# Thread: Playability and shaft- and stringbed- stiffness?

1. Still need to know what string and tension they used in that experiment. Racket is steel or graphite? Feather bird?

Also what's ongebogen and gebogen steel?
I suppose bespanning means stringbed?

2. Do not think so.

We do not work with the tension that was used on the machine but with the stringbed stiffness after stringing and the stiffness of the shaft.
In other words the result of stringing that is felt by the player also.

It is actually the same as the stiffness of a springs which is also specified in kg/cm (lbs/cm, lbs/in)
If this value is 25 kg/cm it means that 25 kg is needed to deflect the stringbed 1 cm.

This is the value that is entered into the calculation.

The player does not feel the tension either, but players think in tension because there is no stiffness values.

With tennis stringers and players think in result, they ask for 34 kg/cm (=DT value).

The same counts for the shaft.

The player does not feel if the shaft is steel or graphite, he feels how stiff it is, and maybe that the graphite racquet vibrates less than the steel one.

This is the main objective of our project;
Find out the final specs that you like as a player and not an adjustment of a machine from a stringer.

3. ## reason for the project

Hi Visor,

Please have a look at this table.

It was the start and the reason for our badminton project.
It actually shows how unreliable “stringing on stiffness” , when it comes to the product that the player gets.

The table shows 5 racquets.
- All strung at the same tensions, by the same stringer with the same machine (a high quality one).
- The resulting SBS varies from 16 to 28 kg/cm.

The major reason for these differences is the difference in elongation characteristic of the strings.

When we would also compare different stringers with different machines the differences would be much bigger.

That is one reason for many players to go to a specific stringer, so that they know what they get.

As soon as they go to another stringer the result can be very different.

This problem does not occuur when the stringer can show that the sbs is the right one for the player.

4. ^

Strange how the 0.73mm Micro legend XL has a stiffer stringbed than the 0.66mm Yang Yang. Shouldn't it be much lesser?

Re SBS testing, have you considered trying to use stringbed frequency to compare and monitor the SBS factor? I use it to monitor my string tension (and also my stringer's string job ) and find that it's quite easy and accurate in keeping track of my preferred tension, even if I changed strings or stringer.

5. ## measuring systems to compare

Strange how the 0.73mm Micro legend XL has a stiffer stringbed than the 0.66mm Yang Yang. Shouldn't it be much lesser?
Apart from the elongation figures the final SBS also depends a lot on the “stretch speed” of the string. In a slow string there is a much friction between the filaments and it takes more time to develop all the elongation. So if the stringer strings fast and clamps before all the elongation is developed, the string looses a lot of tension because the string is till stretching.

That is why we say: A fast stringer is a soft stringer!

Re SBS testing, have you considered trying to use stringbed frequency to compare and monitor the SBS factor? I use it to monitor my string tension (and also my stringer's string job ) and

We have a trauma of the “frequency” principle, our Stringlab 1 works on that principle.
It is much less accurate en difficult to read the frequency, and the fact that you need the calculation from frequency to sbs (including a roote) makes it even more inaccurate).
It was a stupid decision to develop that because we already made a tester in 1989 based on the same principle as the Stringlab 2.

find that it's quite easy and accurate in keeping track of my preferred tension, even if I changed strings or stringer.
Of course it is much better to use any vibration test than nothing. The problem with the vibration test for badminton is that the shaft stiffness is much lower than the sbs.
So the shaft also vibrates.
Do you clamp your racquet down when you do the test?

The figures in the table were measured with this system.

6. Originally Posted by stringtechno
That is why we say: A fast stringer is a soft stringer!
Very very true.
And likewise, a slow stringer is a good stringer.

7. The stringbed frequency method I'm referring to is by using any app in Android or ios for smartphones like CarlTune or ClearTune that uses the mic to listen and measure the stringbed frequency when you strike or strum the strings.

There's also an app specifically calibrated for tennis rackets called RacqueTune, converting frequency Hz to stringbed stiffness in kg/cm. Too bad there's no adaptation for badminton rackets.

8. I know this app.
But the difficulty of this test for badminton is that the frame can vibrate more than the stringbed because it has a much lower stiffness.
So it is difficult to say what the measured frequency actually means for the stringbed.

9. I and a few of us on BC have used the stringbed frequency method to monitor tension for the past 2 yrs with great accuracy and repeatability. I can tell you that the frame doesn't matter as long as you're comparing an isometric racket to an isometric racket.

As long as it's a standard isometric shaped racket with the usual 22x22 or 21x22 stringing pattern, the frequency of the stringbed can be comparable to other brands or types of rackets, irregardless of frame cross section, type, material, or stiffness, ie independent of the frame.

From http://en.wikipedia.org/wiki/Vibrating_string , we can see that there are only 3 variables that affect stringbed frequency :

is the tension,
is the linear density (that is, the mass per unit length) ie. string thickness
is the length of the vibrating part of the string.

Therefore:

• the shorter the string, the higher the frequency
• the higher the tension, the higher the frequency
• the lighter (ie thinner) the string, the higher the frequency

There's also an interesting relationship between frequency and tension in that formula. If one is comparing the same string at two different tensions, then is constant and can also be considered constant (since the few cms in length difference at various tensions are negligible relative to the total length of string), then we can see that we can relate the two frequencies by

f1 / f2 = √(T1/T2)

or

f1 = f2 x √(T1/T2)

The two tensions are also then related by

T1 / T2 = (f1 / f2)²

or

T1 = T2 x (f1 / f2)²

So you see, we can use stringbed frequency to monitor and compare different tensions. Can.

