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  1. #1
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    Default a question: the inside of a dropweight

    Hi All,

    as always, I'm of on a little project tryingsomething new. But I am wondering, what is inside that big drum on a dropweight machine?


    The round bit furthest away is simply welded/attached to the axis, the dropweight part moves it around.
    But the drum closest to us, the one with the gripper on there, does grip to the axis when turned clockwise, but runs free counterclockwise.
    By sound, I don't think it's a ratched...

    So, my question to all who have every taken a stringing machine apart...
    What is inside that drum? do you have any pictures? sketches? anything?

    I'm currently doing some modeling, I'll show you guys what I'm up to

  2. #2
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    Hi Jerby,

    Look closely when you move the bar from clockwise then counter clockwise, do you see the drum with gripper moves in and out a little? Although I never took a part a Eagnas machine before, I believe it is using something simular to a clutch in a car.

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    Took another look...
    my device works slightly different, not like the eagnas.
    the entire axle (is that the word? axis? axel? axle?) is connceted to the gripped, the drum with the dropweight itself is clutching...or something.

    Thanks steven, anyway, this is my project,
    The idea is to get the linear gripper (to be mounted on top of the red roller) as close to my racket as I can, and make it move linear, like it is supposed to
    So I came up with the crutch-sleave mechanism, modeled and all in Pro-Engineer



    The Entire yellow bit is to be separated (linking to my question above)
    And an addition of a ratchet-wheel on the outside, to prevent it from going back (without me wanting it )

    Now I'm just looking for some errors, or whether it will actually work
    (eitherway, just more experience for me)

    EDIT:
    The gripper is still to be mounted on top of the red 'thingy' (roller) and will be placed rather high so the string can be put inside it over the yellow axis.
    Last edited by jerby; 06-12-2008 at 09:45 AM.

  4. #4
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    Default

    I see what you are trying to do. Is this another one of your if I can not stop you, I might as well help you project? Let me know if my reading of your thought is correct. You are trying to simulate the linear pulling motion of electric tensioner while using a drop weight to supply the force? If so, I actually have a solution for you and easier to make. I am at work right now and I will email you the drawing later. I am trying to get YY to file this patten for me.

  5. #5
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    Default

    well, it's still just daydreaming
    and having fun with oru schools 3D-modeling program

    the biggest problems with this design is incorporating the 'ratchet' I asked about in post#1, and a desing-issue: If the string is not tensioned when the linear gripper is at it's full length, you have to repull.
    And, when the puller is at it's furthest position, if the two bars (yellow and blue) "swing over" everything will suddenly release....
    And, at the startposition, the full 28lbs press onto the glidebar, that could create a lot of friction...

    So, enough problems Anybody can talk me out of it

  6. #6
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    I've been trying to remember where I saw a description on how to repair the ratchet mechanism but no luck. I seem to remember that a spring is used. It wraps around the shaft and I think by expanding and contracting the spring is how it grips.

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    Default

    Yeah, I saw one/two photo's on it some year back..Never got round to finding them again...

    Anyway, master Heart, I can always help and try some 3D modeling
    Maybe that would speed up yonex

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    Translating circular motion into linear motion is not easy. I wish you guys success. Have you the two of you thought about the simple pulley and modify it with a linear gripper?

  9. #9
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    Well, after some testing fo my previous model... I can not work effectively.

    Tensioning a string can, sometimes, take 1 1/2 - 2 pulls, a range of motion of mroe than 90 degrees.
    With my jack-sleeve mechanism (crude translation from the dutch 'kruk-sleuf' mechanisme) It's can not allow a turn over 90-100 degrees. because, when moved further, the systems actually draws back and releases tension!

    Now, you could possibly angle back the yellow bars a bit, but the system can never allow more than 2 drops... Not a comfortable margin of error

  10. #10
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    the inside of the drop weight drum is made of 2 parts, one is a female socket which is attached to the string gripper and the other is the male cam which is attached to the tension rod. Inside the female socket there is a clutch spring is loaded and wrapped around the same in a clockwise direction. This allows it to move clockwise and not counter clockwise. The only reason i know this is because i got one used for a great price and the tension rod kept falling and hitting my racket. Turns out there was a damaged stopper screw, DOH!

  11. #11
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    Quote Originally Posted by jerby View Post

    Tensioning a string can, sometimes, take 1 1/2 - 2 pulls, a range of motion of mroe than 90 degrees.
    With my jack-sleeve mechanism (crude translation from the dutch 'kruk-sleuf' mechanisme) It's can not allow a turn over 90-100 degrees. because, when moved further, the systems actually draws back and releases tension!
    well im at college thoroughly bored and stumbled upon this, and was thinking about it and thought can u not put a bar across just infront of the yellow bar so that when it goes past 90 degrees the string rests on the bar (smooth ofc) allowing a greater to be acomplished.

    though this would not be possible due to the straight bars from the clamp thingy to the upright yellow bar but they could be arched, solving the problem to allow say a 100-110 movement possibly more

  12. #12
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    well, yeah, there's no place to fit the bar. But the whole system is a nice idea, but very wrong.

    At 90deg you get a singularity, a point where all the bars are fully extended into a straight line and all forces cancel each other out.
    So, if everything stops exactly at 90deg, you'll have major difficult getting your string loose.
    Also, when you move the yellow bar past 90deg, the red cart will go back, loosening the tension, that's also why 90deg is the limit.

    It was a fun experiment but not tha usefull

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