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Testing the String-bed stiffness of badminton racquets.

Discussion in 'Badminton Stringing Techniques & Tools' started by stringtechno, Nov 4, 2013.

  1. stringtechno

    stringtechno Regular Member

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    For those who are interested hereby an update of our Badminton project.
    Because our Stringlab 2 is in production and because it can also test badminton string-beds, we started a “badminton project” together with a number badminton-specialized-stringers.

    The two badminton stringers work in the top of the Dutch badminton competition, and both guys are very interested in innovation in the badminton world.
    Except those guys our Japanese and US agent (who is Yonex agent) are involved.

    One of the major objectives of the project is to find a relation between stringing tension, the string and the end result of a stringjob, being the stringbed stiffness (SBS)


    The table below shows some test results that we already did.

    [​IMG]

    The upper part shows the SBS of a number of racquets which are all strung at the same tension, (8,6 kg for the mains and 9,6 for the crosses.
    The resulting SBS differs from 16 to 28 kg/cm.

    The lower part shows a number of racquets which were tested on the brainstorm day that we held;
    The stringbed of the 2 racquet at the top were unused and strung at the same tensions, the difference in tension is more than 10 %.
    All these racquets were strung by the same stringer on the same machine.


    People who want to read more about testing stringbeds of badminton racquets can also download this article.
    http://www.stringway-nl.com/pdf/Checking and tuning the stringbed.pdf

    Of course I would like to hear your contribution to this information.
     
  2. kennethfong

    kennethfong Regular Member

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    I quote the PDF file in your link:

    "On many electronic machines the tension
    drops too much before a repull and it
    overshoots the adjusted tension because the
    pulling speed is too high.
    Mechanical “constant pull” work more
    accurate than electronic cp."

    Seems to suggest that dropweight is much better than electronic... But for electronic you did not factor in the pre-stretch function?

    Do you have a list of brands of stringing machines that made up the statistics on the graph on electronic machines?
     
  3. stringtechno

    stringtechno Regular Member

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    The graph shows the tension of our own EM450. Because we were aware of the problem of electronic machines we built in a couple of tricks into this machine. The machine switches back to the lowest speed at 85 % of the adjusted tension and it has special “spring coupling” to make it possible to make small constant pull strokes.
    Despite these tricks the pulling character shows the “teeth” and it is much less accurate than the drop weight.
    The nice thing about a drop weight is that it is very easy to compensate tension with small pulls and it never overshoots the adjusted tension.
    The complexity of electronic machines can impossible beat the simplicity of the drop weight.
    Of course there is a difference between drop weights with a ratchet system and “automatic CP” machines.

    The prestretch function and the constant-pull-accuracy are separate items. It makes the string stiffer (pulls the remaining elongation out of the string) but does not make the machine more accurate.

    The string will certainly loose less tension when the prestretch function is used.
     
  4. visor

    visor Regular Member

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    Interesting...
     
  5. visor

    visor Regular Member

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    Re brainstorm session first 2 rackets :
    you should realize that when strung at same tension, the thinner string will have higher SBS than the thicker string. ;)
     
  6. stringtechno

    stringtechno Regular Member

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    This is often true, but it is our opinion that the SBS depends more on the elongation figures of the string.

    [​IMG]

    It is important that the stringer strings so slow that all the remaining elongation occurs during stringing. If he strings too fast the string will still stretch after clamping and will loose tension.

    The elastic elongation maintains the tension in the racquet, so more elastic elongation means a higher SBS.

    As you can see in the table, not all strings with the same diameter have the same elongation figures.
     
  7. visor

    visor Regular Member

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    ^ That is so true.

    My favourite stringer, when I asked him why his string jobs are so consistent and excellent tension retention, he said it's because he goes slow and lets the string sit at the pulled tension for 2 secs before clamping and proceeding to the next one.

    This is probably more important than prestretch.
     
  8. Maklike Tier

    Maklike Tier Regular Member

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    I don't understand what the point of this is. For any consistency, wouldn't you have to use all of those strings on the one racket? Wouldn't you also have to group each string by thickness?

    Issues would be further exacerbated by using different rackets, as every single racket would contribute to the stiffness of the stringbed through the design of the head, as well as a density of the stringing pattern.
     
  9. stringtechno

    stringtechno Regular Member

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    Stringing slow is much better than using prestretch. Also with prestretch it is important to wait until all the elongation has occured.
    Therefore it is better to use "fast strings" at high tensions. A fast string stretches quicker because there is less friction inside the string (or string material)

    Prestretch pulls the remaining elongation out of the string at a higher tension, so it changes the playability of the string. It will certainly result in less loss of tension during play.
     
