OOAK Table Tennis Forum

Please don't extrapolate my results erroneously and conclude I am promoting things that I am not. I have never said "freq = speed catapult theory", and as the rest of your statement mashes up multiple phenomena it is too disjointed to specifically refute. I know you want people to understand that a blade does not flex and recover while a ball is in contact such that it is the blade recovery that propels the ball off the blade. I AGREE, but you don't seem to understand that I do agree and that I have never disagreed. I have never said "freq = speed catapult theory"

Moving on and without disagreeing, blades DO flex and vibrate during play or else they would not make any sound. Making sound IS NOT EQUAL TO "catapult" theory. Sound does tell you something about the structure of an object. Furthermore, making sound requires energy. If a clamped stationary bare blade makes sound when a TT ball is bounced off of off it, then the energy of that sound has come from converting some of the kinetic energy of the ball into blade vibrations (aka flex), and some of the energy of those modes of blade flexing have been converted into sound waves. Many others have already made the case that blade vibrations remove energy from a collision with the ball. There should be no more argument on this issue -- but I am not betting on it.

Furthermore, our bodies are sensitive instruments, and players do feel real differences in how fast different blades feel, if they feel flexible or stiff or fast or slow. These differences are real physical phenomena and they do involve the object we are playing with even if it has not been fully understood as to what all causes the differences.

Next, the only sources of energy that contributes to rebound velocity of a struck TT ball, is the kinetic energy of the blade and ball just prior to collision. During collision the total energy is redistributed in keeping with Conservation of Momentum and Conservation of Energy. There is no magic creation of energy from the rubber, it too is converting kinetic energy into deformation (more complex than blade deformation) and recovery with some loss of energy occurring during that process.

Finally, in some sports (at least) a player's swing stores energy into the flex of the racket/club/rod (golf, badminton, fishing, ...) and the release of this energy is used to further accelerate the racket face prior to contact with a ball so that the ball rebounds with greater velocity than it would have if there was no flex. I do know that a stiff blade gives me better feedback on exactly where I am hitting the ball during a smash (i.e. subjectively at lease it reduces the dispersion of my smash) but this doesn't prove that there is blade pre-loading prior to ball contact. If the blade gets flexible enough however, this effect will arise. Capturing data from a strain gauge and accelerometers on a TT blade during ball collision could tell us a lot.

A PhD thesis on the issues explored in this thread and the many more issues ignored by this thread can be found by searching for:

"Kwan _2010_ Designing the World's Best Badminton Racket"

I'm amazed that this thread is still going.
The mere mention of looking up a Ph.D. puts it in context.

Well, let's add some gasoline to the fire. If we accept agenthex's logic and empirical evidence--whatever that is or isn't--then am I correct to assume that a balsa core blade's infamous non-linear response to fast strokes is non-existent? In other words, are the rubber, sponge and outer plies, e.g. carbon, etc. a greater factor in ball rebound than the inner balsa core? That the milliseconds the ball resides on the outer surface of a moving blade would have little, if any, relationship with balsa cores beyond the issue of vibration and miniscule energy dissipation? Your clarity would be appreciated.

I suspect the stiffness of the blade plays a major role in the nature of the vibrational sensory feedback you get after the ball strikes the blade and that as much as anything else may account for different preferences in materials. JRS, what do you think about this idea?

_________________
Butterfly Viscaria Black tag
2.2 mm Nexy Karis M on FH and BH

The way I look at it, how the outer layer behaves determines how hard the ball bounces off the blade. And this is due to how the outer layer moves when the ball hits it. It "gives" to some degree. (Whether it bounces back in time to add to the bounce is another issue, let's pretend it doesn't exist to simplify things.) What determines how much it will "give" when the ball strikes? Well, it's own properties (stiffness, hardness, compressibility) would be one factor. Limba would behave differently than, say, graphite/epoxy composite. However, imagine the difference between a 1/32" sheet of limba and a 1/32" sheet of limba with a 1/2" plate of steel behind it. The former will "give" a lot more than would the latter, and would be a great deal slower. So another thing that determines how the surface sheet behaves is WHAT IS BACKING IT UP. Balsa is a great deal softer than, say, maple (or even obeche) and would cause different behavior when used to back up a layer of limba. This is why I think balsa blades behave differently.

