Upgrading the Bee’s Knees
Harvard's RoboBee was given crane fly-inspired legs and smarter controls for softer landings that won't damage its fragile hardware.
Insect-inspired aerial robots have the potential to sidestep a lot of issues we presently experience with larger aerial vehicles, such as the difficulties they have with operating in confined spaces and their limited flight times. We recently took a look at a tiny hybrid robot that flaps its wings while hopping on a pogo stick-like leg to conserve energy, for instance. But miniature robots that are fully airborne have some problems of their own when it comes time to land.
These problems are compounded significantly by the light weight of the tiny machines. Because they are so light, interactions between the ground and their flapping wings or rotors result in the development of vortices of air that bounce them around violently. As often as not, this causes them to make an awkward or hard landing, which can easily damage their fragile components.
Harvard researchers have experienced this particular issue frequently when bringing their own tiny flying robot, called the RoboBee, in for a landing. The best solution they had previously was to get the RoboBee lined up for a landing, then cut the power while it was still in the air. This minimized the formation for ground effect vortices, but also guaranteed a drop from a dangerously high altitude. With this approach, they won some and they lost some.
On balance, this is not exactly an ideal solution, so the team has more recently taken a new approach to the problem. Inspired by the legs of the crane fly, which is known for its soft, graceful landings, they have created lightweight, shock-absorbing landing gear for the RoboBee. To go with this upgraded hardware, the researchers have also developed an updated control algorithm that helps the RoboBee to gradually decelerate as it approaches the ground, further softening the impact.
The new landing gear mimics the long, jointed legs of crane flies, which can absorb the impact forces of landing through compliant, segmented joints. By exploring different leg lengths, joint numbers, and placements, the team created a design that maximizes energy dissipation while minimizing the RoboBee’s tendency to bounce or tumble on contact.
From a control standpoint, the robot was upgraded to better navigate the destabilizing ground effect air currents. The new algorithm allows the RoboBee to anticipate and adjust for these forces, initiating a smooth deceleration pattern just before landing.
In tests, the enhanced RoboBee demonstrated accurate, repeatable landings on both rigid surfaces and on more unpredictable natural materials, like leaves. This dual-pronged advance — bioinspired mechanics and smarter controls — helps shield the robot’s fragile piezoelectric actuators, which are notoriously easy to damage.
Currently, the RoboBee still relies on off-board control and power systems, but safe and controlled landing is a key step toward full autonomy. With improved landing capabilities, the researchers are one step closer to cutting the tethers and giving the RoboBee the freedom to operate autonomously in real-world environments.
