Quadrotors support enhanced locomotion in a new bipedal robot

Humans and animals are the key inspiration for many robotic systems developed to date, as they possess body structures that innately support efficient locomotion. While many bipedal (i.e., two-legged) robots are humanoids, meaning that their body resembles that of humans, others draw inspiration from other animals that walk on two legs, such as ostriches and some other birds.

Researchers at Shandong University recently developed KOU-III a new bipedal robot that can move more efficiently in its surroundings. This robot, presented in a paper posted to the SSRN preprint server, can stand robustly on its two legs, while also effectively performing both walking and jumping motions.

“The name KOU originates from a figure in ancient Chinese mythology named Lie Yukou, who was said to be capable of riding the wind,” Xianwu Zeng, co-author of the paper, told Tech Xplore.

“When developing our robot, we were also inspired by a video uploaded 10 years ago by MSC Lab. KAIST on YouTube. The video showed a bipedal robot constrained to planar motion, achieving a speed of 46 km/h. Seven years ago, Insider Tech uploaded a similar video, which demonstrated an ostrich-inspired robot reaching a maximum speed of 12 miles per hour.”

Inspired by videos of ostrich-like robots, Zeng and his colleagues set out to explore the possibility of changing the constraints of these robots, with the goal of improving their maneuverability and motions during locomotion. This led to the development of their robot, which draws inspiration from legged animals that move leveraging auxiliary mechanisms.

“For instance, humans swing their arms to counteract the angular momentum generated by their legs during high-speed movements, such as sprinting,” said Zeng. “Similarly, ostriches and roadrunners rarely use their wings for flight but flap them during rapid running, jumping, or sharp turns, where the wings serve as auxiliary mechanisms.”

KOU-III, the bipedal robot developed by Zeng and his colleagues, also moves in its surroundings utilizing an auxiliary mechanism. Specifically, it leverages rotors, rotating mechanical systems that stabilize the robot as it moves, while also generating lift to partly support the robot’s weight while it is moving.

“This is especially beneficial during jumping, as the rotors enable the robot to jump higher,” explained Zeng. “This concept was inspired by the jumping behavior of the Red-Capped Manakin, which uses its wings to perform courtship jumps.”

The quadrotor-assisted mechanism underpinning the movements of KOU-III was found to improve both the robot’s motions and stability, reducing mechanical stress during locomotion. Overall, the findings gathered by the researchers highlight the promise of robot-based auxiliary mechanisms for enhancing bipedal robot locomotion.

“The rotors actively provide torques for pitch and roll stabilization, as well as vertical lift, enabling the regulation of angular momentum generated by high-performance legged motion while offsetting part of the robot’s weight,” said Zeng. “Crucially, during airborne jumps, the robot’s posture can be rapidly adjusted using the rotors.”

As part of their study, Zeng and his colleagues also developed a control strategy that plans and executes their robot’s movements. This control algorithm was used to reliably execute standing, walking and jumping actions with the KOU-III robot.

“Unlike direct flight, we can adjust rotor output power—reducing or shutting it down when high mobility is unnecessary and increasing power only when needed,” said Zeng. “This approach reduces energy consumption, minimizes rotor noise, and leverages the strong load-bearing capabilities of legged robots.”

The new robot developed by this team of researchers could soon be improved and tested further across a wider range of scenarios. In the future, it could inspire the development of other bipedal robots and could eventually be deployed in real-world settings, where it could assist humans as they are completing various tasks.

“Building on the successful use of rotors as legged assistance mechanisms, we aim to explore other more efficient and safer auxiliary systems and develop corresponding motion control strategies,” added Zeng. “Additionally, we plan to investigate potential applications for KOU-III, such as exploring narrow, rugged underground caves unsuitable for flight or clearing landmines in abandoned battlefields to ensure personnel safety and facilitate land cultivation.”

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