Robots in Disguise

They may not be from the planet Cybertron, but some recently developed transforming robots are certainly more than meets the eye. That is because these tiny microrobots can not only fly, crawl, and walk, but also shift their shape. Implementing these types of capabilities in a robot that weighs just a few grams would normally be all but impossible, but thanks to a novel actuator design created by roboticists at Tsinghua University, we will have to reconsider what is possible for the tiniest of robots.

Working alongside colleagues from Beihang University, the Tsinghua team has developed a thin-film actuator that can both continuously morph its shape and lock itself into specific configurations. Each individual actuator can either relax itself into a flat sheet, or roll up like a tape measure. By strategically combining several of these actuators together, much more complex movements can be made. When a desired state has been reached, they can lock into place. And despite being light as a feather, the actuators can bear large loads, which allows them to serve as a strong backbone for all manner of transforming robots.

The actuators use a liquid crystal elastomer, which can precisely change shape when heated, to enable continuous, programmable deformation. It is this property that allows a robot to morph smoothly into different forms. To lock a shape once it has been formed, the system incorporates a shape memory polymer that stiffens when cooled, preserving the desired configuration without needing constant energy input. Both the morphing and locking processes are controlled electrothermally, meaning they respond to electrical signals that generate heat, making the entire system compact, efficient, and highly adaptable for small-scale, untethered robots.

To make the actuators, a silicone coating is first spun onto a silicon wafer. Then, a polyimide film is transfer-printed onto the substrate, and a copper layer is added using a combination of electron beam evaporation, photolithography, and wet-etching. The actuator is then precisely laser-cut into shape. When combined with sensors, motors, and Lego-like modular blocks, this actuator forms the backbone of a microrobot that measures just nine centimeters in length and weighs only 25 grams.

To demonstrate their technology, the researchers showcased morphable displays, customizable exoskeletons, and microrobots that can transform between a sports car, winged car, and van that were built with their actuators. The advancements seen in this work hint at potential future applications ranging from toys and educational tools to more serious uses in search-and-rescue missions and exploration of confined spaces.