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My second cannon

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My second cannon

Unread postAuthor: mlz3000 » Tue Nov 16, 2010 10:40 pm

This is my second cannon - the CAKE II.

It is intended to function almost identically to the CAKE I

The valve is a 1" sprinkler valve modded with a blow gun.

I tapped in a shrader for filling with a bike pump, and a 125PSI pop off for safety.



The main changes are as follows:

-The chamber is now 2" x 48" of PVC, resulting in about the same chamber volume, but now in an over/under design.

-All of the fittings are now pressure rated

-The tapped in fittings now go through two layers of PVC.

-The chamber has a 2" threaded outlet which I have an attachment to reduce to 1" for the sprinkler valve. The reason for this is that I am currently working on a 2" piston valve.



I have included the GGDT for launching a golf ball. Does it look like I entered everything correctly? The valve data comes from the GGDT website. The two things I wasn't sure about were the friction value, and whether or not I should change anything to account for the fact that I use wadding.



It still needs a paint job. I'm thinking black for the elbow and tee joints, and blue for the lengths of pipe.

EDIT: Changed the GGDT data to account for the wadding.

EDIT: Added damage pic
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Attachments
CAKE II.jpg
The cannon, alongside the two barrels. The longer barrel is 2"x55" for golf balls, and the shorter barrel is 2.5" x 36" for tennis balls
CAKE II GGDT(2).jpg
Edited the projectile data for the wadding.
CAKE II Damage pic.jpg
A wooden board (0.5-1") from twenty meters with a golf ball. I'll get some more damage pics when I find something that I can punch the golf balls all the way through.
Last edited by mlz3000 on Wed Nov 17, 2010 11:23 pm, edited 3 times in total.
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Unread postAuthor: Lockednloaded » Tue Nov 16, 2010 10:44 pm

I think it looks nicer than the last one, and much safer too. I'm glad you took the general forum advice and rebuilt, you'd be amazed how stubborn people are even when their well-being is at risk
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I love lamp
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Unread postAuthor: mlz3000 » Tue Nov 16, 2010 10:52 pm

I have noticed that! (I have been lurking a bit, and clicking the "random cannon" button often to find some information and inspiration.)

Once I found out that my cannon had not one, but two attributes which made it unsafe, I took it apart and I will never use it again. I can't imagine why someone would risk their well being by using an unsafe cannon. :?

Spudding may be fun, but it's nothing I would knowingly risk serious injury for.
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Re: My second cannon

Unread postAuthor: Ragnarok » Tue Nov 16, 2010 10:55 pm

mlz3000 wrote:The two things I wasn't sure about were the friction value, and whether or not I should change anything to account for the fact that I use wadding.

Friction is usually a fairly minor concern. A rough value will normally do.

As far as wadding... yes, definitely. You should increase projectile mass and diameter as appropriate. (If the wadding is good, near the full barrel diameter is a good bet for that value).

I don't know what your wadding is, but as a rough guess, I'd use 50-60 grams for the mass, and increase projectile diameter to 2".
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: mlz3000 » Tue Nov 16, 2010 11:09 pm

I use cut up pieces of an old dish towel for the wadding.


I'm going to fire it tomorrow at school for physics class, and I would like to have a rough estimate as to the range this will have.

The range formula without air resistance is muzzle velocity squared divided by the gravitational constant times the sine of twice the launching angle.

That math gives me a range of just over 8000 feet at a 45 degree angle. Does anyone know a way to get a number closer to the actual range I'll get? I don't know how much air resistance is going to reduce the range, but 8000 feet sounds like way too much.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 16, 2010 11:45 pm

You're doing quite well :)

The range formula without air resistance is muzzle velocity squared divided by the gravitational constant times the sine of twice the launching angle.

That math gives me a range of just over 8000 feet at a 45 degree angle. Does anyone know a way to get a number closer to the actual range I'll get? I don't know how much air resistance is going to reduce the range, but 8000 feet sounds like way too much.


Image

Air resistance has an enormous effect on projectiles, remember that it affects an object at a rate exponential to its velocity. Have you tried using GGDT's range calculator? It takes air resistance and projecitle density and drag coefficient into account and will give you a more reasonable estimate of range.
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Unread postAuthor: mlz3000 » Wed Nov 17, 2010 12:14 am

jackssmirkingrevenge wrote:Have you tried using GGDT's range calculator? It takes air resistance and projecitle density and drag coefficient into account and will give you a more reasonable estimate of range.


Wow, I didn't even know about that! Much thanks.

Ah, yes, using 0.3-0.4 as the drag coefficient(that's the range of Cd's for a golf ball I got from a quick Google), I get a 544-654ft range. That sounds much more reasonable. :lol:
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Unread postAuthor: Technician1002 » Wed Nov 17, 2010 12:39 am

I was going to guess about 600 feet on that simply knowing the range of my Marshmallow Cannon with the 1 inch valve at 100 PSI. You should be somewhere in the 600 foot ballpark. Due to wind resistance, your optimum firing angel is closer to 30 degrees instead of 45 degrees.

Please post your measured distances when you test it.


EDIT
Found my data. Depending on your valve coef, you may reach cosiderably farther than 600 Feet. You have a larger air chamber and larger valve seat.

My 1 inch valve was providing just short of 900 feet. Your valve seat is larger than 1 inch, but slightly lower effeciency due to the 1 inch valve design.

Dug and located my field day testing of some launchers.
The 100 PSI Marshmallow is the range of a golf ball fired at 100 PSI from my Marshmallow cannon. The 50 PSI shot was with a larger valve cannon with a 3 gallon chamber. The locatons were measured by GPS and directly entered into Google Maps.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 17, 2010 2:25 am

mlz3000 wrote:I use cut up pieces of an old dish towel for the wadding.


You might want to consider something more efficient, what's the discrepancy between barrel and projectile diameter?
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Unread postAuthor: mlz3000 » Wed Nov 17, 2010 8:42 am

A regulation golf ball is 1.680in, and the id of the 2" sch 40 PVC is 2.047in.

The towel seems pretty efficient to me. I can post a pic if you want, but it's pretty smooth, and doesn't seem to have much friction with the barrel. I use multiple layers, but I guess I can see where some air gets through.

I was talking with a friend, and he thought that a sabot sounded like a good idea.

What would you suggest as wadding? (Or sabot material, if I decide to go that route?)
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 17, 2010 9:32 am

mlz3000 wrote:What would you suggest as wadding? (Or sabot material, if I decide to go that route?)


Here's a relatively simple method I like to use, suggested for buckshot in the link but it will work for a single ball, it will provide a much better seal than loose wadding and can potentially be reused.
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Unread postAuthor: mlz3000 » Wed Nov 17, 2010 5:22 pm

Test firing today went well.

I was firing with a bit of wind at my back, and I could get Tennis balls to go about 300ft (from endzone to endzone on the football field).

The golf balls went considerably farther, so much so that I couldn't get an accurate measurement of the distance, but it seemed to be at least 450 feet. I'm going to try to find somewhere with a large enough flat area that I can get an accurate distance measurement.
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Unread postAuthor: Technician1002 » Wed Nov 17, 2010 9:05 pm

Since you are using screw on barrels, you may wish to consider using a golf ball size barrel for launching them without a sabot or wadding.
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Unread postAuthor: mlz3000 » Wed Nov 17, 2010 9:35 pm

I have considered that. Based on how nice it is to use the specialty tennis ball barrel, I figured I would order one of these. I'll probably order it when my piston valve is complete, at which point I'll be ready for some serious performance.
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