Thicker rubbers are softer when using the same sponge material

[brokenball]

The TT manufacturers ratings on their rubber hardness or softness are bogus.
The TT manufacturers usually have only one rating and that is a durometer value from an arbitrary scale.
First, a 2.2 mm rubber is softer than an 1.8mm when the rubbers are made of the same sponge material. The Paddle Palace rubber ratings usually have one rating for all three thickness. Think of a rubber as being made up of layers of 0.2mm sheets. The 1.8mm rubber would be made of 9 sheets and the 2.2 mm rubber would be made of 11 sheets.
Now suppose a 10 N force makes each sheet compress by 5%. Then each sheet would compress by 0.01mm so the 1.8mm rubber would compress 0.09mm and the 2.2mm shet would compress by 0.11 mm. The top sheet will affect these numbers a bit because the top sheet looks like another spring in series.
Two, the durometer readings are not realistic. There is no way a pointy device sticking into rubber resembles a TT ball. How could one use a durometer reading in a calculation. Durometer readings don't even have units!!! A durometer reading doesn't provide any indication of how fast or spinny the rubber is.

A spring constant would be much better.

 

[mocker88]

Yeah. This is a strange way to measure sponges hardness and top sheets. I don't know how to measure things properly, but you have to consider what type of blade you're using. Say that you need to have three typical sorts of blades to start the measuring from. Then you'll have to measure the spin and speed you get out of each variation of blade/sponge and measure this when hitting Slow/Medium/Hard in flat/half closed/closed bat angle.

Scientifically you could surely get an enormous amount of numbers out of this, but I think it would be hard for the common player to get any useful information out of it. Probably there's a lot of things I haven't thought about regarding this, but these are my simple thoughts

 

[lodro]

Yeah. This is a strange way to measure sponges hardness and top sheets. I don't know how to measure things properly, but you have to consider what type of blade you're using. Say that you need to have three typical sorts of blades to start the measuring from. Then you'll have to measure the spin and speed you get out of each variation of blade/sponge and measure this when hitting Slow/Medium/Hard in flat/half closed/closed bat angle.

Scientifically you could surely get an enormous amount of numbers out of this, but I think it would be hard for the common player to get any useful information out of it. Probably there's a lot of things I haven't thought about regarding this, but these are my simple thoughts

oh shit !
Now you started him up again.
He is just looking for people who oppose him in the slightest , just to have an argument and tell us how stupid we are not to understand the sophisticated math. 😁

 

[brokenball]

oh shit !
Now you started him up again.
He is just looking for people who oppose him in the slightest , just to have an argument and tell us how stupid we are not to understand the sophisticated math. 😁

Just grab a beer and more popcorn. You might learn something.

 

[brokenball]

Yeah. This is a strange way to measure sponges hardness and top sheets. I don't know how to measure things properly,

I do.

but you have to consider what type of blade you're using.

No, blades do no have a hardness or softness rating. Perhaps they should have a flex rating but that can wait for another thread to entertain Lodro.

Say that you need to have three typical sorts of blades to start the measuring from. Then you'll have to measure the spin and speed you get out of each variation of blade/sponge and measure this when hitting Slow/Medium/Hard in flat/half closed/closed bat angle.

You are confusing the issue. We only want to evaluate the rubber alone.

Scientifically you could surely get an enormous amount of numbers out of this, but I think it would be hard for the common player to get any useful information out of it. Probably there's a lot of things I haven't thought about regarding this, but these are my simple thoughts

Again you confuse the issue. Why is it that TT players always bring up thinks like the force of gravity from the moon?

Anyway, this isn't too difficult, but it would take some equipment. Sacrifice a new rubber. Cut a square 10 cm by 10 cm. Next mount the rubber on a hard surface so it is flat. Glue might screw up the readings. Now put weights or apply force evenly on the 100 cm^2 rubber using 10 cm x 10 cm plate (actually the plate could be a little bigger because only 10cmx10cm would make contact) and measure how far the rubber compresses. As a function of the force. This can be graphed. It would be easy to generate a spring constant for function now.
It is easy to measure the force to fractions of Newtons and positions to 0.1 of microns. This can be very accurate and would show how linear the rubbers when if comes to compression. In my experience the compression is pretty linear until the rubber gets to the point where is no long can compress or "bottoms out".

I/we ( my company ) sell motion controllers that have been used in tests like these. Normally these are strain vs stress test. Everything is recorded.
Shell tests soil samples this way only they do the tests on core samples. A machine like this would be too hard to setup but the TT manufacturers would rather give you meaningless information.

BTW, what is the force impact between a TT ball and paddle with an impact speed of 10 m/s and it is a flat hit?

