Dwell Time .....

hipnotic said:

Langel, your reasoning is correct but you are missing one thing. The pitch measured on the bounce test only gives you the 6th mode of vibration, the membrane mode. The others modes are not heard but you feel them in your hand. So, there is a correlation between pitch and speed, and that is proven in the several articles i showed, but it is not the only factor.

But i agree with you, after i built a few blades, and successfully predicting their frequencies, i found that the ones with higher frequency weren't necessarily the fastest. The first mode (bending) is very important and what gives that upper gear when you strike the ball hard, basically the flex. The 6th mode (membrane) tells you how hard the blade is. But it is the correlation between these two aspects that defines the performance of the blade in the different speed ranges.

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Yes, what I said there and what I say here is not that there is no corelation - there is a corelation.
What I say is that there are so many corelations which reflect in so many ways, that just a single general assumption is not enough to make a general decision. Its not the single factor - speed range, flex, hardness, dwell, linearity, rubbers characteristics etc., but the personal feel of all these as a system, which makes the real difference and may suit and help a player, or may not.

hipnotic said:

You actually said they are the same thing in this case, which i was trying to refute. But ok, I'm not going to try to change your mind, agree to disagree

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Exactly, "in this case", meaning they're not the same, but in this case it doesn't matter.
Agreed to disagree

langel said:

The dwell depends not only on the amplitude of the deflection, but on the frequency of vibration, and a lower frequency will make it easier to prolong the dwell. Another factor are the rubbers - here many people say that softer rubbers provide longer dwell. Well, in some cases it may be true, and in some it may be not. Softer rubbers with greater trampoline will have less dwell than softer rubbers with less trampoline. And with weaker shots they may have less dwell even from harder rubbers with less trampoline. In my case the above mentioned blade didn't provide its dwell capabilities at close distance with softer and repulsive rubbers, but worked well with harder ones. So every different combination blade+rubbers will have different dwell, providing different feel. One may not think about "dwell", and we usually speak about "feel". While dwell depends on the characteristics of the bat, in fact it depends more on the players' style and his synergy with the bat. A blade with the best dwell in particular speed range may not be the best for a particular style and particular rubbers. So I think it would be better to concentrate in building a bat with the best feeling and comfort in play, giving best confidence. Taking and carrying the ball with prolonged dwell would come with technique development.

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And you continue to talk about dwell as if it's more than an instantaneous reaction. Regardless of how you want to write about this, with "longer" and "less" and "best" and even "prolonged", you are still talking nonsense. The ball makes contact with the racket (blade plus sponge plus rubber) and is gone in single digit milliseconds. There is no prolonged. The difference between 1 millisecond and 3 milliseconds is still so small as to be instantaneous. Earlier you made the absolutely ridiculous claim of 1 second dwell and I'm calling you out. Show us a video of someone in a table tennis match hitting a ball with a dwell time of 1 second and I'll leave you alone. Until then, as far as I'm concerned, nothing you say has any credibility.

I have seen players catch the ball on their paddles. The ball just sits on the paddle. The dwell time in infinite for all practical purposes but we don’t catch the ball during normal play. At warm up type speeds the dwell time might , might, get to 1.5 to 2 milliseconds but at faster speeds the dwell time is closer to 1 millisecond or less. This is not an opinion. I have a high speed camera that can take 2000 FPS easily but standing in front of halogen lamps gets very hot quickly. Paddles seem to vibrate more when in a vise instead of my hand. Makes sense. Hands absorb energy.

my toxic 5 flexes a lot. My firewall plus doesn’t appear to flex at all. I doubt we could see my TBS or TB ALC flex either.

no one is asking the the right question. what are the conditions for increasing dwell time. Softer and thicker rubbers will help but I am talking about the conditions from a physics point of view. What forces are necessary to increase dwell time? Why do softer, thicker rubbers help increase dwell time?

i have been busy this week. I can answer more this week after today.

bircham boi said:

And you continue to talk about dwell as if it's more than an instantaneous reaction. Regardless of how you want to write about this, with "longer" and "less" and "best" and even "prolonged", you are still talking nonsense. The ball makes contact with the racket (blade plus sponge plus rubber) and is gone in single digit milliseconds. There is no prolonged. The difference between 1 millisecond and 3 milliseconds is still so small as to be instantaneous. Earlier you made the absolutely ridiculous claim of 1 second dwell and I'm calling you out. Show us a video of someone in a table tennis match hitting a ball with a dwell time of 1 second and I'll leave you alone. Until then, as far as I'm concerned, nothing you say has any credibility.

