Robots can now walk through muddy and slippery terrain, thanks to Moose-like feet

Roboticists at the Tallinn University of Technology (TalTech) have developed a new class of bio-inspired feet that significantly enhance robot mobility on challenging terrains like mud and wet snow. The findings, published in “Bioinspiration & Biomimetics”, could expand the capabilities of robots, allowing them to navigate in complex natural terrains to conduct sensitive environmental monitoring, aid in agriculture and participate in disaster response.

Robot legged locomotion have been studied for decades, and legged robots are becoming gradually more energy efficient and more versatile. Adjusting the way they walk to the changing terrain allows the robots to navigate grounds with changing properties, yet some types of natural terrains have remained unconquered.

„Muddy and slippery terrains are some of the most difficult to traverse for robots and animals, including humans,“ says Maarja Kruusmaa, Prof. of biorobotics and the team lead. „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.”

Simon Godon, the doctoral candidate at the TalTech Centre for Biorobotics combined his observations in his parents’ cattle farm in Berry, France, with his knowledge in mechanical engineering and biorobotics, proposing high-tech hooves for robots which offer major advantages, especially when walking on mud.

Physical experiments with real moose feet in laboratory conditions have revealed that they really do. When stepping into and out of mud, the split hooves of the moose expand and shrink, thus increasing and reducing its contact area. The biggest advantage however, does not come from the increased surface area, but how the cloven hooves break the suction force as they are pulled back out of the mud.

„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,“ Simon Godon explains. „Mud acts in a similar manner to a wet bathroom tile, creating  under the animal’s feet, making it difficult to get the leg out. Moving hooves breaks that tension.“ The hooves however, do not just make the motion faster and more energy efficient, but also help to avoid fatal situations where the animal sinks too deep, gets stuck and dies.

The researchers designed silicon feet for the legged robot, meant to replicate the same behaviour. Tests in muddy surfaces revealed that the simple modification to robot feet reduces the sinkage of the robot and the suction force by half while the energy consumption of the robot was reduced by up to 70%.

Notably, the researchers have yet to find any disadvantages with the modified robo-moose feet. „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,“ says prof. Kruusmaa and adds: „We therefore recommend robots to keep their shoes on at all times!”