Making a dropweight almost "automatic"

Discussion in 'Stringing Techniques / Stringing Machines' started by enderx1x, Jun 19, 2012.

  1. enderx1x

    enderx1x New User

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    I've read the thread "The physics of a dropweight tensioner" (good description there) and am also aware that stringway manufactures a automatic dropweight. I am not sure how the stringway machines work, but reading the above thread got me thinking about a way to make the bar horizontal after his has dropped.

    The "The physics of a dropweight tensioner" makes it clear that as long as the dropweight is parallel to the ground (or close to it) the tension will be exact (or very close). Then I started thinking, what if i put my klippermate (or any other dropweight) on top of a plane that could be rotated forward and back. If the bar doesn't drop far enough, simply tilt the plane so the side with the bar is down (machine is secured to plane) until the bar is parallel. The same could be done in reverse and the plane could be made to rotate, say 45 degrees in each direction. With 45 degrees as a room for error the bar shouldn't ever have to be dropped twice. It may be a bit of a hassle to put in the clamps with the machine at a angle, but it shouldn't be do bad.

    Thoughts?
     
    #1
  2. jgrushing

    jgrushing Rookie

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    Sounds like a lot of work to fix a problem that really isn't a problem. Getting the bar to, or close to, horizontal is not a problem.
     
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  3. enderx1x

    enderx1x New User

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    Well, if getting the bar close to horizontal is almost always completed on the first try, I don't see much advantage of getting a crank or electric. On synthetics and multis I can see that with experience it will be easy, but stringing poly took me much longer.
     
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  4. Chotobaka

    Chotobaka Hall of Fame

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    Want to make a drop weight "automatic"? Buy a Stringway.
     
    #4
  5. enderx1x

    enderx1x New User

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    Stringway is $900 (with fixed clamps) and I wouldn't want to spend $750 on a floating clamp machine. At that price I could get a 6 point, fixed clamp drop weight and add a wise (+ maybe $100). Now I have never seen a Stringway and have seen that many people on these forums love them which probably means they are good. But, $900 seems to expensive for any kind of dropweight.

    On a different note, does anyone know how the automatic dropweight of Stringway works?
     
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  6. Irvin

    Irvin G.O.A.T.

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    The drop weight is like a lever and if the distance from the pivot to the weight is 10x the radius of the gripper, and if the weight is 6 pounds then the tension applied to the string is 10x6 or 60 pounds. By changing the distance of the weight you get a different tension.

    Most drop weight have a fixed radius from the string gripper to the pivot. I don't know but the one way of making a making a drop weight automatic is to allow the radius to change as the distance to to weight changes. That is what I think Stringway does. Another way is to keep the distance to the weight the same as the bar drops or rises. You could do this by hanging the weight from a cable connected to some type of wheel so the distance with the weight is applied is constant.

    EDIT: Making an automatic drop weight should be simple but no as simple as the ones they have now. If the angle of the bar is less than 5 degrees the distance (on the horizontal) from the pivot changes very little so the tension applied changes very little. But the farther off level the more drastic your tension applied changes.
    One big disadvantage of a drop weight is overshoot. Momentum of the drop weight is stopped by the string and that weight being connected to a lever is being magnified by the lever action and the speed of the fall.
     
    Last edited: Jun 20, 2012
    #6
  7. Radicalized

    Radicalized Semi-Pro

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    There is a small diagram online showing how the Stringway adjusts for string stretch by adjusting another variable to always keep the weight the same distance from the tensioning unit regardless of the angle. Of course, with a standard dropweight, anything above or below causes the weight to be closer, thus changing the torque.

    Also, it may help speed things up. It's all personal what you'll put up with and what you'll pay. And I always call it a "let the bar down slowly weight," not a dropweight.

    With the right amount of time, since Stringway is from the Netherlands, and I don't know a patent number, you might be able to search the Netherlands, Euro, or international patent office websites for information.
     
