Modeling, design and control of low-cost differential-drive robotic ground vehicles: Part II-Multiple vehicle study

Toward the ambitious long-term goal of a fleet of cooperating Flexible Autonomous Machines operating in an uncertain Environment (FAME), this two part paper addresses several critical modeling, design and control objectives for ground vehicles. Within Part I of this paper, a low-cost differential drive robotic vehicle was introduced for FAME research. Suitable nonlinear/linear-models were used to develop inner/outer-loop control laws for a single vehicle; e.g. wheel (and vehicle translational/rotational) velocity inner-loop control, etc. Part II of this paper focusses on the coordination of multiple vehicles. The (faster) inner-loop control law discussed within Part I is used for all (slower) outer-loop control modes demonstrated within Part II. We specifically demonstrate (via simulations and hardware) the following specific outer-loop control laws: (1) Δx-θ separation-direction control, (2) collision avoidance, (3) separation control for a longitudinal platoon of vehicles. Empirically collected data is shown to agree well with simulation results. Reasons for observed differences are provided. The simple separation-direction control structure is adequate because of the (higher bandwidth) inner-loop control law. We observed (and expected) that (1) collision avoidance works well as long as the controlled vehicle is not traveling too fast with respect to obstacles. (2) with respect to platoon control, we demonstrated that feedforward of leader speed information significantly and uniformly improves separation performance as we move rearward in the platoon. In short, many capabilities that are critical for reaching the longer-term FAME goal are demonstrated within this two part paper.