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Slinging analysis from an overhead camera - slow motion video (Read 606 times)
IronGoober
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Re: Slinging analysis from overhead - slow motion video
Reply #15 - Oct 7th, 2020 at 11:04am
 
IronGoober wrote on Oct 7th, 2020 at 10:59am:
[quote author=2B3D3238392E392E5C0 link=1601965620/13#13 date=1602065557]As far as the resolution to angle, I think there might be a change in sign going on towards the end, lost because of the arccos operation?


The lag angle I defined as the difference between hand trajectory vector and the vector of the hand to ball position (i.e. sling cords).  My hand and the sling are always moving anti-clockwise, so their angular relationship should remain between 0 and 180 degrees. I'll need to check this again, I may have messed it up. My hand does actually do a little loop when you see it look like it stops, so It should keep the lag angle close to 90 degrees.

Here is my interpretation of the data assuming it is actually correct (there could be a mistake in the math), the climb to ~90 degrees is the wind up to get the sling in position for the power stroke.  This gave me insight as to where my spit-outs happen (loosing a stone early). Because of my hand motion, and the fact that I almost stop it completely, the lag angle becomes large as I'm not pulling the sling along to counteract drag, this looses tension in the sling and allows the projectile to fall out. After this, the power stroke begins. You can see that the lag angle rapidly drops from ~90 degrees to zero, where the force on the sling is the most because I'm pulling in the same direction as the cords. Because of the acceleration, it starts to swing faster than my arm moves and the lag angle increases again. Eventually my arm moves as far as it can, and I start to roll my wrist, this puts the action closer in line to the sling cords and the lag angle decreases again. This must be to overcome air resistance as the velocity does not increase here, but stays flat. You'll notice the faster throw has a lower overall lag angle in the power stroke (but also a longer path length).

Sarosh, this last downturn with the lag angle shows that elasticity in the cords would be non-beneficial for this particular movement. The stretch would just be wasted as the forces would be stored in the sling and not transferred as efficiently to the projectile.

Just a note about the data, in my calculations the sling positions are mirrored along the x axis from the video, as pixel positions are calculated with the origin in the upper left, and in graphing, the origin is in the lower left.
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Re: Slinging analysis from overhead - slow motion video
Reply #16 - Oct 7th, 2020 at 1:22pm
 
My friend tried to film a pirouette from the bridge. But it was a bad place.
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NooneOfConsequence
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Re: Slinging analysis from overhead - slow motion video
Reply #17 - Oct 7th, 2020 at 6:29pm
 
I’ve been thinking a lot about the “internal ballistics” too lately. A sling is a resonant system. In terms of the direction of the throw, tension on the cord accelerates the ammo on half of the cycle, but it decelerates during the other half. The maximum power comes from a 180 degree rotation that matches the timing of the linear “punch” motion of the arm. The power stroke starts when the ball is perpendicular to the punch and moving backwards. The peak velocity happens when the ball is released perpendicular again but in the forward direction. Past this point, tension on the cord will slow you down again. This means that increasing the length of the power stroke could actually slow down the throw if you over-rotate at the same time.
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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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IronGoober
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #18 - Oct 7th, 2020 at 9:06pm
 
Good discussion. I've done some additional analysis because of all of this.
NooneOfConsequence wrote on Oct 7th, 2020 at 6:29pm:
This means that increasing the length of the power stroke could actually slow down the throw if you over-rotate at the same time.


I agree, if the motion was constrained to be linear. That is where the wrist comes into play. The tight curvature of the wrist movement actually continues to accelerate the sling, even though the arm can't move forward much more, and overall velocity of the hand slows down. (see picture). If you held on longer, certainly the lag angle eventually becomes >90° and you slow down the sling.

NooneOfConsequence wrote on Oct 7th, 2020 at 6:29pm:
In terms of the direction of the throw, tension on the cord accelerates the ammo on half of the cycle, but it decelerates during the other half. The maximum power comes from a 180 degree rotation that matches the timing of the linear “punch” motion of the arm. The power stroke starts when the ball is perpendicular to the punch and moving backwards. The peak velocity happens when the ball is released perpendicular again but in the forward direction.


