Tensegrity Explained

This is actually one of those videos where I explain a thing by making a 2D version of that thing because the 2D version is easier to understand since these two videos are linked in the description and on the card. The difference with this video is that it's not a hydrodynamic mechanism it's a structure a type of structure called a

tensegrity

structure like this beautiful

tensegrity

table here I got from a company called Sterling Engines Dot Code in the UK. It's also where I got my Sterling engine, which you'll recognize from my video. Explaining the entropy link in the description for that, as well as studying engines.

Credit UK does not sponsor this video. I just really like the things they do, but anyway in this video I'm going to explain how a segregated tent look table like this works. making a 2D version, but first let's clarify what the criteria for a tensegrity structure is. The first thing is that you need to have components that are in compression and components that are in tension, so these rods here are in compression and they are compressing. They are made of aluminum, they are very good at that and they have these cables here that are in tension, the cables are really good in tension, the other criterion for a tensegrity structure is that there must be at least two separate parts that are in compression that they are completely separated from each other and only joined by parts that are in tension, so here for example the bottom and the top are separated from each other and do not touch except for these wires that are in tension, so this is An example of a tensegrity structure also has these six wooden rods that are in compression, they are only joined by these elastic parts in tension, so the wooden parts do not touch each other at all and I will tell you a little more about this later because there are some really interesting things about this particular structure, but first let's get back to the table like it's really counterintuitive, right?

Everything is held together by cables, how is that possible? And that's what I want to explain in this video, so here's the 2D version and I built it with rubber bands instead of cables because I want you to see how they bend and stretch when you try to collapse the structure. So why this structure? It's stable, any way you try to collapse the structure it turns out that at least one of the rubber bands ends up stretching and when you stretch a rubber band it gets pulled back, so for example when I try to collapse the structure in this direction, This the elastic band stretches and restores the structure to its equilibrium position and we can look at individual elastic bands, for example, if we try to keep this elastic band and this elastic band the same length and we try to collapse the structure, what would happen?

Well, we need to do this, um, something like that and, of course, in doing so, we're stretching this elastic band in a similar way, if we try to keep these two elastic bands the same length, you know, we're trying to collapse the structure, this one is stretching or If we try to keep these two the same length as they would be, we'd end up doing something like that, wouldn't we? If you try to distort this tensegrity structure, stretching the elastic bands will restore it to its balanced position just to make the point. I've replaced two of the elastic bands with rope, so we can't really stretch these now and Look, we don't have as much freedom of movement.

I can do that and I can do that, and any direction I go with the rubber band ends up stretching a 2D tensegrity structure isn't actually stable in three dimensions, which is why we have it propped up on this tilt that keeps everything from falling apart, so a 2D tensegrity table requires two external cables to remain stable, but to be stable in three dimensions you need to add a third cable like this here and that makes sense intuitively it's the same reason a stool requires three legs to be stable is that old saying two points fix a line three points fix a plane so no matter which direction you try to push the table top on it will stretch the wires in such a way that it restores the balance of the table, which it means there's actually a little bit of lateral movement like that because there's some flexibility in the cables and it's a really strange feeling because you know you can move it laterally like that but it's very strong in the up and down position.

It's very strange. You can even set up some simple harmonic motion on top. It's not that great. In fact, with this design you can adjust the stiffness of the cables. if I let out a little bit of stiffness in these, you get a much wobblier table. Having said all that, it is actually possible to create a stable three dimensional tensegrity table with just two external cables, this one is made from lego and you can see why the center of mass is here. The entire top section wants to, quote, tilt this way, but it can't because of these taut cables and it's only stable as long as you don't push it in this direction.

It is not an official Lego. product, but if you search for tensegrity lego you will find one if you want to make one yourself, strictly speaking, for a structure to be classified as tensegrity, it must follow an additional criterion which is that all parts that are in compression must only be in compression and that's actually not true here, so you have that curvature there, so this part is experiencing a bending force, so there will be a part on the inside that is in compression and a part on the outside that is in tension , which is fine because the target is probably aluminum and aluminum has pretty good tension, but this structure is a tensegrity structure even under strict criteria.

All compression tips are straight. All points in tension are also straight, so points in compression only feel compression. and tension only feels tension, so by building the structure this way you can make it much stronger because the parts that are good for compression only experience compression, the parts that are good for tension only experience tension, you can also make it stronger light. I can use less material to get the same strength as this basswood is good in compression, but if I bend it like this it experiences stress at the top and breaks, which is why NASA is designing a planetary lander based on this exact configuration. because it's incredibly robust, you know you can bounce it, you can land it on a planet, it can get crushed a little bit, but if you put a payload in the middle maybe it will survive and by changing the length of the cables under tension you can move the structure. around robotically because tensegrity structures optimize for strength and lightness and because evolution often optimizes things like strength and lightness, it wouldn't be unreasonable to expect to find tensegrity structures in nature and, of course, In fact, if you look at the bones in your body that are under compression and the muscles, tendons and ligaments in your body that are under tension, you sometimes find them in arrangements similar to tensegrity and, of course, architects and engineers have given good use to tensegrity structures, for example, the Curlipa Bridge in Brisbane, Australia.

Alright, last thing on the subject, if you take a little bit of blue tack and you squeeze it in one direction, it widens in the other direction, which makes intuitive sense and most things behave that way, but not all structures are like this, some structures, when you squeeze them in one direction, will actually contract in the other direction it is called oxetic structure and some tensegrity structures also behave that way, for example the lander structure of the POT. Look, if I separate these two rods, maybe you can see very slightly that the green and red rods also separate, so there I go to the tensegrity structures.

I actually showed the tensegrity structure without even realizing it in a previous video, the first episode of Five Cool Things, so check it out if you haven't already. I have a few more skill sharing course recommendations for you that they are sponsoring. In this video, you've heard me talk about online video learning before because I came to the conclusion that when you're learning something new, it can be a real false economy to try to do it on your own to get ahead on your own. Looking online and things like that, I've realized that if you can anticipate your learning experience, like investing time at the beginning, literally just an hour or so with an expert, someone who really knows what they're talking about, then It will simply be enhanced. your learning once you're practicing on your own here are the recommendations creativity unleashed interesting because it doesn't focus on one specific thing, but if you want to post things online of a creative nature, there are some general lessons you can learn really interesting course hand coding your first website, you know, I think it's very important if you want to create websites to get your hands dirty, get into the code and see how everything works, even if you end up using a cms, how to use notion to organize Your notion of life is so good that if you haven't tried it, you have to try it, but it's not very obvious from the first moment all the ways you can use it, so I really think that a course is useful for the first 1000 people. to go to my special url school dot forward slash stevemold0121 you will get a free trial of Skillshare Premium with no strings attached and it's only ten dollars a month after that, the link is also in the description, so check out Skillshare today.

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