SpudFiles

This is my first attempt at a cannon with a piston valve. It is a 1.5" barrel sealing piston valve with a Bondo piston. The piston was molded in 1.5" PVC, and then I set up a router to make the grooves for the o-rings. The piston valve is piloted by a 1" sprinkler valve, which in turn is piloted by a blowgun with a 0.25" ball valve as a safety. The piston is also easily serviceable through the female adapter. The chamber is 2" sch. 40, and the golf ball barrel is 1.5" SDR 21 sleeved in sch. 80 2" PVC. This thing shoots FAR. With only 50 psi the ball seems like it is immediately in the sky and beyond your vision. When I crank up the pressure, scary scary things happen. At 100 psi I've calculated (without drag) the range to be +/- 550 meters. I can barely see it coming out of the barrel, and when I am no longer able to see it, the ball has not yet reached it's maximum height.

Is there any reason for the skinny section of pipe between the chamber and piston valve? I would think that would limit power.

Nice job on the piston.

Looking good, but your chamber is bigger than your barrel? Your chamber could be cut off at the barrel support and I doubt you'd notice the difference.

The skinny section is because I already had that air tank from a previous launcher, and didn't want to make a new one. Yeah it is a big chamber. When I made that chamber, I didn't know that much about potato guns so I over-compensated I think. I also have a potato barrel for this cannon, and it's nice to have larger volume of air behind that fat spud.

AngryChauncey wrote:The skinny section is because I already had that air tank from a previous launcher, and didn't want to make a new one. Yeah it is a big chamber. When I made that chamber, I didn't know that much about potato guns so I over-compensated I think.

Large chambers are nice if you want to do low pressure lobs. In paticular, tossing eggs and water balloons without breaking them becomes much easier. Did you know it is possible to toss a raw egg a couple hundred feet? Low pressure such as 8-15 PSI works well. Smaller chamber cannons have troble working in that pressure range. Eggs fly very well.

Technician1002 wrote:Eggs fly very well.

There's some irony there somewhere

Nice work on the cannon, there are some areas that can be optimised but a good effort

One thing I have to ask... did you have access to street elbows? I've become addicted to them, as they keep everything nice and compact 8)

I like the triggering setup!! The bondo piston is especially neat! (People like me don't have the patience for that!!)

Very cool build! I have a similar golfball cannon, and I love it!! I'm sure you love yours too

Oh, one more thing... for the barrel support, I would suggest putting some short screws through the tee piece and partially into the barrel sleeve to lock it in place. I use the same setup you do, and it slides a lot!!

Nice job. Any chance of a video?

Pilgrimman wrote:One thing I have to ask... did you have access to street elbows? I've become addicted to them, as they keep everything nice and compact 8)

I like the triggering setup!! The bondo piston is especially neat! (People like me don't have the patience for that!!)

Very cool build! I have a similar golfball cannon, and I love it!! I'm sure you love yours too

Oh, one more thing... for the barrel support, I would suggest putting some short screws through the tee piece and partially into the barrel sleeve to lock it in place. I use the same setup you do, and it slides a lot!!

Yeah the street elbows are convenient. My barrel support doesn't slide at all, but I have that worm-gear band really tight. I spent way too much time on the trigger area just because it looks sick

Moonbogg wrote:Nice job. Any chance of a video?

Yeah I can make a video what do you want to see? Damage, pissed off neighbors...

Looks sweet, and some shooting vids would be a nice touch. I just want to say one thing though, with a gun like this, I think the sprinkler valve was a little overkill, the difference of performance between that and just a blowgun wouldn't be more than 30 FPS. As long as it's servicable though, it's good to know you can swap everything out.

I'd be interested to know how you calculated a 30fps difference between a sprinkler valve and no sprinkler valve...... Anyways it's probably overkill but it looks cool and dumps the air behind the piston wayyyyyyy faster than it really needs to.

It's a rough estimate. I'm just saying that it's like opening the floodgates to let in a fish.

Coodude26 wrote:It's a rough estimate. I'm just saying that it's like opening the floodgates to let in a fish.

You'd be wrong with the 30fps estimate by a very long shot.

It's all about speed, how fast the pilot valve can dump all the air. It's more like trying to push several hundred convicts out the prison gate instead of a hole in Andy Dufresne's cell wall.

I've had performance increase of around 30% over a blowgun and sprinkler valve. In fact, if you use a blowgun on a 2" piston valve that doesn't have o-rings and an average sized pilot volume , you'll be decreasing performance by a significant amount.

The minimum pilot valve for a 2" piston that doesn't have o-rings I would say is a 1/2" ball valve, and anything bigger than that is always better.

It depends a lot on the piston and pilot volume, but on average, I would say most 2" piston valves will barely open with a blowgun pilot valve, and a sprinkler valve could even double the performance.

GGDT gave me 163m/s for my golfball cannon with fairly accurate inputs from the top of my head. If I used a blowgun over a sprinkler valve, I get 69m/s, which as you can tell is a very, very significant difference.

Now, if your piston is o-ringed and your pilot volume that of a snickers bar, it wont make so much difference, but it'll still be definitely be worth it in my opinion to upgrade to a sprinkler valve.

I wouldn't talk out of your you-know-where without having the evidence to back up your claims.

MrCrowley wrote:your pilot volume that of a snickers bar

Is that what they call it in NZ?