# Proposal: experiment with string tension loss

Discussion in 'Badminton String' started by SWC_Ant, Mar 31, 2005.

1. ### SWC_Ant Regular Member

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Hi all!

i have a proposal for an experiment that some of the BF'ers can conduct regarding different strings and tension loss over time, say 1 month.
what we can do is measure out a preset amount of string of each string type, and then put a weight on it. (im not sure how this works, but i'm sure Neil Nicholls knows, because he has done something like this before) then, measure the stretched length. then we can calculate how many mm each pound would stretch the string by initially. we must leave the string at this length, so even if it loses tension, it wont get stretched even longer by 25lb (because when we put our string on the racket, the total length of the string doesn't change, only the tension does). every 24 hours we let the string loose again (so it will return to original length) and measure, the number should increase by a bit because the string is losing elasticy. stretch the string back to the stretched length, and measure the unstretched length again in 24 hours. since the stretched length isn't changing, we can calculate the amount of tension left in the string. over a 30 day period, we can find out how many pounds of tension the string loses.

for example, if our set string length was 1000mm and the original weight was 25lb, then we cut 1000mm of each type of string in our experiment, and put 25lb of weight on it. say that string A gets stretched to 1200mm. then we know that each pound of tension will strech string A by 8mm. then we strech the string to 1200mm again (perferably tied, and not weighed down), and wait 24 hours. by this time the string may have loosened, but the stretched weight isn't going to change, because we aren't leaving 25lb on it.
then, we measure the unstretched length, (for our example we'll say it becomes 1010mm), so that means our tension has become (1200-1010)/8 = 23.75lb. stretch the string back to 1200mm and wait another 24 hours, rinse, repeat

hopefully at the end of 30 days we will be able to draw graphs on tension loss by different strings, and get an idea of which string(s) lose tension the fastest or slowest.

hope this makes sense, and correct me if parts of this may not work.. i dont have any of the required equipment to conduct such an experiment, but im sure there are a lot of BF'ers with access to these things

thanks in advance for any help with this experiment!

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Last edited: Mar 31, 2005
2. ### kwun Administrator

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i like the idea of the experiment. the goal is sound but i think some details needs to be ironed out. you said:

this does not make sense to me. if the string was 1000mm, stretched and then later on it lengthened to 1200mm. then the tension on the stretched string when it is at 1200mm will be 0 lbs.

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3. ### SWC_Ant Regular Member

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i meant, the string would be stretched to 1200mm for 24 hours (which will start off at 25lb, then slowly decrease in tension), then untension it so it would return to normal length, (ie. 1010mm). then you can measure.

thanks for the reply

edit

the original strech would be with a weight (25lb) to see how long the string should become. then the string could be secured at the 1200mm length somehow, because if we leave the 25lb weight on the string it will become more than 1200mm over time, but that doesn't happen in a normal racket

hope this helps

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4. ### Neosakai Regular Member

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Sounds like a cool idea, but you got any pictures of it? Because i'm kinda confused on how it works

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5. ### SWC_Ant Regular Member

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i can't put any pictures up, because i can't conduct the experiment myself but im giving this idea to others so maybe some people can try it and report on the results. Neil Nicholls might know about some parts of it though.. because he did something similar before.. hope he sees this post soon

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6. ### Neil Nicholls Regular Member

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to mimic what happens in a racquet, you would want to stretch it to whatever length the weight stretches it, and then clamp it at the new length.

Part (maybe most) of the tension loss you get in a racquet, though, is from using it. The repeated stretching and contracting breaks up the string at the molecular level.

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7. ### SWC_Ant Regular Member

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yea thats what i meant except i didn't word it that well

i agree part of the tension loss is from using the racket, but if you were to leave the strung racket sitting there for a while there will be tension loss too, and this experiment is trying to measure that. i do believe that tension loss of strings (without hitting birdie constantly) can be compared with each other, and the comparitive results will be good enough (ie. string A loses tension faster than string B), just that the tension may not drop as drastically as normal string that are constantly subject to striking birdies

btw thanks for replying!

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8. ### cooler Regular Member

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not to be sounding rude but this test would be too basic to be useful in understanding tension loss in a real racket. The only knowledge gain here is knowing which string is more stretchy relative to other strings, within an operative range that isn't common in real situation. Variables not considered in your experiment but important are:

2. type of loading? one fix load dont represent real situtation

for a string that measure less than 1mm, measuring length of elongation in mm is quite crude.

