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  1. #1
    Member 11steve11's Avatar
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    4pole 2"X4"X14' Tensegrity Stand

    Uploaded at the following links is my first attempt at a tensegrity stand.
    It is a 4 pole (using 2"X4"X14' lumber) so the 4 of us can hang. Currently in the proof of concept phase; I sould have snapped a picture of the family faces when they were all having a good time at my expence all until we let go and it stood up on its own. The next time I set it up, I'll have a tape measure to get uniform length on the tendons and I'll stake the base down so when one person is in it, it stays on the ground (a little tippy on its own.)

    http://www.hammockforums.net/forum/p...pictureid=8953

    http://www.hammockforums.net/forum/p...pictureid=8954

  2. #2
    Senior Member WV's Avatar
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    It's beautiful ... but, test carefully. It looks like the base is big enough that it won't need to be anchored, but maybe not. Also, I can see those 2-bys bending sideways under the weight of one hanger, much less 4. What material are you using for tendons, and how did you apply enough force to tighten them? Good luck.

  3. #3
    Member 11steve11's Avatar
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    WOW, a reply form WV, thanks.

    Thanks for the reply, this was set up referencing your tensegrity video.

    Quote Originally Posted by WV View Post
    It's beautiful ... but, test carefully. It looks like the base is big enough that it won't need to be anchored, but maybe not. Also, I can see those 2-bys bending sideways under the weight of one hanger, much less 4. What material are you using for tendons, and how did you apply enough force to tighten them? Good luck.
    The 2X4's have a little bow and twist in them under no load. When I put a 130# kid in one hammock and a 225# me on the opposite side the worst 2X4 had no additional bow. I went with 2X4's for their strength when outside of pure compression. The small amount of testing we did we kept to about 1' above ground and when the stand did reach the tip stage with just the 130# son, he was on the ground and the stand was still up.

    I could make the base bigger. The tendon loops are roughly 7'8" apart and are VERY tight using 2500# mule tape. The pole hooks are 13'4" apart; I didnt like the looks of 1 of the hooks when I was done so I may loop the tape around the pole ends in the final version. The top tendons are roughly 11' and are 1800# mule tape. I do not know the lengths of the side tendons, I just tied 3 (of the 8 needed) using slip knots based on where they appeared to be when putting the stand up. One slacked and slipped off the hook when loaded which I figured was a symptom of not having all 8 of the side tendons of the correct length.

    3 of us put it up, the base tendons went on 1st, then I had 2 kids at the ends of 2 poles and I strung the next 2 for the top loop; it kinda stood by itself at that point. The 1 side tendon that was actually doing something was done by twisting the entire assembly and then tying it off to a base hook.

    ??? Is my assumption correct in that If all 8 of the side tendons are on at the correct lengths it will work correctly (not overly loosen or tip?)

  4. #4
    Member snull's Avatar
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    I've wanted to try this looks fun, test with sandbags or weights

  5. #5
    Senior Member WV's Avatar
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    Sounds as if you are going about it carefully and getting good preliminary results. I'm glad I was wrong about the 2x4s bending. I don't know how much mule tape stretches. Ideally a tensegrity prism should have tendons that don't stretch and struts that don't bend. I've had to re-tighten my amsteel tendons after a while. One thing I don't understand about your account is the reference to 8 side tendons. I don't see 8 in the photos, and a four strut tensegrity only needs 4 side tendons, 4 top tendons, and 4 bottom tendons. In the pictures it looks like one of the side tendons is tied to the wrong strut at the ground level, but you've probably already corrected that.

  6. #6
    Senior Member JohnSawyer's Avatar
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    Looks cool. Love that mule tape!
    "Do or do not, there is no try." -- Yoda


  7. #7
    Member 11steve11's Avatar
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    Quote Originally Posted by snull View Post
    I've wanted to try this looks fun, test with sandbags or weights
    We just used bone bags (us) yet suspended very close to the ground.

    Quote Originally Posted by WV View Post
    Sounds as if you are going about it carefully and getting good preliminary results. I'm glad I was wrong about the 2x4s bending. I don't know how much mule tape stretches. Ideally a tensegrity prism should have tendons that don't stretch and struts that don't bend. I've had to re-tighten my amsteel tendons after a while. One thing I don't understand about your account is the reference to 8 side tendons. I don't see 8 in the photos, and a four strut tensegrity only needs 4 side tendons, 4 top tendons, and 4 bottom tendons. In the pictures it looks like one of the side tendons is tied to the wrong strut at the ground level, but you've probably already corrected that.
    Mule tape seems to stretch very little if any. The entire structure does have very little flex yet when we loadedit, it did move as 1 unit. The picture attached is where I got the reference to 8 side tendons from another thread on the forum, you're saying I only need 4? I tied each of the side tendons from the tip to the base of the next strut that would keep the strut rotated UP instead of the one roughly beneith it; maybe incorrect? During the testing, it was never in any way anchored to the ground.

    Quote Originally Posted by JohnSawyer View Post
    Looks cool. Love that mule tape!
    Is cule to use the mule. Thanks for the tape, we'll be re-purposing it all to good use.
    Attached Images Attached Images

  8. #8
    Senior Member WV's Avatar
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    Quote Originally Posted by 11steve11 View Post
    The picture attached is where I got the reference to 8 side tendons from another thread on the forum, you're saying I only need 4? I tied each of the side tendons from the tip to the base of the next strut that would keep the strut rotated UP instead of the one roughly beneath it; maybe incorrect?
    Nope - that's correct. You only need those four. The picture isn't exactly wrong, just different from a uniform semi-regular tensegrity prism.

  9. #9
    Senior Member JohnSawyer's Avatar
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    Quote Originally Posted by 11steve11 View Post
    Mule tape seems to stretch very little if any. ...
    Is cule to use the mule. Thanks for the tape, we'll be re-purposing it all to good use.
    That's the beauty of Mule tape. It's designed to have no stretch over 1000' for safety. When pulling 1000' run through conduit, if it were to stretch and then snap, a lot of energy would be released, which would be dangerous to the operator...

    Glad you can put that tape to good use!
    "Do or do not, there is no try." -- Yoda


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