Definitely. You can see on the Duke, the barrel is resting right on the barbette and the turret has to be completely open at the bottom. You can also see where I filed off some of the brass fitting to help it fit.
Those turrets look taller than the ones I made. Definitely not enough room in there on mine. The breach nut alone is just barely able to fit. With the regular set up Id be putting the barrel through the barbette. The lip on the cap isnt the only hinderance there. I’m kind of a stickler for keeping it looking right, meaning both barrels set up, nothing sticking out at weird angles or through places they shouldnt, etc. I’m going to start printing prototypes in the morning.
Initial prototype looks good. The BB's get a little snug going around the top, but I am just using lung power to test right now as I cant seem to find my 1/8npt hose for my compressor (has anyone seen it? it is blue). I might push the radius out a few more millimeters to relax the bend as I have the room to spare. But I will test with the current bend and see if that would pass for a restrictor tube. The down angle is now 19* and everything will fit under the modified turret cap.
The 'geek breech' cannons were briefly popular b/c they never needed adjusting. It was a piece of fuel hose about 1.5-2" long w/ another tiny (approx 3/8" long) piece of hose squeezed over the middle to provide the compression. The whole thing was then inserted into a brass tube and locked down to the barrel and uptube w/ tiny screws. The drawbacks quickly overcame that advantage. A jam or stuck / oversized bb meant full dis-assembly was required to clear. Also, if the cannon wasn't juuuussst right when built, you scrapped it and started over, rather than swapping parts or tweaking an adjustment.
darkapollo, did you bend your barrel by hand, or with a tubing bender? I'm very curious how well a Fast Gun cannon can work with the bend after the breech. Every design I've seen puts the bend before the breech.
In the CAD design shown above? That is actually 5/16-3/16 nylon pneumatic tube. It bends rather cleanly though that is at the very edge of the smooth radius. If I bump it out another two millimeters it should allow a BB to pass clean.
So initial tests are positive. My bench-top compressor can only get to 60psi. It doesnt quite have enough punch to get through ‘reenforced’ (with silkspan and contact cement) balsa, but the bend has little effect. I have a few things to test. I ordered 5/16 compression T’s and think maybe move the o-ring from the breach to the fitting.
Recent iteration of the design. Going to print and test it. The o-ring is compressed via a screw that slides the entire magazine. Still debating on a big-gun style feed or fast-gun style tube mag. I have the NPT threads down perfect. My last several test prints were sealed and the threads are strong enough to resist 60PSI bursts.
Just keep in mind that barrel length is measured from the restrictor and keep it to the length limit. Looks interesting
Yup. My barrels are already an inch short so I have some room on the back end. I also have a restrictor tube style design as well that will smush the nylon tube down to be an adjustable restrictor that can adapt to irregular BB’s. Basically slitting the nylon tube and using a ball bearing on a spring with a screw to provide a rebound tension.
There we go. minor revision. Will need to take 1/4" off the barrel length to get it within the 5" rule. Same concept, just moved it in and trimmed the nylon tube down.
It may be worth taking a little off the front to get a smoother transition to the bend. Many of my Big Gun ships use steel brake line for their barrels, and after a couple years of fighting the bend is significantly deformed from the repeated shock. You're using plastic, which is even more susceptible to deformation. Also, very curious how you're doing the rest of the barrel, and what joint you'll use. One thing I recently discovered while testing sleeved Big Gun barrels is that even a very small lip inside a barrel can rob the projectile of a lot of energy.
The barrel itself is thick walled stainless tube. It is forced into the 5/16 nylon tube and it is REALLY jammed in there. I have to pull extremely hard to get the barrel out. Both the tube and stainless are 3/16 ID so theres not really any lip. The barrel is beveled so the nylon ‘relaxes’ into the transition (I didnt model any of that). The nylon tube is designed to be an expendable part. It shouldnt see any impact from firing since the round is essentially rolling through the transition. Unlike other designs where the bb is already moving with force when it changes direction, with this, it transitions as it is accelerating. I had contemplated using steel brake line, but the issue was the same as using copper and brass. The only way to join the pieces is with bulky fittings. I knew that I could use my nylon fuel line tool to press the metal barrel into the nylon tube so I chose that. The turret cap is a clamp as well. I attached a picture of my current test rig to better show the design in real application.
Total redesign I have a bunch of cheap pneumatic fittings for my various 3d printers. They are 1/8NPT thread with 1/4" ID. They are smaller than the average brass fitting. I drilled one of them out and I am going to test a new design with a threaded barrel fitting. If that design works, I think I can just use some 1/8 MIP threaded nuts which, when combined with the nylon tube, would negate the elbow issue.
Very cool, your boats coming along nicely! Suuuper interested in how your cannons play out. Feel like ive learned alot from your build
Thank you! I am printing some new test pieces for the new prototype just to see if the threads work out.
OK! I think this is a working design. I tested the breach and it prints perfectly. The threads lock in tight and the oring squishes well. Below will be a normal compression fitting style cannon. I had to thin the top of the turret out more than I wanted, but it is still 1mm thick
So when will you be able to test fire at 150 PSI. As Kotori87 has mentioned about possible deformation of the curved tube could you add support with more printer material so that the curved tube is fully enclosed in a block not just the tubes wall and have the turret top slip over it like top of a board game box.
I am hoping to not need 150psi to fire these. High-volume low-pressure is my goal. I see the popular thing is using tiny 1/16 pneumatic hose which kills volume and flow, and probably explains why higher pressures are used. I am just going off of decades of building paintball guns. I don’t want to use 1/16 hose for the firing air flow.