    #7
  8. enderx1x

    enderx1x New User

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    It does seem that is what Stringway is doing:
    http://www.google.com/imgres?hl=en&sa=X&biw=1400&bih=931&tbm=isch&tbnid=C4EjHW4ifgI5vM:&imgrefurl=http://www.stringway-shop.eu/epages/262587.sf/en_GB/%3FObjectPath%3D/Shops/262587/Products/%2522ML.100%2520ORIGINAL%2522&docid=Tnr2yR1I9vpSAM&imgurl=http://www.stringway-shop.eu/WebRoot/ce_fr/Shops/262587/49AD/01BE/2015/BC45/CDD4/C0A8/8008/C53E/ML_002E_100_0020_Tensioneur_0020_485x600.JPG&w=485&h=600&ei=RPbhT-X5JI6y8ATJo8yHCA&zoom=1&iact=rc&dur=374&sig=111467462006884208690&page=1&tbnh=142&tbnw=115&start=0&ndsp=35&ved=1t:429,r:9,s:0,i:101&tx=64&ty=90


    I'm aware that in a normal drop weight you just have to be close, and the tension will also be very close. I'm not sure what you are trying to say here though about an automatic drop weight.

    This seems a minor problem to me. Just lower the bar at a medium speed instead of dropping it should counter this.
     
    #8
  9. jim e

    jim e Hall of Fame

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    I guess that automatic drop weight machines are nothing new. My old Serrano machine that I used in the 60's till early 70's was an automatic drop weight, as all you needed to do was step on the peddle which raised weight, and also moved tension clamp bar towards the racquet, then release peddle and weight dropped and tension was pulled to set amount on weight bar, no horizontal was needed as it pulls just to set amount at constant pull, as long as the weight bar did not go all the way down to bottom out.

    Below is a picture of that old beast. My Pro Master machine makes this thing seem like an old relic, although I will string a wooden racquet on it when I get them to bring back memories of the past, as it still works after all these years. I bet it was made in the 40's or earlier.

    [​IMG]
     
    Last edited: Jun 20, 2012
    #9
  10. KerryR

    KerryR Rookie

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    Luckily, most of the time,it's very easy to get the bar within +-1" of level, and closer with some minor practice. Luckily, it's not that critical anyway.
     
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  11. enderx1x

    enderx1x New User

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    Radicalized: I searched a found the diagram: http://www.tt-stringer.com/pages.php?page=stringway-technology (scroll down a bit and on the right)

    jim e: I'm wonder if there are any automatic drop weights on the market today that are cheaper than stringways.

    KerryR: With time I can see myself getting close on my fist try, but if that's the case I still don't see much benefit on upgrading.
     
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  12. Irvin

    Irvin G.O.A.T.

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    That was my guess the distances from pivot and weight and pivot to string gripper had to change at the same rate to keep the ratio the same. The problem is I don't think they do but it is not worth arguing about.

    EDIT: And I am not saying they don't.

    EDIT: Also you will see on that same page a little lower down the overshoot produce by drop weights is much more than electronic.
     
    Last edited: Jun 20, 2012
    #12
  13. enderx1x

    enderx1x New User

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    comments in red


    Also, as my original question; would rotating the whole machine to make the bar horizontal give accurate tension?
     
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  14. Irvin

    Irvin G.O.A.T.

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    Absolutely it would.
     
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  15. Irvin

    Irvin G.O.A.T.

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    I believe you are right. But the drop weight will have overshoot where the lockout and (some) electronic machine do not. If you pull more than one with the lockout you can duplicate the electronic.

    EDIT: Overshoot stretches the string more and you will end up with a tighter stringbed.
     
    #15
  16. enderx1x

    enderx1x New User

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    By overshoot, are you talking about having the drop weight go past the point it should normally go, usually because it has force as it falls. If this is the case, lowering the weight slowly would solve this. if not what is overshoot?
     
