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    Posted: 08/27/2013 at 2:53am
Lot of threads and discussions on the equipment forum involve dwelltime.
There seem to be some scientific meassurements with a camera but I can,t find them.
What I read now and then doesn,t tell anything about how much it can vary from things as sponge, sponge thickness, blade, different type of strokes, technicque. aso.

 I have read several times it was in the realm of 0,001 sec.
That,s in millisec but a unit says zero nothing about the precision for meassuring variabillity 
For 1 msec even less then it would for 4 or 5 msec.
1 (with no further digits) can be between 0,5 and 1,5  millisec which has a faktor three (or three hundred percent) possible difference.
A fourth digitnumber and how this fluctuated is needed then to know something about the variation in percentage.
I don,t know wether the camera measured with more precision or if the measuring data was  rounded to millisec.

So question is if someone knows more or where I can find this ?



Edited by mercuur - 08/27/2013 at 3:15am

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 7:39am
ITTF once commissioned some engineers with a very high speed camera to measure the length of time the ball stays on the paddle -- this must have been done at least ten years ago if not more.  I have spent some time trying to figure out where on the web this thing is buried, so far without success. The numbers they came up with were presented with standard errors, which were reasonably small.  Anyway, the bottom line was that the ball stays in physical contact with the surface for such a short period of time that sensory neurons would not be able to measure the true dwell-time -- and we are talking more than an order of magnitude.  I am working from memory here, I read it carefully a couple of years ago, but I don't think they checked multiple blade types, and multiple types of rubbers.  Players can clearly discern that different setups react differently, and often refer to some part of the feeling as "dwell" because that is what it seems like, but that is not what they are feeling, at least not directly.  My theory is that people feel in their hand a complex vibration probably comprised of many different frequencies that is created from the ball striking the rubber on the blade.  Presumably the spectrum of vibrations, and their duration, depend on the blade and rubber, and the vibration lasts much longer than the time the ball is in contact with the blade.  It would be interesting to put pressure transducers on various parts of a paddle and shoot balls at the surface to see what these vibrations look like in terms of power spectrum and duration.  Those kinds of transducers are not very expensive (compared to the cameras), and it would not surprise me if a company like Butterfly doesn't do something along these lines.  Also, to me it seems plausible that something about the vibrations evoked by the ball hitting the surface would have some relationship to the actual dwell time.  Maybe an engineer or physicist could weigh in on this??  From the point of view of physiology, though, the neurons in our fingers and hands, sensitive as they are, cannot possibly measure actual dwell time but they can certainly figure out that different blades and rubbers are different.     

I think there is a thread about this with a link to the pdf of the original study somewhere on OOAK forum.


Edited by Baal - 08/27/2013 at 7:41am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JacekGM Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:56am
To approximate the dwelltime of a blade-rubber combo, one might position the various rackets horizontally flat on a supersensitive and superfast balance and shoot the ball at exactly the same (reasonable) speed vertically from above, at the racket surface. 
The one different thing about this experiment would be that it ignores vibrations yet yields the real dwelltime (...and you can challenge this assumption, of course). One problem I see here, though, is that I am not aware of balances that would be as fast as a camera, but who knows, these days so much is possible...


Edited by JacekGM - 08/27/2013 at 10:18am
(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davidz Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 11:52am

About two years ago, I also learned that the dwell time is 0.001 sec. I believe that is rounded result due to relatively slow camera. Unfortunately, it causes some people to consider the dwell time is a constant regardless of blade ruber type, different tech. etc.

 
The sound frequency is more likely between 700 to 1000 Hz when bouncing a ball using a blade with a rubber. This might indicates the dwell time is 0.001- 0.0014 sec. When hiting a ball, the sound frequency decreases a little, suggesting a longer dwell time. When looping, I guess the dwell time could reach 0.002 to 0.004 (? I did not test this). A frequency measure software should be helpful to measure the blade frequecy under different playing techniques. 
 
This approach assumes the sound frequency is directly tied with blade dewell time.
 
