I made an analysis of some slinging from and overhead viewpoint. It seems that a wider sweeping throw is key to more velocity. Not surprising in hindsight, but I didn't expect this result. It makes sense if you think about how pitchers get maximum velocity, they have maximum path length of their throw.

I was hoping to do more analysis of the angles of release and during the acceleration phase, but there was just too much noise in my data. My hand wasn't moving that much which made calculating the movement path difficult without smoothing it. (which is on the list of things to do).

I have a theory that the movement of the hand effectively gives the sling a much larger radius at the release point, so the typical argument that there are only microseconds error to be accurate is not valid. Because of the large effective radius, the angular error is much smaller which makes it easier for the human brain to calculate the release point. That is the thought anyway. I didn't prove that yet, but I'm heading in that direction.

I was able to do this by making a wooden "L" and lashing it to a step ladder. I rubber banded my wife's phone to it and then had a small bluetooth remote to trigger the video (got it bundled with a cheap tripod from amazon).

This was more work than I thought it would be. Kudos to Sarosh for all of his video analysis. I was really hoping to get the release of the projectile in frame, but I just didn't quite have it pointed in the right spot. I couldn't get much closer to the ladder without feeling like I would hit it when winding up.  I might need a bit more height to capture the entire wind up and release.

Oh well, next time.

https://youtu.be/doTYAGCTdog

This is really great work!

I absolutely agree with your points about the wider sweep. The general point is that in the sling motion the radius of curvature of the motion is almost never just the length of the sling, but is usually significantly larger.

Interestingly, I think there is a contrast with trebuchets here, where you generally want to slow the arm down close to the launch point - in order not to have a madly swinging arm left after the launch. That condition doesn't have to apply so much with a manual sling.

Wow great stuff, I’ll be following your research for sure.
For me I’ve always felt that the relationship between “lag angle” and the power stroke of your hand to be the way to get the most power. So all the powerstroke transfers into the sling and the hand never chases the projectile. Just my thoughts I have no data or proof

Great to see some experimental data on this, well done!

It would be interesting to see with a longer sling as this will inevitably increase the path length a fair bit too.


Quote:

I have a theory that the movement of the hand effectively gives the sling a much larger radius at the release point, so the typical argument that there are only microseconds error to be accurate is not valid. Because of the large effective radius, the angular error is much smaller which makes it easier for the human brain to calculate the release point. That is the thought anyway. I didn't prove that yet, but I'm heading in that direction.

I've always thought there was something like this going on. The sling projectile I feel is moving in almost a straight line at the point of release which allows decent horizontal accuracy without crazy good timing. If you were to just spin a sling in a circle and let go without any throw action it would surely be much harder to attain any horizontal accuracy.

The lag angle is important because it reflects the core physics of the sling.

If you want to accelerate something, you must put energy into it, or 'do work' on it. The source of energy in this case is the motion of your hand, moving at any instant in some direction with a particular velocity.

At that same time, the sling is moving in a circle around the hand, by means of which the sling is tensioned, giving a force. Without this force you can't put any energy in to the sling at all.

But the most critical aspect is the angle between that velocity and the tension force, which is what I think Aussie coined as the 'lag angle'. The power transfer (the energy per unit time) to the sling from the hand is given by

    -Fv cos theta

with the minus sign because of the way the lag angle was defined. I wish I could get together a decent diagram, but I'm sorry I'm unable to do that at present.

There is then also an interesting balance which comes up and is superbly illustrated in IronGoober's video analysis.

You need to be moving the hand to accelerate the sling, but in doing so you tend to increase the radius of curvature of the path of the sling projectile and thus reduce the tension in the sling (given by mv² /r), where r is the radius of curvature of the path at that point and NOT the length of the sling.

@Mersa Lag angles are on the to-do list, I've had similar ideas and wanted to try and confirm them.

@wanderer I'm glad to see some physics equations without having to find them myself.  I think that there will be a physiological limit on maximum lag angle/power transfer that can go into the sling, because our tendons can only handle so much.  I'm going to continue to bring this up, because it has been studied so much more than slinging, but in baseball pitching the limit to how fast a human can throw is the stress on the tendons in the elbow/shoulder. I think somewhere on the order of 80-90N is what a elite athlete can sustain.  Source: https://www.youtube.com/watch?v=8udNOTFiqUs We will likely run into a similar limit with the sling, using the type of motion I am. Piroutte style might be different, since there are different stresses involved.

But last night, I realized that I can accurately estimate where the ball is in my video when it goes out of frame because I have the length of the sling from previous frames (in pixels) and the strands are straight. It should be simple to determine where it would have been. This will allow me to make some better measurements for the last 4-5 frames. and look at the lag angles in more detail.

IronGoober wrote on Oct 6^th, 2020 at 2:27am:

This was more work than I thought it would be. Kudos to Sarosh for all of his video analysis.

Thanks! Nice job with solving the problem of the view angle, I had trouble since my slinging style is slanted or sidearm and I cant get a camera over me .


