New Soft Robot Morphs From A Ground To Air Vehicle Using Liquid Metal

Eddie Gonzales Jr. – MessageToEagle.com – Imagine a small autonomous vehicle that could drive over land, stop, and flatten itself into a quadcopter.

The rotors start spinning, and the vehicle flies away. Looking at it more closely, what do you think you would see? What mechanisms have caused it to morph from a land vehicle into a flying quadcopter? You might imagine gears and belts, perhaps a series of tiny servo motors that pulled all its pieces into place.

Drone able to morph and bends using liquid metal. Credit: Virginia Tech

If this mechanism was designed by a team at Virginia Tech led by Michael Bartlett, assistant professor in mechanical engineering, you would see a new approach for shape changing at the material level. These researchers use rubber, metal, and temperature to morph materials and fix them into place with no motors or pulleys.

Getting into shape

Nature is rich with organisms that change shape to perform different functions. The octopus dramatically reshapes to move, eat, and interact with its environment; humans flex muscles to support loads and hold shape; and plants move to capture sunlight throughout the day. How do you create a material that achieves these functions to enable new types of multifunctional, morphing robots?

“When we started the project, we wanted a material that could do three things: change shape, hold that shape, and then return to the original configuration, and to do this over many cycles,” said Bartlett. “One of the challenges was to create a material that was soft enough to dramatically change shape, yet rigid enough to create adaptable machines that can perform different functions.”

To create a structure that could be morphed, the team turned to kirigami, the Japanese art of making shapes out of paper by cutting. (This method differs from origami, which uses folding.) By observing the strength of those kirigami patterns in rubbers and composites, the team was able to create a material architecture of a repeating geometric pattern.

Edward Barron, Michael Bartlett, and Dohgyu Hwang hold a piece of material that has been warped. Credit: Alex Parrish for Virginia Tech.

Next, they needed a material that would hold shape but allow for that shape to be erased on demand. Here they introduced an endoskeleton made of a low melting point alloy (LMPA) embedded inside a rubber skin. Normally, when a metal is stretched too far, the metal becomes permanently bent, cracked, or stretched into a fixed, unusable shape. However, with this special metal embedded in rubber, the researchers turned this typical failure mechanism into a strength. When stretched, this composite would now hold a desired shape rapidly, perfect for soft morphing materials that can become instantly load bearing.

Finally, the material had to return the structure back to its original shape. Here, the team incorporated soft, tendril-like heaters next to the LMPA mesh. The heaters cause the metal to be converted to a liquid at 60 degrees Celsius (140 degrees Fahrenheit), or 10 percent of the melting temperature of aluminum. The elastomer skin keeps the melted metal contained and in place, and then pulls the material back into the original shape, reversing the stretching, giving the composite what the researchers call “reversible plasticity.” After the metal cools, it again contributes to holding the structure’s shape.

The team’s work has been published in Science Robotics. Co-authors of the paper include graduate students Dohgyu Hwang and Edward J. Barron III and postdoctoral researcher A. B. M. Tahidul Haque.

Paper

news via Tech Xplore 

Written by Eddie Gonzales Jr. – MessageToEagle.com Staff