Lizard robot study reveals keys to optimal locomotion

Could a robot that mimics a climbing and walking lizard provide new insights into the evolution and advantages of different locomotion in humans and other animals?

The answer is yes, according to a new international, interdisciplinary study published overnight in Nature Robotics, co-authored by Dr Christofer Clemente of the University of the Sunshine Coast.

“These findings may also help us build faster and more effective walking robots,” said Dr Clemente, who specializes in the biomechanics of living and extinct animals.

“This could one day be important in overcoming obstacles to finding survivors during search and rescue missions.”

“Our research team developed a lizard-inspired robot capable of running and climbing, and combined biology, robotics and mathematics based on lizard locomotion to understand whether it was better to move with its legs or its spine,” said Dr. Clemente.

“We found that if you want to move fast, you need to use your legs the most and move your spine as little as possible. But using less backbone helps to use less energy.

“We also identified that limb or spine movements tended to decrease stability during climbing, meaning the robots were more likely to fall off the wall.”

Lizards are masters of movement

Lead author Dr Robert Rockenfeller from the University of Koblenz said that overall they found that optimal locomotion required movement of the spine and limbs, which agreed closely with movement patterns among lizards.

“The findings make it possible to detail the degree of evolutionary trade-offs between three key performance criteria – speed, efficiency and stability – and determine the relative strength of these driving selection pressures,” Dr Rockenfeller said.

Dr Clemente said that among vertebrates, movement patterns varied considerably, from the spine-based lateral movements of fish and salamanders to the predominantly limb-based movements of mammals and birds.

“However, lizards use both limbs and spines, which makes them the perfect species to study to help fill in the gaps in understanding why these changes might have occurred,” he said.

The research team’s lizard-inspired robot was capable of level running and climbing on inclined or vertical surfaces, with modifiable leg lengths and the ability to adjust spine and limb range of motion and stride speed.

“We also built a performance landscape to assess its climb efficiency and stability,” Dr Clemente said.

“These data were mapped to findings from a two-dimensional theoretical model of lizard locomotion, as well as measurements of more than 40 species of climbing and running lizards.”

Data was collected from more than 40 species of climbing and running lizards. Photo credit Dr Christopher Clemente.

The findings could lead to ‘steps’ in designing faster and more efficient legged robots.

We were able to define several engineering criteria to consider when developing robotic limb devices capable of traversing a wide variety of environments.

“Lateral sway of the spine should not be an important consideration if maximizing robotic speed is the primary objective, but it may be important for reducing energy consumption.”

Similarly, this understanding can also help design faster, more stable and efficient robotic steps.

Kinematic data collected during level climbing and walking from 44 species with different body plans using body point motion tracking, which were then used to calculate limb and spine range of motion.

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