Lars B. Cremean

The Caltech Multi-Vehicle Wireless Testbed

We introduce the Caltech Multi-Vehicle Wireless Testbed (MVWT), a platform for testing decentralized control methodologies for multiple vehicle coordination and formation stabilization. The testbed consists of eight mobile vehicles, an overhead vision system that provides GPS-like state information and wireless Ethernet for communications. Each vehicle rests on omni-directional casters and is powered by two high-performance ducted fans. Thus, a unique feature of our testbed is that the vehicles have second order dynamics, requiring real-time feedback algorithms to stabilize the system while performing cooperative tasks. The testbed will be used by various research groups at Caltech and elsewhere to validate theoretical advances in multi-vehicle coordination and control, networked control systems, real-time networking and high confidence distributed computation.

Alice: An information-rich autonomous vehicle for high-speed desert navigation

This paper describes the implementation and testing of Alice, the California Institute of Technology’s entry in the 2005 DARPA Grand Challenge. Alice utilizes a highly networked control system architecture to provide high performance, autonomous driving in unknown environments. Innovations include a vehicle architecture designed for efficient testing in harsh environments, a highly sensory-driven approach to fuse sensor data into speed maps used by real-time trajectory optimization algorithms, health and contingency management algorithms to manage failures at the component and system level, and a software logging and display environment that enables rapid assessment of performance during testing. The system successfully completed several runs in the National Qualifying Event, but encountered a combination of sensing and control issues in the Grand Challenge Event that led to a critical failure after traversing approximately 8 miles.

Position tracking for a nonlinear underactuated hovercraft: controller design and experimental results

This paper addresses the position tracking control problem of an underactuated hovercraft vehicle. A nonlinear Lyapunov-based tracking controller is developed and proved to exponentially stabilize the position tracking error to a neighborhood of the origin that can be made arbitrarily small. The desired trajectory does not need to be a specially chosen (e.g., a trimming trajectory). In fact, it can be any sufficiently smooth bounded curve parameterized by time. The nonlinear controller has been experimentally validated on the Caltech Multi-Vehicle Wireless Testbed (MVWT), a platform for the development and implementation of novel single-and multiple-vehicle control designs. Experimental results are given for tracking of prescribed trajectories and for target following.

Model-based estimation of off-highway road geometry using single-axis LADAR and inertial sensing

This paper applies some previously studied extended Kalman filter techniques for planar road geometry estimation to the domain of autonomous navigation of off-highway vehicles. In this work, a clothoid model of the road geometry is constructed and estimated recursively based on road features extracted from single-axis LADAR range measurements. We present a method for feature extraction of the road centerline in the image plane, and describe its application to recursive estimation of the road geometry. We analyze the performance of our method against simulated motion of varied road geometries and against closed-loop detection, tracking and following of desert roads. Our method accommodates full 6 DOF motion of the vehicle as it navigates, constructs consistent estimates of the road geometry with respect to a fixed global reference frame, and requires an estimate of the sensor pose for each range measurement

Stability analysis of interconnected nonlinear systems under matrix feedback

This paper explores the stability analysis problem for nonlinear systems which have general linear feedback interconnections. Systems are often modeled in this manner in the study of decentralized control because many communication topologies can be modeled and analyzed using connections to graph theory. We present necessary conditions for stability of a classification of interconnected systems, and we give some examples to provide insight into this problem. These conditions are related to positive definiteness of matrices associated with the feedback interconnection, and specialize to the common case where the Laplacian matrix of a graph represents the communication topology of the system.

A Platform for Cooperative and Coordinated Control of Multiple Vehicles

The Caltech Multi-Vehicle Wireless Testbed (MVWT) is an experimental plat-form for investigating the increasingly important intersecting frontiers of reliable distributed computation, communication and control. The testbed consists of eight autonomous vehicles equipped with onboard sensing, communication and computation. The vehicles are underactuated and exhibit nonlinear second-order dynamics, key properties that capture the essence of similar real-world applications at the forefront of cooperative control.

A new approach to teaching feedback

The Control and Dynamical Systems (CDS) Department at the California Institute of Technology (Caltech) has revised its entry-level curriculum in dynamics, feedback, and control with the goals of updating the subject matter to include modern tools and making control tools accessible to a nontraditional audience. One of the approaches made was to divide the introductory control theory class into two tracks, with a conceptual track geared toward students who need only a conceptual overview of control tools and an analytical track providing a more detailed mathematical treatment of feedback. The conceptual track, CDS 101, which is mainly discussed in the paper, is intended for advanced students in science and engineering who can benefit from an overview of control techniques but who might not have the need for the mathematical depth underlying the material. Special attention is paid to ensuring that the course is accessible to students from biological, physical, and information sciences, using examples from these domains to illustrate concepts. The goal of the course is to enable students to use the principles and tools of feedback in their research activities.