[SOLVED] ESC only arms when RC Input is used

Hi, on Pixhawk I have servo output 3 set to Throttle and the ESC won´t give the proper beeps for arming. When I set servo 3 to RC Input 3, the ESC immediately arms properly. Then I change it back to Throttle and it works. But when I disconnect and reconnect the battery, I must go through this process again of first setting the servo output 3 to RC Input 3, and then setting to Throttle.
I can´t understand why this is happening and how I can set it up to properly arm the ESC when servo output3 is set to Throttle.

FYI also I have disabled all manner of arming checks.

Thanks in advance for any help.

I solved this issue by changing the PWM output range for Throttle in Pixhawk to match the PWM output range of my TX.