  10. stringtechno

    stringtechno Regular Member

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    I agree on both and that is part of the project;

    With tennis we classify all strings that we test in 4 groups S1 to S4 based on the elongation figures.

    http://www.stringway-nl.com/nl/TAonline/REKTEST RESULTATEN 10-2011in klassen.pdf


    For Tennis we developed the Tension advisor, which calculates the desired SBS in stringing tension for mains and crosses. For badminton this is a little less important, because the difference in head size and number of strings is smaller.
    [​IMG]
     
  11. visor

    visor Regular Member

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    Looking at the string elongation chart, no wonder BG80 is so popular. It has the least total elongation and remaining elongation.
     
  12. mater

    mater Regular Member

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    Is the data showing that with slow stringing, stringers can skip on pre-stretching the strings? Or is pre-stretching still necessary, along with slow stringing?
     
  13. stringtechno

    stringtechno Regular Member

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    [TR]
    [TD]
    [/TD]
    [/TR]
    [TR]
    [TD]The importance of our project is to string so accurately that you can obtain the stringbed stiffness that you want. Stringing accurately actually means, losing as little tension as possible.

    Slow stringing and prestretching have completely different purpose:

    * The importance of stringing slow is that the string gets so much time that all the elongation at the normal stringing tension is developed.
    If you clamp before the string stretched completely it will still stretch after clamping and will lose tension.

    * When a string is prestretched the tension in the string is raised for a short time. This means that the remaining elongation at this higher tension is developed in the string.
    The result of this is that this remaining elongation will not occur during play and the string will lose less tension.

    In tennis I do not like to prestretch, because the string will be stiffer and will lose playability. I prefer to choose a stiffer string instead, for example a S4 instead of a S3.

    I do not know how much effect prestretching has on the playability of a badminton string bed.

    Is prestretch often used in badminton stringing?


    [/TD]
    [/TR]
    [/TABLE]
     
  14. wlotus

    wlotus Regular Member

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    Yes. I believe it's a common practice for many badminton stringers in this forum since it'll provide stiffer stringbed and less lose of tension.
     
  15. visor

    visor Regular Member

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    Prestretch is only used for certain strings that are known for major tension loss, eg. BG65, VS850.

    Strings like ZM62 and BG80 lose playability if prestretched.
     
  16. yan.v

    yan.v Regular Member

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    I've never heard of pre-stretch NOT being used from people that have it on their machine.

    Only exceptions seem to be for very high tensions where manual pre-stretch is used.
     
  17. stringtechno

    stringtechno Regular Member

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    This is interesting.
    Prestretching only makes sense with stretchy strings. Prestretching a stiff string with little remaining elongation (like the BG80) does not do much because there is little remaining elongation to remove.

    I assume prestretching is done to lose less tension?

    Are there any of you who compared playability of a certain string that was strung with and without prestretch?
     
  18. visor

    visor Regular Member

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    I don't know about your stringer but my two favourite stringers do not turn on prestretch function on the machine when stringing strings like ZM62 and BG80. Only when doing BG65 and VS850.
     
  19. stringtechno

    stringtechno Regular Member

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    The basis for our project is that we can measure both SBS and shaft-stiffness of the racquets.
    With the help of these tools we want to find out more about the combination of playability and accurate values.


    [​IMG]

    yux8.jpg

    Does any of you already use a stiffness tester for badminton?

    Does any of you already have ideas about the best combination of shaft-stiffness and SBS?

    The amazing thing with a badminton racquet is the huge difference between sbs and staftstiffness. The sbs goes up to 30 kg/cm while the shaft is less than 1 kg/cm.

    This means mechanically that a badminton player plays much more with the flexibility of the shaft with than with the deflection of the stringbed.

    So one of the questions is: how much sens does it make to string at these high values?

    My colleague is working on a computer model so that we can simulate the badminton stroke at different speeds and see what happens.
     
  20. stringtechno

    stringtechno Regular Member

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    It seems to me that the prestretch function is only felt by the player when the SBS or stringing tension is not too high.

    At what tension are your racquets strung?

    The higher the stiffness the smaller the deflection of the stringbed, and the smaller the difference that a player feels between prestretch and no prestretch.

    Our advise system advises a string in a certain class (S1 to S4) at a certain sbs.
    This means that stretchy strings (comfort string S1) are never advised for high tensions.

    In our opinion it is not a good idea to string a stretchy string at high tensions.

    We test badminton strings at regular bases so forum members like to know figures badminton strings you can let us know.
     

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