I made a mistake in the video. The power stroke actually starts when the sling is at 45° rear-left of the slinger. This makes sense, if you think about a pendulum that is constrained to move in a linear fashion (see image). The maximum transfer of power into the pendulum will be between +-45°. You can see this in the lag angle, it is generally between 45°.

I thought that wrist action was important in slinging, but never had any proof. This does indeed suggest that the wrist action is important at the end and adds a bit more velocity. I think it is important for accuracy as well as it also serves to further increase the effective radius of the ball path, to decrease the effect of mis-timing the release.

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« Last Edit: Oct 7th, 2020 at 10:46pm by IronGoober »  

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Re: Slinging analysis from an overhead camera - slow motion video
Reply #19 - Oct 7th, 2020 at 10:02pm
 
If your power stroke only covers -45 to +45 degrees from immediately behind you, you are only capturing about 72% of the possible acceleration.  That is the majority, but you can get more.

Wrist or no wrist, as soon as the pouch is in front of your hand, any tension on the cord will contribute to deceleration of the ammo with respect to the throwing direction... but forward motion of the hand and wrist actually reduces or removes tension when the pouch is in front of the hand, so forward motion actually helps maintain a steady trajectory for aiming if it is tuned well to the rotation.
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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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IronGoober
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #20 - Oct 7th, 2020 at 11:08pm
 
NooneOfConsequence wrote on Oct 7th, 2020 at 10:02pm:
Wrist or no wrist, as soon as the pouch is in front of your hand, any tension on the cord will contribute to deceleration of the ammo with respect to the throwing direction... but forward motion of the hand and wrist actually reduces or removes tension when the pouch is in front of the hand, so forward motion actually helps maintain a steady trajectory for aiming if it is tuned well to the rotation.


You are absolutely right, the point I was trying to make was that the wrist serves to change the lag angle(and trajectory) quickly to avoid the projectile being in front of your hand. You know, like when you were a kid and another kid wanted to be "in front" of you, but you'd just turn so they weren't "in front" any longer, and they'd just keep having to walk in circles around you (or was this just me and my brother?). If the projectile was at a lag angle >90° and you couldn't change the direction of your hand, yes, you are correct, you'd slow down the sling. But the wrist serves to change the direction quickly and maintain tension on the cord, this will decrease the lag angle to <90° and allow a bit extra acceleration of the shot, albeit for a short time.    You mention forward motion needing to match the rotation, but the hand/arm typically can't move as fast as the projectile near the end of the power stroke, so that is why the wrist comes into play.  That's what I was getting at.

NooneOfConsequence wrote on Oct 7th, 2020 at 10:02pm:
If your power stroke only covers -45 to +45 degrees from immediately behind you, you are only capturing about 72% of the possible acceleration.  That is the majority, but you can get more.


I agree, for the swinging pendulum with a linear movement forward it would be best to go from -90° to +90°.  That might be challenging to realize in practice, especially with learned and engrained movements.

This is going to sound lecture-y, but I'm just thinking "aloud" here (is there a word for thinking in writing?). In theory, the best lag angle is 0°. But as we all know n practice it won't ever be this for the entire power stroke. So, lets say we keep it to 1°. The hand motion would necessarily end up looking like a "J" with a tiny curve at the beginning, to keep up with the increasing projectile speed. To be effective your hand would have to keep up with the 99% velocity of the projectile until the release. By increasing lag angle, the speed at which your hand needs to move to impart energy into the sling decreases. So, it seems there is an optimization here that gets you the best performance when limited by the human body's movement/force limitations.    Calculating forces are on my to do list.
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« Last Edit: Oct 8th, 2020 at 1:00am by IronGoober »  

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Re: Slinging analysis from an overhead camera - slow motion video
Reply #21 - Oct 7th, 2020 at 11:52pm
 
