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Cross Golf Ball - could be perfect ammo ? (Read 25784 times)
Curious Aardvark
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #30 - May 26th, 2008 at 7:11am
 
most of the spin is applied by the pouch.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #31 - May 28th, 2008 at 2:14am
 
[quote author=curious_aardvark link=1189503844/15#26 date=1208444362]nope - they definitely orient point forwards. It's actually using the same principle as a gyroscope. Because you have  athe main mass spinning central to the main body it uses gyroscopic forces to self orient. You can see this with bi conical shaped rocks as well - they fly point forwards and very straight.

Right just for aussieslinger - here are a couple of better pics of a crossgolf ball a normal golf ball and an egg :-)
You can see here that the cross golf ball is actually more like a normal golf ball squashed into a biconical shape - and both have a much smaller volume than an egg :-)
[/quote]
C-A has been kind enough to lend me a golf-cross ball to measure and evaluate. Im not sure if the pictures carry across in the above quote but if not just go back and have a look to refresh your memories.

I measured and weighed the ball prior to giving it a good tryout. The manufacturers have most likely attempted to stick to the mass and volume of a standard ball and merely altered its shape.

Golf-Cross Ball  Length = 58.3 mm   Diameter = 39.2 mm   Regular Gof Ball   Diameter = 42.6 mm

Both types weighed around 45 grams and had a volume of around 40 ml. (cubic centimetres)

(For comparison, a 55 gram egg, L= 54.6 mm, Dia= 42.0 mm,  Vol.= 50 ml.)

Here is a link to a good physics based explanation of why golf balls with dimples fly further than ones without despite the fact that they actually increase drag. In essence it works because a golf ball is hit so as to have a very high amount of backspin which creates lift. The dimples accentuate this effect.

http://math.ucr.edu/home/baez/physics/General/golf.html     (Also look up Golf Ball in Wikipedia)

With biconical or ovoid projectiles backspin can't be used or the projectile would "end over end" in flight. Therfore spin must be axial and acts to stabilize the projectile much the same as rifle bullet. So for slinging projectiles it would probably be better not to have the dimples, merely a smooth surface.

I tried to keep the actual throwing test as objective as possible by alternately using the Golf-Cross ball and a regular ball and at least attempting to sling with the same amount of force.

The first few shots were not particularly successful, the placement of the ball in the pouch and hand position during the release is critical and if released badly the ball will not inevitably self orientate. I threw one or two where it flew through the air completely vertically spinning like a top. I also had a couple that actually spiralled in flight. However after only a few shots I got it working.

As expected it does go well and the first thing I noticed was the path was distinctly more parabolic than that of a golf ball with much less sudden drop off. You can see the axis of the ball changing as it travels along its trajectory so it's always point forward with the air flow even around it. Unlike C-A I found that each shot with the Golf-Crosser went further than the regular ball, but not a lot further; no more than 10% extra. As far as accuracy itself, if thrown well it certainly went straight because a small amount of side spin will be overcome when the ball self orientates. After that it goes completely straight. Again not heaps better than an ordinary ball thrown with no side spin.

So whether you find the Golf-ross ball to your liking depends a lot on your slinging style. If you routinely generate lots of backspin then it's unlikely you'll like them much. For rifle spin slingers they are promising. Like all golf balls I find them a little too light; but virtually indestructible so should last forever, but very expensive if you sling in ball losing prone places.

Used as mould for concrete projectiles it should be very good. As to whether it's worth the trouble and expense of acquiring one rather than using an ordinary egg or an Easter egg is debateable.

Cast in lead they would be extremely heavy at almost exactly a pound in weight.

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Re: Cross Golf Ball - could be perfect ammo ?
Reply #32 - May 28th, 2008 at 10:58am
 
Nice post Aussieslinger.

One (or two) questions.
How far were you actually throwing these?  When you compare the distances is that with the spherical ball thrown with backspin or rifle spin?

