Self-Stability Mechanisms for Sensor-Cheap Legged Locomotion

It is now well established that running animals’ mass centers exhibit the characteristics of a Spring Loaded Inverted Pendulum (SLIP) in the sagittal plane (Blickhan and Full, 1993). What control policy accomplishes this collapse of dimension by which animals solve the “degrees of freedom problem” (Bernstein, 1967)? How valuable might this policy be to gait control in legged robots?