American Institute of Aeronautics and Astronautics, Infotech@Aerospace Conference, Paper No. 2005-7077 1 A Small Semi-Autonomous Rotary-Wing Unmanned Air Vehicle (UAV) Scott D. Hanford * , Lyle N. Long † , and Joseph F. Horn. ‡ The Pennsylvania State University, University Park, PA, 16802 Small radio controlled (R/C) rotary-wing UAVs have many potential military and civilian applications, but can be very difficult to fly. Small and lightweight sensors and computers can be used to implement a control system to make these vehicles easier to fly. To develop a control system for a small UAV, an 8-bit microcontroller has been interfaced with MEMS (Micro-Electro-Mechanical Systems) gyroscopes, an R/C transmitter and receiver, and motor drivers. A single angular degree of freedom test bed has been developed to test these electronics and successful pilot-in-the-loop PI control has been achieved for this test system. A quadrotor with a stability augmentation system that uses these electronics to control the vehicle has also been developed. The future goals of this research are to incorporate more sensors to increase the level of autonomy for UAV operation. I. Introduction Small unmanned air vehicles (UAVs) can be deployed at the front lines of combat to provide situational awareness to small units of troops through real-time information about surrounding areas. 1 Small fixed-wing unmanned and micro air vehicles (such as the Dragon Eye, Aerosonde, Hornet, and Wasp) have become prevalent and have demonstrated impressive flight abilities and levels of autonomy. 2 These UAVs can weigh as little as a few ounces. However, even the lightest models must fly fairly fast to provide sufficient lift for flight. 3 These fixed wing aircraft also need space to turn and although research has studied their capability to fly in small circles over a specified area, they are difficult to fly in confined places, such as urban environments and small indoor spaces. 3,4 Rotary-wing unmanned air vehicles have the potential to be very useful if they can hover and fly vertically. VTOL UAVs such as the Fire Scout and Hummingbird currently have the capability to fly autonomously, land in a specific location and take off again. 1,2 Smaller UAVs with these abilities would have many applications, including flying through buildings for search and rescue or surveillance operations. However, the technical challenges for small rotary-wing UAV systems are numerous. High thrust-to-weight ratios are necessary for the propulsion system. An endurance long enough to perform a meaningful mission will also be important. A careful matching of batteries, electric motors, and rotors will be essential; and these will have to be sized to carry the necessary payload. Incorporating a reliable semi-autonomous control system in these small vehicles, so that the operator does not have to constantly monitor their performance or location, will be very challenging since they will only be able to carry the smallest microprocessor systems and power supplies along with very lightweight and inexpensive sensor systems. In addition, a Global Positioning System (GPS) will not work indoors, so other sensors will have to be used for indoor flight. The software will have to be very compact to fit in the available memory, but powerful enough to provide intelligent control with sensor data of limited quality. II. Quadrotor Background A quadrotor unmanned air vehicle has four rotors and requires no cyclic or collective pitch. A quadrotor UAV can be highly maneuverable, has the potential to hover and to take off, fly, and land in small areas, and can have simple control mechanisms. 5,6 However, because of its low rate damping, electronic stability augmentation is required for stable flight. * NSF Fellow, Aerospace Engineering, Member AIAA, sdh187@psu.edu. † Professor, Aerospace Engineering, Associate Fellow AIAA, lnl@psu.edu. ‡ Assistant Professor, Aerospace Engineering, Senior Member AIAA, joehorn@psu.edu.