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Message started by David_T on Nov 3rd, 2003 at 7:04pm

Title: Projectile Speed
Post by David_T on Nov 3rd, 2003 at 7:04pm
Surely one of us can find someone with a radar gun or some sort of measuring devise to see the speed of a projectile coming out of a sling. Unfortunately, baseball season is over. We have a minor league team here in Greenville and they have a booth at the stadium that you can pay a few bucks and throw some baseballs at a target that will gauge the speed. Maybe next year I will talk to the guy.

Does anyone know if a police radar gun could measure the speed of a slingstone? We have a State Trooper who brings his kids to our daycare. I am going to ask him about it. It would be nice to know what speed I was thowing at.

Title: Re: Projectile Speed
Post by nemesis_3003 on Nov 4th, 2003 at 12:28am
hey david,
where bouts you at????
jack

Title: Re: Projectile Speed
Post by JeffH on Nov 4th, 2003 at 2:11am
O. K., friends, try to follow me here:

Suspend a 100 lb weight of some sort.  It should hang from a fairly long rope.  Set up a table or platform behind it, back several feet.  Get a long round stick and make a holder on the table for it.

Put the stick on the table and hang it out so it touches the suspended weight.  Mark the stick with a line at the point where it enters the holder.  Or mark it with 1/10 ft marks and note which one is at the edge of the holder.

Weigh a stone as accurately as possible.  I would suggest using grams or grains and converting to ounces.

Sling the stone and hit the 100 lb weight.  Measure how far the stick moved into its holder.  Every foot of movement is 100 ft/lbs of energy.  Calculate backwards to find the speed.  You know the ft/lbs and the projectile weight, so this should be easy.

This might be a bit confusing, but it should work.  The only trouble is getting a target that won't absorb too much energy or cause the stone to bounce.  Wet sand might be the trick.

jeff <><

Title: Re: Projectile Speed
Post by Chris on Nov 4th, 2003 at 2:47pm
Getting it to hit the target and transfer all it's energy is pretty tricky.  And eliminating factors like the friction in the rope is impossible.  

I know this is what they do for guns, but I'm not sure how effective it would be for slings.  I wanted to do something similar  year ago, but realized my aim was to poor. :)

A radar gun would be easiest.  I know the baseball ones would work.  The police ones might not be calibrated for anything that small.  

Chris

Title: Re: Projectile Speed
Post by Yurek on Nov 4th, 2003 at 3:27pm
David,

You could also try with your digital camera in a manual mode or with preselection time of the shutter mode. Try to hit the moment just after the release. I know, it's not easy, is a bit like a lottery, but expriments with the DC cost nothnig. Maybe you will succeed to snap the trail of projectile. For example if you will set the shutter at 1/60 s and the trail will be 20" long, then the projectile velocity will be

v = 20 / (1/60) =20 * 60 = 1200"/s = 100 ft/s

It would be good to use a uniform and contrasting background, some wall or the sky, for example. Using of a tripod and a remote control (photographer's security) makes sense too. For the more precise trail measure you may put some scale close the release point.

I think this way of measure should be pretty precise.

Jurek

Title: Re: Projectile Speed
Post by David_T on Nov 4th, 2003 at 6:39pm
Wow!

You  guys sound more like rocket scientists than a bunch of dudes interested in the ancient sling. Thanks and no offense, but I'm with Chris--A speed gun will be easier for me.  ;D ;D

I will let you know what the Trooper says. Anyone see the movie "The Rookie" He stopped on the side of a road that had one of those radar signs that showed your speed as you passed. It may have been "Hollywood half truth" but it showed the speed of a baseball he threw???


Title: Re: Projectile Speed
Post by David_T on Nov 4th, 2003 at 7:18pm
Nemesis,

I am near Greeneville, SC--the north-western part of the state.

Title: Re: Projectile Speed
Post by Whipartist on Nov 4th, 2003 at 7:41pm
Baseball season.  Next season, someone go out there and show those pitchers how to throw.  Maybe we'll get one of them interested.  If a Major League pitcher can pitch at 100 mph.  What speed can he sling a lead gland at?  Hmm.

Title: Re: Projectile Speed
Post by Dan_Bollinger on Jan 31st, 2004 at 12:22pm
I have used the sports device called SpeedChek. Not expensive. I believe it uses an IR or ultrasound method. You throw the projectile over the top of it so it measures release velocity. I hit the device once and busted it up, but it still works. Next time I'll try protecting it with something.

Title: Re: Projectile Speed
Post by Chris on Jan 31st, 2004 at 7:42pm
Welcome Dan,

In your research and experience, how fast do you think projectiles can go?  

Chris

Title: Re: Projectile Speed
Post by Dan_Bollinger on Feb 2nd, 2004 at 8:36pm
Chris,  I don't recall what my tosses measured, its been awhile. Also, I'm not a powerful slinger. Thom Richardson did some tests using a UK military weapons range. Unfortunately, those books are packed away right now. It was published in the Royal Armourie Yearbook.

added:  Found it!  Thom said that the average sling velocity was 31 m/s (69 mph).  

He also said that the almond-shaped lead traveled further than lead balls and outranged stones by about 50%.  

Title: Re: Projectile Speed
Post by jaxslinger on May 18th, 2008 at 12:38am
Hey Siguy,

Any info here?


