Pneumatic Launcher Science Project

[Lentamentalisk]

I am going to make a pneumatic launcher of some sort for a completely open science project that i need to do. I want it to be fairly simple, yet consistent (not like a ball valve where it's ability depends on your agility on the lever,) and hopefully powerful.

So far i have decided to either launch tennis balls or golf balls, as they are easily reusable, though I am open to other ideas.

I am also hoping that i can find a way to make it on the small size i.e. not more that 5' long. That leads me towards some type of coaxial, but so far all of the homemade pistons i have seen here are complicated/tricky to get to work well.

I have an electric compressor who's pressure gauge goes up to 220psi, though it is quite old and may not go up that high any more, and I also have a shock pump good to 300psi.

links to a simple, well working piston valve (if I'm using golf balls or tennis balls i don't want to use a sprinkler because of their low flow,) or any comments will be greatly appreciated.

[iPaintball]

Mine's about as simple as they come:http://www.spudfiles.com/forums/my-new- ... 10669.html

[Lentamentalisk]

ok, so a few questions on that:

1) what kind of rubber thing is that attached to the "pill", and how is it attached?
2) how well does the piston slide in that T?


and one minor addition to the leading post, would it be worth it to take 2 sprinkler valves in parallel, or should i just go buy 2 of McMaster's 3/4" right angle Quick Exhaust Valves, which have a pressure rating of 145psi (I was kinda hoping to be able to take it a little higher, like maybe 200psi.)

[jackssmirkingrevenge]

As pointed out in this thread, wouldn't it be better to define aims for your project, or is this simply one of those "build something that works" deals?

[jimmy101]

To keep it simple, go with a sprinkler valve gun. Building your own valve is a lot more work and really won't get you any extra "brownie points" in a science fair project. So why add the complexity? The performance of a sprinkler valve is more than adequate. A homemade large bore valve will perform better but if the gun launches your ammo out of sight then what good is it for a science fair project? A generic sprinkler valve in a 5' or so long gun should have no problem lobbing a spud (golf ball, tennis ball ...) several hundred feet. Besides, the idea of a simple homemade valve that is also efficient is kind of contradictory.

A golf ball or tennis ball barrel would be nice but the parts can be hard to find. A sabot in a standard pipe diameter would be a bit easier for golf and tennis balls. Spuds are the easiest of all since they will work in any barrel diameter from 1/4" up to about 2", without the need for a sabot.

You really don't need (or probably want) pressure above about 100~120 PSIG. Generic shop compressors will get to that range. A bicycle pump will to without killing you with the effort (as long as the chamber isn't too big). A shock pump is really overkill for a science project and it requires that the gun can withstand the much higher pressures.

A coaxial gun is probably overkill as well and will require a homemade valve. Go with the sprinker valve and, to keep the total gun length to ~5', use a 12"Lx3"D chamber and a ~3.5'x1.5" barrel. Even with an unmoded sprinkler valve the gun should give muzzle velocities of more than 400 fps and ranges of several hundred feet. In other words, much much much more powerful than even a very powerful BB gun, and more powerful than a typical 0.22 cal rifle.

See also a similar thread at http://www.spudfiles.com/forums/science ... ter,0.html

[Hubb]

I take it that you only want to shoot something as far as possible and have it as loud as possible (to impress those who attend). Go with a burst disc or a triggered burst disc. It is about as simple and efficient as you can get.

As far as compact (less than 5 ft) it can be over / under, to compensate for the burst disc.

If you go coaxial, you may find it easier to build a diaphragm rather than a piston valve, especially if you've never constructed such a valve.

Anyway, that's my input. Good luck.

[Lentamentalisk]

thanks for the suggestions!

-Hubb017-
how do i make an activated burst disk? I have always been really into the idea of burst disks, as they are the fastest and cheapest, but i have never been able to think of a way to trigger it when i want it to trigger, rather than just pumping it till it breaks.

[noob of noobs]

I'd also recomend using a sprinkler valve or QEV like jimmy101 just since factory manufactured things are probably more consistent. Also, if you're short on field space like me (stupid suburbs...) then you probably don't want a big mosnter gun since finding your projectile downfield will be hard... But since it is small, a bike pump should suffice for pressurization.
Anyway, good luck!

[Lentamentalisk]

ya, im not just limited in field space, i am limited in that the po-po are not to excited about spudguns, so it cant look too gunny or be too loud. also it would need to be able to be unscrewed or something so that i can carry it on my bike, I cant drive to the place i launch, as its like 2mi over dirt roads, yet still the police found me once...

[jimmy101]

Lentamentalisk, you are limited in field space since anything over a couple hundred feet is difficult to see let alone measure the projectiles travel distance with any accuracy.

With a sprinkler valve gun it is easy enough to just unscrew the chamber and barrel from the valve.

[Hubb]

thanks for the suggestions!

-Hubb017-
how do i make an activated burst disk? I have always been really into the idea of burst disks, as they are the fastest and cheapest, but i have never been able to think of a way to trigger it when i want it to trigger, rather than just pumping it till it breaks.

http://www.spudfiles.com/spud_wiki/inde ... burst_disk

[DYI]

Triggered burst disks are amazingly powerful and efficient, but for your own good, don't use a TBD gun for a science project. Reload times are hideous, performance isn't always consistent (think premature firing), and set up time is really, really bad. And this is at normal, sane pressures. Cranking up the pressure to say, 300 psi with a shock pump will bring a whole host of new problems. They are great for power, but have all of the characteristics that you want to avoid in a science fair project.

Unless you have a whole day for firing, and at least one day before the firing day to fabricate and test disks, and cut gaskets out, plus a very patient audience, I would suggest that you follow Jimmy's idea. From my experience people are more entertained by a low powered launcher that can be fired and reloaded easily and quickly.

[Lentamentalisk]

thank you guys so much for the advice!

[Lentamentalisk]

can any of you link me to the highest flow sprinkler valve on the market?

[DYI]

The biggest sprinkler valves that I know of are 3". That would probably be the highest flow sprinkler valve. The difference between brands is usually negligible.