|
|
Blade Performance Vs Wood Type and Design |
Post Reply | Page <1234> |
Author | ||
Giangt
Super Member Joined: 03/30/2012 Location: Denmark Status: Offline Points: 433 |
Post Options
Thanks(0)
|
|
I did not mind reading all in this thread but who made all the engineering?
|
||
Sponsored Links | ||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
Sorry I got carried away there with reasoning over appeasing the right people. My bad.
For the most part TT companies do very little engineering, and we can now see why they don't need to given lack of intricate coupling between the nature of each component rubber/blade/ball. However there's significant social prestige in online TT circles built on the basis that the system needs to be finely tuned, with sway given to those who supposedly hold the keys to "understanding" the interplay. In reality things don't necessarily turn out well for the guy who points out the emperor has no cloths. Edited by AgentHEX - 12/23/2014 at 7:07pm |
||
JRSDallas
Silver Member Joined: 09/03/2005 Location: USA Status: Offline Points: 585 |
Post Options
Thanks(0)
|
|
Glant -
I did the engineering. It was a fun project for me in 2008 to see what I could understand about the issues by thinking it through. Spare time at home, learned CAD and then ANSYS to do FEA, built a test platform, captured sound data did the Fourier analysis on my PC. Fairly entertaining and I learned something real. I had the background that let me work this problem out myself. |
||
Galaxy T1 89 gm
FH: HRT Huaruite Wujilong 2 - Dragon 2 II, Max, Black Donic Acuda S2, Max, Red |
||
JRSDallas
Silver Member Joined: 09/03/2005 Location: USA Status: Offline Points: 585 |
Post Options
Thanks(0)
|
|
Wrap up: I invite and look forward to seeing any work from anyone on the topic of collision. As for myself, I’m going to move on now and spend more of my vacation time with my wife. Edited by JRSDallas - 12/24/2014 at 3:07am |
||
Galaxy T1 89 gm
FH: HRT Huaruite Wujilong 2 - Dragon 2 II, Max, Black Donic Acuda S2, Max, Red |
||
Giangt
Super Member Joined: 03/30/2012 Location: Denmark Status: Offline Points: 433 |
Post Options
Thanks(0)
|
|
|
||
Giangt
Super Member Joined: 03/30/2012 Location: Denmark Status: Offline Points: 433 |
Post Options
Thanks(0)
|
|
There will always be different types of people that will have an opinion of how a new product is released. Some people will eat all the marketing up to the last bit, some will be more sceptic about their statements etc. The former will of cause buy the new products. There is a saying in Denmark which sounds like: never go down on your equipment! The meaning of this quote is that you have to buy the best equipment to be like the best. Unfortunately if you lose a match you can only blame it on yourself and not the equipment ;) IMO it is constructive to discuss TT and hear other experiences from people. That is one of the reasons that forums like MYTT is existing, but unfortunately sometimes people have more in their mouths than their TT abilities. |
||
Giangt
Super Member Joined: 03/30/2012 Location: Denmark Status: Offline Points: 433 |
Post Options
Thanks(0)
|
|
First of all I want to thank you for all the effort you have put into this. Great job! I have the background as well, but have not taking the time to do any engineering on TT yet. Of cause the difficult part in your calculations would be to determine the right E-modulus of a laminate, but also to verify models by testing. |
||
pnachtwey
Platinum Member Joined: 03/09/2010 Location: Vancouver, WA Status: Offline Points: 2035 |
Post Options
Thanks(0)
|
|
A couple of points.
