View Full Version : X Tensegrity Hammock STand
MacEntyre
05-31-2012, 22:02
Introducing the X Tensegrity Hammock Stand (http://youtu.be/eUyObz5KOWE), with a supporting appearance by the Molly Mac Gear Survival Hammock.
eUyObz5KOWE
In which we go to Trail Days and demonstrate a hammock stand using the original X Tensegrity from Snelson, the NC sculptor who inspired Buckminster Fuller to investigate tensegrity structures. This hammock stand cures the problems that plagued our earlier efforts. The last tensegrity hammock stand that we demonstrated failed due to the asymmetrical load. In this new hammock stand, we solved that problem by binding the struts together so they can help support each other, and no single strut bears a load by itself.
Soon, we will construct a new version of the Tensegrity Hammock Stand for Three Hammocks using this new technique.
Enjoy!
- MacEntyre
lazy river road
06-01-2012, 07:06
Awesome vid. Mac. Really informative and always love the ideas you come up with. I wish I would of seen this in person at TD. Now here is my ?. What are the chances or possibilities that a tensegrity stand could be made with folding poles with a hinge in the middle. If the poles were 9 to 10 ft long and could fold in the middle with a locking hinge then it would make a perfect stand for bringing along for car camping to a campsite where trees might be limited and one has to hang over a designated spot. I have no clue what kind of or lack there of support would provide with a hinge in the middle off the pole but man that would be cool. Thanks for the vid. Mac.
Detail Man
06-01-2012, 07:15
LRR, hinged poles won't work. The loading is such that the center of the strut is where failure will first occur. The last failure Mac refers to had two piece struts that joined in the middle, and was the location of the failure.
very very clever! :thumbup:
while I understand that the integrity of your structure is ingeniously, yet critically dependent on load balance, I'm with @lazy river road in wanting some sort of portability option. such the conundrum to create a getup that finds the sweet spot within the strength vs. weight vs. compactness vs. height vs. cost factors.
MacEntyre
06-01-2012, 08:14
What are the chances or possibilities that a tensegrity stand could be made with folding poles with a hinge in the middle...? ... man that would be cool. Thanks for the vid. Mac.
You are entyrely welcome!
My next one will use 9' sectional poles. I'm working on it!
The last failure Mac refers to had two piece struts that joined in the middle, and was the location of the failure.
Au contraire, DM... they were three section poles, and the failure was in the middle of one section, between two unions. It was due to bending, from the asymmetrical load. I plan to put together that very same tensegrity, with the poles bound together, to show that the key is to have each pole buttress the others.
I'm with @lazy river road in wanting some sort of portability option.
Absolutely! I'm working on it!
First I will use the sectional mil surplus poles I have on hand. They will work fine for car camping. Then, I will develop a lighter sectional pole, aiming toward something that can be carried.
I'm also going to put color coded rings on all the ends, so there are no lines to connect, just rings with the lines already on them.
Lastly, I will either replace the fence winder with a ratchet winch, or use something even simpler. The Bob Dustrade folding saw comes to mind...
Thanks for the kind words!
- MacEntyre
Quite a collection of testers at Trail Days, Mac. Considerable idea-power there. Did you learn a lot?
Nice work MacEntyre.
I came up with the same design about 12 months ago and made it on a small scale with some dowel and some cord. It was a pain in the butt to get it all together and I figured that it wasn't going to be practical based on the problems I had getting the pole lengths right and getting the tension where it needs to be to support a reasonable weight.
It is great to see that you managed to overcome these problems and create a working stand. Well done! :thumbup1:
Wise Old Owl
06-01-2012, 08:58
Why would a sleave of aluminum say 6" and brazed so one half slides into another?
MacEntyre
06-01-2012, 11:26
Quite a collection of testers at Trail Days, Mac. Considerable idea-power there. Did you learn a lot?
Yep! Someone suggested a hard joint device, but TZ nixed it because it would create a hot spot for failure. The best idea was from LDCakes, who suggested adding two pockets to the Survival Hammock! Dutch did not say much...
I came up with the same design about 12 months ago and made it on a small scale with some dowel and some cord.
How about that! That's right after I realized the X Tensegrity could be tilted like a jack and used to support a single hammock! It has taken me a while to get around to making it...
It was a pain in the butt to get it all together...
That's an attribute of tensegrity structures.
I figured that it wasn't going to be practical based on the problems I had getting the pole lengths right and getting the tension where it needs to be to support a reasonable weight.
Making it practical is a huge challenge. It will never be idiot proof. When I realized that rings would work for attaching the tendons, the IQ required to assemble one fell considerably!
It is great to see that you managed to overcome these problems and create a working stand. Well done! :thumbup1:
Thank you very much! The key is to bind the crossings. That way the struts that have a bending moment, from directly carrying the load, are reinforced by the other struts.
Why would a sleave of aluminum say 6" and brazed so one half slides into another?
Yes, unions are no trouble. I prefer inside joints.
richtorfla
06-01-2012, 11:43
Really nice job figuring this thing out. Nice and compact. Interseted in seeing one at the 9 foot sections. So I have to ask: what is the set up time the way it is now and how is it going to be when you use the rings? I like how you figured out the ratcheting system. Like I said Nice Job!
I absolutely love this!!! Good job!!
