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Project 16: A full-auto mag-fed shotgun

brushless shotgun flywheels

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#1 snakerbot

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Posted 19 February 2022 - 04:47 PM

IMG_3902.JPG

 

A while back I was looking at Domochevsky’s Rail Cleaner. If you’re not familiar, it’s a flywheel revolver with shells that feeds a cluster of 4 darts into a set of very tall flywheels to fire all four at once. I thought it was a neat design, but that it had some glaring flaws:

 

- It was closed source (sort of).

- It used DC motors.

- It was not fully-automatic.

 

So I set out to fix them. Initially I entertained the idea of keeping the Rail Cleaner layout, putting some brushless motors in, and automating the feed with a stepper or something, but was not confident in reliably advancing and stopping a large, heavy cylinder. I next considered mag-fed and still feeding from shells, and was thinking of ways to eject the shells automatically when I had a eureka moment. I realized I didn’t need to use shells if I could feed a two-wide stack of darts in a magazine and strip two rows off the top with each shot.

 

A prototype magazine literally made out of cardboard and hot glue proved the feasibility of the magazine and a printed magazine and flywheel cage followed. At this time all that remained was building the full blaster.

 

Before going too deep into the mechanicals though, A little bit on its performance. Velocity is ~95fps and it’ll do about 7 shots (so 28 darts) per second. It’s weird about darts. It’ll fire basically anything, but waffles and blue/green sureshots yaw sideways *hard* as soon as they exit the barrel. Elites and ACCs don’t, but their aerodynamics are crap so it kind of doesn’t matter. I suspect what’s happening is that as the darts are leaving the flywheels, the sideways loading from the flywheels at the back of the darts forces the darts to yaw (lay a couple darts next to each other on a table and press two flywheels against them near the tail to see what I mean.) at which point the heads drag against the control bore asymmetrically and the drag on the outsides forces them out at an angle. This at least partially explains why narrow-headed darts aren’t affected – only foam contact on the sides means less friction, but that doesn’t explain everything. Accufakes sometimes shoot straight and sometimes don’t. Adventure Force max accurate don’t work super well despite the narrow heads. Testing with menguns that I accidentally ended up with after thinking I was buying brick tips is promising.

 

Errata: The flywheels are a pain to print due to the steep overhang and mine came out quite rough there. The groove fillers are also *very* close to the wheels, so sanding may be required to clean up the flywheels, the cage, or both.

 

I went with using the T19 drivetrain stack for all the parts that weren’t unique to P16 since I liked the ergonomics and functionality and couldn’t be bothered to custom design an entire blaster when the core of P16 is just a magazine, breech, and flywheel cage. To that end, the grip base, grip frame, grip panels, trigger, magazine catch (use the full length one), drive housing, drive spacer, drive cover, crank, crank pin bushing, stock base, stock, stock pad, and velocity and selector knobs could all be unmodified T19 parts. P16-unique parts are therefore a breech, bolt, flywheel cage main and cover, flywheels, ESC covers, muzzle device, and rail segments. I kept the T19 knurled styling for the new parts for consistency, and because I found I actually quite like the way it looks. I did use the modified velocity knob, grip frame, and stock base as described in my MEGA T19 po  st here, although this blaster predates that one, so this was actually the first use of those modified parts.

  

I changed the full-auto operation of the bolt for reliability reasons. Rather than the bolt motor spinning at a constant speed, it moves at full speed for one cycle and then stops before pausing and starting again. This means the bolt stays back longer allowing the darts to rise up in the magazine.

 

More about the magazine: it uses some design ideas from torukmakto4’s rapidmag heavy. The dovetail pattern between the two halves have some notches that take a decent bit of force to snap together, but hold together with no hardware or glue. Only tested with petg and the deformation required to get these together might cause pla to just break. Even some brands of petg, like yoyi, have had dovetail teeth snap off. Overture has been fine though. If you need to get them back apart, I’ve had success seperating the halves by pulling the front and back apart at the open top end to make a gap in one or two dovetail sets, then working a small straight blade screwdriver in the slots and progressively moving down the magazine.

 

Filaments are Snolabs Reicher blue, Makeshaper white, green, and transparent orange petg, and a tiny bit of overture white tpu on the grip scales. That tpu really doesn’t do much. It feels different since it has that characteristic rubbery texture, but it doesn’t squish or anything, at least not with only 1mm of it. Motors are Turnigy V-Specs since I still have a decent stash of them.

 

Files at https://drive.google...9vP?usp=sharing

 

A look down the back of the flywheel cage at the wheel geometry:

IMG_3919.JPG

 

A shot of the new larger bolt face:

IMG_3922.JPG

 

Magazine:

IMG_3913.JPG

 

Magazine dovetail closeup:

IMG_3915.JPG

 

EDIT: Firing video


Edited by snakerbot, 20 February 2022 - 02:47 PM.

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#2 Silly

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Posted 19 February 2022 - 09:06 PM

Super cool! Any chance we can get a firing demo vid? What kind of mag spring did you use, two drum springs? 


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#3 snakerbot

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Posted 20 February 2022 - 02:48 PM

Super cool! Any chance we can get a firing demo vid?

 

Added to the OP.

 

What kind of mag spring did you use, two drum springs? 

I did some early testing with two, but the final version only uses one, which is why you can see an empty spring slot in the magazine pictures.


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#4 Daniel Beaver

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Posted 21 February 2022 - 06:49 PM

Interesting, I hadn't heard of this concept before of feeding in 4 darts at a time.


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#5 Meaker VI

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Posted 09 March 2022 - 06:14 PM

Youve got to start crossposting these things man, I didnt see this. Very cool execution of the concept.
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