Until recently my main TX was a Turnigy 9X and I (like many others) was using a hacked in 6 position POT switch to select modes on my various aircraft. Unfortunately the 9X has died so has been replaced by a shiny new 9XR. Rather then hack apart the 9XR (too pretty) I wanted to experiment with using the existing controls to select modes on my aircraft. I have seen several tutorials on this but none met all of my requirements below. Apologies if I have simply rediscovered something already posted by someone else.
The method I used was to combine the 3 position switch (ID0/1/2) with the Aileron Dir switch. Between these two switches there are six possible combinations which neatly matches the 6 modes of the APM ecosystem.
I am using an 8 channel system and wanted to only use one channel for mode. To do this I created a “fake” channel 9 representing the position of the aileron switch which I then mixed with the results of the 3 position switch to achieve 6 switch combinations.
Step 1 – On the SETUP 02 page for the model in question change the Proto setting to add additional channels to the model (10CH in my example). As the hardware I use can only send/receive 8 channels these will be ignored by the TX/RX module.
Step 2 – on the MIXER page for the model Set the following Mixes (note that all values are minuses)
CH5 -100% CH9 ID0
-35% CH9 ID1
-10% CH9 ID2
CH9 -125% FULL AIL
This sets up the three position switch on channel 5 and then applies a large offset to the value from this switch based on the position of the Aileron Dir switch (CH9). The result is 6 possible channels as per the picture below that map neatly to the PWM inputs required by the APM. Note that you can set the actual mode to be whatever you want in MP.
One important note to consider – This switch combination has 2 very easy to use “panic” modes. At any time you can flip both switches up or both switches down with one movement that doesn't require much thought. I suggest you make sure that suitable modes are set up for these. My setup is to have FBWA (perhaps Stabilise for copter) when both switches are up and RTL when both switches are down. This came in handy the other day for me when due to a bad throttle calibration I had a copter shoot into the air uncommanded as soon as it armed - all I had to do was whack both switches down and let the APM do the rest all the way back to landing.
In theory the same mix should work on any TX with these capabilities. I hope this is helpful to people and happy to discuss or take feedback if there are better ways.