A Distributed Avionics Package for Small UAVs Jack Elston * , Brian Argrow † , Eric Frew ‡ University of Colorado, Boulder, CO, 80309, USA This paper presents the design and implementation of a distributed computing architec- ture used to accommodate a wide range of operational environments. The architecture’s advantages include fault-tolerance and redundancy through an abstracted high and low- level bus protocol, and significant system scaling enabled by its modular nature. The current implementation was created for use in an avionics context, where it accommodates many payload sizes, levels of complexity, and configurations. Each of these advantages are evident in one of the many RECUV (Research and Engineering Center for Unmanned Vehicles at the University of Colorado) sponsored projects that use this system. This paper will describe some of these projects and how each maintains very different system requirements, ranging from providing a full-featured avionics system, to enabling control of a micro-UAV. I. Introduction U sing a modular architecture for an embedded system provides many advantages over a single board solution. Customization and system-reconfiguration are simplified, and upgrading the system is signifi- cantly less expensive and time consuming. Modular architectures enable piecewise development and testing of a system, so long as a well defined interface exists between modules. Tasks can be decentralized within a group, and each component can be later added to the final system. Each subgroup is able to maintain “ownership” of one particular node, and can be responsible solely for its development and maintenance. In the case of multi-stage projects, modularity ensures a smooth transition from a finalized deliverable to the next step in the development process. A modular architecture also allows for each system to be studied and understood within its own context, and therefore lends itself well to teaching applications. A course may be be constructed of separate units which focus on a single subsystem of an avionics package. An example division of these topics may be: sensor fusion and interface, control algorithms, communication protocols, and filtering. Each subsystem can be taught, constructed and verified without requiring full knowledge of the rest of the system. Not only does a modular approach allow the benefit of focusing on one part at a time, it also enforces the correct method of designing and testing complex systems. The functionality of a modular system relies heavily on the definition and adherence to a strict interface. Each component can be designed and constructed independently, but must conform to set guidelines to perform as a system. This encourages a fairly high level approach to the design phase, and a significant amount of time must be spent on defining separate subsystems and their interfaces before any work is done. Similarly, modular design highlights the value of developing a good testing algorithm. Each component should be tested independently before integration to simplify and reduce system level problems. Focusing on the specific example of avionics systems, two main alternatives exist to constructing a modu- lar system. In the past, many avionics packages were designed using a federated architecture, where aircraft control is managed through several essentially independent systems. Some inter-system communication is performed in this architecture, but is kept to a minimum to decrease each system’s complexity and inter- dependence 1 (which could lead to multiple failures). Not only does this architecture require a tremendous amount of resources, but it also makes reconfiguring the system very difficult. Another common architecture, especially for use in very small UAVs, is the single board solution. 23 A single board avionics package requires * Graduate Research Assistant, Department of Aerospace Engineering Sciences. Student Member † Associate Professor, Director Research and Engineering Center for Unmanned Vehicles. Senior Member. ‡ Assistant Professor, Department of Aerospace Engineering Sciences. 1 of 10 American Institute of Aeronautics and Astronautics Infotech@Aerospace 26 - 29 September 2005, Arlington, Virginia AIAA 2005-6984 Copyright © 2005 by Jack Elston. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.