Three legs good, two legs better Thursday, 23 February 2017

Swiss researchers have discovered a faster and more efficient gait, never observed in nature, for six-legged robots walking on flat ground.

The team from Ecole Polytechnique Federale de Lausanne (EPFL) and the University of Lausanne carried out a host of computer simulations, tests on robots and experiments on fruit flies 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. The tripod gait involves having three legs on the ground at all times, two on one side of their body and one on the other.

They found that the common insect tripod gait came out on top when they optimised 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, even though 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 EPFL's Pavan Ramdya. “Ground robots should therefore break free from only using the tripod gait”.

They then 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 researchers 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 – and watched what happened. They found the flies began to use bipod-like leg coordination similar to the one discovered in the simulation.

[Photo: Alain Herzog/EPFL]