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  1. #1
    MacEntyre's Avatar
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    Tensegrity Fail!

    At Linville Gorge last weekend, Hooch broke my Tensegrity Stand!

    (...not really, but don't tell Hooch!)



    Clearly, there is a need for a load analysis that takes into account the particular tensegrity geometry.

    I'm pretty certain that my new stand won't have these problems. It's the Tensegrity Stand for One Hammock Which Requires No Stakes.

    Meanwhile, I'll try my 4" diameter bamboo for the Tensegrity Stand for Three Hammocks!

    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
    www.MollyMacGear.com

  2. #2
    Hooch's Avatar
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    RIP Mac's Tensegrity Stand. How little we knew thee. . . .
    "If you play a Nicleback song backwards, you'll hear messages from the devil. Even worse, if you play it forward, you'll hear Nickleback." - Dave Grohl

  3. #3
    Rikall's Avatar
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    Quote Originally Posted by MacEntyre View Post
    I'm pretty certain that my new stand won't have these problems. It's the Tensegrity Stand for One Hammock Which Requires No Stakes.

    Meanwhile, I'll try my 4" diameter bamboo for the Tensegrity Stand for Three Hammocks!
    Looking forward to the photos/video. The stand for one sounds very interesting.

  4. #4
    Poppabear's Avatar
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    Quote Originally Posted by Rikall View Post
    The stand for one sounds very interesting.
    I second that! I'm extremely interested in Tensegrity Stand for one hammock. I will be watching closely for news on it.
    Terry

  5. #5
    Knotty's Avatar
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    That's what happens when you live on the bleeding edge of hammock technology.
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  6. #6
    MacEntyre's Avatar
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    Knotty, I think I know what happened... the more the struts are inclined (base smaller than top, and tops brought toward the ground) the more the tendons exert non-compressive forces. I think we brought the tops down low enough that the struts leaned excessively, and the tendons then put a bending force on the struts.
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
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  7. #7
    WV's Avatar
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    Quote Originally Posted by MacEntyre View Post
    Knotty, I think I know what happened... the more the struts are inclined (base smaller than top, and tops brought toward the ground) the more the tendons exert non-compressive forces. I think we brought the tops down low enough that the struts leaned excessively, and the tendons then put a bending force on the struts.
    Mac, I think you're probably right that the angle of the struts relative to the ground is a significant factor, but I believe the reason is that the weight of the hammocks and occupants pulling down is what exerts non-compressive forces. Theoretically the tensegrity tendons are in equilibrium, regardless of the sizes of the base and the top. It's the additional load from the hammocks which the tensegrity structure distributes throughout the the structure, but which is not in balance so the struts eventually bend.

    One of these days I'll make a six-strut tensegrity. I recall that the more struts, the closer they are to vertical, especially if the base and top are the same size hexagons.

  8. #8
    dejoha's Avatar
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    I am starting to worry more about my tensegrity stand. At first I thought I should invest in thicker amsteel, but watching the video and seeing the bent pole, I wondered if it were something else. I also found that i had better results with the poles at a higher angle, which also makes the distance from ground higher.

  9. #9
    Senior Member GrayDog's Avatar
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    Since the hammocks are not static could that be causing the change in force from pure compression?
    hammock [ham-uhk] noun
    Man's successful attempt to sleep on a cloud

  10. #10
    MacEntyre's Avatar
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    Quote Originally Posted by WV View Post
    Mac, I think you're probably right that the angle of the struts relative to the ground is a significant factor, but I believe the reason is that the weight of the hammocks and occupants pulling down is what exerts non-compressive forces.
    I meant to mention that as well. Tensegrity prisms are not designed to be loaded the way we are loading them. Ideally, the load should be in line with the struts, which allows the tendons to distribute the compressive load throughout the structure.
    Quote Originally Posted by dejoha View Post
    ...i had better results with the poles at a higher angle, which also makes the distance from ground higher.
    I would love to figure out how to analyze the loads for a particular geometry, so we can know how close to the edge we are when our struts are not vertical.

    Quote Originally Posted by GrayDog View Post
    Since the hammocks are not static could that be causing the change in force from pure compression?
    Static or dynamic, the loads are not in line with the struts, therefore they impose a bending moment. We depend on the tendons to distribute that oblique load so that the struts see only compressive loads. Apparently, that dependence is misplaced.
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
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