Plane/Rover: EKF Failsafe isn't documented

[ES-Alexander]

The failsafe is referenced in at least one common file (which should maybe be removed from Plane, since it explicitly mentions just Copter/Rover?), but the link goes out to Sub because the EKF Failsafe page isn't included in Rover or Plane.

Currently both firmware have single-page failsafe docs, neither of which mentions the EKF failsafe. Plane mentions it in the quadplane docs, but doesn't specify how to configure it.

I'm unsure whether the preferred solution here is to split the Plane and Rover failsafe docs into separate pages with a landing page (and making the EKF Failsafe page "common"), to match the Copter and Sub approaches, or have some kind of shorter form docs for the EKF failsafe that get included in their existing single-page docs.

[rmackay9]

Thanks for this. For rover we should certainly link the EKF failsafe page from the general failsafe page.

BTW, if Rover users are suffering from the EKF failsafe it is likely because of issue ArduPilot/ardupilot#31402 which is fixed in 4.7 thanks to this PR ArduPilot/ardupilot#31632

In earlier version the AHRS_OPTION parameter also exists so users could manually set it.

BTW, I don't think Plane has an EKF failsafe but I leave that to the Plane experts to answer

[ES-Alexander]

if Rover users are suffering from the EKF failsafe...

Interesting to know about, but unrelated in this case :-)
I'm making a big features+testing spreadsheet with Willian (for Sub/Boat in the context of BR priorities/requirements for releases), and while filtering features per vehicle type I happened to find that the EKF Failsafe (which seemed to be general functionality) wasn't mentioned in the Rover docs, despite having parameters for it, so I dug a bit deeper and raised the issue to discuss the documentation approach :-)

[Hwurzburg]

All vehicles have EKF failsafe, but nonVTOL plane falls back to DCM where as VTOL planes have the actions listed in the wiki (although pretty buried).....I think the common page should be tailored for each vehicle site, since they have differing actions, and referenced in each vehicle's list of failsafe like all the others