Avionics System for a Small Unmanned Helicopter Performing Agressive Maneuvers

An Xcell-60 5 ft rotor diameter hobby helicopter was instrumented to perform autonomous aggressive maneuvers. Avionics system, state estimator design, and vibration isolation are presented in detail. Analysis of helicopter dynamics based on flight data is given. 1 Ph. D. candidate, Department of Aeronautics and Astronautics, [email protected] 2 M.S. candidate, Department of Electrical Engineering, [email protected] 3 Professor of Electrical Engineering, [email protected] 4 Associate Professor of Aeronautics and Astronautics, [email protected]. Corresponding author. Introduction Recently there has been considerable interest in applications of small unmanned helicopters. Most of research was concentrated on achieving greater autonomy, for example using imaging sensors to perform a navigation task (International Aerial Robotics Competition, research at Carnegie Mellon Robotics Institute). One interesting feature of small-size unmanned helicopters is their outstanding maneuverability, because they are not constrained by human presence onboard. A small hobby helicopter with vibration mounted film camera was used to create a highly agile falcon-eye video for a National Geographic TV documentary, aired in January 2000. During the videotake a 5 ft rotor diameter helicopter was manually flown between skyscrapers in Bronx. Wide maneuver envelope and hovering capability of small helicopters can potentially be used in urban warfare. To make aggressive maneuvering safer and decrease overarching dependence on skills of a pilot, it is necessary to design a feedback control system with adequate closed loop bandwidth. We are preparing a demonstration of fully autonomous flight featuring aggressive maneuvers, including split-S and longitudinal loop. This paper describes an avionics system we implemented to achieve high-bandwidth feedback control, robust to modeling errors and gusts. Vibration isolation with proper frequency characteristics is essential for high-g flight of a rotorcraft. We summarize our successful vibration mount design in the paper. Description of a test vehicle Our test vehicle, shown in Figure 1, is an alcohol-powered Xcell-60 hobby helicopter. Figure 1. M.I.T. Xcell-60 with avionics system It has a two-blade teetering rotor augmented with Bell-Hiller stabilizing bar. Rotor diameter is 5 ft. Gross takeoff weight (with 7 lbs of avionics added to the airframe) is 18 lbs. A well-trained RC pilot has performed high-speed 2 g turns, full longitudinal loops, and high-rate stall turns with the data acquisition payload. Rotor speed range is 1500-1700 RPM. An electronic governor maintains commanded rotor speed by adjusting throttle commands. A hobby gyro provides proportional negative feedback of measured yaw rate to tail rotor pitch, thereby augmenting yaw rate damping. The