In this link it says that in v3.3 channels 9 to 12 are now supported as AUX channels but how do you use or set them up. I have a 10 channel radio and only see and can use up to 8 channel, where are the channels above 8 hidden.
You have a couple of options here. The Pixhawk has 8 regular outputs and 6 Aux ports. The 6 Aux ports can be turned into channels and output PWM if you like. The default is the first 4 are PWM channels 9, 10, 11, and 12 with aux port 5 and 6 being set as relay switches that can change from 3.3v to 0v by assigning a switch to the relay pin or programmed in a mission.
So when it says in the Standard Params list that Channel 9 for example can be set for RTL and Channel 10 can be set to Autotune that is not correct, they can only be used to control devices connected as you would a servo or switch, no wonder I am getting confused
You need to look at the Full Parameter list to see all the options.
If you want one of the channels to control the copter then you would use those options. The channel must go above 1800 PWM to activate the function selected.
If you want to control a Servo then you need to use RC9_FUNCTION and set it to RC Passthru so that the channel data passes straight through to the aux pin. Some people do this to control landing gear.
But don’t do both otherwise bad things could happen.
So you have RC1 - RC8, and RC9 - Aux1, RC10-Aux2, RC11-Aux3, RC12-Aux4