IronGoober wrote on Oct 6^th, 2020 at 2:27am:

Because of the large effective radius, the angular error is much smaller which makes it easier for the human brain to calculate the release point. That is the thought anyway. I didn't prove that yet, but I'm heading in that direction.

since the path is not a circle that is the proof that every point on the projectile path has it's own curvature (in other words the curvature isn't a constant) and by having a lower curvature (bigger radius) for the same velocity(=dx/dt ) your dθ/dt is smaller dx=R*dθ => dθ=dx/R (bigger R gives smaller dθ where R has to do with the path and not the sling length)
It's not if but what style/technique/equipment makes the curvature smaller.


wanderer wrote on Oct 6^th, 2020 at 6:59am:

You need to be moving the hand to accelerate the sling, but in doing so you tend to increase the radius of curvature of the path of the sling projectile and thus reduce the tension in the sling (given by mv2 /r), where r is the radius of curvature of the path at that point and NOT the length of the sling.

by length of the sling you mean stretch or the length?
I've been thinking how much energy is absorbed/lost by stretching in the cords or if the smoothness felt by using stretchy cords adds any benefit.

the lag angle with that cos(theta) explains very nicely why you shouldnt struggle before releasing that is when theta is close to 90° => power transfer is 0.


wanderer wrote on Oct 6^th, 2020 at 3:27am:

Interestingly, I think there is a contrast with trebuchets here, where you generally want to slow the arm down close to the launch point - in order not to have a madly swinging arm left after the launch. That condition doesn't have to apply so much with a manual sling.

I dont know about this, I think it would be pretty awesome if the arm stopped by itself . with heavy stones it'll be easier but when going for speed there is going to be wasted energy.

Sarosh wrote on Oct 6^th, 2020 at 10:45am:

I've been thinking how much energy is absorbed/lost by stretching in the cords or if the smoothness felt by using stretchy cords adds any benefit.

I think it depends on the release mechanics. If the hand is slowing down a lot, then maybe. If you look at this plot, the hand does slow down at the end (where the arm is almost fully extended and wrist action begins).  This could mean that some stored energy in the strings would have time to recoil and add energy to the projectile. But it would also add a component of velocity toward the thrower, which might not be beneficial.  Because of this, you'd have to release sooner and reduce the length of the power stroke.

Actually, I'll revise my statement. I think in the end, elasticity isn't beneficial for a sling for attaining more projectile speed.  It might be useful for a cleaner release though, because it could help get the sling out of the way of the projectile faster.

Hmm... that's a thought. What if we added a small elastic to the release cord side of the sling?? The elastic would be shorter than the release cord. This way, the sling still functions as intended, but the stored energy will be released only when the release cord is loosed. This way it will pull the release cord out of the way of the projectile faster... I might have to try this. It might make the loading and wind up weird, but once it gets going, it would be fine.. Just needs the length tuned properly.

Update: Added extrapolated data from calculated ball positions.

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IronGoober wrote on Oct 6^th, 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.

Great stuff with this by the way.

I also feel that a forward step helps, but again I’m only hypothesising.

joe_meadmaker wrote on Oct 6^th, 2020 at 11:01pm:

'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.

I'm glad this is of interest to this community. I really wish I had a better way of doing all of this. It was a real hack job. If I had a more streamlined way of doing it, I would do all of these suggestions.

I wanted to measure all 6 of my throws and then plot them all on the same plot for direct comparison, but just getting the 2 was like, 6 hours of messing around. Now that I have some of the workflow in place it would be easier. But I'd like to setup an automated tracking program, I was having a lot of trouble using any of the Fiji plugins to work as intended.  If this were better data I'd write a paper on it.  I actually think that would be a great accomplishment for the community, for us to gather our resources, share data and write an open source paper on slinging mechanics.

This paper on throwing mechanics was neat. I think it would be great if we could do something similar.
https://www.mdpi.com/2076-3417/9/5/999

Alright gentlemen, here is my analysis of the lag angles. No interpretation yet. I stayed up too late finishing this. Darn Excel and its tiny parentheses!!

There is a lot of noise in the data at the point where my hand is changing direction. This is with using 3 point averaging of the positions to try and get it smoother.

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IronGoober wrote on Oct 6^th, 2020 at 10:38am:

@wanderer I'm glad to see some physics equations without having to find them myself.

I feel the difficulty here is more one of knowing where to apply the equations meaningfully, and perhaps more importantly being able to explain the motions with high-school physics. (One can write full equations for a lot of this, but they will not mean much to anyone without a fair degree of specialist knowledge.)
That needs notions like the curvature of a general path in space (the trajectory) to be understood. The matter of the forces and torques relating to physical limits I have to admit I think less about, but they are certainly interesting!


Sarosh wrote on Oct 6^th, 2020 at 10:45am:

by length of the sling you mean stretch or the length? I've been thinking how much energy is absorbed/lost by stretching in the cords or if the smoothness felt by using stretchy cords adds any benefit.

I was referring to radii in the same sense as you were, as the radius of curvature of a path in space. As far a stretching, ie. strain energy stored in the cords of the sling, I do believe this has an influence mostlin in pouch behavior. Think that when you release the cord, how does the pouch 'know' you have done it? It's not instantaneous, but depends on the speed at which a strain wave will travel up from the release point to the pouch. A wave of compression, or ripple, traveling up the cord towards the pouch could certainly influence release characteristics, particularly the way the resulting impulsive torque on the projectile affects its spin.