Through all this thread there has been talk of frequency but not amplitude. If one works through the math you will see the amplitudes are very small. Most likely too small for any contribution to the catapult effect. JRS Dallas also pointed out that the ball and blade restoring to the normal shape must be in phase or energy will be lost. I tried to use the analogy of a spring board diver on another forum but apparently no one dives. The same affect occurs when jumping on a trampoline. You must jump at just the right time. In TT the ball and blade properties are fixed so even if the vibration or flexing of the ball are significant enough the chance that it would do it in phase with the ball is small. Another issue is damping. A blade can vibrate at a frequency but what about the decay of the amplitude at that frequency. Blades with greater damping will also tend to be slower but for the most part the ball leave the paddle so quickly the damping probably doesn't affect the speed after impact much because the ball is gone. As far as the dwell time. We have been over this before on mecuur's very long thread. The dwell time is in the range that AgentHex says it is. Baal once did a "napkin" calculation and he came up with an answer closer to 1 millisecond than 3 or 4. In addition I have the high speed videos taken at 2000 FPS. If you remember my Toxic 5 hard bat vibrated or flexed a lot whereas my Firewall Plus didn't appear to flex or vibrate at all but obviously it vibrates because I can hear it. It is just that the amplitude is small. I think it is safe to say that in general blades that vibrate at a higher frequency are faster. I don't have any blades that violate that general rule. I think JRS Dallas did a good job of showing that the position of the ply of wood relative to the center makes a big difference. I just think JRS Dallas should have examined the impact of the ball and paddle a little more. I don't find the higher harmonics that useful. The primary mode of vibration and the frequency of the TT ball is think could be useful for further research because this gets back to the ball and blade restoring their shape in phase. I think it would be interesting to put an accelerometer on the back side of the paddle. When I find one that can handle 20gs and has bandwidth of 10Khz I will start to get interested. The accelerometer, CPU and battery can probably be put together so it weighs about the same amount as a sheet of rubber. |
||
pnachtwey
Platinum Member Joined: 03/09/2010 Location: Vancouver, WA Status: Offline Points: 2035 |
Post Options
Thanks(0)
|
|
Merry Christmas. It has been a long time. I still had private messages in my in box. They are obviously old now.
|
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
> Then why is there any further discussion?. Its useful. OK subject closed. Apparently not.
I mean what you said is clear and the meaning not in dispute, and it seems you understood what I meant, too; the combination of which is a christmas miracle compared to most of these discussions. For example no one is disputing that frequency is some indicator, only how good it is. This is not a trivial question given the nature of the problem as mentioned, and thus not conducive to easy answers. > However since our beam is a symmetric multi-layer stack of rectangles (of different material), and having correctly applied the Parallel Axis Theorem, the correct moment for each layer is as I previously presented....A page from Stokey Chapter 7 Vibration of Systems Having Distributed Mass and Elasticity shows that I have used the correct axis of rotation and have correctly calculated the moment for a cantilever. By extension, this means my equation is correct and that the effects I calculated based on layer placement are correct. Note that page doesn't contain your specific sub-equation for inertia of the sublayers. You know, the part that uses the PA theorem. I pointed out specifically why just that part is wrong, in very explicit detail. To be clear, I'm not contending the rest of it. You added that part, which is why I called it a corrective factor (to the original equation such as in the book), because it tries to "correct" the original inertia var. Again, the contention is that the bit you added is done incorrectly, specifically because you don't use the same axis of rotation with that PA theorem subequation. Again, it would really help if you just drew out where the axis around which the inertial is calculated for the original equation and your two PA axis's (you know, the ones mm's apart). I'd do it but this is one of those things which is more illustrative if you did yourself. > Of course it is agnostic, it solves for a symmetrically laminate beam. I can extend it but I don’t need to prove anything here. Let's go through the logical steps one by one: 1. Your claim is that frequency is a good indicator for speed ostensibly because it accounts for ply depth (and you certainly made sure of that in your equation modification). 2. However, it also gives the same answer for two sides of a blade with complete different material on each. A vibration frequency is inherent to the object and can't be "extended" away. 3. Clearly 1 and 2 cannot be simultaneously true. I've only pointed out a sim to speak of how a solid collision actually happens, and how it's nothing like how your frequency "extension" attempts to correct for it. Usually when two things are correlated in a relevant way in the natural world they work through similar mechanisms. That's for example one way we can tell piracy and global warming aren't. > So when I followed your link it did not lead to a plot, just an equation with no discussion of causal parameters. Just FYI, but Wolfram Alpha by default plots any sane equation as it d, which is why I used it for illustration. It's not meant to be causal, just a point that the right answer for speed vs anything is that general shape thus anything quite dissimilar is well off. The only reason why stiffness or freq even work at all is because COR for a TT blade is somewhere in the ~0.5 ballpark where all these indicators have slopes close enough to ~1 to not matter too much. The other related point that was probably missed is that if you simply transform whatever other "kind of correlated" indicator into that shape it'll give much better estimates. This can be done with any number of methods just as subbing x for y in a plot mirrors along the y=x axis. Edited by AgentHEX - 12/27/2014 at 6:49am |
||
jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
Post Options
Thanks(0)
|
|
Hmm AgentHEX seems to be making some points and JRSDallas has equations and graphs ..... will someone be explaining what's going on in plain English - so I can follow along?
