Slinging.org Forum - Answer: Spin rate of a stone

Sarosh

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Answer: Spin rate of a stone
Nov 11^th, 2018 at 8:00am

https://youtu.be/m4tX1kCz-rY
in case of a mistake in math please point it out .
what do you think creates the different frequencies?

the question topic : http://slinging.org/forum/YaBB.pl?num=1541623411

from the video description: Quote:

more questions arise : how much is the projectile deflected by the contact with the sling after release?

Could this spin rate be too much stabilization for the projectile's flight, making it fly with nose-high orientation? What can be done to control the spin rate? and then experiment on different spin rates and their effect on projectile's flight.

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Tint Interfector Viris Spurii Past Moderator Offline Posts: 2335 Hong Kong Gender:	Re: Answer: Spin rate of a stone Reply #1 - Nov 11^th, 2018 at 8:16am Wow! Very nice video! The result was suprising to me. Thanks for putting in the tennis balls comparison
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Teg

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Re: Answer: Spin rate of a stone
Reply #2 - Nov 11^th, 2018 at 1:49pm

Well done!

Sarosh wrote on Nov 11^th, 2018 at 8:00am:

what do you think creates the different frequencies?

For the other frequencies and also the amplitude modulation I think you don't have to look into precession. Rotation around its other two rotation axes should do the trick as you typically have 2 to 3 main frequencies.
You could check if the modulation of the amplitude has the same frequency as another sound signal.
You could also throw a perfect disk or a perfect cylinder or any object with rotational symmetry (a glans Wink

. Then I would expect to hear only one (strong) frequency.

As a next step I would look for harmonics.
Shot 7 of the 4 flop stones: The first three frequencies are roughly harmonics of each other. Was that stone not very square? Two opposing edges roughly the same height, with the other two opposing edges differing in height? Then these three frequencies should also show the same loss in rps over time (scaled, of course, with the harmonic order).

Same with shot 8, the last two frequencies.

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Mersa Interfector Viris Spurii Offline Druid Posts: 2615 Australia Gender:	Re: Answer: Spin rate of a stone Reply #3 - Nov 12^th, 2018 at 3:54am Nice video. You may be the best at editing on this site . Love the analysis you show on lots of your videos.
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Curious Aardvark past-administrator Offline Taller than the average Dwarf Posts: 13965 Midlands England Gender:	Re: Answer: Spin rate of a stone Reply #4 - Nov 12^th, 2018 at 7:10am so how fast were they spinning ? I either missed that bit or you did The even sized rectangular 'stones' are probably the only ones yopu could get an accurate spin rate on. As They are easy to measure. Oh yeah moved this to 'Here be maths' For obvious reasons
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Sarosh

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Re: Answer: Spin rate of a stone
Reply #5 - Nov 12^th, 2018 at 7:25am

@

Mersa
thanks man

Curious Aardvark wrote on Nov 12^th, 2018 at 7:10am:

so how fast were they spinning ?

tennis ball: 3600-7200rpm, visual data

stones: 6000-11000 rpm (with a possible 20000rpm throw), audio data

Curious Aardvark wrote on Nov 12^th, 2018 at 7:10am:

Oh yeah moved this to 'Here be maths'

could you please make 'Here be maths' accessible to guests and not logged in members?

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timpa Interfector Viris Spurii Offline Stones in the horizon Posts: 1521 Finland	Re: Answer: Spin rate of a stone Reply #6 - Nov 12^th, 2018 at 5:51pm The result is surprising. I would also like to try this. Maybe with the camera.
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NooneOfConsequence

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Re: Answer: Spin rate of a stone
Reply #7 - Nov 15^th, 2018 at 1:00am

timpa wrote on Nov 12^th, 2018 at 5:51pm:

The result is surprising. I would also like to try this. Maybe with the camera.

If you throw your camera, you’ll make us all dizzy!

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“My final hour is at hand. We face an enemy more numerous and cunning than the world has yet seen. Remember your training, and do not fear the hordes of Judas. I, without sin, shall cast the first stone. That will be your sign to attack! But you shall not fight this unholy enemy with stones. No! RAZOR GLANDES! Aim for the eyes! May the Lord have mercy, for we shall show none!“ -Jesus the Noodler

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Curious Novice Tiro Offline Slinging: Getting the most bang for you buck Posts: 33 South Carolina Gender:	Re: Answer: Spin rate of a stone Reply #8 - Nov 15^th, 2018 at 9:14pm The high rate of spin does help explain why some ammunition disintegrates when slung. It would be interesting to design a sling bullet that breaks in a controlled manner from the spin after it leaves the pouch in order to obtain a shotgun effect on the target without sacrificing accuracy.
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NooneOfConsequence

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Re: Answer: Spin rate of a stone
Reply #9 - Nov 22^nd, 2018 at 8:49am

I’m sure you could design an exploding bullet, but it would be really difficult to make a reliable one. Getting the materials to break consistently is difficult, but there are other challenges too. You can’t assume that the bullet spins perpendicular to the direction of travel unless you have more drag on the tail. Adding drag for aerodynamic stability will cost you some velocity at distance. With a sphere or (American) football shape, the spin will probably be at an angle... which means your shotgun pattern will be inconsistent.

You might try making a clay bead by using too much clay in a clay roller. This leaves a small hole in the middle which acts as a weak point. Put a plastic cup around the clay bullet (like a shotgun shot cup). This would serve two purposes: add drag for stabilization, and hold the bead together during the release when it’s most likely to explode prematurely. The cup would have to fall away quickly and the bead would have to break into evenly sized chunks... still a difficult task, but that’s how I would approach your exploding ammo design.

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“My final hour is at hand. We face an enemy more numerous and cunning than the world has yet seen. Remember your training, and do not fear the hordes of Judas. I, without sin, shall cast the first stone. That will be your sign to attack! But you shall not fight this unholy enemy with stones. No! RAZOR GLANDES! Aim for the eyes! May the Lord have mercy, for we shall show none!“ -Jesus the Noodler

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Sarosh Interfector Viris Spurii Offline Posts: 1183	Re: Answer: Spin rate of a stone Reply #10 - Nov 28^th, 2018 at 11:21am https://www.youtube.com/watch?v=___3fLsS7Bg Y sling spin rate w/ tennis ball: 2400rpm some stones feel like they have much less spin.
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Tint

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Re: Answer: Spin rate of a stone
Reply #11 - Nov 28^th, 2018 at 6:04pm

So do we want more spin on our throws? Or less spin?
Does having more spin helps with accuracy? Does it create more damage on impact?
Wouldn't less spin means a faster projectile because the energy are used to push it forward rather than making it rotate?
My guess is being able to control the spin is necessary for pin point accuracy...but how?
I am very curious!

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Tint Interfector Viris Spurii Past Moderator Offline Posts: 2335 Hong Kong Gender:	Re: Answer: Spin rate of a stone Reply #12 - Nov 28^th, 2018 at 6:07pm Thanks so much for the video! You are really on to something here.
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