Tensegrity Wiki

https://tensegritywiki.com/index.php?title=Main_Page

by graderjs • 3 years ago

94 39 3 years ago

Hmmm, site seems a bit slow - must be the HN hug.

I love the bizarre contraptions/models made to demonstrate tensegrity, but they always seem very impractical. However, they've got pages on bicycle wheels and suspension bridges though the term "tensegrity" is rarely mentioned with them.

I do have issue with their description of bicycle wheels though:

It makes no difference where you compress the rim of the cycle wheel; the load is equally distributed through the spokes to the hub.

The load is not distributed equally, but the spokes directly below the hub will be under greater compressive stress (though still in tension).

dcanelhas• 3 years ago

Since the spokes would buckle at the merest whiff of compressive stress, we can assume the hub to be "hanging" by the spokes that attach to the top of the wheel. However, if that was the only force acting on the wheel, it would allow the rim to deform into an ellipse, so the spokes that radiate sideways are also under tension to hold the rim into a circular shape.

I think the description of even load might not be too far off, but I haven't looked at it in depth.

ndsipa_pomu9• 3 years ago

we can assume the hub to be "hanging" by the spokes that attach to the top of the wheel

That's a common misconception of how bike wheels work, but it's more accurate to consider the hub to be propped up by the reduction in tension in the spokes below it.

There's a more detailed analysis here: https://www.astounding.org.uk/ian/wheel/

From these figures, I conclude that it is perfectly reasonable to say that the hub stands on the lower spokes, and that it does not hang from the upper spokes. It is also wrong to say that the force distributes all around the rim and all the spokes contribute to holding up the hub - over a third of the spokes have an effect that pulls the hub down!

agumonkey• 3 years ago

I wonder if bike wheels are considered tensegrity structures.

Also, could homes leverage this for seismic proofing ?

ndsipa_pomu9• 3 years ago

See https://tensegritywiki.com/index.php?title=Bicycle_Wheel

The answer appears to be both yes and no.

Also, could homes leverage this for seismic proofing ?

Likely not practical to use pure tensegrity design (i.e. each element is purely in tension or compression) and the open nature of tensegrity structures would leave little privacy. However, reinforced concrete combines the compressive strength of concrete with the tensile strength of iron to make a strong building material (e.g. for resisting earthquakes) though a tensegrity design wouldn't have any need for reinforced concrete as the compressive struts would never be in tension or under bending stress.

mjhay• 3 years ago

The section about criticism of a bike wheel as a tensegrity structure is vague. As the other sections say, all spokes are always under tension, and the rim is always under compression. There's only one compressive member (the rim), so I guess you can't really say the compressive components are disconnected.

The only way I could see it failing the definition is with the hub. The hub has different parts under compression and tension, in that the flanges where the spokes attach are under tension, but the axle exerts compression on the bearings underneath it, even though almost all of the hub body should be under net deviatoric tension.

IAmLiterallyAB• 3 years ago

I didn't know what tensegrity was and the Wiki is... very unhelpful. Almost cult like. Here it is verbatim:

What is tensegrity?

Tensegrity is the way the world organizes itself. Build or buy a model and experience it yourself!

Why learn about it?

Whatever your goal in life, it's good to understand how the world works. Tensegrity, discovered about 60 years ago, is a new way of understanding forces at play. Whether you are building a business, designing household objects, building robots, or trying to live sustainably in a resource-challenged world, tensegrity offers innovative ways of thinking about how parts and wholes interact.

What is Tensegrity Wiki, The Encyclopedia of Tensegrity?

This website is a wiki dedicated to exploring the field of tensegrity, a subset of energetic-synergetic geometry. It is intended to use the "power of crowds" to fine-tune and make available accurate knowledge about tensegrities. This includes all aspects of tensegrity including structural tensegrity sculptures, dynamically adjusting tensegrity robotics, biotensegrity as expressed in cellular mechanics, biotensegrity as expressed in mammalian anatomical fascial/bone structure, tensegrity therapy as a set of mind-body practices, tensegrity as it illuminates ancient philosophies of harmony, music and dance inspired by tensegrity, and so on.

dale_glass• 3 years ago

It means "tensional integrity". Structures that are held stable by tension.

Things like this:

https://img.mrvcdn.com/g/fb/kf/S9514e6355f474ca4b09db84ad4e3...

It's a thing that's only being held in that position by chains under tension.

It looks very weird at first, but after looking closer it starts making sense. For the upper piece to fall for instance, the outer chains would have to collapse, but the middle chain makes that impossible. For it to tilt, one chain would need to get longer, but it can't. Etc.

IshKebab• 3 years ago

Yeah that's insane. Tensegrity is a portmanteau of tension and integrity. It literally just means structures that achieve integrity (rigidity) through tension. Ideally in a confusing looking way and to support a coffee table.

ndsipa_pomu9• 3 years ago

Wikipedia probably explains it better https://en.wikipedia.org/wiki/Tensegrity

I'd blame Buckminster Fuller for the cult-like descriptions of it as he did seem to be as much a marketer as a designer.

My take-away from tensegrity is that it's a design whereby the elements are either purely tensile (strings) or purely compressive (struts) which makes a structure very light and strong. However, it's often a lot simpler (cheaper) to make a design that uses modern materials that function well under compression and tension.

