Researchers were interested in creating a hopping robot that would be able to maintain a stable jump up and down, but they struggled to do so because stabilization is easily lost between jumps.
They fixed this by applying a special motorized tail that could move up and down or side to side to correct stabilization problems during ascent and decent through hopping. The two motors that were connected via belts were essentially creating a spherical joint.
As we edge closer to hopping robots, the wheel may no longer be necessary in future robotics. We're getting ever-so-closer to real-like AT-ATs like from Star Wars despite how small scale these are.