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Concave vs. Convex Loop (Which is which/better?)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Loop40mm Quote  Post ReplyReply Direct Link To This Post Topic: Concave vs. Convex Loop (Which is which/better?)
    Posted: 06/28/2012 at 11:33am

This is an amazing discussion.  I would’ve never thought of the concave loop, even though now I realize I am using the concave loop in one or two situations.

 

Concave loop against topspin

 

I watched the Kong Ling Hui 1 hour 23 minutes video.  I saw one clip where KLH used the concave loop.  Instead of the convex counter loop against topspin, he used concave loop to hit. It is not for long distance loop.  Some beginners would’ve smashed the ball against topspin and the ball sails out of the table.  With concave loop, one hits and loops the ball.  The loop neutralizes the topspin. 

 

Concave loop against long pips chop

 

I use convex loop against inverted rubber underspin.  I start with a very low stance. Initially the paddle is open but ends up at a certain angle(perhaps 45 degrees).  The trajectory of the loop varies depending on the lift.

 

Against long pips underspin, I use concave loop to deal with the timing issue. Initially the paddle is open but after extending the arm, the paddle is still open. The combination of bat speed and angle of paddle have to be appropriate, else the ball goes long.

 

The other option to handle the long pips underspin is to use the rolling loop which has a delayed effect in hitting the ball, thus solving the timing issue.  This is the convex loop.

 

Receive serves

 

With penhold, recently I started using concave loops to receive serves on the forehand side.  It seems to be a safer shot for me.

 

Using concave loop for pips

 

I think pips player can make use of the concave loop, since I interpret the initial contact of the concave loop being a hit. 

 

Which one is better?

 

Personally I think the advantage goes to convex loop against topspin.  The topspin with the convex loop with the paddle closing brings the ball back down to the table better than the concave loop.  For convex loop, if the paddle angle is more open than it should be at the time of contact, the balls goes out of the table. 

 

Against inverted underspin, I will experiment with concave loop.  It depends on the skill level of the player. For a control game, concave loop might be a safer shot.  There seems to be more techniques involved in convex loop so the margin of error may be higher.

 

It is a humble experience in playing table tennis.  There is always one mountain higher than another mountain.

 

 

 

 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 1:01pm
Originally posted by reflecx reflecx wrote:

Here are 3 players with straight forward swing.

 

Actually, and I know I am being picky because I am defending a position, that stroke is still curved. Just not in the plane of reference you are looking at. Well partially. If we were looking from the top down you would clearly see that the paddle travels along an arc. You can partially see this in the pictures where you can see the curved part of the line that is tracing the stroke path. This point is not mutable as the arm has a relatively fixed length. The point you are making, I think, is that in the vertical side plane, or the stroke plane, there is no upward or downward curvature. I would argue that this is still not the case. 

Originally posted by racquetsforsale racquetsforsale wrote:

For you KLH fans, traces of his loops @ 17:40. Different angle though.



Good one but same as above. I would still contend that there is a curve based on what's happening at 4 mins in. What I perceive is that the curve has been compressed and accomplished with the forearm and wrist. To me this seems to occur in the transition between the backwards and forward motion of the swing. 

Same thing with Timo.



His is a little different in that his elbow tends to start moving forward before his wrist, kind of like a mini baseball pitch. The paddle, however, moves through a tight curve pivoting at the wrist. 


Originally posted by icontek icontek wrote:

Originally posted by racquetsforsale racquetsforsale wrote:

For you KLH fans, traces of his loops @ 17:40. Different angle though.




At 26:50 you can see traces of KLH's CONVEX loop.

It would seem the Chinese coach intends different strokes for different shots.

Is convex used for driving against underspin? I can't tell from the ball feeds, but I suspect so.

I agree in part but I think basic personal preference and ball height matter more. WLQ tends to use a downward(negative) curvature on most of his strokes. This is good up until the relative ball height makes this untenable. Once the ball reaches a certain height you need to change to a upward(positive) curvature to "cover" the ball. This is where you see the follow through change to  a more horizontal finish. Reverse all that for underspin.