 
 
 
 
 
 
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mercuur Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 2:48pm
Handmuscles act on a bat with some muscletension.
There is inner awareness for this type of tension from neuronsystem. 
So hitting a ball, the ball hitting the bat ,this tension interacts and reacts. That can be part of sensing the ball.

The other part is more from sensory feel.. These can be combined for the whole experience then.

How fast the neuronal system works for that doesn,t matter much. That,s more for processing and combining these two types of feel. I can,t see why that can,t be done afterwards or even other then that. Somewhat similar to the residue vibrations of a blade.
Trained more specific this processing and combining would be better and quicker.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 3:36pm
Fatt, I think you are right that we don't actually have to measure it in real time.  Over at OOAK forum there is a thread in the blade section by Kees on "The Function of Feedback in Blades" that talks about the point you raise.  The idea is that we use mechanical feedback from blades to decide what to do on the next shot, not the one we just hit, which is what I think you are saying.  I think that is really important for sure. 

My idea is little bit different (and not incompatible with that one).  It is that something about the vibrations in the handle is directly related to the true dwell time, and that is what the sensory cells in our hands and fingers are picking up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 3:51pm
Mercuur, the sensory elements in the muscles in your hand and fingers (called muscle spindles) detect the length of your muscles, and there are sensory elements in the tendons where the muscles attach to the bone that detect the tension.  However, those systems are very very slow, even compared to the vibration sensing neurons in your skin.  They would contribute to your ability to measure the size of a handle and how hard you are gripping. They would probably not contribute much to the feeling one has from striking the ball, including the sense of "dwell", whatever it might actually be. 

Basically, this all comes down to two questions:  (1) why do different blades feel different (which you can often tell immediately) and  (2) what effect does it have on how you play (which you figure out a bit from trial and error, but making use of this sensory input).  Well, also a third question, why do we like what we like?

Some people would argue that you should use a blade that gives you as much sensory input as possible, and therefore a blade with more vibrations ought to be better. More information should mean better motor responses, or so you would think.

For some reason though, blades that seem to dampen out quite a bit of that vibration (e.g. Butterfly ALC blades) are very popular (I like them better than any other kind of blade myself) and they are even used by top players in the world who don't really need the power that they generate. 

I have to admit I don't understand why I don't like much vibration in my blade, and why blades like Viscaria, TBS, TB-ALC etc. feel so pleasing to many players.  You would think it would make no sense. 

Edited by Baal - 08/27/2013 at 3:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tt4me Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 3:53pm
@mercuur, this forum is not the place to ask this question.  I would go to a physics forum or even make a request of a TV show that makes high speed videos.

Did you post the same question of the German TT forums?

Edit:
I just posted my comment and I see Baal's above posted while I was writing mine.

@Baal, why do you always derail the threads on dwell time?
Anton was asking about how long the ball stays on the paddle.  mercuur is asking the same thing.  You always want to get into the physiology of what is felt rather than the physics of what is really happening.

This is why I made the comment about this forum not being the place to ask this question.
If you ask the same people the same question you will get the same answers.  Look at Baal's comments in Anton's thread and compare them with Baal's comments in this thread.

mercuur needs to seek new people.



 




Edited by tt4me - 08/27/2013 at 4:03pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Baal Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 6:31pm
Well, anyway, the dwell time has been measured and it is really really short and it was measured reasonably reliably in answer to OP.  I think the link to the paper can be found in the thread started by Anton.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mercuur Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 6:34pm
Kees his article about feedback was interesting to read back then. All these subjekts seem to overlap anyway. That,s part of it. Kees and I also happen to overlap each other for that I lived in same city for eight years, Never met him tough I think and only played there for competition playing for other clubs. 
Level back then was higher Dutch national youth league and lower Dutch natonal seniorleague.

But his article would also be bull for science when dwell couldn,t be experienced directly at all and compared for things and changes. Or all off this article would also be from residue vibrations. I don,t feel them as too disturbing mostly but also not really contributing for this feedback.

