Hi @v-to,
Thank you for getting back to me! To be completely honest with you. I was always able to change the mode, but I keep getting an error:
CMD: Unexpected command 11, result 0
Although the mode does change as I get feedback from the pixhawk and I can also see it in Mission Planner. Do you also get the same error?
Another thing you’ve mentioned was that you had been able to work with a SERVO using DO_SET_SERVO. I guess you’re referring to MAV_CMD_DO_SET_SERVO, (command 183). Is that right?
I’ve tried to use it by issuing
rosrun mavros mavcmd int 183 1 1023 0 0 0 0 0
But I’m getting the error
CMD: Unexpected command 183, result 3
I’ve also tried to publish it to OverrideRCIn with no luck.
rostopic pub /mavros/rc/override mavros_msgs/OverrideRCIn -r 50 ‘[1021, 0, 1500, 0, 0, 0, 0, 0]’
I mean… it doesn’t give any error this one, but it also doesn’t make the servo move! 
I’m sorry for dumping all of these doubts, but I’ll pick your mind for some info if you don’t mind!