Originally posted by pnachtwey pnachtwey wrote:

   ...but if the paddle attitude is always changing the resulting timing errors will result in poor control.  However, if the paddle attitude can be kept constant during the up swing it may work.   The big question is will this make any practical difference?   Most of us can swing far faster than what is necessary anyway.
 

This a point I agree with. I think that different players have come up with different solutions. Here is what I am perceiving. If you look at KLH and Timo video above there seems to be a lot of paddle movement in the transitions and just prior to ball contact. Here's the catch, his body is relatively still and the movement is simpler,"straight back/straight forward". Now look ML below. Very little attitude variation at the paddle, but serious body movement to cycle the paddle around. The same with RSM. 

 

RSM vid will not embed




Originally posted by power7 power7 wrote:


Zeio, I don't think the answer to the better understanding of TT will be found in relativity, quantum mechanics, or other esoteric fluid dynamic prinicples.  You think the PRC with their millions of engineers graduating every year wouldn't have 1 or 2 TT fanatic pursuing dead-end corolation already.

Your naivete is showing. Our whole modern society is based on pursuing so called dead-end correlations. I admit we are amateurs, both in TT and science, or at least I am, but that does not mean the effort is irrelevant.  I will also admit that this is not what you should be thinking about in the middle of a point but it does effect training protocols. 
Example-http://www.wired.com/playbook/2012/06/ff_superhumans/ Btw Lolo is seriously hot!


I was thinking about this relative to backhands and came up with an interesting conjecture(sorry gotta use it or lose it). SH players almost almost always have to use a downward(negativ) curvature to their stroke. I can't think of an example where this is not the case. So then I thought is there an example of an upward(positive) curvature BH? You guessed it rpb. The screw BH, done most notably done by WH, has a upward/outward(positive) curvature. SH players cannot do this shot without some difficult contortions of the wrist and elbow. I almost never see a SH player do this type of BH on a regular basis. 





Edited by V-Griper - 06/27/2012 at 1:29pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 12:54pm
Originally posted by power7 power7 wrote:

26:50 is about attacking a loop.  The segement was about quick counter hit to loop, followed by attacking a loop.  Ma demostrates the drill, 3 hit counter hit to loop, 3 attacks to loops.
 
17:40 is about FH looping off BH side.  The segment prior was FH loop off the FH side 1 meter back.
 
Zeio, I don't think the answer to the better understanding of TT will be found in relativity, quantum mechanics, or other esoteric fluid dynamic prinicples.  You think the PRC with their millions of engineers graduating every year wouldn't have 1 or 2 TT fanatic pursuing dead-end corolation already.

Excuse me?  First thing first, all physics referred to herein is only high-school level.  I wouldn't have needed to write all this if only those who were quick to point out "what is wrong" would have instead enlightened me on "the right way."  A picture speaks a thousand words?  I doubt it in face of people's superstitions being challenged.


Edited by zeio - 06/27/2012 at 12:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 12:26pm
Originally posted by pnachtwey pnachtwey wrote:

Originally posted by zeio zeio wrote:

It's not as simple as just attaching to the paddle an accelerometer.  I will save it for a separate post.
What difference does it make?  A 3D accelerometer will provide a lot of information that video systems can't.   The frame rate of the video system must be very high.   High speed cameras are very expensive.


The difference is huge.  The common elements of motion from velocity, acceleration, and momentum etc. to their angular counterparts are all vectors, which unlike scalar values, have both a magnitude and a direction associated with them.  Whether you're working in a 2D or 3D environment, in order to make correct and useful interpretations of and comparisons between the data collected from different subjects, it is necessary you have a reference point in place to compare against.  This is because the accelerometer measures the proper acceleration.  Nothing beats cameras when it comes to that.
Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote power7 Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 11:09am
26:50 is about attacking a loop.  The segement was about quick counter hit to loop, followed by attacking a loop.  Ma demostrates the drill, 3 hit counter hit to loop, 3 attacks to loops.
 
