Change default flying mode, Takeoff command in manual

Hello,

I have Pixhawk connected to a raspberry pi, i have installed mavproxy on the raspberry pi in order to
control the pixhawk, however i have noticed that the pixhawk has set up Manual flying mode by default,
I’m trying also to turn on the motors using takeoff ALTITUDE_IN_METERS command provided by the mavproxy but nothing is happening, I can arm the motors using arm throttle command, i also noticed that
I’m not able to change the flying mode using the mode command, even I am correctly executing the command and receiving:
Got MAVLink msg: COMMAND_ACK {command : 176, result : 0}
from the pixhawk, also I am running px4 as flight stack on the pixhawk.

Thanks

I like to refer my previous answer.