Pre flight failure with Optical Flow on Ground

[AlexKlimaj]

In current main, with optical flow fusion enabled, I am unable to arm in altitude or position mode. If I take off in manual I am able to switch to altitude and position no problem.

On a larger quad with long landing gear, this issue doesn't present itself. It appears to be a problem with the optical flow close to the ground.

https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/ekf2/Utility/PreFlightChecker.cpp#L85-L91

[AlexKlimaj]

#20940

[AlexKlimaj]

It looks like this is still an issue that was introduced with this commit.
#20414

https://github.com/PX4/PX4-Autopilot/pull/20414/files#diff-a40788d784ca3877b825cbf025e2f84b154faf5182ae81a27defa625f27cffa3R943
Starts off with real values then goes INF pretty quickly.

 I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I.NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
.I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I0NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
0I      NFO  [ekf2] test_ratio_max: 0.00000     of_vel: 0.00006 vel: 0.00006
        IoNFO  [ekf2] test_ratio_max: 0.00000   of_vel: 0.00006 vel: 0.00006
oIfNFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
fI_NFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00006 vel: 0.00006
_IvNFO  [ekf2] test_ratio_max: 0.00308  of_vel: 0.05552 vel: 0.05552
vIeNIFO  [ekf2] test_ratio_max: 0.00003 of_vel: 0.00563 vel: 0.00563
eIlNNFO  [ekf2] test_ratio_max: 0.00003 of_vel: 0.00563 vel: 0.00563
lI:NFFO  [ekf2] test_ratio_max: 0.00006 of_vel: 0.00783 vel: 0.00783
:I NOFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
 I0N FO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
0.. 00004       vel: 0.00004
I0N[FO  [ekf2] test_ratio_max: inf      of_vel: inf     vel: inf
0IuNFO  [ekf2] test_ratio_max: 0.00000  of_vel: 0.00004 vel: 0.00004
I0NaFO  [ekf2] test_ratio_max: inf      of_vel: inf     vel: inf
II0NvFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
WARN  [health_and_arming_checks] Preflight Fail: velocity estimate error
N0FcO  [ekf2] test_ratioINFO  [ekf2] test_ratio_max: inf        of_vel: inf     vel: inf
_I      NaFO  [ekf2] test_ratio_max: inf        of_vel: inf     vel: inf
mIvNnFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
aex:: 0.00000   of_vel: 0.00004 vel: 0.00004
IlN1FO  [ekf2] test_ratio_max: inf      of_vel: inf     vel: inf
II:N2FO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
N F5O  [ekf2] test_ratio_max: 0.00000   of_vel: 0.00004 vel: 0.00004
I0N:FO  [ekf2] test_ratio_max: inf      of_vel: inf     vel: inf
II.NuFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
N0FaO  [ekf2]INFO  [ekf2] test_ratio_max: inf   of_vel: inf     vel: inf
 I0NvFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
tI0NcFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
e0sat_ratio_max: 0.00000        of_vel: 0.00004 vel: 0.00004
I0NnFO  [ekf2] test_ratio_max: inf      of_vel: inf     vel: inf
II
NnFO  [ekf2] test_ratio_max: inf        of_vel: inf     vel: inf
NIFNoFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
INFO  [ekf2] test_ratio_max: inf        of_vel: inf     vel: inf
OIINdFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf
 INNeFO  [ekf2] test_ratio_max: inf     of_vel: inf     vel: inf

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-maintainers-call-april-04-2023/31415/1

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-maintainers-call-april-11-2023/31524/1

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-maintainers-call-may-02-2023/31955/1

[dirksavage88]

I'm seeing the "Preflight Fail: velocity estimate errors" when only using optical flow.

Using commit hash: 7eb6535

Pretty much the same optical flow issues in #21055

Is there a way around this for the time being, or just wait for the fix? For reference I'm using the Bitcraze flowdeck v2 (pmw3901) over SPI bus. I am able to see the optical flow sensor messages and have a vl53l1x distance sensor. Tried raising the drone 1m off the ground as you had done in #21358 but still getting constant spamming of velocity estimate errors in the system console.

Could the conditional rangefinder param (EKF2_RNG_CNTRL) be a factor here? I have it enabled but not conditional. Also no GPS to fall back on either, just optical flow and the distance sensor.

[junwoo091400]

Is there a way around this for the time being, or just wait for the fix?

During a community qna call, @dagar hinted that we can have a quick safeguard fix to get around this issue. Could you comment on this?

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/px4-maintainers-call-may-23-2023/32245/1

[AlexKlimaj]

#21769

[bresch]

Fixes merged