In March 2019 engineers at MIT showed off Mini Cheetah, a small four-legged robot, performing a 360-degree backflip, which MIT said made it the first four-legged robot to do so. The robot weighs about 20 pounds and is built so its legs can swing in wide arcs, letting it walk right-side up or upside down and recover quickly when knocked over.
Mini Cheetah was developed in the lab of mechanical engineering professor Sangbae Kim. Compared with the lab’s earlier, larger Cheetah robots, the Mini was designed to be cheap, rugged, and modular, built from low-cost off-the-shelf-style electric motors so that it could be bumped, dropped, and experimented on without fear of expensive damage. During testing it bounded along at roughly five miles per hour.
The backflip itself came from solving a large nonlinear trajectory optimization that worked out the precise torques each joint needed, given the robot’s mass and the limits of its motors. Kim framed the broader goal as giving robots the kind of agile, animal-like mobility that lets a dog scramble over obstacles and follow a person anywhere.
For a general reader, the acrobatic Mini Cheetah is memorable not as a stunt but as a demonstration that small, affordable, robust legged robots had reached a level of dynamic control once reserved for expensive one-off research machines.