Researchers at Caltech  have built a bipedal robot that combines walking with flying to create a new type of locomotion, making it exceptionally nimble and capable of complex movements.

Part walking robot, part flying drone, the newly developed LEONARDO (short for LEgs ONboARD drOne, or LEO for short) can walk a slackline, hop, and even ride a skateboard. Developed by a team at Caltech’s Center for Autonomous Systems and Technologies (CAST), LEO is the first robot that uses multi-joint legs and propeller-based thrusters to achieve a fine degree of control over its balance.

Bipedal robots tackle complex real-world terrains by using the same sort of movements that humans use, like jumping or running or even climbing stairs, but they are stymied by rough terrain. Flying robots easily navigate tough terrain by simply avoiding the ground, but they face their own set of limitations: high energy consumption during flight and limited payload capacity. LEO aims to bridge the gap between the two disparate domains of aerial and bipedal locomotion that are not typically intertwined in existing robotic systems, according to Kyunam Kim, Postdoctoral Researcher at Caltech and co-lead author of the Science Robotics paper that featured the robot.

By using a hybrid movement that is somewhere between walking and flying, the researchers get the best of both worlds in terms of locomotion. LEO’s lightweight legs take stress off of its thrusters by supporting the bulk of the weight, but because the thrusters are controlled synchronously with leg joints, LEO has uncanny balance.

LEO stands 2.5 feet tall and is equipped with two legs that have three actuated joints, along with four propeller thrusters mounted at an angle at the robot's shoulders. When a person walks, they adjust the position and orientation of their legs to cause their center of mass to move forward while the body's balance is maintained. LEO walks in this way as well: the propellers ensure that the robot is upright as it walks, and the leg actuators change the position of the legs to move the robot's center of mass forward through the use of a synchronized walking and flying controller. In flight, the robot uses its propellers alone and flies like a drone.

In the real world, the technology designed for LEO could foster the development of adaptive landing gear systems composed of controlled leg joints for aerial robots and other types of flying vehicles. The team envisions that future Mars rotorcraft could be equipped with legged landing gear so that the body balance of these aerial robots can be maintained as they land on sloped or uneven terrains, thereby reducing the risk of failure under challenging landing conditions.

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