10. This is interesting,

It is probably works with this app, because the mass of the string is the mass in the calculation.
And it does measure the frequency of the stringbed because much “over critical” compared to the vibration of the shaft. The shaft works as an "isolator" then.

This is certainly different compared to our test where we connect the tool with the string bed.

What do you get when you use the transformation to kg/cm when you use the Tennis formula, is the calculated DT value much too high?

It could be right when divide the Dt value by the roote of the ratio of the masses (of the tennis and badminton string in the racquet?? Or just the roote of the ratio in volume.

11. I do Have a question the following test are done on different rackets & different strings.

All the rackets are unique in the construction of frame & shaft (ie percentage of graphite used)

Hence some can resist & maintain more tension where as some racket heads get smaller when we string at certain tension.

Not all the rackets reduce in size of their head at same ratio which directly affects the stiffness of the strings.

Secondly All the strings are also different make & thickness which also contribute to the Stiffness.
For example Microlegend XL is .73mm thick where as BG-65 is .70mm thick which also contribute.

We need to isolate the problem here whether it is stringer or the set of racket & strings.

To check if the problem is with stringer you need to strings at least 2 or more NEW rackets of same model & same set of string on same machine at same tension & then check the stiffness.

If there is a difference in stiffness then there is fault of stringer.

I think it is very difficult to get the stiffness of two different rackets same, Unless you have some kind of formula for racket head flexibility & string thickness.

Originally Posted by stringtechno
Hi Visor,

Please have a look at this table.

It was the start and the reason for our badminton project.
It actually shows how unreliable “stringing on stiffness” , when it comes to the product that the player gets.

The table shows 5 racquets.
- All strung at the same tensions, by the same stringer with the same machine (a high quality one).
- The resulting SBS varies from 16 to 28 kg/cm.

The major reason for these differences is the difference in elongation characteristic of the strings.

When we would also compare different stringers with different machines the differences would be much bigger.

That is one reason for many players to go to a specific stringer, so that they know what they get.

As soon as they go to another stringer the result can be very different.

This problem does not occuur when the stringer can show that the sbs is the right one for the player.

12. All the rackets are unique in the construction of frame & shaft (ie percentage of graphite used)

Hence some can resist & maintain more tension where as some racket heads get smaller when we string at certain tension.
This is interesting to hear how much do they get smaller?
I think it is very difficult to get the stiffness of two different rackets same, Unless you have some kind of formula for racket head flexibility & string thickness.

It is not the thickness of a string that decides about the loss of tension but the elongation character. Therefore we do stringtest to measure those figures. If you look at the table below you can see that it is not so that the thinner strings are also the stiffer ones

This table shows the figures of the badminton strings that were used

http://www.racquetsportsindustry.com...nger_from.html
Concerning the relation between headsize, number of strings and stiffness we use our Tension Advisor for tennis, this is used since 1989.

It is the intention of the badminton project to obtain this relation for badminton also.

13. Originally Posted by visor
Still need to know what string and tension they used in that experiment. Racket is steel or graphite? Feather bird?

Also what's ongebogen and gebogen steel?
I suppose bespanning means stringbed?
"Gebogen steel" means bended shaft ("ongebogen" is not bended); and yes

14. I am really looking forward to the product you are developing.
I am also interested to help you collect more data or any kinda help (if you think I am up to it.)

15. I am also interested to help you collect more data or any kinda help (if you think I am up to it.)

If you are interested to join the project you can still use the special offer for the members of the badminton project team.
If you write me an email to Stringway.fred@gmail.com I can send you more information.

16. ## 2 different racquet mechanics

There are quite some badminton stringers already working with the Stringlab tester so we get some feedback from them also. We try to combine the information about the playability from players with the computer model that we are making.

It seems that there can be 2 different hits with very different influence from stringbed stiffness and shaft stiffness:

1. The “slow motion” back- or forehand from the back of the field that is intended to reach the end of the court on the other side.
In this case the shaft bends on impact of the shuttle and the flexibility (spring back effect) will generate shuttle- speed. More flexibility can result in more speed and less effort needed to reach the end of the other court.
The string bed is hardly deflected because the stiffness is much too high in relation to the stiffness of the shaft. It works like the 2 spring model, the most flexible spring deflects and does the work.

2. The “fast motion” hit like the smash generated with a lot of wrist action.
This hit works completely different. Pictures of smash-hits show that the stringbed deflects quite a lot.

We think that it works as follows:
The fast sweep from the wrist accelerates the racquet head. When the head hits the shuttle the shaft is of no importance anymore.

It is a collision between the racquet head at very high speed and the shuttle. Because the speed is so high the force of the impact is so high that the stringbed deflects.

This would mean:
- If a player wants speed in case 1 he needs a flexible shaft. The string bed only may have influence when the SBS is very low.
- If a player wants fast smashes he feels the “sprineffect” of the stringbed, lower SBS means faster smashes.

This picture shows the fast speed movement from the computer model. It shows that the stringbed is deflected and the shuttle has left stringbed while the shaft is still bend backwards.
So the bending energy of the shaft did not generate shuttle-speed.

We think that it would be nice when we can generate better advises for players with different preferences based on the models.

17. Originally Posted by stringtechno
- If a player wants fast smashes he feels the “sprineffect” of the stringbed, lower SBS means faster smashes.
Interesting post.

But shouldn't that be higher SBS means faster smashes?

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