Flapping wings produce lift and thrust in bio-inspired aerial robots, leading to quiet, safe, and efficient flight. However, to extend their application scope, these robots must perch and land, a feat widely demonstrated by birds. Despite recent progress, flapping-wing vehicles, or ornithopters, are to this day unable to stop their flight.
Now, researchers at the Swiss Federal Institute of Technology Lausanne (EPFL) have developed a method that allows a flapping-wing robot to land autonomously on a horizontal perch using a claw-like mechanism.
To validate their method, researchers developed a prototype flapping-wing robot (ornithopter), which has a wingspan of 1.5 meters (59 inches) and weighs just 700 grams. Designed by Raphael Zufferey, a postdoctoral fellow at Switzerland’s EPFL research institute, the robot was built and tested in collaboration with colleagues at the University of Seville as part of the European Union GRIFFIN project.
The ornithopter was equipped with a single carbon-fiber-bodied, spring-loaded mechanical claw, a fully on-board computer, and a navigation system, which was complemented by an external motion-capture system to help it determine its position. The ornithopter’s leg-claw appendage was finely calibrated to compensate for the up-and-down oscillations of flight as it attempted to hone in on and grasp the perch.
The claw was designed to absorb the robot’s forward momentum upon impact and close quickly and firmly to support its weight. Once perched, the robot remains on the perch without energy expenditure. The bistable claw appendage can grasp a branch within 25 milliseconds and re-open.
Zufferey and his colleagues succeeded even with all these factors to consider, ultimately building not just one but two claw-footed ornithopters to replicate their perching results. For future work, the researchers are already thinking about how their device could be expanded and improved, especially in an outdoor setting.
“At the moment, the flight experiments are carried out indoors because we need to have a controlled flight zone with precise localization from the motion capture system,” said Zufferey. “In the future, we would like to increase the robot’s autonomy to perform perching and manipulation tasks outdoors in a more unpredictable environment.”
This work paves the way for the application of flapping-wing robots for long-range missions, bird observation, manipulation, and outdoor flight.
- Raphael Zufferey, Jesus Tormo-Barbero, Daniel Feliu-Talegón, Saeed Rafee Nekoo, José Ángel Acosta and Anibal Ollero. How ornithopters can perch autonomously on a branch. Nature Communications, 2022; DOI: 10.1038/s41467-022-35356-5