17:40 is about FH looping off BH side.  The segment prior was FH loop off the FH side 1 meter back.
 
Zeio, I don't think the answer to the better understanding of TT will be found in relativity, quantum mechanics, or other esoteric fluid dynamic prinicples.  You think the PRC with their millions of engineers graduating every year wouldn't have 1 or 2 TT fanatic pursuing dead-end corolation already.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote icontek Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 10:21am
Originally posted by racquetsforsale racquetsforsale wrote:

For you KLH fans, traces of his loops @ 17:40. Different angle though.




At 26:50 you can see traces of KLH's CONVEX loop.

It would seem the Chinese coach intends different strokes for different shots.

Is convex used for driving against underspin? I can't tell from the ball feeds, but I suspect so.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pnachtwey Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 9:33am
Originally posted by zeio zeio wrote:

It's not as simple as just attaching to the paddle an accelerometer.  I will save it for a separate post.
What difference does it make?  A 3D accelerometer will provide a lot of information that video systems can't.   The frame rate of the video system must be very high.   High speed cameras are very expensive.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote reflecx Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 8:56am

Here are 3 players with straight forward swing.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 7:19am
Originally posted by racquetsforsale racquetsforsale wrote:

That concave trace is a result of swinging about the shoulder socket. It's human anatomy and again I don't think one should proactively try to trace that curve because it happens naturally.

For the longest time, I thought my swing was pretty much on a plane (close to tracing a line when viewed from the side like in the picture), but it turned out to be concave. In addition, my swing angle turned out to be larger than what I thought---it was close to 60 degrees but I thought I was swinging at 45 degrees.

In human anatomy, motion "is produced by the skeletal acting as simple lever machines."  Simple movement like bending an elbow can therefore be defined as rotation about a fixed axis.  More complicated movement can then be defined as a combination of rotations about different axes.  Given these conditions, it follows that the tip of any body part undergoing motion, when traced out, would show a curved path.

However, this naturally occurring phenomenon is being ignored, denied, and attacked by those who hold the notion that their swings couldn't be any straighter.  The rationale behind it is most probably the belief that distance reigns over time, and if that is the case, then any deviation from it is either outright wrong or a waste of effort.  Now that there are signs they may be proven otherwise, they come up with doubts and that evidence be shown.  From his limited access to source material, V-Griper is trying his best to fill those requests.  But as I see it, that curve there is still not enough to get things changed.  Well, as V-Griper puts it, this is nothing new as the history of Science has shown.

Here I have on hand another essay paper(more like a book by its page count) about the biomechanics of the backhand loop stroke written by a German.  He went to great lengths to actually set up a complete environment to collect concrete data of the whole motion of the test subjects outfitted with markers all over their bodies.  It's not as simple as just attaching to the paddle an accelerometer.  I will save it for a separate post.


Edited by zeio - 06/27/2012 at 7:29am
Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote racquetsforsale Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 5:21am
For you KLH fans, traces of his loops @ 17:40. Different angle though.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote racquetsforsale Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 5:14am
That concave trace is a result of swinging about the shoulder socket. It's human anatomy and again I don't think one should proactively try to trace that curve because it happens naturally.

For the longest time, I thought my swing was pretty much on a plane (close to tracing a line when viewed from the side like in the picture), but it turned out to be concave. In addition, my swing angle turned out to be larger than what I thought---it was close to 60 degrees but I thought I was swinging at 45 degrees.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/27/2012 at 4:45am
The following is the section of that video where Wang Liqin demonstrates the forehand forward loop.

57s in, the trajectory of the ball and the path of his swing are traced out and superimposed on the screen.

Below is the same image overlaid with the brachistochrone curve grabbed from Wikipedia.  As his swing is carried out in 3D(traveling between different planes) and under real-world constraints, I have expected the curve to exhibit more differences from the 2D brachistochrone curve(static plane).  Much to my surprise, it appears that both curves follow an identical path from start to impact.


Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote racquetsforsale Quote  Post ReplyReply Direct Link To This Post Posted: 06/26/2012 at 2:36pm

Putting physics and metrics aside for a moment and going on feeling alone, I find linking the finish and start of the stroke via a curved path as WLQ is doing requires less effort than stopping the stroke at the end, reversing in the opposite direction, and stopping again before starting the stroke again, all on a more linear path.

Swinging and recovering in a continuous loop also helps with establishing a good rhythm and keeping the rally at a steady pace. This is desirable especially when warming up or drilling the basic counter or loop. In these situations, there's nothing more annoying than a hitting partner who can't more or less feed the same ball to you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/26/2012 at 12:14pm
Notwithstanding pnachtway's objections and the lack of hard data, let's go ahead and form a hypothesis, based on the premise, that the principles underlying the mechanics of the brachistochrone curve apply to what we are doing in TT. 

Let's use the video of WLQ counter hitting. I think this is the least ambiguous with regard to whether or not his stroke follows a curved path.



From the ready position. The paddle/arm follows a curved path down and back. It then follows a less pronounced curve up/forward through ball contact and follow through, at which point the stroke cycle starts again.

If the brachistochrone curve principles apply, then this is the shortest possible cycle time of the stroke. It would be faster to take the paddle back along a curved path than it would be to take the paddle straight back. Needless to say this would be somewhat counter intuitive but it wouldn't be the first time.

Now if we could figure out a reasonable way to substantiate this with some empirical evidence we would have a stronger base for training.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/26/2012 at 4:19am
Originally posted by power7 power7 wrote:

Originally posted by zeio zeio wrote:

I am getting there.

Forget the maths and the gravity.  The keyword here is time.  It is time, not distance, that really matters in producing the best swing.  And for that to happen the best path to follow during a swing is a curve that most closely resembles the brachistochrone.  Concave or convex, positive or negative, however you name it.  It may sound counter-intuitive, but the longer path does produce the least time and we see signs of it in videos of the pros.  And one thing is for sure, that path has never been and probably never will be a straight line as those who are in denial of any curvature in swing mechanics may have imagined.  They could have been doing it all along without even realizing.

The answer is out there, that the way we live, the tools we use, and the many things we come across during our lives are largely inspired by Nature.  As it turns out, we humans tend to ignore it and overcomplicate things.  As Johann Bernoulli himself has put it - "Nature always tends to act in the simplest way, and so it here lets one curve serve two different functions, while under any other hypothesis we should need two curves..."
This isn't non-Euclidean geometry, so the linear path takes the least amount of time.  Nor is this a gravity power problem with no friction.

The modelling is incorrect.  

The only thing applicable is Bernoulli's principle on the ball spinning creating low pressure systems thus make the ball "curve" in flight...



The brachistochrone problem was solved and proven in the Euclidean space in the 17th century.  The classical mechanics was developed during this period as well.  Non-Euclidean space did not emerge until the early 19th century.  What matters though is that the brachistochrone was first experimentally observed under the hypothesis of Galileo in the physical space, which, by Albert Einstein's theory of general relativity, is curved.  As the balls are traveling at far below the speed of light, the classical mechanics used to solve the problem is extremely accurate.  Unless you are hallucinating or something, I don't see how this model can be labeled wrong.

Yes, the reason a table tennis ball curves can be explained by the Bernoulli's principle.  But the Bernoulli's principle alone is insufficient in describing the sequence of events leading up to the pressure difference.  The boundary layer separation is necessary to fill the void.
Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote king_pong Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 8:23pm
I'm enjoying this thread as well.  I was away for the weekend, and see that I've missed a lot.  
The posting below by V-Griper is the closest I've gotten to anyone informing me which are concave and which are convex loops. Smile  Would love to know what people think/believe Smile

Originally posted by V-Griper V-Griper wrote:

Here is WLQ counter hitting. He is clearly guiding his paddle in a modified circular path. I say modified because the take back is like a semi circle but the forward part is flattened out. 



