OOAK Table Tennis Forum

A guy on another forum used a high speed camera to film a ball strike from a robot on a blade. He got about a 3mm deflection. That was without the blade being swung.

Ive owned a xiom v1 and found it stiff by my standards but ive spent a long time using and building very flexible blades. My blades deflect 3mm just throwing a ball at a fully rubbered bat. They bend a lot more than that during a counterloop, too much in fact. If youve seen high speed pictures of a tt ball being hit you'll know how much forces are involved. They dont compress like that easily.

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

I get "flex" and "hard vs. soft" blade feel mixed up a lot I must admit. But we all agree that some blades have less vibration and that the ball rebounds off some blades faster than others with identical rubber.

Thank you foam.

Note that the blade need not 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, to make a difference (because it will unload the rubber, understand?). That is, a flex of about .1mm is already enough to make a difference. I have ordinary blades here that flex more than that under light pressure.

> Of course a table tennis blade isn't near a tennis racket and the impact of the balls aren't comparable...

Yes, this is one of the key differences to remember when reading research papers on tennis. A TT ball is <3 grams with a ~200g racket not including the weight of the hand/arm. The momentum transfer equation is such that almost nothing happens to the racket side.


> A guy on another forum used a high speed camera to film a ball strike from a robot on a blade. He got about a 3mm deflection. That was without the blade being swung.

Link? I find this quite hard to believe from first principles. If the blade flexes 3mm, how much was the rubber deflecting given that it's much softer? Was it going through the wood?

In any case none of this matters. The weak link in the system past the rubber isn't the neck of the blade but the wrist. It's conceivable that the impulse of the impact changes the wrist angle ever so slightly, but the time it takes for a much larger mass to move a few mm is MUCH higher than the light ball on the rubber. By the time it's moved a fraction of a mm, the ball has already left the racket.

edit: more technically stated, recall the relative mass of ball vs racket and two most basic physics principles:

1. "equal and opposite force"
2. F = ma

The force on ball and bat system for the collision are equal. The m's are two orders of magnitude apart, which makes the accelerations same difference apart. This by definition means for every unit the ball is speeding up to launch off the racket, the racket is moving at only 1/100 of that. Or in other word, even if the racket was made of wet board its flex is irrelevant to the shot.

Had a chat with the guy that I bought the V1 off this evening and he said that with heavy rubbers on it - he likes Chinese rubbers - the V1 flexed but he did say that it was a bit hard on touch - probably due to the hard outer pile which is walnut. Other reviews describing the V1 one on the OOAK - describe the V1 as fairly stiff.

Compared with the older blades that I've owned like the Clipper CR non-WRB, Xiom Zetra Quad, Hayabusa ZXi and in particular a Donic Black Devil balsa I would have rated the V1 at a 6.0 on a scale of 1-10. Looking back at Xiom's description - sufficient deformation - sums it up if one is aggressive enough.

That said If your V1 had pips on one side I could see how it would seem stiff.

So would it be correct to say that the type / weight of rubbers on the blade can increase the flex in a blade ?
Does hardness / softness of the outer pile have any impact on the flex ?

I used the v1 with heavy rubber both sides and yes rubber weight makes a huge difference. When I was building flexy blades I found very hard woods were the best. Soft woods flex a lot but they absorb the energy too. To get that really pronounced kick in your hand you are best going thinner on the blade and using hard springy wood on the outer plys. I had one blade of 4.7mm thickness with walnut outers.not easy to get blades that thin to come out straight so commercial blades will never be that thin.

The most powerfuil usable thin blade I have at the moment has very hard outer plies, then ayous,then some exotic elastic core wood. It's -off. You can't feel it kick a lot because I had to use a soft wood for the handle due to weight.

I made a seven ply that I never got around to using because it is 100grams but only 5.5mm thick.. Its one I would call excessively flexible. Its made from all kinds of exotic woods with a walnut core.. I was starting to try archery woods to get massive kick but sometimes just getting way too much flex (and weight).

One good compromise was a walnut-ayous outer blade with some exotic elastic core who's name I also forget. This one gets a really big wobbly going just dropping a ball on it from like 20cm about it.

But also a very successful one was just koto-limba-ayous with a total thickness of 5.2mm with a 162?mm long head. That's a very good blade at 89 grams. Its very similar to the osp expert but a little bit sharper feeling.

