Bird Anatomy Makes The Better-Legged Robots Than The Humans Do

Researchers at the Max Planck Institute for Intelligent Systems in Stuttgart, Germany, have invented a legged robot based on bird biology. This robot balances speed and walking efficiency.

Image credits: Pixabay

Alexander Bardi-Spröwitz, a researcher at Max Planck Institute for Intelligent Systems was trying to design a bipedal (two-legged) robot resembling the structure of a bird. The problem was that the biologists were unable to explain the bird anatomy based on technical or engineering terms. “It’s not their goal to build a robot,” said Bardi-Spröwitz. “It’s a bit frustrating for me as an engineer because I need certain types of information.”

To know more about bird anatomy, he met Monica Daley, a veterinary scientist at the Royal Veterinary College in England. She offered him the position of postdoctoral alongside her veterinary students. “That got me thinking about how we use our understanding of locomotion and animals to develop more agile robots,” said Daley. The two researchers and Bardi-Spröwitz’s lab members then developed a BirdBot (a bipedal robot) that may work in terrains such as dense forests where wheeled robots cannot move.

The reason behind making a BirdBot was that, like humans, birds can also walk on two legs. “Given that there are around 10,000 living species of bird and only one species of human, birds have a lot to offer us in understanding how bipedalism can work,” said Peter Bishop, a biomechanics researcher at Harvard University’s Museum of Comparative Zoology.

This type of information is important for those roboticists who want to create bipedal locomotive machines. “Doing so is quite hard because there are lots of very harsh impacts,” explained Bardi-Spröwitz. “It’s as if you were to continuously land an aeroplane.” A bipedal robot not only has to deal with the motions such as walking or running but also needs to balance on one foot.

The research team made a spring-loaded system that can switch between extended flexed limb positions so that the BirdBot can be kept in an upright position while moving. “The key point was to think of the foot as the mechanical trigger to switch between those two states,” said Bardi-Spröwitz. Like humans, birds too have tendons (tissue connecting bones to muscles) in the joints that form a pulley like structure which helps the connected bones to move. A bird limb’s tendons and muscles can span up to five joints. Hence, a BirdBot uses a five-joint network for locomotion.

This setup allowed the bird’s leg to move faster than its nervous system could operate. Nerve impulses take time to travel from brain to muscle. But, with the help of the five-jointed muscle network, a bird can stimulate each muscle at the same time. “It’s kind of like the puppet master controlling everything from the top,” said Daley. This muscle network terminated the need for complicated pressure and balance sensors in the BirdBot’s legs. This made the robot sleeker, about 75 per cent less power-intensive and scalable in size.

“What they’ve shown is that, by using this stable joint, you have a very elegant way to be energy efficient,” said Markus Heller, a biomechanical engineer at the University of Southampton in England. “And you have that without the need of a very complex control mechanism.”

The current version of BirdBot can only move forward and backwards but not sideways. Therefore, Bishop wants to see improvements in the designs of future BirdBots. “All the limb joints are simple hinges, so the robot is more like ‘2.5-D,” said Bishop.

Bardi-Spröwitz visualizes the bipedal robots to help humans in agricultural and forestry practices. According to him, the wheeled robots like tractors used by farmers are useless on densely or uneven wooded terrain. “Legged robots can overcome those obstacles where wheeled robots are currently blocked,” said Bardi-Spröwitz.

This research brought all the engineers and biologists closer to understanding the complexity of birds’ and humans’ bodies. “We visited the moon 50 years ago,” said Heller. “But if you ask us today, ‘How does a knee really work?’ I think we’re still not quite sure about all the details of that.”

The detailed research has been published in Science Robotics.