Again. This time the well referenced ML slow mo FH.  Similar motion. Starting from the ready position. Paddle goes down, then back beside the right knee. Then slightly up and then flattens out as it moves forward into the ball.



So the question is why do a circular motion at all? Why not do more of a straight back and strait forward motion? 

Like this.



Or this.



Iwill grant you that Timo and BP are still making a slightly squashed oval, albeit slight, but it looks nothing like what WLQ and ML are doing.

Some related questions-
Why is ML's elbow so close to the body on the take back? why does the paddle usually stop beside the knee? Why does ML's knee seem to collapse inward slightly?(So does RSM's btw https://www.youtube.com/watch?v=RMVzq-OnBcM&feature=player_embedded)

I am interested in peoples opinions. 

P.S. Please refrain from playing the "Chinese vs Euro" card. It gets old. I want you guys to think not recycle arguments.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 3:42pm
Originally posted by power7 power7 wrote:

http://www.google.com/products/catalog?q=accelerometer&hl=en&rlz=1C1CHKZ_enUS437US437&prmd=imvnsr&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&biw=1024&bih=673&um=1&ie=UTF-8&tbm=shop&cid=14940118607995515195&sa=X&ei=rb3oT__EF6HY0QG5iPSMCg&ved=0CJQBEPMCMAA

$25 USD...cheaper than some popular rubbers.

 
This issue came up in another post and we kicked around the idea of collecting hard data.

pnatwey works with that kind of equipment for a living. He knows exactly what it would take and how to do it. It is a matter whether or not he wants to put in the time. I would be willing to put money in the pot for equipment depending on the cost estimate.


Edited by V-Griper - 06/25/2012 at 3:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 3:28pm
Originally posted by pnachtwey pnachtwey wrote:

I find it interesting but we don't swing using gravity alone.   It is would very nice to put a  3D accelerometer on the back of a blade to see what is really happening.  It doesn't surprise me that some of the authors didn't get any attention without hard data.


Alright, you've got the know how, let's get some hard data then. How cost prohibitive is it?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pnachtwey Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 3:14pm
I find it interesting but we don't swing using gravity alone.   It is would very nice to put a  3D accelerometer on the back of a blade to see what is really happening.  It doesn't surprise me that some of the authors didn't get any attention without hard data.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 11:51am
To keep things straight, the energy source behind the two balls is actually the potential energy.  Potential energy can exist in quite a few forms, and each of them comes from a particular type of force, namely the conservative force.  In the brachistochrone problem, the force of gravity used to initiate a change of state from rest to motion is a type of conservative force and it gives rise to gravitational potential energy.  As the balls trace down the paths, the potential energy within them is converted into kinetic energy.  By the conservation of energy, in a closed system where friction is neglected, both potential and kinetic energy are conserved.  In layman's terms, the balls are powered by an engine that is 100% efficient with no loss.  Theoretically speaking, they start off at the same level of potential energy and should end up with the same final velocities at the end of the paths.  In an experiment run in Germany where kinetic energy is not conserved due to friction, the final velocity of the ball along the brachistochrone curve has been found to be greater than that of the ball along the straight line, as cited by this source.  So it looks like the brachistochrone is also more efficient in aspects other than time.

For table tennis, we draw on a number of potential energy.  When one winds up during a backswing, elastic potential energy is stored in parts of the body, waiting to be released.   Chemical potential energy from food is transformed into kinetic energy when we do work to swing the paddle back and forth.  When players lower their stances, they also gain gravitational potential energy.  Instead of using the gravitational potential energy gained from the force of gravity alone to start motion as in the brachistochrone problem, the goal here is to make the most out of the additional potential energy available to us to overcome gravity in a three dimensional swing.

