  Robotic swimmers are currently a subject of extensive research and
development for several underwater applications. Clever design and planning
must rely on simple theoretical models that account for the swimmer's
hydrodynamics in order to optimize its structure and control inputs. In this
work, we study a planar snake-like multi-link swimmer by using the `perfect
fluid' model that accounts for inertial hydrodynamic forces while neglecting
viscous drag effects. The swimmer's dynamic equations of motion are formulated
and reduced into a first-order system due to symmetries and conservation of
generalized momentum variables. Focusing on oscillatory inputs of joint angles,
we study optimal gaits for 3-link and 5-link swimmers via numerical
integration. For the 3-link swimmer, we also provide a small-amplitude
asymptotic solution which enables obtaining closed-form approximations for
optimal gaits. The theoretical results are then corroborated by experiments and
motion measurement of untethered robotic prototypes with 3 and 5 links floating
in a water pool, showing a reasonable agreement between experiments and the
theoretical model.
