A newly developed bipedal robot can seamlessly switch between walking and flying, and it’s the combination of these two skills that really sets this futuristic machine apart.
Introducing LEONARDO, or LEO for short. The name is an acronym for LEgs ONboARD drone, which nicely but insufficiently describes this robot. The Caltech engineers who built LEO didn’t just slap a pair of robotic legs onto an aerial drone—they had to design the bot with both walking and flying in mind and develop specialized software to integrates its various components.
LEO is still a prototype—a kind of proof-of-concept to see if a bipedal flying robot can perform tasks that would otherwise be difficult or impossible for ground robots or aerial drones to accomplish on their own. In the future, a full-fledged version could be tasked with difficult or dangerous jobs, such as inspecting and repairing damaged infrastructure, installing new equipment in hard-to-reach places, or attending to natural disasters and industrial accidents. Eventually, a LEO-like robot could even transport delicate equipment to the surface of a celestial body, such as Mars or Saturn’s moon Titan. More ominously, the agile bipedal flier could be used in defense or warfare.
LEO’s sci-fi attributes are not an accident. In an email, the team told me they were inspired by the fictional flying humanoid robot Astro Boy and the Iron Man-like jet suits built by Gravity Industries’ Richard Browning. Ultimately, however, the purpose of the project was to study the intersection of walking and flying from a dynamics and control perspective and to “give unprecedented walking ability and to solve problems posed by hybrid locomotion,” as the team explained in a video. The Caltech is team is also hoping to build adaptive landing gear for vertical take-off and landings (VTOL) on difficult terrain.
Nature figured out this trick long ago, as birds, bats, insects, and many other organisms can switch back and forth between these two modes of locomotion. It provides a distinct evolutionary advantage. Robots, on the other hand, tend to be specialized and capable of moving in only one of these two ways. There are pluses and negatives to this: Ground robots are sure-footed, sturdy, and capable of carrying heavy loads, but they struggle in difficult terrain and cannot reach high places. Aerial drones are highly mobile and capable of flying in all sorts of environments, but they can’t stay aloft for long due to the high energy demands of flight, and they’re bad at performing fine manipulation tasks. Hence the desire to create a machine that can leverage the best of both worlds.
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To achieve balance on the ground and agility in the air, LEO had to be carefully designed. Kyunam Kim, Soon-Jo Chung, Elena-Sorina Lupu, and Patrick Spieler explained in an email that this required sturdy but lightweight components, as well as algorithms for controlling LEO’s four propellers and leg joints “in a synchronous manner to ensure that LEO walks or flies without losing its balance.” The two disparate domains “are not typically intertwined in existing robotic systems, and we had to tackle a rich set of engineering problems that were not well-studied in other robotic systems,” they added. A research paper outlining this work was published today in Science Robotics.
LEO weighs just 5.7 pounds (2.58 kg) and stands 2.5 feet (75 cm) tall. Like a bird, the robot uses its slender, multi-jointed legs to push off the ground and provide an assist during takeoff. LEO’s tilted electric thrusters—the four propellers—are synched to these jumps. LEO walks as if on high heels, but these heels allow for balanced standing; should the conditions warrant, however, LEO’s propellers could always kick in to ensure further stability. Batteries, sensors, and the required processing power are packed into the robot’s torso, allowing for full autonomy and no clunky wires.
“We note that the optimization of LEO’s energy consumption was not a priority in this work,” the team explained in its email. “Instead we focused on a wide range of capabilities.”
In tests, LEO moved back and forth between agile walking and flight, which it did to avoid challenging obstacles and to perform difficult tasks in which balance was needed—including skateboarding and walking on a slackline. LEO’s design enabled “dynamic bipedal walking with complex ground interaction, while preserving the flight performance of a multi-rotor vehicle,” as the team wrote in their email. The team claims that LEO is the first bipedal robot to perform slacklining, albeit with help from its propellers.
With the combined power of walking and flight, the team hopes to enable a wide range of robotic missions, such as high-voltage line inspection and the monitoring of tall bridges. These bots could inspect aging infrastructure, work in disaster scenarios, and even explore distant worlds.
Writing in an associated Focus article, Stefano Mintchev, a researcher at ETH Zurich’s Department of Environmental Systems Science, said LEO’s abilities require trade-offs:
The propellers are tilted to be more effective in stabilizing LEO’s walk, but this choice reduces their efficiency during flight. To minimize the weight that needs to be lifted, the legs are slender and underpowered. LEO needs constant support from the propellers during walking, which makes it more energy hungry than a purely terrestrial robot would be…[The] extent of these trade-offs, and thus how close a multimodal robot is to a purely terrestrial or aerial robot, is reliant on design choices. Minimizing trade-offs remains a daunting challenge.
Mintchev, who wasn’t involved in the new study, offered his advice to the team, saying they should keep being inspired by nature. He pointed to flying snakes, who flatten their bodies to improve gliding.
For sure, there’s room for improvement, but LEO is the first of an entirely new breed of robot. With Astro Boy being a key inspiration, these scientists still have a long way to go.