I never play with a clock in my hand tough.
I don,t compare my experience for TT with reading and seeing a clock. Better keep these things apart offcourse.  I learned to play before technical, physics education. That makes it easier for me maybe.
But the word dwelltime or dwell doesn,t need the idea of a clock either. Longer or shorter dwell also comes along in reviews for instance. That could just the same be trajektory.
I take a sidestep now and then to this type of video,s and this involves a clock then with dwell is 0,001 sec. That,s physics then because a clock, is used as physics tool. Still if we keep these things apart or try this the discussion stays pure and interesting and about tt and equipment also.

@Baal,

I don,t mean that precisely.
It,s more a basetension or sort of an equilibrium build with the bat. The ball comes in reacts on this and what it reacts to also fluctuates from this a little.  Enough to sense it in fingers and hands immediately independant of a sensory uptake from the skin contact with a bat.

One type of feeling could feel the collision more and other the bats reaction to the collision ?

I really don,t believe a sience forum could answer all this or people wouldn,t even go into it..
But I,m not out for finding thruths like that anyway.  Not for my own either.
Yet it,s fun to conversate about ithis on this forum as I heard last week our summer holliday was extended with another two weeks pause.
I suspect this is mostly the reason for my current activity on the forum as a compensation and surrogate for playing. Normally I can deal with it better because I know the date it starts again to look out for. This time they criminally changed the date Smile.



 


Edited by mercuur - 08/27/2013 at 6:41pm

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 6:58pm
Originally posted by fatt fatt wrote:

anton started the discussion a while ago and he was on par with baal's line above.
mytabletennis.net/forum/forum_posts.asp?TID=53771

what I failed to understand at the time is the following: even if we all agree that neurons cannot process in real time the info related to dwell, why does it seem so difficult to accept that after the info has been processed, 'long' after the ball has left the paddle, one is able to not forget about characteristics that induce the concept of dwell when comparing those characteristics from one blade to another (or one rubber to another), all other parameters remaining equal?



"Dwell" is just a psychological concept we relate to certain feel (perhaps persistence in certain frequencies). There's no way to even tell if what one person means by "dwell" is same as anothers'. All we know is that between product X and Y, if a "reviewer" says X is more in certain feel than Y (as unreliable as that already is), when others try X & Y they each attribute some subset of that diff to the concept. IOW, it's a complete crapshoot what anyone really means by it.

Feel is important because it provides info on how the shot was hit thus allowing more prep for reaction, but not trivial to characterize without some srsly sophisticated study.


Edited by AgentHEX - 08/27/2013 at 7:03pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cole_ely Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 7:31pm
How do you define dwell to measure it? Do you start from the moment the ball touches rubber and end when it no longer touches? Do you start when the ball stops its forward momentum and stop when it begins to move the other way?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 7:35pm
There's the physical dwell defined by the former (~1/2 the latter) and psychological dwell defined by the stuff inside people's heads. These two are different enough that using the same word for both is confusing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stiltt Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 7:51pm
The way I understand "dwell" it does not need to be quantified and can only be measured relatively to another object. eg XZQ has more dwell than Schlager Carbon; Bluefire M1 has more Dwell than Tenergy 05.

For blades it is a mix of flex (more = more dwell) and softness of the outer ply or plies (more = more dwell); for rubbers it's a mix of elasticity of the topsheet (more sling shot effect = more dwell),  bounciness of the sponge (less = more dwell) and resistance of the sponge (more about this below).

It is interesting to note that more dwell does not necessarily mean less speed and that's why I find the concept intriguing and useful; to explain that we can achieve more speed and spin without loss of control which at first sounds like heresy.

About the resistance of the sponge: it can be thought as the time the sponge takes to compress and the time it takes to release the stored energy; on the Bluefire M1 that compressing time is longer (more dwell) than on the T05 and yet the Bluefire is not slower: the sponge takes longer to compress but will release the ball faster (more dwell but no loss of speed).

We may need somebody who has an understanding of dwell (other than intuitive like me...) and does NOT lack the scientific background to put it in words that can be accepted by all as useful a tool to describe a rubber.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:12pm
I don't think it's helpful to assume causal relationship between any physical attribute of the blade and psychological terms. For example, it's already established that humans can't necessarily feel the "flex" per se anyway. They can however feel frequency/magnitude of vibrations of the blade. Maybe some people describe high magnitude low freq as dwell, maybe some define it as the height of the shoulder in elasticity function (when a bat's elasticity stops being linear), and everything in between.

