Tensegrity World

Definition

Tensegrity, or tensional integrity is defined on wikipedia as:

… a structural principle based on a system of isolated components under compression inside a network of continuous tension, and arranged in such a way that the compressed members (usually bars or struts) do not touch each other while the prestressed tensioned members (usually cables or tendons) delineate the system spatially.
https://en.wikipedia.org/wiki/Tensegrity

I would describe it as way of designing structures that rely on tension, rather than compression for their integrity.

Examples

My favourite example is the Manhattan Skwish toddler toy:

Swish Classic – Manhattan Toy – £14/$16

Available since 1992 – this award winning Skwish Classic, by Manhattan Toys has been entertaining and educating toddlers (and their parents!) for decades. What makes this toy so interesting, is that it’s built with tensegrity using elasticated bungee cords. This means the entire structure is flexible (squishy if you will!) and really very tactile and intriguing.

If you’ve ever played with one, you’ll know what I mean. If you haven’t and you want to understand tensegrity for yourself – get one!

If this isn’t yet a design classic, it should be. Robby builds furniture and sculptures based on tensegrity principles. This is a great example because it’s clear that none of the solid (in-compressible) pieces touch. It’s the tension in the wires that gives this pieces its integrity.

A 3D printed “Impossible Table” based on tensegrity principles.
Design on thingiverse by Oak600, this print is by aiminqi

Currently (summer 2020) youtube is awash with video of people making tensegrity tables based on this design. Also known as “impossible tables” the weight is transferred from the top to the base via tension in the centre string, the outer strings provide stability. See below for more details on how these impossible tables work.

History

The term Tensegrity was coined by Buckminster Fuller in 1955 as a portmanteau of “tensional integrity”.

Richard Buckminster Fuller holding up a tensegrity sphere in 1979.
The Buckminster Fuller Institute

However, it was Kennith Snelson, one of his students at the time, who discovered it in 1948. He preferred the term floating compression, but I guess tensegrity is catchier.

Chapter 2 Tensegrity: 60 Years of Art, Science, and Engineering ... — The First Tensegrity Structure of Snelson (1948)

Kenneth Snelson, Sculptor Who Fused Art, Science and Engineering ... — An undated photo of Kennith Snelson – the actual discovered of tensegrity.

If you’d like to dig deeper into the controversial origins of tensegrity, you could do worse than reading this research paper on the topic.

How “Impossible” tables work

Lewis Matheson of @Physics Online does a far better job of explaining these structures using lego than I ever could with the written word. Take it away Lewis:

What isn’t tensegrity?

Tensegrity can mean different things to different people, but in my opinion a true tensegrity structure must:

be stable even if turned upside down or on it’s side (i.e. it does not depend on gravity for integrity).
rely on tension (at a push I’d allow magnetism) for integrity
contain at least two independent/separated in-compressible beams/components (they should “float”)
be pre-stressed

For instance, this is not tensegrity:

The system is not stable if turned upside down (it’s relying on gravity). And there is no seperation between the base and the bottle, the bottle is clearly being help up by compression.

Neither is this:

For the love of God I cannot figure out how this Tensegrity is ...

This isn’t tensegrity at all – it’s a trick! the photo is actually upside down, with the block hanging from the plate.

This one doesn’t even claim to be tensegrity – it’s an “impossible table” alright, but the top it held up with clear acrylic (the edges of which appear to have been photo-shopped out in that thumbnail!).

A collection of the best tensegrity table build videos from across youtube.

this video is a two for one – it has a sculpture and a table. It’s a little unfinished as they’re not stained or polished, and they stress test the table past it’s limit pretty much as soon as it’s built! That said, it’s a great demonstration of what can be done in a short space of time. Oh, and they only use a single string/rope!

I like how simple this is – basic tools (mitre saw, hack saw and orbital hand sander) and an easy to follow build. This one is made using chain for strength, but I think it could benefit from some way of adjusting the tension on the chains.

I was in two minds about posting this as a DIY table, but that has more to do with my lack of metal working equipment and skills than it does the video. This table is a beast, made of huge steel box section. It might not be the easiest to make, but it’s certainly sturdy!

This is a small desk ornament / table – the plant pot gives a good idea of it’s scale. It might not be a large tensegrity table, but the build demonstrates amazing craftsmanship and he even shares his “oops” moment. I especially like that he explained what knot he used to tension each of the four outer lines (a taught-line hitch).

This one is less of a table in the traditional sense, and more of a desk sculpture. It’s worth checking out though because the centre “tension” on one of them is fine using magnets – magtegrity?

this person takes the magnet idea from above to another level by embedding the magnets inside the structure. A painstaking build, but an epic (if tiny) result!

This built is a little disappointing, not least because he doesn’t show the finished item in use (there are also some questionably unsafe uses of a router too!). It does feature the ability to tension the chains though – which could help with stability, it’s just a shame he doesn’t show how well that works (or not!).

It’s getting pretty clear after watching this many videos that large tensegrity tables are not very functional, they simply wobble too much and have the potential to be knocked over.

That said, both of those issues might be able to be addresses by the use of racking. I’m going to find some tensegrity structures featuring diagonal supports (and ideally chains) to see if they can reduce or even eliminate the wobble.

The wobbliness in the above tensegrity tables doesn’t seem to be an issue when it comes to tensegrity chairs though:

It’s nice to watch someone using traditional tools and reclaimed wood. This chair turned out really nicely – though I think there a bit too much rope, that maybe detracts from the structural rope elements. Regardless, Amir is a pleasure to watch!