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As a mild criticism of the above argument: if you are asking for proof of "1 second dwell", may I ask for a reference to back up 'single digit milliseconds' claim? Humans are not very good at understanding the scale of things at that level (everyone has some idea what 1 second is, but millisecond is harder to grasp, our internal clocks are not that precise), so a guesstimate of that type is frequently wrong.

Also - difference in 1 ms and 3 ms is actually HUGE. Interaction between ball and rubber obviously matters (otherwise we'd all be playing with bare blades), so tripling the time of contact is probably not trivial.

P.S. Found a reference that quotes 4ms impact time (ball being dropped from a moderate height on inclined rubbered surface). So, yes, single digit ms is about right for their experiment that used slower ball speed, I suspect, compared to actual TT rally and no human performing the stroke, which should matter somewhat too.

http://www.physics.umd.edu/courses/Phys405/Hill/Fall05/Information/AJP/AJP00482.pdf

At about 1:39 in this video, the girl's shot has a much longer than normal dwell time. You could say she carries the ball and I am not sure it should be legal. But the ball is in contact with her racket for close to a second on the video.


In my photo of Mark serving, you can see he holds the ball on the rubber for a long time during the serve. The ball is in contact with the rubber for several inches of the stroke even though this is still only a fraction of a second because his racket is actually moving quite fast from the whip mechanics:



I already posted that but it is worth noting the relation to that and the next video. This video was originally posted by Suga D years ago for a different thread with a similar subject. You can see on the loop that the player holds the ball on his blade face for quite a long time in relation to the stroke and to normal contact.


I could not get a good angle where you could see that the ball is held on the rubber to make a screen shot like the one above of Mark. But you can see he holds the ball on the rubber and pulls the ball to increase the spin. Here too, the stroke is quite fast and the time the ball is on the rubber is still only a small fraction of a second. But you can still see how he holds the ball on the rubber for much longer than one would think possible.

So, again, I will say that this is based on the skill in the hands of the player. And it really about exactly what Der_Echte and Monster were discussing. Touch and feeling are necessary for high level play. And the sooner a player learns that the art of soft hands and adjusting grip pressure, how your hand holds the racket and how the racket touches the ball, and the idea that you want to be trying to pay as much attention to what your hand feels while you are contacting the ball, the more possible it is to try to develop these skillz that are generally untaught.

By the way, everything I have said so far in this thread, at least from my perspective, should be obvious from that video of Marcos Freitas I posted. Try some of those things. Practice them. I guarantee they will help you contact the ball in a way where you can create extra dwell time because you will refine your skillz in the art of how you touch the ball. Any of them. All of them. They are worth practicing.

I have consistently said that the application of this or that grip pressure at impact is a very important and chronically under discussed topic.

Sent from my SM-N950U using Tapatalk

Der_Echte said:

I have consistently said that the application of this or that grip pressure at impact is a very important and chronically under discussed topic.

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And you have been consistently correct about this for a long time. This is why the goon squad is always chasing after you thinking you are using highly boosted Pro and National versions of rubbers you don't even use. Little did they know, you real secrets are grizzly bear sweat, banana peels and grip pressure.

UpSideDownCarl said:

At about 1:39 in this video, the girl's shot has a much longer than normal dwell time. You could say she carries the ball and I am not sure it should be legal. But the ball is in contact with her racket for close to a second on the video.

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I'm sorry to bang on about this, but if you are even close to correct then I'm going totally insane. The shot you refer to is part of a point in which the ball is struck 25 times in 12 seconds. Even with dodgy youtube and even dodgier maths, I calculate that's half a second per shot - and that includes the time it takes for the ball to travel from one end of the table to the other. Ball travel time is by far the larger part of time involved. If we apply dodgy maths 101 and remove an estimate for travel time, then ball contact time is much reduced. For example, if ball travel time is 90% of the time (and that's a very, very conservative estimate) then ball contact time is .05 of a second. But we know from video evidence - see brokenball's comment: "At warm up type speeds the dwell time might , might, get to 1.5 to 2 milliseconds but at faster speeds the dwell time is closer to 1 millisecond or less. This is not an opinion. I have a high speed camera that can take 2000 FPS easily" - contact time is much, much smaller than .05 second.

