Cooperative aerial transportation of cable-suspended loads is commonly studied using multirotor unmanned aerial vehicles (UAVs). However, non-stop UAVs such as fixed-wing carriers offer improved endurance and range, but cannot rely on hovering. This motivates the study of load-transport strategies in which the vehicles remain in continuous motion along closed periodic paths. Inspired by the classical synchronization of metronomes, this paper investigates whether phase synchronization emerges in a mechanically coupled multi-drone system transporting a shared cable-suspended load. The drones are controlled to follow an assigned circular path using path following such that no strict timing along the path is forced. This allows their phases to slowly evolve through the coupled dynamics.
The paper models each drone as a point mass constrained to a closed geometric path and connected to the rigid load by an elastic cable. A reduced phase model is derived by linearizing the cable-load dynamics around a nominal periodic state and applying the method of averaging to separate the slow phase drift from the fast oscillations. The resulting model contains phase-coupling terms between the drones and is used to predict the phase-locked states and test if they are locally stable, i.e., the system naturally tends towards them. Numerical simulations confirm that mechanically induced phase synchronization can occur through the shared load for the considered set of parameters. The simulations additionally confirm the stability trends suggested by the averaged model and that there exist phase-locked states in which the load maintains an effectively constant pose while the drones maintain motion along their paths.