An interesting experiment would be a Rohacell or Spider-foam cored blade.

Iskandar

Just a small note. What we were discussing at the beginning of the thread was one particular mode of bending, i.e. lengthwise. Some people were claiming that (the best looping) blades would bend lengthwise (like a rainbow) when the ball was struck, and you could do this with finger pressure on certain "flexible" blades. That's what the "flex" in the subject line is, not other modes of bending or vibration. If we're now discussing something else, that's fine, but I just want to make this clear.

(So far, I've not found any such blades, nor have I seen any photographic evidence that any exist, other than that 3mm thick rec room paddle from a couple pages back, and that probably loops as well as a sack of potatoes does.)

Iskandar

Regarding JRS' last post, it is often said that making a blade slightly smaller makes it faster. Is that not true?

_________________
Butterfly Viscaria Black tag
2.2 mm Nexy Karis M on FH and BH

It's certainly what a lot of people believe..

Iskandar

I believe it, but not for any rational reason. JRS would be able to give me a rational reason one way or the other.

_________________
Butterfly Viscaria Black tag
2.2 mm Nexy Karis M on FH and BH

Ever try playing with one of the mini bats? Hard to hit the ball 10 feet.

Is this the kind of flex we are referring to?.. or is this just marketing hype then..??


STIGA Carbonado 145 & 190 With TeXtreme® Technolo…: http://youtu.be/V884HyOG-hw

HnG

_________________
Laziness is the mother of all evil... but she is a mother and you should respect her!

Carbon blades (whether Carbonado or not) would be the last blades I'd expect to flex like a banana (er, I mean, flex like a diving board - bananas don't really flex after all, they start out curved). What Stiga's talking about is probably vibrational (or local) stiffness. I don't know what sort of carbon fiber they're using in the Carbonado, but they claim it's different (and from what I gather, it's probably just an open-weave cloth). Applying it at a 45 degree bias seems to be a novel idea, yet I wonder why it should be. It's been known for ages that using carbon/glass cloth with a bias weave makes aircraft wings and other parts torsionally stiff. Here's a "Carbonado 45" glider wing:



http://home.hccnet.nl/l.wakkerman/pos_v ... ouw_7.html

People have known this since the Wellington bomber in WWII with it's geodesic construction.



I just got one of these in the mail yesterday:



5.2mm thick blade, supposedly 100% limba (though I have my doubts). If anything is "flexy", this will be. Only 74 grams. We'll see how it plays tomorrow.

Iskandar

Sorry for bringing up the old post. Are there many people choosing new blade by holding the grip and bending the blade surface?
By doing this, will it cause the damage to the blade? As the Carbon/Arylate/ Fiber and the wood could delaminate due to bending..

I doubt it.. As you note, it's not possible to cause appreciable flexing without applying so much force you'd cause damage.

Iskandar

From the world of tennis EJ'ing...



Quite a few take-aways from this video.

1) In tennis, you can actually demonstrate flex in a racket. And measure it, too, no doubt. Try that same test he did with a table tennis blade. Make a video. I'll bet you can't.

2) Apparently this "blade" works well with "soft sponge". It apparently "firms up" when you hit hard. What's the table tennis analogue to this? I'm not sure. Does the Viscaria behave like this?

3) This is a "beginner's blade". And he (an actual "pro" in the sense that he makes a living selling tennis stuff) uses it himself.. and highly recommends it. Shades of what.. the M8???? Unlike the M8, it isn't cheap... You wonder if it hasn't already been cloned and pirated in China...

Iskandar