- I see that point has been made later in the thread.. I had to write this without having read the following remarks properly.


Sarosh wrote on Oct 6^th, 2020 at 10:45am:

I dont know about this, I think it would be pretty awesome if the arm stopped by itself . with heavy stones it'll be easier but when going for speed there is going to be wasted energy.

I think one always has to have some intent to reduce the arm speed for practical reasons, but I agree with your point. Can't resist pointing to a video channel which is by a young British engineer. He's into trebuchets and various other things, and his videos are concise, and I think really excellent merging of practical matters with what seems to be a very good understanding of the 'theory'.

https://www.youtube.com/channel/UC67gfx2Fg7K2NSHqoENVgwA

Mersa wrote on Oct 6^th, 2020 at 4:22am:

For me I’ve always felt that the relationship between “lag angle” and the power stroke of your hand to be the way to get the most power. So all the powerstroke transfers into the sling and the hand never chases the projectile. Just my thoughts I have no data or proof

That is exactly what the little equationlet that I posted shows.
IronGoober wrote on Oct 7^th, 2020 at 3:20am:

There is a lot of noise in the data at the point where my hand is changing direction. This is with using 3 point averaging of the positions to try and get it smoother.

Great work, and I well understand how much work these things can be! I'd suggest the plot before the cusp in not really much interest anyway - its just setting things up for the power stroke which begins as you accelerate beyond the cusp. To me the noise is darn good (ie. low) - amazing what a few years advance in video technology can do!

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 paths show very clearly the hand path kind of trying to maintain as big an angle as possible, until basically one gets to the point where things are turning too fast or you run out of room to keep the move going.

re. taking steps forward, they definitely can help, but generally if one changes ones action to do that, if you keep the rest of your form similar you would expect to have to increase the length of the sling. There are scaling laws in the dynamics air resistance bends the solutions) which mean a longer path length for the drive has to scale with the sling length.

wanderer wrote on Oct 7^th, 2020 at 6:12am:

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 and the hand to sling position. These two vectors.  It doesn't actually change sign if you think about it, me and the sling are always moving anti-clockwise, so their angular relationship should remain between 0 and ~90 degrees (it can go higher if my hand slows).

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. 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.

IronGoober wrote on Oct 7^th, 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.

My friend tried to film a pirouette from the bridge. But it was a bad place.

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.

Good discussion. I've done some additional analysis because of all of this.

NooneOfConsequence wrote on Oct 7^th, 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 7^th, 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.

---

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.

NooneOfConsequence wrote on Oct 7^th, 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 7^th, 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.

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.

Archaic Arms wrote on Oct 7^th, 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* :) ). 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).

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.

Amazing

joe_meadmaker wrote on Oct 6^th, 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.  ;)

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.

wanderer wrote on Oct 9^th, 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.

@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.

IronGoober wrote on Oct 9^th, 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. 

Wow amazing!!! 

This is good stuff! Eventually it should move to "Here be Maths" but I'm enjoying the debate it's getting here.

This data could be use pretty impressively for a thesis, if anybody's looking to publish in an Archaeology journal....

Speaking of maths... I think for the sake of search engines we should change the privacy settings on that section so people can view it without logging in.

Or we keep it to ourselves so the lurkers must join (as it twiddle my fingers to sinister music)

Mersa wrote on Oct 13^th, 2020 at 6:14pm:

Or we keep it to ourselves so the lurkers must join (as it twiddle my fingers to sinister music)

I’m pretty sure all seven people on the planet who would’ve joined slinging.org to participate in the maths section have probably already signed up. If we want a members-only section to encourage new members, it should be called “Here be free cash” :)

But if we rename the Maths section to be about cash, people will be confused, despite the fact that money is basically just math that rules your life.

I would agree about the privacy setting though. I'll see what I can do.

wanderer wrote on Oct 7^th, 2020 at 6:12am:

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?

You were right. I don't know how I missed this. You are absolutely right on the switch of the hand motion to ball motion and the change is sign of the "lag angle". I had to go back to frame by frame to see it. I thought I was correct that it stayed above zero and always the same sign, but nope. You were right. It's obvious now that I see it.

I’m not concerned with the numbers but this was an excellent angle to view a sling throw. Nice job.

dork wrote on Dec 1^st, 2020 at 7:37pm:

I’m not concerned with the numbers but this was an excellent angle to view a sling throw. Nice job.

Yes, I've been wanting to do it for years, but didn't really have the means. The real trick was to get a bluetooth remote for a phone camera, so I could trigger it on and off quickly. Having 240 fps was also kind of necessary, since 30 fps would just be too slow to get any meaningful data.

Updated plot with the lag angles corrected for the change in sign.

Interestingly, the lag angle isn't 90 degrees upon release. This means that acceleration of the projectile is happening until the moment of release.

I want to redo this analysis with a throw that isn't done for speed, but when I'm trying for accuracy, to see if there are any major differences.

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