FLCS V2.1. AHRS, Autopilot, Gyro Stabilized Gimbals Control, Ground Control Station

Transcription

1 AHRS, Autopilot, Gyro Stabilized Gimbals Control, Ground Control Station The platform provides a high performance basis for electromechanical system control. Originally designed for autonomous aerial vehicle control, the platform can also be used for advanced gyro-stabilized platforms, homing control systems, motion control or other sensing and control applications. The platform is an enhanced version of prior FLCS V1.3. The includes: Powerful base CPU - STM32F407 Double DATA Link to the Ground Control Station Hardware based serial boot loader for easy loading of new software High performance U-Blox LEA-7 GPS Module Active on board antenna for increased sensitivity and jamming reduction UART(3), SPI, driver on board for spare port USB port for system service Spare analog and digital I/O ports Eight (8) Isolated and dedicated PWM servo outputs. Servo outputs can control position servo, continues rotation servo or coreless DC motors. Four (4) input capture port connector (PWM), could be connected to any PPM receiver ADC input port 3 analog input signals, resolution 12 bits EEPROM for configuration settings 1

2 Three status LED s (red, green, blue) 3 axis gyro (angular rate sensor) 3 axis accelerometer 3 axis magnetometer Barometric pressure high resolution sensor with accuracy, 10 cm and fast conversion down to 1 ms Auto Pilot software for rigid or rotary wing UAV Roll, Pitch, Yaw or Pan&Tilt gyro stabilized camera control Ground Control Station Dimensions 6x6 cm, weight 30gm Application areas include, but are not limited to: UAVs (AUVs, UAS, etc) has an excellent GPS module on board (U-Blox series) with both on board and off board antenna capability. Double Data Link provides secure connection to GCS with up to 200 Kb. The four PWM inputs could be used for PPM connection to the platform. Ground Control Station software allows you to modify, download and upload control law parameters in of-line mode. has on board inertial measurement sensors, but is able to work with the external IMU or AHRS unit. The onboard AHRS includes: 3 axis rate sensors to measure angular rate ; 3 axis accelerometers to measure linear acceleration; 3 axis magnetometer to measure magnetic flux (typically used for compass type heading derivation) and barometer. There are two independent loops which recreate the orientation and position of the vehicle: adaptive 9 state filter and Kalman filter. Three stage Cascaded Extended Kalman Filters work independently, each imparting the information that it estimates to the stage below. This three stage filter assumes the least coupling. MEMS GYRO ACCELEROMETERS TWO STATE MAGNETOMETER ONE STATE GPS FOUR STATE Pn, Pe, Vn, Ve 2

3 Acc X, Y, Gyro(deg/s) X, Y, Pos (GPS) X, Y, Inertial Navigation System with/without GPS Pos X, Y, Velocity of Vehicle Odometer of Vehicle Pos X, Y, Estimated altitude is calculated by adaptive filter with two inputs: baro altitude and GPS altitude, which gives about 40 cm vertical accuracy. The combination of all these capabilities with the on board ARM processing power allows a full attitude heading reference system (AHRS) with GPS position, velocity and time updates all in one tiny package. Usually low cost MEMS filter fails, when the vehicle dynamics are sufficiently large that accelerometer output no longer provides a good estimate of the gravitational direction. This is particularly the case for a fixed wing UAV maneuvering in a limited space and making repeated rapid turns. The platform, like any device designed to utilize GPS and IMU / AHRS data, has the following list of limits: roll pitch yaw RMS static 0.52deg RMS static 0.55deg RMS dynamic 0.608deg RMS dynamic 0.64deg RMS static 0.58deg RMS dynamic 0.67deg Saturation of maximum rate in any axis for any amount of time will result in an incorrect attitude estimate. The longer the saturation duration, the more error will be present in the attitude determination, but good attitude estimator recovers the orientation even with roll angular velocity of 5.5 turns/s. MEMS motion sensor: ultra-stable three-axis digital output gyroscope. The sensor has a full scale of ±250/±500/±2000 dps and is capable of measuring rates with a user-selectable bandwidth. Acceleration sensor has linear acceleration full scales of ±2g / ±4g / ±8g / ±16g Excessive acceleration can include acceleration above the rated levels in continuous application (static / low frequency g s), more elusive vibration (sinusoidal / random) or shock (impulse / random) events that may not show full saturation of the accelerometers in data output, but have affected the sensors internally and corrupted the values. Continued 3

4 acceleration above the limits or excessive vibration / shock events can corrupt the output acceleration. The new nonlinear complementary filter, augmented by a simple first order model of vehicle dynamics, provides excellent attitude estimates for a fixed wing UAV. The key contribution is to develop a model of the non-inertial acceleration of the airframe that can be used to compensate the accelerometer output to obtain a zero bias estimate of the gravitational direction. The model is based on a simple centripetal force model derived from the airspeed and the rate of turn of the vehicle. However, the angle-of-attack of the airplane is significantly higher during a sharp turn, and this must be modeled to correctly align the compensation terms for the accelerometer output. We address this problem by incorporating a simple first order model of the angle-of-attack dynamics of the airframe driven by the pitch rate measurement obtained from the gyro output. The combined system is simple to implement and achieves excellent performance, given the minimal data that is available. The algorithm is verified on experimental data from a fixed wing air frame. The performance of the algorithm is confirmed by comparison with an attitude estimate obtained from a full INS/GPS. Ground Control Station software removes magnetometers sensitivity to hard and soft iron effects, as well as induced magnetic fields from high current. Saturation of the local magnetic field is easily identified, but lower level influence on the sensor can result in pervasive errors as well. Calibration of the vehicle in the final configuration will help prevent errors introduced by hard iron in the local area. Magnetic field full scale of ±1.3 / ±1.9 / ±2.5 / ±4.0 / ±4.7 / ±5.6 / ±8.1 gauss. Two types of GPS receivers could be used - with external antenna or patch antenna. Horizontal position accuracy m Vertical position accuracy - 3m Velocity accuracy - 0.1m/s Heading accuracy deg Max 4g Interface UART or I 2 C compliant Control Ground Station (CGS) Computer 1: 4

5 Receives position and orientation data from Autopilot Sends/ receives data and commands to autopilot control law parameters, waypoints, etc. 3D visualization of position, velocity and orientation of UAV in 3D terrain Tactical UAV simulator, full mission builder ACMI Friendly User Interface Control Ground Station (CGS) Computer 2 (Telemetry): Video surveillance with gyro stabilized on-board camera Receives complementary data 5