Let me introduce myself...
Posted: Wed Jan 31, 2007 9:09 am
First off, I'm not really a novie at this stuff. I've looked into and researched pneumatic spudguns at length. Something about launching things hundreds of feet into the air seems really cool to me.
My first gun (no pics, sry) has a 5' long, 1.5" diameter barrel (SCH 80, I think) and a 18" long, 3" air chamber with a ball valve (yeah, I know, not the most efficient). The barrel-to-chamber ratio is about 1:1.5, or at least as close as I could make it. It launches pretty well. I used those small potatoes (kinda pinkish and round) and my best shot with that was 450ft @ 110psi with no wind. Depending on wind strength and direction and my reaction time of opening the ball valve, the majority of the time it will launch potatoes about 250-400ft, which I think suffices for my first potato gun.
That's about it, but I got plans to make another gun, but with a somewhat complex valve operation (piston valve variation) so that all of the pressurized air is released almost instantly.
I'll try to explain what I want to do.
The barrel is inside of the air chamber and almost go to the other end (but leaves room). That end of the chamber will go down to about 1.5" and then back up to a much smaller 2.5" chamber. Let's call the 1.5" length the "bridge".
Here's how the operation should work (i'll post a pixel art explanation here later this weekend):
There is a rod that extends from the large chamber to the small chamber, and it has rubber discs of some sort (think sink drain stopper) at either end. I would first pressurize the small chamber so that the rubber stopper is pressed against the "bridge" and creates a seal (hopefully).
So now only the small chamber is pressurized (@ ~110-120psi). As the rod is pushed towards the end of the small chamber, it is also pushed against the barrel end to create another seal. So now the large chamber is completely sealed up and ready to be pressurized. (this is when I put the potato in the barrel) I would then fill it to no more than 10psi less than the small chamber (so @ ~100-110psi), otherwise equilibrium may set the gun off prematurely.
To fire the gun, I would release (probably via ball valve) the air in the small chamber. The pressure would drop inside the small chamber and the pressure inside the large chamber would force the small chamber rubber seal to open (by being forced back by the large chamber's pressure). As that happens, the other end of the rod moves away from the barrel opening and is forced against the end of the "bridge" and creates another seal. At this point, the only exit for the large chamber air is the entire opening to the barrel.
The only drawback is that setting it up takes some time, but then again, cannons weren't quick to prep either.
It's fast, and dumps all the air almost at once. That's me, and those are my plans.
My first gun (no pics, sry) has a 5' long, 1.5" diameter barrel (SCH 80, I think) and a 18" long, 3" air chamber with a ball valve (yeah, I know, not the most efficient). The barrel-to-chamber ratio is about 1:1.5, or at least as close as I could make it. It launches pretty well. I used those small potatoes (kinda pinkish and round) and my best shot with that was 450ft @ 110psi with no wind. Depending on wind strength and direction and my reaction time of opening the ball valve, the majority of the time it will launch potatoes about 250-400ft, which I think suffices for my first potato gun.
That's about it, but I got plans to make another gun, but with a somewhat complex valve operation (piston valve variation) so that all of the pressurized air is released almost instantly.
I'll try to explain what I want to do.
The barrel is inside of the air chamber and almost go to the other end (but leaves room). That end of the chamber will go down to about 1.5" and then back up to a much smaller 2.5" chamber. Let's call the 1.5" length the "bridge".
Here's how the operation should work (i'll post a pixel art explanation here later this weekend):
There is a rod that extends from the large chamber to the small chamber, and it has rubber discs of some sort (think sink drain stopper) at either end. I would first pressurize the small chamber so that the rubber stopper is pressed against the "bridge" and creates a seal (hopefully).
So now only the small chamber is pressurized (@ ~110-120psi). As the rod is pushed towards the end of the small chamber, it is also pushed against the barrel end to create another seal. So now the large chamber is completely sealed up and ready to be pressurized. (this is when I put the potato in the barrel) I would then fill it to no more than 10psi less than the small chamber (so @ ~100-110psi), otherwise equilibrium may set the gun off prematurely.
To fire the gun, I would release (probably via ball valve) the air in the small chamber. The pressure would drop inside the small chamber and the pressure inside the large chamber would force the small chamber rubber seal to open (by being forced back by the large chamber's pressure). As that happens, the other end of the rod moves away from the barrel opening and is forced against the end of the "bridge" and creates another seal. At this point, the only exit for the large chamber air is the entire opening to the barrel.
The only drawback is that setting it up takes some time, but then again, cannons weren't quick to prep either.
It's fast, and dumps all the air almost at once. That's me, and those are my plans.
