Dwell Time .....

[IB66]

I’ve heard that Ma Long had been working on keeping his head still (not static, reducing or controlling) to help get better consistency, if your head moves a lot then the accuracy is harder to achieve as the brain has to allow for the head movement as well, which in turn reduces accuracy of the decisions made.

 

[brokenball]

You guys keep mixing up dwell time or contact time with the "touchy feelly" time.

 

[Dr Evil]

There's the perception/feeling of dwell time, and then there's the actual duration of contact. As brokenball says, two different things. The contact duration is a few milliseconds, not enough time for the signal to get to your brain, let alone be processed into a conscious perception. What you feel consciously is your brain's after-the-fact best guess as to what happened in a roughly 10 millisecond window around the moment of contact. The guess won't mirror reality; there's no direct conscious representation of the difference between a 1 and 2 millisecond contact. And you're not feeling the contact directly in any case, but via vibrations in the blade against your fingers and palm. But there will probably be a difference in the induced nerve signals, and so there might be a useful interpretation of the difference; the 2 millisecond contact might feel heavier or deeper, or it might just feel longer. But the conscious sensation will be at best only indirectly correlated to the actual contact duration, and it won't be consciously felt until tens of milliseconds after the actual contact. If the sensation is useful it will be as feedback for hitting the next shot, not for the shot as you're hitting it.

 

[UpSideDownCarl]

Nice post Dr Evil. Yep. And not just for the next shot. But the feedback is most useful for, over the course of months, refining how you "touch" the ball when you make contact.

I also think it is possible that some of what people are feeling as dwell time is vibrations in the wood as a result of how the rubber of the topsheet is stretched and distorted by the pull from the tangential contact of the ball on the rubber as the rubber grips the ball. The feeling of longer contact may have more to do with the contact stretching the rubber a little as the sponge is compressed. Not the compression of the sponge, but how the ball pulling on the rubber that is gripping the edge of the ball as the racket is sort of swiping past the ball.

[edit: Funny. I looked through some comments and find on the second page me saying the same thing about the feeling of dwell time possibly having to do with the feeling of the rubber getting distorted by tangential contact. I guess I repeat myself over years without remembering having said things. ]

 

[brokenball]

What does what you feel or how you feel it have to do with the original question which is
"What blade has the longest dwell time"
This isn't about what you feel. You aren't calibrated anyway.
What you feel isn't going to change the trajectory anyway.
Dwell time is about what really is happening during contact.
This video is about 10 years old. It is dark because of the high frame rate and that the shutter is only open of 100 micro seconds. If I left the shutter open longer the picture would be brighter but then it would b blurry. It is best to download the video and view it using VLC in loop or repeat mode and scan frame by frame.
Given that the frame rate is 2000 FPS you can estimate the speed, spin, contact time and whether or not the blade is vibrating or the ball deforming. The ball is 40 mm in diameter so count the frames in frame by frame mode for the ball to travel half its diameter.
The blade is a Firewall+ and the rubber is T25.
I was using a Newgy 2050 to shoot the balls. The speed was about 15.
[video]https://deltamotion.com/peter/TableTennis/iSpeed2/movie/4B03742m.avi[/video]

The video is short because I was standing in front of a lot of halogen lamps that are very hot.
Now I have LED lamps and a much better color camera but can't get motivated to use it outside of work.

 

[UpSideDownCarl]

You are right. The point of distinguishing what you feel from what is happening is that, what we feel is not actually dwell time.

But it is interesting, if, over months, what you feel helps you refine how you touch the ball when you contact the ball in your stroke, it can help you improve your shot quality.

But, from the perspective of dwell time, the important issue is that what you feel and what the dwell time actually is, cannot be the same thing since dwell time is too short for you to actually feel it.

 

[GusShnaps]

It's not possible to adjust your stroke DURING contact (unless you have the tackiest rubber on the universe). There's just not enough time to react. Your reaction comes "a long time" after the ball has made contact.

Dwell time exists, because it will stretch the topsheet and compress the sponge, staying there (even if only for a really short amount of time), but you can't feel it, you feel the vibrations that come from your blade, which is called feedback.
Maybe that's how people notice if a ball has more or less dwell on a certain rubber (?).
1:07

Not sure if the images are real cause it's an advertisement, but they do illustrate what I believe happens during contact.

