实时飞行控制:嵌入式传感器校准和数据采集

A fixed-wing aircraft balances four forces: aerodynamic lift, aerodynamic drag, propulsion system thrust, and weight. These forces must be in equilibrium for the aircraft to maintain steady flight. Additionally, the aircraft must balance moments about the roll, pitch, and yaw axes to achieve stable flight and respond to disturbances like wind gusts.

An inertial measurement unit (IMU) typically contains three sensor types: accelerometers to measure linear acceleration, rate gyroscopes to measure angular velocity, and magnetic field sensors to measure the direction and strength of the local magnetic field. The IMU is often coupled with a GPS system and mounted near the aircraft center of gravity with sensor axes aligned to the aircraft body.

A precision rate table rotates at user-defined velocities following rate commands, enabling determination of the relationship between voltage readout and angular velocity. By testing the IMU at different positive and negative constant rotation rates with zero as baseline, a linear fit to the data allows calculation of speed from gyro voltage, establishing the gyroscope's calibration curve.

Signal filtering reduces the impact of noise and outliers on processed data quality. Moving average and median filters are applied to each data channel to attenuate high-frequency signal noise. However, filtering introduces a time delay in the processed data, which must be considered when designing real-time flight control systems.

A flight control system acquires measurements of current altitude, roll, pitch, and yaw angles, as well as airspeed. Once sensor data is collected, it is filtered to reduce noise, then aggregated into a full estimate of aircraft state. This state estimate is used to issue motor and control surface commands updated in real-time to maintain stable flight.

Before flight testing, charge all batteries and test components prior to installation. Ensure at least three people—the pilot in command, visual observer, and ground station operator—are briefed on the flight plan. Start data acquisition on the ground station, confirm the flight area is clear, and arm the motors only after all safety checks are complete.

During calibration, the accelerometer must be oriented in different directions to measure gravitational acceleration. The IMU is positioned upward to collect -1 G data, then flipped downward to collect +1 G data. This procedure is repeated for each axis (x, y, and z) to fully calibrate the accelerometer's response to gravitational forces along all directions.