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

I'd love to see that. Do you have a link? Bending any of my blades by 3mm (even the very thin Palio 08) would require more pressure on the tip than I'd be willing to exert. Which is a lot. I don't see how a ball strike from a robot would do it. Also, since the contact time would be very short, this means that the blade would be bending and rebounding 3mm in milliseconds - which would mean it's not just vibrating, but violently buzzing.

Incidentally, the phenomenon of pips deformation in the rubber can be seen in this video at the 3 minute mark:



Iskandar

I don't know if I can find the video but I'll have a look. You can do the experiment yourself by clamping a blade and putting a marker 3mm behind the top of the head then throw a ball at the bat. Some of my commercial blades leave a mark, meaning that they did bend 3mm. But 3mm is nothing at all for some custom made blades. That seven ply I mentioned above does 8mm with finger pressure easily.

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

Incidentally, I think if you wanted a genuinely flexible blade that would bend with (strong) finger pressure you could build one using this material:

http://www.aliexpress.com/item/Free-Shi ... 77806.html



Comes in many thicknesses - 1.5mm would perhaps be too thin, 2mm or 3mm would likely be about right. It's hard - rings like a bell when struck. Yeah, technically illegal. And the main reason I haven't tried it yet is that I'd need a water jet to cut it - that stuff would ruin a band saw blade in no time. I suspect G10, phenolic (paxolin) or even masonite might work.

Wonder what it'd play like. Probably not really usable, but it will truly be "flexy".

Iskandar

Thanks for starting this thread, as I have the same thought on my head!

Well, I had my own theory flexible bats. I had the idea that in phase 1 going back (flexing) blade stores energy, and in going forward (phase 2) it releases the energy, same as rubbers. You see it most easily with playing ox pimples or hardbat rubbers.

And same as with rubbers, you can use the flex either to accelerate the ball or to brake the ball depending when the ball leaves the bat. If ball leaves the bat in phase 1, the stored energy will be left in the blade.

Also the speed of the flex is crusial, if the flexing time is very fast, you need very short dwell to benefit from the flex. If the flex is very slow, then you could just lose power, because the blade is in the phase 1 when the ball leaves the bat. So the flexing process must be at the sweat spot time to be usefull.

We have some cheap and thin hardbat type of 1$ blades. They are actually crap. The blades are so rubbery flexy that they suck the life out of ball and it's hard just the get the ball over the net. I think it's because of the slow flex, it doesn't return the stored energy.

My Defplay flexes notisable amount when bent. I had used flex as an explanation to the different kind of behavior in ox pips plays. My observation has been, that Defplay gives more varied speed compared to stiffer FW+ in ox pushblocking and I blame the flex.

Anyway, it's interesting to hear from other theories.

The best vid I know of is this: https://www.youtube.com/watch?v=vP_hNJcGDmY

The ball is moving quite fast given this is shot at 1000fps (and also massively lit given the diminutive shutter speeds). The blade is a w6.

The key thing to note is that

1. the ball leaves the rubber within the space of <1 frame (<1ms), well before the blade moves. You can frame-by-frame using J/L keys in youtube.

2. the blade moves only because the clamp at the right isn't solid enough (just like your wrist in TT). There's zero flex in the face of the blade no matter the frame.

Also note again this is a 100% tangential hit, which is the best possible scenario for blade flex, quite different from a loop. If the blade is bending only a couple mm on a loop, through simple trig it would be bending maybe 10mm on a hit of same speed but different angle which I doubt any blade can survive.





Ball dwell on the racket is <1ms assuming a rigid blade (note the ball was on the racket for <1 frame in the video above). You can also calculate this from the standard acceleration equation assuming a given rubber deflection (~2mm) and incoming speed.

Accelerating something the mass of a racket+hand several mm in the millisec range of time requires a degree of force that would surely tear wood apart.


edit:

But to be fair let's work out that assumption where the racket flexes back with the ball, and do the math:

timing calc: http://www.calculatorsoup.com/calculato ... nt_v_t.php
power = m*v^2 / t

Racket: 200g, ball speed: 20m/s, "flex": 2mm -> 0.2ms
Power = .200*20^2 / 0.0002 = 400k

Let's also do so for a bullet fired out of a gun:

Bullet: 10g, speed 200m/s, barrel length: 100mm -> 1ms
Power = .10*200^2 / 0.001 = 400k

I really don't think any TT player hits the ball with the power of a gunshot, not even foam. The ball sure wouldn't fare well.

