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  1. #181
    MacEntyre's Avatar
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    Quote Originally Posted by WV View Post
    MacEntyre may have some suggestions.
    I believe the struts should be as close to vertical as is practical, in order to avoid compression failure. Unfortunately, for our purposes the tensegrity works better when the struts are inclined from the vertical. I seek a way to quantify this compromise, so that we can determine how to build them safely.

    My focus is on a stake-less, portable tensegrity stand for a single hammock. I wish I had more time to work on it!
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
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  2. #182
    Agfadoc's Avatar
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    What a great thread, I would hate to see it die out. I am very intrigued by the design and am thinking of making one for my backyard and Car camping exclusively. The minimal amount of material and the ability to take apart easily for winter storage and transport is very appealing. Has there been any more development on the Tensegrity stand?

    I too am a big guy (250) and am thinking 2" thick walled tubing, 12' poles, I am thinking of using 3 independent 1/8 or 3/16 braided steel cables for top ring, 3 for the bottom with U loops and caribiners at each end... but I don't know the stretch variables of it.

    Or I can just make three of the portable wood stands. But I sure like this better!
    Last edited by Agfadoc; 03-13-2011 at 11:21.

  3. #183
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    Reading this thread made my head hurt. But it does look cool.
    Custom Bridge Hammocks

    Mackinac Bridge Hammocks

  4. #184
    Senior Member WV's Avatar
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    Quote Originally Posted by Agfadoc View Post
    What a great thread, I would hate to see it die out. I am very intrigued by the design and am thinking of making one for my backyard and Car camping exclusively. The minimal amount of material and the ability to take apart easily for winter storage and transport is very appealing. Has there been any more development on the Tensegrity stand?

    I too am a big guy (250) and am thinking 2" thick walled tubing, 12' poles, I am thinking of using 3 independent 1/8 or 3/16 braided steel cables for top ring, 3 for the bottom with U loops and caribiners at each end... but I don't know the stretch variables of it.

    Or I can just make three of the portable wood stands. But I sure like this better!
    What a coincidence, Agfadoc! I haven't done much with tensegrity hammock stands for a while, but I decided to bring one to the MAHHA hang in PA to help out with the hammocks on display, so this morning I took down the one in the back yard and did some calculations so I could convert it from a 3-strut stand to a 4-strut stand with a longer hanging distance. What we've found is that it's very important to pay attention to the strength of your materials. Some work better than others; some don't work at all. The bigger the stand, the more stress on the system. I don't know of any problems with 7/64" Amsteel for tendons, but your proposed steel cables should be fine, too. Personally, I find working with Amsteel easier on my hands. As an aside, you probably know this, but I once heard a great piece of advice about working with cable clamps: "You don't put a saddle on a dead horse."

    When people have had problems, it has been the strength of the struts, so 2" thick-walled pipe sounds good. I hope it's good enough. Let us know what you use and how it holds up. Keep us posted as you go along, too.

    Another side-note: I have made some tensegrities on a smaller scale recently. I had a tensegrity stove stand that let me sit in my hammock and cook at knee-level. It was made with carbon-fiber arrow shafts and kevlar kitelines, but it weighed 3 ounces - almost as much as the stove it was supporting. I wanted to make another stand for an even smaller stove (Bushcooker LT I from FourDog), so I used 1/8" cf tubing with 1/16" cotter pins pushed into the ends for connectors. Combined weight of stove and stand is now 2.8 ounces.

  5. #185
    Agfadoc's Avatar
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    Quote Originally Posted by WV View Post
    What a coincidence, Agfadoc! I haven't done much with tensegrity hammock stands for a while, but I decided to bring one to the MAHHA hang in PA to help out with the hammocks on display, so this morning I took down the one in the back yard and did some calculations so I could convert it from a 3-strut stand to a 4-strut stand with a longer hanging distance. What we've found is that it's very important to pay attention to the strength of your materials. Some work better than others; some don't work at all. The bigger the stand, the more stress on the system. I don't know of any problems with 7/64" Amsteel for tendons, but your proposed steel cables should be fine, too. Personally, I find working with Amsteel easier on my hands. As an aside, you probably know this, but I once heard a great piece of advice about working with cable clamps: "You don't put a saddle on a dead horse."

    When people have had problems, it has been the strength of the struts, so 2" thick-walled pipe sounds good. I hope it's good enough. Let us know what you use and how it holds up. Keep us posted as you go along, too.

