Thicker rubbers are softer when using the same sponge material

[lodro]

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.

Our friend BB is very selective who he answers and what he answers.
You may notice that my """very important question""" in post #18 has simply been ignored.
Does it mean there might be a flaw in his academic formula that was not considered.????
Do we all need more popcorn and more beer ????
Life is complicated, so many questions 😂

 

[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?

The property of the rubber doesn't change depending on the shape that is impacting it but the results will be different.

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 ?

You are supposed to be eating pop corn, drinking beer and enjoying the show.
You didn't make it clear. Is the ball dropping at 30 degrees from horizontal when you flat hit the ball?

The reason thicker rubbers ( sponges ) are softer should be intuitive but I guess not.
Think of each square centimeter as a small spring. Springs in series make the total softer. Springs in parallel make the all the springs harder.

Series and parallel springs - Wikipedia

en.wikipedia.org

It is that simple.
Yet the Paddle palace would have you believe that a 1.8mm and 2.2mm rubber made of the same material have the same hardness when the sponge spring changes by 10% due to thickness changes.

The durometer readings are misapplied when it comes to TT. In industry the durometer reading is used to test the durability of a material like belts on a conveyor. The only place I can see durometer readings having a place in TT is to measure the durability of the top sheet by itself. We all know the top sheets will wear out. Eventually you start to see the pips and the surface changes. On top of that the rubber starts to loses its spring effect as it dries out an turns to anti. Also, durometers are too sharp and not shaped like TT balls. Finally, a durometer reading doesn't have units.

But this is NOT what I was talking about when I started this thread. This thread is about how sponge thickness affects the perceived hardness.

 

[igorponger]

TOO THICK, TOO DULL.

A while ago, ITTF asked for players' feedback on the non standard rubbers ranged from 4.10 to 4.80 millimeters total thickness.
A batch of over thick Butterfly Tenergy were submitted for the tests. THE 4.10 was found too dumb, and 4.30 found utterly unplayable.

 

[brokenball]

TOO THICK, TOO DULL.

A while ago, ITTF asked for players' feedback on the non standard rubbers ranged from 4.10 to 4.80 millimeters total thickness.
A batch of over thick Butterfly Tenergy were submitted for the tests. THE 4.10 was found too dumb, and 4.30 found utterly unplayable.

Yes! That is because sponge absorbs energy. It doesn't produce energy.

 

[JJ Ng]

Yes! That is because sponge absorbs energy. It doesn't produce energy.

Lol, I was laughing my rear end off when I read your comment....

 

[brokenball]

Lol, I was laughing my rear end off when I read your comment....

Why?

 

[JJ Ng]

Why?

Lol, because people always think the thicker the sponge the better it is! But then they forgot....the sponge is to absorb the energy, not to impart energy. Hence your comment is spot on!

 

[blahness]

Lol, because people always think the thicker the sponge the better it is! But then they forgot....the sponge is to absorb the energy, not to impart energy. Hence your comment is spot on!

Yes that is correct, but you only got half the story imo. More thickness = more energy that can be absorbed and then released later into the ball = higher ball quality.

Basically, higher thickness allows you to put more energy into the ball without the sponge bottoming out. Same with hardness - the harder the sponge is the more energy is required to compress it and thus when it rebounds, more energy goes back into the ball.

With softer sponges, you can hit hard up till a certain limit after which no matter how much you increase power the outgoing ball won't go any faster or spinnier. I had that experience when playing with the Hurricane 8-80 which is why I eventually switched back to D05.

 

[zeio]

I tried the Blue Whale 3 (its price put Tenergy to shame) once back in 2011 or so. That rubber couldn't be used in sanctioned tournaments because of its thickness (~4.16-4.2mm), but the extra thickness made it feel so good to play with.

The thicker the sponge, the harder it has to be so that it doesn't react much to low power shot, especially for tacky rubbers. It's akin to drawing a strong bow.

 

[kapahoo]

I tried the Blue Whale 3 (its price put Tenergy to shame) once back in 2011 or so. That rubber couldn't be used in sanctioned tournaments because of its thickness (~4.16-4.2mm), but the extra thickness made it feel so good to play with.

The thicker the sponge, the harder it has to be so that it doesn't react much to low power shot, especially for tacky rubbers. It's akin to drawing a strong bow.

On the other hand - the harder the sponge, the less likely you will hit through it so thickness is not needed.

 

[zeio]

That is easy to solve. People would just boost the crap out of it. The problem has always been the thickness limit. That's why H3 was most commonly available in 2.2 around early 2009, then 2.15 caught on and now 2.10 is the standard.

 

[brokenball]

Thicker sponges do not return the same percentage of energy as the thinner sponges.
First there is the internal friction. More sponge, more friction.
Second, the potential energy in the sponge must now accelerate the ball AND the sponge.
Third, the rubber can not keep accelerating and will slow down as it approaches it initial position so the ball and rubber will separate.
Think about this.
When the ball hits the rubber, the rubber and compress as he ball comes to a momentary stop. When the ball first touches the rubber the rubber compress at the rate of impact. However when the rubber expands it doesn't go back to the initial position at the same speed. It slows to a stop.

One point I would like to make about "bottoming out"
First when flat hitting do you care? Now the sponge isn't absorbing any energy.
Second the ball compress a lot. Look at my recent thread where I compress a TT ball.
When hitting the ball at an angle like the 30 degree or 2 o'clock position. impact must be broken down into a normal and tangential force. The normal force will be cos(30 deg) or .866 of the total force so the sponge is less likely to "bottom" out. If you hit the ball at the 45 degree position to get more spin the force will be reduced even more.

