Quick question, the clippard solenoids are limited to 100 psi. Is this enough to get the shot out the barrel at a reasonable speed? If not then they go the way of the do-do bird.
one way that you can reinforce the flat end cap is by lasercutting a stiffener and putting it to the outside. properly designed you can offload enough of the load to make it work properly, but it might be a bit thick. fast gun wise we've used some other clippard solenoids that are rated higher. don't forget to also look at the flow rate the solenoid can provide, as you might be able to do with one large higher pressre rated solenoid than several smaller, marginal ones.
Just to give you an idea about airflow requirements, a single MJV-2 valve is capable of firing (maxing out the foam-test) with any single round we use, provided it has a long enough barrel and a large enough accumulator. Generally that is about 8in long or more (including the bend and riser), and between 1.5 to 2cu.in. accumulator. It is rated for 25 SCFM at 100psi. It is utterly unable to fire multiple barrels, even with a double-size accumulator, and it struggles to reach full foam-penetrating power with barrels under 6in. I have also experimented with JLEV in-line quick-exhaust valves. These are rated for 58SCFM at 100psi, so they do great with any single-barrel operation. The larger your accumulators, the better they'll work. But even the JLEVs struggle with multiple-barrel operations. I experimented with a two-barrel .177" bb design, that incorporated every efficiency trick I know. It required a much larger accumulator than normal and still barely punched foam at 150PSI. There is a very good reason why we make our own big-bore buna ball valves. It is extremely difficult to get enough airflow without it. I don't know what kind of airflow solenoid valves are capable of, so I'll leave that up to you to decide.
I can give you three reasons: weight, area, and cost. My 1/96 Shimakaze can't afford the weight of a clippard valve per barrel. Also, I'm very tight on room in places. And it's much cheaper to make a ball valve that can supply multiple barrels than to buy clippard valves or solenoids for each barrel. That's my 2 cents, take it for what it's worth.
@Greg: What exactly are you referring to with stiffener? Just an additionally ring underneath? As far as the clippard solenoid it is the ES-3W-6, though looking at it again it has a low scfm rating. The kip solenoids aren't that much better, they just can operate at a higher PSI. The reason I'd rather have multiple solenoids is for the purpose of adjusting each gun individually. @Kotori: Okay thanks for the run down. The following thought didn't occur to me until this morning but, because I'm using the O-rings in the each barrel to restrict the shot I don't need the large accumulator capacity nor the higher flow of current Big Gun cannon valves. All higher flow is going to get me is a faster response time, though that might be desirable in and of itself. I have no idea as to how much faster or slower response time would be affected so I will have to find that out I guess.
That is why I'm trying to design something different that will help cut down on space requirements. As to the cost requirement, it will be a bit more expensive to have a solenoid per gun than to make your own buna ball valve. Thing is I don't have the tooling to make my own valve and so I'd have to send off for one, which is enormously expensive. That is where I'm coming from.
Not just a ring of stiffener. if you look at my cannon plans you will see what I mean. I had a cross stiffener machined into the upper cap that doubled as a magazine split (so the cannon would be fast gun legal) along with generous fillets at the top. I still had a 0.125 inch thick top but it never spanned further than about 0.6" from any reinforcing rib. if I had it to do again I would go up to 1/4" thick just for safety and retain the stiffening.
One other thing to remember. portions of the cannon that do not see constant pressure do NOT have to seal. they just have to leak at a slow enough rate to not influence things. one advantage of this... areas where the material would tend to tear from the pressure can be made a relatively wide interface with no adhesive between them (or a gasket, something that can not take tension. this will allow parts to deform, reducing local stressses greatly.
I'll write up a more detailed message tomorrow but I suspect you guys may have a basic concept error about the functional similarities and differences between Big Gun and Fast Gun cannons, and how both designs address cannon efficiency. For now, I will say that even the basic Big Gun cannons are not as inefficient as you might think. Teggethoff and Prinz Eugen each guzzle down 8-9oz of CO2 in a single sortie, but that's because they're firing about 450 rounds apiece. I equipped them with 20-oz bottles because they actually carry over 900 rounds in their magazines, and they need that endurance for Campaign, Last Man Standing, and Maker Faire. That's roughly 50 rounds per oz of CO2, and T and PE's guns are among the least efficient designs out there.
