New muscle-powered robot-leg jumps higher, reacts faster than ever before

The majority of the current walking robots are powered by motors. But a new age is dawning, one in which robots are powered by muscles rather than electric motors. Muscles might offer robots the same movement and flexibility as live beings.

And researchers at ETH Zurich and the Max Planck Institute have been working to make it possible. They have developed a small-scale robotic leg that mimics the muscular structure of animals.

Surprisingly, this muscle-powered robotic leg can perform complex movements like jumping and adapting to uneven terrain.

“If we combine the robotic leg in 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,” said  Robert Katzschmann, one of the lead developers from ETH Zurich.

How it works

Inspired by animals, this “musculoskeletal” robotic leg moves using artificial extensor and flexor muscles .

The leg is driven by electro-hydraulic actuators that are attached to the robotic skeleton via tendons.

The press release noted that the actuators are plastic bags filled with oil, resembling those used for making ice cubes. In addition, a black, conductive electrode partly covers both sides of each bag.

Thomas Buchner, the co-author of the study, explained that “as soon as we apply a voltage to the electrodes, they are attracted to each other due to static electricity. Similarly, when I rub a balloon against my head, my hair sticks to the balloon due to the same static electricity.”

The voltage provided to the actuators’ electrodes determines their movement. As the voltage increases, the electrodes move closer together, shifting the oil into the actuator and shortening the bag.

When paired on a skeleton, these actuators mimic the “paired muscle movements of living creatures” by contracting one muscle while extending the other.

A computer code and high-voltage amplifiers are used to control which actuators contract or extend.

Energy-efficient robotic leg

Interestingly, the robotic leg prototype can jump thanks to its capacity to raise its weight explosively.

The researchers highlighted the robotic leg’s high adaptability could be beneficial for developing advanced soft robotics.

Moreover, this musculoskeletal system is “elastic”, allowing for flexible adaptation to the terrain.

“It’s no different with living creatures. If we can’t bend our knees, for example, walking on an uneven surface becomes much more difficult. Just think of taking a step down from the pavement onto the road,” said  Katzschmann.

Unlike electric motors that rely on sensors to determine the leg’s position, the artificial muscle adapts to the appropriate position through interaction with its environment. This adaptation is controlled by only two input signals: one for bending and one for extending the joint. This allows the robotic leg’s musculoskeletal system to adapt to the landing surface.

In terms of energy efficiency, the new robotic leg is more efficient as compared to standard robotic leg powered by an electric motor.

“On the infrared image, it’s easy to see that the motorized leg consumes much more energy if, say, it has to hold a bent position,” Buchner added in the press release.

The electrostatic properties of the artificial muscle ensure a stable temperature in the electro-hydraulic leg.

The researchers acknowledge that their current system while promising, has some jumping limitations.

They plan to address these limitations, enabling the development of fully functional walking robots with artificial muscles.

The study is reported in the journal Nature Communications.