The unique shot itself: Playing the video at .25 normal speed and counting frames, it takes 4 frames at the very most to play the shot. According to google, conventional frame rates are from 24 to 60 frames per second. Therefore, at the slowest likely frame rate, 4 frames = .16 second. Not "close to a second". Next up is the question of how the ball is contacted. It's impossible to tell from the video and I doubt the player herself even knows what actually happened. Did she "carry" the ball? Or did she hit it multiple times? We've all hit the ball multiple times; double hits are common, triple highly unusual but I imagine most of us have done this at some time or other. Did she hit the ball twice, three, four or more times? It's impossible to tell. Even if she hit the ball only twice, then that reduces contact time to .08 second. If four or more times?

Finally, her stroke is so utterly unusual surely you can't include it as an example of what everyone else is thinking of as dwell time. That's a bit like saying, "I saw a green sheep once, therefore the colour of sheep's wool should include green." Rather, this particular shot is an example of what dwell time does NOT look like.

UpSideDownCarl said:

Some of dwell time is in the hand. The skill of the player can cause the ball to hold on the rubber a tiny bit longer. Softer blades help you develop this skill. But in the end, the skill is in the hand. Some people have good touch and good feeling. Others do not.

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Okay, Marcos Freitas has crazy skills. Love it. The video demonstrates a range of things that most of us can only aspire to. However, does the video demonstrate that dwell time when playing a stroke can be prolonged to anything like the times claimed by some? Answer: no.

Play the video at .25 speed. During the "backspin catcher" sequence, it's easy to see that every single time the ball bounces repeatedly on the blade before coming to rest. Each time the ball bounces - the dwell time - is miniscule. That is dwell time, not the ball sitting on the racket at the end of the catch. Similarly, in the last section on "grabbing and punching" it's perfectly easy to see that the ball is bouncing before coming to rest. Insane skills? Yes, yes, yes. Demonstration of loooong dwell time? No.

The real secret to dwell time is twofold:

1) holding the racket VERY FIRMLY

2) Hitting the ball across in a way where it .. uhmm... travels diagonally on the rubber. Not sure how to explain this without an image.

Isn't anybody going to do some rough math?
Years ago Baal did some "napkin" calculations that were pretty close given the assumptions.
I am pretty sure normal blades do not affect dwell time much.
I would bet a lot that plastic balls have a shorter dwell time than celluloid balls because plastic balls do not indent as easily as celluloid balls.

There are too many opinions.
There is little understanding.
Asking the right questions and searching for the answers is the key to understanding.

I will start by asking some questions.
If a ball traveling at 10 m/s contacts a paddle and decelerates and a constant rate. What what will be the deceleration rate if the ball travels:
1 mm before stopping?
2 mm before stopping?
3 mm before stopping?
What is the deceleration time?
Which if these 3 options seems the most reasonable. The ball will deform a little. The rubber will compress a little
The blade may flex a little.
Will all of this add up to 1mm, 2mm or 3mm?

bircham boi said:

Finally, her stroke is so utterly unusual surely you can't include it as an example of what everyone else is thinking of as dwell time. That's a bit like saying, "I saw a green sheep once, therefore the colour of sheep's wool should include green." Rather, this particular shot is an example of what dwell time does NOT look like.

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Perhaps my method of calculating the time was flawed. But yours seems more flawed to me than mine was. You are trying to calculate the time of her contact by what happens in other shots in the rally which are much faster. Not sure how an average makes much sense.

I calculated by the fact that the ball contacts her racket on the one shot in question shortly after the YouTube clock hits 1:40 and ends shortly before the YouTube clock hits 1:41. It could be a little less than half a second. But not much. And it is definitely longer than the 5/100ths of a second you propose. She catches the ball, slowly spins and changes direction with the ball on her racket.

