Unified control keeps small surface boats on track after thruster failure
Constraint-Unified MPC for Over-Actuated Surface Vehicles with Post-Detection Fault Reconfiguration
Robotics
Summary
Small robotic boats that perform choreographed routines need to follow exact paths while dealing with limits on how hard each thruster can push. The authors created a control system that combines path following, deciding how much each thruster should push, and respecting thruster limits into one calculation. It also handles thruster failures by switching off failed thrusters detected by a fault detector. Tested on real boats in lakes and exhibitions, their system keeps the boats close to their planned paths even after losing one or two thrusters, performing better than previous methods.
What this means in practice
- •For marine robotics teams: Control multiple small surface vehicles precisely in coordinated aquatic shows, maintaining performance even after thruster failures.
- •For industrial robotic fleet operators: Operate fleets of over-actuated robots under actuator failure conditions while maintaining accurate path following and efficient actuator usage.
Authors
Sebastian Burmester, Ruiheng Jiang, Noa Sendlhofer, Raffaello D'Andrea, Aswin Ramachandran
Abstract
Choreographed aquatic performances require small autonomous surface vehicles to track precise paths under per-thruster force and rate limits, including after thruster failures. We report a deployed system in which trajectory tracking, thrust allocation, and the per-thruster force and rate limits are resolved in a single quadratic program over the per-thruster commands, with fault reconfiguration entering through one binary flag per thruster from an external detector. The system has driven a fleet in live performances on Lake Zürich and at the Time Space Existence 2025 exhibition in Venice. The field campaign measures 1.6 cm root mean square position error in a 10-minute hold and 4.3 cm over a 10 m square at 0.6 m/s. At 0.5 m/s, losing the front thruster increases the error to 11.6 cm, while losing the starboard-side thruster increases it to 11.5 cm. Losing two thrusters simultaneously leaves the craft tracking a 0.4 m/s square with a root mean square position error of 1.25 m. Compared to our own cascaded baseline, the unified formulation tracks the nominal square to the same few centimeters and holds station more tightly with roughly half the thruster force. The architectures separate after a thruster failure, where the unified controller stays within 24 cm of the reference path while the cascade leaves it.