BirdBot gets a walk-up start

The mad scientist brigade has taken inspiration from the emu in their quest for high-efficiency robotics. What could possibly go wrong?

Clearly, they’ve never met one.

Admittedly, it wasn’t just the emu they were thinking about. Instead, it was the amazingly efficient balance and movement of birds’ legs in general. It just so happens that emus – and ostriches – represent the pinnacle of this evolutionary achievement.

Their legs are backwards. Their knees bend in the opposite direction to ours. And, as their lower leg swings forward, their foot flops down. Turns out, it’s a technique that’s far more mechanically efficient than our own. Naturally, it’s a lesson we’ve learnt the hard way.

Dozens of bipedal robot designs continue to teeter about testing sites after decades of research. Their heavy metal bodies are studded with motors, actuators and gears. Software algorithms are still struggling to coordinate everything for basics such as balance and motion.

But the Max Planck Institute for Intelligent Systems and the University of California, Irvine believe that approach is bird-brained.

Instead, they’ve shown their bird-leg inspired robotic mobility system is 300 times more energy efficient. And far easier to balance.

Instead of cramming every joint with motors, they’ve applied a network of artificial muscles and springs extending from the hip through bird-like joints to a simple spring-loaded foot. The ‘muscles’ are primed when the leg is pressed into the ground and placed under load. They release their mechanical spring energy as the leg straightens to move forward.

Only two motors are needed per leg. One is in the hips to get the legs swinging. The other is in the knee to lift the leg. The rest of the walking action is purely the result of the leg’s shape combined with the tendon-like effect of cables and pulleys.

The system has many benefits, say the researchers, who published their work in Science Robotics.

Not only do the tendons return energy to the system, the natural mechanical motion dramatically reduces the computing power needed to control its movements and balance.

Birdbot leg
Three leg configurations for the static load calculation. Credit: Alexander Badri-Spröwitz et al / Science Robotics

“The structure with its multi-jointed muscle-tendons and its unique foot movement can explain why even heavy, large birds run so quickly, robustly, and energy-efficient,” says study co-author Professor Monica Daley. The bird doesn’t need to think. The leg adjusts mechanically.

Now the research team is thinking about scaling up their robot.

The principle applies “whether it’s on the scale of a Tyrannosaurus Rex or a small quail, or a small or large robotic leg”, says Daley. “Theoretically, metre-high legs can now be implemented to carry robots with the weight of several tons, that walk around with little power input.”

She should know better.

Forget the tyrannosaurs and velociraptors of Jurassic Park. Even the famous AT-ST walking tank of Star Wars doesn’t count.

It was the Great Emu War that long ago taught us the dark side of bird walks. Emus can reach speeds of up to 50 km/h and leap 2m tall fences. They can take migration distances of up to 1000km in their stride, and their powerful talons can tear deep into the flesh of humans and other animals.

Little wonder the emu was behind Australia’s most ignominious battlefield defeat.

In late 1932, soldiers armed with heavy machineguns were sent into the Campion district of Western Australia to confront perhaps 20,000 flightless invaders which were said to be damaging crops

The first assault failed miserably: all attempts to surround the feathered fiends and herd them into fields of fire failed miserably. Following attempts to chase the emus with a machine gun mounted on the back of a truck was equally embarrassing. It couldn’t keep up as the artfully intelligent avians ducked and weaved across the rough terrain.

With egg on its face, the Australian army gave up after just one week. Some 2500 rounds of ammunition had been fired. Thousands of emus had been engaged. Only about 100 had been bagged. “If we had a military division with the bullet-carrying capacity of these birds, it would face any army in the world… They can face machine guns with the invulnerability of tanks,” the operation commander, Major G P W Meredith, later stated.

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