dwelltime

The point in bringing up simulation is that the system shouldn't be difficult to fully characterize. Simulation generally requires some level of measurement anyway even if only for sanity check.

AgentHEX wrote: JacekGM wrote: Because I find it hard to believe that differences in physical dwelltime between different rubber/blade combos are not relevant to the feel of the racket, and hence to its performance in the hands of a player. It is relevant to the feel of racket, but feel of the racket doesn't matter to performance in anything but very short term because your senses will remap a given feel to certain expectation automatically. For example, I can switch to inverted BH instead of LP (surely more than most changes) and only experience temp drop of performance for maybe few hours.

Well, if you think information will stop dumb claims and crackpot theories have I got some great investment opportunities for you.

AgentHEX wrote:  For example, I can switch to inverted BH instead of LP (surely more than most changes) and only experience temp drop of performance for maybe few hours.

Pretty much what I expected.

JacekGM wrote: So, the experiment I offered to measure the dwell time is pretty much conceptually ignorable, is it not?

No, I don't think so. 

Baal wrote: tt4me wrote: 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. I'm not sure I understand your point.  If the subject is uninteresting to you, why do you weigh in on the thread?  I am pretty sure I am not getting what you are saying because you did seem earlier to be interested.  I'm not trying to be hostile at all, I just don't get what you are saying here. I am sure there are all sorts of different ways one could measure the dwell time given the funds to do it.  There is a consensus that the true dwell time is too fast for nervous system to measure it directly, and yet people have preferences for blades, rubbers, etc.   I find this interesting and am curious how people can do it, and do it fairly reproducibly.  This is a forum about all aspects of table tennis, and some things are interesting even if they don't make you a better player.

Baal wrote: I found one study (but it's not the one I am looking for, at least I don't think so). http://www.ittf.com/ittf_science/SSCenter/docs/200200027%20-%20Tang%20-%20Speed.pdf This one used a golf-swing robot and a camera operating at 4500 Hz.  All you can see from this one is that dwell time is less than 7 ms (still to fast to measure with your neurons).  What they were mainly trying to do is compare 38 and 44 mm balls.  I am still trying to remember where to look for the other paper that measured dwell with a bit more resolution.

tt4me wrote: Baal wrote: I found one study (but it's not the one I am looking for, at least I don't think so). http://www.ittf.com/ittf_science/SSCenter/docs/200200027%20-%20Tang%20-%20Speed.pdf This one used a golf-swing robot and a camera operating at 4500 Hz.  All you can see from this one is that dwell time is less than 7 ms (still to fast to measure with your neurons).  What they were mainly trying to do is compare 38 and 44 mm balls.  I am still trying to remember where to look for the other paper that measured dwell with a bit more resolution. If the camera could record at 4500 FPS then why didn't they do so when they had the chance?  This is a missed opportunity.

I know.  It is frustrating that the only picture they show is at 7 ms!  I think there is another article where they actually did measure it.  Even more frustrating is that I can't find it!!!!!  

Please don,t laugh to soon for this .

I first wondered how a 1000 hz camera can possibly make a movie/video of 0,001 sec (the relevant part). 1000 Hz corresponds to a frequency 1 /ms. One frame for a millisec would more be a fotograph. A slowmotion of a photograph does nothing for that. 

So then I wondered how they dealt with slow motion and change  of sequency for slowmotion.
Slow motion affects clocks seen on video also. 
So did they correkt the cameraclock for this or not or does it do this by itself ?

Assume for a moment that it wasn.t corrected and let me try to make a scenario of what could have happened....
 
Videos like this don,t show running clocks filmed simultaneous with the bounce right ?.
Suppose a video would show this.

Clocks in slow motion are also slowed down.

So it would also show more time then the cameraclock for say ten (10) frames for making the relevant part of these videos.
Simply because the frequency got sequency is slowed down ánd this clock also ftom slowmotion but not the cameraclock if it runs the same as for making the video.
When a clock runs too fast it shows less timereading for same period. The timereading would be shorter then.



Edited by mercuur - 08/28/2013 at 1:44pm

Well, the study I mentioned used a camera at 4.5 khz.  So if the true dwell time was 1 ms, Nyquist theorem says they should have been able to see it.

You are a crystallographer?

I don't take all science ecually serious.
They likely use a camera packed out of a box with a manual that tells nothing about science use like this.

A frequency of 1000 hz is definitely too short for 0,001 sec to give a filmic illusion.
These where the values that did go round here.
I even used them myself few times in my posts without noticing.
These values combined are ridiculous.

But I let it rest further here.






Edited by mercuur - 08/28/2013 at 2:12pm

Baal wrote: 4500 frames per second camera is what they said they used.  But in any case, they didn't show an image except at 7 ms, ball was already off the paddle. I don't know where the 1000hz number came from. Jacek, I work on ion channels.

Baal wrote:   There is a consensus that the true dwell time is too fast for nervous system to measure it directly,

No there isn't. In fact, I'm not sure you think it's true at all.

JacekGM wrote: Baal wrote: Jacek,  I also agree that the actual dwell time of the blade is strongly correlated with some other aspect of the blade that gives rise to something we can detect, and I would be very curious to know what it is.  The most likely thing (if I am correct in this) is the pattern of vibrations that move down the handle, characteristics of which would presumably depend on blade and rubber. Absolutely, yes. I just thought about this issue last night.... So, the experiment I offered would require that the horizontally (flat) oriented paddle be held in some kind of palm-like clamp, which should be very doable. As you suggested, the (complex) vibration pattern will certainly influence dwelltimes of various rackets.

The vibration freq/magnitude are indicative of mechanical energy loss, which is causal to general elasticity. Dwell time itself is irrelevant in this given a material can be soft AND elastic, or hard AND less elastic.

OK, Fine  Your points are granted.  Anyway, the camera was at 4500 frames per second.  The exact dwell time is very short.  Anything else you want to add?