IMPORTANT TIP FOR ANYBODY CHANGING THEIR OS
Note: for the FRAMBUESA OS, ArduCopter.elf does not come pre-installed on the OS, so you will definitely need to copy the older version of ArduCopter, from the old OS, to the newer OS. This will give you continuity. See instructions below:
1, before loading the new OS onto the MSD card, copy the ArduCopter.elf file (which you are currently using successfully) onto a usb drive. Or you can upload it to the cloud. Make sure you change the name to something like: ArduCopter.elf.oldversion
2, load up the new OS onto your MSD card, as normal.
3, in the home/erle directory and look for your existing ArduCopter.elf file. (This will not be present in FRAMBUESA OS)
In the same home/erle directory, download/copy ArduCopter.elf.oldversion.
Now, you will have both the new version of ArduCopter, as well as your older (tried and tested) version.
If you ever need to use the older version, you can do this by simply renaming the 2 files:
1, shut off the APM: sudo systemctl stop apm.service
2, rename the files as follows:
ArduCopter.elf >> ArduCopter.elf.newversion (not necessary for FRAMBUESA OS)
ArduCopter.elf.oldversion >> ArduCopter.elf
3, restart APM: sudo systemctl start apm.service