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  1. Николай Петров is offline
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    #1

    How to measure blade speed?

    Hello guys I was looking into two blades (Stiga offensive cr,wrb) and (Stiga offensive nct) btw my question is not only for these two blades I am just giving them as an example so Rev spin show that the cr-wrb is a lot faster and harder than offensive nct while stiga website shows the exact opposite It is really confusing for me who to believe and btw it is really confusing to me how to measure blade speed in general specially when it comes to off plus and carbon blades how can an all wood blade be faster than carbon blade and how can some alc blades be faster than some zlc I am talking about websites that show these scales like revspin for me blades speed is a lot more confusing than rubbers and where can you really compare two blades because blade is something you buy for years ahead rubbers can always change but I want to buy a blade that I will stick for year at least not that I change rubbers that much but If lets say I am picking between two blades that are 300$ I want to know what I am buying and it seems like you cant compare it anywhere or at least I don't know who to believe maybe just listen to people's opinion on the blades idk really confusing topic for me I hope someone has the answer to that.

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    #2
    Independent expert estimation should be of real assistance. Contra Catalogue is the best reference source, to my own mind.
    https://www.contra-luebeck.de/media/...al/126/#zoom=z

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    Last edited by igorponger; 01-30-2021 at 06:12 PM.

  3. lodro is offline
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    #3
    I know exactly how you feel...............and have no answer to your problem.
    It feels like the different manufacturers have their own """NUMBERS"""
    and it is impossible to compare apples with apples.

    As one way seems to be buying lots of different blades and finding finally one that does the trick, one can't help thinking that this is the general plan of the manufacturers.

    If you have a coach, he/she should advise you.
    If you play in a club, and see a player playing like you think you could play, ask if you could have a play with their racket.

    Otherwise you end up like so many of us as an :Equipment Junky

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  4. Николай Петров is offline
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    #4
    Quote Originally Posted by lodro
    I know exactly how you feel...............and have no answer to your problem.
    It feels like the different manufacturers have their own """NUMBERS"""
    and it is impossible to compare apples with apples.

    As one way seems to be buying lots of different blades and finding finally one that does the trick, one can't help thinking that this is the general plan of the manufacturers.

    If you have a coach, he/she should advise you.
    If you play in a club, and see a player playing like you think you could play, ask if you could have a play with their racket.

    Otherwise you end up like so many of us as an :Equipment Junky
    Yeah man but I feel like I know more about equipment than my coach he suggest to most people like tibhar and andro stuff which I am not a big fan of I prefer stiga or butterfly blade and chinese rubbers and I am the only penholder in the city that I know off so its kinda hard to try peoples racket but your advise is right.
    Last edited by Николай Петров; 01-30-2021 at 05:51 PM.

  5. lodro is offline
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    #5
    difficult indeed.
    Re penholder: many top chinese penholders use ST or FL handles instead of the dedicated penhold-handles, i do not know why but i am sure they know best. I am mentioning this because it should not stop you trying other peoples rackets just because they use ST or FL handles.

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    #6
    You can check below chart for some reference points.

    https://docs.google.com/spreadsheets...Lfg/edit#gid=0

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  7. lodro is offline
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    #7

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    Last edited by lodro; 01-30-2021 at 10:51 PM.

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    #8
    Quote Originally Posted by Jim
    You can check below chart for some reference points.

    https://docs.google.com/spreadsheets...Lfg/edit#gid=0
    The comment I saw in the spread sheet it that higher frequency blades are usually faster. Why usually?
    What if the blade vibrated at twice the frequency? Would it be faster yet?

    What I know for certain is that if the frequency is too low the ball will bounce off the paddle before the paddle will rebound so the energy the paddle absorbed will not be returned to the ball.

    The next thing to think about is spring board divers. If they adjust the spring board so it is too stiff or too compliant they will not get the best height from their jump. Another consideration is the damping of the paddle. How fast does the frequency decay. What is the amplitude of the fundamental?
    If the amplitude is very small it makes little difference what the frequency of vibration is because it will not absorb or return much.

    The threads above don't begin to ask the right questions and if you don't know the right questions you will not be looking for the right answers.

    If I were testing paddles I would bounce balls off of it. I might cover the the paddle with hard bat rubber.

    I have posted a video of my Toxic 5 being hit by a ball. You can see the frequency and amplitude of vibration.

