Scientists have built a shape-shifting robotic drone that transforms from a ground vehicle to a quadcopter, an advance that may lead to novel machines that can perform diverse functions under different conditions and self-heal after being damaged.
The researchers from Virginia Tech in the US first developed a multifunctional material that could change shape, hold the shape, and return to the original configuration, and to do this over many cycles.
“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,” Michael Bartlett, assistant professor in mechanical engineering, said in a statement.
The scientists then turned to the Japanese art of kirigami, which involves making shapes out of paper by cutting, to create a structure that could be morphed.
Then they developed an endoskeleton made of a low melting point alloy (LMPA) embedded inside a rubber skin.
When a metal is stretched too far, it becomes permanently bent, cracked, or stretched into a fixed, unusable shape, however, the special liquid metal embedded in rubber could turn this typical failure mechanism into a strength, researchers say.
This composite, when stretched holds a desired shape rapidly, a feature which is perfect for soft morphing materials that can become instantly load bearing.
To return the structure back to its original shape, the team incorporated soft, tendril-like heaters next to the alloy mesh that cause the metal to be converted to a liquid at 60 degrees Celsius (140 degrees Fahrenheit).
The composite’s elastomer skin keeps the melted metal contained, and at the same time it also pulls the material back into the original shape.
This reverses the stretching and gives the soft material “reversible plasticity,” researchers say, adding that returns to the original structure after the composite cools.
“These composites have a metal endoskeleton embedded into a rubber with soft heaters, where the kirigami-inspired cuts define an array of metal beams. These cuts combined with the unique properties of the materials were really important to morph, fix into shape rapidly, then return to the original shape,” study co-author and graduate student Dohgyu Hwang said.
Using this kirigami-inspired alloy design, researchers could create complex shapes, from cylinders to balls to the bumpy shape of the bottom of a pepper.
They say the material could change shape very quickly, in some cases under one-tenth of a second, and it could also be healed multiple times by melting and reforming the metal endoskeleton if the composite broke.
Applying the new material with onboard power, control, and motors, the team created a functional drone that autonomously morphs from a ground to air vehicle.
Researchers also created a small, deployable submarine that could retrieve objects from an aquarium by scraping the belly of the sub along the bottom.
“We’re excited about the opportunities this material presents for multifunctional robots. These composites are strong enough to withstand the forces from motors or propulsion systems, yet can readily shape morph, which allows machines to adapt to their environment,” said Edward J. Barron, another graduate student and co-author of the study.
“We demonstrate this material through integration with onboard control, motors, and power to create a soft robotic morphing drone, which autonomously transforms from a ground to air vehicle and an underwater morphing machine, which can be reversibly deployed to collect cargo,” the scientists wrote in the study.
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