So does that feeling of flex come from what the blade is doing to the ball? Or does it even exist? I use a reasonably stiff blade (Butterfly Viscaria) and I never feel lik the blade is flexing.

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Butterfly Viscaria Black tag
2.2 mm Nexy Karis M on FH and BH

To provide some the context here, through the theory and empirical evidence I've known for a while much of what blade "flex" isn't (it's certainly not the blade flexing, esp. not the blade flexing back to "catapult" the ball which is physically impossible). But I could only guess as to what it is because I personally didn't feel anything resembling "flex" until a bit back when I started powerlooping*. This thread makes a case for where the feeling of flex likely comes from for powerloopers considering the body of evidence.

*To explain further, this is also a commonly misunderstood term considering the ubiquity of reviews which claim fairly fast blades to be a "powerlooper's dream". A powerlooper is probably better described as a fastlooper. foam's comment above on how someone with a fast swing and slow blade loops the ball above is poignant here (I was being bit facetious calling it a drive). Slow/"flexy" blades allow you to keep the racket face more open when swinging fast through the ball because they're so damn slow, which makes them much more tolerant to control imprecisions. They're by definition the powerlooper's dream since it "feels like you can't miss" in comparison to fast blades.

Why is this relevant? Getting the rubber to really contort and give off that movement which kind of feels like "flexing" is mostly a function of racket speed. You can usually only pull off the speed necessary when looping, aka powerlooping. It's MUCH easier to powerloop with the slow/flexy blade so it's also a much more accessible feeling since most club players lack the motorskill to do it with a composite or such; iow, slow blades can start to bottom out the rubber for them while hard blades can't. For further context, it's not common to power loop with any consistency and be <2k level for long which is why it's the first option for training juniors. Powerloopers who develop the timing do so with a fast blade tend to be significantly higher since you can kill against almost anything long if you're in position. (Most of the lower level blade reviewers are brushloop/countering rather than swinging fast through the ball).

The kick you feel is definitely the blade returning to it unflexed state. I don't feel like the kick accelerates the ball (much) what I think happens is that a flexible blade in its "loaded" flexed state is a faster blade than its unflexed state.

When using flexible blades it becomes very obvious its got a lot of different speeds depending on how you are hitting the ball. It makes sense to me that on a slow swing the ball loses a lot more energy on hitting the blade than it does when swinging fast and the blade is "pre bent and loaded" in that state the blade can't bend much more and most of its potential energy absorption is lost plus its become more springy. If that makes any sense, that's how it feels to me. I do feel like when a blade is pretty loaded you do get some acceleration on the ball, you can feel that when looping against a loop, you get a feeling of the ball digging in very deep and shooting out much later than it should have resulting in a missed return.

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

> what I think happens is that a flexible blade in its "loaded" flexed state is a faster blade than its unflexed state.
> when swinging fast and the blade is "pre bent and loaded" in that state the blade can't bend much more and most of its potential energy absorption is lost plus its become more springy.

The rebound of the blade face on a loop is almost entirely downward, so a bouncy/elastic blade like a composite is the last thing you want. In fact that's why those blades are so hard to loop with compared to slow ones: the slightest "overhit" in the direction of the blade face on a fast stroke will ruin the shot.

It's entirely the slowness of these so call "flexy" blades which makes them forgiving of slightly ragged fast strokes. The lack of springy is only reason you can open up that blade angle without too much precision, and why the inability to do so with a composite causes you to believe those blades can't spin the ball as much. On open face shot like blocks the slow speed is a problem, but on loop most of the force (and rebound) comes from the rubber so it's not as much of a liability. I also fastloop with a slow blade so I know this well when trying fast setups.

> If that makes any sense, that's how it feels to me.

Yes, it's how it might feel. Many folks (like Larry Hodges, lol) still feel the ball "dwells" on the blade when all physical evidence like the video above shows otherwise but hopefully we're better than that here. Given this is a physical effect, there's a right answer.