Does it make multiple contacts? Good question and good point. It is possible. But it is also possible that, because she is moving and changes directions while carrying the ball, that it is just one contact. Regardless of whether she catches the ball cleanly or there is more than one hit, she holds the ball on there longer than most.

You complained that this isn't a normal stroke. But when you asked for a long dwell like that while attacking langel, you did not specify what kind of stroke. You simply said:

bircham boi said:

If what you say is even remotely true, then you should have no problems producing a video with "a dwell of a second". Please provide us all with the evidence to prove this ridiculous claim.

But I know - and you know - you can't provide such a video because it doesn't exist.

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Well, she has the ball on her racket for quite a long time. I am not so sure my method of calculation is perfect. I will assert it is closer than yours. And if anyone has a good stop watch and wants to time it, I say, go ahead. I have a feeling brokenball may have the tools to tell us a better approximation of how long she holds the ball on the racket.

Now I don't really care about dwell times of a second because it is true that in normal play that does not happen. But it is also true that you can hold the ball on the racket a little longer than the normal 0.5-1 milliseconds. I gave two decent examples that are fairly easy to see: Mark Croitoroo serving. He did that serve for me, solely for the purpose of recording a backspin serve where he held the ball on the blade face for longer to generate crazy backspin. I promise, the spin on that serve was crazy. And then the loop from the video I got from Suga D. You can see on that pull ball loop that the guy in the video holds the ball on for a long time. I would say Mark's serve and that pull ball loop, the contact time is probably about 3 milliseconds. So it is still really short. But a lot longer than a normal dwell time. And the skill for that is in the hand of the player.

As far as the backspin catcher; that is definitely not about long dwell time. That is actually about having the control to make the dwell time so short and so thin that the ball keeps spinning and is not grabbed by the topsheet. There are 100s maybe 1,000s of contacts in the short time the ball is on the rubber in that. But the info is, that the skill is in the hands to lengthen or to shorten dwell time.

Anybody know how to find that video of the Japanese guy who, returning serve, catches the ball on the racket, runs around the net and smashes it? That video explains what brokenball is talking about with catching the ball and infinite dwell time. And it is possible. Most of the time, when someone catches the ball, there are bounces. But not always.

If you're talking about Dwell Time in the context of measured, phisics and factual manner, yes, there's no difference in measured dwell time between blades and rubbers. There's no difference in dwell time between pimple-in, pimple-out, long pimple, anti and hard bats according to the experiments conducted by Butterfly using 8000 FPS high speed camera. I think Baal mentioned in similar therad before but we can only distinguish the difference in dwell time if it's more than 10ms. There's abslutely no way we can tell the difference if it's less than 1/8000 second and it definitely does't show in 100/60FPS youtube video.

Other feedbacks such as rebound speed, rebound angle, vibration and sound gives us the percieved "dwell time".

Perception is important because telling somone to serve with backspin as if the "ball stays on the blade as long as possible" helps him/her spin more because brushing motion gives you longer percieved dwell time.

But saying that X bat or Y rubber gives you longer (measured) dwell time is simply wrong but Butterfly themselves use this term for marketing purpose, strange world!

@UpSideDownCarl

The touch required to create a perceptible difference in dwell time, and when I say perceptible I mean by the person who is playing, does not come that easy .

No matter how much @Der_Echte likes to disagree with me, you and I know how good his touch is. I find it pointless to argue with guys who have not either done it themselves or seen international players play in person from 10 feet away to know what it is . You have I know so I am telling you this debate really not worth it.

I have seen a couple of players , one of them is a taiwanese women's national team players and a few others in the bay area .. and you can clearly see when they serve what dwell time means and feels like ... its almost as if they catch the ball and throw it .. so its a bit like experiencing an emotion .. you can read all about it books and argue about it all you like with Physics and maths but if you haven't felt it yourself , you will never know what it is.

Thats why I like the word "feel" and why its used so much in Chinese Table tennis vocabulary ... it says a lot without saying that much ..

That Der_Echte is such a disagreeable guy... almost as bad as that BH-Man over at MyTT. Almost. And dude can't brew a cappuccino for crap. WTF man.

ttmonster said:

Thats why I like the word "feel" and why its used so much in Chinese Table tennis vocabulary ... it says a lot without saying that much ..

