RAVEN, a Drone That Can Hop Like a Bird
RAVEN (Robotic Avian-inspired Vehicle for multiple ENvironments) © Alain Herzog CC BY SA
The majority of drones used today rely on rotors for flight. Most of these drones have four rotors, while larger drones may have six to eight rotors. This design provides drones with ease of mobility and powerful flight. However, there are a few disadvantages to rotor-based drones. They generate a lot of noise, and as airspace becomes more crowded with drones, this could lead to undesirable noise pollution. Rotors also require a considerable amount of power to operate. The average drone, like a DJI Air or Mavic, has a flight time of 20 to 40 minutes. This flight time depends on the ratio of the drone’s weight and flight demands to the size of its battery.
For drones intended for longer flight durations, a fixed-wing design is optimal. Fixed-wing drones are lighter and can glide, making flight more streamlined and energy-efficient. While rotor drones can be launched vertically from a variety of environments, launching a fixed-wing drone is more complicated. Like an airplane, a fixed-wing drone requires space for takeoff. This space could be a runway or a launching device. A team of researchers from the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland has developed a prototype fixed-wing drone that does not depend on traditional launching methods.
While looking out his window at the EPFL Laboratory of Intelligent Systems (LIS), Doctoral Assistant and PhD student Won Dong Shin was captivated by how crows and ravens use their legs for mobility and propulsion. “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,” says Shin. “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.”
Under the guidance of Professor Dario Floreano, Director of the LIS, Shin collaborated with LIS biologically inspired robotics Postdoctoral Researcher Hoang Vu Phan, Auke Ijspeert of EPFL’s BioRobotics Lab, and Monica Daley from the Neuromechanics Lab at the University of California, Irvine. Together, the team first researched the incredibly strong, flexible, and agile legs and feet of birds. Using this data, they designed RAVEN (Robotic Avian-inspired Vehicle for Multiple ENvironments), a fixed-wing drone with a split V-shaped tail. RAVEN has a single motor driving a small propeller on its nose, which uses minimal power.
What makes RAVEN truly unique is its legs, which allow it to walk, hop, jump, and launch itself into flight. Shin and his team gave RAVEN lightweight legs with springs and hinges to mimic the movement and propulsion of a bird’s legs. They also paid special attention to the design of the drone’s feet. The feet needed to articulate in order to adjust for walking on different surfaces, grasping for landing, and folding for flight.
“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,” Professor Floreano said. “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.”
Shin and his team published a paper titled “Fast ground-to-air transition with avian-inspired multifunctional legs” detailing the results of the RAVEN prototype on December 4, 2024, in Nature Portfolio, an online journal supporting groundbreaking research. The paper highlights how Shin and his team believe that a drone like RAVEN could have a lasting impact on the design of future drone models. “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,” Professor Floreano said. “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.”
By mimicking the versatile movement capabilities of birds, the team at EPFL has paved the way for more energy-efficient, agile, and adaptable drones. As research in this area continues, we may soon see drones that not only perform more effectively but can also seamlessly transition between different modes of movement, revolutionizing industries from surveillance to delivery and beyond.
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