 

[igorponger]

THE SPECIFICATION OF SPONGE HARDNESS IS MEANING VERY LITTLE IF ANY. WE NEED SCHOB's TESTS ON EVERY SPONGE.

Look, while going for shopping on marketplace, one can see a huge LOT of rubber products labeled as having sponge hardness of 36 degree. Yet, despite the similarity of numbers, all the rubbers do play utterly different game. That's to say that the sponge HARDNESS NUMBERS as usually appearing on sponge and packages are purely misleading information, of no real usefulnes.
We strongly suggest that all the sandwich rubbers on market should be labeled with a digital index by Schob resilience scale. The Schob's numerical index will tell you how much projective speed the specific sponge could produce at ball impact. Eg. in laboratory tests Tenergy index came out 48%, Rozena index 42%. That is clearly indicative that Tenergy projective power (generally known as trampoline effect) is much better than that on ESN tensors. So far, we do see no other rubbers comparable to Tenergy in the scope of projective power, even though they all being similar in Hardness degree 36.

YES, SCHOB's INDEX IS THE MOST USEFUL TECHNICAL INFORMATION ON EVERY SPONGE, of which we fully convinced.

[video]

 

[brokenball]

The Schob device is best for measuring normal COR. I agree, it would be much better than what we have right now.

 

[AchyGeorge]

Questions for brokenball,
Do you think that the hardness of a material will change depending on if hit by a house brick, a table tennis ball or a needle?

Following on from the above, will the hardness of a material change if it is 1mm, 1cm, 10cm, 1m thick?

 

[Kuba Hajto]

Questions for brokenball,
Do you think that the hardness of a material will change depending on if hit by a house brick, a table tennis ball or a needle?

Following on from the above, will the hardness of a material change if it is 1mm, 1cm, 10cm, 1m thick?

Different durometers have different shape. I assume that this suggests that hardness will be different based on the tool shape.

 

[Trevize84]

Personally I believe all this is pointless because the current status of the production system is close to alchemy rather than engineering. What I think is:

1. Production system has a huge degree of error. You barely get 2 pieces of the same rubber with the same characteristics, I doubt you can compare characteristics of different rubbers and different brands. No matter what the measurement tool is.

2. Hardness of sponge is only part of the equation, you also need to factor in the hardness of the top-sheet otherwise 2 rubbers with same exact sponge and different top-sheet can feel one the opposite of the other.

3. Even if you know hardness of sponge+topsheet, glue and varnish matter and they're not negligible. Also the blade matter, because the behaviour of the rubber may change completely depending on underlying blade. On top of this production error on blades is even worse than the one of rubbers.

4. Good luck against people boosting their equipment.

 

[Kuba Hajto]

I don't think the exact number matters. I would say only comparatively between rubbers it matters. For me this is indication:

• Ok this rubber might be suitable for me, its soft enough
• Oh hell no, in my current condition I will never hit through a 60 degree brick

 

[lodro]

Also the blade matter, because the behaviour of the rubber may change completely depending on underlying blade.

I sure agree with just about everything you say but this here sentence made me wonder.
Of course I know the experience of finding a rubber to be completely un-playable on one blade and then become my favorite on another blade.
But has the rubber really changed itself ?
Is the rubber really being influenced by the blade ?
Or is it simply that the combinations of rubbers and blades give different results while the characteristics of both blades and rubbers in themselves remain the same ????

Or am i just splitting hairs ??? 😁

 

[Trevize84]

But has the rubber really changed itself ?

I can't say this is always the case, but I cannot exclude that characteristics of the rubber are affected by the presence of a softer or a harder underlying layer(s). I'm not the right type of engineer to evaluate these kind of things, but I wouldn't be surprised if a softer blade might enable effects into the sponge that will feel as if the sponge was softer than it is. Something like when you punch the sand and you feel it hard and touching it slowly makes you feel it soft. Now imagine you punch it but something under the sand absorb the impact so that the sand behaves as if your punch was a soft touch. I'm just guessing, I'm an information engineer not a mechanical engineer.

 

[lodro]

I can't say this is always the case, but I cannot exclude that characteristics of the rubber are affected by the presence of a softer or a harder underlying layer(s). I'm not the right type of engineer to evaluate these kind of things, but I wouldn't be surprised if a softer blade might enable effects into the sponge that will feel as if the sponge was softer than it is. Something like when you punch the sand and you feel it hard and touching it slowly makes you feel it soft. Now imagine you punch it but something under the sand absorb the impact so that the sand behaves as if your punch was a soft touch. I'm just guessing, I'm an information engineer not a mechanical engineer.

this is what this whole thread is possibly all about. One side tries to impress us with technical/ mathematical theories and "measurable" facts and figures, which to me are honestly worth "Sheit" because us Table tennis players , at whatever level we play, know that it is ""how it feels is what counts""" 😁

 

[brokenball]

Questions for brokenball,
Do you think that the hardness of a material will change depending on if hit by a house brick, a table tennis ball or a needle?

