Researchers look to nature to design six-legged robots

Once again, engineers are looking towards nature to help design and build efficiently moving robots.

Photo courtesy of EPFL/ Alain Herzog.

Swiss researchers at École polytechnique fédérale de Lausanne (EPFL) and the University of Lausanne in Lausanne (UNIL) looked at how both vertebrates and insects run and walk to determine the best motions and movements to integrate into robotic design.

Vertebrates’ legs exhibit minimal contact with the ground when they are running. However,  six-legged insects run fastest using a three-legged, or “tripod” gait where they have three legs on the ground at all times — two on one side of their body and one on the other. Traditionally, engineers have been inspired to use this tripod gait when designing six-legged robots.

Yet, the researchers believe they have found a better, more efficient way to allow bio-inspired robots to move on the ground —a bipod gait structure.

The scientists carried out a host of computer simulations, tests on robots and experiments on Drosophila melanogaster — the most commonly studied insect in biology.

“We wanted to determine why insects use a tripod gait and identify whether it is, indeed, the fastest way for six-legged animals and robots to walk,” said Pavan Ramdya, co-lead and corresponding author of the study.

To test the various combinations, the researchers used an evolutionary-like algorithm to optimize the walking speed of a simulated insect model based on Drosophila. Step-by-step, this algorithm sifted through many different possible gaits, eliminating the slowest and shortlisting the fastest.

The researchers found that the common insect tripod gait did emerge when they optimized their insect model to climb vertical surfaces with adhesion on the tips of its legs. By contrast, simulations of ground-walking without the adhesiveness of insects’ legs revealed that bipod gaits, where only two legs are on the ground at any given time, are faster and more efficient.

Interestingly, in nature, there are no insects that actually walk this way.

“Our findings support the idea that insects use a tripod gait to most effectively walk on surfaces in three dimensions, and because their legs have adhesive properties. This confirms a long-standing biological hypothesis,” said Ramdya. “Ground robots should therefore break free from only using the tripod gait.”

The researchers built a six-legged robot capable of employing either the tripod or bipod gait. The bipod gait was again demonstrated to be faster, corroborating the simulation algorithms’ results.

Finally, the experimenters examined real insects. To see if leg adhesion might also play a role in the walking coordination of real flies, they put polymer drops on the flies’ legs to cover their claws and adhesive pads — as if the flies were wearing boots. The flies quickly began to use bipod-like leg coordination similar to the one discovered in the simulation.

“This result shows that, unlike most robots, animals can adapt to find new ways of walking under new circumstances,” said Robin Thandiackal, a co-lead author of the study. “There is a natural dialogue between robotics and biology: Many robot designers are inspired by nature and biologists can use robots to better understand the behavior of animal species. We believe that our work represents an important contribution to the study of animal and robotic locomotion.”

The researchers’ findings are published in Nature Communications.

www.epfl.ch