Sorry, I’m getting my *nix and devices mixed up. 
The radio is /dev/ttyUSB0 (on Raspberry Pi And Linux Mint (i386) that I have tested)
Okay, I ran
’cd /dev’ then ‘ls -la tty*’ and it came up with the list as you described. I then ran groups and it came back with ‘laurence adm dialout fax cdrom floppy tape sudo dip video plugdev fuse lpadmin sambashare’
It isn’t connected to the Internet at this point. I need to get a multi box for the office so I don’t have To run an extension cord to get the Pi in range of an Ethernet cable plugged into the modem. 
I couldn’t be bothered to run the extension cord.
OK, cool.
Now with your quad or whatever on and your radio plugged in to the Pi, you can type the command Bill was talking about:
$ screen /dev/ttyUSB0 57600
and hopefully you will see all kinds of crap in the terminal. Crap being a technical term. 
I’m pretty sure there is an SI unit for crap as a standard measure of volume… okay, so I plugged it in and fired up the pixhawk typed the magic commands and I got the screen full of crap. It just ticks over and scrolls past. I’m guessing that is the open connection? When I tried connecting through Planner it said that there is an error opening the port the device or resource is busy?? By the way, thankyou both for helping me suss this out.
You need to close the screen session first as it will be hogging the device. CTRL-a, k and the select Y for yes
You guys are awesome! It seems to be working now. Thanks heaps for you patience and help.
Hi guys, I went to fire up APM planner today and for some reason it gets stuck at the opening screen where it says starting user interface. The program just locks up and won’t have a bar of it. It was working fine previously, I tried to reinstall and still the same result.
Trying deleting the APM Planner.ini config file in your home directory under .config/com.diydrones/
cd ~/.config/com.diydrones
rm APM\ Planner.ini
It doesn’t delete any log file or missions etc, just UI settings.
Hope that helps
Hi Bill, thanks for your really fast reply I tried entering your command and it came back with no such file or directory.
Just use the File Manager to find it (my command might have a typo) you can see hidden files in the file manager by pressing ctrl + h
I found the file through file manager and deleted it. She’s totally poked. [emoji43][emoji88][emoji317]… No response, the program won’t even open. I might reflash, reload APM and start all over again from scratch…