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.
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.
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
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.
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.
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.
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).
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
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.
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).
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.
> 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.
> 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!
It's fine to subtract out the preload if you're talking about stiffness rather than simply strength, and that's a valid way of using words and a valid way of analyzing a bike wheel, but not so uniquely-valid that hanging from the top spokes can be called a misconception.
Yeah, the link ignoring preload (but using preload as an argument as to why the spokes don’t buckle) to say the lower spokes hold the bike up isn’t convincing to me. The lower spokes are still in tension during normal loads, therefore they are pulling the hub down, not pushing it up. And the rubber band thought experiment is no longer required when these rope-like spokes are now available.[1]
> A wheel with wire spokes works the same as one with wooden spokes except that
the built-in force in its spokes is different. In a wooden-spoked wheel, force is
transmitted from the ground to the hub by compressing the bottom spoke. This
spoke becomes shorter as it furnishes the upward force to the hub. As in a
wooden-spoked wheel, the bottom spokes of a wire wheel become shorter under
load, but instead of gaining in compression, they lose tension. With the same
load, the net change in force is the same for both wheels. The algebraic sum of
negative and positive forces (compression and tension) is the same.
> That the bottom spokes support the wheel need not be taken on faith. An
experiment will show that only a few spokes at the bottom of the wheel are
affected by a vertical load. The relative tension of a spoke can be found by
plucking it like a guitar string. The pitch of a spoke, just as the pitch of a guitar
string, increases with more tension and decreases with less tension.
I’m still not convinced that a significantly large decrease in tension of a few lower spokes and more distributed increase in tension of other spokes means that the bottom ones are logically pushing up on the hub. That difference in forces is just the nature of a point load being reacted to at a distant location. If you push on a string or spoke that is in tension, it doesn’t push back, it just pulls less.
Maybe the issue in trying to describe this system is that saying the wheel hangs from the upper spokes is also not a totally correct simplification. It’s more correct to say all the spokes are in tension and in equilibrium with each other.
The forces aren't distributed equally around the spokes. There's barely any change in force to the spokes above the hub, and the majority of the change in force when putting a load on a wheel is in the three or so spokes below the hub.
For the hub to be considered hanging from the rim, then there should be a significant change in the tension of the upper spokes when the wheel is loaded, but that does not happen. It may sound funny, but the reality is that there is only a significant change in tension in the bottom spokes.
That you see more change in tension in the bottom few spokes is irrelevant to the explanation of how the wheel supports a bike. My professional experience is this area (preload of structures, beard turning grey) and I had to think a bit to gain confidence in my thinking and explanations. I'm not replying to prove you are wrong, I am an expert in this field and I am enjoying trying to elaborate on my reply.
I understand that there is significant change (reduction in tension) in only a few spokes, but there _must_ also be a corresponding increase in tension to other spokes to keep equilibrium. Not distributed equally but absolutely distributed in a way that keeps equilibrium of forces within the wheel. It's distributed among many more spokes because that's how structures work. The rim's stiffness determines how this happens.
A mechanical engineer designing a wheel knows that the wheel fails as soon as the bottom spokes have zero tension and fail by buckling. And the analysis works if you assume no buckling, ignore most of the spokes and just check the "red areas" in FEM or hand calculations and make sure the compression forces are less than the design preload. But this doesn't mean that in the physical world, the bottom spokes are "pushing up the bike". It's just a convenience of the problem.
So let's simplify things. Imagine if there was only one spoke on the top and one spoke on the bottom, and the wheel is locked from rotating. Consider each spoke is a tension spring in tension, because they are. They can provide a tension force but are almost as useless as a string in compression (indeed, one of my comments linked to a new type of spoke that is literally a string). Each spoke is installed by tightening it to stretch it slightly and make a preload according to Hooke's law. Each spoke is tightened to get about 1000N of tension preload[1]. Note here that it's impossible to do this exercise with only one spoke, at least two spokes are required to tension them.
State 1: The bike and wheel are held off the ground, and the wheel has negligible mass so each spoke has 1000N of tension.
State 2: A person gets on the bike, resulting in a 500N force at the bottom of the wheel. This is roughly correct for a 100kg person, if front and rear wheel are loaded equally. The bottom spoke will compress and have a resulting 500N of tension preload. The top spoke will stretch and have a resulting 1500N of tension preload. Both spokes are still in tension and _pulling_ the hub to the wheel. But clearly the top spoke is stretched more than State 1 and the bottom spoke is stretch less than state 1. More stretch of a spring = more force, but less stretch of a spring = less force. How can it be said that the bottom spoke is holding the wheel up if basic physics says it is providing less force than before?
State 3: leave the top spoke and cut the bottom spoke. The top spoke's preload goes to zero and the top spoke will actually have its tension reduced from 1500N to 500N.