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  17. KerryR

    KerryR Rookie

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    Yeah. That's pretty much the case. I can string a little faster on my lockout (Ektleon H) than I can on my K-mate, but only enough to matter if I'm doing several back-to-back paid string jobs. I also find the stability and height of my lockout more comfy and convenient, and I also slightly prefer the fixed clamps of the lockout. But, I prefer the consistency of the pull with the dropweight...
     
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  18. Irvin

    Irvin G.O.A.T.

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    No by overshoot I am talking about the tension pulled on the string. It takes some force to stop the weight from falling. A moving weight will apply more force than a stationary force. Force = Mass x Acceleration.

    EDIT: Here is what I am talking about:
    The faster you string on a drop weight the more overshoot you have. For the lockout to be as accurate as an electronic it will take any pull and your stringing speed would be slower.
     
    Last edited: Jun 20, 2012
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  19. enderx1x

    enderx1x New User

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    I find that I can usually "feel" how much further the drop weight has to go and can stop it without putting much if any overshoot. This takes maybe a few seconds more and I have only strung a couple of frames.
     
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  20. KerryR

    KerryR Rookie

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    It'd be interesting to quantify 'average' overshoot with a drop-weight. I wonder if most players would actually be able to feel the difference in the finished product? I'm thinking not.
     
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  21. Ramon

    Ramon Hall of Fame

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    It might be more of a difference than you think. I have a calibrated drop weight machine, but when I use soft strings I suspect it's overshooting by at least 7 pounds.
     
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  22. enderx1x

    enderx1x New User

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    Is this when you just drop the weight, or are you carefully lowering it?

    Also, while this extra "prestretch" may make a difference, the final tension is the same with any constant pull machine.
     
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  23. Ray_cn

    Ray_cn New User

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    Don't only adjust the angle between the lever and the gripper too bigger. Release the string and repull is better.
    And for dp, one string per time is better. especialy for soft string.

    DP's princple is much like a hand crane that could elevate a car.

     
    #23
  24. enderx1x

    enderx1x New User

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    I'm not sure if I understand your post correctly, but yes for a normal drop weight if the angle isn't correct I pull again. What I was talking about is tilting the whole machine until the drop weight is horizontal.

    For any machine tensioning one string per time is better, and I have not ever heard of it being done any other way, if that's what you are asking?
     
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  25. Ramon

    Ramon Hall of Fame

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    I lower it carefully, or at least I think I do. I'm definitely not letting it freefall from the top. I use my hand to slow the fall and let go when it's almost at tension. After it reaches tension, I let mains stabilize for at least 5 seconds and crosses for at least 20 seconds. I'm not saying that I can't go slower. That's a possibility, but it's not like I'm rushing through it and dropping it.
     
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  26. enderx1x

    enderx1x New User

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    Wow, and it still overshoots by 7 pounds. Have you measured that it was 7 pounds, because while I don't doubt you this is much more than I expected?
     
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  27. Ramon

    Ramon Hall of Fame

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    Here's my evidence. Keep in mind my drop weight is calibrated using the Alpha calibration device.

    1) I measured string factors on RacquetTune for at least 5 different strings. The soft ones (multi, gut) consistently read about 7 pounds high on fresh string jobs. Poly hybrids are much closer (about 2-4 pounds).

    2) I originally ordered my racquets from TW and TE, one with NXT the other with Premier LT both at 58 pounds. The NXT from TW came in shipped at 50.9 and the Premier LT from TE came in at 54.7. So neither one seems to be exceptionally high. When I string my racquets with similar multis, I have to string them at 50 lbs, they come fresh off the stringer at 57 pounds, go down to about 52 pounds 24 hours later, and then settle down to about 49-51 pounds after several hours of play. In other words, I'm getting the same tension at 50 pounds as I would from TW or TE if I asked for 58 pounds.

    3) The guy who strung my racquet before was even lower than TW and TE. On the same string job he would have been 7-8 pounds lower than them.

    The same thing happens when I string different racquets with different string patterns. This difference is consistent.
     
