  Terrestrial animals and robots are susceptible to flipping-over during rapid
locomotion in complex terrains. However, small robots are less capable of
self-righting from an upside-down orientation compared to small animals like
insects. Inspired by the winged discoid cockroach, we designed a new robot that
opens its wings to self-right by pushing against the ground. We used this robot
to systematically test how self-righting performance depends on wing opening
magnitude, speed, and asymmetry, and modeled how kinematic and energetic
requirements depend on wing shape and body/wing mass distribution. We
discovered that the robot self-rights dynamically using kinetic energy to
overcome potential energy barriers, that larger and faster symmetric wing
opening increases self-righting performance, and that opening wings
asymmetrically increases righting probability when wing opening is small. Our
results suggested that the discoid cockroach's winged self-righting is a
dynamic maneuver. While the thin, lightweight wings of the discoid cockroach
and our robot are energetically sub-optimal for self-righting compared to tall,
heavy ones, their ability to open wings saves them substantial energy compared
to if they had static shells. Analogous to biological exaptations, our study
provided a proof-of-concept for terrestrial robots to use existing morphology
in novel ways to overcome new locomotor challenges.
