Autonomous ornithopter can land like a bird

Researchers have developed a unique landing gear that makes it possible for flapping-wing ornithopters to land like birds.

Although a bird perching on a branch appears to be an easy manoeuvre, the act of perching actually involves a complex balance of timing, high-impact forces, speed, and precision. Because of the precision needed, no flapping-wing ornithopter has been able to master this move – until now.

Researchers from the Swiss Federal Institute of Technology Lausanne have developed a unique landing gear that now makes perching possible. This was built and tested in collaboration with colleagues at the University of Seville, where the 700-gram ornithopter itself was developed as part of the European project GRIFFIN.

The work, ‘How ornithopters can perch autonomously on a branch,’ is published in the journal Nature Communications.

Advantages of the ability to perch

“This is the first phase of a larger project. Once an ornithopter can master landing autonomously on a tree branch, then it has the potential to carry out specific tasks, such as unobtrusively collecting biological samples or measurements from a tree. Eventually, it could even land on artificial structures, which could open up further areas of application,” said Raphael Zufferey, a postdoctoral fellow in the Laboratory of Intelligent Systems (LIS) and Biorobotics ab (BioRob) in the School of Engineering and first author of the study.

The ability to land on a perch could provide a more efficient way for ornithopters, which have a limited battery life, to recharge using solar energy, potentially making them ideal for long-range missions.

“This is a big step toward using flapping-wing robots, which as of now can really only do free flights, for manipulation tasks and other real-world applications,” Zufferey added.

Modifying ornithopters

The team managed many factors to ensure that an ornithopter could land on a perch without any external commands. For instance, the ornithopter had to be able to slow down significantly as it perched, whilst maintaining flight, and the claw needed to be strong enough to grasp the perch and support the weight of the robot, without being so heavy that it could not be held upward.

“That’s one reason we went with a single claw rather than two,” Zufferey stated.

The robot also needed to be able to perceive its environment and the perch in front of it in relation to its own position, speed, and trajectory.

To achieve this, the ornithopter was equipped with a fully onboard computer and navigation system, which was complemented by an external motion-capture system to help it determine its position. The claw was calibrated to balance the up-and-down oscillations of flight as it attempted to home in on and grasp the perch, and was designed to absorb the robot’s forward momentum upon impact and to close quickly and firmly to support its weight. Once landed, the robot should remain on the perch without energy expenditure.

Despite the many factors that needed to be taken it account, Zufferey and his colleagues successfully built, not just one, but two claw-footed ornithopters to replicate their perching results.

Future uses of the device

The team is already looking ahead and considering how their device can be expanded and improved, particularly 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 localisation from the motion capture system. In the future, we would like to increase the robot’s autonomy to perform perching and manipulation tasks outdoors in a more unpredictable environment.”

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