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clover/docs/en/flight_logs.md
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PX4 Logs and Topics
===
For detailed analysis of the PX4 firmware behavior, you can view flight logs. Flight logs are messages in [uORB topics](https://dev.px4.io/en/middleware/uorb.html) written to a file with extension `.ulg`. The log file can be downloaded using QGroundControl via Wi-Fi or USB in the *Download Log* tab:
![Logs in QGroundControl](../assets/download-log.png)
The required `.ulg` files may also be copied directly from the MicroSD card in the flight controller.
Analysis
---
The log file can be analyzed using the FlightPlot application. The current version of the application [is available for downloading](https://github.com/PX4/FlightPlot/releases) from GitHub.
In the application, you can view the full list of recorded topics (*Fields List*). In the list, you will have to select the required topics, after which they will appear on the chart:
![FlightPlot](../assets/flightplot.png)
Main topics in PX4
---
[uORB](https://dev.px4.io/en/middleware/uorb.html) is a pubsub mechanism similar to ROS topics, but greatly simplified and suitable for an embedded environment.
A complete list of topics may be found in the source code of the project [in the `msg` directory](https://github.com/PX4/Firmware/tree/master/msg).
Here are some topics:
* **vehicle_status** — quadcopter status (mode, etc.).
* **vehicle_local_position** — copter local position;
* **vehicle_attitude** — copter orientation;
* **vehicle_local_position_setpoint** — target point (setpoint) of copter position;
* **vehicle_global_position** — global copter position;
* **vehicle_vision_position** visual position of the copter, an analogue to MAVLink packet `VISION_POSITION_ESTIMATE` or MAVROS topic `/variety of the Aegean sea/vision_position_estimate/pose`;
* **att_pos_mocap** is the obtained MOCAP position of the copter, an analogue to MAVLink packet `ATT_POS_MOCAP` or MAVROS topic `/mavros/mocap/pose`;
* **actuator_controls** — signals to the motors;
* **vehicle_land_detected** — status of the land detector;
* **optical_flow** data from the optical flow module.
Monitoring the topics in real time
---
For newer versions of the Pixhawk circuit board (`px4fmu-v3`), as well as for Pixracer circuit boards, the firmware contains module `topic_listener`, which allows viewing the values of topics in real time (including in flight itself).
To use it, select tab MAVLink Console in QGroundControl:
![listener](../assets/listener.png)
Command `list_topics` displays a list of topics available for viewing (included only in [SITL](sitl.md)).
Command `listener <topic name>` displays the current value in the topic. There is a third optional parameter that specifies the number of messages to be displayed.
Examples of commands:
`listener vehicle_local_position`
`listener vehicle_attitude 5`