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Science project help

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Science project help

Unread postAuthor: squidman » Mon Sep 24, 2007 8:03 pm

I'm a 12th grader in physics and i've been making comubustion guns for about a year and i was thinking about doing a pneumatic cannon for a science project, but i don't really have a good knowledge of the actual science that goes into a cannon so i have a few questions.

1. How do i find a C:B ratio and what is it?

2. What would be a good C:B ratio for a cannon that is shooting golf balls?

3. How do i find muzzle velocity and what is it?

I'm thinking of building a cannon with interchangeable barrels of the same diameter but at different lengths to find which barrel would get me the best distance and muzzle velocity.

Maybe a 3"x18" chamber???
I really do need some help and any suggestions would be well appreciated.
Thanks
Thanks
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Unread postAuthor: JDP12 » Mon Sep 24, 2007 8:05 pm

wow. squidman. let me give you three suggestions

1. Spudwiki
2. Google.
3. Search
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"Some say his pet elephant is pink, and that he has no understanding of "PG rated forum". All we know is, he's called JSR. "
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Unread postAuthor: thespeedycicada » Mon Sep 24, 2007 8:13 pm

search in fact you dont need to search use the wiki or better yet read a few posts of others before you make a stupid pointless one like this its really not that hard its basic knowledge you could learn in ten minutes of reading the forums/searching jeeezz.
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Unread postAuthor: iPaintball » Mon Sep 24, 2007 8:22 pm

Since you are new here, I'll help you out.
1. The Chamber:Barrel ratio refers to the volume of your chamber in relation to the volume of your barrel. Ideally, 1.5:1 is most efficient, but you can take it all the way up to 4:1 without losing power. If you want to find it, divide your barrel volume by your chamber volume.
2. Mentioned above.
3. Muzzle velocity refers to the speed at which the projectile is traveling as soon as it leaves the muzzle of your gun. This can be found using a chronograph.

By the way, welcome to SpudFiles! I hoped I helped
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Unread postAuthor: squidman » Mon Sep 24, 2007 8:45 pm

thanks iPaintball, i was begining to think everyone on this site was an arrogant douche bag.
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Unread postAuthor: thespeedycicada » Mon Sep 24, 2007 8:52 pm

Sorry dude but between the two other posts like this today,me having the flu,and losing the piston for my new gun i just had no patience sorry for taking all the crap i had today out on you.
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Unread postAuthor: JDP12 » Mon Sep 24, 2007 8:58 pm

umm hey now squidman. Same as speedy, I've had a really, really crappy day. I didnt mean to be rude, it's just that this can be answered fairly easily. Sorry for getting a little irritated
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Unread postAuthor: Redcoat » Tue Sep 25, 2007 4:35 am

Well to work out muzzle velocity look here it is a free non-electronic way to measure muzzle velocity from hang time.

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Unread postAuthor: jackssmirkingrevenge » Tue Sep 25, 2007 5:18 am

I'm thinking of building a cannon with interchangeable barrels of the same diameter but at different lengths to find which barrel would get me the best distance and muzzle velocity.


By changing the barrel length, you're altering the chamber:barrel volume ratio. What exactly are the objectives of your science project? If you fix what you're trying to achieve your project will be more valid and be carried out in a more scientific manner.

For example, say the aim was to investigate how the speed of the golfball changes with barrel length, you would need a fixed chamber volume and valve at a fixed pressure, and barrels of various lengths. You'd also need a way to measure the speed of the golfball. There are relatively cheap meters you can buy but if you don't want to go through the expense, you can set up your own arbitary measurements, for example you can set up a box'o'truth style setup using sheets of thick cardboard and judge power by the amount of sheets each shot penetrates.

The above is just an example, give us some detail on what you want to achieve and these arrogant douchebags will be more than happy to help :)
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Unread postAuthor: psycix » Tue Sep 25, 2007 10:00 am

People on spudfiles are always ready to help, but they may get angry when you ask questions that can be found too easily by a horde of noobs who want to have us do the thinking for them.

So if you use search on the forum and spudwiki and google, then you will find what you need 9 times out of 10. If you really cant find it:
We want to help you more then ever :)

Welcome to these forums.
Enjoy your stay on spudfiles
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Unread postAuthor: williamfeldmann » Tue Sep 25, 2007 10:26 am

Squidman, I would like to know more about your project and/or what it is you would like to do with the project.

