RTL: Perform transition towards home location

[dayjaby]

Describe problem solved by this pull request
Followup on #14728. To prevent performing a transition while still loitering around the home location, this PR makes sure that the drone heads towards the home location before triggering the transition. For this purpose, it is reasonable to add a new parameter RTL_LOITER_RAD to allow the user to set a loiter radius for the altitude descending that still allows the drone to turn towards the home location before initiating a transition.

Test data / coverage
Sitl gazebo log: https://review.px4.io/plot_app?log=b71abace-d7ba-4f9d-a2ef-71ac005d09e1

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.

[sfuhrer]

@dayjaby there were a lot of VTOL RTL changes coming in with #16377, resulting in conflicts here that would need to be addressed first.
I general I think having a separate loiter radius during RTL could make sense (beside NAV_LOITER_RAD). And I agree that doing the transition towards home would be much better in most cases.
Could you rebase and then share some logs/screen recordings of how it looks like?

[LorenzMeier]

@dayjaby Do you have time to rebase this?

[dayjaby]

Sure! Did not notice Silvans message.

[dayjaby]

Log file: https://logs.px4.io/plot_app?log=455021db-8971-4254-a61f-51a95cbfb88f

The transition overshoots a little, which can be compensated by setting larger loiter radius, for example 70m instead of 50m: https://logs.px4.io/plot_app?log=a8c69cac-4c30-4546-9579-ea48f7886047

[dayjaby]

@sfuhrer can you check this?

[sfuhrer]

@dayjaby It needs another rebase. Otherwise I think it's a nice improvement with rather minimal changes. I wonder though if we shouldn't just use NAV_LOITER_RAD for the loiter radius (I know, previously I commented otherwise, but we really only should introduce new params if we're really convinced) - I guess you introduced a new one to specifically be able to tune if for the optimal distance required to finish the transition right over home?

[dayjaby]

@sfuhrer "Right over home" not so much, but rather having not too high turning angles, especially close to home.

In the future I would like to perform the back transition against the wind. Are the values from the wind_estimator reliable enough for that?

[sfuhrer]

"Right over home" not so much, but rather having not too high turning angles, especially close to home.

Makes sense. But then I guess it's okay to use NAV_LOITER_RAD, or do you see a reason why the RTL loiter should have different radius than the Hold loiter? Both could e.g. be set to 75 for a 2m wingspan VTOL.

In the future I would like to perform the back transition against the wind. Are the values from the wind_estimator reliable enough for that?

I would say so yes, especially as during the loiter down you can estimate the wind quite well

[dayjaby]

I think the descend loiter radius should in general be higher than the normal loiter radius. While descending you gain more speed, so having less sharp turns might be beneficial. This also means that you can descend faster with a larger radius. If this benefit can be neglected, we can go for the NAV_LOITER_RAD approach.

[sfuhrer]

I think the descend loiter radius should in general be higher than the normal loiter radius. While descending you gain more speed, so having less sharp turns might be beneficial. This also means that you can descend faster with a larger radius. If this benefit can be neglected, we can go for the NAV_LOITER_RAD approach.

@RomanBapst what's your opinion here? I still feel like having just one loiter radius param for now would be better, and add a separate one if flight testing shows the clear need for it.

[RomanBapst]

@dayjaby I'm not quite following how this should work. Where are you now triggering the transition once the home waypoint is reached?

I tested in SITL and I had a flyaway so I think something is not quite right.
Could you please re-test?

[mrpollo]

Hey @dayjaby can you please help us address some of the reviewer comments above? we would love to get this merged soon

[dayjaby]

@RomanBapst I am sorry; a slice of code did not survive one of the rebases. Thanks for testing it! This time I tested it properly: https://logs.px4.io/plot_app?log=aa3bf100-4cb5-453b-9dcb-a4738ab04126

The backtransition is done if the default acceptance radius is reached.

[dayjaby]

@julianoes Regarding the failed SITL test: I am pretty sure this PR does not influence any iris flights. I also tried your failure injection and it lands successfully.

pxh> failure gps off
WARN  [failure] inject failure unit: gps (4), type: off (1), instance: 0
WARN  [simulator] CMD_INJECT_FAILURE, GPS off
pxh> WARN  [commander] Failsafe enabled: no global position
INFO  [commander] Failsafe mode activated
INFO  [tone_alarm] battery warning (fast)
WARN  [ecl/EKF] 143604000: GPS data stopped
WARN  [ecl/EKF] 143604000: GPS data stopped
WARN  [ecl/EKF] 143608000: GPS data stopped
INFO  [ecl/EKF] 143608000: reset position to last known position
INFO  [ecl/EKF] 143608000: reset velocity to zero
WARN  [ecl/EKF] 143608000: stopping navigation
INFO  [ecl/EKF] 143604000: reset position to last known position
INFO  [ecl/EKF] 143604000: reset position to last known position
INFO  [ecl/EKF] 143604000: reset velocity to zero
INFO  [ecl/EKF] 143604000: reset velocity to zero
WARN  [ecl/EKF] 143604000: GPS data stopped
INFO  [ecl/EKF] 143604000: reset position to last known position
INFO  [ecl/EKF] 143604000: reset velocity to zero
WARN  [ecl/EKF] 143604000: stopping navigation
WARN  [ecl/EKF] 143604000: stopping navigation
WARN  [ecl/EKF] 143604000: stopping navigation
WARN  [ecl/EKF] 143612000: GPS data stopped
WARN  [ecl/EKF] 143612000: GPS data stopped
INFO  [ecl/EKF] 143612000: reset position to last known position
INFO  [ecl/EKF] 143612000: reset velocity to zero
INFO  [ecl/EKF] 143612000: reset position to last known position
WARN  [ecl/EKF] 143612000: stopping navigation
INFO  [ecl/EKF] 143612000: reset velocity to zero
WARN  [ecl/EKF] 143612000: stopping navigation
INFO  [commander] Landing detected
INFO  [commander] Disarmed by landing
INFO  [commander] Failsafe mode deactivated

Do you have any idea what's wrong here?

[RomanBapst]

@dayjaby This is now the same default as NAV_LOITER_RAD. Does this really makes sense?

[dayjaby]

I think not, but I would like some test flights first before setting it to a more sane value.

[RomanBapst]

@dayjaby I have one last comment regarding the parameter default. Please advise on that. Other than that I think this PR is good to go.

[dayjaby]

@dayjaby I have one last comment regarding the parameter default. Please advise on that. Other than that I think this PR is good to go.

@RomanBapst Comparing the two previous log files (https://logs.px4.io/plot_app?log=a8c69cac-4c30-4546-9579-ea48f7886047 and https://logs.px4.io/plot_app?log=455021db-8971-4254-a61f-51a95cbfb88f), by just increasing the descend loiter radius from 50m to 70m, the roll angle when backtransition commences decreases from 42 degrees to 15 degrees. Let's go for this value?