Robot studies shed fast light on insect evolution


Engineers have found a better six-legged gait than nature has devised. Anthea Batsakis reports.


Six-legged robots, modelled on the movement of insects, have long been favoured by robotics researchers seeking to develop mobile machines capable of taking the rough with smooth.

Hexapods, as they are known, have huge advantages in applications such as search and rescue missions. Six legs are better than four or two for navigating unsteady terrain; and, says Queensland University of Technology robotics engineer Jonathan Roberts, provide useful spares. “Six or eight-legged robots can survive a broken leg,”he says.“Having these backups are always attractive in robotics.”

Now a team of Swiss and US scientists have worked out a way to make such robots go faster, by modelling and varying the natural gait of fruit flies.

Fruit flies, like most other six-legged insects, use a“tripod gait, keeping three legs in contact with the surface at all times. The tripod gait has also been the basis for the walking style of six-legged robots (known as hexapods).

Researchers have discovered a faster and more efficient gait, never observed in nature, for six-legged robots walking on flat ground.
EPFL/ALAIN HERZOG

By simulating and testing different gaits for six legs, the researchers found the speediest results with a “bipod gait”– a walking style requiring only two legs being in contact with the ground at a time. It’s comparable to the gait used by horses or dogs.

Perhaps the more interesting aspect of the research, though, is that lead researchers Pavan Ramdya, from the University of Lausanne, and Robin Thandiackal, from Ecole Polytechnique Fédérale De Lausanne, then“reverse-engineered” their findings with experiments on fruit flies.

Fruit flies might not be the Usain Bolts of the insect world but they do have the ability to walk upside down, thanks to the sticky pads on their legs.

When the researchers disabled that stickiness using drops of polymer, the flies took on the same quicker bipod gait modelled by their algorithm.

“It's really interesting that by doing these simulations, and thinking about robot theory, they figured out that there should be another way nature can work,” says Roberts, who was not involved in the study. “Often scientists observe nature and try and work out why something happens, but this is kind of the reverse.”

The findings, published in Nature Communications, suggest that sticky feet makes the quicker bipod gait less feasible, much like trying to run with chewing gum stuck to each shoe. The tripod gait, on the other hand, helps insects keep grip when they're climbing on walls and ceilings and might be why its so commonly used.

There's a bit of an underlying assumption that the tripod gait is the basic gait [for six-legged insects],”sys David Merritt, an entomologist from the University of Queensland, “but this study has shown us that insects probably modify their gait based on what environment they're in.”

Anthea Batsakis is a freelance journalist in Melbourne, Australia.
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