Just going to chip in that I think this is really quite interesting
work! I'm very impressed with effort that's been put into this.
Outside of the body motions, another way to increase power and accuracy is by using a sling that opens as fast as possible. This means that you can put more velocity into the sling before it opens, as the time for the sling to open soaks up some of the power-stroke. It also improves accuracy as different projectile weights results in substantial changes in the time it takes for the projectile to leave the sling. I think you might know where I'm going with this...
I'll post a picture tomorrow.
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #22 - Oct 8th, 2020 at 1:12am
 
Albion Slinger wrote on Oct 7th, 2020 at 11:52pm:
Just going to chip in that I think this is really quite interesting
work! I'm very impressed with effort that's been put into this.
Outside of the body motions, another way to increase power and accuracy is by using a sling that opens as fast as possible. This means that you can put more velocity into the sling before it opens, as the time for the sling to open soaks up some of the power-stroke. It also improves accuracy as different projectile weights results in substantial changes in the time it takes for the projectile to leave the sling. I think you might know where I'm going with this...
I'll post a picture tomorrow.


Yes. I agree. NOC (and others) have mentioned things like this multiple times in the past. Many of his discussions were what inspired me to finally do this analysis (as well as all of the great work from Sarosh). I've been wanting to for many years. I'm hoping that others will look into other aspects of slinging like release cord and pouch interference using similar methods. There is a lot to be learned. 240 fps is not the best, but it is still useful. Of course 1000 fps would be better (*said loudly in NOC's direction* Smiley ). A roboslinger is obviously the best and most consistent way to do it, but not a full requirement. I think filming releases by a hand sling would still be useful (*Said loudly at everyone else).
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #23 - Oct 8th, 2020 at 11:39pm
 
This is definitely a step in the right direction IG. Nice work!

As to the action of the wrist, I wouldn’t describe it as changing the direction so much as decreasing the radius, which has the effect of increasing the speed to preserve the angular momentum. It’s just like the classic physics demonstration where a person is spinning in a chair and they go faster when they tuck their arms in.

As to the 1000fps camera... I’m not going to have a lot of time to mess with it this year, but if you do and if you keep creating excellent content like this, then why don’t you just borrow it for a while?  PM me your address, and I’ll send it on over.
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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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Re: Slinging analysis from an overhead camera - slow motion video
Reply #24 - Oct 9th, 2020 at 5:50am
 
Amazing
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #25 - Oct 9th, 2020 at 7:54am
 
joe_meadmaker wrote on Oct 6th, 2020 at 11:01pm:
IronGoober wrote on Oct 6th, 2020 at 2:27am:
It makes sense if you think about how pitchers get maximum velocity, they have maximum path length of their throw.

I'm curious about how much of a difference the forward step makes.  Like you (and definitely others), I use a forward step when slinging.  What happens to the results if you don't take that step and just use a rotation of the body?  If you recreate this experiment, I would be interested to see that comparison.


Concerning the path length of the 'drive', I tend to think of it this way. We've seen various use of the 'simple pendulum' analogy, but there is more to be squeezed from that.

We know the 'period' of a simple pendulum (twopi sqrt(L/g)) which is the time it takes to swing back from an extreme position in its swing back to the same place. We also know it takes a little longer for wide swings, but actually not very much.

In the analogy with the sling, rather than 'g' due to gravity it is due to the acceleration of the hand, the 'pivot' of the pendulum. Consider how far that point has to move from rest during a half swing of the pendulum and you arrive at a 'notional drive length', say D,  which is straight and a multiple of the length of the sling.

The result is
     D =  (1/2) (pi k)2 L,

making D about five times the length of the sling. Most importantly it is independent of the acceleration applied.

Having got the foot in the door with that, we need to look at what freedom we have to alter the dynamics in practice. One thing is curving the drive path, but the other thing is to have the 'pendulum' already swinging about the pivot. In that case the time the pendulum is in the lower half of its possible motion is decreased. So by increasing the initial angular rotation about the pivot, considering the situation at the beginning of the power stroke of the action we can apply the same acceleration pattern and use a shortened drive length.

So, the argument here is that the early part of the sling action is to set this initial rotation for the sling to tune the physically realizable path length to the sling length.

Hope that makes some sense.  Wink

There is another wrinkle in all this. The actual path length can be 'folded' if the drive is actually started when the hand is moving backwards, rather than at rest, so there is a suggestion that the effectiveness of the throw could be increased by recognizing that. If you want an analogy to that folding, we throw things up in the air and they come back to the same height, ie. havn't moved at all in height during a period of acceleration.
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Re: Slinging analysis from an overhead camera - slow motion video
Reply #26 - Oct 9th, 2020 at 11:42am
 
wanderer wrote on Oct 9th, 2020 at 7:54am:
There is another wrinkle in all this. The actual path length can be 'folded' if the drive is actually started when the hand is moving backwards, rather than at rest, so there is a suggestion that the effectiveness of the throw could be increased by recognizing that. If you want an analogy to that folding, we throw things up in the air and they come back to the same height, ie. havn't moved at all in height during a period of acceleration.


Yes... I was planning to shoot a video of this soon, but you scooped me Wanderer!  The power stroke starts with a backward pull, then a push, which has to be timed to the acceleration of the sling pouch.   To my knowledge, it's a slinging style we've never seen before on here... I would call it "Fist pump" style because the direction change during the power stroke looks a lot like a fist pump.

It's basically a novelty slinging style like Turkey or Kung Fu Meteor Hammer styles unless you can eek out extra performance after a lot of practice.  The Fist Pump style is also really hard on your elbows unless you take extreme care not to overextend on the final thrust.  You have to move your hand extra quick to keep up with the ball at the end of the throw because it started accelerating during the reverse thrust.  If you're not paying attention, you will run out of arm and overextend your elbow before you finish the throw, especially when you are first trying to figure out the timing of the style.
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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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Re: Slinging analysis from an overhead camera - slow motion video
Reply #27 - Oct 9th, 2020 at 3:10pm
 

@wanderer I think we are discussing very similar things. Though I think that starting a powerstroke while moving the hand backwards would have a big effect on accuracy. To keep both intact, The power stroke could be a "J" with a small curvature at the beginning. To keep the lag angle ~30-45° (which I believe is about optimal for keeping hand velocities realistic), the curvature of the hand motion would necessarily need to start small and become wider and wider as the ball picks up velocity. This can be accomplished (and is somewhat already in my current throw mechanics) by a rotation of the shoulders at the beginning of the throw with minimal hand/arm movement. Then the arm would need to sweep forward as the ball accelerates.

@NOC. A very generous offer. I'm undecided if I want to borrow your camera though, that puts a lot of pressure on me (plus I don't wanna break it)! Lol.  I'm leaning toward yes, but I'll PM you if I decide it's worth the pressure. 

Also, I would like to see the motion you and wanderer are describing (fist pump). I think I understand, but seeing is much better than just thinking about it.
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« Last Edit: Oct 9th, 2020 at 5:05pm by IronGoober »  

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Re: Slinging analysis from an overhead camera - slow motion video
Reply #28 - Oct 9th, 2020 at 3:55pm
 
IronGoober wrote on Oct 9th, 2020 at 3:10pm:
@NOC. A very generous offer. I'm undecided if I want to borrow your camera though, that puts a lot of pressure on me (plus I don't wanna break it)! Lol.  I'm leaning toward yes, but I'll PM you if I decide it's worth the pressure. 


FWIW, I spent all of about $100 for the camera on EBay a couple of years ago, and I probably overpaid for it.  The 1000fps resolution is terrible, but you can get some good info out of it if you set up your shots right.  The 480fps mode is a little better but still not great.   

I bought the camera specifically for investigative slinging, so I'd be happy to see it get some more use, but no pressure either way.
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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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Re: Slinging analysis from an overhead camera - slow motion video
Reply #29 - Oct 11th, 2020 at 2:59am
 
Wow amazing!!!
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