Researchers at the Harvard Microrobotics Laboratory at the Harvard John A. Paulson School of Engineering and Applied Science (SEAS), along with the Wyss Institute for Biologically Inspired Engineering, have developed a RoboBee powered by soft artificial muscles. The microrobot is capable of crashing into walls, falling on the ground, and colliding with other RoboBees without suffering damage. In what is a big moment for robotics, the RoboBee is the first microrobot powered by soft actuators that is able to achieve controlled flight.
Yufeng Chen is first author of the paper and a former graduate student and postdoctoral fellow at SEAS.
“There has been a big push in the field of microrobotics to make mobile robots out of soft actuators because they are so resilient,” said Chen. “However, many people in the field have been skeptical that they could be used for flying robots because the power density of those actuators simply hasn't been high enough and they are notoriously difficult to control. Our actuator has high enough power density and controllability to achieve hovering flight.”
The research was published in Nature.
One of the problems that the researchers dealt with was power density. They looked to the electrically-driven soft actuators that were developed in the lab of David Clarke, the Extended Tarr Family Professor of Materials. The soft actuators are created by using dielectric elastomers, which are soft materials that have strong insulating properties. When an electric field is applied, the dielectric elastomers deform.
After improving the electrode conductivity, the actuator was able to be operated at 500 Hertz. This is similar to previously used rigid actuators in robots.
One of the other issues with soft actuators is that the system often becomes unstable. To get past this, the researchers developed a lightweight airframe. It consisted of a piece of vertical constraining thread in order to prevent the actuator from buckling.
Within the small scale robots, the soft actuators are able to be swapped out and assembled easily. The researchers developed multiple different models of the soft-powered RoboBee in order to showcase the various flight capabilities.
One of the models has two wings, and it can take off from the ground. However, this model has no further control. A four-wing, two actuator model is capable of flying in a crowded environment. Within a single flight, the RoboBee is able to avoid multiple collisions.
Elizabeth Farrell Helbling is a former graduate student at SEAS, and she co-authored the paper.
“One advantage of small-scale, low-mass robots is their resilience to external impacts,” she said. “The soft actuator provides an additional benefit because it can absorb impact better than traditional actuation strategies. This would come in handy in potential applications such as flying through rubble for search and rescue missions.”
Another model is the eight-wing, four-actuator RoboBee. It is capable of performing controlled hovering flight, which is the first time it has been demonstrated by a soft-powered flying microrobot.
The researchers are now looking to increase the efficiency of the soft-powered RoboBee. It still has a long way to go before catching up to traditional flying robots.
Robert Wood is a Charles River Professor of Engineering and Applied Sciences in SEAS. He is also a core faculty member of the Wyss Institute for Biologically Inspired Engineering and senior author of the paper.
“Soft actuators with muscle-like properties and electrical activation represent a grand challenge in robotics,” says Professor Wood. “If we could engineer high-performance artificial muscles, the sky is the limit for what robots we could build.”