  We derive a hybrid feedback control law for the lateral leg spring (LLS)
model so that the center of mass of a legged runner follows a curved path in
horizontal plane. The control law enables the runner to change the placement
and the elasticity of its legs to move in a desired direction. Stable motion
along a curved path is achieved using curvature, bearing and relative distance
between the runner and the curve as feedback. Constraints on leg parameters
determine the class of curves that can be followed. We also derive an optimal
control law that stabilizes the orientation of the runner's body relative to
the velocity of the runner's center of mass.