Quote:
Hmm. Although there is definitely friction between the pouch and the projectile upon release, I would suggest that by far the strongest source of rotational momentum is the rotation of the sling.

I don't think so. The spin rates we observe seem to me to be far too high to come just from that.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #33 - May 29th, 2008 at 6:55am
 
wanderer wrote on May 28th, 2008 at 10:58am:
Nice post Aussieslinger.

One (or two) questions.
How far were you actually throwing these?  When you compare the distances is that with the spherical ball thrown with backspin or rifle spin?

Quote:
Hmm. Although there is definitely friction between the pouch and the projectile upon release, I would suggest that by far the strongest source of rotational momentum is the rotation of the sling.

I don't think so. The spin rates we observe seem to me to be far too high to come just from that.


I tried the balls in a couple of different parks so initially had to keep the throws down to around 70 - 80 m. as I was scared of losing the ball in the surrounding bushes. In another park throws to a max. of 150 m or so. I'm not a particularly strong distance slinger but if I was ever to top 200 m the golf cross ball would be the one I would do it with.

By using multi-coloured tennis balls I have been able to observe that I always throw with essentially a rifle spin (when throwing Fig.8 or simple overhead). Additionally the ball always breaks to the right when it hits the ground which would be consistent with it spinning clockwise, from my point of view. That's probably why my round golf ball shots don't go as far. They don't get the benefit of the backspin generated lift and have a lower sectional density than the GX balls.

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Re: Cross Golf Ball - could be perfect ammo ?
Reply #34 - May 30th, 2008 at 5:48pm
 
Whereas the rotation of the pouch imparts spin to the projectile the greatest effect comes from the pouch on release, otherwise all overhand throws would impart topspin and only underarm styles would impart only backspin. In fact the opposite is generally the case with overarm casts more likely having backspin and underarm shots leaving the pouch with marked topspin as they roll forward out the pouch.

In a typical Fig.8 shot just prior to the instant of release, with a speed of 45 m/s and an effective radius of around 1.2 m or so, the pouch and stone are rotating forward at a shade under 360 RPM. Yet judging from the pitch of whirring stones as they fly of into the wide blue yonder, they may be spinning as fast as 50 revs/sec. (even faster in the case of very small stones) Also the plane of rotation can be in just about any orientation. In some cases with a particularly narrow grip, where consistency is harder to achieve, it can even vary from shot to shot.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #35 - May 30th, 2008 at 10:35pm
 
Please correct me if I'm wrong, but did I not read earlier that the dirrection your hand is facing on your release dictates the spin?  I believe that it was that if your hand was facing forward on release it gives a "rifle" spin.  I tried searching for the thread, but couldn't remember what exactly what was said...  I typically cast with my palm facing in toward my shoulder, and that seems to impart a wicked backspin judging from how tennis balls react when they hit the ground.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #36 - May 31st, 2008 at 1:15am
 
BrianGrubbs wrote on May 30th, 2008 at 10:35pm:
Please correct me if I'm wrong, but did I not read earlier that the dirrection your hand is facing on your release dictates the spin?  I believe that it was that if your hand was facing forward on release it gives a "rifle" spin.  I tried searching for the thread, but couldn't remember what exactly what was said...  I typically cast with my palm facing in toward my shoulder, and that seems to impart a wicked backspin judging from how tennis balls react when they hit the ground.  


Yes you are right, I should have put more of a qualification on it, as the comment is based on my personal experience and may vary a bit depending on how any given slinger holds his sling. Of course the spin is caused by the forces put on by the pouch and not the hand directly and it is the actual orientation of the pouch at release that is critical.

The pouch does not release the projectile instantly or evenly. When the release cord is let go that side of the pouch opens and allows the projectile to roll out which imparts very rapid spin independent of the initial rotation of the sling. You can readily observe this by dangling a loaded pouch well clear of the ground and merely letting the release cord go. Note how quikly the projectile is spinning as it falls to the ground under only gravitational force. When subjected to the much higher centrifugal forces generated during an actual throw this spin is correspondingly faster. To get "rifle spin" the pouch needs to be moving side-on to the direction of motion at release. That way the spin is imparted axially as when footballers, both in American football and in Rugby, throw the ball.

