Researchers at the University of Michigan have unveiled an ingenious new robot called SKOOTR that can "skate" around in a remarkably stable manner on just three radially-symmetric legs. The key innovation behind SKOOTR is combining the omnidirectional maneuverability of a ball robot with the stability and versatility of a multi-legged robot design.

The central component of SKOOTR is a large spherical body that can passively rotate, similar to a rollerblade wheel or office chair caster. Mounted on top of this sphere is a central hub holding the robot's electronics, with three legs extending outwards. Each leg has two joints allowing it to flex and extend, with a hybrid "foot" that can switch between a rolling caster mode and a high friction rubber grip.

"We use a servo to switch between a passively rolling caster or a grippy rubber foot," explained Talia Y. Moore, an associate professor at Michigan and co-author on the SKOOTR paper. "The rubber foot provides friction so that it can use a leg to push against the ground, while the rolling caster allows other legs to maintain their position while rolling along."

This ingenious hybrid leg design allows SKOOTR to utilize multiple locomotion modes. In its primary "skooting" gait, two legs remain planted on the ground with rubber feet while the third leg uses its caster wheel to propel the body forward by rolling. The robot effortlessly transitions between rolling directions by simply lifting and replanting its legs, exhibiting remarkable stability and maneuverability.

"Due to this combination of the central sphere and multiple legs, SKOOTR is incredibly stable," Moore said. "We have been doing lots of experiments with SKOOTR and it's basically impossible to flip it over while it is operating."

But SKOOTR is capable of far more than just skating around. By coordinating all three legs to lift and reposition the central sphere, the robot can climb over obstacles and even ascend stairs – feats that would be extremely challenging for other spherical or wheeled robots.

The key inspiration behind SKOOTR's novel design came from Moore herself rolling around on an office chair. "I realized that the passively rolling office chair could easily spin in any direction, and I could use my legs to perform a variety of maneuvers while staying remarkably stable," she recalled. This biological inspiration carried through to SKOOTR's radially symmetric configuration, mimicking creatures like brittle stars or spiders.

While an undergraduate student named Adam Hung initially built the first SKOOTR prototype during a summer break using a 3D printer, the design has since been refined and tested extensively in Moore's robotics lab. The large spherical body at the robot's core can be easily swapped out for different sizes or hollow variants that could potentially carry payloads.

Looking ahead, Moore and her team plan to further explore the benefits of radial symmetry and hybrid leg designs for enabling new forms of efficient, stable robotic locomotion. They already have a collaboration lined up with neuroscientists interested in using SKOOTR as a model system for studying octopuses and other radially symmetric organisms.

With its effortless mobility, adaptability, and inherent stability, SKOOTR represents an exciting advance in legged robotics. This skating tri-pedal robot hints at the transformative potential of drawing unconventional inspiration from nature to develop innovative new machines suited for the future of robotic applications.