There are two types of logs that can be used to diagnose problems while running ArduSub, or to retrieve data for post-processing.

Telemetry logs

Ground Control Station (GCS) software will store all of the autopilot telemtry in a log. These telemetry logs contain all of the MAVLink messages received in their binary format. MAVProxy and QGroundControl save telemetry logs locally in a .tlog file. Telemetry logs are the preferred way of diagnosing most problems.

Once connected to the autopilot, MAVProxy will save all telemetry to a file called 'mav.tlog'. The mav.tlog file is saved under the same path from which MAVProxy was run. By default, QGroundControl only begins logging telemetry after the vehicle has been armed. QGroundControl can be configured to log telemetry while the autopilot is disarmed in the General tab of the Application Settings menu (click the purple 'Q' icon in the menu bar). Select the option to save logs 'even if vehicle was not armed' in order to log telemetry while disarmed. QGroundControl saves the telemetry logs in the 'Telemetry' directory under the 'Save Path' that is specified in the General tab of the Vehicle Seup menu.

DataFlash logs

DataFlash logs are saved by the Autopilot directly to on-board memory (SD card in the case of the Pixhawk), regardless of a telemetry connection. These logs are saved in a .bin file. DataFlash logs are capable of logging data at a much faster rate than telemetry logs. The DataFlash logs are named and saved in ascending order. If GPS is available, the logs will be dated according to the GPS timestamp. DataFlash log files can be opened and inspected with MAVProxy, APM Planner 2 or Mission Planner.

By default, a new dataflah log file is created when the vehicle is initially armed, and logging is performed only while the vehicle is armed. The LOG_DISARMED parameter can be set to 'Enabled' in order to begin a DataFlash log as soon as the autopilot is booted, even before arming. With LOG_DISARMED enabled, logging will be performed whether the vehicle is armed or disarmed, until the vehicle is powered down.


DataFlash logs can be retrieved in two ways:

  1. Remove the Micro SD card from the Pixhawk and plug it into your computer to view and transfer the logs using a file explorer like a regular USB drive.

  2. Download the logs remotely via QGroundControl or MAVProxy.

    • Log downloading via QGroundControl

      Click the Analyze icon at the top of the window. The icon looks like a magnifying glass over a document.

      Click the 'Refresh' button to view available logs.

      Select the log you would like to download, and click 'Download'.

      Multiple logs can be downloaded by highlighting the desired logs before clicking 'Download'.

    • Log downloading via MAVProxy

      While connected to the autopilot via MAVProxy, type 'log list' in the MAVProxy console to list the available DataFlash logs onboard the autopilot.

      Type 'log download X' to download log number X

      While the log is downloading, you can type 'log status' to view the status of the download, or 'log cancel' to cancel the download.

Log Analysis

Telemetry logs and dataflash logs are stored in different formats, and contain different (but in many cases overlapping) data. The log entries for telemetry logs are the MAVLink messages that are documented here and here. The log entries in dataflash logs are self-documented in their binary format, but the formats can also be determined by looking at the code here.

Below is a brief description of some tools that are available for viewing and extracting data from logs.


MAVExplorer is a command line/graphical tool used to plot log data. MAVExplorer supports both telemetry logs and dataflash logs, and is included as part of a MAVProxy installation. Please refer to the MAVExplorer documentation for more information. Note, the log file name should not contain any spaces when using this tool


mavlogdump.py is a command line tool used to filter and export log data to plain-text files like .csv or .json. mavlogdump.py supports both telemetry logs and dataflash logs, and it is just one of many such log analysis tools included as part of a pymavlink installation (also installed with MAVProxy). Note, the log file name should not contain any spaces when using this tool

