Sustained flight of an untethered flying-insect-inspired robot named the RoboBee X-Wing has been demonstrated in a paper in Nature this week. The small robot is less than five centimetres long, weighs just 259 milligrams, and might be useful for environmental monitoring or navigation in confined spaces.

Flying vehicles have high energy requirements, especially at small scales. Commercially available power sources, such as lithium-ion batteries, can weigh up to several times the desired mass of an insect-sized vehicle; as a result, such robots have needed to be tethered to off-board power supplies. Solar cells are an attractive alternative power source, but for state-of-the-art vehicles untethered flight would require impractically large light intensities, around 5-7 times the intensity of the Sun.

Noah Jafferis, Farrell Helbling and colleagues address some of these issues with a vehicle design that builds on prior work. They improve the actuator efficiency and use four flapping wings (instead of two) to increase the lift force without substantially increasing the power requirements. Its thrust efficiency matches that of similarly sized insects. At the low voltages used in this experiment to improve the lifetime of the vehicle during testing, the robot achieves sustained untethered flight for approximately half a second.

Further improvements are needed to enable continuous outdoor flight, the authors note; the vehicle requires intense light to generate sufficient power for take-off (over three times the intensity of the Sun). However, they add that their vehicle has an extra payload capacity that could carry a larger power supply for future autonomous flight experiments.