We know Boston Dynamics is keen on four-legged robots, even creating a cheetah of its very own. So is the Ecole Polytechnique Federale de Lausanne in Switzerland; its Cheetah-Cub has been in development at the Biorobotics Laboratory since 2008.
Teaching a quadruped robot to walk can be a tricky business, though. Something called a Central Pattern Generator (CPG) network is used to generate movements according to a repetitive pattern. But no matter how robust the rhythm of the movements is, it can be tough to implement outside of a lab environment, where the ground won't necessarily always be even.
Enter the Italian Institute of Technology (IIT). The team there broke down the movements of horses via motion capture into what it calls "kinematic Motion Primitives" (kMP), analyses of the trajectories of limbs and bodies, translated into data that can be fed into a CPG.
IIT broke down the motions required for walking, trotting, and galloping, creating cycled sequences for the cat-size Cheetah-Cub to mimic on its spring-based limbs. It also developed transitional movements, so that the robot could move between each gait smoothly.
The results were varied. Walking and trotting seemed to go fine, but galloping was a little more awkward, as the robot doesn't have a flexible spine that can expand and contract over its legs like the bunching of a real animal's body at top speed.
You can see Cheetah-Cub in action in the video below, and see the project paper online: "Horse-like walking, trotting, and galloping derived from kinematic Motion Primitives (kMPs) and their application to walk/trot transitions in a compliant quadruped robot."