Jack talked about one potential project. Another might be comparing valves (granted we know each valves performance, but it would make a good project anyway for new people). Yet another might be using different barrels and possibly using a rifled barrel, testing accuracy and range. Or you could do all three, since cost is not really that prohibitive, 4 GB barrels might cost a bit, maybe $40 total, but you only need one chamber. A ball valve will run maybe 5 bucks, sprinkler 20 bucks by the time you mod it, you can build a barrel sealing piston in a 2" tee for under $15.

Depending on your school, they might even fund parts of the experiments, like buying supplies, some schools have special funds for doing so, ask your teacher, worst that can happen is they say no. They also might have a chronograph, just ask the teacher. Also, you would have access to the football field for a perfect testing range.
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Unread postAuthor: squidman » Tue Sep 25, 2007 6:23 pm

My project is about finding the best barrel length for a set chamber. By best barrel i mean one that gets me the best distance at a set angle, the highest muzzle velocity, and maybe power(i like the box of truth thing jack mentioned)


I was planning on using a modified sprinkler valve(which i have never done) and a 3"x18" chamber. With my new knowledge of C:B ratios i have figured that a 6' barrel will give me a 1:1, 4' will give me a 1.5:1, 3' will give me a 2:1, and a 29" barrel will give me approximatly 2.5:1. I will find which of these ratios is the best for firing a golf ball.

I am using a sprinkler valve so the judges won't have any argument of human error, like they would if i use a hand turn ball valve. Also what size valve would be best for this cannon??

I know i need a 1 1/2" size barrel. But is sdr 21 or 26 hard to find?? i live like an hour from the nearest lowes or home depot, but could i find it there?? and do i really have to sleeve it with a 2" pipe?? is that just a precautionary thing, or is it necessary??

Oh and i didn't mean anything by the other comment.

Thanks guys.
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Unread postAuthor: thespeedycicada » Tue Sep 25, 2007 6:29 pm

a 1 inch sprinkler valve will be the easiest to find anything larger is a total pain.i dont think you can always find sdr 21 at home depot but only use it as a golfball barrel never as a chamber one more thing sleveing is only a method of making a golfball barrel you dont need to if you can find sdr 21.
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current projects: co-axial piston valve.Status DONE!
S.P.E.C.S update mk 1 construction begining in febuary all the maths for it are done plans are drawn up and parts are listed.
NEXT project:auto piston valve.
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 25, 2007 11:16 pm

By best barrel i mean one that gets me the best distance at a set angle, the highest muzzle velocity, and maybe power


All these factors are a function of the velocity - since you're not changing the weight or shape of the projectile, or the angle of firing, and assuming atmospheric conditions are similar, the ball which goes the furthest or penetrates the most sheets of cardboard has the highest muzzle velocity. If you're going to do a lot of tests, I think you'll find that measuring distance will be cheaper than all the cardboard you'd have to waste ;)

longer barrel = more power is only true until you reach a certain barrel length, after that the power actuall starts to go down. If I were you I would use a smaller chamber (5" of the pipe you're using for the barrel, makes ratio calculation easier as you just have to measure the relative lengths of chamber and barrel plus it helps with economy too ;) ) and start out with a very low ratio, say a 5' barrel to give you a 1:12 ratio, then start shortening the barrel. Instead of having a lot of interchangable barrels, why not just have on long barrel and progressively hack it down in 5" increments (but make sure you take several measurements per length to make sure your results are scientifically valid).
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Unread postAuthor: clide » Wed Sep 26, 2007 1:06 am

Unless you are using a low pressure then the your barrel will be very long relative to the chamber before you will start to see a decrease in performance. As jack mentioned, a small chamber would help by keeping everything a manageable length.

You probably won't be able to find golf ball barrel at a Lowes or Home Depot, but check some irrigation or plumbing supply stores. For scientific tests it is really nice to have because of the consistency of golf balls in both weight and size. You don't HAVE to sleeve a golf ball barrel, but it is usually good practice. If you barrel is long then it might start flopping around on you.
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