SpudFiles

An even easier piston is a rubber stopper you buy at the hardware store. The 3/4" ones are a good 3/4" piston.

warhead052 wrote:*facepalm* I really wish I got more pictures of the cannon I made for a friend. It used a 2" by 2' chamber, and a 3/4" QEV with a 1/4" blowgun, and a 2" by 2' barrel. I shot a nerf pocket vortex about 200 meters before it starting falling back to earth.

100m would be a better estimate. My V.A.L. 1.5" porting piston canon could only shoot a pocket vortex about 90m; they're far too light to travel much further.

like how far will I get outta a golf ball at 125 psi???

Short of using a 1.5" or larger piston valve, best you can hope for is about 250m-300m in distance and about 400fps in my opinion. Obviously, higher pressures will help a fair amount and it would be possible to get better performance than the figures above. Short of using high pressures, longer-than-average barrels and larger-than-average chambers will do little to increase performance.

A cannon of mine for comparison:
>1.5" galv. iron chamber 40cm long
>Golf ball barrel 120cm long
>3/4" QEV
>300PSI

Distance: ~300m
Velocity: Probably around 400-450fps

With a decent piston valved cannon you would be pushing about 600fps and 400-450m with a golf ball.

If you don't want to make a piston valved cannon, make a fuel metered combustion. You will out-perform a 1.5" piston valved cannon with a decent propane or MAPP metered combustion.

I built a simple ball valve 1 1/2 inch ball valve golf ball cannon for a friend. A ball valve is pretty slow opening but has excellent flow. The ball valve cost a packet but it was well worth it when a golf ball went at least 200 meters

jazzman56 wrote:A ball valve is pretty slow opening but has excellent flow

It has a high flow potential. In 99% of cases, the projectile will be long gone before the valve is open a decent amount.

I quickly modelled a ball valve cannon in GGDT and assuming the valve takes 400 milliseconds to open fully (which is normal I believe), the projectile is out of the 140cm barrel after only 35ms. The graph also says the chamber only has the chance to drop from 120PSI to 90PSI before the projectile is gone.

I'm not sure whether when valve position = 1.0 it means the valve has full flow, but when I look at the graph for this ball valve it gives a value of 0.09 after 35ms. The valve is at 9% flow when the projectile leaves the barrel?

Anyway, I don't mean to disrespect your cannon. My only intention was to provide some more information for the topic author to influence his decisions towards better valves or combustion cannons

My golf ball cannon could chuck a golf ball over 500 meters. You just can't do that with a sprinkler.

Im going to research a shit load today about piston valves and how they work and so on. I want to stay away from combustions for now until I have the pneumatics down.

mattyzip77 wrote:Im going to research a crap load today about piston valves and how they work and so on. I want to stay away from combustions for now until I have the pneumatics down.

Same here dude