The timing problem is not really a problem as we have all witnessed.  This is what training is for.  One may be a fluke, two could be coincidence, but three is a trend.  Every pro may approach it differently, but the basic rule still holds.  Just because the human nature within most of us tends to think only the pros can do it well should not deter the rest from pondering, discussing, and mimicking, for this is how one gains knowledge.

Of all western sources I've managed to dig up, only those in skiing and surfing is the brachistochrone curve ever directly mentioned and applied for performance gain.  Not to worry, here is a thesis just about its application in table tennis, titled "Kinetics Analysis of the Kinetic Chain of the Execution of Strokes in Succession while in Motion in Table Tennis" by 賈鵬(Jia Peng) and published in 2007.  I do not have access to the full paper, but the abstract will suffice.  Below is an excerpt about the benefits of integrating the brachistochrone curve into stroke mechanics.

(3)人体在移动后动力再链接包含了“引拍、挥拍、还原”的周期过程,尤其在连续击球时,“引拍、挥拍、还原”的线路轨迹、周期长短、频率高低以及击球前的准备充分程度都直接影响击球的效果。在研究过程中把“引拍、挥拍、还原”的轨迹、周期、频率和单摆、锥摆的轨迹、周期、频率运用力学的方法做了详尽的比较分析,也利用“最速降线”对“还原、引拍”进行了力学上的比较分析,得出人体在持拍连续击球的时候,利用近似椭圆的轨迹特点,利于发挥速度、频率优势,在节奏快的激烈对抗中获取时空上的利益,以期能够获得技战术上的优势。
(3) The kinetic chain of the human body after some displacement involves a cycle of "backswing, swing, and recovery".  The path, period, and frequency of the cycle, as well as the level of readiness before each stroke all have a direct effect on its result.  During research, the path, period, and frequency of the "backswing, swing, and recovery" and of the simple pendulum and the conical pendulum are given extensive comparative analysis using kinetics.  The same analysis is also performed using the "brachistochrone curve" for the "recovery and backswing."  The results derived suggest that when the human body executes shots in succession, use of the ellipse-like path facilitates the play of speed and frequency to get the upper hand in space-time during a fast-paced and fierce confrontation in hopes of gaining further technical and tactical advantages.

At this stage, we see the potential advantage of applying the brachistochrone curve for the recovery and backswing before and after a swing.

Other than the thesis above, there is another user by the name "jlw" posting about the brachistochrone curve(1), (2).  The poor dude got practically zero constructive feedback.

Edited by zeio - 06/25/2012 at 12:02pm
Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 11:49am
Originally posted by pnachtwey pnachtwey wrote:

Originally posted by zeio zeio wrote:

And for that to happen the best path to follow during a swing is a curve that most closely resembles the brachistochrone.

The brachistochrone works because the brachistochrone allows the ball to drop or accelerate faster initially.  This isn't the case with a swing that opposes gravity.

I know where you are going with this.  You are thinking of the brachistochone with a upwards swing where the swing starts out shallow to get moving and then starts in the upwards direction.  Good one, but if the paddle attitude is always changing the resulting timing errors will result in poor control.  However, if the paddle attitude can be kept constant during the up swing it may work.   The big question is will this make any practical difference?   Most of us can swing far faster than what is necessary anyway.


I would say that the paddle angle can and is kept constant by the better players who seem to be using a more circular motion.

ML seems to hold blade angle more constant throughout his swing cycle than Timo. At least that I can perceive. BP seems to hold paddle angle more constant than ML or TB but I am not sure he could generate the paddle acceleration that ML or TB can.

Imo minimizing timing errors is mainly a nervous system issue. I see a lot of players with very inefficient strokes who have incredible timing because they do exactly what you say, they hold the paddle angle relatively constant. 

I was practicing with a beginner Yesterday and he could do 150 ball rallies. I noticed, however, that in order to keep his paddle condition constant he made all kinds of contortions with his wrist elbow and shoulder.

