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.
I believe bicycle wheels also work in the same way.
The axel hangs from the top spokes rather than sitting on the lower spokes.
Similar way. Tensegrity has some structure in compression. In the table above it’s the y structures connecting the central string. A bike wheel is largely tension unless you count the rim
Well, it’s all tension if you don’t count the rim.
Isn’t the rim part of the structure and under compression?
Make a bike wheel out of string and let us know how it works. My guess is it won’t take torsion real well as you are fighting a lot of mechanical advantage from the hub to the tire. Breaking I can see working pretty well but accelerating may be an issue. It would be cool looking if not practical.
Acceleration and deceleration are the same axial forces, just opposite. accelerating will be harder though because the string has way more give than metal spokes do you’ll be absorbing that give on each push of the pedal
I am lazy and I usually coast to stops so it is questionable if the friction on the hub is more than the air friction on the tire, not to mention the friction on the spokes themselves. If you have rim brakes yes, I can see the hub wanting to keep turning and giving you grief and if you have coaster breaks the hub would slow down and the rim turning would give you grief. If you just let off and coast to s stop, if you are lucky, the losses will be near the same. I used to ride my bike around a lot in the wintertime and the mantra was never change anything if you can help it. Make every move as smooth as slowly and smoothly as you can.
Just had to look into this and found:
https://www.pinkbike.com/news/newmen-components–first-look.html
Check this out. It seems like these dudus are using polyethylene rope as bicycle spokes:
https://gearjunkie.com/berd-bicycle-spokes-soft-uhmwp-polymer
Made one of these for my son after watching a TKOR video. He bought it to school and confused all his friends. Pretty cool.
This was Buckminister Fuller’s “Tensegrity” portmanteau. You used to be able to buy models at science museums.
That was a blast from the past! I remember his book, “operating instructions for planet earth,” very eco minded.
He also loved the term “dymaxion” (I thought his dymaxion house was the inspiration for the housing in the Jetsons, but never found a source)
Tensegrity is responsible for geodesic domes. Fuller’s work.
Related by the man and some of the math, but I don’t think his domes (geodesic polyhedra) are derived from tensional integrity.
The kid toy is a “Skwish” designed by the late Tom Flemons and made by Manhattan Toys. Fuller made up the catchy name, bu artist Kenneth Snelson may have made the first tensegrity; he built scores of them. TensegrityWiki.com is a great source for more info, and for applications in biology look at biotensegrity.com or search biotensegrity, Stephen M Levin, Graham Scarr, Danièle-Claude Martin or see research by Donald Ingber at Harvard’s Wyss Institute
Closed in spaces, parallel plane suspension ends, and extra braces ruin illusion. Thin clear fishing line or sewing thread help. Empty aluminum cans arent very heavy. Clear container with liquid or maybe with pennies or …
I guess is arguably better then printing another baby yoda.
I’ve made one of those, that very design, too. Assembly was tricky, but I achieved it by first setting one triangular plate on a table, then a soda can on top of the plate, then the other plate on top of the can, to have a stable and consistent spacing between the two plates.
Then I tied the corner strings on, with the can still in between the plates.
Once the strings were tied tightly, I removed the can, glued on the two “arms” into their positions, and tied on the final string, pulling it tight.
This method worked for me on the first try.
If you are going to build a small model you could likely get away with making a loop in the string and putting a toothpick in it and rotating the toothpick to make a “splice” of the size required to get the right tension. Once you are there, put a drop of superglue on the “splice” and snip most of it and the toothpick away.
This too:
https://hackaday.com/2019/11/29/building-your-own-tensegrity-structure/
That is the second to last link in the post.
How did you know?
(oops)
I couldn’t wrap my head around this when I saw it last week. It’s a pretty awesome and simple design in fairness.
But makes up for beautiful structures. I am really tempted to use it in interior design/furniture making. Might mess around a bit with the idea.
I wish I was home and had my shop. I want to make a stool. I am thinking 2 5 sided pyramids (4 “sides” and a base) set half of one face apart from each other. Screw eyes in the corners and centers and plastic bailing twine for the “string”. Something to play with when I get home and back to my tools.
It’s only common sense. No mystery here.
Only common sense… The most poignant mystery is how these senses, if you will, are so frequently absent or scantly considered that the implicit or explicit is stated as common. Such structural understanding is likely common for students of its specific study, whereas a doctoral professor of literary history of many years in practice might be utterly stupefied. I wonder if it is common. Is it possible that it should be considered common for its everyday use & interaction? If there is indeed that frequent an encounter with what perhaps should be common, yet the sense of knowledge and understanding is not present, do we feel it accurate & acceptable to continue with common for a descriptor? If so, then why is this device still so intriguing after years of presence? Simply tension and compression, of arguably wide understanding, applied in rather uncommon ways.
A bicycle wheel of spokes sans rim would cease to be a wheel, no? Remove the spokes and keep the rim? Absurd!! It’s common sense!
Good point. As human beings we are terrible statisticians, every child thinks the world has always been the way it is and laughs when older people tell them about things that came before. Think about some of the groundbreaking science of the past: Isaac Newton writing down F=ma for the first time was a revolution, but to us it’s obvious. Were the people of the past stupid to not know these things? No, it’s just that things we think are common sense aren’t.
Saabman
> The axel hangs from the top spokes rather than sitting on the lower spokes.
Nope.
A bicycle wheel is a pre-stressed structure. The load both sits on the lower spokes (reduces the tension) and hangs from the upper spokes (increases the tension).
Which is why if your spokes are not tight enough, the wheel can taco.
Neat, I’d like to see that as a small coffee table, stand, whatever kind of furniture. It wouldn’t be very practical but would look cool in your front room.
The Baseball hall for the 1996 Atlanta Olympics is constructed the same way. As a structural engineer I spent more time looking at the roof than at the Basketball.
This would be a good speaker stands….👍
I just made a model coffee table like this…it was a prototype but I will make a real one soon….