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PostPosted: 30 Dec 2011, 13:48 
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I see, perhaps the jerk actually happens before the contact, when I realized mid-swing that I was making the wrong stroke. I don't know if 1/1000th of a second is right, but it does seem to me that the contact time is almost certainly too short for any reflex based on feedback from the contact.


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PostPosted: 30 Dec 2011, 17:12 
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I have based my estimate of 0.002 on German manuals for table-tennis dating from the 38 mm ball era. Dwell-time is a controversial subject, even if it has been measured. I couldn't readily find a specific up to date experiment, scientifically documented, but maybe the following will do. It involved using a high-speed camera (4500 Hz) see: http://www.ittf.com/ittf_science/SSCent ... 0Speed.pdf. In this article there is a series of 3 pictures taken at t=0, t=0.007 sec and t=0.013 sec, while the ball is bouncing off. At t=0.007 the (40 mm) ball is centimeters away from the bat. Dwell-time must be less than that.

About reaction-time, you can test this yourself. Use your bat to put massive backspin on a ball while bouncing it up and then try and catch it in the other hand; if there is enough backspin on the ball, the ball will roll out of your hand before you can close it. The trajectory of the ball on the palm of your hand is several centimeters; on your bat it is only a minute fraction of that; if you cannot close your hand fast enough - and this is a reflex resulting from touch, a very quick one, as it evolved in tree-climbing ancestors depending on it for their live - no reflex will be fast enough to change anything while the ball is on your bat.

The point I wanted to make originally is that a blade offering good feedback is necessary in learning to perform the strokes technically perfect, which in turn is necessary because if they're not, they're not - adjustment during the crucial stage of the stroke (i.e. on contact) is out. Bad or low feedback in a blade will interfere with your development a s player, which is to be avoided.


PS [dd 8-01-2012] I found the manual. Richtig Tischtennisspielen, by M. Sklorz, R. Michaelis, ed. 1979 BLV Verlagsgesellschaft mBH, München. It also states that the ball is on the bat for 0 mm to max 10 mm of its total trajectory (max when smashed hard, 0 mm when blocked). Max ball speed is said to be around 170 km/h.

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PostPosted: 18 Feb 2012, 21:22 
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Great article and discussion!

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FH: Andro Hexer HD
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PostPosted: 19 Feb 2012, 08:21 
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Yes interesting read. On the question if it is possible or impossible to adjust on contact. I think it is possible. The distance to the brain is not that important for this. This is for visual processing information or hearing. Eyes are further distance. Feedback is immediately at the hand. Same as reacting on touching somthing hot it can be much quicker.


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PostPosted: 30 May 2012, 14:23 
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The fastest conducting nerve fibers in mammals --the ones with the thickest myelin sheeths -- conduct at about 200 meters/sec. The sensory fibers that detect vibration (associated for example with Pacinian corpuscles in skin) are only about half this fast, but the motoneurons that project from spinal cord to hands are among the fastest. Let's assume that both conduct at 200 meters/sec. You also have to factor in a 0.5 millisecond delay for each chemical synapse. Let's assume only four synapses needed to make an adjustment based on a purely somatosensory reflex from hands to brain and back to hands. It would probably be more than this You are looking at a minimum of 10 milliseconds, almost certainly bit more than that. For a visually guided motor response, there would be several more synapses involved. At least two, just within the retina, two more to get to primary sensory cortex, at least three more to get from visual cortex to the muscles in the hands and arms. Slower still.

As Kees says, there is absolutely no way you could adjust on contact.

Hookshot's point about the quick-draw guy, it takes him 145 ms to react to the light pulse, because there are more synapses involved. It would be much the same if he was reacting to a stimulus applied to his skin. Once he makes a decision to draw, only two synapses and a few milliseconds of conduction time, so that would be faster. Still not fast enough to react to a ball on the blade.

