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The physics of the sling (Read 46181 times)

simia Junior Member Offline "sumus romanus et non barbari" latin Posts: 64 cleavland-akron Gender:	Re: The physics of the sling Reply #45 - Feb 4^th, 2006 at 10:51am right i forgot to add in the speeding up of the last roitation and many tricks used to make the rock go faster. i also made my formula for over headso it wouldnt work for many other methads. how much was your high speed camera?
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simia Junior Member Offline "sumus romanus et non barbari" latin Posts: 64 cleavland-akron Gender:	Re: The physics of the sling Reply #46 - Feb 4^th, 2006 at 10:55am by the way does the speed of the rock increace after you releace it (this is all from a geometry student so i mighht be missing a key componet later on in my student cureer
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Matthias

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Re: The physics of the sling
Reply #47 - Feb 4^th, 2006 at 12:20pm

No speeding up unless you have some sort of tricked out rocket assist glandes. This is a fundamental law of physics.

Most newish digital cameras, video cameras, webcams will give you 30 frames per second, but as I said, it really isn't fast enough. My attempt at getting around this is to use a long exposure (1-2 seconds) and a high speed stroboscopic flash. The other possibility is an external mechanical shutter.

(image by Andrew Davidhazy - http://www.rit.edu/~andpph/text-digital-stroboscopy.html)

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Matthias Past Moderator Offline Posts: 1418 Gatineau/Ottawa QC, Canada Gender:	Re: The physics of the sling Reply #48 - Feb 4^th, 2006 at 12:22pm Quote: OK, How do you do a "Bernini"? ??? Bernini
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bigkahuna past-moderator Offline Posts: 3894 Delaware, USA Gender:	Re: The physics of the sling Reply #49 - Feb 4^th, 2006 at 5:02pm Got it. Thanks.
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simia Junior Member Offline "sumus romanus et non barbari" latin Posts: 64 cleavland-akron Gender:	Re: The physics of the sling Reply #50 - Feb 4^th, 2006 at 5:34pm a rocket assited rock interesting
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DesertPilot

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Re: The physics of the sling
Reply #51 - Aug 23^rd, 2007 at 12:59pm

Are people still interested in studying the physics of the actual throw? As someone who does this sort of thing for a living, I just couldn't resist the temptation to write a simulator. I started with Yurek's post of several years ago, assumed the sling could be modeled as a coupled pendulum with the inner pendulum (the arm) with variable radius driven by an external torque (muscles, grunt, snort), while the outer pendulum is the sling. Then I got carried away, added a crude Markov chain Monte Carlo procedure to optimize performance for different hand trajectories, and threw in simple graphics capability to create... RoboSlinger 1.0! This was... way too much fun. I'll try to attach a test run to this post.

NOTE: The hand trajectories I used during development are entirely unrealistic. I rather doubt that for-real human beings, with actual shoulder and elbow joints, could ever throw in such a smooth spiral arc -- hence the name 'RoboSlinger'. But this code can handle any type of throw for which one has data. I've thought of some cheap simple ways one could photograph trajectories, measure velocities, etc., without fancy motion-capture equipment for a slinger with a reasonably flat and consistent overhand, horizontal, or underhand shot. If anyone's interested, I can post details. A figure-eight might be harder...

test_run_00a.jpg (176 KB | )

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Dravonk Funditor Offline Posts: 773 Aachen, Germany Gender:	Re: The physics of the sling Reply #52 - Aug 23^rd, 2007 at 4:04pm Cool! In which system did you implement the simulation? And is it 3D or just 2D?
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Re: The physics of the sling
Reply #53 - Aug 24^th, 2007 at 1:45am

Dravonk wrote on Aug 23^rd, 2007 at 4:04pm:

In which system did you implement the simulation? And is it 3D or just 2D?

I wrote it in MATLAB, and it should be fairly easy to port to other packages like IDL. I'd be happy to send you the code if you're interested. It could also be ported to C/C++, but that would lose the MATLAB user interface and graphics. This version is simple 2D. I plan to add 3D and the effects of gravity and air drag when I have a chance. I could also imagine replacing that simple 'inner pendulum' with a full-fledged biomechanical simulation of the slinger's rotation and throw, but at that point, this would stop being a part-time hobby and become a full-fledged academic research project, and I can't imagine what funding agency would ever support such a thing. NASA ('An Extremely Low-Cost Space Propulsion System')? The DOD ('Robust Technology for Munitions Deployment')? The EPA ('High-Speed Movement of Solid Debris')? The Department of Agriculture ('A Portable Faunal Control Apparatus for Stock Managers')? None of these alternatives seem likely

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Re: The physics of the sling
Reply #54 - Aug 24^th, 2007 at 3:54am

Maybe it would run in Octave, too, that is a free software similiar to Matlab. I am definitly interested.

