  Robots excel at avoiding obstacles but struggle to traverse complex 3-D
terrain with cluttered large obstacles. By contrast, insects like cockroaches
excel at doing so. Recent research in our lab elucidated how locomotor
transitions emerge from locomotor-environment interaction for diverse locomotor
challenges abstracted from complex 3-D terrain and the strategies to overcome
them. Here we built on these fundamental insights to develop a
cockroach-inspired legged robot, Omni-Roach, that integrated these strategies
to achieve multi-modal locomotion and provide a robophysical model to study the
trade-off between multi-functionality and performance. The robot was based on
the RHex design with six compliant legs and featured a rounded body with two
wings that can open and a tail with pitch and yaw degrees of freedom. After two
development and testing iterations, our robot was capable of overcoming all
locomotor challenges with a high performance and success rate. It traversed
cluttered rigid pillars only 1.1x robot body width apart, a 2.5x hip height
bump, a 0.75x body length gap, densely cluttered flexible beams only 65% body
width apart, and self-righted within 4 seconds. Systematic beam traversal
experiments further revealed that a downward-pointing tail oscillating
laterally helps roll the body into beam gaps and break frictional and
interlocking contact to traverse. Our work highlights the usefulness of
multi-functional appendages and exaptation for large obstacle traversal.
