OOAK Table Tennis Forum

I don't think you understood what I was describing there at all. I will try again another day. Someone needs to send you a decent blade that's what I think.

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Donic defplay senso
Haifu whale soft (grips-euro)
Nittaku pimplemini 1.0mm

Ok Im going to make a little video about flex showing you just how much blades do bend and how easily they bend. If you still think they snap after bending 2mm after seeing this well then either you need to go to the mental home, or I have a lot of broken blades . I'll make the video tomorrow.

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Donic defplay senso
Haifu whale soft (grips-euro)
Nittaku pimplemini 1.0mm

Oh Jeez, another agent hex attack. Sorry, not going to waste time on this. Insulting me with a "lol"? Really?
-Larry Hodges

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http://www.TableTennisCoaching.com

For a loop, isn't the point that, for flex to do anything to help the loop, wouldn't the flex and rebound have to happen almost perpendicular to the direction of flex to which most people are referring? Wouldn't the flex/rebound have to occur parallel to the length of the blade face, or, really, on a slight bias, but mostly parallel to the blade face? Wouldn't the the flex/rebound being referred to only have any effect if you were flat hitting the ball?

On a loop the blade face is going through space in a way where the edge is leading like it is cutting through the air rather than the way an oar would push water or the way you would fan yourself with your racket.

So, if the edge of your blade was leading the stroke, cutting through the air, how would the flex/rebound--pushing the ball off the blade face towards the ground--help a loop in the first place?

Thank you again foam. A video of a ball hitting the blade (and rebounding slower than it arrived) would be helpful, as it will show how much the blade deforms. But, a video of a blade striking a ball - and forcing a rebound much faster than the ball's original speed - would be much more interesting. I'll suggest a way to make the deformations easier to see, as follows.

I have suggested a "thought experiment" approach to this problem, which you could also do in reality (if you really need to) with one trip to a good hobby shop. It goes like this:
1) Would a 1.5mm thick 1-ply ayous blade flex? (yes, probably catastrophically)
2) How about one 3mm thick? (I guess yes, easily observably. How easily it will break I don't know. Do you know, Foam?)
3) How about 6mm? (The answer is yes: a) if 3mm flexes then how much a 6mm will flex can be roughly estimated with a simple formula which has already been mentioned. The answer is not zero.) It would be easier to observe, photo, video the flex in a 3mm thick blade, and we could then estimate the flex of a 6mm very easily.

Lastly, as I said, it is not necessary that the blade flex an amount comparable to the thickness of an uncompressed rubber (although it might). It is enough that it flex some fraction of the thickness of a fully compressed rubber, as that would unload the rubber. (If the wood gives .1mm, and the fully compressed rubber is thus .6mm instead of .5mm, then the force exerted on the ball would be less, the ball would stay on the rubber longer (oh...??), etc., etc., etc.) But since tenths of millimeters would be hard to capture on video, I suggested extrapolating from thinner blades.

To upsidedowncarl:
Your question is interesting and I hope someone talks about it, but the thread wasn't about that. The original post's claim is that "blades don't flex".
Having said that, I'll still mention the last paragraph of my previous post which is probably relevant to your question.

More for anyone interested:
The relationship between force and height of a compressed spring is linear up to a point. But a steel coiled spring can "stack" and become like solid steel if compressed that far. A ping-pong* rubber similarly squeezed enough could become as hard as, uh, squeezed solid rubber, whatever that is. I'm sure it is many times less compressible than sponge.

So, as the rubber gets compressed, as those last few tenths of millimeters of rubber are approached there is a much quicker ramp-up of the force applied to the ball.

That is why a couple of tenths of millimeters of flex - which you won't catch on video without very serious equipment* - can make a big difference in how much force is applied to the ball, and therefore how long the ball will stay on the rubber, etc. Hey, It looks like my hand and my mind were sufficiently serious equipment*. I hope the same is true for you!

Blade weight:
In light of the above, here is what's wrong with the references to the total blade weight made in the thread: if the deformation is only tenths of millimeters in depth (see the above for why this is meaningful) then the wood directly under the ball moves that much, but progressively farther from the ball, less. So, the effective diameter (no need to define it exactly) of the amount of wood involved could be, say, 20mm. What is the weight of that? 10g? Here is the point: the weight of the ball is not tiny compared to that. So it is not impossible that the ball could move that much wood in the available time. Can I get a witness?

What you're saying is that the process of accelerating the blade significantly bends it (like storing energy in a spring) upon which it's released on impact. What I'm saying is that even if this were physically possible the resultant rebound in a closed angle loop points mostly downward; and that downward application of force by the blade is ironically why springy/elastic (ie. fast) blades are difficult to loop with, a fact which you very much acknowledge.

The key physical misunderstanding here is that we tend to equate "elastic/springy" to soft like a rubber band where we can visually see the deformation, when hard materials have more rebound (you just don't see the "spring" being stretched). That physical deformation ("flex") of the wood fibers on a microscopic level results in energy loss.




That was merely a funny fact, just as Larry Hodges being magically summoned whenever his name is mentioned or uses the chewbacca defense of "I coach very many kids therefore I win" or goldfish loses their pigment when kept out of the light are funny facts.

> For a loop, isn't the point that, for flex to do anything to help the loop, wouldn't the flex and rebound have to happen almost perpendicular to the direction of flex to which most people are referring?

Yes, if what they're saying is true a slow/flexy blade would work wonders for hitting, but in reality are just slow for open blade shots no matter how fast you swing.

> 3) How about 6mm? (The answer is yes: a) if 3mm flexes then how much a 6mm will flex can be roughly estimated with a simple formula which has already been mentioned. The answer is not zero.)