    #27
  28. enderx1x

    enderx1x New User

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    What you have is different than what I was thinking. I was thinking the drop weight would dip a bit lower and pull higher tension but then level out at the correct tension, not end up at a higher tension. However, if the end result is consistently at higher tension, then the result is consistent which is what is important. Because you are aware of this, you can adjust your starting tension to get a "real" tension of whatever you want.
     
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  29. Ramon

    Ramon Hall of Fame

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    That's correct. The weight never moves up. It only moves down. At least it's consistent. I'd be lost without RacquetTune!
     
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  30. Ray_cn

    Ray_cn New User

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    I saw someone stringing 2 strings per time in the Decathlon, using wilson Baiardo.

    The difference is between 1 and 3 grammers. I think it is not too much difference.

    But that stringer don't need to rotate the racket, save time, and the tension is acceptable.

     
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  31. Ray_cn

    Ray_cn New User

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    For the " tilting the whole machine until the drop weight is horizontal." is a good idea.

    That is what the Stringway do. It's a smart invention. They lift left side of rotation for the tensioner. Then make the right holding its horizontal position eg. correct tension. I think the max lift degree is enough for most strings.

    "Lifts automatically at the position of the tenionhead"
    http://www.stringway-nl.com/USA/

    [​IMG]


     
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  32. enderx1x

    enderx1x New User

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    I believe you are talking about the concorde system and I believe the purpose of that is to eliminate friction when you tension the mains in the throat. The reason is that without that system (what I and most people use now without to much problem) when you tension a main under the throat the string will rub against the racquet. However, this is not too much of a problem.
     
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  33. Ray_cn

    Ray_cn New User

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    I think you should forget the "Constant Pull" concept.

    After read many about the dropweight and constant pull, I think "constant pull" is a wrong or not very useful concept for most dropweight machine. And even no dropweight can do that except the Stringway.

    Maybe only Stringway call its machine is "ConstantPull" because it "Lifts automatically at the position of the tenionhead. " and "The string is tensioned at the right tension now (independent of the angle of the drop weight lever)." and "3) The tension is maintained during the slow elongation of the string." But I didn't have one to learn how does it work.

    Most stringer always using Pre-Stretch,Tension-Adjustment for each string, and Knot-Tension. Some electronic has Speed-Adjustment for softer string or hard string. All these is to make sure the string tension accurate. These methods are popular used by manual or electronic stringer in the world.

    Even using a Stringway machine, maybe you should stringing with these methods too.

    Here is my some opinions about the dropweight.
    http://tt.tennis-warehouse.com/showthread.php?t=428903

    If you want a automatic dropweight machine, here is a sample. Just change the weight, for example, the basis weight is 50lbs. you can put a 5lbs weight on it. Then it is 55lbs. Or you take the 5lbs out, it is 50lbs. It's simple and easy to diy.
    [​IMG]
     
    #33
  34. Irvin

    Irvin G.O.A.T.

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    'Ray_cn' you have so many bad assumptions in your post I don't know where to start. Let me just comment on constant pull. Any machine that continues to pull tension is constant pull. Let's take a lockout. It pulls until it locks out then stops so it is not constant pull. Any drop weight that uses gravity to pull is constant pull unless gravity stops pulling for some reason. It make not always pull at a constant tension but drop weights are always pulling. Don't assume constant pull is constant tension.

    For a stringing machine to have 360 rotation you need to pull from below the stringbed. You can do that by either tilting the racket or placing the tensioner below the stringbed. There are other ways of doing it but things start getting in the way.
     
    #34
  35. Radicalized

    Radicalized Semi-Pro

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    Stringway's Concorde system, which tilts the racquet for 360 rotation and eases tensioning of the center mains, is a separate option. It has nothing to do with the automatic tension head. You have to rethink some of your ideas.
     
    #35
  36. Irvin

    Irvin G.O.A.T.

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    Easy enough to do. I have a digital scale with a peak setting. Drop the weight and look for the peak after you know what the tensioner is set for.
     
