Twin Leg Pairs

Start with imagining a typical humanoid robot. At the hips there would be 2 legs descending. However, in this design, just below the hip-joint, for each leg, there is another joint, where the leg can split to become two legs, one behind the other. Thus 4 separate legs can reach the ground (think of the 4 upper edges of a pyramid), giving the robot good stability.

The robot can walk in a mostly ordinary quadruped manner. There will be some differences because the legs all connect in a single region (not hugely unlike an insect, except the insect has 6 legs instead of 4), whereas the typical quadruped has well-separated pairs of legs.

However, whenever needed, and because of the way the legs are connected, a two-legged gait is also possible (sometime after the robot's balancing software gets perfected --that is considered to be a rather tough problem in robotics). Consider the left side of the robot, where first a short leg-length descends from the hip, as originally described, after which a special joint connects two more-ordinary legs (each with whatever other joints are desired for overall flexibility).

Imagine the special joint to be pliers-like, such that the two legs could nestle like the jaws of long-nose pliers (there is no equivalent of pliers-handle here; there is only joint and jaws- equivalent). When nestled, the two legs are equivalent to a single leg. On the right side of the robot we have the same sort of leg- arrangement, and thus when the two pairs of legs are nestled, the robot can theoretically move in a two-legged gait, and more- closely resemble a human. This could be good if you needed the robot to sit in a car seat and drive --having 4 splayed legs simply wouldn't work.

That's all.