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Possible way to clock your stone speed. (Read 25855 times)
dork
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Possible way to clock your stone speed.
Nov 20th, 2007 at 10:21am
 
I have no idea if this would work.

What if you were to make a frame probably square with an axle through it. On the axle would light weight plastic that would take up the inside of the frame. The axle would have to be very well lubricated. Then hook up some kind of speedometer to it. As the stone passes through, it spins the plastic and axle (like the spinny things in a pin ball machine) and regesters on the speedometer. I think as long as the plastic is light enough, energy wouldn't really be lost.

Anyone think this would work? The obvious answer would be to try it. Dah
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Re: Possible way to clock your stone speed.
Reply #1 - Nov 20th, 2007 at 11:50am
 
My suspicion would be that you'd end up either putting your missile through the plastic or just smashing the frame.
Light plastic would be no good. Possible if you used a thin sheet of aluminium it might work. But plastic will just get punctured. :-)
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Re: Possible way to clock your stone speed.
Reply #2 - Nov 20th, 2007 at 12:31pm
 
You might have problems with energy losses.  Every bit of energy that went into deforming the plastic, making a loud noise, or making the target vibrate would get lost to the system and wouldn't get measured by the speedometer.  And you wouldn't be able to use conservation of momentum for a system like this because some of the projectile's momentum would get transfered through the bearing system to the earth.

I still think a ballistic seems the best way to go.  It might suffer from energy losses as well, but if could figure out a way to track the darn thing while it twisted and swung after getting hit by an off-center shot, you could use conservation of momentum to get the projectile speed.

NOTE: In theory, if you can measure the path of the hand and sling, you can figure out the timing information, projectile speed, etc., by measuring the speed of the slinger's hand at the moment of release.  This might be well within the range of a cheapo sports radar gun.  I keep promising to post the equations... someday.  I've turned them into a PDF file, but I still haven't gotten around to scanning them in.  Maybe over Thanksgiving...

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Re: Possible way to clock your stone speed.
Reply #3 - Nov 20th, 2007 at 12:51pm
 
Still the easiest method for measuring average velocity is to attach a firework snapper above the rock on the release side of the pocket and have a helper with a stopwatch standing equidistant to you and a sheet of plywood or other acoustically suitable target, situated so as not to see you or the target.  Snap, he starts the stopwatch, thud, he stops it.



Bodda bing Bodda....



Bang.



TS
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Re: Possible way to clock your stone speed.
Reply #4 - Nov 20th, 2007 at 7:16pm
 
Nice to hear from you again TS.

In another life you must have been a sound effects man. It used to be, "badum dabum" or something similar. Now it's Bodda bing Bodda??

Probably the easiest way to get a reasonably accurate determination is to video yourself. Get a good, wide, side-on shot and use a brightly coloured projectile, preferably with a wall or fence as background. Then if you review the video frame by frame you should be able to see how far the ball has travelled against the background. A bit of number crunching with your trusty calculator should give you its velocity. You will of course have to know how many frames per second your camera opeates at.

A-S
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Re: Possible way to clock your stone speed.
Reply #5 - Nov 21st, 2007 at 1:28am
 
Hey A.S.


Quote:
Probably the easiest way to get a reasonably accurate determination is to video yourself.



Having done so on numerous occasions, I feel confident in advocating the former as the easiest method by which to obtain very accurate average velocities.  


Quote:
In another life you must have been a sound effects man.



As crazy as it sounds.....some seem to consider me a 'sound' effects man in this one.



(Buddum Bum)


Shocked



TS
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Re: Possible way to clock your stone speed.
Reply #6 - Nov 21st, 2007 at 4:23am
 
Greetings again TS,

To be honest I haven't tried the hidden stopwatch assistant method. I imagine that the idea of being unable to see the slinger is that you respond only to the audio cue and do not anticipate either the release or the strike, and presumably the response delay is the same, givng the correct interval. Over what distance do you measure? I assume that anything less than 10m would be pretty hard to catch. Have you cross checked the result by another method?

Regards,

Aussieslinger
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Re: Possible way to clock your stone speed.
Reply #7 - Nov 21st, 2007 at 7:18am
 
TS is wrong again - another one to add to his collection - the timing should be from the throw (and you don't need to hear a firework to detect a throw) until the stone is SEEN to hit the target, since over a hundred yards, the sound would take approximately 1/3 of a second to cover the distance, which would interfere with an accurate estimate of projectile speed.

SV

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Re: Possible way to clock your stone speed.
Reply #8 - Nov 21st, 2007 at 12:07pm
 
well if the listener was placed equidistant between the slinger and the target - then hearing would work fine. And a snapper would give a distinct sharp sound that might be easier to distuinguish than the longer and softer sound of the sling.

lol dissing it just cos it's ts isn't terribly logical (captain) :-)
As a home use method it's as good as anything else, in that it relies entirely on the observer having very good hearing and reflexes.
Obviously a human observer free measurement method would be preferable - but you should be able to get a reasonable apporximation with ts method. Just apply commonsense to the position of the observer.
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Re: Possible way to clock your stone speed.
Reply #9 - Nov 22nd, 2007 at 5:30am
 
Sure if you are going to time over 100 m then a hand held stopwatch would give accurate timing ie. the human reflex factor is minimized. But how much of the stone's original velocity is lost by the time it covers 100m; perhaps 50%(?), so the calculated velocity will be well below the actual release velocity.

Whether you position yourself mid-path and use audio cues, or use visual ones, I imagine that the hardest part would be to accurately snap the stop watch, especially if the distance over which the flight is measured is small.

It has just occured to me that it would be quite possible to stand next to the slinger and still use audio cues. Just deduct the 1/3 second or whatever it may be, that the sound takes to return from the target from the measured time to give the true flight time.

However, I am sure TechStuf has it all in hand. After all he says he has done it many times, presumably with consistent results. All I asked was whether he had cross checked his results with another method.

I have done my video method only once, but it gave good results; two frames to travel 5m, giving a speed of 40 m/s. Seems reasonable.
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Re: Possible way to clock your stone speed.
Reply #10 - Nov 23rd, 2007 at 4:13am
 
Welcome back TS.

Why not put your camera behind a shelter with the lens coverred by wire mesh or thick glass and sling from various distances toward the camera. If the camera has a high frame rate the release should be seen quite easily and if it has sound the impact should be heard immediatly. I thinking this would give a % less error.

OR

C_A should run on to the field when there is a international cricket game on, bump the bowler out of the way and sling towards the batsman's wicket. Maybe they would have recorded it on their radar and other goodies like slow motion cam, trajectory cam, birds eye view and the newest slowmotion infrared camera. You would not get more accurate than that.

Grin
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Re: Possible way to clock your stone speed.
Reply #11 - Nov 24th, 2007 at 5:09am
 
why not use a chronograph and get your ammo to travel between the traps. I've used chronographs to determine the velocity of my paintball gun, so I am within allowable limits for tournements etc.
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Re: Possible way to clock your stone speed.
Reply #12 - Nov 24th, 2007 at 10:52am
 
As a kid I seem to remeber going to the county fair, seeing a booth where you could find your pitching speed. They had a back drop with a target on it. The target had some kind of meter in it that registered pressure. It would tell you your speed by the amount of force the baseball exerted on the target.

Any possible way to make something like this on a simple scale.
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Re: Possible way to clock your stone speed.
Reply #13 - Nov 24th, 2007 at 11:07pm
 
for all the time and energy your going to spend building this device which may or may not work. Why not buy a chronograph from ebay or a yard sale or flea market?
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Re: Possible way to clock your stone speed.
Reply #14 - Nov 25th, 2007 at 1:19am
 
Chronograph?
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