I think I have most of the pics, drawings added to the first post in this thread, at least enough that if we wanted to look at design improvements it wouldn't get too confusing.
So I've been working on my cannon design and have run into a few questions. 1) How big of a hole do I need in my bushing to have enough airflow? 5/8'',3/4"? 2) What is supposed to hold the bushing + gun down to the cannon base, just the sheer weight of the gun, or something else? Beaver
That would be something else!!! If the top part isnt secured to the breech , trust me....it will fly. You have the holes in the ball valve assembly for the hold down screw, but they are not shown in the bearing mount.
Most cannon bases have a couple of set-screws through the sides, to grab onto the bushing. I have seen people try to thread it in, but that doesn't work well. I would recommend you counter-sink the holes, for better accuracy when drilling and tapping the set-screw holes, and to allow you to use screws with a full-size hex head that can take more torque without stripping. As far as ID of the bushing, remember the thumb-rule. You want the total cross-sectional area of the airflow path to remain constant (or shrink) as it travels from accumulator to muzzles. When in doubt, make your bushing ID the same as the buna-ball valve ID.
OK, so two set-screws holding the bushing to the base, and the flange on the bushing keeps the gun from flying off the base. I think I'm going to use a 5/8" bushing. If it ends up being too small, I can upgrade to 3/4". Also, do I want the buna-ball to be the same dia. as the valve hole, or a little bigger? Thanks, Beaver
You definitely want the buna ball to be larger than the valve hole. Otherwise you'd need a ridiculous amount of travel on the valve in order to move the ball out of the flowpath. In my cannons, I used around 3/4" dia. buna balls. I have seen people build cannons using faucet washers, and in some ways those are more ideal. But the ones I saw had difficulty sealing the hole in the middle of the faucet washer, and were prone to leakage.
Ok, I'll get 3/4" buna-balls. I think soon I'll be ordering parts from Mcmaster to start building cannon design Mk-1. Beaver
A point to remember, your ball seat area needs to be smaller in diameter than the bore of the MPA-7 actuator.
Ok, the MPA-7's bore is 7/8", and the ball seat area is 5/8", so I should be good. I'm just curious, but why does it need to be that way? Ordered the buna balls from Amazon today. Beaver
If the ball seat is bigger than the mpa7 bore there would be more effective pressure seating the ball than would be available to un seat it when the mpa7 was energized. In other words, if air pressure in the accumulator is the same as that applied to the mpa7, and the ball seat is the same size as the mpa7 bore, they would both generate the same amount of force, effectively canceling each other out and no movement would be possible.
The canceling-out effect Cannonman described *can* be averted by using a higher pressure to the actuators, but that isn't recommended. Higher pressure requirements in the actuator requires more time for pressure to build up. This can result in a noticeable lag (as much as one second) between pulling the trigger and the cannon firing, and you have to hold the trigger down that entire time. Fortunately I have never encountered this myself, but I did see it in a few ships where people used MPA-5's instead of MPA-7's.
OK, thanks for explaining it. Buna-balls arrived today. Now I think I'm ready to order the ABS from Mcmaster to start on design Mk-1. Sorry for derailing your thread, Cannonman. :blush: :blush: :blush: Beaver
I was looking at Canonmans initial drawings, after I experienced a cannon failure during testing of an older cannon using a similar assembly. The screws holding the rotation bearing in from underneath are a failure point, as is the flare holding the bearing onto the breech riser. In the case of the cannon failure here, the screws tore free from the manifold, and as a result the entire upper part of the cannon detached from the breech . On close inspection, the flared area was showing signs of stress cracking around the flare. This can be avoided by having the bearing fitted into the manifold from the top, and the breech riser inserted through the bearing with a flange on it. I believe this is the accepted norm now anyway. Further to this, I personally use a large diameter bearing for the rotoation. As this prevents the standard method of fitting the shot height adjuster screws from underneath, I fit them in from the side, using the screws to locate and retain the barrel risers as well as set the height of the shot in the feed area.
