  Faced with strong demand for robots working in underwater pipeline
environments, a novel underwater multi-model locomotion robot is designed and
studied in this research. By mimicking the earthworm's metameric body, the
robot is segmented in the structure; by synthesizing the earthworm-like
peristaltic locomotion mechanism and the propeller-driven swimming mechanism,
the robot possesses unique multi-mode locomotion capability. In detail, the
in-pipe earthworm-like peristaltic crawling is achieved based on
servomotor-driven cords and pre-bent spring-steel belts that work
antagonistically, and the three-dimensional underwater swimming is realized by
four independently-controlled propellers. With a robot covering made of silicon
rubber, the two locomotion modes are tested in the underwater environment,
through which, the rationality and the effectiveness of the robot design are
demonstrated. Aiming at predicting the robotic locomotion performance,
mechanical models of the robot are further developed. For the underwater
swimming mode, by considering the robot as a spheroid, an equivalent dynamic
model is constructed, whose validity is verified via computational fluid
dynamics (CFD) simulations; for the in-pipe crawling mode, a classical
kinematics model is employed to predict the average locomotion speeds under
different gait controls. The outcomes of this research could offer useful
design and modeling guidelines for the development of earthworm-like locomotion
robots with unique underwater multi-mode locomotion capability.
