Robotic legs inspired by emus use less energy to run

Robotic legs that mimic flightless running birds like emus and use just two motors per leg can run more efficiently than more complex devices

By Matthew Sparkes

Robotic legs with an unconventional design inspired by emus can run 300 per cent more efficiently than the same device would if designed traditionally. The technology could be used in prosthetics and exoskeletons, say its inventors.

Alexander Badri-Spröwitz at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany, and his colleagues have done away with the usual approach where every joint in a robotic limb has one actuator to open it and one to contract it. Instead, their BirdBot uses just two motors in each 3D-printed leg and long artificial tendons that cover more than one joint, mimicking the anatomy of certain birds that have lost the ability to fly and instead evolved to run efficiently along the ground.

“We’re using just two actuators, one to move the leg back and forward, and one to lift it. Just the bare minimum required,” says Badri-Spröwitz. “Usually in robotics, you’re looking to improve efficiency by just 10 per cent or so, but we’re seeing a 300 per cent increase.”

The motors pull the tendons. Power is stored in a spring during compression and released when each foot strikes the floor, to help drive the robot forward.

Taking many actuators, sensors and electronics out of the system makes the robot lighter and cheaper to manufacture. It can also stand upright using no power.

The BirdBot reached a speed of 75 centimetres per second in tests on a treadmill. Guides are currently required to keep the robot running straight and true, but the focus of the research was efficiency, not balance, says Badri-Spröwitz.

Shival Dubey at the University of Leeds in the UK says the design is more efficient than more complex devices, but may also be less adaptable when it comes to carrying loads of varying weight.

“In traditional leg robots, we use actuators at each joint in order to move that particular joint. They’re using less energy in comparison to that and fewer electronic components,” he says. “They’ve done a good job in demonstrating or replicating the movement of the bird, but doing other tasks will need further fine-tuning.”

Journal reference: Science Robotics, DOI: 10.1126/scirobotics.abg4055