I've setup my 9x for in-flight-adjustments, allowing me to tune my PIDs while flying. I have OpenTX installed on my 9x.

Since my only 3 position switch is already in use, I've setup the dial like a 3 position switch. Moving the dial will switch between adjusting P, I and D. I only adjust the roll and pitch axis, yaw will need to be tuned separately.

I've mixed the TRN and GEAR switch in my radio so that when the GEAR switch is down, flipping on TRN send the channel high and when GEAR is up, flipping TRN sends the channel low. This way, I can control the direction of PID value (up or down) with GEAR then make a small adjustment by flipping the momentary TRN switch on and off.

Here's how I mixed the switches in OpenTX:

The PID specified by the dial are only adjusted up or down according to the direction of the GEAR switch when TRN is flicked on for a moment. No adjustment takes place until TRN is flipped on.

The adjrange command is:

adjrange index slot range-channel range-start range-end adj-function adj-channel

To configure BetaFlight, paste this into the CLI:

# adjrange
adjrange 0 0 3 900 1300 6 1
adjrange 1 0 3 1300 1700 7 1
adjrange 2 0 3 1700 2100 8 1


This will make AUX2 (channel 7 on my radio, which is the HOV THR dial) control which parameter to tune P, I or D, when the TRN switch (channel 6 on my radio) is flipped on. Recall that by mixing the GEAR switch in, we can control which direction the signal goes (high or low) when `TRN is flipped.

You can test your setup by going to the PID tuning tab in the CleanFlight Configurator and using your radio to adjust the PIDs. Hit refresh in the configurator and you should see new values.

Note that the PIDs are not saved after disarming. To save my PIDS, I plug the multirotor into a computer, open the PID Tuning tab and hit save.