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

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V-Griper View Drop Down
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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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racquetsforsale View Drop Down
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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 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: 06/27/2012 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 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 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 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 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 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 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 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 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
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: 06/27/2012 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 Loop40mm Quote  Post ReplyReply Direct Link To This Post 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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