An Attitude Heading and Reference System: Basic Concepts and Prototype

This article proposes a basic platform for inertial measurements. In order to control an autonomous vehicle, it is fundamentally important to know its attitude. For aerial vehicles, this information is critical to determining the control loop's feedback parameters. For manned aircraft, roll, pitch and yaw can be obtained through orientation by an inertial reference, usually the ground, or instruments such as an artificial horizon or a compass. Still all of them are dependent on pilot interaction. For unmanned platforms, it becomes necessary to use an electronic device capable of measuring physical quantities related to that goal. A device that aggregates these sensors is called IMU (Inertial Measurement Unit). An IMU contains inertial sensors that measure linear acceleration and angular rate, among other physical data. Through reading and fusing these data it is possible to obtain attitude information which, applied to flight history, can help to determine the position relative to an initial position, as well as feeding the control loop with the necessary data to control actuators, in a way that allows an aircraft to be stabilized or maneuvered to follow a predetermined trajectory, fulfilling the role of replacing a pilot. Our proposed platform is composed of sensors for inertial measurements, as well as a basic firmware capable of estimating the attitude of the platform, effectively creating an attitude heading reference system (AHRS).