MacEntyre
06-01-2012, 21:06
...what is the set up time the way it is now and how is it going to be when you use the rings? I like how you figured out the ratcheting system. Like I said Nice Job!
Thank you very much!
It only takes a few minutes to set it up, but with rings it will go a long way towards idiot proof... only one way will it work.
I absolutely love this!!! Good job!!
Thank you!
Very Cool idea.
I appreciate the kind words... it has been in the works for a while.
Over a year ago, I tried to find someone at NCSU who could help me calcluate the loads on a tensegrity. No one responded. Turns out I did not need to calculate loads, but rather to share them.
- MacEntyre
born2roam
06-04-2012, 03:57
I really liked that! Thanks.
I am way over my head with the tensegrity stands like WV and your's, but thanks for the info....
Grtz Johan
Did you ever build a bigger one? And how about a multi-hammock setup?
MacEntyre
08-10-2014, 06:20
Did you ever build a bigger one?
Nope... we used the strut material in building a rabbit run. ;)
The important thing is that by making the X Tensegrity stand we solved the problem with the previous Tensegrity stand. Just lash the struts at the intersection, so that each provides support for the other.
And how about a multi-hammock setup?
The X Tensegrity is simply a small 3 strut Tensegrity tipped over on it's side. If you build a large 3 or 4 stut Tensegrity stand, just orient it such that the struts cross right by each other. Essentially, that means making the base smaller... so you may need guys to keep it from tipping over. Anyway, with the struts touching at the crossing point, lash them there, and you are all set!
Latherdome
12-25-2016, 18:09
MacEntyre, you leave me hanging! :-) Here I was about to shell out for almost 50' of pricey carbon fiber poles to try to build a 2.5lb TurtleCarbon stand that would pack to 21.5" long, when I stumble last night onto this, that promises to do the job with just 27', fewer splices, more elaborate cordage, and way cooler looks! And you built a rabbit run instead? Did Big Turtle send by their thugs to stifle this idea before it threatened their hegemony?
When you tipped the stand up around the 10 minute mark, I wondered: couldn't the same structure hold 2-3 hammocks with some good staking?
GadgetUK437
12-25-2016, 18:35
Like this,
https://www.hammockforums.net/forum/attachment.php?attachmentid=104753&d=1426023913
from here,
https://www.hammockforums.net/forum/showthread.php/20209-Tensegrity-stand-for-multiple-hammocks/page8
Latherdome
12-25-2016, 22:32
Like this, [snip] from here,
https://www.hammockforums.net/forum/showthread.php/20209-Tensegrity-stand-for-multiple-hammocks/page8
Well, that's sort of the prequel to this thread. It seemed like a great head of steam was building and then it fizzled 2.5 years ago. I was hoping to avoid the iterative prototyping process using relatively inexpensive materials we've seen here, that are too heavy or bulky to pack all day, and leap straight to a proven optimal design in carbon, amsteel, Dutch bits, which I think could come to around 25" and under 3 lbs and accommodate 1-3, whether in a hotel, a bedroom, on a beach, or a mountaintop. I suspect the raw materials cost of carbon makes a commercial product un-viable in consideration of the liabilities involved, but there's no markup or liability for DIY... Mmmm tubes: https://dragonplate.com/ecart/categories.asp?cID=263
MacEntyre
12-27-2016, 10:51
And you built a rabbit run instead?
Sorry! I should get three 9' aluminum poles, fabricate three unions, and make the final Tensegrity Stand.
The X Tensegrity Stand was made with 8' poles, and that is a bit short.
The 9' poles would be cut, but not in half... probably 3' and 6' pieces from each.
If the unions are strong, the 9' poles could be cut into (3) sections each 3' long, for better packing.
Or you could cut one pole into (3) sections 3' long, and the other two poles 3' and 6'... pack all the 3 footers, and use the 6 footers for hiking poles.
...couldn't the same structure hold 2-3 hammocks with some good staking?
Yes.
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.
Don't fall on it!
Latherdome
12-28-2016, 13:54
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=PVC-Fittings-6-ways&p_id=486-007&xm=on&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.
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...
142706
MacEntyre
12-30-2016, 07:59
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.
Latherdome
12-31-2016, 14:58
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:
142843
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.
Ever since the first postings about the 3 person tensegrity stand like 10 years ago, it seems that everyone assumes the lower triangle has to be smaller (and therefore the stand has to be staked out securely). But it doesn't.
You still want to connect the poles at their crossing point by lashing or with something like Latherdome's octahedron, because it makes things way stronger and/or you can use flimsier poles. But then you can think of it as really 6 separate poles making 2 pyramids stacked on top of each other with the upper one upside down. The lower poles don't have to be shorter than the upper ones at all. If you just extend the lower legs a foot or two, the points of the lower triangle will stick out beyond the hammock ridgelines. Then there's plenty of stability with even one person and it's totally freestanding. Minor increase in weight for peace of mind and more places you can set it up...
P.S. If you have a socket on top of the octahedron, you could hold a trekking pole in it to support the center of a large tarp covering the whole thing like a circus tent or "German scouting tent" so water doesn't collect.
P.P.S. You don't even have to have the same angle to the ground with the poles in each pyramid. For example, you could make the lower pyramid "shallow" to splay the legs out further at the expense of some height.