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range estimates for TB gun

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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range estimates for TB gun

Unread postAuthor: FishBoy » Tue Dec 16, 2008 8:44 pm

This is a design for a commisioned tennis ball gun I will be building in a few weeks, pretty simple & nothing really out of the ordinary, but anyone got any good guesses as far as range?

edit- forgot to upload pic
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Unread postAuthor: starman » Tue Dec 16, 2008 9:52 pm

It is my opinion that you will be wasting effort and resources building a 2 tank unit in this configuration unless your customer has insisted on this design. I would recommend 1 3" x 20-28" tank and 1 sprinkler. You really won't be able to use any more power for distance shooting a tennis ball.

The main reason is distance will only be so far no matter how powerful cannon you have...you're lookin' at the 200 - 300 yrd range in the best conditions. They are like shooting ping pong balls...the drag to mass ratio is just too high..and they are that way by design.
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Unread postAuthor: cheeseboy » Tue Dec 16, 2008 10:07 pm

yeah I agree with star man 200-300 yards but that's being a bit optimistic, I am estimating you're using about 100psi? and yeah switch to one chamber, because 2 sprinklers hooked up to 1 pilot causes more air to be released before firing, this in turn should cause slower opening times, so I think 1 chamber is better as it will also save you money on fittings. how much do you get paid to make these anyway?
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Unread postAuthor: ALIHISGREAT » Wed Dec 17, 2008 4:45 am

tennis balls have a drag coefficient of like 0.8, compared to 0.5 of a regular sphere and 0.2-0.3 for a golf ball. so you won't be getting too much range out of that.
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Unread postAuthor: Ragnarok » Wed Dec 17, 2008 4:55 am

ALIHISGREAT wrote:so you won't be getting too much range out of that.

Actually, a regular sphere is about 0.4, and a tennis ball is actually about 0.3, about the same as a golf ball.

The fuzz has some similarity aerodynamically to the dimples on a golf ball. However, tennis balls are not as optimised as they could be in an attempt to slow down the balls to make the game playable.
The trouble with a tennis ball is not it's drag coefficient, but it's large diameter and low mass, which gives it poor ballistic performance.

Good for what it was designed for, poor for range.

~~~~~

Personally, I'd have the sprinkler valves on the other side of the elbows so the cannon wasn't so wide. It will add dead space, but add practicality.

That of course assumes you are set on the 2 tank/2 valve design.
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Unread postAuthor: FishBoy » Wed Dec 17, 2008 9:32 pm

well, let me change my question, what would be a way to keep the size and price about the same but make it better (in any way)?
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Unread postAuthor: starman » Wed Dec 17, 2008 9:59 pm

Ragnarok wrote:
ALIHISGREAT wrote:so you won't be getting too much range out of that.

Actually, a regular sphere is about 0.4, and a tennis ball is actually about 0.3, about the same as a golf ball.


I disagree with your tennis ball cd number being as low as .3. I've never seen a tennis ball cd list that low...the numbers I've seen have varied from .5 - .8 or so. Care to give us your sources for that? .3 is down in the golfball range.
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Unread postAuthor: jook13 » Wed Dec 17, 2008 10:13 pm

well, let me change my question, what would be a way to keep the size and price about the same but make it better (in any way)?


The first thing that comes to mind is piston valve. You would get MUCH better flow than those sprinklers, plus a piston can be made for less money.
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Unread postAuthor: FishBoy » Wed Dec 17, 2008 10:21 pm

I know that, but I'm sticking with sprinkler valves on this one, I have made pistons before.
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Unread postAuthor: roboman » Wed Dec 17, 2008 10:26 pm

Try racquetballs! They're about the same diameter as a tennis ball, and they are much more aerodynamic.
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Unread postAuthor: FordGtMan » Thu Dec 18, 2008 12:40 am

I doubt racquetballs are aerodynamic considered how much they slow down when being hit. They are meant for extreme drag to make the match fair on the first serve :lol:
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Unread postAuthor: jimmy101 » Thu Dec 18, 2008 12:23 pm

starman wrote:
Ragnarok wrote:
ALIHISGREAT wrote:so you won't be getting too much range out of that.

Actually, a regular sphere is about 0.4, and a tennis ball is actually about 0.3, about the same as a golf ball.


I disagree with your tennis ball cd number being as low as .3. I've never seen a tennis ball cd list that low...the numbers I've seen have varied from .5 - .8 or so. Care to give us your sources for that? .3 is down in the golfball range.


The SpudWiki Ammo page lists the Cd as 0.283 (ya, and it's accurate to three sig figs :D ) The Cd was calculated from the terminal velocity of 70MPH (100 FPS).
http://www.cord.org/uploadedfiles/CTNJune2002.pdf
http://www.gantless.com/paper.html

http://www.acoustoscan.com.au/ISSS/Free ... s%20II.pdf
Lists the Cd as ~0.6.
http://www.aeromech.usyd.edu.au/15afmc/ ... C00075.pdf
Lists the Cd as about 0.6. At speeds well below the terminal velocity some TBs have Cd below 0.4. At about 80% of the terminal velocity and above the Cd stabilizes at about 0.6. This last reference is probably the most difinitive.

So, it looks like a Cd of ~0.6 is suitable for speeds above 70 FPS.
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Unread postAuthor: FishBoy » Sun Dec 21, 2008 8:58 am

Sorry for kicking up a slightly dead topic but I'm trying to finalize this design.

2 questions:
1- Will there be a significant difference between using 2 sprinkler valves or 1?

2- Could I put an adjustable hop-up (machine screw) on this/would it be effective?
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Unread postAuthor: roboman » Sun Dec 21, 2008 11:40 am

1. You might get a higher flow rate, but I'm not sure. A manifold would probably work just as well.

2. I'm not sure how much friction it would provide, and if you're using a TB barrel, the tennis ball wouldn't spin very much, due to the high amount of friction in the barrel itself. The fuzz on the ball would most likely get caught in the machine screw, and there is even a possibility that the ball would get stuck in the barrel!
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