I agree with your observation here. I came to the same conclusion. If you have some math to back up the ideas, I'm all for reading through it! Either way, it sounds like your thoughts are matching my theories. ...the maximum power of these cannons is defined as how much pressure can you have left at the end of the barrel. -- So with that in mind, how to keep the most pressure at the end of the barrel? Minimize the pressure differential needed to keep the piston extended. Ensure enough air is in reserve at the o-ring, such that the pressure drop to fill the barrel is minimal. Without doing a bunch of math, FOR MY DESIGN, my take-aways are: Make the barrel as tight-tolerance as the round will slide through freely. Makes perfect sense and my next revision will start pushing the limits here. Increase the volume inside the cannon. This is done by simply having a bigger magazine. As you pointed out, there is a size limit where bigger doesn't hit harder. I'm interested to see if there is an obvious minimum magazine size where the cannon starts hitting softer. Reduce the amount of air velocity that can escape the piston. This could affect rate of fire in my design. I will likely not mess with this. Reduce the resistance required for the internal cannon air to escape through the barrel. I might toy with a gas line blowing down the barrel. ... although NONE of what I just said is useful for Big Gun at all!! Today's cannon already hits significantly too hard for Big Gun already. I can see why the fast gunners are getting seduced trying to find ways to ink every FPS out of their cannons!
Eh, you're entering the realm of diminishing returns. Like you said, there's a point where throwing more gas at it will not increase fps because you run out of barrel time. Sounds like yours are hitting plenty hard right now. Find a way to make them sound scary and people will fear you more than 2-3 more fps. Lol
bahahhahahahahahaa!! Maybe I’ll put a scary muzzle brake on the end. I’m going to pick up CO2 & a pack of 7/32” bearings tonight. Now I just need to find a o-ring with 7/32”-ish ID. I doubt scaling up will take that much time, maybe I’ll have a big gun cannon by the weekend!
Update - First pass scale up for 7/32" has been sent to the printer! I was also able to find a couple of good o-ring options at Home Depot. Not sure which is going to be the winner. I had to increase the length of it by 0.1" as well as bend the S-curve; otherwise the second round would pass by the piston. Looks like a 3 hour print time... I think I'll relax a bit & see how it turns out in the morning!
Printer’s layer height remained the same and so did the threads. Only the spaces which move the bearings changed diameter.
good morning! In what way do you mean? It “probably” hits hard enough for big gun, but I can tell the ball isn’t gathering as much speed when it leaves the barrel. In the video I have the barrel gap at .26”, which is .04” too large for 7/32” (.218”). I brought it down to .24” last night and it did hit harder. I’m going to try .23 & .22 as well; we’ll see how tight it can be without causing a jam. I tried the slo-motion video setting on the iPhone; but it wasn’t fast enough. I only caught the ball in a frame or two; which does make perfect sense now that I see it. I’m going to stop by HDepot today and pick up some blue foam; for penetration testing.
With the new cannon tech working out, I woke up this morning with an idea in my head for a novel rotate system. This post is useless without a video! A servo will mount underneath the second spinner, and because the second spinner's size the servo's rotation should match nearly 1-1 with that of the cannon. This should give me precise tracking of the cannon direction using a regular servo instead of the awful & expensive winch servo.
Justin, have you considered printing the barrels slightly undersize then reaming them out to a precise ID? That gave better results for me than just printing at a smaller diameter.
Thank you! I’m “trying” to avoid too much post processing. We’ll see if it’s good enough once I get some rounds through the foam.
I am personally offended by this post. Who doesn't want so much gas that their cannons sometimes blow little puffs of gas for realistic gunsmoke effect? https://photos.app.goo.gl/PTDCxei8LBQRQSdP7 (this boats cannons are completely silly and unnecessary)
OMG - Even the 1/4" Big Gun cannons using dump valves don't make that much smoke! ... or maybe everything is just warmer here in Texas?
Update - the first test of the cannon rotation went OK. I learned: -.255” is correct slot diameter for my plastic ball bearings. - The bearing sleeve must nearly be an discrete number of bearings. - 270 degree servo is only capable of 270 degrees on a bench, and not with a real radio. - to get a 270 degree servo past 180 degrees, you need a servo range extender to get you to 500:2500 uS PWM. - Servo manufacturers are liars. - It’s better to put the bearing loading tubes away from the pressure points. With that; I have a new print cooking and another Amazon package on its way!
CANNON ROTATE TEST!! It’s pretty darn good! - There is still too much resistance to rotation, I believe the balls are still binding. I’m going to sit down with it this week and really try to understand how to remove or re-think this issue. As a result of the resistance, the cannon isn’t perfectly tracking the target position. So I need to get it figured out. https://youtube.com/shorts/6i6A-FdEJi8?feature=share
Updates - I made some good progress smoothing out the turret rotate. I found that 4 balls in specific places is a lot smoother than a plastic ball bearing. Photos coming once I get it printed. While I’ve been pushing prints; I started on the pump again. I saw Greg used a plastic pump tube & thought… why not!!?