It's worth noting again that our personal mental feelings/definitions for these words are NOT shared, which makes mapping any such thing to how something feels largely pointless.

As a separate topic, it's perfect feasible that a softer sponge (longer physical, not psychological dwell) is also more elastic. But again as established, this is not something anyone can take advantage of themselves. In fact it's when the intuition of softer = slower breaks down that our minds develop even more elaborate myths (like OP) to retain misleading generalizations. This is part of why sharing feelings with others is like a chinese and japanese person communicating in writing. The words look the same but can mean different things.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tt4me Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:31pm
Originally posted by AgentHex AgentHex wrote:

"Dwell" is just a psychological concept we relate to certain feel (perhaps persistence in certain frequencies).
No!!!  

dwell time = contact time.  Baal and others have high jacked and misused the term dwell to mean how long you feel the ball.

@Cole and @Fatt, the contact or dwell time is the time the ball is in contact with the rubber.  Simple. Dwell time is hard to measure unless one has a high speed camera with a very high frame rate.  Then one can count the number of frames the ball is in contact with the rubber and multiply that by the period between frames.  VLC is very good  at step through videos frame by frame or playing the videos back in slow motion.

@mecuur, knowing the dwell time is not going to make you a better player.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:36pm
Again, there's the physical dwell and what people feel as dwell. You cannot deny the latter any more than you can deny sadness because it's not some easily visible physical phenomenon in itself. It if helps you can think of it as any number of words with multiple, equally valid definitions. It's unfortunate if people conflate them, but that's a different problem than validity of each in and of itself.






Edited by AgentHEX - 08/27/2013 at 9:37pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:43pm
This conveniently segways to an illustration worth mentioning. When you feel, say, "sad", what you're really saying is "this is how I feel when such and such type events occur" not that the event is itself sadness. You might be able to empathize when someone else feel emotions akin to this about it or similar events to the point where you share the same word to describe it, but you never know what they themselves feel. It's philosophically questionable whether this sort of quite common and valid linguistic usage is conducive to further clarification beyond a certain level.

Edited by AgentHEX - 08/27/2013 at 9:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smackman Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:54pm
chuck Norris is so good at TT he can dwell time loop all the way around the ball

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 9:56pm
Chuck norris don't even need to play because his opponents always forfeit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tt4me Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 10:11pm
Originally posted by AgentHEX AgentHEX wrote:

Again, there's the physical dwell and what people feel as dwell.
This must be some medical term for the delay in sensation that would be better than dwell.

Quote
 You cannot deny the latter any more than you can deny sadness because it's not some easily visible physical phenomenon in itself.
I am not arguing with what Baal says.  I simply think it is off topic.  It has nothing to do with Anton's or mercuur's original question.  Being off topic delays getting to the truth.   In this case it has delayed getting to the truth a lot and in general been a big time sink.

Reading through Anton's thread again I see mention of dwell times of up to 5 milliseconds.  I wonder how that was determined?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 10:26pm
It's perhaps OT to the topic of physical dwell but not the topic of the psychological. I'm the last person you need to advise that using technical words to describe the latter can be annoying. However, what people feel is equally "truthy" and probably more material to their game even if it's more nebulous.

Frankly nothing I've seen about the technical aspect implies it's that complicated. The only significant ambiguity is that different parts (pips bend, sponge compress) contribute differently to the whole on a contiguous scale that varies according to speed/spin and direction of incoming shot. Eg, japanese synthetic pips have more mechanical elasticity, but how much compared to softer natural rubber? 20%? 50%? How much % does that vary from touch to power stroke?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JacekGM Quote  Post ReplyReply Direct Link To This Post Posted: 08/27/2013 at 11:04pm
Originally posted by cole_ely cole_ely wrote:

How do you define dwell to measure it? Do you start from the moment the ball touches rubber and end when it no longer touches? Do you start when the ball stops its forward momentum and stop when it begins to move the other way?