State 4: leave the bottom spoke and cut the top spoke. The bottom spoke's preload goes to zero and the bottom spoke will experience 500N in compression, immediately buckle and the rider will fall.
There's a 500N force from the ground pushing up on the rim. The bottom spoke will thus have a 500N reduction in tension which balances and results in no movement of the hub. The top spoke doesn't change in tension as it's still balancing the 1000N of the bottom spoke and rim forces.
State 3 is a different scenario and in that instance, the hub is hanging from the rim. I don't see how it helps with the comparison as that's nothing to do with a wire wheel. In reality, you'd expect to see the rim buckle as the forces are now being applied purely at the top rather than opposed spokes distributing the 1000N between top and bottom.
I agree with state 4, but again, that's a different system and doesn't help clarify what's happening.
> While it’s easy to believe a bicycle spoke would simply collapse under the weight of bike and rider, he goes on to explain that the tension created in a spoke during the wheel building process (called ‘pre-tension’) is what allows the lower spokes to bear the load without buckling, as they would if there was no pre-tension. ‘Every spoke on the unloaded wheel has a tension of the order of 100lb [445N]. When the axle is pressed towards the ground with a force of 100lb, the only significant effect on spoke tensions is to reduce those directly below the hub – typically, one reduces to about 50lb and spokes to each side of that one reduce to about 75lb. This is exactly what one would see with solid wooden spokes like an old wagon wheel – the bottom one would carry 50lb and those to either side of it would carry 25lb. The difference with wire spoked wheels is that a wire spoke cannot carry a compression load – it will collapse. So all spokes are ingeniously pre-tensioned. A wire cannot carry a compression load of 50lb, except when it already carries a tension load exceeding that.
> ‘Of course a bike wheel will collapse if the upper or horizontal spokes are removed,’ Papadopoulos adds. ‘But that is essentially because the altered structure has a very different load path, and furthermore is unable to supply the required pre-tension. We can’t use that collapse to conclude that the typical wheel carries load through the upper spokes.’
If you make a free body diagram and check the sum of vertical forces you’ll find that you cannot change the tension in one spoke without a corresponding equal (in total) reaction in others. I reduced it down to two spokes so that this becomes trivial to do.
> There’s vigorous disagreement over whether a bike in effect hangs from the upper spokes (those above the hub as you view the bike from the side) or rather is being supported by the lower ones, acting like tiny pillars. ‘The latter view, odd as it seems, is definitively the case,’ says Jim Papadopoulos from Northeastern University’s College of Engineering in Boston, USA, and the co-author of Bicycling Science.
> While it’s easy to believe a bicycle spoke would simply collapse under the weight of bike and rider, he goes on to explain that the tension created in a spoke during the wheel building process (called ‘pre-tension’) is what allows the lower spokes to bear the load without buckling, as they would if there was no pre-tension. ‘Every spoke on the unloaded wheel has a tension of the order of 100lb [445N]. When the axle is pressed towards the ground with a force of 100lb, the only significant effect on spoke tensions is to reduce those directly below the hub – typically, one reduces to about 50lb and spokes to each side of that one reduce to about 75lb. This is exactly what one would see with solid wooden spokes like an old wagon wheel – the bottom one would carry 50lb and those to either side of it would carry 25lb. The difference with wire spoked wheels is that a wire spoke cannot carry a compression load – it will collapse. So all spokes are ingeniously pre-tensioned. A wire cannot carry a compression load of 50lb, except when it already carries a tension load exceeding that.
I'm not sure if you realize that you're agreeing with me.
Go ahead and apply enough force to the hub to exactly cancel out the preload. Then when the bottom spoke has zero tension, cut it, and observe that the bicycle is unaffected.
Is your position that the load is then being carried by a spoke that doesn't even exist?
If so that's fine, but it is a stretch to call any other view a misconception.
In your scenario, I'd expect the wheel to either collapse or to spread the load to the remaining spokes below the hub. It's not a separate system where you can remove a spoke without affecting the whole structure (though you can remove some spokes and the wheel will still function, but won't be as strong).
The easiest way to test it is to pluck the spokes when no-one is sat astride a bike to determine the rough tension/pitch of the spokes (choose just one side if it's the rear wheel as spokes will be at different tensions for the different sides if the wheel is dished). Then get a friend (or enemy) to sit on the bike and again pluck the spokes to see if the extra load has resulted in an increase of tension in the upper spokes (i.e. hanging from the top of the rim) or whether the lower spokes have a decrease in tension (i.e. supported by the bottom spokes with a compressive load).
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.
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.
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.
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
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...
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?
> 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.
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.
The fork, which connects to the axle, is under compression, though. Since that connects to the wheel rim purely through tensile members, I think it's fair game to call it a tensegrity structure.
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.