So I didnt want to do this, but for sake of sanity while I work on designing something custom, I modified the turret cap to give it more room without making the cap look out of scale.
Ok. I think this is a solution. Don’t mind the T fitting.. My 90* elbows arent here yet I picked up some ¼” vinyl tube to protect the barrels and had an idea. If the canon was straight but the barrel was angled down, that would solve the space issue. I cut the back off an old barrel (it was 3” and thin brass anyway) and that fits inside the 5/16 fitting to compress the O-ring. The ⅜ OD vinyl tube just has enough squish to fit through the 5/16 compression nut. The old barrel back is forced through the tube locking it in place. The ¼” barrel is then slipped in (this will be clamped inside the turret) and with very little effort, it can be turned down to what ever max angle I can get. Is it perfect? No, but it should work. I will need to chamfer the leading edge a bit, but easy enough.
Will the vinyl tube actually hold a seal under pressure? If it does, could this be used for a depression mechanism?
The breach part will. It is compressed around the brass tube. The barrel section will be clamped to the turret base, or you could probably get away with a zip tie. Yes there is plenty of flex for a depression mechanism. It should take the path of least resistance which would be pushing the bb and not trying to force the barrel out. Since this is not a sealed system, pressure would not be building after the bb passes the oring. I was thinking maybe putting a small flair on the steel barrel as added insurance.
It will be clamped down which would prevent it from flying out or leaking. I am not relying on friction alone
Current status: micro magazines feed pretty well. This is just the mock up but it shoots well enough to move on to the next part of the design.
Woo! After many iterations with my FDM printer, different layer heights, different cross sections, I just could not get any of the 50rd magazines to flow as well as the 25rd that I printed ages ago. I know it was due to different filament manufacturers. The black one is from eSun and the gray is Inland. Same settings but the Inland is whispy which leaves too many burrs inside (and in some cases an impenetrable wall of blobs and zits). Since ABS is hit or miss sticking to my print bed, Ive been using PETG. So after many attempts, I decided to print them on my MSLA resin printer. And it is almost perfect. The only snag is in the loading. After a BB rolls into the spiral it quickly drops out the bottom. The inlet is flat and the coil is symmetrical. I sacrificed an angled inlet to save about ½” of length. These are designed to fit in a very compact space so the shorter I could make them, the better. They also fit exactly 50rds in the coil (not counting the inlet and outlet coil) Now to tweek the magazine-chamber section for more consistent loading. I knew this design would need improved but it works as a proof of concept. It may actually work as is, but I havent tested it with air pressure yet.
Print it with transparent resin so we can see inside in all seriousness, even if it only ends up translucent, that will still help you spot any issues with the cannon when you test it. Very helpful.
The drop test went extremely well. Once the magazine was loaded, a dozen BBs rolled out from the bottom of the canon. A quick shake got another dozen to roll out. The air ‘assist’ sits at the feed ramp to help agitate the BBs and rebound them to the firing chamber. I was contemplating picking up some Sirayatech ABS Like or Clear Blue but eeeech that’s an extra expense I don’t need when I already have good resin. I don’t use my MSLA printer often enough to warrant buying more resin right now.
What does the plastic do in high heat. In the summer it could be near 100 outside air temp. But inside your ship it’s much hotter sitting out in the water. If the plastic heats up are the bbs going to jam. Something to think about.
It is PETG so similar glass transition and thermal expansion as ABS. Not sure on the resin but I doubt the thermal expansion is going to tighten it down more than the clearance (the MSLA is much tighter tolerance than FDM). The coil is 5.5mm printed in resin with a tolerance of +\- 50 microns (.05mm). Which is way less than the +.2mm clearance I use for tight fit on my FDM prints.
Have to pause on canon testing until I get some more fittings to plumb the airlines, so I decided to repaint the boat the almost correct color.
Testing the magazines. Loading issues are from the piston position. This was only a few rounds as I didnt feel like chasing 50bb’s across the floor.
Have you tested with the elbow and o-ring in place? Without getting the magazine up to pressure, you cannot see the full interplay of pressures, flows, and other forces. If it is actually having feed issues when fully assembled, can you provide further details on the failure? From the video, it looks like it failed to feed after several rounds. But was it able to feed again after several seconds of not firing, or did you need to whack it to make it feed again? Does it feed at lower rates of fire but fail at higher rates of fire? How does the tweak affect it? How does the amount of ammunition remaining in the magazine affect it? Are your 3d-printed parts actually holding pressure, or are they leaking through micro-pores between the layers? These are the juicy details that help diagnose the particular failure and solution you're facing. And yes, I've encountered (and dealt with) all of those in my own cannons. That said, if your printer is able to produce magazines that consistently pass the roll test but fail to feed when actually firing, the most likely problem is that the radius of the coil is too tight. Simple solution, enlarge the radius.
Right now, it was just a feed test to see if the magazine could successfully feed the gun. I only have 60psi from my airbrush compressor so a full power test will have to wait. I have 2 HPA tanks at 3k and 4.5k, but until I can get the feed issue fixed, I don’t want to waste the air. So what I see happening is the piston is not reliable. When it stops feeding, the piston doesnt drop far enough. I put an adjustment screw on the bottom for fine tuning. If I give it like, one turn, it will drop and the next round loads. But then it wont fire because the air just goes around the piston instead of pushing it up. So, I lower it a turn, raise it a turn and it will fire a few more shots. I DO have a magnet on the chamber. The air input is on the sides of the cap so I am FAIRLY sure that is part of the issue. Heh, I only had a few rounds in it in the video. My test button is… finicky at best. I can click it a dozen times and itll work but then, for the next dozen clicks it wont register.. I blame my Supper Shoddy™ Crimp n tape job on the wiring. Itll fire as fast as I can click, so long as the piston and trigger behave. Still messing with the piston. Thats the hang up right now. I havent been able to get the piston to reliably clear to test the full magazine. The core and coil is resin printed inside of the FDM shell. I should hope thats not leaking 99% sure it is the piston. I can see the tip of the next bb and as soon as the piston clears it jumps in. Ill try to get you a video of that. I have a different cap to try that inlets from the bottom. I used the side inlet so I could add a fine tune screw. Thinking about it further, it might be from the air pressure getting too low to push the piston…
Further testing showed two things: The side air inlets on the previous cap were the cause of inconsistent shooting. Under 55psi, there is not enough air pressure to push the piston up. So, I swapped the cap for one with bottom inlets and between 55 and 60psi (my airbrush compressors max is 60) it has no loading or firing issues. Next up… is.. I guess 120-150psi tests.
