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  1. #21

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    Quote Originally Posted by MacEntyre View Post
    Sorry! I should get three 9' aluminum poles, fabricate three unions, and make the final Tensegrity Stand.
    My place is now an orgy of clattery 3/4" PVC pipe (2x9' and one 6.75') and tangled cordage as I prototype, bloody-knuckled. I'm having trouble with the cordage: not wanting to commit to lengths just yet, all the connection points slide, so it's a bear getting it to stand up absent final tension. Also I fantasize about lacing it up in a manner that tensions everything by tightening just one line, but my "Spock's luthier" side hasn't caught up to how.

    Is it essential to lock down/prevent sliding at some or all of the connection points? Which?

    I think I can do the cordage as 4 color-coded whoopie loops rather than 12 discrete runs.

    Also planning to break down into 4 or even 5 segments because has to pack onto bicycle: 30" too long. This way the short pole is 3 27" segments, and you can add a 4th for multi-hammock mode (but then the cordage lengths change).

    For ease of field deployment, thinking of a rigid 6-way union so it doesn't collapse before cordage taut: just ordered this for prototyping: https://flexpvc.com/cart/agora.cgi?p...n&ppinc=detail . Do you see a problem with a rigid orthogonal union given 9' poles? Would fix the union at the 1/4 point of the longs and at 1/3 of the short. Looks like your version had a more shallow X.

    Quote Originally Posted by MacEntyre View Post
    The X-Tensegrity Stand for one hammock is the same as the original, tipped over, with one short strut.
    You could tip over any symmetrical tensegrity stand and have the same thing.
    It's just that your hammock would be hanging over the end of a pole.
    I'm thinking all 3 poles have to be same length if it's to work for more than 1 hammock at once, but then, lower head than foot could be a selling point when the hang points are too short to permit adjustment...

    Screen Shot 2016-12-28 at 12.39.23 PM.png
    Last edited by Latherdome; 12-28-2016 at 16:57.

  2. #22
    MacEntyre's Avatar
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    You'll get it done, given your approach. Color coding the tendons of the same length is a good idea.
    You still need a winch of some kind to tighten the last tendon you attach.

    A Tensegrity structure is not meant to support a hammock, so that load puts it out of kilter.
    They are meant to be a support structure, or a component of a column.
    In other words, the load from hammocks produce a bending moment that isn't there if it is used as an insert in a stack of Tensegrities.
    All struts are supposed to see only compression. All tendons are supposed to see only tension.
    Hang hammocks, and suddenly there are bending moments that threaten the struts.
    Therefore, I found that by adjusting the Tensegrity so that the struts touched where they cross,
    and lashing them tightly together, they would support each other and mitigate that bending moment.
    A custom connector would accomplish the same thing, but the one you listed won't work.
    The angles are wrong.
    - MacEntyre
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
    www.MollyMacGear.com

  3. #23

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    I confirm that the orthogonal union won't work, at least not without the base being so narrow as to mandate staking. Looks like the proper angles are captured more or less by a truncated octahedron rather than a cube:

    Screen Shot 2016-12-31 at 11.14.10 AM.jpg

    Found an elegant way to lace with a single continuous line, but seems to me ultimately that connection points must be locked down for stability under load, so better to do as 4 loops with lark's heads at the attachment points (eyebolts?), and whoopie/soft-shackle connects. Final tensioning: lashing loops mid-span in the smallest triangle, and cinch tight toward the central union. Central union just tripod lashing using zing-it.

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