The formula is ~X^3 relationship, correlated to the stiffness of materials vs thickness. A 6mm blade will flex ~1/8 of a 3mm, reflecting ~8x stiffness. I've actually mentioned this in reply to your PM.

> Lastly, as I said, it is not necessary that the blade flex an amount comparable to the thickness of an uncompressed rubber (although it might). It is enough that it flex some fraction of the thickness of a fully compressed rubber, as that would unload the rubber.

The whole argument of the blade "rebounding" doesn't even make sense to whose who're familiar with the shot. Such a stroke is far more effective when you maintain racket acceleration through the ball (foam of all people should know this), and that force would keep compressing it rather than the "release" which would only happen if you stop (ie decelerate) before contact. Try this with a spring if it's confusing.

> A ping-pong* rubber similarly squeezed enough could become as hard as, uh, squeezed solid rubber, whatever that is.

In TT the phenomenon is called bottoming out the rubber, and it's most obvious on hard smashes (tangential to to the racket) with soft sponge since it's done against a hard surface, but actually happens a lot more for loops since they're swung much faster. The funky feeling of pips bending to their stops when a rubber gradually bottoms out in the direction parallel to the surface is what I believe is often described by better players as flex.

edit:

>A video of a ball hitting the blade (and rebounding slower than it arrived) would be helpful, as it will show how much the blade deforms. But, a video of a blade striking a ball - and forcing a rebound much faster than the ball's original speed - would be much more interesting.

The video above shows an impact. The laws of physical motion only cares about relative velocities, etc, so whether the ball approaches the bat or vice versa is irrelevant. You can verify this in any physics text. The only known exception is when velocities approach the speed of light which I assure you is not the case here.

It is an interesting theory. I don't know one way or the other. It is possible and what we feel and what causes what we feel is often different from what we think causes what we feel. So I will try not to go there.

But what I can say is that, it does not make sense to me that blade flex perpendicular to the force applied in a loop would help in any useful way. It also seems to me that the affect of the topsheet on a loop is more at issue than anything else and the effect of the sponge on a euro/japan rubber has more to do with allowing the the ball to sink in enough so that more of the topsheet can grab the ball.

I don't know that the sponge rebound actually would propel the ball forward either. But the force of the ball being pulled by the grab of the topsheet would both spin and propel the ball.

Even in a blade that did flex easily when force is applied perpendicular to the blade face, would it actually flex with the force being applied by the ball on a loop, given that the force is being applied at a very low angle like 3-8 degrees to the blade face.

Is what I am saying clear?

If you wanted to do a flex test on a blade, if you set something up to fire a ball at the blade, say the ball was being shot straight down at the blade, the angle of the blade face should not pointing straight up. But almost directly to the side so the edge is pointing almost straight up.

How much force in that direction would need to be applied to a flexy blade for us to be able to see enough flex (say 0.1-0.3mm) for that to add something useful to a loop? Which direction would the blade be supposed to flex?

1) Someone emailed me that you'd posted another nasty note about me. Email is not magic.
2) When have I ever used the supposed "chewbacca" defense that you accuse me of using? (Answer: never. You made it up. When you lie about someone, what does that make you?)
-Larry Hodges

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http://www.TableTennisCoaching.com

Folks who know of you won't doubt this statement, and others who don't are about to experience its veracity. They can already see you have no plan to contribute substantive but feel justified to make everything about yourself.

Btw, "you'd posted another nasty note about me", curious choice of words from someone known for pedantry throwing around accusations of lying.

edit: to clarify, this is literally the second time I've ever had anything to do with Hodges, but his reputation precedes him.

What you're saying is correct to best of my knowledge. We know that the ball's own deformation tends to account for much if not all of the resulting bounce against hard surfaces (such as blades): http://cofrest.info/md3.htm

The better way to think of it is that a very hard surface (like the table or Schlager carbon) lets the ball do its thing, and less elastic ones subtract from the rebound and purposely so.

This is less likely the case with a much softer rubber surface, against which I doubt the ball deforms much at all. This implies the something which provide the rebounding forces is not the ball which leaves the rubber/sponge.

So sum up: against a blade (very significant component of flat shots) or table the ball is what rebounds, against the rubber (main component of loops) it's logically the rubber.


I think you mean do the video above but for a spinned ball from a robot or such.

You can still abstract the impact into the direction into the surface and direction parallel to it. We already know about into the surface, and I don't think a softer force (like for the loop) would change much. The more interesting part of other direction is what's happening inside the rubber so the ball has to hit right at the edge in order to reveal what's going on there.

From a technical standpoint it's also difficult because getting that kind of resolution at that speed is very expensive. Notice the video above is pretty pixelated because affordable commercially available imagers are limited in bandwidth so for speed they trade off resolution, which you need to see the pips clearly. I think precise offset-timed photos from a very sensitive sensor might work (for the super-technical: equivalent-time sampling is necessary instead of real-time).

The flex is at least as easy to perceive with thin strokes, where the force applied has a very small component in the "direction of flex". This may seem to support the theory that what we perceive as flex is not really flexing of the blade. That assumed support ignores simple geometry...

Exaggerated view:

Blade in neutral state (yellow) and flexed (blue with dotted contour).

Thin impact (dotted line from the ball) creates small flex. Because of the angle of impact, this small flex may add significantly to the time of contact between ball and rubber (illustrated by the continuous line), and hence also increase the margin of error.

I believe this to be significant. Also, when flex is small, thinning/stacking of "elasticity components" will not occur so easily, so linearity is more likely.

Makes sense to me.

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Rating in the middle/low range in the region.
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