You may be right. I know that on most fast guns you’re probably looking at 50-60 rounds per oz of CO2. The biggest difference is the speed of each shot and how it is achieved. My understanding of Big Gun cannons is they need lots of CO2 on hand because they need high flow rates to keep PSI at a point where it will sufficiently accelerate the shot out of the barrel and because they are firing several cannons at once. Fast Gun cannons use roughly the same amount of CO2; however, they are also firing each shot at much greater velocity. They do this by using the O-ring interrupter, which detains the shot long enough for the CO2 to build up pressure behind the shot thus giving it more energy/speed over the same length of barrel. Therefore, my reckoning is that if I use an O-ring interrupter breach, but fire at slower velocities then I can achieve reduced space requirements of the accumulator due to higher energy transfer efficiency. So I hope anyway
One other thing to keep in mind.... if you can supply thermal energy to the regulator and tank, you can greatly reduce your gas consumption. as an example if your 150psi CO2 line sits at 25C vs -25C you will use ~23% more gas per shot in the -25C case vs the 25C case.
In Big Gun, we have run many rounds of experiments throughout the years, systematically trying out different accumulator sizes, valve flow-rates, barrel lengths, and cannon shapes. Those experiments formed the basis of our cannon construction thumb rules as early as the mid-90's, and every round of experiments since then confirms them. I wrote up those rules and design principles several years ago, back when this forum first started. I'm not sure what happened to that thread but it really should be stickied... Anyway, I wonder if anyone has done similar systematic experiments with Fast Gun cannons. How do variables like barrel length, riser height, and cannon flow-rate affect performance? How do they each relate to each other? Does a faster valve flow-rate just increase your max firing rate, or does it affect your muzzle velocity as well? At what point do longer barrels stop yielding performance increases, for a given valve flow-rate and riser height? How does a taller riser affect performance, and at what point does it start limiting your effective rate of fire, for a given valve flow-rate? Has anybody tested the exact same cannon with several different valves, to compare their muzzle velocity in single-fire and rapid fire?
I have done some limited testing, faster flow rate does decrease the cycle time and hence the maximum fire rate. It has some effect on muzzle velocity as well, going from 1/16 id line to 1/8 id line raised the peak velocity I was able to get out of my test cannon about 10 fps roughly, but allowed the cannon to fully pressurize and fire much quicker. Each inch of barrel length increases the peak velocity roughly 20 fps but I have only tested 3", 4", and 5" barrels. Longer barrels are impractical and start to look goofy. One old hullbusters has an article graphing up to 24" barrel length. We have also found the barrel id also has a major impact on final velocity. Fast gun cannons do not include the riser in the usable barrel length because the projectile stops at the breech and allows pressure to build up behind it, before it squeezes its way through the O ring and gets blown out the barrel. The exact pressure at which the projectile passes the O ring varies somewhat from shot to shot and causes velocity fluctuations. Lubricants seem to make this worse. Fast gun bb cannons using 1/16" id line can get 90 plus shots per ounce of CO2. I get around 60 shots per ounce using 1/8" line. The major functional difference in the projectile stopping at the breech allowing pressure equalization inside the cannon and the large volume of the cannon itself vs the cannon plus barrel combination means any advantage super high flow valves could give is mostly negated, because the fresh supply of gas doesn't have time to reach the projectile as it travels down the barrel. Some high performance cannons provide a bypass that allows gas within the cannon but far away from the breech a quicker path to the breech area. I will say the one time I experimented with a O ring cannon and 1/4" bearings was frightening. Lowering the pressure may not help as much as you would think. Ron Hunt
Hmmmm....well that might be a knife in the back for this idea.... On to other news, I just got a quote back from the laser cut people and it will cost me $80 for my 1st rendition cannon magazine assembly. Note that I did have to buy a larger sheet of ABS than needed because I couldn't fit all the pieces on the smallest sheet which will hike up the price a bit. I have no idea how that compares to the cost of one of the traditional magazine assemblies. I believe Kotori said he paid $24 for two sets. Is that right Kotori? Granted, this mag assembly is more complex and does more, but maybe not $70 more. On another front, I am mostly finished with my 2nd Variation with the only thing holding it up is completion of CO2 valve integration still up in the...air? cyberspace? where ever it is? I was going to model in my cannon breach assembly...but baby duties apparently come first... Again, thanks for all the chit chat on the topic guys. There has been a ton of good info posted and it has really helped out! So please keep talking.