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  37. RetroSpin

    RetroSpin Hall of Fame

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    Eagnas Logic 90. $459.00
     
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  38. enderx1x

    enderx1x New User

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    That would be good to know. Do you mind doing one test where you lower very quickly, and one very slowly?

    Has anyone on these boards tested the quality/accuracy of this machine, because with what I've seen on these boards some Eagnas machines are good and some aren't.
     
    #38
  39. Ray_cn

    Ray_cn New User

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    Thanks for discussing my opinion. I'm learning the princple of stringing machine from beginning. If it's wrong i'll fix it.

    I just thought it should be constant tension to pull the string from this paper:

    "Strings need between 3 and 10 seconds time to stretch when they are tensioned. A constant pull tension unit keeps the tension in the string constant during this elongation of the string.A nonconstant pull tensioner looses tension depending on the type of string and on the speed of pulling"

    http://www.stringforum.net/nl/download/The_Importance_Of_Constant_Pull.pdf

    So to avoid the string elongation, it should be constant pull with constant tension.

    I think the string's elongation property maybe different for different tension, and different speed eg.length of the pulling time.

    According to the "speed of pulling", if a crank pulling slowly enough then it is most like constant pull with constant tension. For example 60lbs is the correct tension, pulling slowly, when the header arrive at 58lbs, pulling more slowly to the end. Such as some electronic machine's speed adjustment. But not like electronic machine, crank do that depend on the stringer's experience.

    For manual machine, crank or dropweight, only stringway call its constant pull with constant tension.
    I don't know how does it do that. Most dropweight's tension is depend on the angle according to the f = (M g / r) (cos Q) R in lethalfang's topic. It must has some additional function to do that.
    "The string is tensioned at the right tension now (independent of the angle of the drop weight lever)."

    Accordint to this pic, when the crank locked, but the spring is still working(If the crank's princple is same as i painted, tension head locked, but not locked both side of the spring, and the spring is a "Compression Spring"). I think it is still pulling too. Crank is continually pulling by the spring, as the continually pulling by gravity in dropweight.

    But both are not pulling at the correct tension according to the string elongation. It's easy to notice this by the indicator in dropweight, but not easy to find this in crank, because the indicator is still at the correct tension number. When the string elongating, the spring is loosing, the lever is droping. We can caculate the current tension by angle "a" or angle "b". Sorry,long time didn't do caculating job, can't write a accurate formula as lethalfang's. If the angle "a" is -90, tension is 0 in dropweight. If the spring loose to the max, it's 0 too. So we have to both adjust the angle in the dropweight, and repull in the crank.

    In this case, the string elongating speed is always slower than the speed of gravity or spring returning to 0 tension. otherwise, gravity or spring didn't pulling the string. If I said dropweight is not continuously pull in previous opinion, it's my mistake, didn't notice the speed is different.

    We have to adjust the lever if it is not at the horizon position whether pulling slowly or not, because the angle between the lever and the gripper is constant, that mean the string length can't be changed automaticly. But if a crank pulling slowly, maybe don't need to release and pull again, the string length can be changed when the tension head moving on the rack. But pulling speed control need a good skilled stringer's experience.

    If the stringer can't wait the elongation time(2-3seconds in that paper) or experience is not enough to control the pulling speed as what the electronic machine do. Then using Pre-Stretch is better. Maybe most stringer using this method, all electronic machine provide this function. And I think the speed control on electronic machine is same as the constant pull with constant tension function.


    [​IMG]
     
    #39
  40. Ray_cn

    Ray_cn New User

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    I can't edit my topic, Here is the supplementary:

    "So to avoid the string elongation, it should be constant pull with constant tension for a period(2-3seconds in that paper)." The pulling time maybe different for different strings. In mechanics of materials, time is most important for affecting the string's deformation.
     
    #40
  41. Irvin

    Irvin G.O.A.T.

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    Would not mind at all but I don't have a drop weight.

