Amplitude Control for Parallel Lattices of Docked Modboats

TL;DR

This paper presents a control strategy enabling a lattice of Modboat robots to swim as a single unit, avoiding unintentional undocking and minimizing internal forces, verified through experiments on various lattice sizes.

Contribution

It introduces a novel control method for parallel lattices of Modboats to achieve coordinated swimming without holonomic modules.

Findings

Control strategy prevents unintentional undocking.

Controller performs consistently across different lattice sizes.

Pure yaw control causes lateral movement that the framework cannot counteract.

Abstract

The Modboat is a low-cost, underactuated, modular robot capable of surface swimming. It is able to swim individually, dock to other Modboats, and undock from them using only a single motor and two passive flippers. Undocking without additional actuation is achieved by causing intentional self-collision between the tails of neighboring modules; this becomes a challenge when group swimming as one connected component is desirable. In this work, we develop a control strategy to allow parallel lattices of Modboats to swim as a single unit, which conventionally requires holonomic modules. We show that the control strategy is guaranteed to avoid unintentional undocking and minimizes internal forces within the lattice. Experimental verification shows that the controller performs well and is consistent for lattices of various sizes. Controllability is maintained while swimming, but pure yaw control causes lateral movement that cannot be counteracted by the presented framework.