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Golf Ball hop-up

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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Golf Ball hop-up

Unread postAuthor: AngryChauncey » Sat Oct 24, 2009 5:34 pm

This is a very quick and preliminary method of adding hop-up to any launcher that shoots round objects like golf balls or super balls. It is a 2" cpl. with a machine screw going through it, and threaded onto the machine screw is a beveled hard rubber washer that I found in the hardware store around the bathroom faucet section. The cpl. is simply put on the end of the barrel, thus giving backspin. The screw makes it easily adjustable. To my amazement, the golf ball (that I've calculated to go over 550m at 100 psi using the equation r=[v^2/g]x[sin2theta]) did not rip off the washer. Unfortunately since I am in high school AP physics, I have no idea how to calculate the range with the backspin factored in.
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This is what she looks like.
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This view shows the screw.
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Unread postAuthor: Technician1002 » Sat Oct 24, 2009 7:15 pm

Might wish to put that in a metal fitting. PVC doesn't survive repeated impacts.
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Unread postAuthor: AngryChauncey » Sat Oct 24, 2009 7:26 pm

Yeah I fear it's only a matter of time before it tears itself apart. I'm going to try and use my neighbor's lathe and make a similar fitting out of aluminum.
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Unread postAuthor: Technician1002 » Sat Oct 24, 2009 8:12 pm

A better bet is s strip of foam tape glued inside the barrel for the last couple feet. There is no impact and the side with higher friction will spin the ball. It is less likely to change the aim drastically.
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Unread postAuthor: AngryChauncey » Sat Oct 24, 2009 9:17 pm

Wouldn't that affect the power significantly? I could also see that getting torn out of the cannon on the first shot.
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Unread postAuthor: mark.f » Sun Oct 25, 2009 6:00 am

Very good. Also, simply a piece of 1/8" thick rubber gasketing can be glued into the coupling, like clide did on one of his golfball cannons.

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Re: Golf Ball hop-up

Unread postAuthor: Ragnarok » Sun Oct 25, 2009 6:42 am

AngryChauncey wrote:That I've calculated to go over 550m at 100 psi using the equation r=[v^2/g]x[sin2theta]) did not rip off the washer. Unfortunately since I am in high school AP physics, I have no idea how to calculate the range with the backspin factored in.

I wouldn't fuss about calculating with the backspin yet. You've not yet accounted for drag, which is a far bigger concern.

Suffice to say, you're not going to see that kind of range even with the backspin. The furthest I've heard of a golf ball going (without a tail wind) is about 450-500 metres, and it was doing Mach 1.5 at the muzzle.
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Does that thing kinda look like a big cat to you?
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Re: Golf Ball hop-up

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Unread postAuthor: AngryChauncey » Sun Oct 25, 2009 6:36 pm

Well Ragnarok a professional golfer can hit at the most 450 meters, and they are not reaching mach 1.5. The ball of a pro golfer leaves the tee at an average of 70 m/s. I calculated the velocity of my launcher with photo gates, and yes my calculation does not factor in drag, but golf balls experience little drag because of the dimples. Don't make assumptions based on things you don't know.
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Unread postAuthor: Technician1002 » Sun Oct 25, 2009 7:20 pm

AngryChauncey wrote:Well Ragnarok a professional golfer can hit at the most 450 meters, and they are not reaching mach 1.5. The ball of a pro golfer leaves the tee at an average of 70 m/s. I calculated the velocity of my launcher with photo gates, and yes my calculation does not factor in drag, but golf balls experience little drag because of the dimples. Don't make assumptions based on things you don't know.


Do you have a reference. I only found these;
http://www.wellsphere.com/exercise-article/how-far-can-you-hit-a-golf-ball/
http://www.academy.com/index.php?page=content&target=sports_tips/golf/how_far
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Unread postAuthor: AngryChauncey » Sun Oct 25, 2009 7:32 pm

In the second link it says, "Many players hit the ball a lot farther with each club, while some don't hit it quite as far." Take a look at this link: apparently I fell short with my estimate, with 515 meters being the longest. I wasn't talking about amateur golfer's average drive distance, I was talking about the LONG BOMBS to make a point.


http://www.travelandleisure.com/article ... d-drive/1/


Also this is one of the moderator's (MrCrowley) quotes regarding someone saying they shot a potato 1/2 a mile.
Scroll down to the bottom of this URL and you can see this response:
http://www.spudfiles.com/forums/the-hat ... 18972.html



Nice cannon, well built. Considering building my own one now, why not ya know :D

The distance seems sketchy to me, i've maxed out 2" housed piston valved launchers with 1.5" x 5' barrels launching golf balls and frozen potatoes at about 450m at over 120 PSI. That's about 1500 feet or about 490 yards. Using HGDT with this cannon's specifications, I get a distance of over 1100 feet, can't seem to do anything that's not drastic to get it to go above 1500 feet, let alone 2600 feet.