                    Brett

Title: Re: Projectile Speed
Post by aussieslinger on May 18th, 2008 at 1:22am

Dan_Bollinger wrote on Feb 2nd, 2004 at 8:36pm:
Chris,  I don't recall what my tosses measured, its been awhile. Also, I'm not a powerful slinger. Thom Richardson did some tests using a UK military weapons range. Unfortunately, those books are packed away right now. It was published in the Royal Armourie Yearbook.

added:  Found it!  Thom said that the average sling velocity was 31 m/s (69 mph).  

He also said that the almond-shaped lead traveled further than lead balls and outranged stones by about 50%.  


The easiest way of accurately measuring sling speed without any special equipment is by looking at the recorded sound wave with a program like "Audacity". Your laptop will probably have the sound recording facility inbuilt.

Sling at a target a few metres away. The "swish" sound of the release and the whack of the projectile hitting the target are very readily both heard and seen on the graph so the time interval is accurately known from the scale. Measure your slinging distance with a tape measure and work out the speed with your trusty calculator. Easy!!

BTW 31 m/s (or 69mph) is very slow; even my 14yo daughter easily exceeds that. Any of the experienced slingers on the forum will be doubling that or more. Baseball pitchers and cricket bowlers get 100+ mph speeds without the aid of a sling.

Title: Re: Projectile Speed
Post by Thomas on May 18th, 2008 at 9:59am
Aussie

I used that sound program you recommended to time an air pistol. The published muzzle velocity is 400 fps. I fired through two paper targets spaced 19feet apart, the farthest one at 10 m or about 33 feet. I used a tiny Sansa recording mp3 player located at the midpoint of the two targets. My measurement was 320fps, which seems reasonable.

tom

Title: Re: Projectile Speed
Post by JTK on May 18th, 2008 at 10:51am
u can use a digital camera to record your throw, time the stone from realese to hit, and find the distance of the throw.  the formula would be distance/time=feet/yards/meters per second

Title: Re: Projectile Speed
Post by aussieslinger on May 18th, 2008 at 6:27pm

Thomas wrote on May 18th, 2008 at 9:59am:
Aussie

I used that sound program you recommended to time an air pistol. The published muzzle velocity is 400 fps. I fired through two paper targets spaced 19feet apart, the farthest one at 10 m or about 33 feet. I used a tiny Sansa recording mp3 player located at the midpoint of the two targets. My measurement was 320fps, which seems reasonable.

tom


Thanks for letting me know. I'm glad that my suggestion was of use. Your result seems very consistent with expectation. The 400 fps is undoubtedly a slightly optimistic muzzle velocity and .177 cal air rifle pellets lose velocity extremely quickly. Additionally penetrating the first sheet of paper would have also wiped off a few fps. Would it be possible to get a truer reading by bringing the target closer and using the report of the pistol as the timing start?

Aussie

Title: Re: Projectile Speed
Post by aussieslinger on May 18th, 2008 at 6:38pm

JTK wrote on May 18th, 2008 at 10:51am:
u can use a digital camera to record your throw, time the stone from realese to hit, and find the distance of the throw.  the formula would be distance/time=feet/yards/meters per second


Hi Justin,

Your method works perfectly and I also used it before I hit on the sound recording idea which for me is easier. If you get a good side view you can also see how far your ball travels between frames. I used this technique to cross check the results I got from the sound recording method.

Aussie

Title: Re: Projectile Speed
Post by Thomas on May 18th, 2008 at 7:58pm
Aussie

I used the two page method because that will be my slinging setup outdoors in the park after the target frames are ready. The sound record also includes the discharge sound. The sounds from a slinging setup should be virtually identical and the tiny sound from the sling itself will be useless unless I find some of those pull string firecrackers.  

tom  
 


Title: Re: Projectile Speed
Post by jaxslinger on May 18th, 2008 at 9:36pm
Thomas,

 Sorry that I used all the old ones you had back in 1980.They were in the bathroom inside that tan camera bag.I'm sure we can find them in FLA.

Title: Re: Projectile Speed
Post by aussieslinger on May 18th, 2008 at 11:57pm

Thomas wrote on May 18th, 2008 at 7:58pm:
Aussie

I used the two page method because that will be my slinging setup outdoors in the park after the target frames are ready. The sound record also includes the discharge sound. The sounds from a slinging setup should be virtually identical and the tiny sound from the sling itself will be useless unless I find some of those pull string firecrackers.  

tom  
 


Maybe your sling is quieter than mine but I had no trouble hearing or recording the swish, even outdoors. Try it as you may save yourself a good deal of work. The beauty of this method is that it eliminates the need for accuracy in your slinging. I was just banging away at my "couldn't possibly miss it at that range" garage wall at a distance of 8.1 metres.

Even if it really doesn't work you may try adding a small whip cracking tail to your sling which should make a louder swish and have no effect on velocity. Should be easier than the double screen method.

Aussie.

PS. I used the comparatively small distance of 8 metres because the projectile's speed loss should be minimal and the time interval is large enough to be measured with a high degree of accuracy. This gave me a very close approximation of release velocity. The two screen method would be very useful for determining how much velocity drops off at any given distance from the slinger. Provided you can record the sound of the release you would be able to calculate both the average velocity for the entire cast and the final velocity between the screens, all from the one sound recording. INTERESTING! Please write up your results if you go down this path. If you want to be super pedantic you could assume the speed of sound at 300 m/s and make corrections to the time intervals according to their individual distances from the recording device.

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