8note• 3 years ago

The pure compression isn't a big deal on it, but the big thing vs a truss is that the compression elements don't touch each other, only tensions elements

HDevo• 3 years ago

While I agree that the home page and navigation could be better structured, there is at least a Basic Concepts page linked in the sidebar. That page links to much more helpful description: https://tensegritywiki.com/index.php?title=Tensegrity

whiddershins• 3 years ago

Structural forces, roughly speaking, are compression, tension, and shear.

Compression is like stacking bricks. Bricks are very strong in compression, but very weak with tension, which is why we have arches and flying buttresses.

Steel is great for both which is why we have skyscrapers.

Compression forces are easier to intuit, so for example we tend to think if the human body as a stack, each bone resting on the one below it.

But in reality the human body is also tensegretic. All the muscles and tendons and ligaments pull you upright. This is also how we have suspension bridges.

A purely tensegretic structure would use no compressive force, you can create a tensegretic dodecahedron with chopsticks and rubber bands, it will have no two chopsticks touching each other, yet it maintains the structure.

You can probably find instructions for how to make one in 10 minutes at home and you might achieve a different intuition about how real world structures operate.

algorias• 3 years ago

Some good answers in the sibling comments. Perhaps the canonical example in the human body is the spinal column. It is extremely flexible with many degrees of freedom, while remaining stable to external shocks. This is because it has many small muscles connecting vertebrae to each other, over both short and long ranges (you know, kinda like a skip list).

damontal2• 3 years ago

I first heard of this as a sort of practice based on the writings of Carlos Castaneda. He wrote these very interesting and entertaining books about his anthropological studies of a Yaqui Indian shaman which were later revealed to be mostly made up. The books were so compelling that they drew true believers and a practice of movements dubbed Tensegrity was developed.

graderjs3• 3 years ago

Hahah, that's hilarious. I wonder if Buckminster Fuller knew about this when he coined the word? Or maybe he didn't coin it...maybe these guys got there first! haha :p ;) xx;p

damontal2• 3 years ago

There are entries for Castaneda on that wiki.

scrollbar• 3 years ago

That's what I thought of too. Just finishing reading Sorcerer's Apprentice - a kind of slog of a read written by one of the insiders of the Castaneda cult. I wonder if he "borrowed" the name...

graderjs3• 3 years ago

Is the guy really a cult leader tho? Hahaha, this thread is totally not about this guy but OK: I guess he’s got a cult on your mind if you keep thinking of him while this is actually about something else. Wouldn’t that be your problem tho, not about this guy?

EamonnMR• 3 years ago

Thrilled to see a wiki off of fandom.

xwdv• 3 years ago

My most surreal encounter with tensegrity was at a dinner party I was invited to in Dubai where an entire dining table was built around the concept. It was a massive table that seated about 25 people, looked like it defied gravity and only the chains kept it from floating away. To this day I’m still not sure how it worked. I could not build such a table even after having seen it.

The other people there were all influencers with at least a million or two in followers and some people had 10s of millions and with verification across multiple social media platforms. I was fortunate enough to be friends with one of these people due to our history in the Silicon Valley startup scene in the early 2010s.

The food was otherworldly, things I hadn’t seen before and may never see again, not really even sure what I ate. If you looked closely you might see hints of slavery and human trafficking, and prostitution discussed fairly openly among some guests while on a balcony overlooking the city lights. A vape pen comes in handy for getting your foot in the door to some conversations.

knaik94• 3 years ago

On Aliexpress I found out some alternative lego compatible brick sets that take advantage of the Tensegrity principle. Here's a picture of the house from Up and a mini millenium falcon. [1][2] They were not the easiest sets to build and keeping the balance in the correct position is hard, but it's fun.

The tolerance for the lengths to maintain the correct tension is a lot tighter than I expected. I imagine it would be a little more forgiving if everything is scaled up. I saw some space related sets and floating boats from the anime One Piece as well on there. What is in and out of stock is not very consistent, and I haven't seen some of the sets I own in a while. I did not have to use glue but I did have to get creative in terms of wrapping things in a certain way, or connecting the things to an alternate hole. The manual was optimisitc.

There are some really interesting user created designs you can buy instructions for, but not every set from aliexpress is there.

https://rebrickable.com/mocs/?q=tensegrity

[1] https://twitter.com/Knaikk/status/1487889972816453635

[2] https://twitter.com/Knaikk/status/1655580332341489673

dugmartin• 3 years ago

If you are interested in Bucky Fuller's tensegrity models you can explore them online here:

https://collections.carli.illinois.edu/digital/collection/si...

Or if you happen to be in Carbondale, Illinois, USA you can view them in person at the SIU Museum: https://museum.siu.edu/. Bucky was a "University Professor" (a position created for him) at SIU in the 60s/70s.

porkbeer• 3 years ago

Kinda sad to see Buckys work reduced to this mess.

tudorw• 3 years ago

have a look at biotensegrity too :)

tristanho• 3 years ago

Related: I've ordered this build-your-own tensegrity kit, which is really fun to build https://pretenst.com/

Very different to read about vs get a feel for them in your hands.

They also have an open-source simulator for the structures https://github.com/elastic-interval/pretenst https://pretenst.com/app/#construction;Halo-by-Crane (written in Rust!)

Tensegrity Wiki

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