git submodule init
Submodule ‘modules/PX4Firmware’ () registered for path 'modules/PX4Firmware’
Submodule ‘modules/PX4NuttX’ () registered for path 'modules/PX4NuttX’
Submodule ‘modules/uavcan’ () registered for path ‘modules/uavcan’
git submodule update
fatal: reference is not a tree: 51858c810a3cb086d7c2041328bd32adec9fa724
Unable to checkout ‘51858c810a3cb086d7c2041328bd32adec9fa724’ in submodule path ‘modules/PX4Firmware’
I tried ‘git submodule update’ in ardupilot directory
[quote]
Sven@Cromartie /c/Users/funky/Documents/GitHub/ardupilot
$ git submodule update
fatal: reference is not a tree: 51858c810a3cb086d7c2041328bd32adec9fa724
Unable to checkout ‘51858c810a3cb086d7c2041328bd32adec9fa724’ in submodule path ‘modules/PX4Firmware’[/quote]
I’ve just been going through similar issues with this when trying to build Ardupilot.
This seems to have helped me at least download the GIT submodules with getting constant errors.