Fixed-wing pitch and roll offset clean up #16792

sfuhrer · 2021-02-08T19:33:29Z

Replaces #11845.

Describe problem solved by this pull request

replace minimum pitch angle set by mission item during fixed-wing takeoff by vehicle parameter (FW_TKO_PITCH_MIN)
apply pitch offset centrally in fw_pos_control
removes (unused/unnecessary) FW_RSP_OFF param

Describe your solution
The following parameters are now all referring to the same "absolute" pitch angle.

FW_P_LIM_MIN (no change for AUTO and LOITER, other modes: now absolute, before PSP_OFF was added to min after TECS)
FW_P_LIM_MAX (no change for AUTO and LOITER, other modes: now absolute, before PSP_OFF was added to max after TECS)
FW_TKO_PITCH_MIN (new param)
FW_LND_FL_PMIN (now absolute, before PSP_OFF was added after TECS)
FW_LND_FL_PMAX (now absolute, before PSP_OFF was added after TECS)
FW_MAN_P_MAX (no difference, pitch_sp = manual_input * FW_MAN_P_MAX + PSP_OFF, constrained to +/-FW_MAN_P_MAX)

"Absolute" pitch is defined as

for VTOL, the angle of the multicopter propeller plane relative to the ground (0 pitch for level MC flight)
for FW it can be more freely defined, but in general having it parallel to the wing makes most sense (adaption of FW_PSP_OFF may be necessary) (is this correct or can/should we define it closer @RomanBapst ?)

FW_PSP_OFF is the pitch angle required for level flight at trim airspeed. TECS gets the absolute pitch minus the offset, and also all the min/max parameters are used inside TECS are offset by the offset prior passing them into TECS.

Describe possible alternatives
Pass the absolute pitch angle into TECS, together with the offset parameter, and initialize the pitch (output) at the offset value.

Test data / coverage
SITL tested with VTOLs and Plane.

sfuhrer · 2021-02-08T19:38:57Z

Don't know exactly how/why, but this seems to fix the fixed-wing takeoff.
(#16787, #16639)
FYI @ryanjAA , please verify.

dagar · 2021-02-08T22:14:07Z

src/modules/fw_pos_control_l1/FixedwingPositionControl.cpp

@@ -1838,17 +1836,14 @@ FixedwingPositionControl::tecs_update_pitch_throttle(const hrt_abstime &now, flo

 	if (_vehicle_status.engine_failure) {
 		/* Force the slow downwards spiral */
-		pitch_min_rad = M_DEG_TO_RAD_F * -1.0f;
-		pitch_max_rad = M_DEG_TO_RAD_F * 5.0f;
+		pitch_min_rad = radians(-1.0f);


Note, we should revisit engine failure.

Do you know of anybody that uses it actually?

I did a few years ago. I'd bet people don't even know it exists.

dagar · 2021-02-08T22:15:32Z

Thanks for finally taking care of this @sfuhrer.

FYI @Antiheavy, no more takeoff pitch via mission item (fat finger friendly).

dagar · 2021-02-08T22:18:45Z

While we're on the subject, has anyone ever actually use FW_RSP_OFF or was it added for "consistency"? It might be better to purge it.

LorenzMeier · 2021-02-08T22:25:52Z

Purge it!

ryanjAA · 2021-02-08T22:35:50Z

Thanks @silvan and @dagar Never used roll offset and don't really see a use.

Tested in SITL - a few things. It doesn't cause the plane to flip if it gets above 20º pitch up but its not exactly working.

It is still speeding up to ~trim speed before pitching up - I even set rwto_airspd_scl to 100 just to be sure.

Secondly you have to have the mission planning pitch set to 0 (when planning a mission) or QGC gets mad and spits out some errors (probably the intention).

On QGC 4.1.1 release when I initiate the mission I get an "unable to start mission, vehicle rejected arming" but it still arms and flies it. When I switch to QGC 4.0.11 it doesn't do that and just flies the mission.

In both cases though it still speeds up to around trim speed before pitching up but this is good that there is not more looping on takeoff.

Lastly, so how do we control the desired pitch now on takeoff? Is that RWTO_max_pitch now? On sitl having that set to 20 gives me a pitch sp of ~14º on takeoff.

Antiheavy · 2021-02-09T00:27:18Z

FYI @Antiheavy, no more takeoff pitch via mission item (fat finger friendly).

hoooray!

has anyone ever actually use FW_RSP_OFF or was it added for "consistency"? It might be better to purge it.

I've never heard of anyone using this. I supposed I can imagine some "creative" aircraft designs that might have a use for something like this, but seems unlikely. There are already other (more preferred) ways to account for flight controller mounting angles, right?

CarlOlsson · 2021-02-09T09:31:19Z

for FW it can be more freely defined, but in general having it parallel to the wing makes most sense (adaption of FW_PSP_OFF may be necessary)

What is the benefit of not defining "zero pitch" as zero pitch angle of the autopilot? This way you can directly check the logs and set parameters based on the vehicle_attitude without subtracting/adding any offset

sfuhrer · 2021-02-09T09:34:38Z

It is still speeding up to ~trim speed before pitching up - I even set rwto_airspd_scl to 100 just to be sure.

That's how it looks atm. Having never before used FWRTO I actually don't know what exactly to expect, but it seems to set the pitch setpoint correctly to the takeoff sp (FW_TKO_PITCH_MIN, in this case 15°) after reaching 130% of FW_AIRSP_MIN (1.3*10=13m/s). I don't know though why the pitch then doesn't follow the setpoint..

Secondly you have to have the mission planning pitch set to 0 (when planning a mission) or QGC gets mad and spits out some errors (probably the intention).

