I found the problem. There is something wrong with the Prolific USB-Serial converter. Now I use a sparkfun ftdi converter and now I have ttyUSB0 available. This is the USB port on the accesory bay
glad you got working
Sorry to resurrect a bit of an old thread but I'm trying to connect to the pixhawk directly on the Solo. I saw someone said that they used the gimbal cable? Can you use mavlink commands to interface with the drone that way?