  The controlled actuation of hydraulic and pneumatic actuators has unveiled
fresh and thrilling opportunities for designing mobile robots with adaptable
structures. Previously reported rolling robots, which were powered by fluidic
systems, often relied on complex principles, cumbersome pump and valve systems,
and intricate control strategies, limiting their applicability in other fields.
In this investigation, we employed a distinct category of functional fluid
identified as Electrohydrodynamic (EHD) fluid, serving as the pivotal element
within the ring-shaped actuator. A short stream of functional fluid is placed
within a fluidic channel and is then actuated by applying a direct current
voltage aiming at shifting the center of mass of the robot and finally pushed
the actuator to roll. We designed a ring-shaped fluidic robot, manufactured it
using digital machining methods, and evaluated the robot's characteristics.
Furthermore, we developed static and dynamic models to analyze the oscillation
and rolling motion of the ring-shaped robots using the Lagrange method. This
study is anticipated to contribute to the expansion of current research on EHD
flexible actuators, enabling the realization of complex robotic systems.
