In a groundbreaking development, researchers at ETH Zurich and the Max Planck Institute for Intelligent Systems (MPI-IS) have unveiled a new robotic leg that is not only more energy-efficient than traditional designs, but also capable of high jumps, fast movements, and adaptability to uneven terrain – all without the need for complex sensors.

Unlike conventional robotic legs that are powered by electromagnetic rotary motors, the researchers' new design is inspired by the musculoskeletal systems of living creatures. By using electrohydraulic actuators, or "artificial muscles," the robotic leg can mimic the paired contractions and extensions of human and animal limbs.

"While inventors and researchers have been developing robots for almost 70 years, they have all been powered by motors, a technology that is already 200 years old," said Robert Katzschmann, a researcher at ETH Zurich and co-lead of the project. "This in part suggests why they lack the mobility and adaptability of living creatures."

The team's new design, dubbed "HASEL" (Hydraulically Amplified Self-healing ELectrostatic) actuators, is a game-changer. These actuators are essentially oil-filled plastic bags with electrodes coated on either side. When a voltage is applied, the electrodes are attracted to each other, causing the bag to contract and push the oil to one side – mimicking the movement of a muscle.

"As one muscle shortens, its counterpart lengthens," explained Thomas Buchner, a doctoral student and co-first author of the team's publication in Nature Communications. "The researchers used a computer code that communicates with high-voltage amplifiers to control which actuators contract, and which extend."

This muscle-powered design not only makes the robotic leg more energy-efficient than those driven by electric motors, but it also allows for greater adaptability to the environment. Unlike traditional robotic legs that rely on sensors to constantly monitor the angle of the joint, the HASEL actuators can adapt to the terrain through interaction with the environment.

"Adapting to the terrain is a key aspect," said Toshihiko Fukushima, another doctoral student and co-first author. "When a person lands after jumping into the air, they don't have to think in advance about whether they should bend their knees at a 90-degree or a 70-degree angle. The same principle applies to the robotic leg's musculoskeletal system; upon landing, the leg joint adaptively moves into a suitable angle depending on whether the surface is hard or soft."

The researchers' findings demonstrate the significant potential of this new technology. By introducing a novel hardware concept that mimics the biological mechanisms of living creatures, the team has opened up new possibilities in the field of robotics.

"The field of robotics is making rapid progress with advanced controls and machine learning; in contrast, there has been much less progress with robotic hardware, which is equally important," said Christoph Keplinger, a researcher at MPI-IS and co-lead of the project. "This publication is a powerful reminder of how much potential for disruptive innovation comes from introducing new hardware concepts, like the use of artificial muscles."

While the current prototype is still limited in its ability to move freely, the researchers are optimistic about the future applications of their muscle-powered robotic leg. Potential use cases range from highly customized grippers to rescue robots that can navigate uneven terrain.

"If we combine the robotic leg with a quadruped robot or a humanoid robot with two legs, maybe one day, when it is battery-powered, we can deploy it as a rescue robot," Katzschmann said.

As the field of electrohydraulic actuators continues to evolve, the researchers' work stands as a testament to the power of bioinspired design in driving innovation in robotics. The muscle-powered robotic leg represents a significant leap forward, paving the way for a new generation of robots that can interact with their environment with greater agility and adaptability.