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    #9
    In my opinion frequency is a good indicator for blade speed. Anyway, it only indicates the base speed of a blade with low impact of the ball and not its reaction with high impact nor its catapult.
    TT gearlab instead brings 2 different indices which totally makes sense. E.g. the base speed of a normal alc blade can be the same as a blade Hinoki, but the Hinoki blade will usually be bouncier and quicker on harder shots... this difference is not measurable with the simple frequency test (slightly bouncing the ball on the bare blade)

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  10. zeio is offline
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    #10
    Heavy or light shots won't change the natural frequencies of a blade, but the amplitude, hence the name natural frequencies.

    The relevant modes of vibration for a blade are the out-of-plane bending modes, the torsional modes and the membrane modes, which are simplified as primary, lateral and central deflections by the TTGear Lab. What people have been recording and collecting into a table are the frequencies of the membrane modes, which are where the sound comes from the most when a blade is under impact. The in-plane bending mode is another mode that's rarely discussed/measured, which is actually very prominent in serving/pushing/looping/chopping.

    Whatever the case, the natural frequencies are only a loose indicator of the speed of a blade.

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    Last edited by zeio; 01-31-2021 at 03:13 PM.
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    #11
    Quote Originally Posted by Creek
    In my opinion
    That is the problem.

    frequency is a good indicator for blade speed.
    It is just one indicator. What about damping and amplitude? No one mentions that.

    Anyway, it only indicates the base speed of a blade with low impact of the ball and not its reaction with high impact nor its catapult.
    Where is the distinction of low or high speed impacts made? I do believe that the impact speed makes a difference. If the ball hits the paddle and bounces off so fast that the blade does not keep up with the ball on the rebound then that energy in the blade is lost. This would be similar to what you see in my Toxic 5 video.
    Basically, I believe there are certain impact speeds/contact times that are optimal for each of the paddles listed in the data base. Notice that all the frequencies are not that different. There are no 5000 Hz paddles.
    I think this is another Goldilocks situation where there will be a certain range of frequencies that will be optimal but these frequencies will change once you put a rubber on the blade.

    [/quote]
    TT gearlab instead brings 2 different indices which totally makes sense. E.g. the base speed of a normal alc blade can be the same as a blade Hinoki, but the Hinoki blade will usually be bouncier and quicker on harder shots... this difference is not measurable with the simple frequency test (slightly bouncing the ball on the bare blade)[/QUOTE]
    What about damping or internal friction? If the blade doesn't stay in contact with the ball during the rebound that energy is lost.

    No one has addressed the problem of the spring board diver. The board can be tuned by the diver for his weight. If the board is to compliant or too stiff the diver will be able to achieve an optimal jump.

    A collision is all about energy. Energy out vs energy in. The ball, rubber, blade and even your hand absorb energy. What determines the rebound speed is how much energy is retained by the ball after the rebound. I put the Toxic 5 in a vise so the human factor was left out. It is clear to see the Toxic 5 does not keep up with the ball on the rebound which is why the Toxic 5 is so slow. The Toxic 5 is an extreme case. However, I doubt that many paddle keep up with the ball all the way during rebound.

    There are plenty of examples of a mass on a spring on the internet but I haven't found one with a mass impacting a spring that takes into account the mass of the spring and the internal friction or damping factor of the spring.

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  12. lodro is offline
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    #12
    Quote Originally Posted by Creek
    In my opinion frequency is a good indicator for blade speed. Anyway, it only indicates the base speed of a blade with low impact of the ball

    So, this is how they then measure the basic frequency of a blade, by dropping a ball on it and measuring it with the frequency -meter ?????????

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    #13
    Quote Originally Posted by lodro
    So, this is how they then measure the basic frequency of a blade, by dropping a ball on it and measuring it with the frequency -meter ?????????
    If you want to measure the speed of the paddle then measure the speed of the paddle.
    It would be better if the dropped a ball on the blade and measured how fast the rebound speed was vs the impact speed. Actually, this should be done for different impact speeds. What I suggest would be a true indication of the speed of the blade. Anything else is just a distraction.

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  14. Der_Echte is offline
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    #14
    I think this is another Goldilocks situation where there will be a certain range of frequencies that will be optimal but these frequencies will change once you put a rubber on the blade.
    A collision is all about energy. Energy out vs energy in. The ball, rubber, blade and even your hand absorb energy. What determines the rebound speed is how much energy is retained by the ball after the rebound.
    Now we talking good sense in this conversation.