Maybe this is more realistic:

Sometimes you react and adjust right after you feel it: 1:07

In this case, it happened a bit after contact (if you play it in slow motion it's easier to notice) and because the quality of the shot wasn't as Adam expected.

Might've gotten some stuff wrong, but that's kind of what I imagine.

 

[zeio]

FFS, stop complicating things. That's like saying "ratio of tangential COR to normal COR" is different from "throw angle".

Dwell time = contact time/duration. Look up studies and research papers on tennis. The terms are interchangeable.

For a decade, every such topic gets turned into a debate on nomenclature. Seriously, get over it.

 

[Brian Zhao]

Innerforce ZLC for the win!

 

[Hysteresis]

cannot be the same thing since dwell time is too short for you to actually feel it.

This is why we keep having this argument Carl. It's not too short for you to feel (even though technically I agree you arn't feeling the dwell time anyway, you are just inferring it from other sensory information). That's not how reaction times or nerve conduction times work.

It's a latency, the signal takes longer for you to register than the actual event, but after the event has finished, you do still receive it. That is to say, you still receive enough tactile information to infer if your contact was longer or shorter, you just won't be able to tell while the ball is still in contact with the rubber.

People here (at least have been posting recently) generally agree you can't use this information on the stroke you are currently feeling, but the point is you can feel things that are shorter than your reaction time, or whatever time, it just registers after the triggering event has finished.

 

[IB66]

Dwell time (duration), if I’m correct, is the amount of time the ball is in contact with the racket surface during impact. Which in effect is impact duration.

if you miss the ball completely there is zero dwell time / impact duration!!
if you perform a hypothetical perfect scoop (no micro bounces) and catch the ball on the racket, then the dwell time / impact duration would last until the ball was removed. !!!

Therefore, dwell time / impact duration is the only duration of time that the ‘touchy feely’ vibrations are able to be transferred into racket.

These vibrations probably last longer than the impact duration / dwell time duration and it’s possible they feel amplified depending on the frequencies and resonance of the vibrations, materials, glues used etc etc etc

Perhaps the OP’s original text in the opening post should have asked ‘which blades have the highest capability to transfer touchy feely info during the impact duration / dwell time duration !!!!

 

[UpSideDownCarl]

This is why we keep having this argument Carl. It's not too short for you to feel (even though technically I agree you arn't feeling the dwell time anyway, you are just inferring it from other sensory information). That's not how reaction times or nerve conduction times work.

It's a latency, the signal takes longer for you to register than the actual event, but after the event has finished, you do still receive it. That is to say, you still receive enough tactile information to infer if your contact was longer or shorter, you just won't be able to tell while the ball is still in contact with the rubber.

People here (at least have been posting recently) generally agree you can't use this information on the stroke you are currently feeling, but the point is you can feel things that are shorter than your reaction time, or whatever time, it just registers after the triggering event has finished.

This is just semantics. I don't disagree with anything that you have said in a real way.

Perhaps we can infer longer dwell time from what we feel. But what we feel is vibrations from the wood that last longer than the time the ball is on the blade face. Which is what I was implying in the statement you seemed to pick from my post.

So, all you say is fine as long as it is clear that, since the vibrations in the wood that indicate things like the ball coming in contact with the rubber and maybe the stretch and grab of the rubber from how the ball contacts, we feel something that indicates these. But what we feel is not the actual time the ball is on the blade or the actual contact. We feel something that points to the contact that lasts longer and may reach our hand after the ball is already gone.

But the semantic games do not interest me. Nor how long the ball is actually on the rubber. And usually, the amount of time is very short, even in those instances I used video to show at the beginning of this thread however long ago that was.

What interests me is that, the feedback we receive can still be useful in helping you improve how you contact the ball and how much spin you generate. That won't be useful on the shot where you are taking the stroke. I don't think it will be useful in the next shot either unless you already have the skill to touch the ball in various ways. Where I believe the feedback is most useful is in helping someone, over time, over months, maybe years, develop the skill to touch the ball in certain ways that allow the topsheet to grab the ball more fully and be stretched by that gripping of the ball, such that more spin is imparted to the ball during the stroke.