Thanks
|
||
Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(1)
|
|
JRS modified a relatively straightforward book equation to correct for offset plies of a TT blade, and I believe the way the modification was done is wrong. It's done in a way which "makes sense", which I guess make it harder to figure out for the person it made sense for. In ELI5 terms, an object has greater rotational inertia when it's moved further away from the axis of rotation. In physics there's a certain way to calculate this for the distance between the axis of rotation and the center of gravity of the object. With a TT blade that rotational axis is nearer the end of the blade (where you presumably hold it) and the line to its center is along the length of the blade. But JRS is calculating that line from the center outward towards the face. From first principles when you move the object (plies in this case) in same direction as the one the object swings in, it doesn't really change inertia at all which so the correction was unnecessary. Those few mm are not very consequential in term of results since the correction is small anyway compared to the other blade dimensions (parameters used elsewhere), but the conceptual error is not the greatest. --- In his post above JRS just says the original book equation is right, which it probably is, but that's not what I'm talking about. Edited by AgentHEX - 12/27/2014 at 7:54am |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
There was also IMO an overemphasis on freq as the indicator of
merit, which is what likely caused mistake. IOW, there's an
overriding belief that freq explains everything, such as speed differences
between blade sizes. In that case different blade sizes don't differ
much in speed so freq predicting it does clearly doesn't explain it. In this case freq doesn't differ for outward displacement of plies, so it doesn't explain blades being bit faster with harder plies on the outside rather than inside either. The internal motivation to explain that phenomenon with frequency is what probably led to the modification.
|
||
Krantz
Super Member Joined: 05/14/2009 Location: Poland Status: Offline Points: 276 |
Post Options
Thanks(0)
|
|
Calculating the distance from the center towards the face is crucial for measuring the stiffness of the blade and I am surprised that you seem to ignore this fact - properties of such composite constructions are being deeply studied in modern technology and manufacturing in things like rocket fuel tanks, super-light sport yachts and even cars bodies. If you mean that these calculations are wrong then please say exactly where the mistake is, because so far you are only presenting puzzles to readers and giving some homework to OP and personally I wouldn't even expect to get a serious answer for such nonconstructive critique. |
||
pnachtwey
Platinum Member Joined: 03/09/2010 Location: Vancouver, WA Status: Offline Points: 2035 |
Post Options
Thanks(0)
|
|
Good one AgentHEX. I love it.
Obviously frequency isn't the only indicator. I have mentioned damping before but this topic always seems to be ignored. A few pages back you posted a series of wave equations but there was no damping term in those equations. If there were there would be a exp(-t/τ) where the tau in the denominator is the time constant of decay. Anything that vibrates has a damping factor or it would vibrate forever. In practical TT player terms, hands provide damping. A lose grip (more damping ) results in a slower return than a tight grip ( less damping). My Toxic 5 video shows the blade vibrating like crazy but it is in a vice. I doubt it would vibrate like that in my hand. Here is an example of what I am talking about http://ldf.mendelu.cz/und/sites/default/files/soubory_akustika/acoust_lect_damping.pdf There is more. Those that want to can find the rest of the document. Edited by pnachtwey - 12/27/2014 at 2:02pm |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
Someone asked for a simple summary to help grasp what's going on. Please at least try to understand the easy explanation before criticizing the original arguments. The basic physics of beams and inertia have nothing specific do with composite constructions and applies to any and all physical matter. |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
The long term effects of dampening (ie on vibrations) wouldn't affect the collision since the ball is well and off the blade as you're aware of. However the immediate dampening/inelastic effect of material, mostly the rubber and wood, would effect the energy lost during collision. That's why I mentioned thinking of this like a simulation rather than modeled equations, mostly to consider the details of what's actually going on during the relevant timeframe. In this case what's going on is the ball is largely the object doing the bouncing (deforming and rebounding with its own dampening), and everything else is better framed as a modifier to this behavior (in this case the dampening providing some "cushioning"). That's actually part of why these loosely affiliated indicators sort of work out: incidentally because nobody thought to change the main body of relevant factors. That and they're being used in the "slopey" part of COR, where any positive slope we're comparing against close enough to 1 has the appearance of sane results. ----- It's also worth stepping back and considering why these indicator happen to work. For frequency it appear for an object of given size, higher vibrational freq are correlated with lower energy loss. Something like elastic stiffness is similarly correlated with kinetic energy loss (of the ball here) in inelastic collisions. Note both of these are inverse correlations with the ball's collision COR. For visual thinkers, their inverse correlate to the loss, in a COR plot the space between that wolfram function and y=1. Edited by AgentHEX - 12/27/2014 at 5:58pm |
||
jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
Post Options
Thanks(0)
|
|
This is quite interesting, so from a blade design point of view: what are the most important things a designer should focus on when building the ideal wood blade.
