  This study presents a modular, electronics-free, and fully onboard control
and actuation approach for SMA-based soft robots to achieve locomotion tasks.
This approach exploits the nonlinear mechanics of compliant curved beams and
carefully designed mechanical control circuits to create and synchronize
rhythmic deformation cycles, mimicking the central pattern generators (CPG)
prevalent in animal locomotions. More specifically, the study elucidates a new
strategy to amplify the actuation performance of the shape memory coil actuator
by coupling it to a carefully designed, mono-stable curve beam with a
snap-through buckling behavior. Such SMA-curved beam assembly is integrated
with an entirely mechanical circuit featuring a slider mechanism. This circuit
can automatically cut off and supply current to the SMA according to its
deformation status, generating a self-sustained rhythmic deformation cycle
using a simple DC power supply. Finally, this study presents a new strategy to
coordinate (synchronize) two rhythmic deformation cycles from two robotic
modules to achieve efficient crawling locomotion but still use a single DC
power. This work represents a significant step towards fully autonomous,
electronics-free SMA-based locomotion robots with fully onboard actuation and
control.