Following on from the above, will the hardness of a material change if it is 1mm, 1cm, 10cm, 1m thick?

No,

Questions for brokenball,
Do you think that the hardness of a material will change depending on if hit by a house brick, a table tennis ball or a needle?

Following on from the above, will the hardness of a material change if it is 1mm, 1cm, 10cm, 1m thick?

I thought I made that clear. The thicker the rubber the software it will be..
Why? Think about it.

 

[Trevize84]

this is what this whole thread is possibly all about. One side tries to impress us with technical/ mathematical theories and "measurable" facts and figures, which to me are honestly worth "Sheit" because us Table tennis players , at whatever level we play, know that it is ""how it feels is what counts""" 😁

That's also the point of view of engineering. Response to inputs is what an engineer cares about when designing a system. Response function of a rubber is what the player feels, hardness it's a property that affects response function, but what matters is the function rather than the properties. However I doubt you'll ever get datasheets plenty of charts showing mechanical characteristics varying blade or glue or varnish. And the reason because we're not going to get data sheets, in my opinion, isn't the difficulty in measuring rubber's characteristics. I think the reason is that every rubber sheet should have its own datasheets because production error is too high. This would eventually bring to different tiers of quality for the same product (which is what we already know it happens, like when in his videos Timo Boll measures the weight of dozens of rubbers before glueing them).

 

[brokenball]

Different durometers have different shape. I assume that this suggests that hardness will be different based on the tool shape.

No. How can the object that hits the rubber change the property of the rubber unless it damages the rubber. Think! The object hits the rubber with a force. That force is distributed over the contact area.
The force is distributed evenly with a 10cmx10cm plate. It makes doing the calculations easy. The impact area of a TT ball is about a 1 cm circle. The force is not distributed evenly because the ball is round. This complicates things.. Calculus is required in this case.

So what is the force of impact of a TT ball traveling at 10 m/s and it is flat hit?

 

[lodro]

So what is the force of impact of a TT ball traveling at 10 m/s and it is flat hit?

just making sure : I can "flat-hit " a ball that comes towards me at a (let's say) 30 degrees angle.
Will this make a difference in the "calculations" of the force of impact ?

 

[brokenball]

Personally I believe all this is pointless because the current status of the production system is close to alchemy rather than engineering. What I think is:

1. Production system has a huge degree of error. You barely get 2 pieces of the same rubber with the same characteristics, I doubt you can compare characteristics of different rubbers and different brands. No matter what the measurement tool is.

Some brands are better than others but I know that some rubber millers don't have very good quality control. My first Apollo rubber was extremely tacky. Now they are on version 5 or so and each is different. Is that because they are different batches. Anyway, my second Apollo sucked.

2. Hardness of sponge is only part of the equation, you also need to factor in the hardness of the top-sheet otherwise 2 rubbers with same exact sponge and different top-sheet can feel one the opposite of the other.

The TT ball hits the top sheet and the force of the top sheet pushes on the sponge.
The top sheet does stretch kind of like a trampoline and reduce some of the force on the sponge. BTW, this is why is like the term trampoline effect rather than catapult. Catapult is so wrong.
There are complex formulas for computing how a trampoline is affected by the impact of a jump. There is nothing for TT. TT is so backwards.

3. Even if you know hardness of sponge+topsheet, glue and varnish matter and they're not negligible. Also the blade matter, because the behaviour of the rubber may change completely depending on underlying blade. On top of this production error on blades is even worse than the one of rubbers.

Are another one of those that want me to take into account the force of gravity of the moon? I am only trying to evaluate rubbers. I already mentioned in the first post that that is too thick will affect the results. Therefore the glue must be very thin.
BTW, the earth wobbles 4.67 km due to the gravity of the moon. Does it matter? do you feel it?

4. Good luck against people boosting their equipment.
A phrase I learned in the navy. "harassments, no matter how trivial, if continuous, will be effective"
You can substitute propaganda or facts..

 

[Trevize84]

Are another one of those that want me to take into account the force of gravity of the moon? [...]
BTW, the earth wobbles 4.67 km due to the gravity of the moon. Does it matter? do you feel it?

Well, at least before excluding these, we should prove they are negligible. But I was talking about glue and blade which are a little closer to the rubber than Moon, so perhaps some investigation won't hurt.