Estimation of inertial properties for a multilift slung load

A method to estimate mass, center of mass, and moments of inertia of a multilift slung load is described. An analysis of system dynamics relates slung load response to cable tension, and a means to estimate cable tension without a direct cable force sensor is described. Three different estimators (least squares, maximum likelihood, and Kalman filter) are derived and compared for this estimation problem. Flight tests performed in a motion capture studio are used to demonstrate the utility of the proposed approach. Payload mass is estimated with less than 3% error without the use of a cable tension sensor. Mass added to the payload to intentionally change the center of mass and moment of inertia is used to verify the estimation of center of mass and moment of inertia, with center of mass estimates estimated to well within one centimeter of the true location. Trajectory tracking tests comparing uncompensated (i.e., nominal) center of mass and compensated (estimated) center of mass show that payload position tracking is essentially unchanged. However, payload orientation, cable tension, and rotorcraft position tracking are significantly improved when the estimated center of mass is incorporated into the feedback loop.