To install mavlogdump.py, install pymavlink from pip:

pip install pymavlink

To use mavlogdump.py, refer to the output of mavlogdump.py --help:

usage: mavlogdump.py [-h] [--no-timestamps] [--planner] [--robust] [-f]
                     [--condition CONDITION] [-q] [-o OUTPUT] [-p]
                     [--format FORMAT] [--csv_sep CSV_SEP] [--types TYPES]
                     [--nottypes NOTTYPES] [--dialect DIALECT]
                     [--zero-time-base] [--no-bad-data] [--show-source]
                     [--show-seq] [--source-system SOURCE_SYSTEM]
                     [--source-component SOURCE_COMPONENT] [--link LINK]

example program that dumps a Mavlink log file. The log file is assumed to be
in the format that qgroundcontrol uses, which consists of a series of MAVLink
packets, each with a 64 bit timestamp header. The timestamp is in microseconds
since 1970 (unix epoch)

positional arguments:

optional arguments:
  -h, --help            show this help message and exit
  --no-timestamps       Log doesn't have timestamps
  --planner             use planner file format
  --robust              Enable robust parsing (skip over bad data)
  -f, --follow          keep waiting for more data at end of file
  --condition CONDITION
                        select packets by condition
  -q, --quiet           don't display packets
  -o OUTPUT, --output OUTPUT
                        output matching packets to give file
  -p, --parms           preserve parameters in output with -o
  --format FORMAT       Change the output format between 'standard', 'json',
                        and 'csv'. For the CSV output, you must supply types
                        that you want.
  --csv_sep CSV_SEP     Select the delimiter between columns for the output
                        CSV file. Use 'tab' to specify tabs. Only applies when
  --types TYPES         types of messages (comma separated with wildcard)
  --nottypes NOTTYPES   types of messages not to include (comma separated with
  --dialect DIALECT     MAVLink dialect
  --zero-time-base      use Z time base for DF logs
  --no-bad-data         Don't output corrupted messages
  --show-source         Show source system ID and component ID
  --show-seq            Show sequence numbers
  --source-system SOURCE_SYSTEM
                        filter by source system ID
  --source-component SOURCE_COMPONENT
                        filter by source component ID
  --link LINK           filter by comms link ID

mavlogdump.py Examples

Print out all STATUSTEXT messages in the log file:

mavlogdump.py --types=STATUSTEXT test.tlog 
2018-05-15 12:59:42.57: STATUSTEXT {severity : 6, text : ArduSub V3.5.3 (ad81760b)}
2018-05-15 12:59:42.57: STATUSTEXT {severity : 6, text : PX4: 8d505a02 NuttX: 1a99ba58}
2018-05-15 12:59:42.57: STATUSTEXT {severity : 6, text : PX4v2 00400027 32365109 36363331}
2018-05-15 13:00:46.97: STATUSTEXT {severity : 4, text : Motor test timed out!}
2018-05-15 13:00:47.87: STATUSTEXT {severity : 6, text : ArduSub V3.5.3 (ad81760b)}
2018-05-15 13:00:47.88: STATUSTEXT {severity : 6, text : PX4: 8d505a02 NuttX: 1a99ba58}
2018-05-15 13:00:47.88: STATUSTEXT {severity : 6, text : PX4v2 00400027 32365109 36363331}
2018-05-15 13:00:49.05: STATUSTEXT {severity : 2, text : 10 second cool down required}
2018-05-15 13:00:49.05: STATUSTEXT {severity : 4, text : Arm motors before testing motors.}
2018-05-15 13:00:49.06: STATUSTEXT {severity : 4, text : motor test initialization failed!}

The output can be filtered based on message type, and also based on conditions in the message fields.

Export all ATTITUDE messages to a .csv file:

mavlogdump.py --types=ATTITUDE --format=csv test.tlog > test.csv

Export all SCALED_PRESSURE2 messages to a .csv file, filter by showing only messages while vehicle was armed

mavlogdump.py --types=SCALED_PRESSURE2 --condition HEARTBEAT.system_status==4 --format=csv test.tlog > test.csv

Export all messages to a human readable file, filter to discrete time span (only two seconds here)

 mavlogdump.py --condition 'SYSTEM_TIME.time_unix_usec>1526496245000000 and SYSTEM_TIME.time_unix_usec<1526496247000000' test.tlog > test.log

Mission Planner

Mission Planner is a ground control station software like QGroundControl. Mission Planner does not have support for operating ArduSub, but the log files produced by ArduSub are compatible with the graphical analysis tools in Mission Planner. See the Mission Planner log analysis documentation for more details.

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