According to Information Arts by Stephen Wilson, sophisticated motion is a challenge being explored by many researchers. Humanlike motion is very difficult as robots need to be created with foot re-positioning, center of gravity, and overall dynamic walking abilities. Research labs like MIT’s Leg Laboratory have built many monoped, biped, and quadruped robots to test the ability of robots in humanlike walking.
These are some of the robots:
The first robot that the leg lab built was the Planar One-Leg Hopper (1980-82). It “explores active balance and dynamic stability in locomotion. Experiments with the Planar One-Leg Hopper showed that balance could be achieved with a simple control system. The control system has three separate parts: one controlling forward running speed, one controlling body attitude, and one controlling hopping height.”
The Planar Biped (1985-90) is a two-legged robot that has the ability to run with two legs connected to pivot joints at the hip. By extending and retracting the legs, it can step forward with control of feet positioning.
The Quadruped (1984-87) was made to explore running on four legs.
Here are three videos of it trotting, pacing, and bounding:
The 3D Biped (1989-1995), to me, is one of the coolest and cutest. It runs and hops on two legs and has the ability to perform a flip that many humans cannot even do. It has the strength to pull a carriage with a human sitting in it. Here is the video of the flip: