We’re still a ways away from electric sheep roaming the fields pretending to bleat but robotics researchers continue to look to nature for four-legged inspiration. Meet Cheetah-Cub, a European Commission-funded research project, out of Swiss University the École Polytechnique Federale De Lausanne‘s biorobotics lab, that’s about the size of a house cat.

As its name suggests, Cheetah-Cub takes its cues from feline morphology with strings replacing tendons and actuators sited in the legs to do the work of muscles. The result is a robot that runs like a cat and is, according to its inventor Alex Sproewitz, the fastest robot for its size (under 30kg). To look at it’s like a miniature and less scary version of Boston Dynamic’s terrifying Big Dog bot. The latter is likely faster, being much taller, but for a bot with a mere 0.15m leg-length Cheetah-Cub can really go some — hitting a max of 1.42m/s or almost seven body lengths per second.

The Cheetah-Cub researchers have been aiming for fast gait first, with the bot’s design, but do also plan to work on improving its rough terrain traversing capabilities — including Big Dog-style “stand-up capabilities” – as the work progresses, says Sproewitz. Building legged robots capable of dynamic locomotion in rough terrain is a big challenge on both “the mechatronic level, but also for control”, he adds. So as scary as these bots inevitably look as they scuttle about on their test walkabouts there’s no fear of us humans having to outrun any of them yet.

There’s also no danger of Cheetah-Cub heading for any kind of commercial implementation any time soon, of course. It’s pure research. The road to a future infested with mechanical animals requires a lot more robotics researchers to put their heads together in the interdisciplinary areas of biomechanics and computational neurocontrol.

On the question of the role biology plays when designing legged robots, Sproewitz said he distinguishes between bio-inspired robotics, which is what the Cheetah-Cub project is aiming for, and the more faithful copying of bio-mimicking robotics. Cheetah-Cub’s tri-segmented leg design is therefore a bio-inspired “blueprint”, rather than a direct mimicking of a cat. ”We tested a leg design with the proposed pantograph [three-segment] structure, and a second (even more successful) leg design where several additional features were merged into,” he says.

This same blueprint approach is how the researchers are approaching the bot’s locomotion controls. “Our implementation of a mathematical model of a central pattern generator (CPG) is a simplified version of what was identified in vertebrate and invertebrate animals. A full copy of e.g. a spinal cord would not be feasible: complex networks of neurons with very different functionality exist in the spinal cord of larger animals,” he says. “Many researchers dedicate their entire career in identifying fragments of those networks.

“Again, currently we apply relatively simple models of CPGs. We assume that CPG networks responsible for locomotion have evolved, but have been partially maintained from simpler vertebrates (like lampreys and salamanders) up to humans. Therefore: Cheetah-cub robot is a natural continuation of Biorob’s research with its Lamprey/Salamander robot, and the implemented CPG control.”

[Image: Biorobotics Laboratory, EPFL]

By Natasha Lomas