Also thought a short film interlude might help everyone to relax a bit: enjoy voilin wood resonance. ... Edited by jrscatman - 12/27/2014 at 6:26pm |
||
Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
I think it's easier to learn a slower setup since it provides a larger range of physical motion to work with. A racket that doesn't allow the user to manipulate the ball as much least they miss tends to nudge players down a more tactical path. But this is still a sport where physical motion is more foundational given that better players can easily beat lesser ones with simply better shots, whereas the same can't be said for strategy as anyone who's ever been beaten by a kid with a proper loopdrive can attest to. That's why effective development programs mostly focus on getting the quality shots down first, and it's just easier for the less than athletically gifted (perfect timing, perfect swing control, etc) to do so with slow control equipment. |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
The thing is it's pretty easy to make a TT blade because the ball doesn't stick around for the vibration/resonance or other wood properties. It does change how you feel/perceive the equipment, but not so much the shot. It's understandable that's not what anyone least a community heavily invested in equipment wants to hear. But to be fair, I also have a rather large bag of TT blades and rubber (really they wouldn't all fit in any bag). |
||
jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
Post Options
Thanks(0)
|
|
But you must agree, each blade plays differently, how would you account for the difference? JRSDallas suggested frequency, is there some other property or properties we can use to measure blade performance?
|
||
Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
It's worth taking another step back for a meta-discussion of this topic. The holy grail we're after is the ratio of the ball's speed coming off the blade divided by its speed going in for all such speeds. This can be done by a machine which controls for and measures ball speed, or equivalently by drop the ball from ever greater heights.
Since such a contraption is a pain to build, and meticulously dropping and measuring heights is also bit annoying (the ITTF does this for one height on the sanctioned balls against a hard platform, effectively placing a ceiling of ~.85 on the ratio above). Thus all these other numbers advanced are just somewhat more amenable proxies for this value. They're useful enough to indicate this blade is likely faster than that blade, but even in a more limited capacity they each have advantages and drawback. Personally I just look at the thickness with some adjustment for harder or softer plies (esp composite ones), and it's ~80% effective for <<20% of the work. As to playing differently, other than this speed metric it's just a subjective feel of what happens after the ball's left the blade. Some people for whatever reason don't like certain sounds or vibrations; for example I've been told ~ALL wood blades feel hollow, and a hard sponged Yinhe Moon I just tried on a Sweden Classic sounded broken/cracked etc. This has a significant internalized effect on confidence to swing for shots, etc; and because of that discomfort we're not likely to put in time to get used to a setup (compare this to folks expending considerable effort adjusting to pro setups obviously too fast for them, for similar psychological causes). Of course there's no social currency in presenting this as a largely subjective evaluation, so there's a tendency to attach "reasons" via peudo-technical terminology to support a personal bias. Blade X is good because of this and that nebulous aspect. As mentioned manufacturers are more than happy to play this game of attributing near-magical properties to a very easy to make piece of wood/fiber. |
||
JacekGM
Platinum Member Joined: 02/17/2013 Location: USA Status: Offline Points: 2356 |
Post Options
Thanks(0)
|
|
This is a fantastic thread. Some people well familiar with Newtonian physics take on the aspect of how blade design will affect it's performance. Great, and thank you, and please continue...
