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Cables in tension passing through board with holes.

  1. Mar 29, 2014 #1
    Hey guys,

    I'm looking for examples of real life systems which uses a board with holes to redirect cables in tension (as opposed to pulleys) for some inspiration on a project I'm working on.

    I've attached an schematic of what I mean. I've tried searching google for systems but it's a hard thing to describe accurately. Also any advice as to how to improve on this design is greatly appreciated.

    Thanks in advance.
     

    Attached Files:

  2. jcsd
  3. Mar 29, 2014 #2

    SteamKing

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    I think you misunderstand the purpose of using pulleys in tension systems. Yes, the direction of the tensile elements can be changed by the placement of the sheave w.r.t. the load and the pulling force, but in many applications, a system of sheaves is used to provide a mechanical advantage, in order to move a large load using a small input force.

    It's not clear what your design does except to provide a means to apply several tension forces to a single load. In rigging applications, this is usually accomplished by the use of spreader bars or lifting frames.
     
  4. Mar 29, 2014 #3

    Baluncore

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    Industrial sewing machines have polished ceramic eyes to guide the thread from the bobbin to the machine.

    Control cables in aircraft run through the structural ribs of the airframe.
     
  5. Mar 29, 2014 #4

    AlephZero

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    True, but if there was nothing to stop a cable rubbing against the holes where it changes direction (as in the OP's diagram), I don't want to fly until somebody redesigns the cable run :eek:

    The OP didn't give much detail about the design, but it looks a "good" way to break the cables by frictional wear and/or fatigue, if the position of the bend along the length of the cable keeps changing.
     
  6. Mar 29, 2014 #5

    Baluncore

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    FreshVeggies. First a belated welcome to PF.

    In education it is most important to produce a quick result. Learning about practicalities is a most important part of the education process. I will support anyone who is prepared to try something practical, even if I think there will be problems in the longer term.

    I maintain an irrigator that pulls itself along a wire. The manufacturer did not count on the wire being covered with wet grit and so cutting the steel guide eye from the front of the steering mechanism. I replaced the eye with a porcelain insulator from an electric fence and the problem was greatly reduced. When wear does occur, the eye can be quickly rotated or replaced.
     
  7. Mar 29, 2014 #6

    AlephZero

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    Eh??? You don't need to any education to produce a quick result. Just throw together the first random ideas that come into your head.

    Agreed, but ...
    ... there are more effective ways to learn than by wasting time and money building something that is designed to fail. And if you don't bother to test it under conditions that make it fail, you learn nothing anyway.

    I suppose there are some people who can only learn that sticking their hand in the fire will burn them by actually doing it, but that doesn't mean it's the best teaching or learning strategy.

    In the engineering sector that I work in, nobody builds and tests things "to find out what will happen" any more. They build and test things to verify that they do what they are supposed to do. That's a BIG shift in attitude.
     
  8. Mar 29, 2014 #7
    Thanks for the warm welcome and advice guys, and sorry for not making what I'm trying to do clearer.

    Basically the board is there to redirect the cable to specific force vectors. The object that's being loaded is being loaded slowly from 0 [N] to x [N] and then held at x [N] statically to measure the resultant force on the object. Also this is a small scale design with cheap, easy to replace cables/sting/rope/etc.

    The main issue I am currently having is that some outlier force vectors which require testing are near parallel with the board. That's why I asked for examples to see it there were low friction ways which to redirect cables that aren't pulleys. (because the use of the board with holes is mandatory)
     
  9. Mar 29, 2014 #8

    Baluncore

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    Last edited: Mar 29, 2014
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