Then there is the 1800 level player at our club who has to quit training for a couple of days if he does a lot of looping. His loop mechanics are so bad(FH & BH) I worry about him tearing his rotator cuff. He has already had minor tearing in his shoulder muscles. 

The ball may not care what you do prior to and after contact but your body sure does.



Edited by V-Griper - 06/25/2012 at 11:51am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 9:41am
I love things that challenge my intuitive assumptions about how things work. Even if this is not substantially relevant to TT it is still cool.

Thanks Zeio.


Sorry won't embed.





Edited by V-Griper - 06/25/2012 at 9:47am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote V-Griper Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 9:28am
There is also conservation of momentum and energy. 

If you use a more straight forward/straight back motion you have to expend a lot more effort accelerating and decelerating the paddle. 

By following a more circular stroke path momentum and energy are conserved.

There is also adjustment to incoming ball to consider. As an example if you look at ML slow mo vid again, when ML begins the forward part of the stroke, you can see there is more of an virtical component to his stroke. To me this is where the height adjustment is being made for the height of the ball. However there is still a forward component to the stroke. It's just more efficient. 


BTW this is the best thread in awhile. Clap This is where we challenge our assumptions and refine our paradigm. 

Time to get your geek on Tongue


Edited by V-Griper - 06/25/2012 at 9:32am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krantz Quote  Post ReplyReply Direct Link To This Post Posted: 06/25/2012 at 6:52am
Nice observation about brachistochrone curve. For now it tells me that we cannot outright exclude the possibility that a curved motion may be “faster” then a motion along a straight line. Here are few other possible explanations why curved motion (with a long follow-through) can be a good option:

1. It may be easier to aim with that kind of swing. While it’s true that all it really matter is an angle (direction, speed) of a racket at point of contact it may be easier to adjust these factors during longer swing. Compare this to shooting with a rifle and with a pistol. If you adjust your sights perfectly then it doesn’t matter which gun you shoot with, but it is easier to adjust sights of a rifle because of longer distance between a notch and a bead - and this results in overall better accuracy of a rifle. Consecutively, a longer curved swing with a long follow through may just help you in placing the ball at the exact point you aim.

2. Generally, the harder you hit, the more closed the angle of a racket should be. A positive arc of a movement assures just that. At the beginning of a swing the racket’s speed is low, so its angle is open. While you accelerating, you are continuously closing the angle and during the whole swing their combination is just about right to place the ball on the table. Moreover, I would say that this option of closing the angle is on the safe side of an error margin - closed angle is good. If the angle is to low then in order to prevent the ball from hitting the net you have to just hit harder - and hitting harder in order to not miss the table is a win-win scenario. 

3. Natural ready position between shots is with a hand relatively low. Sufficient reason that we don’t wait for a ball with a hand raised high is that it would be to tiring. But quite often we have to hit the top part of the ball – the only way we can do this (from this low hand starting position) is by performing this curved, positive arc motion. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote pnachtwey Quote  Post ReplyReply Direct Link To This Post Posted: 06/24/2012 at 6:47pm
Originally posted by power7 power7 wrote:

This isn't non-Euclidean geometry, so the linear path takes the least amount of time.  Nor is this a gravity power problem with no friction.
You assume that the velocity profiles are the same.   If there is no friction then the speeds will be the same at the bottom of the ramps but the cycloid ramp will allow the ball to accelerate to faster.   The area under the velocity curve,  the distance,  traveled will be greater when comparing with the constant acceleration ramps at the same time.

Quote
The only thing applicable is Bernoulli's principle on the ball spinning creating low pressure systems thus make the ball "curve" in flight..
So far yes,  lets wait for zeio to make his case.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote power7 Quote  Post ReplyReply Direct Link To This Post Posted: 06/24/2012 at 4:02pm
Originally posted by zeio zeio wrote:

I am getting there.

