RTL issues with multiCopter

[santiago3dr]

Quadcopter running pixracer (v4)
two possibly related issues

• upon engaging RTL, copter does not climb to set RTL altitude
• if engaging RTL twice in the same flight, the second instance of RTL veers in the wrong direction; heading is corrected half way through the return path

both issues present:
https://logs.px4.io/plot_app?log=a229d06a-b4f6-4333-ae1c-246c3f90f8b1
https://logs.px4.io/plot_app?log=c6d5b63b-c467-491b-83b3-cfb39064abeb

altitude issue present:
https://logs.px4.io/plot_app?log=f999958f-6a2f-419a-8a1c-e812045e8be7

using the same version of master on fixed wing, RTL looks to be working fine:
RTL set to 60m:
engaging rtl below set altitude:
https://logs.px4.io/plot_app?log=ac6e62a9-6c02-4e3d-a9c3-132c2adfd0c8

engaging rtl above set altitude:
https://logs.px4.io/plot_app?log=2ead01d6-a13d-4df6-b261-54c1ec2137ab

@dagar @sanderux @priseborough

[dagar]

The veering in the wrong direction particularly concerns me.

[dagar]

The climb is broken because the default MC max return altitude (-1 to disable) is respected. https://github.com/PX4/Firmware/blob/master/src/modules/navigator/rtl.cpp#L78

[dagar]

@santiago3dr could you expand on the second point? Is it only the heading that's wrong, or does RTL actually fly in the wrong direction?

[santiago3dr]

just ran 2 flights on the same copter to replicate this issue
https://logs.px4.io/plot_app?log=ddbab0b2-d1e5-4f3b-8371-7d30915499ba
https://logs.px4.io/plot_app?log=6cced4c1-6a59-4a23-a67f-68c72032ccea

none of the rtl attempts rose to set rtl altitude
in the first flight, the second and third rtl engagements veered in the wrong direction, correcting half way and on the second flight, this happened only on the third attempt at engaging rtl

[santiago3dr]

was able to reproduce this on the snapdragon flight controller (EAGLE)
https://logs.px4.io/plot_app?log=5f0f6037-8fd8-416d-a0c4-f00b6494e677

it seems rtl finds a direct path to the first rtl trajectory
@dagar

[MaEtUgR]

Could very well be related to #6679 (comment)
FYI @Stifael

[dagar]

Fix for the altitude here - #8272

[Stifael]

Or we would bring this #8101 in.
That get_rtl_altitude function is not needed anymore

[Stifael]

The problem with the strange rtl direction behavior sounds familiar, and the issue was caused by having the previous setpoint not reset correctly. I will look into it today.

[dagar]

Please give this PR a try. #8272

[Stifael]

I confirmed now that one issue (there might be more than that) is that the previous setpoint gets reset to the wrong setpoint.
For instance:

• vehicle is in mission
• user/system demands rtl -> current setpoint is equal to home setpoint
• user demands again mission: previous setpoint gets set to current setpoint, which is set to home. Consequently, the vehicle will follow the line home-current setpoint.

[dagar]

@santiago3dr various navigator fixes have made it into master. Please reopen if this isn't completely resolved.

[santiago3dr]

@dagar
tested with master, 3 attempts at RTL, all successful; all rose to set altitude and took a direct path to home location
https://logs.px4.io/plot_app?log=4f166b9d-fd36-452c-be7b-9d2b600f1561