New two-legged robot walks like an animated character

Researchers at Disney have designed a new robot that not only looks like an animated character but also mimics its walk.
Beginning with an animation of a diminutive, peanut-shaped character that walks with a rolling, somewhat bow-legged gait, researchers analysed the character's motion to design a robotic frame that could duplicate the walking motion using 3D-printed links and servo motors, while also fitting inside the character's skin.
They then created control software that could keep the robot balanced while duplicating the character's gait as closely as possible.
Katsu Yamane and Joohyung Kim of Disney Research Pittsburgh and Seungmoon Song, a PhD student at Carnegie Mellon University's Robotics Institute, focused first on developing the lower half of such a robot.

"Walking is where physics matter the most. If we can find a way to make the lower half work, we can use the exact same procedure for the upper body," Yamane said.
An analysis of the animated character showed that its ankle and foot had three joints, each of which had three degrees of freedom. Integrating nine actuators in a foot isn't practical, researchers said.

Researchers realised that the walking motion in the animation wasn't physically realisable - if the walking motion in the animation was used on a real robot, the robot would fall down.
By studying the dynamics of the walking motion in simulation, the researchers realised they could mimic the motion by building a leg with a hip joint that has three degrees of freedom, a knee joint with a single degree of freedom and an ankle with two degrees of freedom.

Because the joints of the robot differ from what the analysis showed that the animated character had, the researchers couldn't duplicate the character's joint movements, but identified the position trajectories of the character's pelvis, hips, knees, ankle and toes that the robot would need to duplicate.
To keep the robot from falling, the researchers altered the motion, such as by keeping the character's stance foot flat on the ground.
They then optimised the trajectories to minimise any deviation from the target motions, while ensuring that the robot was stable.