that had been re-purposed into a piston. The theory was that when the salvo tank filled the pump would also fill - pushing the pump handle out like a piston and closing the breech. The problem, is that as soon as the salvo fired the piston retracted prematurely and half the air was blasted back out of the breech. I realized I would need a separate delayed valve to open the breech shortly after the dart had left the barrel on a delay. I looked briefly at the big salvo valve assembly.  As the o-ring on the salvo trigger passed the buttons it bumped them open - venting and firing the tanks. To date I'd only looked at that valve group using the traditional pump input in the back to fill from so any space between the trigger o-ring and fill line would remain pressurized. Experimentation with this failed though. As the trigger o-ring passed a button valve it would leak air from the reserve. 

 

My revisit - and the progress to date is again based on a big salvo valve assembly. My "erueka!" moment came when I realized that the big salvo trigger (something I had looked at before but had given up on) was comprised of 4 individual button valves/check valves - so why not fill from one of the back legs (instead of the normal always open fill line - since it operated as a check valve) and add a bumper to the salvo trigger stem to open the fill while the o-ring sealed in pressure!

 

With the trigger fully retracted the valve group is sealed and the bumper opens the 3rd leg - filling the panther tank and retracting a piston - closing the breech and loading a dart. As the trigger piston begins to move backwards, the bumper slides off of the 3rd leg, (closing off the air reserve) and then the o-ring on the trigger piston bumps the first leg (firing the panther) and a fraction of a second later (hopefully long enough for the dart to leave the barrel) it bumps the second leg venting the piston and allowing the breech to be pulled open by a spring - chambering the next dart. When the trigger retracts the o-ring reseals the valve assembly and the third leg is bumped open again - priming the tank and closing the breech. The fourth leg won't be used.

 

FB_IMG_14877105067201.jpg

 

I modeled up a longstrike trigger, added a riser with a big salvo trigger stem and then added the extension bumper on the end of it and sent it through my printer.

FB_IMG_14881728966951.jpg

 

The white piece is my final 3d printed piece. It was a drop in perfect fit. Not bad for my first ever time modeling with anything, huh? (I used autodesk fusion 360 and printed in PLA)

 

So far, proof of concept has only happened as far as blowing into the third leg while sliding the trigger rod around inside. The 3rd leg air inlet shuts off at the appropriate time so I really, really think it'll work!

 

I bought a small piston on amazon and will be leveraging it's travel long enough to open and close the breech. I'll be picking up the fittings for the piston on my way home from work today. For my air reserve I'm using a banded rf20 bladder. I've still got some bridges to cross but for the first time in years, there is a light at the end of the tunnel!


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#2 Meaker VI

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Posted 01 March 2017 - 07:06 PM

Since you likely missed it, I should probably leave this here, though I appreciate that you've got some more documentation here than he's released (yet).


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#3 Draconis

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Posted 01 March 2017 - 08:14 PM

This is awesome, man!  Great job on the modelling, that trigger looks perfect.

 

Since you likely missed it, I should probably leave this here, though I appreciate that you've got some more documentation here than he's released (yet).

 

But with pneumatics, why would a person need electronics too?  EEs, amirite?

 

My revisit - and the progress to date is again based on a big salvo valve assembly. My "erueka!" moment came when I realized that the big salvo trigger (something I had looked at before but had given up on) was comprised of 4 individual button valves/check valves - so why not fill from one of the back legs (instead of the normal always open fill line - since it operated as a check valve) and add a bumper to the salvo trigger stem to open the fill while the o-ring sealed in pressure!

 

I modified a Triple Strike and a Big Salvo in a similar fashion.  I found that there is just enough space in that circular end cap on the valve tube that I could drill and tap for 1/8" NPT, thus allowing a connection for an external tank.  It works really nicely, allowing the built-in pump to pressurize, while also allowing semi-automatic firing.


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[15:52] <+Noodle> why is this so hard?

#4 jwasko

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Posted 01 March 2017 - 08:20 PM

Well Meaker, Prometheus is full auto (but I suppose it could be programmed otherwise?). I appreciate that this is semi-auto.

