RoboBee: Micro flapping wing robot lands safely on plant leaves

Researchers at the Harvard Microrobotics Laboratory have developed a tiny flapping-wing robot modeled on the crane fly, which can land on plant leaves with its filigree landing frame. RoboBee is equipped with a special landing control system and its legs are articulated to enable it to land safely.

The new RoboBee, a further development of the original RoboBee, which is already several years old, weighs just 0.1 g and has a wingspan of 3 cm. The wings are driven as flapping wings by piezoelectric actuators. The problem with such systems is the ground effect that occurs during landings, air turbulence caused by the flapping wings, which can lead to instability during landing. However, a crash during landing would be fatal for the small flying robot, as the actuators and delicate wings used are very sensitive and could be damaged as a result.

“In the past, if we wanted to land, we had to switch off the flying vehicle slightly above the ground, simply drop it and pray that it would land upright and safely,” explains Christian Chan, a doctoral student who led the mechanical redesign of the flying robot.

Absorbing impact energy with a mechanical landing frame and special landing algorithm

To ensure a safe landing, the scientists looked at a biological crane fly, as described in the study “Sticking the landing: Insect-inspired strategies for safely landing flapping-wing aerial microrobots”, published in Science Robotics. These insects can perform elegant landings on a wide variety of surfaces. To achieve this, the researchers first had to minimize the speed of the robot as it approached the landing surface to dissipate the impact energy as quickly as possible during landing. The scientists took the legs of the crane fly as a model, which consist of long, articulated appendages that can cushion landings. The researchers recreated the system, tested various materials and finally integrated it into their RoboBee.

In addition to the mechanical requirements, the scientists also adapted the flight control of the small flying robot. In doing so, they were also guided by the landing behavior of crane flies, which accelerate from a hovering flight, decelerate towards the landing target and touch down at a low-impact speed. The remaining impact energy is then absorbed by the mechanical landing gear.

The researchers added the necessary control sequence and evaluation of the sensors to their external control system, as the RoboBee is still connected to it by cable. In addition to the control signals, it also receives its energy via this.

Equipped in this way, the RoboBee can land precisely on various surfaces – including plant leaves. However, the cable connection turned out to be an obstacle. The researchers now want to free RoboBee from this shackle and miniaturize the sensors, control system and power supply so that they can be built directly into the flying robot. RoboBee should then also be able to fly autonomously so that it can be used for artificial pollination in agriculture, for example. However, the challenges involved in miniaturizing the components are extremely high. They are considered the triple Holy Grail for tiny flying robots.

(olb)