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PostPosted: 30 May 2012, 22:54 
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Great article Kees. a fun fun read. I think since there is alot of knowledge here in the forum we sometimes forget the time it takes to research this kind of really cool stuff. There is a difference between dwell time, vibration frequency, linear/nonlinear, impact time and impact force against impact velocity..the list can go on. Think about the fact we all change rubber to get the maximum results in our shots. Everytime we change a blade, we change the rubber/blade match. Since not all rubbers play the same on each blade. Flex-dwell-time-vibration-reaction- linear motion- harmonics. The different types of wood and other fibers used make a harmonic interlude of a self serving blade, with respect of the estimated energy lost due to impact vibrations. Too many time I have taken fast blades/ or all+ blades and put the same rubber on each and because of the type of wood used the rubbers play totally different. That is why we can find blades as well as rubber that might use the term "GEARS" . I have two right now that are both All+ blades and the rubbers used play different on each. BUT one has 5 gears and one had 3. One is better at the short game and loops better and has better control. The other is harder and stiff and has alot of vibration. Matching a rubber with a blade that has matching harmonics can add to performance. Think of it as Tuning a blade that is in tune with the rubber. IMHO average human reaction time is 180-220 Millisecounds

Peace GIG...gotta get back to work :Chop: :rock:

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PostPosted: 31 May 2012, 01:15 
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Baal, MichiganBob, thanks! I have found it very difficult to get players even to listen to simple scientific truths. Your help is invaluable.

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PostPosted: 31 May 2012, 01:33 
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No, thank you Kees for giving me something interesting to think about, which is what is it that makes us like some blades/rubbers more than others. I have a pretty well developed explanation for why people care about only a few grams of weight in their blade, and it is in some ways an extension of your idea that feedback affects your expectations for the next shot. Collectively these ideas suggest that anyone can get used to anything reasonable over time. It suggests to me that EJing is about the worst thing you can do since you are impeding the ongoing motor learning process that you need to get better or develop new skills.

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PostPosted: 31 May 2012, 02:02 
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Kees is correct regarding blade feedback on developing players as well as players that welcome the feedback as part of their game. When I looped alot many years ago I used a blade with alot of flex and good feedback. Loops were strong and control was really good. As I changed my game to blocking and hitting I used stiffer blades that had less control less feedback and also had more speed. I, Like Baal choose my blades up front when I can. Weight is "VERY" important to me and cannot be top heavy but weight is central. I like 82grams myself for max performance. I will bring my scale to check every blade until I find the correct one. My current two set-ups are my Donic Burn ALL+ with Palio LP ox, Donic Big slam on the FH. Both work well together and I find with the strong Tensor effect I get the shared tensor on the BH as well, A little faster LP and crisper hit. On the Giant Dragon Balsa Power Plus I took the Xion Yanus DF off the Burn and put it on the Balsa blade with the Crop Circles. The Crop circles bacame slower and much better control and the Yanus DF really shined in this combo. Loop is strong and control is really good. Like I said match the rubber with the blade not the blade to the rubber.

Time for me to go back to work...
Peace GIG
:rock: :Chop:

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New blade set-up... Nittaku Monophonic with Dawie 388d-1 ox and Big slam max ( really like this one) down to FH rubber selections--I like it better than talon
flaired handle and 90 grams


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PostPosted: 06 Feb 2013, 11:28 
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Let's say there's
1. rotation as a whole in the hand
2. displacement as a whole in the hand
3. deformation = a change of shape, not *as a whole*, absorbing some of the energy that would have caused rotation and/or displacement
4. vibration = the deformation springing back

A rigid blade of the same mass should have stronger rotation and displacement, because the forces that cause those are not being absorbed by deformation.
I feel rotation in my rigid blade when I hit off-center, and I feel displacement e.g. 1) backward in proportion to the hardness of the hit and 2) sideways caused by the opponent's spin.

I feel this cleanly and sharply. *With regard to the function of feedback in blades* why do I need deformation and vibration?

Edit: Once the ball is gone, the force that produced the rotation and displacement is gone. That was the information, the "signal". Then the energy stored in the deformation is dumped into the natural resonances of the blade; it loses its information about how the ball was hit. That is "noise".
*On the topic of the function of feedback in blades*, it seems to me that the desired information is in the rotation and displacement. Its function is to inform me, and a rigid blade does that.

The topic of the function of *flex* in blades is covered in other threads. Here I wanted to argue that with regard to *feedback*, a rigid blade is not inferior.


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PostPosted: 14 Jan 2014, 10:43 
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Yeah, violins USUALLY have spruce (or similar) construction, however:

http://www.nytimes.com/2006/11/28/scien ... .html?_r=0

Image

Iskandar


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