How can I connect FrSky D8R-II PLUS 2.4Ghz 8CH Receiver to my Navio 2 ?
FrSky D8R-II PLUS does not have PPM or S.bus output by default, so the only option to connect it to Navio2 is using PPM encoder.
There is an option to reflash the receiver to get PPM output: Flashing Frsky D8R-II Plus for CPPM (27ms) - RC Groups