    In order for a lockout to tension as a constant pull you have to pull again. A constant pull (electronic) pulls to a set tension and stops (as a lockout) then it automatically pulls again when the string stretches and the tension falls (unlike a lockout.) So if you want to use a lockout and get the same results you would have on a constant pull you have to manually pull again.

    http://www.youtube.com/watch?v=3aYI5DXQxSA&feature=plcp

    The spring on a lockout has nothing to do with the pulling action. The spring controls how much resistance (string tension) is required to engage the lockout. Once the tensioner lockout out the brake is holding tension on the string. If the brake slips the tension will fall no matter what you set the tension on the tensioner. If you would like I can make a video of just how the lockout works.
     
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  42. Ray_cn

    Ray_cn New User

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    No problem. I have no that too:p

    Yes, pull again is a method. I saw that video many times to see what happend when it locked. My tension head not in hand now.

    Another method is to pull slowly according to that paper and a stringer reply in my post. He wait about 10s for the elongation stop in dropweight. Then pull slowly about 10s before reach the tension is a metod too. For example 60lbs, spend 10s from 58lbs to 60lbs before it locked.

    Look at this pic, I repost here. The 3point limit the length of the spring continually pulling. But it is a limit. Not mean spring didn't continually pulling. It pulling shorter than dropweight. Dropweight could stop at -90degree, the tension is 0. For the crank, spring stop at the pulling begaining.

    The locker locked the head axle, not lock the spring. The lever stopper stop the spring pulling.

    Look at that video 3:46-3:51, the lever leave the lever-stopper about 2-3mm. That mean the string, lever,spring is in tension balance. But when the string elongated, the spring will pull it continually according to the lever theory, but pull at a lower tension as the dropweight do. And will stop pulling when the lever reach the lever stopper. It is very short. But the indicator is still at the correct tension. Not like it shown clearly on dropweight.

    If you can try please wait some time to see if the lever return back to the lever stopper. Using a softer string mabe show clearly and quickly. If it returned, then it mean that the spring continually pulling as the gravity pulling.

    I look at that video it is about 2-3mm after repull, maybe equal to the distance between the lever and the lever stopper. So maybe waiting the string elongation stop is ok.



    [​IMG]
     
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  43. Ray_cn

    Ray_cn New User

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    This is most like the crank tension head. The green parts are not locked. So when the string elongated for senconds, the spring will pull the lever to a angle "c" which limited by stopper. "c" is much smaller than 90 in dropweight. But maybe enough.

    So crank has continually pulling too as in dropweight. But shorter.
    [​IMG]
     
    #43
  44. Irvin

    Irvin G.O.A.T.

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    The problem with your scenario is in reality the green part ARE LOCKED.

    EDIT: The spring provides no pulling action on the string as shown in your diagram.
     
    #44
  45. Ray_cn

    Ray_cn New User

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    Could you please show me where the green part being locked? It's a problem no tension head in hand, have to wait 1week to get it:(

    Just saw it is lifted by the string in that video, but didn't find where is the locker of the green part. The locker only lock the brake pads in the head.
     
    #45
  46. Irvin

    Irvin G.O.A.T.

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    Marietta, Ga
    No problem but I am getting ready to go out for dinner will make a video later tonight.
     
    #46
  47. Ray_cn

    Ray_cn New User

    Joined:
    Jun 20, 2012
    Messages:
    27
    Thanks, just want to learn where its locked and whether the lever will return to the stopper after the string elongated for a while.
     
    #47
  48. Irvin

    Irvin G.O.A.T.

    Joined:
    Mar 15, 2007
    Messages:
    12,080
    Location:
    Marietta, Ga
    Now I see what you mean. The spring arm will not go against the stopper and there is some tension on the string from the spring. If you raise the tension on the dial even after it is locked out the tension will go up. But if you let it sit the tension will fall. Many people assume that a constant pull tensioner will pull at a constant tension where the crank will not it will pull to a set value and then stop and the tension will fall. A drop weight will pull to a set tension then rise or fall ever so slightly depending where the bar is above or below horizontal. Electronic pull at a constant tension.
     
    #48

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