Formatting .msg files for uORB topic creation

I am attempting to create a custom uORB topic with the overall goal of logging sensor data received via MAVLink on my computer and eventually on an SD card. I have tried to follow the user guide’s instructions on how to add a uORB topic, but when I try to build the firmware I get an error. I believe the problem lies in the format of the .msg file I am putting in the /msg folder. The file I created is far larger in size than the prebuilt files included in /msg, and when I use a .msg file reader to read the prebuilt files the type of file that I created is “multipart-alternative” and the prebuilt files are “text/plain”, even though they are both .msg files.

My understanding is that all I need to do is create the .msg file that has what I want to be saved included inside, and when I build the firmware the necessary C++ files will be generated for me. Is there a step that I am missing? If not, then how am I supposed to format my .msg file? I used Outlook to create it and as far as I know that is the only way to make a .msg file on Windows.

I am still new to all of this, so I would appreciate any advice. The error I get when I try to build is below:

Traceback (most recent call last):
  File "tools/", line 545, in <module>
    generate_idx, f, args.temporarydir, args.package, args.templatedir, INCL_DEFAULT)
  File "tools/", line 138, in generate_output_from_file
    msg_context, filename, full_type_name)
  File "/usr/lib/python3.6/site-packages/genmsg/", line 285, in load_msg_from_file
    text =
  File "/usr/lib/python3.6/", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd0 in position 0: invalid continuation byte
[18/1127] Generating ../../../platforms/nuttx/NuttX/nuttx/.config
ninja: build stopped: subcommand failed.
make: *** [Makefile:230: px4_fmu-v3_default] Error 1