Drone Leverages Bird-Like Design for Versatile Flight

Researchers from Ecole Polytechnique Fédérale de Lausanne have developed a drone equipped with bird-like legs that can walk, hop, and leap into the air. This design significantly expands the range of environments in which unmanned aerial vehicles (UAVs) can operate. The study was published in the journal Nature.

The phrase "as the crow flies," commonly used to describe the shortest distance between two points, has been taken quite literally by the Laboratory of Intelligent Systems (LIS), led by Dario Floreano at EPFL’s School of Engineering, with the development of RAVEN (Robotic Avian-inspired Vehicle for multiple ENvironments).

Inspired by perching birds like crows and ravens, which frequently transition between the air and the ground, the drone's multipurpose robotic legs allow it to take off independently in areas previously inaccessible to winged drones.

Birds were the inspiration for airplanes in the first place, and the Wright brothers made this dream come true, but even today’s planes are still quite far from what birds are capable of. Birds can transition from walking to running to the air and back again, without the aid of a runway or launcher. Engineering platforms for these kinds of movements are still missing in robotics.

Won Dong Shin, Ph.D. Student, Laboratory of Intelligent Systems, Ecole Polytechnique Fédérale de Lausanne

The design of RAVEN aims to minimize mass while maximizing gait versatility. Shin, inspired by the proportions of bird legs and extensive observations of crows on the EPFL campus, developed a set of unique, multipurpose avian-inspired legs for a fixed-wing drone.

To achieve an optimal balance between leg complexity and the drone's total weight (0.62 kg), Shin combined mathematical models, computer simulations, and experimental prototypes. The resulting legs position heavier components closer to the drone’s body, while a system of springs and motors mimics the function of avian tendons and muscles.

The legs feature two articulated structures, with lightweight, bird-like feet using a passive elastic joint to support a range of walking, hopping, and jumping movements.

Translating avian legs and feet into a lightweight robotic system presented with design, integration, and control problems that birds have solved elegantly throughout evolution. This led us to not only come up with the most multimodal winged drone to date but also to shed light on the energetic efficiency of jumping for take-off in both birds and drones.

Dario Floreano, Professor and Head, Laboratory of Intelligent Systems, Ecole Polytechnique Fédérale de Lausanne

Better Access to Deliveries or Disaster Relief

Previous robots designed for walking were too heavy to jump, while those built for jumping lacked the ability to walk. RAVEN’s design addresses both challenges, allowing it to walk, cross gaps, and jump onto surfaces up to 26 cm high.

The team also tested various methods of flight initiation, including standing and falling take-off. They found that leaping into the air was the most effective way to utilize both potential energy (height gain) and kinetic energy (speed).

To adapt bird biomechanics to robotic locomotion, the LIS researchers collaborated with Auke Ijspeert from EPFL's BioRobotics Lab and Monica Daley's Neuromechanics Lab at the University of California, Irvine.

These results represent just a first step towards a better understanding of design and control principles of multi-modal flying animals, and their translation into agile and energetically efficient drones.

Dario Floreano, Professor and Head, Laboratory of Intelligent Systems, Ecole Polytechnique Fédérale de Lausanne

The findings offer a lightweight design for winged drones that can navigate uneven terrain and take off from confined spaces without human assistance. This research also highlights the advantages and limitations of strong legs in birds that often transition between air and ground.

These capabilities could enable the use of these drones for delivery in restricted spaces, disaster relief, and inspection. To improve landing across various conditions, the EPFL team is already working on enhancing leg control and design.

“Avian wings are the equivalent of front legs in terrestrial quadrupeds, but little is known about the coordination of legs and wings in birds – not to mention drones. These results represent just a first step towards a better understanding of design and control principles of multimodal flying animals, and their translation into agile and energetically efficient drones,” Floreano said.

NCCR Robotics and the European Union’s Horizon 2020 funded the study.

Video Credit: Ecole Polytechnique Fédérale de Lausanne

Journal Reference:

‌Shin, W. D., et al. (2024) Fast ground-to-air transition with avian-inspired multifunctional legs. Nature. doi.org/10.1038/s41586-024-08228-9.