Robotics

New rubbery film rockets into the air like a grasshopper

The researchers liken the functionality of their material to the way in which grasshoppers store energy in their legs before leaping
The researchers liken the functionality of their material to the way in which grasshoppers store energy in their legs before leaping

In a serendipitous discovery, engineers at the University of Colorado Boulder (CU Boulder) have developed a material that first deforms and then shoots into the air when it is heated. The researchers say the material could one day be used to help soft robots jump or lift objects.

As part of a study, researcher Tayler Hebner, who earned her doctorate degree in chemical and biological engineering at CU Boulder in 2022, and her colleagues were looking at the different ways in which a class of materials known as liquid crystal elastomers acted when exposed to heat. These materials are the solidified and elastic version of the liquid crystals used inside displays such as those in laptop screens or TVs, and may even one day be used in windshields to protect pilots from getting temporarily blinded by laser pointers.

“We were just watching the liquid crystal elastomer sit on the hot plate wondering why it wasn’t making the shape we expected," Hebner said. "It suddenly jumped right off the testing stage onto the countertop. We both just looked at each other kind of confused but also excited.”

Further investigation with colleagues from the California Institute of Technology revealed that the cause of the leaping behavior was due to the fact that the film, which was about the size of a contact lens, consisted of three layers. When heated, the top two layers shrink faster than the bottom layer, causing it to form a cone shape. Eventually due to a buildup of tension, the cone inverts, striking the surface on which it is being heated and snapping up into the air. In tests, the researchers found that in just six milliseconds, the film could soar to almost 200 times its thickness.

“When that inversion happens, the material snaps through, and just like a kid’s popper toy, it leaps off the surface,” said study co-author Timothy White, professor of chemical and biological engineering at CU Boulder. In this regard, the research echoes that carried out at Harvard University in 2020 in which the design of a popper toy inspired an actuator that might one day help soft robots get across tough terrain.

The researchers compare the action of the film to the way in which grasshoppers achieve their impressive displays of leaping and believe it too could have a place in the development of soft robots – those machines that operate without metallic or other hard materials such as those that walk as fast as humans using light and magnetic fields.

“In nature, a lot of adaptations like a grasshopper’s leg utilize stored energy, such as an elastic instability,” said White, “We’re trying to create synthetic materials that emulate those natural properties.”

As part of uncovering the structure of the films being used, the research team discovered that their material could also be made to jump by cooling instead of heating it. They also say that by adding legs to the film, the material can gain directional control. While the team admits that the material may not become a primary locomotion source in soft robots, they feel that the discovery helps add to the knowledge of how to make these innovative machines function better, as it shows the potential of materials to store and then release energy under certain conditions.

“It’s a powerful example of how the fundamental concepts we study can transform into designs that perform in complex and amazing ways,” said Hebner.

The research has been published in the journal Science Advances. You can see the material in action in the video below.

Source: CU Boulder

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3 comments
TpPa
many - many years ago my Dad came home from doing some contract work for 3M and came home with a handful of little toys and gadgets, one of them was a so called coin the size of a quarter with stickers on it to make it look as such. It was made of two diff metals, and it was concaved a bit, you pushed that concave the other way and warmed the metals with your fingers for they would stary that way. Then you would set in on a cool counter top and it would go back to it's original shape shooting it up a foot or more. It was maybe 1/16" thick so that would be a jump closer to 400 times it's thickness.
windykites
I have watched more exciting videos!
Sergius
This interesting combination of liquid crystal alignment with the flexibility of an elastomer could mean a revolution in modern sensors, so necessary for autonomous systems...