ULog and Vibration Analysis
PX4 flight logs are typically saved to the SD card in .ulg format. The default logging policy is determined by the parameters in the current product firmware. In general, the fl…
3 min read · English documentationPX4 flight logs are typically saved to the SD card in .ulg format. The default logging policy is determined by the parameters in the current product firmware. In general, the flight controller starts logging after it is armed and stops logging after it is disarmed.
Logging Trigger Modes
Regular users are not advised to modify the default logging policy. If an adjustment is required, first confirm the meaning of the current SDLOG_MODE options in QGC, then make the change, restart the system, and read the parameter back.
| Common Value | Common Meaning | Use Case |
|---|---|---|
-1 |
Disable logging | Not recommended for regular use |
0 |
Start after arming and stop after disarming | Routine flight testing |
1 |
Start after power-on and stop after disarming | Record some states before arming |
2 |
Start after power-on and stop at power-off | Record the complete power-on process; produces larger files |
3 |
Controlled by AUX1 | Control via an auxiliary remote controller channel |
4 |
Start after the first arming and stop at power-off | Record the complete state after the first arming |
The table is provided for diagnostic reference and does not declare the default values for all PX4 builds. Refer to the current parameter description in QGC.
Downloading via QGC
Prerequisites
- QGC is connected to FlyCore-FC;
- The SD card is installed correctly and log writing has finished;
- The time, airframe model, parameter version, and anomaly observed for the flight to be analyzed have been recorded.
Follow the video to open the log download screen in QGC and save the required .ulg file:
After downloading, verify the file time and size, ensure that the file corresponds to the target flight, and archive the log together with the parameter backup.
Flight Review
Flight Review can display the flight path, attitude control, sensors, vibration, motor outputs, and EKF status. The tool is available at PX4 Flight Review. For instructions, see the Flight Review documentation.
Data notice:
Uploading a log sends flight data to an external service. If the data involves sensitive locations, missions, or customer information, it should first be sanitized, or an approved offline analysis tool should be used.
- Upload the
.ulgfile corresponding to the current flight. - Wait for processing to finish, then open the flight report.
- Associate the report with the airframe model, PX4 build, parameter version, and anomaly record.
- Based on the observed anomaly, inspect the sensor, control, actuator, EKF, and vibration charts.
Vibration Charts
The following charts are used to locate the source of an anomaly. The example patterns and values are provided for diagnostic reference only and are not mandatory acceptance thresholds for FlyCore products:
- Raw Acceleration: Check whether the raw acceleration on the X, Y, and Z axes exhibits continuous high-amplitude vibration, impacts, or saturation.
- Acceleration Power Spectral Density: Identify the frequency range in which vibration energy is concentrated, and compare it against motor speed, propellers, and airframe modes.
- Actuator Controls FFT: Check frequency peaks in the rate control outputs to help determine the relationship between structural vibration and control response.
Raw Acceleration
Acceleration Power Spectral Density
Actuator Controls FFT
Troubleshooting Sequence
- Check whether the propellers, motors, or arms are damaged or loose.
- Check whether the FlyCore-FC vibration isolators are installed correctly and whether the wiring harness restricts the vibration isolation.
- Compare motor speed with the spectral peaks, and eliminate powertrain imbalances one by one.
- Record changes to the structure or filter configuration. Change only one item at a time and collect a new log after each change.
- Any filter parameter adjustment should be based on the parameter definitions of the current PX4 firmware and actual measured logs.
