Roboticists at Tallinn University of Technology (TalTech) have unveiled an innovative advancement in robot mobility, with the development of a new class of bio-inspired feet designed to help robots navigate some of the most difficult and variable terrains, including mud and wet snow. These findings, recently published in Bioinspiration & Biomimetics, promise to significantly expand the operational capabilities of robots, enabling them to traverse complex natural landscapes for various important tasks, such as environmental monitoring, disaster relief, and even agriculture.
The research team, led by Maarja Kruusmaa, a Professor of Biorobotics at TalTech, aims to overcome one of the biggest obstacles in legged robot design: navigating terrains with inconsistent and challenging surfaces. While robot locomotion, particularly legged motion, has made significant strides in efficiency and versatility over recent decades, it remains a challenge to adapt robots to traverse terrains such as mud, wetlands, and icy snow. These terrains remain one of the toughest challenges for robots, which often become immobilized or inefficient when navigating such surfaces. This inability restricts the accessibility of important environmental spaces, such as coastal marshes, bogs, river estuaries, and fields.
“Muddy and slippery terrains are some of the most difficult to traverse for robots and animals, including humans,” says Prof. Kruusmaa, emphasizing the substantial limitations imposed by these natural obstacles. She continues, “This means that most robots cannot access a wide range of highly important terrestrial environments, including wetlands, bogs, coastal marshes, river estuaries, and fields, which are abundant in nature.”
The roots of the solution stem from an unconventional inspiration found in nature. Simon Godon, a doctoral candidate at the TalTech Centre for Biorobotics and lead researcher on the project, observed the behavior of animals—particularly the feet of animals that navigate such challenging environments. Growing up on a cattle farm in Berry, France, Godon was exposed to firsthand experiences of animals, like moose, moving across muddy, wet surfaces, and he became fascinated with the mechanics of how their feet interact with the environment.
Drawing on his understanding of mechanical engineering and biorobotics, Godon proposed a unique solution: bio-inspired hooves for robots. By mimicking the mechanics of cloven hooves, the feet of moose, the team hypothesized that robot feet could significantly enhance mobility on muddy terrain. Moose hooves, known for their split, or cloven, structure, serve to expand and contract as they step into and out of muddy surfaces, effectively increasing and reducing their contact area in a way that optimizes movement. The real key to the design, however, lies not just in surface area but in how the hoof structures handle the suction force encountered when stepping into the mud.
Experimental studies involving real moose feet conducted under laboratory conditions demonstrated how these cloven hooves provide a distinct advantage in muddy environments. As moose feet sink into the mud, the split hooves function similarly to a suction cup. When attempting to lift the hooves, the suction generated by the sticky, wet mud makes it hard to remove the feet from the ground. The split hooves, however, break the suction when moved, making it easier to lift the foot free. “We found that the moose’s hoof behaves similarly to a suction cup, like how you manage to stick your fingernail under its surface and break the suction force,” Godon explains. This ingenious process prevents the animal from getting stuck in the mud, a potentially life-threatening situation that could lead to the animal sinking and possibly dying.
Drawing from these insights, the research team at TalTech devised robotic feet made of silicone designed to replicate the behavior of moose hooves. These high-tech, flexible feet feature a split structure that reacts dynamically to the pressures of mud and wet snow. Extensive tests on robot mobility across muddy surfaces revealed a remarkable difference. The modifications resulted in a significant reduction in sinkage—by as much as half—and dramatically decreased the suction forces encountered by the robot. The change in foot design also reduced energy consumption by up to 70% during locomotion on these difficult surfaces, making robot movements faster and more efficient.
The results of the experiment have been highly promising. Not only did the silicone feet reduce the negative impact of mud, but they also contributed to improved robot stability in such conditions. So far, the team has yet to identify any drawbacks to these innovative robotic feet. According to Prof. Kruusmaa, the modified feet may even enhance robot mobility on uneven surfaces, providing the robot with additional stability. “We speculate that, on the contrary, the split hooves may even have advantages on uneven terrains, giving the robot or the animal some extra stability,” Kruusmaa notes. She goes on to suggest that keeping the “shoes” on at all times might prove useful for robots in general, improving performance across different landscapes.
The development of these bio-inspired feet for robots is just one step in the broader mission to enable robots to play a more significant role in natural environments, where navigating challenging surfaces is often crucial for performing important functions. In agriculture, robots with the ability to navigate muddy fields could be used for planting, monitoring, or harvesting crops. For environmental monitoring, robots capable of traversing wetlands, coastal marshes, and bogs could be instrumental in gathering data in remote, sensitive locations with minimal human intervention. Robots equipped with this type of mobility could also be crucial in search-and-rescue missions in natural disaster scenarios, where rough and inaccessible terrain often poses a significant barrier to rescue efforts.
What the researchers have developed, therefore, represents a significant leap forward in the potential of legged robots. The advancement may open doors to a wider range of applications where robots can assist in scenarios too difficult or dangerous for humans or conventional wheeled robots. This includes areas where land conditions vary unpredictably or where sensitive ecosystems require careful monitoring.
As roboticists continue to push the boundaries of what these machines can do, innovations like these are vital in bridging the gap between traditional engineering and nature’s wisdom. By studying the ways animals interact with their environment, engineers can create more adaptive, robust systems that mirror nature’s designs. With the development of these bio-inspired feet, robots will have an enhanced ability to move across wet, muddy, and unstable terrains, thereby taking one step closer to becoming valuable companions in real-world applications in remote and rugged environments.
Reference: S Godon et al, Robotic feet modeled after ungulates improve locomotion on soft wet grounds, Bioinspiration & Biomimetics (2024). DOI: 10.1088/1748-3190/ad839c