The project is an implementation of Sreenath et al.’s modeling and control of a quadrotor with a cable suspended load. The system is modeled using the Newton-Euler approach and its dynamics are split into cable taut and nontaut dynamics with a continuous switching case between the two. The differential flatness properties of the quadrotor-load system are then used to derive a nonlinear cascaded control pipeline with errors operating on R^3, S^2, and SO(3) configuration spaces.
The load position and attitude, and the quadrotor attitude controllers are designed to be a proportional derivative controller with feedforward terms from the inverted dynamics. The system was discretized and implemented in simulation where it was tested with three load trajectories: a step input, a sinusoid and ramp in x-z, and a 2D lemniscate in x-y. The original PD controller proposed in the literature suffered from a steady-state error, which this codebase solved by introducing an integral term in the form of a PID controller.
Open Source Code: https://github.com/yvesdaoud/QuadrotorWithCableSuspendedLoad
References
Sreenath Koushil, Taeyoung Lee, and Vijay Kumar. “Geometric control and differential flatness of a quadrotor UAV with a cable-suspended load.” 52nd IEEE Conference on Decision and Control. IEEE, 2013.
Yves Daoud 