More pics to come, I'm having a hard time posting tonight. Either my computer is acting up or the website has something going on. More tomorrow!
Shown with a spare set of internals alongside. The end cap has been unscrewed from the end to show its inside. For those that may want to attempt something like this, it is important to provide for "breakaway" of the piston. There is a small recess in the side of the end cap to allow air to spread out and push on the bulk of the bottom of the piston without having to move the piston any to expose the entire surface area of it to air pressure. Another option would be to leave plenty of clearance between the piston in its at rest position and the end cap, taking into account any lubricant or water that might be in there. You do not want the piston to contact the end cap in any case, or it takes spring pressure off of the ball seat. Basically speaking as far as breakaway goes..... if the piston is real close to the end cap at rest, and the piston and end cap are both flat, and there is a heavy coat of lubricant there, it can cause a seal of sorts between the two, effectively blocking off most of the piston to air pressure, which then causes the need for excessive pressure to get the piston to start to move, or "breakaway".
The recess in the rear of the piston was actually there to reduce weight, not provide breakaway. I machined away almost any material anywhere it wasn't necessary to eliminate weight. The recess around the outside of the part that goes from the outlet on one side to the outlet on the other was also machined away solely to reduce weight.
Your piston/pushrod assembly looks a lot like the one I'm doing, with differences due to me using a printed piston vice brass. What diameter piston is it that you're using? Did you Buna ball need drilling, or did it come drilled? You do really good work
Thanks Tugboat, it always gives me a warm, fuzzy feeling (mostly fuzzy) when someone appreciates the effort! The bore diameter for the piston is .750". I will have to measure the actual piston when I get home, but as long as there is a few thousandths clearance between the piston and walls you should be good. The important thing is to size the bore and groove in the piston properly to give the proper amount of crush to the o ring. Mine are a little tighter than I should have made them. I used Parker's size recommendations for a dynamic o ring, but should have taken into account the fact that it did not really need to hold air pressure, other than for a short burst during firing, so I should have opened the bore up some to allow it to slide easier in the bore. Better yet would have been a cup seal, but I didn't want to use the tiny amount of extra length it would require. I did drill the balls. I think I drilled them 1/16" but don't go all the way through. I chucked them lightly in the lathe to make sure the hole would be centered. I made my piston and push rod in one piece, but just because it was no big deal for me to do so. Your plans will work great. When we print a part and need smooth finishes or threads we just print the feature (we print the threads as well) bit add enough material that we can machine it to the desired dimension and finish after printing. I don't know how accurate and capable your printer is, but for example, I would print the 15/32 threads oversize, then spin a die down it to make a nice thread. The only reason to pre print them on your part as opposed to just printing the boss to thread later is to allow the die to start perfectly straight, and make it easier to thread since you wouldn't be trying to cut off all the material with you die.
I've got a decent lathe that I can clean up parts with, and there are postproduction tricks I can use on the valve body to smoothe it and make it stronger. But my design right now is not going to have threads. If there was an easy-to-get insert with 15/32-32 threads I'd consider using them, but for the moment, I'm going to try printing the whole thing apart from the rod, ball, and barrel. (okay, maybe the 10/32 barbs will be brass too)
There is a 15/32 - 32 insert available - Clippard part number 15027. I machine off the hex side and re-thread it 3/8-24. Then I tap the valve 3/8-24 and screw the fitting on. That gives me nice brass threads to attach the MPA-7 to the cannon.
For the actual ship's cannons, I think that using that part will be good. For the little torpedo cannon, I want to go as light as possible (If it works) sso I'll try the printed parts for the one-shot deal. For the Dual 1/4", I'm going to be using 2" O.D. ABS tubing (1/4" wall thickness) for the accum, with ball valve welded to that, with the 15027 welded into the ball valve body, with an MPA-7 threaded into that. You experienced BG and BaS guys think I should go with 3/4" Buna ball for the full-up cannons, or is 5/8" enough?
Woo Hoo!! I finally got a pump to work underwater!! I even ordered another of the original motors to try.... same problem. By sheer luck, when I went to find an alternative, these in-runners were finally back in stock at Hobby King. I ordered one, made a new pump cover to accommodate it, and promptly forgot I had done either of the above. I found the pieces while cleaning up my mess (trying to find Uritski's rudder tube.. still MIA). I tossed them together and it works very well - even UNDER water!! Pumped 1 GPM so I will have to throttle it back some. It pumped great for such a tiny pump, and primes instantly. It actually sucks the water up to it if held barely over the surface. Now I just have to figure out where to mount it.
Not to derail this thread, but have you though of the possibilty in modifiying this design to work as a cut off switch for our AOS ships to prevent firing into the air on a heel over? That "rocking gimble" looks like it could be converted to a cutt off switch.... just curious!
I'm not too familiar with the AOS side of the hobby so I wasn't aware that there could be that issue. Sounds like that could be solved with a simpler gimbal with a weight suspended from it that would interrupt the fire signal with a microswitch if the boat rocked too far. Thoughts?
That's what I was thinking, nothing complex, just a weight and microswitches to interrupt a NC switch in the firing pathway.
I need some help here: 1) Any big gun guys know of a rule (any rule set) that limits number of torpedo rounds, and if so how many? 2) Anyone have a recommendation on mAh needed for a battery? I can hunt down motor specs if need be.... or a general guess is good for now.... problem is I'm out of weight and space.
Given how tight Othar was on weight, and I didn't use a gyro... it's gonna be interesting to see it get powered.
Fast forward to current time........ I have been a bit ahead of this build compared to what I have had time to post, but here is where I am in present time. The psedo sheeting is tape that I applied to see if I could assemble it after it was sheeted. I am dry assembling now, and if I get it together, I will disassemble, sheet and paint. What you see here weighs 1.5 Lbs with the decks which aren't shown. There are several components not in there yet... and that superstructure thing also needs to have its chance to weigh things down..........
I realized the last pic didn't show much as far as internal layout, so here's a better one. From left to right...... Rudder servo, aft battery, Gyro (which could get eliminated), Gear box/ drive motor, pump, torpedo, firing valve and servo, gage, co2 regulator/ canister, forward battery. The electronics are distributed about. Still need at least 1 more speed control, torpedo barrels and mags, co2 lines, some additional wiring Etc.
Stupid Gyro!!!! On to version 3..... as expected the last version precessed backwards. Oh well, I had to try it since it was the path of least resistance to see what I really needed. I think I have it now. After the last failure, I rigged up a quick and crude device to reverse the precession. It was certainly crude, but effective,. Although I couldn't get the boat to balance itself upright I did get it to balance itself on the lower corner of it's hull. This just happened to be where the crudeness of my test system balanced out. Back to the drawing board.... Most new parts already designed, half are built... Fingers are crossed.