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    #15
    As i said, it is a reference point, but nothing definitive.

    I will leave to other to answer for the science behind it as im not too interested.

  16. Hysteresis is offline
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    #16
    If we are defining the 'speed' of a blade as just how hard the ball bounces off the blade, then just do the bounce test. Vibration is irrelevant.

    Any correlation between frequency and 'speed' are most likely co-causational. In that wood is not a particularly elastic material. So any deformation is likely to result in considerable loss of useful kinetic energy.

    It just so happens stiffer blades both deform less (thus losing less energy), and independently also vibrate at a higher frequency (eg via common experience/sense).

    I don't think the springboard example is particularly relevant here. The ideal springboard jump is that you end up simulating something close to an idealised elastic collision between a person and the springboard anyway, but with more steps. Much like a gravitational slingshot, if you are doing it right, the result is something close to just bouncing object a off object b. It just so happens a person/spaceship isn't something that would survive the straight foward collision with the springboard/celestial object. It takes more complicated mechanics to ensure the person/spaceship bounce off in one piece, but you don't end up with more energy efficiency than just an elastic impact. In fact, if you do the calculations of a perfectly ideal springboard jump, gravitational slingshot, or elastic impact, they are mathematically identical.

    I mean, we are talking about a collision of a 2.7g object at pretty mild speeds against a wooden board. The ball is obviously hardy enough to survive the impact, irrespective of how hard the bat is. We are talking about something very close to the ideal elastic collision already.

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    Last edited by Hysteresis; 01-31-2021 at 03:36 PM.

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    #17
    Quote Originally Posted by Hysteresis
    If we are defining the 'speed' of a blade as just how hard the ball bounces off the blade, then just do the bounce test. Vibration is irrelevant.
    Yes!

    Any correlation between frequency and 'speed' are most likely co-causational. In that wood is not a particularly elastic material. So any deformation is likely to result in considerable loss of useful kinetic energy.
    It isn't perfect but think of archery bows and other ancient weapons of war. It depends on the wood.

    It just so happens stiffer blades both deform less (thus losing less energy),
    You mean absorbing less energy. Now there is less to loose.

    I don't think the springboard example is particularly relevant here. The ideal springboard jump is that you end up simulating something close to an idealised elastic collision between a person and the springboard anyway, but with more steps.
    The point is that the spring board is "tuned" to the divers impact. Why aren't there any 5000 Hz blades?

    Much like a gravitational slingshot, if you are doing it right, the result is something close to just bouncing object a off object b. It just so happens a person/spaceship isn't something that would survive the straight foward collision with the springboard/celestial object. It takes more complicated mechanics to ensure the person/spaceship bounce off in one piece, but you don't end up with more energy efficiency than just an elastic impact. In fact, if you do the calculations of a perfectly ideal springboard jump, gravitational slingshot, or elastic impact, they are mathematically identical.
    But the impacts are not perfectly elastic. If you just bounce balls off the blade the blade and ball will absorb all the energy. Now the blade has been deformed in the form of potential energy. Now the energy of the needs to accelerate the blade and the ball not just the ball. The energy energy required to accelerate the blade is lost to the ball so hopefully the blade does not absorb much energy unlike my Toxic 5.

    I mean, we are talking about a collision of a 2.7g object at pretty mild speeds against a wooden board. The ball is obviously hardy enough to survive the impact, irrespective of how hard the bat is. We are talking about something very close to the ideal elastic collision already.
    No, This is an opinion.

    There is a specification for how high the ball must bounce from 30 cm on to a steel plate. The steel plate is so stiff/hard it absorbs almost no energy so this effectively measures the coefficient of restitution of just the ball by itself. The COR of a TT ball on a steel plate is about 0.9.
    See the sports section.
    https://en.wikipedia.org/wiki/Coeffi...of_restitution

    Here are some facts.
    The COR bouncing off of wood will be much less.
    The COR of a ball hitting wood is about 0.5
    Even less if you add rubber.

    See page 7. I know the document is old and for the 38mm balls I think. I got it off the ITTF website years ago.
    I have posted this document many times but no one seems to understand it.
    https://deltamotion.com/peter/TableT...-%20Impact.pdf
    BTY do a search for Konrad Teifenbacher. To verify the source.

