Flapping Oscillatory Soft Robot Mimics Flying Insect

UCLA materials scientists have unveiled a new light-responsive, flapping actuator that functions like the natural contracting and relaxing muscle movements of insect wings. The innovation marks a major milestone in the development of autonomous, untethered robotic systems powered by light.

“High-power autonomous soft actuators are in high demand but have faced challenges, including their dependence on tethered power and control systems,” said study lead Ximin He, an associate professor of materials science and engineering at the UCLA Samueli School of Engineering. “We have designed a trilayer, light-driven, self-activated oscillation actuator that allows for untethered energy input and autonomous controls.”

A UCLA research study detailing the new actuator design was recently published in Nature Materials. In their experiments, the researchers saw a power output of 33 watts per kilogram — comparable to the amount produced by some flying insects and 275 times more powerful than previous demonstrations of flapping-wing actuators that utilize similar principles. The results suggest the design is a significant step toward generating enough sustained lift for a small aerial robot that flies much the same way some insects do.

“This work represents a significant leap in soft robotics by generating an autonomous oscillatory motion that’s exclusively fueled by a constant light source while also demonstrating an output power large enough to build practical, insect-sized flying robots,” said Ximin He.

The team’s actuator design features a pair of liquid crystal-elastomer layers of light-sensitive materials aligned to flex in opposite directions. Sandwiched between them is a neutral layer of a silicone polymer. When the actuator senses natural light, the top and bottom layers flap in alternating directions, mimicking insects’ flapping wing muscles. With constant light, the actuator demonstrated a flapping speed of up to 13 beats per second, or nearly 780 beats per minute.

Previous flapping mechanisms with light-sensitive materials have used either single or double flexing layers. The new design enables the actuator’s two layers to flex in sequence, powering an upstroke and counteracting downstroke while the neutral third layer allows for improved bending. The researchers dubbed the new mechanism FLaPTOR, short for “flapping trilayer oscillatory robot.”

“This work represents a significant leap in soft robotics by generating an autonomous oscillatory motion that’s exclusively fueled by a constant light source while also demonstrating an output power large enough to build practical, insect-sized flying robots,” He said.

In addition to conducting lift tests, the researchers also evaluated the actuator’s performance in several applications, including propelling a small boat (1.6 millimeters per second) and moving a robot back (0.76 mm/sec) and forth (2.5 mm/sec) across guidewires.

While the actuator’s response to natural light has its limitation, FLaPTOR can also utilize a broad range of the light spectrum, including blue, green, red, near-infrared and simulated solar light.

“The actuator’s demonstrated high power output using only natural light suggests that with further refinements of the light source, the device could be used in untethered, autonomous flight for small robots, about the size of a bee,” said Yusen Zhao, the study’s first author and a materials science graduate student advised by He.

Besides the potential for use in small flying robots, FLaPTOR could also be reconfigured to propel walking robots or robots that float on water. The design’s light-detecting properties could also be useful in sensing or energy-conversion applications.

The paper’s other authors include graduate students Zixiao Liu, Pengju Shi and Yichen Yan, postdoctoral scholar Chi Chen and Ph.D. graduate Yousif Alsaid — all current or former members of He’s research lab at UCLA. He is also a member of the California NanoSystems Institute at UCLA. The study was funded by the Air Force Research Laboratory and the Office of Naval Research.