I do believe that rubbers bottom out. I like Rakza7 but I wouldn't use Rakza 7 soft 1.8mm on my BH.

 

[OldUser]

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. 😁

Totally agree, in my country we name that "enculer les mouches", I let you do the math translation

 

[brokenball]

There are always those that want to be ignorant but still talk about what they are ignorant about.
Lodro, you are supposed to be eating pop corn and and drinking beer.

 

[Trevize84]

Personally I appreciate @brokenball 's posts about the topic. As an engineer I like this aspect of the game although having little spare time I prefer to practice more with experimental results rather than mathematical modelling I appreciate though the effort of explaining the basic model behind this. My mind was already thinking at MATLAB doing accurate simulations. Perhaps measuring key parameters of commercial equipment and simulating outcome of Blade+Rubber combinations 😜

 

[zeio]

I went back to read the original post. Man, what a trick to lower my IQ. The premise of this thread is beyond dumb. I doubt the hard-headed engineer has read the standard before sprouting all that crap. "A spring constant would be much better"? FFS, the Shore hardness incorporates the spring constant in its equation!

 

[brokenball]

I went back to read the original post. Man, what a trick to lower my IQ. The premise of this thread is beyond dumb. I doubt the hard-headed engineer has read the standard before sprouting all that crap. "A spring constant would be much better"? FFS, the Shore hardness incorporates the spring constant in its equation!

Another cheap shot by Zeio.
What part is dumb?
Your IQ didn't need any help.
A spring constant would be much better than durometer reading that has no units. The problem I is that is isn't perfectly constant. I proved that with my compression tests. I can work around that. Durometer tips are the same shape as TT balls.
So instead of saying what I said is beyond dumb. Give an example. Zeio can't.

 

[NextLevel]

Yes that is correct, but you only got half the story imo. More thickness = more energy that can be absorbed and then released later into the ball = higher ball quality.

Basically, higher thickness allows you to put more energy into the ball without the sponge bottoming out. Same with hardness - the harder the sponge is the more energy is required to compress it and thus when it rebounds, more energy goes back into the ball.

With softer sponges, you can hit hard up till a certain limit after which no matter how much you increase power the outgoing ball won't go any faster or spinnier. I had that experience when playing with the Hurricane 8-80 which is why I eventually switched back to D05.

Yes, sometimes people focus on the sponge using the model of a cushion and forget that the sponge also has the effect of a trampoline.

 

[brokenball]

Yes that is correct, but you only got half the story imo. More thickness = more energy that can be absorbed and then released later into the ball = higher ball quality.

But you must hit the ball faster/harder do put that extra energy into the sponge. With the conditions but a thinner sponge, where does that energy go and how much of it is returned?

Basically, higher thickness allows you to put more energy into the ball without the sponge bottoming out.

True, but hard you flat hitting? if you are brushing the ball at 2 o'clock, not all of the energy goes into compressing the sponge but instead stretching the top sheet? Also, I have proved in a different post that the ball absorbs a lot of the energy.

Same with hardness - the harder the sponge is the more energy is required to compress it and thus when it rebounds, more energy goes back into the ball.

Maybe true. It depends on how elastic the hard sponge is. I have a Chinese anti called guard. The rubber is very hard and inelastic so is very slow. You can push on it and see your finger depression for a second or so. The key thing is when the rubber is expanding, it must accelerate not only the ball but also the rubber and eventually the top sheet can't keep up with the ball

With softer sponges, you can hit hard up till a certain limit after which no matter how much you increase power the outgoing ball won't go any faster or spinnier. I had that experience when playing with the Hurricane 8-80 which is why I eventually switched back to D05.

Softer sponges require ones brushes more to avoid bottoming out the sponge. However, I ask again. If you flat hit with soft where does all the energy go if the soft rubber is not absorbing the energy? I do agree that if the soft sponge bottoms out that it changes the spin to speed ration which will probably case the ball to go into the net EmRathich did get this right.

 

[brokenball]

Our friend BB is very selective who he answers and what he answers.
You may notice that my """very important question""" in post #18 has simply been ignored.
Does it mean there might be a flaw in his academic formula that was not considered.????
Do we all need more popcorn and more beer ????
Life is complicated, so many questions 😂

Sometime I get busy. I am "camping" now but I have internet.
The answer to your very important question is probably yes but your questions isn't defined well enough. If you are simply asking if the ball hits the paddle at a 30 degree angle then the normal impact speed is cos(30deg) times the impact speed. The tangential impact speed is sin(30deg) times the impact speed. The normal impact speed will be less so it won't compress the sponge as much or tend to bottom out. The tangential impact speed will stretch the top sheet some. The pips will bend underneath to allow this. The sponge may stretch a little tangentially.

Really, the sin() and cos() thing is basic. What stretches tangentially the most is unknown....... for now. Obviously we don't know what stretches tangentially the most. We can't see this with a high speed camera but the top sheet and sponge can be tested separately. I bet someone know.
My spider sense tell me the top sheet stretches tangentially the most.

Yes, sometimes people focus on the sponge using the model of a cushion and forget that the sponge also has the effect of a trampoline.

Yes, but if you paid attention I did a test and showed how much force is required to compress a rubber in increments of 0.001 inches.
It is not linear at the start because not much of the ball has made contact with the rubber yet. After that it is pretty linear.
So what is your point or are you just trying to confuse the issue?

BTW, the math for a real trampoline is quite complex. So how does it apply to TT rubbers?