    BTW. this document was generate to dispel TT mysticism. See the second paragraph of section 1.
    Apparently Konrad Teifenbacher has had problems trying to explain what is really happening too.

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    #18
    Just a brief explanation to those who are not familiar with the frequency reading:

    Every object vibrates when subjected to an external excitation, a table tennis racket is no different. Like Zeio pointed out, this excitation produces several modes of vibration, each with its own deformed shape. In a TT blade the two modes that matter the most are the 1st (flexural mode – first pic) and the 6th (membrane mode – second pic).

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    The first mode (usually in the hundreds Hz) is directly related to the stiffness, and would provide much more information, but o measure it specialized equipment is required. The 6th mode is the central deflection, so it's also connected to the hardness of the blade. It is also related to the pitch we hear when we bounce a ball on the blade, so it is easy to measure. This can be done by using a spectrum analyzer app on your phone. But how does this relate to TT blades? Well, a stiffer material will vibrate at a higher frequency, and generally speaking, stiffness is related to speed. So, higher Hz -> More stiffness -> More speed. However, this is just a general assumption because many other variables play a part in the speed of a blade like hardness (of the whole composition, not just the top ply) and the nature of the wood itself. This method is merely a nice reference point when comparing blades with a similar structure, in those cases it's true that the blade with the higher frequency (stiffness) will be faster.

    I don't even like the word speed in this context, a TT blade is inanimate object and doesn't input energy on his own, it's just a rebound platform for the ball. The rebound it produces can be different depending on the impact speed and the composition of the blade itself. Some blades will produce a fast rebound on low impact shots, but lose power on high impact shots, and vice-versa. So, the "speed" of a blade would be more like a curve rather than a fixed number that most manufactures randomly put out.

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    #19
    Sometimes I wonder why I bother. Sometimes you guys make me want to scream something not nice.
    I have seen this frequency BS go on long enough. Frequency does have something to do with it but there is more.

    Quote Originally Posted by hipnotic
    Just a brief explanation to those who are not familiar with the frequency reading:
    The first mode (usually in the hundreds Hz) is directly related to the stiffness, and would provide much more information, but o measure it specialized equipment is required. The 6th mode is the central deflection, so it's also connected to the hardness of the blade. It is also related to the pitch we hear when we bounce a ball on the blade, so it is easy to measure. This can be done by using a spectrum analyzer app on your phone. But how does this relate to TT blades? Well, a stiffer material will vibrate at a higher frequency, and generally speaking, stiffness is related to speed. So, higher Hz -> More stiffness -> More speed. However, this is just a general assumption because many other variables play a part in the speed of a blade like hardness (of the whole composition, not just the top ply) and the nature of the wood itself. This method is merely a nice reference point when comparing blades with a similar structure, in those cases it's true that the blade with the higher frequency (stiffness) will be faster.
    Answer this. If the ball hits the paddle and vibrates as you say then that energy is still in the paddle and NOT BEING TRANSFERRED TO THE BALL.
    An audio spectrum analyzer is good for getting a general idea. A laser sensor would be better because then it is possible to see how each square cm of the blade is vibrating. It may be possible to get a small accelerometer to do the same thing. The energy can be computed at that point then all the energy calculations for every square cm of the paddle can be summed to get the energy the paddle has absorbed and NOT RETURNED TO THE BALL. Think about it. No one has and it has been a decade at least.
    Here is a quiz.
    If you had a laser measuring system that can measure at a specific point, then what information would you need to calculate the energy in the paddle at that point?

    Did you read the Tiefenbacher document? The COR for the TT ball bouncing off of steel and bouncing off of marble are much different yet they are both "stiff".

    I don't even like the word speed in this context,
    ???

    Some blades will produce a fast rebound on low impact shots, but lose power on high impact shots, and vice-versa.
    People generate power. The blade transfer energy to the ball but not all of it.
    Explain this. Lose power or lose energy? What is the vice-versa case. Lets see data. I want facts.

    So, the "speed" of a blade would be more like a curve rather than a fixed number that most manufactures randomly put out.
    A curve?

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  20. Der_Echte is offline
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    #20
    Has anyone noticed that at the time of my posting on this thread, that 14 of the last 15 threads that TTD Members have made posts have been on EQUIPMENT THREADS?

    Anyone see a small pattern with the tendencies and preferences of our TTD members?

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