 

[IB66]

One of the other sensory indicators is sound, this can sometimes be far more revealing than the ‘feel’. You become use to how your set up sounds, what noise is produced for fine brushing, looping, flat hitting etc.

 

[brokenball]

But what does the "touchy feelly" time have to do with the equipment?
You guys are talking about the player using the 'feel' of impact to modify strokes.
These are two different discussions.
The OP have made it clear this thread is about the blade not perception. The rest is off topic.
Tell us all. Would this blade feel like it has more "dwell time" because if vibrates longer?
[video]https://deltamotion.com/peter/TableTennis/Toxic%205%20in%20Vise.mp4[/video]
You can see the contact time is short compared to the time the paddle vibrates.

This video shows why JRS Dallas' research was misguided. Look at it carefully.
The video is shot at 2000 FPS but the paddle is in a vice so I didn't need to stand in front of hot halogen lamps.
What you should notice is that the ball leaves the paddle before the paddle can spring back to aid in the pushing the ball back. All the paddle absorbs a lot of energy when being pushed back that isn't returned to the ball. Yet you can see the paddle almost shimmer with higher frequencies that also don't help in pushing the ball back. A faster paddle will will bend a little at contact but maintain contact with the ball as it springs back. This will result in more of the impact energy being transferred back to the ball.

It is the primary mode of vibration that is important, not the fourth.
Ideally the paddle will rebound and keep in contact with the ball as long as possible to return more energy if that is what is desired. This really should be looked at through the lens of a spring board diver where the spring board is adjusted or 'tuned' be vibrate in sync with the diver.

 

[UpSideDownCarl]

And, interestingly, I think what helps someone get more spin might be the vibration being slow enough that the blade does not push back on the ball and add to the speed.

But I am not sure this is the case.

Also, on spin contact the contact would not be direct like this. So, it would be interesting to see that; I just am not sure that would be so easy to catch on video. But the video is pretty cool.

 

[Hysteresis]

But what does the "touchy feelly" time have to do with the equipment?
You guys are talking about the player using the 'feel' of impact to modify strokes.
These are two different discussions.
The OP have made it clear this thread is about the blade not perception. The rest is off topic.
Tell us all. Would this blade feel like it has more "dwell time" because if vibrates longer?
[video]https://deltamotion.com/peter/TableTennis/Toxic%205%20in%20Vise.mp4[/video]
You can see the contact time is short compared to the time the paddle vibrates.

This video shows why JRS Dallas' research was misguided. Look at it carefully.
The video is shot at 2000 FPS but the paddle is in a vice so I didn't need to stand in front of hot halogen lamps.
What you should notice is that the ball leaves the paddle before the paddle can spring back to aid in the pushing the ball back. All the paddle absorbs a lot of energy when being pushed back that isn't returned to the ball. Yet you can see the paddle almost shimmer with higher frequencies that also don't help in pushing the ball back. A faster paddle will will bend a little at contact but maintain contact with the ball as it springs back. This will result in more of the impact energy being transferred back to the ball.

It is the primary mode of vibration that is important, not the fourth.
Ideally the paddle will rebound and keep in contact with the ball as long as possible to return more energy if that is what is desired. This really should be looked at through the lens of a spring board diver where the spring board is adjusted or 'tuned' be vibrate in sync with the diver.

The reason why everyone veered off topic, is because the original post is 2 years old. And the original question, while technically may have an answer, is probably in practice, meaningless.

My guess is the rubber has VASTLY more to do with the dwell time, than the actual blade, since it would have significantly lower Young's modulus than the blade itself. Meaning that it both deforms more during contact, and snaps back slower than the blade after deformation.

The only part that is actually controversial after the thread was necroed, was that someone claimed dwell time as a concept is meaningless because of reaction times. So that's what the conversation has been about that.

 

[Gwenved]

This is just semantics. I don't disagree with anything that you have said in a real way.

Perhaps we can infer longer dwell time from what we feel. But what we feel is vibrations from the wood that last longer than the time the ball is on the blade face. Which is what I was implying in the statement you seemed to pick from my post.

