I connected the PPM encoder to a Futaba receiver as outlined in the builder course and everything worked as advertised. As the Navio 2 is supposed to be able to decode s.bus, I thought I would get rid of some wires and use s.bus. I disconnected the PPM encoder from both the receiver and the Navio 2, substituted a male to male JR plug servo extension lead wire cable and, when starting QGroundControl, received "PreArm: Radio fail safe on Failed pre-arm check. In addition, radio calibration failed. Have I hooked up the s.bus correctly and has anyone had success with the Navio 2 and Futaba s.bus?
I found the problem. I incorrectly plugged the servo extension lead wire cable into the receiver. (duh!)