However, the problem I have here is that the OP title is - to me - actually misleading. For I do not care that much about blade performance (does anyone?) Rather, I care about racket performance. Although the influence of the rubber sheet(s) has been, shyly, mentioned here and there above, there is this formidable component conveniently dropped from this discussion altogether: the quality and quantity of the glue layer(s). Oh, and the various types of handles, too, and also how the type of rubber on the other side affects the performance of a given racket side... Oh, boy... I do have a problem, I guess because I play with a racket and not with a blade... |
||
(1) Juic SBA (Fl, 85 g) with Bluefire JP3 (red max) on FH and 0.6 mm DR N Desperado on BH; (2) Yinhe T7 (Fl, 87 g) with Bluefire M3 (red 2.0) on FH and 0.6 mm 755 on BH.
|
||
pnachtwey
Platinum Member Joined: 03/09/2010 Location: Vancouver, WA Status: Offline Points: 2035 |
Post Options
Thanks(0)
|
|
This thread is interesting if you are going to make your own blades. Other than that most people will find a blade that feels good and play with it. If one puts identical rubbers on two similar blades they won't play that differently and there is no impulse ( trajectory ) that one paddle can generate than another can't. I don't feel there is much difference between my Samsonov Alpha with H3 Neo than my TBS with S2 on it. Yes they feel different but I can play the same way with both. People are very adaptable. I find the blade makes more of a difference when playing hard bat or with long pips 0X than with inverted because there is no sponge to mask the performance of the blade. |
||
jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
Post Options
Thanks(0)
|
|
I am also very interested in the feel of the blade, but don't know how to measure it or describe it. I have been watching lot videos about luthiers on youtube. They say every instrument they make is unique. A lot of what they do is by feel. One mentioned, he doesn't measure the thickness of the wood - he just feels for the correct stiffness - when gets there he stops.
|
||
Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
||
AgentHEX
Gold Member Joined: 12/14/2004 Location: Yo Mama Status: Offline Points: 1641 |
Post Options
Thanks(0)
|
|
> However, the problem I have here is that the OP title is - to me -
actually misleading. For I do not care that much about blade performance
(does anyone?) Rather, I care about racket performance.
The same aforementioned restitution ratio exists for rubber, except since the ball grips the surface the input parameters of spin and angle need to be characterized in addition to speed alone. > I have been watching lot videos about luthiers on youtube. They say every instrument they make is unique. A lot of what they do is by feel. With a musical instrument the notes required are standardized frequencies which human hearing can be well attuned to. |
||
Baal
Forum Moderator Joined: 01/21/2010 Location: unknown Status: Offline Points: 14335 |
Post Options
Thanks(0)
|
|
This is surprisingly true for blades too considering they are fairly mass produced. I have a bunch of Viscarias and two feel much h better than the others. Its not just weight. I guess that is what happens when you make things out of wood. |
||
jrscatman
Premier Member Joined: 10/19/2008 Status: Offline Points: 4585 |
Post Options
Thanks(0)
|
|
It's very much an art rather than science.
|
||
Butterfly MPS
FH: Donic Acuda S1 BH: Palio CK531A OX |
||
JRSDallas
Silver Member Joined: 09/03/2005 Location: USA Status: Offline Points: 585 |
Post Options
Thanks(0)
|
|
Edited by JRSDallas - 01/01/2015 at 8:22pm |
||
Galaxy T1 89 gm
FH: HRT Huaruite Wujilong 2 - Dragon 2 II, Max, Black Donic Acuda S2, Max, Red |
||
Baal
Forum Moderator Joined: 01/21/2010 Location: unknown Status: Offline Points: 14335 |
Post Options
Thanks(0)
|
|
I can't figure out what point this comment was supposed to be making since some stringed instruments are clearly better than others and there is a lot of variability (especially when, as with table tennis blades, they are mostly made of wood). And of course, musical instruments don't produce pure sine waves, which is why a lute and a violin sound different even when they play the same note. |
||
Post Reply | Page <1234> |
Tweet
|
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |
Forum Home | Go to the Forums | Forum Help | Disclaimer
MyTableTennis.NET is the trading name of Alex Table Tennis Ltd. |