EPFL researchers have built a drone that walks, runs and leaps with the help of bird-like legs, greatly expanding the range of potential environments accessible to unmanned aerial vehicles.
“As a crow flies” is a common idiom for the shortest distance between two points, but the Institute for Intelligent Systems (LIS), led by Dario Floreano at the EPFL School of Engineering, has translated this expression literally into RAVEN (Robotic Avian- Inspired vehicles for different environments). Multifunctional robotic legs designed based on perching birds such as ravens and ravens that frequently transition between air and ground will enable autonomous takeoff in environments previously inaccessible to winged drones.
“Birds were the original inspiration for airplanes, and the Wright brothers made this dream come true. But even today’s airplanes are still far from what birds are capable of,” says LIS doctoral candidate Shin Won-dong. “Birds can go from walking to running and soaring into the air without the aid of a runway or launcher. In robotics, we don’t yet have an engineered platform for this kind of movement.”
RAVEN’s design aims to maximize gait versatility while minimizing mass. Inspired by the proportions of bird legs (and his long observations of crows on the EPFL campus), Shin designed a custom, multifunctional set of bird legs for fixed-wing drones. Using a combination of mathematical models, computer simulations and experimental iterations, he achieved the optimal balance between the complexity of the legs and the overall drone weight (0.62 kg). The resulting legs keep the heavier parts close to the ‘body’, while the combination of springs and motors mimics the powerful avian tendons and muscles. Composed of two articulated structures, the lightweight bird-inspired feet utilize passive elastic joints to support a variety of postures, including walking, running, and jumping.
“Converting a bird’s legs and feet into a lightweight robotic system presented design, integration and control challenges that birds have elegantly solved over the course of their evolution,” Floreano said. “This allowed us not only to develop the most versatile winged drone to date, but also to reveal the energy efficiency of jumps for takeoff in both birds and drones.” This study was published in: nature.
Improved accessibility for deliveries and disaster relief
Existing walking robots were too heavy to jump, and jumping robots did not have feet suitable for walking. RAVEN’s unique design allows it to walk, traverse gaps in the terrain and even jump onto elevated surfaces as high as 26cm. Scientists also experimented with different modes of flight initiation, including standing and falling takeoffs, and found that jumping into flight was the most efficient use of kinetic energy (speed) and potential energy (increase in height). LIS researchers collaborated with Auke Ijspeert of the EPFL BioRobotics Lab and Monica Daley’s Neuromechanics Lab at the University of California, Irvine to apply new biomechanics to robot locomotion.
In addition to illustrating the costs and benefits of powerful legs for birds that frequently move between air and ground, the results provide a lightweight design for winged drones that can move over rough terrain and take off from confined locations without human intervention. These capabilities allow drones to be used for inspection, disaster mitigation, and delivery in limited areas. The EPFL team is already working on improved bridge design and controls to facilitate landings in a variety of environments.
“Although the wings of birds are identical to the forelimbs of terrestrial quadrupeds, very little is known about the coordination of legs and wings in birds, let alone drones. These results are intended to better understand the principles of design and control in birds. “It’s just the first step, turning flying animals into agile, energy-efficient drones,” says Floreano.
