Improve offboard failsafe

[benjinne]

Describe problem solved by this pull request
Closes #16534 using 2nd proposal of adding a new parameter to allow for failsafe on RC only.

Describe your solution
Change the following:

• When Both offboard and RC are lost, use OBL_ACT instead of OBL_RC_ACT
• When only offboard is lost and RCL_EXCEPT is enabled use OBL_ACT instead of OBL_RC_ACT
• When only RC is lost and RCL_EXCEPT is disabled, use NAV_RCL_ACT
  

Describe possible alternatives
The outcomes in the table were picked by my intuition, but can change if needed.

Test data / coverage
All scenarios in table tested and verified using jmavsim and offboard_control example in px4_ros_com.

[dagar]

The table is quite helpful, I'll review this.

Any input here @Jaeyoung-Lim @bperseghetti?

[julianoes]

I commented on small nitpicks for the MAVSDK tests part.

Other than that, I think your table make complete sense, and the implementation looks correct.
This is really well done and communicated, thanks a lot for the issue and PR!

[julianoes]

The one CI error doesn't look related.
Thanks for the fixes @benjinne, that was quick.

[MaEtUgR]

My mistake that the result wasn't the most appropriate in all cases:
https://github.com/PX4/PX4-Autopilot/pull/17785/files#diff-16343101332933c8491a2460368615ae5861531c321280d0468f7be6733b8661R752

@benjinne I fully agree with your intuitive resolution of failsafe cases. Thanks so much for the contribution of the correction, the tests and the very clear description. 👍 🙏

[DiegoHerrera1890]

Hello. Where shall I change these parameters?
Thank you.

[benjinne]

In QGC there's a search option or they can be set in the mavlink console

[DiegoHerrera1890]

I'm running gazebo and PX4... So in QgroundControl shall I change those parameters?

[benjinne]

Yes, or if you're running make px4_sitl gazebo in that terminal you can use the param command to get and set parameters like param set RCL_EXCEPT 4 to disable offboard RC lost checks

[DiegoHerrera1890]

thank you so much! it works!!

[MaEtUgR]

@DiegoHerrera1890 Just for reference you can also change them using the QGC GUI like this: https://docs.qgroundcontrol.com/master/en/SetupView/Parameters.html on a real vehicle as well as the simulation (take care to connect to the right instance).

[benjinne]

@julianoes Hey, I'm trying to write MAVSDK tests for these cases, however there's no way to stop sending offboard setpoints abruptly. From what I see, only _offboard->stop() is available which changes the flight mode to hold and stops setpoints. Is there another way, or does the offboard MAVSDK plugin need another function?

[julianoes]

@benjinne I guess we need to add some functionality to MAVSDK which allows you to have more fine grained control over when the setpoint should be sent.

I've created mavlink/MAVSDK#1630 to collect requirements around this, please add a note about the behavior that you would like to see there.