Harvard's RoboBee project has been at the forefront of microrobot technology for years. We've watched with interest as subsequent developments have allowed the tiny machine to fly, swim, hover, perch and lose its tether. In a new development, RoboBee has become the first microrobot to achieve controlled flight using soft actuators – the artificial muscles that let the machine move.
The main benefit of soft actuators is improved resilience – already a strength of microrobots thanks to their low mass. Having soft artificial muscles lets the RoboBee avoid damage when crashing into walls, falling to the floor or bumping into other RoboBees.
The difficulty is making soft actuators powerful enough to achieve flight while granting sufficient control for the microrobot to be able to hover. Harvard's soft actuator technology is thought to be the first to make these breakthroughs.
The new developments is the work of the Harvard John A. Paulson School of Engineering and Applied Science (SEAS) and the Wyss Institute for Biologically Inspired Engineering. The researchers built on existing electrical soft actuator technology using 100-milligram-elastomers that deform when exposed to an electric field.
It was by improving the conductivity of the electrodes applying the field that the researchers were able to match the performance of the rigid actuators traditionally used in microrobots, achieving a power density of 600 watts per kilogram.
Further, the researchers achieved improved stability, building a lightweight airframe to house the microrobot with a piece of thread used to prevent the actuator buckling – something that soft artificial muscles have been historically wont to do.
The researchers demonstrated the technology in both a two-wing and a four-wing RoboBee. The two-wing variant can take off from the ground, while the four-wing model, complete with two actuators, can continue to fly despite sustaining several collisions in an obstacle-strewn environment.
They even flew two four-wing models to show they can continue flying after colliding with each other. They have also built an eight-wing model using four actuators.
These soft-actuator versions of the RoboBee are currently tethered when in flight, with power provided via offboard amplifiers and navigation via an external motion capture setup.
The researchers hope the technology could have applications in search and rescue, potentially allowing robots to actually fly into rubble and confined spaces.
They say the soft actuators are easy to assemble and replace, but the next challenge is to improve their efficiency, which is behind typical microrobots with rigid actuators. If efficiency can be matched, then according to senior research author Robert Wood, "the sky is the limit for what robots we could build." There's also the thorny issue of that tether to do away with once more.
The team's research paper, Controlled flight of a microrobot powered by soft artificial muscles, has been published in the journal Nature. You can see these latest RoboBees in action in the video below.
Source: Harvard John A. Paulson School of Engineering and Applied Science (SEAS)