 

I'm actually working on a mag-fed semi-auto myself but it's using 2-3 off-the-shelf valves (one could be replaced with a big salvo or panther tank, though). I like that shmee's design looks able to trigger a QEV-style tank and control the pneumatic cylinder all from one valve assembly.

 

 

Although I'm starting to wonder: do we really need a pneumatic cylinder to open and close the breech? What if we simply link the breech to the trigger via linkages as in a stryfe or via rack and pinion as in a hailfire? Maybe that's more double action than semi-auto, but then everyone calls Stryfes "semi-auto."

 

Edit: For instance the stryfe's pusher extends roughly 30mm or 1.18". That should be just enough length to chamber a 1" long stefan.


Edited by jwasko, 01 March 2017 - 08:48 PM.

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#5 Meaker VI

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Posted 01 March 2017 - 10:57 PM

Although I'm starting to wonder: do we really need a pneumatic cylinder to open and close the breech? What if we simply link the breech to the trigger via linkages as in a stryfe or via rack and pinion as in a hailfire? Maybe that's more double action than semi-auto, but then everyone calls Stryfes "semi-auto."

 

Edit: For instance the stryfe's pusher extends roughly 30mm or 1.18". That should be just enough length to chamber a 1" long stefan.

Not a terrible idea; I'd been wondering about something similar. I'd think you could even get a full-length chamber if you were OK with longer/harder trigger pull than a stryfe, which isn't an unreasonable assumption.


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#6 shmmee

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Posted 02 March 2017 - 11:14 AM

This is awesome, man!  Great job on the modelling, that trigger looks perfect.

 

 

But with pneumatics, why would a person need electronics too?  EEs, amirite?

 

 

I modified a Triple Strike and a Big Salvo in a similar fashion.  I found that there is just enough space in that circular end cap on the valve tube that I could drill and tap for 1/8" NPT, thus allowing a connection for an external tank.  It works really nicely, allowing the built-in pump to pressurize, while also allowing semi-automatic firing.

Thanks! I'm still floored that it came out looking so close to the original. I spent a couple hours on it last night and It looks like I might have to revisit it once more (not surprisingly). I need to make that third leg bumping nub a little bigger or different shaped. I seated the valve in epoxy putty (I greased the O.D. of the valve so it's not stuck permanently) and with the trigger fully forwards, (where the third leg should be open and fill the tank and piston legs) I've found the third leg to be closed... though the thought just barely occurred that since I also plugged off the pump fill line with epoxy putty and o-ring is on the opposing side sealing off the vent, the system may actually just be sealing properly and lung power isn't enough to blow open the tank and piston leg valves... The stupid thing might of been working as per designed and I just didn't realize it... I'll hook it up to a bike pump this evening and see how it acts. Once the trigger and valve is placed and working I'll be able to move on to a rough function test with a reserve tank, panther tank and piston all hooked up.

 

When you modded your big salvo to do the same, did you notice much air leaking from the reserve as you pulled the trigger? When I tried something similar I think I remember loosing a significant amount of air from my reserve tank with each trigger pull. It wouldn't be too bad if I was using a compressor or a regulated HPA tank, but with a hand pumped system it was a deal killer. 

*Edit, after some thought, The leakiness was observed using a hornet trigger stem which had a double o-ring so I just assumed the salvo's single o-ring would be even more leak prone. I'd be thrilled to be proven wrong!

 

With this build, I'm so concerned with efficiency that i'm even going with 1/8" tubing from the salvo valve to the piston since any air in that line will be vented off and wasted. I'm crossing fingers and hoping it allows enough flow. The salvo valve stem ID's look to be about that size anyway so there will be a bottle neck regardless.

If memory serves, my banded RF20 bladder runs around 50 psi. If my full size panther tank runs happy on that I might swap in a smaller second gen panther tank just to see how much of a performance drop there is. I'd love to be able to get a few more shots off of a full bladder if performance doesn't suffer too much with a smaller tank.