Cole,

In the post (vide infra) I meant dwell time of a racket setup as from the moment the ball touches the rubber of the racket and up to the moment it leaves the rubber. Isn't that the "dwell" we intuitively expect?

To approximate the dwelltime of a blade-rubber combo, one might position the various rackets horizontally flat on a supersensitive and superfast balance and shoot the ball at exactly the same (reasonable) speed vertically from above, at the racket surface. 
The one different thing about this experiment would be that it ignores vibrations yet yields the real dwelltime (...and you can challenge this assumption, of course). One problem I see here, though, is that I am not aware of balances that would be as fast as a camera, but who knows, these days so much is possible...
Leaving the realm of physics for this topic may bring us to another lively discussion where everyone is right ... in their own way. However,  the experiment needs to be very simple and we need a good tool to measure the dwell. A superfast balance (scales?) with output recording could do the job, as could a number of other devices.
(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tt4me Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 12:27am
Originally posted by AgentHEX AgentHEX wrote:


Frankly nothing I've seen about the technical aspect implies it's that complicated.
Then why hasn't anybody figured it out? Why do these threads on dwell time reappearing? 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote JacekGM Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 12:27am
A crude example how such superfast balance would work:

Time  (milisec)           Weight read-out (grams)
0.00 0.00 (Tared)
0.2 0.7
0.4 1.9
0.6 2.9
0.8 3.6
1.0 3.1
1.2 2.2
1.4 1.0
1.6 0.6
1.8 0.2
2.0 0.0
2.2 0.0

Dwell time= 2.0 miliseconds



Edited by JacekGM - 08/28/2013 at 12:30am
(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 12:40am
Originally posted by tt4me tt4me wrote:

Originally posted by AgentHEX AgentHEX wrote:


Frankly nothing I've seen about the technical aspect implies it's that complicated.
Then why hasn't anybody figured it out? Why do these threads on dwell time reappearing? 



Figured out what? You can model/CAD the bat and use FEA to simulate the physics. But what's the point?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JacekGM Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 12:43am
Originally posted by AgentHEX AgentHEX wrote:

Originally posted by tt4me tt4me wrote:

Originally posted by AgentHEX AgentHEX wrote:


Frankly nothing I've seen about the technical aspect implies it's that complicated.
Then why hasn't anybody figured it out? Why do these threads on dwell time reappearing? 



Figured out what? You can model/CAD the bat and use FEA to simulate the physics. But what's the point?

 
For different rubber-blade combos I would rather measure things than simulate. The purpose would be to determine which racket allows a longer dwell time, or the optimal dwell time for a player, etc.
(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AgentHEX Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 12:57am
Huh? It should be clear from the info above that dwell time doesn't matter. Who cares if it's 1ms or 5ms? You body can't react that fast anyway, thus it's just matter of feel. How anyone prefers feel is subjective.

Btw, this bit isn't necessarily correct:
Quote Anyway, the bottom line was that the ball stays in physical contact with the surface for such a short period of time that sensory neurons would not be able to measure the true dwell-time -- and we are talking more than an order of magnitude.


Why not? Being able to sense the approx "dwell" by proxy of vibrations isn't nearly as hard as reacting within the window.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tt4me Quote  Post ReplyReply Direct Link To This Post Posted: 08/28/2013 at 1:01am
Originally posted by JacekGM JacekGM wrote:

For different rubber-blade combos I would rather measure things than simulate. The purpose would be to determine which racket allows a longer dwell time, or the optimal dwell time for a player, etc.
I agree that measuring is better than simulating but there are too many combinations to measure.  How would you measure?  Once there is accurate data on each rubber and each blade then one can simulate all the different combinations. We know this will not happen but NO ONE is going to simulate all the combinations of rubber and blades and I don't think that is the point since many rubbers are similar and so are many blade.

I don't see why you guys persist in knowing the dwell time.  It won't make you a better player.   When I play with my hard bat I know the dwell time is short.  The dwell time is probably short when I play with my LPs too.  It doesn't bother me because I expect it.






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