Many birds are capable of transitioning effortlessly between flying and ground movement. Although their forelimbs have evolved into wings mainly for flying, their hindlimbs serve multiple functions. This includes walking, hopping, leaping, and generating the propulsion required for launching into the sky. These capabilities have inspired engineers to explore multimodal functionalities in aerial robots to expand their range of applications across diverse environments.
In the similar efforts, EPFL researchers have developed RAVEN (Robotic Avian-inspired Vehicle for multiple ENvironments), which uses its bird-inspired multifunctional legs to jump rapidly into flight, walk on the ground, and hop over obstacles and gaps similar to the multimodal locomotion of birds.
The design of RAVEN focuses on enhancing gait diversity while significantly reducing overall mass. Drawing inspiration from the elegant proportions of bird legs – along with meticulous observations of crows on EPFL’s campus – LIS PhD student Won Dong Shin created custom, multifunctional avian legs for a fixed-wing drone. He utilized a mix of mathematical models, computer simulations, and practical testing to strike an optimal balance between the complexity of the legs and the total weight of the drone (0.62kg).
The resulting leg design positions heavier components near the ‘body,’ while a combination of springs and motors replicates the strong tendons and muscles found in birds. The lightweight, bird-inspired feet consist of two articulated structures that incorporate a passive elastic joint, allowing for a range of postures for walking, hopping, and jumping.
“Translating avian legs and feet into a lightweight robotic system presented us with design, integration, and control problems that birds have solved elegantly over the course of evolution,” says Dario Floreano, EPFL’s School of Engineering. “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 takeoff in both birds and drones.”
RAVEN features an innovative design that enables it to walk, navigate uneven terrain, and leap onto surfaces as high as 26 centimeters. In their research, scientists explored different modes of flight initiation, including takeoffs from a standing position and free-falling. They found that jumping into flight made the most efficient use of kinetic energy (speed) and potential energy (height gain).
Collaborating with Auke Ijspeert from EPFL’s BioRobotics Lab and Monica Daley’s Neuromechanics Lab at the University of California, Irvine, the LIS researchers have successfully integrated avian biomechanics into robotic movement, paving the way for remarkable advancements in robotic locomotion.
The findings not only highlight the high costs and advantages of robust legs in birds that frequently transition between air and ground, but they also offer a lightweight design for winged drones that can move on rough terrain and take off from restricted locations without human intervention. These capabilities make such drones invaluable for inspection, disaster response, and delivery in constrained environments.
The EPFL team is now working on improved design and control of the legs to ensure seamless landing across diverse settings.
“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 says.
Journal reference:
- Won Dong Shin, Hoang-Vu Phan, Monica A. Daley, Auke J. Ijspeert & Dario Floreano. Fast ground-to-air transition with avian-inspired multifunctional legs. Nature, 2024; DOI: 10.1038/s41586-024-08228-9