Effects of Open-Loop Leg Forcing in Rotary and Radial Directions

In legged locomotion, the active forcing contributed by the leg can be considered to act in rotary and radial directions relative to the leg. Rotary forcing acting perpendicular to the leg, such as forcing due to hip torque, and radial forcing acting in the direction along the leg from foot to hip, are both present in animal locomotion. Given that these directions are orthogonal, simple rotary and radial leg forcing could be considered as basis functions of leg forcing. A systematic comparison of these types of actuation on the dynamics and energetics of legged locomotion would be valuable for the field of legged robotics, and for developing testable hypotheses regarding human and animal locomotion.