A low-cost experimental rig for multi-DOF unsteady thrust measurements of aquatic bioinspired soft robots

The design, calibration and testing of an experimental rig for measuring 2-DOFs unsteady loads over aquatic robots is discussed. The presented apparatus is specifically devised for thrust characterization of a squid-inspired soft unmanned underwater vehicle, but its modular design lends itself to more general bioinspired propulsion systems and the inclusion of additional degrees of freedom. A purposely designed protocol is introduced for combining calibration and error compensation upon which force and moment measurements can be performed with a mean error of 0.8% in steady linear loading and 1.7% in unsteady linear loading, and mean errors of 10.2% and 9.4% respectively for the case of steady and dynamic moments at a sampling rate of the order of 10 Hz. The ease of operation, the very limited cost of manufacturing and the degree of accuracy make this an invaluable tool for fast prototyping and low-budget projects broadly applicable in the soft robotics community.