Because the pouch is on the ends of fairly long pieces of flexible cord, any small change in hand orientation is not immediately transferred to the pouch, especially so if the cords are held in a narrow grip. So to get the final pouch orientation that you want you may have to experiment around a bit with both the way you release, and with the way you hold the pouch at the commencement of your throw. If you look at Mark Weaver's video in "Guides and Articles", you will see he holds the pouch so that the strings are orientated vertically, ie. the release cord is above the retention. Similarly his right thumb which grips the retention cord is orintated so the nail is upward, ie. his wrist is vertical. I prefer to start with the pouch held horizontally so the cords are side by side. My release is palm forward, similar to an ordinary throw, so that with follow through it finishes palm down. That way the ball comes out of the pouch cleanly and I get far fewer instances where the projectile "rolls down the cord" on release.

I stress that all of the above is merely by way of explanation not necessarily recommendation. Experiment and see what suits you, especially as what you call wicked backspin is generally seen as an asset rather than a liability because you will get greater distance with it than without. Verbal explanaions are always difficult so if anything is unclear please let me know.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #37 - May 31st, 2008 at 8:03am
 
Aussie wrote on May 30th, 2008 at 5:48pm:
In a typical Fig.8 shot just prior to the instant of release, with a speed of 45 m/s and an effective radius of around 1.2 m or so, the pouch and stone are rotating forward at a shade under 360 RPM. Yet judging from the pitch of whirring stones as they fly of into the wide blue yonder, they may be spinning as fast as 50 revs/sec.


You are correct, of course. I hadnt spotted that. Curse my feeble brain!

I wonder if the staff-sling could benefit from a small redesign, mounting the cords side by side on a Y shaped end, similar to the design of an elastic slingshot? That way you would get a very consistent release with rifle-like spin. Would the accuracy improve?
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #38 - May 31st, 2008 at 10:01am
 
Sorry but I don't know, I have no experience of staff slings. However the key to accuracy in any shooting device is consistency, everything as close as possible to exactly the same from shot to shot. So my feeling is that there would not be a marked difference as even though the orientation of the spin would be altered I am not sure if there would be any inherent improvement in consistency. Nevertheless a small amount of experimentation is worth any amount of theorization. I would love to know what you find.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #39 - Jul 17th, 2008 at 9:47pm
 
I'll try again...
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #40 - Jul 17th, 2008 at 10:21pm
 
as far as casting them/molding try some shape lock of friendly plastic http://www.stewmac.com/shop/Tools/Clamps,_support_tools/Friendly_Plastic.html
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #41 - Jan 31st, 2010 at 11:19am
 
BUMP
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #42 - Apr 20th, 2011 at 4:41am
 
Hello two years ago I tested some of these balls at long distance, and I didn’t almost the same distance that normal golf balls. Think that the sling shots objects normally in the “three angle on movement”  , flat angle, vertical angle, and sagital I don’t  know the name in English , So I think this one is a bit big for throw because at the beginning it spots lot of air. There is a moment during the flight of the object that lose rotation  and the shape of the golf ball can help aerodynamic but you have lost power at the beginning when the ball get out of the sling.
Roman slingers where using the bullets and they had the same problem but the bullets where smaller and heavier in respect to the size.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #43 - Apr 20th, 2011 at 3:41pm
 
I would have with pleasure such a ball.
I would pour him to me in lead.
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Re: Cross Golf Ball - could be perfect ammo ?
Reply #44 - Apr 21st, 2011 at 12:20pm
 
Unfortunately I only had the one crossgolf ball. Last we heard of it aussie posted it to someone in the states who was going to use it to make moulds.

And neither the ball or the person has been heard from since lol

The general consensus was that it doesn't travel any further than a round ball - BUT (very important) it pretty much always goes straight !
Which round golf balls almost never do (at least for me anyway).
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