I am setting up an FMUK66 with my own system. The radio system I am using has the ability to set the outputs to SBUS, non-inverted SBUS, and PPM. PPM so far is the only signal that the FMUK66 wants to work with. I have a battery cell checker that also features an RC check mode than can decode SBUS and it can see the channels just fine, so the issue is at the FMUK66. QGround control seems to have no way to force a radio mode, is this automagical configuration or what?
V1.12 did just break RCINPUT. There is a fix posted, but not pulled to master just yet.
It will get done this week I expect.
This link should take you to the pending pull request:
PX4 does autodetection of the receiver signal. It can not be set manually.
Which FW Version are u using? If it is the new v1.12 please try an older version like v1.11.3