The variables affecting efficiency in Fast Gun cannons have always fascinated me. It's all the same variables as in Big Gun, but the numbers and how they interact is so different. In Big Gun, the three biggest factors in a cannon's effectiveness are barrel length, accumulator size, and valve flow-rate. Barrel length directly affects how long the accelerating gasses can act on the projectile. Thus, with enough gas and enough flow, a longer barrel will result in a higher velocity. Since barrels are limited to scale length in Big Gun, barrels range between 6 to 9 inches long, with about 1/4 to 1/3 of that length in the vertical direction. The next variable is accumulator size. As the projectile travels down the barrel, the CO2 gas expands to fill its new volume. Some leaks by, but we'll ignore that for now in our ideal Big Gun cannon. The result is that the gas pressure drops as the projectile travels down the barrel. If your barrel is too long, your gas pressure will drop so much that you'll actually start to slow down the round. The final major variable is flow-rate. In Big Gun, flow-rate isn't just affected by the size of the valve. Another huge player in this is the convoluted path the gas must take from the valve through the distribution manifold, to each of the different barrels. This is highlighted in the efficiency differences between canister-type and classic indiana-type cannons. Since canister-type cannons have a more efficient air path, they have a higher effective flow-rate for a given valve size, with very noticeable increases in their efficiency. If a cannon doesn't have enough gas flow, the gas pressure will drop once the projectile passes a certain speed. The higher your flow-rate, the faster it can go without losing pressure. Those three major variables work together into the following thumb-rules. For a barrel of average size (between 6 to 9 inches total), the cannon should have between 1.5 to 2 cu.in. of accumulator volume per barrel (3 to 4 for a twin, 4.5 to 6 for a triple, etc), and the cross-sectional area of the valve should be at least equal to the sum of the cross-sectional areas of the barrels. I personally take the Russian route with my guns and go for the upper end of accumulator volume, and proportionally over-sized valves. Fast Gun cannons are also most likely affected by the same variables, just a little differently. Barrel length is obviously the same, longer barrel means longer acceleration means higher velocity. Accumulator size is a bit different, since what Fast Gun considers an accumulator is functionally different from the Big Gun accumulator. The closest equivalent is the riser portion of the cannon, as the only effective pressurized gas-storage volume at the moment the projectile is released from the o-ring. As the magazine empties, it will also contribute to the effective accumulator volume. I predict that as the magazine empties, muzzle velocity will increase because of the additional volume, can anyone confirm? The effect of flow-rate is also very different from Big Gun, since the o-ring acts as an effectively unlimited-flow equivalent to the Big Gun buna ball valve. Ron, you mentioned that larger gas lines and higher-flow valves have a measurable increase in velocity. This is probably because they are contributing to effective accumulator size, dumping in extra gas to make up for some of the pressure drop as the projectile travels down the barrel. Ron, you mentioned that you once tried out a 1/4" o-ring cannon. Did you ever measure its velocity? Big Gun 1/4" cannons reach full strength around 150 to 160fps.
No I never measured the velocity, I did it back in 1993 before I got any cool gadgets for the workshop. I expect it was higher than 225 fps though. Took out my 1/8 plywood radio box when I test fired it at my ship, and back then we had no control over the gas pressure except by chilling the tank. Ron Hunt
So just a quick update, I went ahead and ordered that first variant design that I posted and I've been working on finishing up details for the 2nd variation. I've got 3 different valve setups: Clippard soleniods(not sure will work / cleanest setup), Kip soleniods(will work / expensive!), and then Clippard MAV-2(will work / cheapest/ moderate difficult setup). I know for a conventionaly built Big Gun cannon these three don't have the flow capacity needed, though the MAV-2 comes close as there would be 1 per cannon. With an o-ring breach, they should all work. My biggest issue right now is the o-ring breach. With the fittings I have available to me or have seen online there just isn't enough room between barrels. So I'm trying to come up with alternatives. I'll post some screen shots once I get them.
look back at how I did my O-0ring breech. I think you could do somehting similar from laser cut plastic...
Yeah, I'm actually in the process of modeling it in so that I can look at that possibility or the possibility of having it printed 3D...Call for Tugboat!
