Wheel-legged robotic system moves more efficiently in a wide range of environments

Most existing robots designed to move on the ground rely on either wheels or legs, as opposed to a combination of the two. Yet robots that can seamlessly switch between wheeled and legged locomotion could be highly advantageous, as they could move more efficiently on a wider range of terrains, which could in turn contribute to the successful completion of missions.

Researchers at The Hong Kong University of Science and Technology (Guangzhou) recently developed FLORES, a new wheel-legged robot that could better adapt to its surroundings and move smoothly in different environments.

The new robot, presented in a paper published on the arXiv preprint server, can traverse uneven terrains using its legs, switching to wheeled locomotion to move faster on smooth surfaces, all while retaining its stability.

“In my recent paper, I explored the design and evolution of wheel-legged robots, focusing on combining the advantages of wheeled and legged robots,” Zhicheng Song, first author of the paper, told Tech Xplore.

“The inspiration came from observing existing models like ANYmal and B2W, which integrate wheels into legged robots, and the more traditional wheeled robot mobED, which I personally consider as a form of a wheel-legged robot due to its innovative design. While mobED is fundamentally a wheeled robot, my perspective is that it integrates leg-like features, thus positioning it closer to the concept of a wheel-legged structure.”

The B2W and mobED models are wheel-legged robot designs introduced in earlier papers. The first of these models builds on the body structure and capabilities of legged robots, while the second starts from a wheeled robot design, adding legged locomotion strategies.

“My idea was to redesign robots like B2W towards a more car-like design,” said Song. “The primary objectives of the FLORES project are to achieve more efficient locomotion on relatively flat terrain while retaining the ability to overcome obstacles such as stairs. This dual approach aims to create a more versatile and efficient robotic platform”.

FLORES, the new robot designed by Song and his colleagues, has a distinctive front leg configuration that sets it apart from earlier wheel-legged robot designs. This unique characteristic can boost its navigation efficiency and improve its adaptability across a broad range of scenarios.

“Our robot replaces the conventional hip-roll degree of freedom (DoF) of the front leg with hip-yaw DoFs, and this allows for efficient movement on flat surfaces while ensuring adaptability when navigating complex terrains,” explained Song.

“This innovative design facilitates seamless transitions between different locomotion modes (i.e., legged locomotion and wheeled locomotion) and optimizes the performance across varied environments. Our distinctive joint design enables the robot to exhibit novel and highly efficient locomotion gaits that capitalize on the synergistic advantages of both locomotion modes.”

The researchers created a prototype of their robot and tested it in a series of real-world experiments, comparing its performance to that of other traditional wheel-legged robots developed in the past. Notably, they found that their robot moves more efficiently, especially in situations where it needs to steer and change direction often.

“In our straight-line motion and turning motion experiments with both our robot and other wheel-legged platforms, we observed that our robot’s energy consumption was only 30% and 35% that of others, respectively,” said Song.

“I believe FLORES is well-suited for collaborative tasks alongside humans, particularly in environments where the primary terrains consist of relatively flat surfaces and stairs. In these scenarios, our robot can navigate with high locomotion efficiency.”

The FLORES robot could soon be improved further and tested in more real-world experiments carried out in various settings. As part of their future research, Song and his colleagues would like to attach a lightweight arm to the robot’s body, as this would allow it to tackle object manipulation tasks.

“I am also in the progress of performing the sim2real transfer for serval bipedal locomotion, which can handle more extreme situations,” added Song.

“For instance, when confronted with an extremely narrow single-plank bridge, all existing legged robots struggle to cross it, while our robot can effortlessly switch to bipedal mode to successfully navigate such a scenario, by using its rear legs as lower limbs and aligning its wheels in a straight line to improve lateral movement.”

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