Sure piston valves have less flow and 'open' slower, but i'm using more pressure and potatoes aren't exactly the most aerodynamic projectile and it's not like you're a few hundred feet off, this is about 1500 feet.
BTW, you can download HGDT from here:
http://thehalls-in-bfe.com/HGDT/
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Unread postAuthor: Ragnarok » Sun Oct 25, 2009 7:46 pm

AngryChauncey wrote:Don't make assumptions based on things you don't know.

So, you're saying the fact I can write a simulator that accurately and reproducibly matches real world ballistics must be a fluke chance. The fact that most forum regulars will happily trust what I say on matters of ballistics is a mistake. The thousands spent towards studying engineering at university would be a waste, and the hundreds, if not thousands, of hours I have spent trying to learn ballistics have all gone down the drain as well.

... or perhaps that's a whole bunch of things you didn't know and made an assumption about.

You're also making the crucial error of assuming yards and metres to be interchangeable.

But golf balls experience little drag because of the dimples.

Drag Coefficient of a golfball: ~0.3.
While this is less than a normal sphere (or at least, a relatively "rough" sphere of 0.4-0.5), it does not qualify as "little drag", particularly given that its mass is so low.

Golf balls have a ballistic coefficient of around 100 kg m<sup>-2</sup>. At any real velocity, you can't start to even begin to consider drag to be somewhat negligible until you're dealing with values of 5000+ kg m<sup>-2</sup>, and preferably at least 10000 kg m<sup>-2</sup>. Even then, I wouldn't be so naive as to do such a thing.

A professional golfer can hit at the most 450 meters

A drive like this is utterly dependent on weather conditions (most importantly, a very good tailwind), the right backspin, and there is absolutely no guarantee of it happening. Most professional golfers have an average drive of about 250 metres, a value that is of far more use to us than a wishy-washy couple of times in a professional career distance (which is very unlikely to be 450 metres. Many never manage even 400.)

I take it you're probably not familiar enough with the subject of ballistic drag to have done the sensitivity studies that I've done, but the simple fact of the matter is that golf ball range (and indeed, the range of anything with relatively poor ballistics) is very much a matter of diminishing returns. Moderate velocities will go a respectable way, but increase that velocity, and you will be presented with less and less increase.

~~~~~

I assure you, until you have accounted for drag, then don't muck around with trying to account for lift.
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Unread postAuthor: AngryChauncey » Sun Oct 25, 2009 8:01 pm

Congratulations you are an engineer. I keep saying that I'M NOT TALKING ABOUT AVERAGES, I'm talking about a max range.. So you've calculated a max range of a golf ball, (I presume it's less than 515 meters) and that is supposed to prove wrong every distance beyond that ever achieved by a golf ball in the history of the universe? Just because you can spend money, doesn't mean that you can't be wrong about something.
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Unread postAuthor: Ragnarok » Sun Oct 25, 2009 8:28 pm

AngryChauncey wrote:Congratulations you are an engineer.

You're not very good with these assumption things, are you? I remain a way from being qualified. :tongue3:

So you've calculated a max range of a golf ball and that is supposed to prove wrong every distance beyond that ever achieved by a golf ball in the history of the universe?

Nope, never said that. For one thing, my calculations don't figure for tailwinds (mostly because they're entirely unpredictable), which are the main cause of long golf drives. But in still air, a 300 metre drive would be really, really pushing it. Any range beyond that calls for assistance from the wind.

A good pneumatic can put a golf ball in the realm of 400 metres (I will be honest, and say I think MrC's distances are a mite optimistic, but I suppose the prevailing wind direction for him could be a tail wind, which would make it feasible).
It takes something obscene to get things 500 metres in still air.

Anyway, what I'm trying to tell you is:
1) That your "drag-less" figure doesn't tell you anything useful.
2) That drag is a far more important consideration than lift. Indeed, you can't even meaningfully calculate lift without working out drag first.

I keep saying that I'M NOT TALKING ABOUT AVERAGES

Since when does saying something once count as "keep saying"?

Anyway, I've "kept saying" (in the same sense) that it's the average that's important, not the freak once in a lifetime super drives that where the golfer has found some luck and is daft enough to be golfing in a force nine gale.
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Unread postAuthor: AngryChauncey » Sun Oct 25, 2009 8:44 pm

Okay. I know that calculations in a vacuum have really no practical relevance when it comes to projectile motion, I know that my calculations aren't accurate, but when I see that ball come out of the launcher, (if I see it at all) it looks like a hell of a lot more than 300 yds. I am an aspiring engineer myself and I know that I lack the experience and know how to make a good estimate about projectile ranges, and that yes, 550m is probably too far. All I was trying to say was that a golf ball can go damn far, especially out of a cannon.
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Unread postAuthor: Technician1002 » Sun Oct 25, 2009 9:29 pm

This reminds me of range testing my t shirt cannon. I was having difficulty reaching 400 feet with a rolled up shirt. On a windy day, I got one over 500 feet. A tailwind really helps.
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