Hi @etienne, the sequence is tike this:
First rising beeps: # of beeps = # of LiPo cells in series detected
Low beep after: input signal detected
Last high beep: input signal is ‘neutral’/zero speed, and esc is now armed and ready to spin.
It sounds like you aren’t getting a signal from the autopilot. Are the lights on the pixhawk blinking? Does it connect in QGC?