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9. ### SWC_Ant Regular Member

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if you want to know how stretchy strings are relative to each other, here's a post that answers that question http://www.badmintoncentral.com/forums/showpost.php?p=229044&postcount=31

what we're trying to find here is tension loss of strings over time

the string may measure less than 1mm in diameter, but the length can be changed a lot when there is tension on the string, as Neil found out earlier here http://www.badmintoncentral.com/forums/showpost.php?p=229005&postcount=29 ... at 24lb, 240mm of BG66 string stretches to 261mm, a 9% increase

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10. ### kwun Administrator

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interesting point. but let's start from the simpliest case. that is, a continuous constant load with tension similar to a normal stringing tension. this somewhat emulate the string strung on a racket without being hit. ie. string it and let it sit for a few days. in a racket situation, the load actually descreases over time, but we gotta start simple...

and i think that's where SWC_Ant is close.

with continuous a load of 25lbs, which is within the bound of the tension that people uses.

and yes. if we use a long enough string, i don't see a problem with precision. i typically see a stretch of around 5mm everytime i tighten a segment of string on the stringing machine, a stretch of string 1-2meter will give approx 3cm of stretch when going from 0->25lbs tension. not a lot, but probably adequate.

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11. ### SWC_Ant Regular Member

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kwun:
what we meant was measure how long the string will become with 25lb tension, and then take the string off and clamp it separately, at the measured length, so that throughout the experiment, the clamped length will remain the same (just like the strings on the racket will always be stretched to that length), but the tension will decrease
however, this way, the load will not be 25lb all the way, because the load is lowering as tension drops

again, thanks to all who have replied as soon as we get everything set.. we'll need someone to do the experiment

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12. ### Neil Nicholls Regular Member

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I'm not sure you can deduce the tension loss from the change in unstretched length.
I think you need a method of measuring the tension while it is still stretched. Something like a Stringmeter which is used for tennis.

Maybe leave some string tensioned on a drop-weight machine.
As the string loses it's ability to hold tension, the weight will drop. As the weight drops, it pulls less tension.
The downside to this is that the weight will continue to lengthen the string.

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13. ### SWC_Ant Regular Member

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if we had extremely accurate weights/tensions, when we're measuring the tension loss we can put on weights until the string gets back to the stretched length.. i dont know if that will work better

its best if we dont let weight continue to lengthen the string, because on a normal badminton racket that doesn't happen

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14. ### Neil Nicholls Regular Member

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but on a normal badminton racket you don't take the tension off and let the string contract to it's original length and then re-stretch it either.

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15. ### SWC_Ant Regular Member

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you're right, that doesn't happen either.. but its the best way to measure... i think.. unless someone comes up with a better idea

btw how does a drop weight stringing machine help with this experiment? i dont quite understand because i have absolutely NO idea how stringing machines work :crying: ...

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16. ### cooler Regular Member

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furthermore, baddy strings are elastic. If tension is below yield stress point, the string will retract a bit when load is removed. At what instant would u take the length measurement? Will you able to measure each string length with the exact relaxation period because each string type will have different retraction rate. Because a relaxed string has slack, u have to give it some tenison to straighten it out for reasonable length measurement. If u put a slight tension to straighten out the string for measurement, technically, one is deforming/stretching the string during measurement. This add inconsistency into the experiment.

Each time u remove load and reclamp, u also introduce errors.

I dont see the benefit of doing this type of experiment because i dont get any useful data out of it. Sorry being so critical.

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17. ### Neil Nicholls Regular Member

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I'm half with you.
Are you interested in tension loss between getting your racquet strung and playing with it. What if that gap is 2 weeks, or 1 month?

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18. ### Neil Nicholls Regular Member

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ah,
how about you attach some scales to one end of the string, tension it, and then clamp everything off. So you go: fixed point, scales, string, fixed point.
Then you just have to record the reading on the scales at whatever time intervals you like.

You're stuck without your scales for that time though.

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19. ### kwun Administrator

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you are assuming the "hook" of the scale doesnt move...

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20. ### SWC_Ant Regular Member

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you mean something like this? (excuse the bad drawing im sorta busy and rushing through things )

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