 

Well Meaker, Prometheus is full auto (but I suppose it could be programmed otherwise?). I appreciate that this is semi-auto.

 

I'm actually working on a mag-fed semi-auto myself but it's using 2-3 off-the-shelf valves (one could be replaced with a big salvo or panther tank, though). I like that shmee's design looks able to trigger a QEV-style tank and control the pneumatic cylinder all from one valve assembly.

 

 

Although I'm starting to wonder: do we really need a pneumatic cylinder to open and close the breech? What if we simply link the breech to the trigger via linkages as in a stryfe or via rack and pinion as in a hailfire? Maybe that's more double action than semi-auto, but then everyone calls Stryfes "semi-auto."

 

Edit: For instance the stryfe's pusher extends roughly 30mm or 1.18". That should be just enough length to chamber a 1" long stefan.

Jwasko, I'd be very curious to see how you approached your build. I couldn't come up with anything that relied soley on off the shelf parts!

 

Not a terrible idea; I'd been wondering about something similar. I'd think you could even get a full-length chamber if you were OK with longer/harder trigger pull than a stryfe, which isn't an unreasonable assumption.

The option for a trigger actuated breech has definitely crossed my mind. My first true air powered semi auto was based off of a dart tag blaster -specifically because the turret is trigger actuated. When dealing with hand pumped nerf pneumatics, air is a valuable resource and any savings in mechanical movements would be used for dart propulsion instead. My clip fed  prototype was designed around 1.5" darts, and I'm trying to remember the reasons I went with a piston instead of full length darts there but I think it was motivated by not wanting to rework all my 18 round mags to take half length darts. With this revisit, that decision was reinforced by my new groups distrust of half length darts, so sadly, I've got to plan on needing a full 3.125" of travel on the bolt sled. Leveraging the .5" inches of travel this trigger has into that distance would probably be too heavy of a trigger pull. 


Edited by shmmee, 02 March 2017 - 11:32 AM.

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#7 Draconis

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Posted 02 March 2017 - 05:15 PM

When you modded your big salvo to do the same, did you notice much air leaking from the reserve as you pulled the trigger? When I tried something similar I think I remember loosing a significant amount of air from my reserve tank with each trigger pull. It wouldn't be too bad if I was using a compressor or a regulated HPA tank, but with a hand pumped system it was a deal killer. 

*Edit, after some thought, The leakiness was observed using a hornet trigger stem which had a double o-ring so I just assumed the salvo's single o-ring would be even more leak prone. I'd be thrilled to be proven wrong!

 

I don't remember them leaking much, if at all, but I am certain that I added a bunch of grease to help prevent it too.


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#8 NerfGeek416

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Posted 03 March 2017 - 12:19 PM

The Hailfire has a longer throw on it's pusher with a much smoother trigger pull than the stryfe. It uses a rack and pinion gear setup.

I get that mags are cool, but if you're running slugs, aren't hoppers just as effective and much easier to build?
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#9 jwasko

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Posted 04 March 2017 - 10:06 PM

The Hailfire has a longer throw on it's pusher with a much smoother trigger pull than the stryfe. It uses a rack and pinion gear setup.

I get that mags are cool, but if you're running slugs, aren't hoppers just as effective and much easier to build?

 

Yes, if you're willing to steal the internals the hailfire is definitely the way to go (racks seem expensive to buy outright...even lego parts). I figure stryfe-style would be easier to replicate even just out of some sheet plastic, as opposed to trying to buy racks and pinions..

 

A hopper is way easier, but I'm not a fan of them anyway. I usually use RSCBs, but a box mag has a higher capacity before becoming unwieldy. My personal dream is a top loading fixed magazine (in the style of the Magnus and Han solo blaster). It could be even easier to top off than a hopper/rscb.

 

Bonus is you could use rubbery dart heads without all the trouble they cause with hoppers.

 

And, yeah. That too.


Edited by jwasko, 04 March 2017 - 10:10 PM.

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