Turnigy 9x mixing for ArduPilot Mega

Tom Paton deserves a PhD in obscure radio settings for figuring out how to mix Turnigy 9x mode switches:
        http://rcav.posterous.com/programming-an-ardupilot-mode-switch-for-turn
He has a great writeup explaining the details of what he did... here's my quick-ref version.

ArduPilot Mega Functionality

       THR-CUT    F-MODE    POS        FUNCTION
           FWD    N           0        manual
                  1           1        stabilized
                  2           2        fly-by-wire-a
          BACK    N           3        auto
                  1           4        loiter
                  2           5        rtl

Basic Idea

• Set the Throttle Hold Button to control Channel 5.
• Add a mix, such that putting the F-MODE into NORM position subtracts 20.
• Likewise, for F-MODE in position 1, subtracts 50.
• Likewise, for F-MODE in position 2, subtracts 100.
• This gives us 6 discrete values that will be broadcast on channel 5.
• These 6 values map to the APM control function values.

Setting The Mix

• Set Channel 5 to Throttle Hold
          [FUNC SETTING] [AUX-CH]
                CH5    THRO-HOLD
• Set mixes 1-3
          [FUNC SETTING] [PROG MIX]
  
                  MIX1    MIX2    MIX3
          STATE     ACT    ACT    ACT
          MASTER    GYR    GYR    GYR
          SLAVE     FLP    FLP    FLP
          OFFSET    000    000    000
          UPRATE   -020   -050   -100
          DNRATE   -020   -050   -100
          SW        ID2    ID1    NOR
   
• Check the Settings with the Display Menu.  There should be 6 discrete values.
          [FUNC SETTING] [DISPLAY]

 Further Mixing Information

The manual has a unique perspective on mixing.