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Much agree with all you said in the post, especially with the quote.

langel said:

Its not the single factor - speed range, flex, hardness, dwell, linearity, rubbers characteristics etc., but the personal feel of all these as a system, which makes the real difference and may suit and help a player, or may not.

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Hey, Carl. Not trying to argue, just clarifying what I'm trying to say.

Originally Posted by UpSideDownCarl
Perhaps my method of calculating the time was flawed. But yours seems more flawed to me than mine was. You are trying to calculate the time of her contact by what happens in other shots in the rally which are much faster. Not sure how an average makes much sense.

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I agree that an average is not much sense when it comes to that one particular shot. I was simply pointing to a general sense of dwell time in general play.

Originally Posted by UpSideDownCarl
I calculated by the fact that the ball contacts her racket on the one shot in question shortly after the YouTube clock hits 1:40 and ends shortly before the YouTube clock hits 1:41. It could be a little less than half a second. But not much. And it is definitely longer than the 5/100ths of a second you propose. She catches the ball, slowly spins and changes direction with the ball on her racket.

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I can't see much point working from the YouTube clock. It's much easier to see what is happening when viewing in .25 speed, then pausing and advancing frame by frame. Here is what I see:

First contact with the ball and next 3 frames:








It's clearly visible in the last frame that the ball has already left the bat. These were the frames I did my calculation on, allowing for a maximum contact of four frames. Calculation 1 : 4 frames at 24 fps = 0.16 sec. Calculation 2 (also possible) : 3 frames at 60 fps = 0.05 sec.


What I failed to do was follow the action and record the second period of contact. There are a number of frames where the player's bat is chasing the ball. The last of these is:




Second contact plus next 3 frames:









The second last frame is somewhat problematic. Because the ball begins to travel in the direction of the table and the bat is behind it, it's impossible to tell if the ball has already left the bat. Let's give it the benefit of the doubt and the next frame too, even though I think the ball is no longer in contact with the bat. Same calculations as before: If the ball is not bouncing on the rubber, then contact time, i.e. dwell time, is maximum .16 sec.

Originally Posted by UpSideDownCarl
Does it make multiple contacts? Good question and good point. It is possible. But it is also possible that, because she is moving and changes directions while carrying the ball, that it is just one contact. Regardless of whether she catches the ball cleanly or there is more than one hit, she holds the ball on there longer than most.

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Sorry, but there's something going on here which is hard to deny. If you look at the first four frames posted and then compare with the last four, you'll notice a strange phenomenon . First four: ball on black rubber. Last four: ball on red rubber. This is the perfect example of the sorts of thing which happen all the time in table tennis arguments: we jump to conclusions without first examining the evidence. And then we offer "evidence" which we think supports our preconceived ideas. Surely it makes more sense to examine the evidence and only then draw a conclusion. The ball hits the black rubber and then hits the red rubber. The ball simply can't be carried on the bat.

Originally Posted by UpSideDownCarl
Now I don't really care about dwell times of a second because it is true that in normal play that does not happen. But it is also true that you can hold the ball on the racket a little longer than the normal 0.5-1 milliseconds...
I would say Mark's serve and that pull ball loop, the contact time is probably about 3 milliseconds. So it is still really short. But a lot longer than a normal dwell time.

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But that is demonstrably NOT "a lot longer". At the most - if your estimates are correct - it's 2.5 milliseconds longer. Yes, it's 7 times as long as .5 of a millisecond, but in human measurable terms it's virtually undetectable. It's much more accurate and far less misleading to leave it at "it is still really short".
,
In the end, we're wasting our time arguing about things which are not helpful. Whether it's .05 millisecond or 3 milliseconds, talking about dwell time is distracting us from the one thing which is needful: make the best contact to achieve the result we're looking for. Visualising the ball being dragged across the face of the rubber may be helpful as a tool for making good contact when serving, but... talking about it in terms of dwell time leads us to attempt something which is impossible. There are numerous threads across the tt forums which harp on about which equipment will give the best dwell time. But the only real discussion which is worth having is the one you keep coming back to: it's the skill of the player.