Pauses Provide Effective Control for an Underactuated Oscillating Swimming Robot

We describe motion primitives and closed-loop control for a unique low-cost single-motor oscillating aquatic system: the Modboat. The Modboat is driven by the conservation of angular momentum, which is used to actuate two passive flippers in a sequential paddling motion for propulsion and steering. We propose a discrete description of the motion of the system, which oscillates around desired trajectories, and propose two motion primitives - one frequency based and one pause-based - with associated closed-loop controllers. Testing is performed to evaluate each motion primitive, the merits of each are presented, and the pause-based primitive is shown to be significantly superior. Finally, waypoint following is implemented using both primitives and shown to be significantly more successful using the pause-based motion primitive.