tensegrity

6 Articles

Build This Halloween-Themed TensEGGrity Sculpture

October 21, 2022 by 5 Comments

Tensegrity sculptures are fun things, and often sold as office desk toys or scientific novelties. You can build your own too, and [seabirdhh] has whipped up a fun holiday-themed version.

The first part to build is the egg-hat-stand. This consists of the base of the structure, with the “hat” of the egg character hanging in the center. The other half of the structure is built separately, with the rest of the “egg head” sitting in a cup in the bottom of the upper structure. A series of nylon threads are then tied between the components. These can then be tensioned to give the structure its shape, allowing the egg’s “hat” to hover above its “head”. [seabirdhh] passes the nylon threads through small pieces of rubber that allow the tension to be adjusted just right. Too little and the structure falls down, but too much, and it will bend over time. Tuning it carefully is key.

It’s a fun build, and a cheap way to experiment with tensegrity concepts at home. You can even use these same techniques to build a quadcopter, or apply them in the world of LEGO. Video after the break.

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Quadcopter With Tensegrity Shell Takes A Beating And Gets Back Up

November 5, 2020 by 11 Comments

Many of us have become familiar with the distinctive sound of multirotor toys, a sound frequently punctuated by sharp sounds of crashes. We’d then have to pick it up and repair any damage before flying fun can resume. This is fine for a toy, but autonomous fliers will need to shake it off and get back to work without human intervention. [Zha et al.] of UC Berkeley’s HiPeRLab have invented a resilient design to do so.

We’ve seen increased durability from flexible frames, but that left the propellers largely exposed. Protective bumpers and cages are not new, either, but this icosahedron (twenty sided) tensegrity structure is far more durable than the norm. Tests verified it can survive impact with a concrete wall at speed of 6.5 meters per second. Tensegrity is a lot of fun to play with, letting us build intuition-defying structures and here tensegrity elements dissipate impact energy, preventing damage to fragile components like propellers and electronics.

But surviving an impact and falling to the ground in one piece is not enough. For independent operation, it needs to be able to get itself back in the air. Fortunately the brains of this quadcopter has been taught the geometry of an icosahedron. Starting from the face it landed on, it can autonomously devise a plan to flip itself upright by applying bursts of power to select propeller motors. Rotating itself face by face, working its way to an upright orientation for takeoff, at which point it is back in business.

We have a long way to go before autonomous drone robots can operate safely and reliably. Right now the easy answer is to fly slowly, but that also drastically cuts into efficiency and effectiveness. Having flying robots that are resilient against flying mistakes at speed, and can also recover from those mistakes, will be very useful in exploration of aerial autonomy.

[IROS 2020 Presentation video (duration 14:16) requires free registration, available until at least Nov. 25th 2020. One-minute summary embedded below]

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A Levitating Lamp Without Magnets

June 10, 2020 by 9 Comments

If you think of levitating objects you probably think about magnets but this is not what [Aaron Hung] used to build his levitating LED lamp. To be fair, his lamp is not really levitating but merely generates the illusion through the principles of tensegrity. We have featured a number of tensegrity structures over the last months but this is maybe the first time somebody has used it to build a daily-use item.

In his instructable [Aaron Hung] points out that according to Earnshaw’s theorem magnetic levitation using static magnetic fields like those of permanent magnets is actually impossible. If you are interested, the Wikipedia article also explains why floating superconductors and the Levitron toy do not contradict this theorem. (TL;DR: they’re dynamic.)

Coming back to [Aaron Hung]’s tensegrity lamp, the construction is rather simple and only requires an Arduino Nano, a Neopixel ring, a 9 V battery some wood or cardboard, and fishing line. The tensegrity part of the lamp consists of two similar pieces of laser-cut wood which are held together by fishing line so that the top part seems to float in mid-air. Normally, tensegrity structures are very fragile so [Aaron Hung] added some extra lines for stability which allowed him to hang the lamp from the top section without collapsing the whole structure. After coding some animations for the Neopixel ring and adding a paper lampshade the project was finished.

We would like to see more tensegrity versions of classic DIY projects and it was fun to see that similar objects were already built from Lego.

[Video after the break].

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A Lego Tensegrity Structure

April 28, 2020 by 14 Comments

Tensegrity structures are an impressive demonstration of how to achieve mechanical stability through tensile forces. Since the topic is currently trending it was probably only a matter of time before somebody like [Alexandre Thiery] came with the idea to build a tensegrity model from Lego.

In the GIF below that [Alexandre Thiery] shared on his Twitter account you can see his kids admiring the model. Tensegrity structures consist of elements under constant tension – in most cases strings – and components under compression, in this case beams of Lego. By combining these elements, one can build stable structures that seem to float in midair. A simple daily-life example for tensegrity is a balloon where the skin is the tensional element while the air inside is the component under compression.

[Alexandre Thiery] has come up with the clever idea to simply clamp the strings between two Lego blocks. This certainly paves the way for other more complicated Lego-based tensegrity structures that we will likely see in the future. [Alexandre Thiery] also recently extended his model by stacking an identical structure on top of it.

If you do not have any Lego at hand just fire up your 3D printer to make a tensegrity physics toy or a floating table.

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Table Held Up By Strings Teaches Physics

March 25, 2020 by 34 Comments

If you’ve never heard of a tensegrity structure, you should stop now and watch the video below. In it, [The Action Lab] shows a 3D printed table that is held up only with strings. We didn’t say suspended by strings but held up. Or so it appears. The model is from Thingiverse, but it is one of those things you have to see to believe.

The basic idea is pretty simple. Strings have a lot of tensile strength but collapse under the slightest compressive force. The arrangement of strings puts the force on the center string which is essentially hanging — the force is pulling the string down. The other three strings aren’t just for show, though, they keep the structure from tipping over in any one direction.

There are actually real-life examples of these kinds of structures. The video shows the Skylon at the Festival of Britain as one example and an Australian bridge. The video also makes the point that the human body uses tensegrity, since tendons are very similar to the strings in the model.

This would be a great experiment for a homeschooler or even kids cooped up in quarantine. The print itself doesn’t look very challenging, although the assembly might be a bit tricky.

This isn’t the first structure like this that we’ve seen. If the talk about tendons makes you think this might be useful in robotics, you’d be correct.

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Building Your Own Tensegrity Structure

November 29, 2019 by 37 Comments

It seems that tensegrity structures are trending online, possibly due to the seemingly impossible nature of their construction. The strings appear to levitate without any sound reason, but if you bend them just the right way they’ll succumb to gravity. 

The clue is in the name. Tensegrity is a pormanteau of “tension” and “integrity”. It’s easiest to understand if you have a model in your hand — cut the strings and the structure falls apart. We’re used to thinking of integrity in terms of compression. Most man-made structures rely on this concept of engineering, from the Empire State Building to the foundation of apartment building.

Tensegrity allows strain to be distributed across a structure. While buildings built from continuous compression may not show this property, more elastic structures like our bodies do. These structures can be built on top of smaller units that continuously distribute strain. Additionally, these structures can be contracted and retracted in ways that “compressionegrities” simply can’t exhibit.

How about collapsing the structure? This occurs at the weakest point. Wherever the load has the greatest strain on a structure is where it will likely snap, a property demonstrable in bridges, domes, and even our bodies.

Fascinated? Fortunately, it’s not too difficult to create your own structures.

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