A low cost, sensor-less drag force estimation methodology via measuring of motor currents

Modeling and control of underwater vehicles presents the challenge of sufficiently identifying acting hydrodynamic forces. Modern approaches assume the use of direct sensor measurements, which usually involves expensive and complicated setups. In this paper, a new approach to estimating hydrodynamic drag forces is proposed that does not employ a force sensor. The developed methodology involves processing the system responses and motor current measurements. A low cost towing carriage system is developed, driven by a 2-axis servomechanism with composite chains, off-the-shelf electronics and custom software running on the BeagleBone embedded platform. The sensor-less methods are described and the resulting drag estimates are experimentally compared to measurements produced by a 6-DOF force sensor, showing the merits of the developed methods.