Pneumatic Pumpkin/Apple Blaster Cannon

[nhobbs]

Hey all, I know this is a spud site but I am hoping to get some feedback on building a Pumpkin/Apple blaster since the theory of how it works is basically the same. We run an agritourism venue and are hoping to build a Pumpkin/apple blaster. It is made out of steel. I am pretty good with everything except two points. First, What size solenoid valve do I need to dump the needed air into the launch barrel if I am dumping 100psi for approximately 1/10 sec? Second, is it ok to simply pipe the air directly into the launch barrel or does it need some kind of deflector or method of dispersing the pressurized air? I am concerned that 100 psi released suddenly could pierce the pumpkin or apple versus launching it out. I am including a youtube link below so that you can see what I am referring to.

[farcticox1]

Here is a pumpkin launcher, it is a much bigger project than an apple launcher, pretty simple though, only 35-50psi. You're gonna need a big compressor to keep this supplied. Can't see what he is using, might be high pressure air tanks
[youtube][/youtube]

[jackssmirkingrevenge]

Hey all, I know this is a spud site but I am hoping to get some feedback on building a Pumpkin/Apple blaster since the theory of how it works is basically the same.

Welcome to the forum! While nominally it's "spud" guns, the vast majority of projectiles we talk about here are not in fact potatoes, so no worries.

solenoid valve

As close as you can to the barrel diameter will give you the best performance, though at this scale it might get expensive.

One way to achieve great performance with a simple mechanism is to use a burst disk, ie sandwich a sheet of frangible material between the barrel and the chamber, then pressurize the chamber until the disk bursts et voila.

The only disadvantage really is that it increases your reload time and the moment of firing can be a little unpredictable, but in the context of what you're trying to achieve that might not be too much of an issue.

I am concerned that 100 psi released suddenly could pierce the pumpkin or apple versus launching it out.

For fragile projectiles like farm produce you want higher volumes at lower pressure, and a barrel as long as possible so you can spread out the acceleration.

[mrfoo]

The bigger the thing you want to launch, the more flow you need; you need to get a lot of air into the barrel, fast. So the bigger the valve, the better, ideally you'd be looking at something equal to the barrel diameter. A big QEV piloted by a small solenoid might be an option, see http://www.spudfiles.com/post387622.html#p387622 for example.

If you have a big, fast, valve, you won't have a small, high velocity jet of air impinging on the projectile, instead you get a "wall" of compressed air. Piercing the projectile then becomes less of an issue, but disintegration under acceleration does. So you want less pressure, but massive flow and a long barrel to keep the acceleration under control. This means you will need a large chamber. For really delicate projectiles, you might want to consider using a sabot.

[Moonbogg]

I think there is no better apple blaster than Technician's QDV apple cannon design. I don't know if it's suited for a semi-commercial application like this though. You can maybe rig it up to be more automated and whatnot, but that takes design work. I get the feeling the OP wants to just buy a valve and put it between a chamber and barrel, so I don't know.



Here. Like this.

[nhobbs]

Hey guys, thanks for the replies!

You're gonna need a big compressor to keep this supplied. Can't see what he is using, might be high pressure air tanks

We have a big compressor so the air should not be an issue.

So you want less pressure, but massive flow

The guys that have made these for farms such as ours state that they use 100psi in the chamber and they use some kind of solenoid valve that is open for 1/10 of a second. That way the chamber is able to keep up with repetitive firings. I am not sure if 100 psi will destroy the apple or not if it is piped directly to the barrel without some kind of deflection.

You can maybe rig it up to be more automated and whatnot, but that takes design work. I get the feeling the OP wants to just buy a valve and put it between a chamber and barrel, so I don't know.

I am actually planning for it to be fully automated so that it can meet the needs of repetitive sequential use. My plan includes a safety switch that will prevent firing if the breech is open, a reset switch that will not allow repetitive firing unless the breech is cycled (to cut down on unnecessary firings that would waste air), a solenoid valve (probably 1/2 in unless there is a better suggestion), a timer to keep the valve open for a programmed length of time upon activation, and a firing trigger.

Here is the guy that I am trying to model it after.....

[youtube][/youtube]

[Moonbogg]

I'm used to thinking about dumping the whole chamber for every shot, so I'm not sure what size valve you'd need. What you can do is browse the pneumatic cannon section to get a feel for what size valves are being used for a given cannon size. I'd like to help more here, but it sounds like a question about air volume as it relates to the valve size, having repeated shots and yet still maintaining adequate performance so the apple doesn't just fall on the floor as it exits the barrel. I've never dealt with these issues before.
As far as needing to spread out the force of the injected air; I've never heard of that being an issue before. As long as there isn't a small nozzle right in front of the apple, I can't imagine the air destroying the apple, but I could be wrong I guess. I've never had to think about these questions before. If it were me, I would allow for adjustability in the design in this regard. Don't back yourself into a corner where you have a hard fixed output location that can't be moved or adjusted. If you are facing an unknown, then allow for adjustability in the design so you can experiment.
You can also just get your chamber working and rig up a test barrel so you can experiment with how the apples behave. You might need to experiment with different valve sizes and distances between the apple and the air inlet before assembling the cannon in final form. I'd make a test cannon to test the performance and when you are happy with the configuration, then you can make it solid and pretty and finalize all the little details. Just a thought.

[jackssmirkingrevenge]

If you're looking for efficiency then a timed valve is a better idea.

Are you actually planning on having some sort of "magazine" feed?

What performance are you looking for really?