  In this paper, we present a framework rooted in control and planning that
enables quadrupedal robots to traverse challenging terrains with discrete
footholds using visual feedback. Navigating discrete terrain is challenging for
quadrupeds because the motion of the robot can be aperiodic, highly dynamic,
and blind for the hind legs of the robot. Additionally, the robot needs to
reason over both the feasible footholds as well as robot velocity by speeding
up and slowing down at different parts of the terrain. We build an offline
library of periodic gaits which span two trotting steps on the robot, and
switch between different motion primitives to achieve aperiodic motions of
different step lengths on an A1 robot. The motion library is used to provide
targets to a geometric model predictive controller which controls stance. To
incorporate visual feedback, we use terrain mapping tools to build a local
height map of the terrain around the robot using RGB and depth cameras, and
extract feasible foothold locations around both the front and hind legs of the
robot. Our experiments show a Unitree A1 robot navigating multiple unknown,
challenging and discrete terrains in the real world.
