  We present a highly reactive controller which enables bipedal robots to
blindly walk over various kinds of uneven terrains while resisting pushes. The
high level motion planner does fast online optimization for footstep locations
and Center of Mass (CoM) height using the decoupled actuated Spring Loaded
Inverted Pendulum (aSLIP) model. The decoupled aSLIP model simplifies the
original aSLIP with Linear Inverted Pendulum (LIP) dynamics in horizontal
states and spring dynamics in the vertical state. The motion planning can be
formulated as a discrete-time Model Predictive Control (MPC) and solved at a
frequency of 1k~HZ. The output of the motion planner using a reduced-order
model is fed into an inverse-dynamics based whole body controller for execution
on the robot. A key result of this controller is that the foot of the robot is
compliant, which further extends the robot's ability to be robust to unobserved
terrain changes. We evaluate our method in simulation with the bipedal robot
SLIDER. Results show the robot can blindly walk over various uneven terrains
including slopes, wave fields and stairs. It can also resist pushes while
walking on uneven terrain.
