As most of you may or may not know, I've been a big proponent of using PPM Sum (aka CPPM) with the Ardupilot since I first figured out how to make it work.  The simplicity of just running a single wire from the Rx to the APM is very attractive.  It eliminates 7 possible failure modes (losing the wire connecting channels 2-8) which could result in loss of control.  There's only 1 wire to get rig…