six-legged robot

Insect-inspired, six-legged robot boasts superior speed to its natural counterparts

A six-legged robot inspired by insects that can move around an environment at a high speed has been developed by researchers at École Polytechnique Fédérale de Lausanne (EPFL).

When vertebrates run, their legs exhibit minimal contact with the ground. But insects are different and actually run fastest using a ‘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.

The EPFL research team has found a faster way for robots to traverse flat ground, provided they don’t have the adhesive pads used by insects to climb walls and ceilings.

The designers believe that insect-inspired robots should make a break with the tripod-gait paradigm and instead consider other possibilities including a new ‘bipod’ gait.

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 of the study.

To test the various combinations, the researchers used an evolutionary-like algorithm to optimise 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 findings shed new light on problems for biologists and robotics engineers alike. 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 - although in nature no insects 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 (below) capable of employing either the tripod or bipod gait. The bipod gait was again demonstrated to be faster, corroborating the simulation algorithms’ results.

Real insects were examined to see if leg adhesion might also play a role in the walking coordination of flies. They put polymer drops on the flies’ legs to cover their claws and adhesive pads - as if the flies were wearing boots - and watched what happened.

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 behaviour of animal species. We believe that our work represents an important contribution to the study of animal and robotic locomotion.”

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