Maybe we could run the "virtual slinger" as a free software project here? I guess we have a few engineers and programmers here. Matthias made a simulator, too, didn't he? Maybe we could combine the efforts of the two first simulators to start the free project.

We could improve it over time to get it more and more realistic. The weight distribution of the arm and the strengths of the different muscles would be nice to know. But I have no clue where you might find that information.

And once we have got it realistic enough, we can put a self-evolving neural algorithm behind it so it tries out millions of different styles and tells us which style is the most effective. ;-)

(Yes, I like daydreams and high set goals...)

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Zwiebeltuete Descens Offline Fly! Angel, fly! Posts: 143 Germany, near Nuremberg Gender:	Re: The physics of the sling Reply #55 - Aug 24^th, 2007 at 5:32am There should be certainly very interesting results coming from such simulations, but I doubt I have enough knowledge to help in this area.
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wanderer Interfector Viris Spurii Offline Posts: 1360 Texas Gender:	Re: The physics of the sling Reply #56 - Aug 24^th, 2007 at 8:28am Desert Pilot, Nice simulation. I think there's lots of interesting stuff to learn about the sling from examining the physics, even if some others here may not . I'd be interested in the simulations you used - they sound pretty fancy, although most of the words you used seemed familiar!
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slingbadger

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Re: The physics of the sling
Reply #57 - Aug 24^th, 2007 at 10:26am

Another part of the physics of the sling is what happens after you release.
The angle and speed of the stone make a big difference in where things end up.
A 45 degree angle launch will yield different results than a 30 degree launch.
Also, wind is a contributing factor. Iv'e deliberatly launched at an angle to winds to see what kind of curved path the stones take. Anyone familiar with a boomerang will know what that is about. I've had some interesting results.

The greatest of all the accomplishments of 20th cent. science has been the discovery of human ignorance The main difference between genius and stupidity is that genius has it's limits.-Einstein I'm getting psychic as I get older. Or is that psychotic?

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DesertPilot

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Re: The physics of the sling
Reply #58 - Aug 24^th, 2007 at 1:46pm

[quote author=Dravonk link=1091676756/45#54 date=1187942073]Maybe it would run in Octave, too, that is a free software similiar to Matlab...[/quote]

It should definitely run in Octave. I even had that in mind when I chose MATLAB. If you let me know what way is most convenient for you, I'd be happy to send you the code. (And yes, you can use it to try things like 300' slings with projectile velocities of Mach 1.2!) I could also post the basic equations I used if anyone's interested. There aren't very many, and people could ignore them as they saw fit.

I too have dreamed about the muscle/joint-movement/neural-network/genetic-algorithm idea to design... the [i]Ultimate Throw[/i]! But I tried something similar several years ago to evolve a robot walker, so I have a very good idea just how time-consuming such a project might be. Still, I may have an idea where to look for throw measurements for baseball pitchers. If I can find it, I'll post the links...

One thing I've noticed is that since the sling has a fixed length, it can only fit between the path of the hand and the path of the projectile in one particular way. This means that in the absence of air drag, you can determine the complete trajectory, speed, and acceleration of the hand and sling from path information and launch velocity alone, without any other time data at all! You could get the path information by taking a long exposure of a slinger with a white glove and a white sling pouch. You could determine launch velocity by throwing the projectile at a projectile trap -- something like a bucket of mud -- hanging from a rope and measuring how far it swings. In practice you'd need a good slinger with a consistent throw, and it would probably take many tries (and many buckets of mud) to get good data, but it might be worth a try. I'll try to attach a diagram to show the camera setups for horizontal and vertical throws. I apologize in advance for the poor quality of the art...

BothSlingers03.jpg (167 KB | )

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wanderer

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Re: The physics of the sling
Reply #59 - Aug 26^th, 2007 at 1:42am

You might also try a stroboscopic picture. With flourescent markers on the sling and the hand you should be able to manage a reasonable result by slinging illuminated by either a fluorescent light, or better maybe, a big street light.

As far as slinging at buckets of mud etc. I'm not sure many of us have had much success with ballistic pendulums, particularly if we have to back off the speed to be accurate enough to hit the thing.

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