fw_pos_control_l1 add new simple min groundspeed

[dagar]

This introduces a new FW parameter FW_GND_SPD_MIN to set the desired minimum groundspeed. This replaces existing logic which projects your current airspeed to the ground and has weird coupling with large pitch changes.

Fixes #10078

[LorenzMeier]

Makes sense

[Antiheavy]

I believe this looks correct.

[dagar]

We should be able to test this effectively in SITL, although a real flight never hurts.

[Antiheavy]

We should be able to test this effectively in SITL, although a real flight never hurts.

happy to flight test. might not be until next week based on weather here this week.

[Antiheavy]

Flight tested successfully. We set FW_GND_SPD_MIN very low (1 m/s) and see that the airspeed remains very steady even when flying into a headwind where it would previously have increased airspeed such that ground speed >= fw_airspd_min (14.3 m/s in our case). You can see ground speed is allowed to go below 14.3 m/s in our log. We believe this is working correctly.

Flight log:
https://review.px4.io/plot_app?log=7113bba3-2e45-4b01-8d59-a97ea66e93f7

[Antiheavy]

Been flying this a lot lately. Works great and improves flight control in windy conditions. Would be nice if it made in into Master IMHO.

[LorenzMeier]

Needs a squash and merge.

[Antiheavy]

This would be good to get in for v1.10. Been flying a version of it successfully for several months, 100's of flights.

[Antiheavy]

@dagar I think this is good to go? we've been flying it a lot lately and it works as intended.

[LorenzMeier]

@Antiheavy Could you ping me on any other PRs in similar states that really should go in?