Forget the maths and the gravity.  The keyword here is time.  It is time, not distance, that really matters in producing the best swing.  And for that to happen the best path to follow during a swing is a curve that most closely resembles the brachistochrone.  Concave or convex, positive or negative, however you name it.  It may sound counter-intuitive, but the longer path does produce the least time and we see signs of it in videos of the pros.  And one thing is for sure, that path has never been and probably never will be a straight line as those who are in denial of any curvature in swing mechanics may have imagined.  They could have been doing it all along without even realizing.

The answer is out there, that the way we live, the tools we use, and the many things we come across during our lives are largely inspired by Nature.  As it turns out, we humans tend to ignore it and overcomplicate things.  As Johann Bernoulli himself has put it - "Nature always tends to act in the simplest way, and so it here lets one curve serve two different functions, while under any other hypothesis we should need two curves..."
This isn't non-Euclidean geometry, so the linear path takes the least amount of time.  Nor is this a gravity power problem with no friction.

The modelling is incorrect.  

The only thing applicable is Bernoulli's principle on the ball spinning creating low pressure systems thus make the ball "curve" in flight...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote zeio Quote  Post ReplyReply Direct Link To This Post Posted: 06/24/2012 at 2:20pm
Originally posted by hobbes203 hobbes203 wrote:

@Zeio

Couldn't resist answering that question, both objects are of the same mass and has the same qualities (same kinetic and static friction, etc), and the ramps are also equivalent, then both would hit the bottom at the same time whether they slide or roll. Easiest way to do this is energy, but I'll leave it at that.

The important question is what are the accelerations of the objects at the bottom? (Answer should be a vector quantity, magnitude and direction).

Given a very, very general scenario, the comparison of the balls at the bottom of the ramp can be applied to the moment a table tennis ball at a fixed point is contacted by the concave and convex strokes. At this point, I won't try to get into springs, torque, friction, and the magnus effect. Generally, the ballistics of the ball is determined by the magnitude and acceleration at different contacts of a controlled ball. 

I'm no expert but really just try the strokes for yourself, have a robot hit one spot and hit the ball at the same spot with controlled similar-accelerated but different swings.

Also pnachtwey +1 from me Big smile

Both objects are identical in size, shape, and weight etc.  They are under uniform gravity.  Friction or frictionless does not affect the outcome.

They reach maximum velocities at the bottom.  Assuming no friction, the vertical accelerations of both objects are constant but of different values as they run down the paths.  This difference in vertical acceleration is what separates the two.

Quote Our intuition would most likely tell us that any object allowed to fall under the influence of gravity alone would take the natural straight line course despite the  object being  constrained to travel as quickly as possible – travel of least time. And we are inclined to come up with such a conclusion for it’s the seeming natural appearance of events – the Aristotelian method of deducting scientific conclusions.

Viscaria FL - 91g
+ Neo H3 2.15 Blk - 44.5g(55.3g uncut bare)
+ Hexer HD 2.1 Red - 49.3g(68.5g 〃 〃)
= 184.8g
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 06/24/2012 at 2:19pm
The reason why a follow through matters is because a swing that results in a proper follow throw begins before you hit the ball, and therefore affects the way you hit the ball.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 06/24/2012 at 2:15pm
There is more than one way to skin a cat.  That is why several different players who have been in the top five in the world appear to have a different swing, and they all have great forehands.  Also, it is very very hard to remodel a stroke once it is formed -- and in adults in general.  It can be done, but it takes a long time.  That may not be apparent from an engineering perpective, but it is true from a physiological perspective.  Those motor patterns get really engrained.  Tape yourself and find out.  It may feel like you are making big changes in your stroke and when you actually see it, you just look like you.  (Especially once you play a match).  Feel and reality do not always coincide.  The most important things are (1) does your swing produce reasonable spin, pace, and accuracy, and (2) can you maintain your balance so as to be able to hit the next ball?  If you forehand does this with consistency than it doesn't matter if you look like WLQ, ML, or the Dalai Llama.  You will be good.  And Bernoulli, Gauss, and Laplace be damned.    
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