So, all you say is fine as long as it is clear that, since the vibrations in the wood that indicate things like the ball coming in contact with the rubber and maybe the stretch and grab of the rubber from how the ball contacts, we feel something that indicates these. But what we feel is not the actual time the ball is on the blade or the actual contact. We feel something that points to the contact that lasts longer and may reach our hand after the ball is already gone.

But the semantic games do not interest me. Nor how long the ball is actually on the rubber. And usually, the amount of time is very short, even in those instances I used video to show at the beginning of this thread however long ago that was.

What interests me is that, the feedback we receive can still be useful in helping you improve how you contact the ball and how much spin you generate. That won't be useful on the shot where you are taking the stroke. I don't think it will be useful in the next shot either unless you already have the skill to touch the ball in various ways. Where I believe the feedback is most useful is in helping someone, over time, over months, maybe years, develop the skill to touch the ball in certain ways that allow the topsheet to grab the ball more fully and be stretched by that gripping of the ball, such that more spin is imparted to the ball during the stroke.

That's starting to be interesting.
I agree with you, the inputs we take from there are not usable directly in the shot or in the next one too due to our reaction time, and are not more than the result of training which finally is learn, understand and apply. that's help us to chose the right stroke depending on what we want to do when the ball arrives...when we have time for it.
As table tennis is a reflex game you have to train a lot to solve all those situations when the ball arrives quicker than your reaction time because all your strokes have to be "natural" and have to get out without thinking, fluently. Training some strokes is most of the time boring but that's the only way to dominate them...all those strokes we use during the game have to be innate, our brain has to work for strategy, not to correct our defects during the game...

 

[Gwenved]

The reason why everyone veered off topic, is because the original post is 2 years old. And the original question, while technically may have an answer, is probably in practice, meaningless.

My guess is the rubber has VASTLY more to do with the dwell time, than the actual blade, since it would have significantly lower Young's modulus than the blade itself. Meaning that it both deforms more during contact, and snaps back slower than the blade after deformation.

The only part that is actually controversial after the thread was necroed, was that someone claimed dwell time as a concept is meaningless because of reaction times. So that's what the conversation has been about that.

I've introduced the reaction time in the post, then what's the reflex.
It's not only young's modulus you can add poisson's modulus too. But the fact is not here. I agree talking about dwell time for a blade is a non sense as we play with a bat which is blade + rubbers. Each combination will have a different dwell time, and combinations will be increased by foam thickness.
Dwell time in itself has 0 ( zero) interest, it's only a data. 2 combinations with the same dwell time can have different reactions, so different feeling. As example during a dwell time of 10 milliseconds the ball can get into the rubber from 0.0001mm to 2.0 mm so the rebound will be different and the catapult effect too. Dwell time is different for each stroke with the same combination. It's not a fair value.
That's why (appart the too short time of dwell time) we can't use it as direct info when playing and for me it's a myth as all the people seems to associate more dwell time to more control.

 

[Baal]

People talk about being able to feel something they they call dwell time. I'm not sure what exactly they are feeling but it has to be some other feature of their equipment or some "placebo" that their brains construct as they feel, hear, and see results of a shot. Of course, there is an ACTUAL dwell time of ball on the rubber and somewhere years ago I saw a paper from Japan where somebody measured it with a fancy videocamera. It was a bit less than a millisecond. The fastest neurons in your body can conduct an impulse at 200 m/s. Let's say your hand is ~1 m from your spinal cord. An action potential will travel 0.2 m in 1 millisec. Thus, at the time when the ball is on it's way back to your opponent, the sensory nerve impulse has not yet reached your elbow. But the blade may still be vibrating from the impact for quite a while after the ball leaves. I'm guessing that is what people feel, and maybe the vibration takes longer to dampen out on some setups than others. If so that will depend on how hard you hit, maybe where on the blade you hit, or blade angle to ball and probably other stuff too, including the construction of the blade.

Anyway, I mentioned this a bit above but these are some numbers.

 

[Baal]

Here is another thing I wonder about. Let's say we took five offensive blades of various sorts, and ten experienced players chosen to be at a playing level close to the median of the members of this forum, whatever that is. Let's say we put Tenergy 05 on the blades. How much aggreement would there be on the relative "dwell times" of the blades? I'm guessing maybe not that much.