    Another side-note: I have made some tensegrities on a smaller scale recently. I had a tensegrity stove stand that let me sit in my hammock and cook at knee-level. It was made with carbon-fiber arrow shafts and kevlar kitelines, but it weighed 3 ounces - almost as much as the stove it was supporting. I wanted to make another stand for an even smaller stove (Bushcooker LT I from FourDog), so I used 1/8" cf tubing with 1/16" cotter pins pushed into the ends for connectors. Combined weight of stove and stand is now 2.8 ounces.
    I was playing with tent poles and saw your picture with a stove on it.. .. Have you improved upon it?


  6. #186
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    Quote Originally Posted by MacEntyre View Post
    Dave made his with chain link fence pipe, made of steel. Aluminum poles are harder to come by in 10' lengths.

    I'm working on finding or making proper end fittings as well.

    - MacEntyre
    If you will find a sign shop that makes lighted signs, they use 1" AL square tubing in thin walled and thick walled. I'll bet they'd sell you a few 10' lengths.
    DIY Is my thing.

  7. #187
    Senior Member WV's Avatar
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    Quote Originally Posted by Agfadoc View Post
    I was playing with tent poles and saw your picture with a stove on it.. .. Have you improved upon it?

    That's a Bushcooker LT II on a tensegrity stand made from carbon fiber arrow shafts cut in half (~16" long). I wanted something that would pack a bit smaller, so I modified the struts, adding ferrules and internal 3/32" bungees.

    The smaller Bushcooker LT I is the stove I mentioned above with a stand made with 1/8" carbon fiber tubes. The struts also break down into shorter lengths, but they're too small to get bungees into. I don't anticipate much more development of these stands - they work fine as is. (I am working on a wind-screen/heat exchanger that attaches to my cooking pots, though. Fourdog is adding some brackets to my small Snow Peak pots (600 ml. and 450 ml., respectively, for the two stoves.) I'll post about them some time in April.

  8. #188
    Senior Member WV's Avatar
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    Quote Originally Posted by nik.martin View Post
    If you will find a sign shop that makes lighted signs, they use 1" AL square tubing in thin walled and thick walled. I'll bet they'd sell you a few 10' lengths.
    Actually, one of the drawbacks of using fence rails (aside from the the fact that they are just barely strong enough) is that they are only 10' long. You really need struts 12' long or longer to make a hammock stand.

  9. #189
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    I've got one of these assembled but I'm having some trouble getting it sufficiently rigid. I'm using steel struts from an old swing set and 1/8" Amsteel tendons. Working from dejoha's measurements, I've currently got:

    struts: 12' 6"
    bottom tendons: 6'
    top tendons: 11'
    side tendons: ~9' - final tightening done here

    I'm having some trouble figuring out how things work in a tensegrity. Should I be able to get it sufficiently rigid just by cranking down on the side tendons, or do I need to adjust my bottom and top lengths too? Right now when I load a hammock, the top tendon above it becomes quite slack and the whole structure becomes unstable to the point where one person is not strong enough to hold it down while someone else gets in the hammock.

  10. #190
    Senior Member WV's Avatar
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    Quote Originally Posted by Jared View Post
    I've got one of these assembled but I'm having some trouble getting it sufficiently rigid. I'm using steel struts from an old swing set and 1/8" Amsteel tendons. Working from dejoha's measurements, I've currently got:

    struts: 12' 6"
    bottom tendons: 6'
    top tendons: 11'
    side tendons: ~9' - final tightening done here

    I'm having some trouble figuring out how things work in a tensegrity. Should I be able to get it sufficiently rigid just by cranking down on the side tendons, or do I need to adjust my bottom and top lengths too? Right now when I load a hammock, the top tendon above it becomes quite slack and the whole structure becomes unstable to the point where one person is not strong enough to hold it down while someone else gets in the hammock.
    Given fixed top tendon length, bottom tendon length, and strut length, you should be able to make a rigid tensegrity simply by tightening all the side tendons, BUT there is a range of possible values for those first three lengths. AND it is not all that simple to tighten it enough. I can calculate whether your given lengths will make a tensegrity if I have one more fact: how many struts you are using. I assume 3, but 4 might be okay, too. With that information I could tell you how tight your side tendons need to be and how high your hammock will hang. (I'm guessing that you might need to shorten your top tendons a bit.) Let me know how you are tightening those side tendons, too. You need to get some mechanical advantage somewhere - it's not just a matter of pulling on a whoopie sling.

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