Tensegrity Wiki
tensegritywiki.com
tensegritywiki.com
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.
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.
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.
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.
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
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).
I think the description of even load might not be too far off, but I haven't looked at it in depth.
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!
> 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.
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.
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.
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.
[1]https://www.parktool.com/en-us/blog/repair-help/wheel-tensio...
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.
From this article: https://www.cyclist.co.uk/in-depth/the-science-behind-spokes
> 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.’
> 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.
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).
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!)
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.
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 guess it’s a big tent! Hahaha
Also, could homes leverage this for seismic proofing ?
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.
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.