Yes that's the intention - #11845 (comment)

On QGC 4.1.1 release when I initiate the mission I get an "unable to start mission, vehicle rejected arming" but it still arms and flies it. When I switch to QGC 4.0.11 it doesn't do that and just flies the mission.

Can confirm, have the same behavior on latest QGC, doesn't seem to happen always though.

Lastly, so how do we control the desired pitch now on takeoff? Is that RWTO_max_pitch now? On sitl having that set to 20 gives me a pitch sp of ~14º on takeoff.

Mainly FW_TKO_PITCH_MIN no? Can you share some plots - as in my case it set the pitch setpoint to what I specified there.

ryanjAA · 2021-02-11T04:59:24Z

Will provide some plots shortly. Going to take another pass at this.

RomanBapst · 2021-02-11T07:18:02Z

What is the benefit of not defining "zero pitch" as zero pitch angle of the autopilot? This way you can directly check the logs and set parameters based on the vehicle_attitude without subtracting/adding any offset

@CarlOlsson Yes, I agree. I think the pitch angle reference should be the output of the estimator. For VTOL this will most likely coincide with the motor plane.
Then we use FW_PSP_OFF to specify a trim pitch value required for straight and level flight in fixed wing mode.
Then in the logs you can directly associate estimated pitch angle with all the limits you define using parameters.
E.g. if you set FW_MAN_P_MAX to 30 degrees you will see the pitch value saturate at that value in the log.

@sfuhrer Let me know what you think, maybe there is something we are missing here.

sfuhrer · 2021-02-11T13:31:13Z

I think the pitch angle reference should be the output of the estimator

The question is how you mount the autopilot in the body, resp. what you define as your level horizon. For a MC/VTOL there can be no question: level horizon has to be set such that without wind, the drone stays stationary. For FW I just don't see what the analogy would be, and thus proposed the "parallel to the wing". Wikipedia defines it as "xb axis - positive out the nose of the aircraft in the plane of symmetry of the aircraft" - that may be even simpler to be used as a definition.

sfuhrer · 2021-02-11T18:09:08Z

While we're on the subject, has anyone ever actually use FW_RSP_OFF or was it added for "consistency"? It might be better to purge it.

Agree on purging it - see a29161c2d5aa533eb4a4acb73a90fe4dbbb10b80

- remove mavlink mechanism for setting minimum pitch

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

LorenzMeier · 2021-02-12T13:03:36Z

CI is failing - probably real!

- this mission rejection was only added recently in #16792 - causing QGC compatibility issues mavlink/qgroundcontrol#9464

sfuhrer requested review from dagar and RomanBapst February 8, 2021 19:33

sfuhrer force-pushed the pr-FW-pitch-offset-cleanup branch from 8a036f4 to 2054b12 Compare February 8, 2021 19:34

sfuhrer added the Fixed Wing 🛩️ label Feb 8, 2021

sfuhrer added the Admin: Cleanup (housekeeping) 🧹 label Feb 8, 2021

dagar reviewed Feb 8, 2021

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dagar added this to the Release v1.12.0 milestone Feb 9, 2021

sfuhrer mentioned this pull request Feb 9, 2021

fw_pos_control_l1: apply pitch setpoint offsets centrally #11845

Closed

sfuhrer force-pushed the pr-FW-pitch-offset-cleanup branch from 2054b12 to a29161c Compare February 11, 2021 18:02

sfuhrer changed the title ~~Fixed-wing pitch offset clean up~~ Fixed-wing pitch and roll offset clean up Feb 11, 2021

sfuhrer mentioned this pull request Feb 12, 2021

fixedwing runwaytakeoff (RWTO) broken #16787

Open

dagar and others added 3 commits February 12, 2021 03:02

fw_pos_control_l1: add takeoff minimum pitch parameter

0419ed6

- remove mavlink mechanism for setting minimum pitch

fw_pos_control_l1: apply pitch setpoint offset centrally

99c6b90

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

Fixed-wing: remove roll offset param (FW_RSP_OFF)

43cba8e

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

sfuhrer force-pushed the pr-FW-pitch-offset-cleanup branch from a29161c to 43cba8e Compare February 12, 2021 02:04

dagar approved these changes Feb 12, 2021

View reviewed changes

dagar enabled auto-merge (rebase) February 12, 2021 04:59

RomanBapst approved these changes Feb 12, 2021

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dagar merged commit 31a6edf into master Feb 12, 2021

dagar deleted the pr-FW-pitch-offset-cleanup branch February 12, 2021 18:57

Jaeyoung-Lim mentioned this pull request Feb 14, 2021

14/02/2021 Upstream merge ethz-asl/ethzasl_fw_px4#8

Merged

DonLakeFlyer mentioned this pull request Feb 19, 2021

Mission transfer failed. Error: Param 1 invalid value. Item #0 Command: Takeoff Value: 15 mavlink/qgroundcontrol#9443

Closed

dagar mentioned this pull request Feb 20, 2021

mavlink: remove MAV_CMD_NAV_TAKEOFF mission rejection if pitch is still being set #16902

Merged

dagar added a commit that referenced this pull request Feb 21, 2021

mavlink: mission ignore takeoff pitch error

bbc7219

- this mission rejection was only added recently in #16792 - causing QGC compatibility issues mavlink/qgroundcontrol#9464

mrpollo mentioned this pull request Apr 28, 2021

CI SITL plane failures #16639

Closed

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Fixed-wing pitch and roll offset clean up #16792

Fixed-wing pitch and roll offset clean up #16792

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Fixed-wing pitch and roll offset clean up #16792

Fixed-wing pitch and roll offset clean up #16792

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