Pr port hf4 hf5 fixes to 4.6.3

[vigneshm-debug]

This PR has porting of ArduPlane hotfixes 4 and 5 (versions V4.5.7.4-hf4/hf5 and V4.5.7.5-rc1) to the 4.6.3.

https://www.notion.so/airbound/backporting-HF4-HF5-to-4-6-3-38121adf4be980fb8fa9cb9bd17600c1?v=29721adf4be981d59032000c1dc9579e&source=copy_link

[greptile-apps]

Greptile Summary

This PR backports ArduPlane hotfixes HF4 and HF5 to the 4.6.3 branch, covering tailsitter stability, thrust vectoring, auto-bailout logic, and Pixhawk6C-bdshot tuning parameters.

• AC_AttitudeControl.cpp: Attempts to pass raw gyro yaw through to the rate controller during large thrust errors and reset the yaw I-term, but writes to the member _ang_vel_body.z instead of the local ang_vel_body.z — the assignment is overwritten by _ang_vel_body = ang_vel_body at the end of the function, so the gyro passthrough has no effect.
• AP_MotorsTailsitter.cpp: Correctly adds yaw headroom limiting so pitch + yaw never exceeds tilt servo range, with a limit.yaw flag when clipped.
• autobailout.lua: Renames AUTOB_MODE_DLY → AUTOB_BTRN_DLY, inverts trigger from landing-detection to VTOL-flight monitoring with a back-transition settle timer, and adds mode exclusions; leaves is_vehicle_landing() as unreachable dead code.

Confidence Score: 3/5

The attitude controller fix in AC_AttitudeControl.cpp is broken as written and should not be merged without correction; the remaining changes are sound.

The yaw gyro-passthrough fix writes to the member variable _ang_vel_body.z but the function ends with _ang_vel_body = ang_vel_body (local), which silently discards the assignment. During large thrust-error recovery the rate controller will receive the error-derived yaw target rather than the raw gyro — exactly the condition the fix was meant to address. All other changes appear correct.

libraries/AC_AttitudeControl/AC_AttitudeControl.cpp — the member-vs-local variable mix-up needs to be corrected before merging.

Important Files Changed

Filename	Overview
libraries/AC_AttitudeControl/AC_AttitudeControl.cpp	Fixes yaw rate passthrough for large thrust errors — but writes to the wrong variable (_ang_vel_body.z instead of local ang_vel_body.z), so the fix is overwritten at line 969 and has no net effect on yaw control.
ArduPlane/quadplane.cpp	Adds weathervane gain reduction (1/3 of max) during tailsitter QRTL position 2 approach; exposes tailsitter_in_vtol_transition() as a public method. Changes look sound.
ArduPlane/quadplane.h	Moves Log_Write_AttRate() to private section and adds tailsitter_in_vtol_transition() to public API — matches the implementation changes.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/scripts/autobailout.lua	Refactors bailout trigger from landing-detection to VTOL-flight monitoring with a back-transition settle delay; renames AUTOB_MODE_DLY to AUTOB_BTRN_DLY. is_vehicle_landing() is now dead code.
libraries/AP_Motors/AP_MotorsTailsitter.cpp	Adds yaw headroom limiting for thrust vectoring: constrains yaw so pitch + yaw <= 1.0 and sets limit.yaw when clipped. Logic is correct.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/defaults.parm	Vehicle-specific tuning: halved roll/yaw angle P gains, tightened pitch limits, added TECS_SPDWEIGHT, lowered TRIM_THROTTLE.
libraries/AP_Scripting/docs/docs.lua	Adds Lua binding documentation for quadplane:tailsitter_in_vtol_transition() — matches the new C++ binding.
libraries/AP_Scripting/generator/description/bindings.desc	Registers tailsitter_in_vtol_transition as a Lua-accessible singleton method on QuadPlane — correct and consistent with the implementation.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Lua as autobailout.lua
    participant QP as QuadPlane (C++)
    participant AC as AC_AttitudeControl
    participant Motors as AP_MotorsTailsitter

    Note over Lua: update() every 50ms
    Lua->>QP: tailsitter_in_vtol_transition()
    QP-->>Lua: bool (new binding)
    Lua->>QP: in_vtol_mode()
    QP-->>Lua: bool
    Note over Lua: in_vtol_flight() guards monitoring
    alt in_vtol_flight() and armed and delay elapsed
        Lua->>Lua: check pitch vs AUTOB_PIT_LIM
        alt "pitch bad for > AUTOB_PIT_TOUT ms"
            Lua->>QP: vehicle:set_mode(QLOITER)
        end
    end
    Note over QP: vtol_position_controller() QRTL path
    QP->>QP: weathervane set_gain(wvane_max_gain/3)
    Note over AC: attitude_controller_run_quat()
    AC->>AC: compute local ang_vel_body
    alt "thrust_error > 2x threshold"
        AC->>AC: "_ang_vel_body.z = get_gyro().z [BUG: overwritten]"
        AC->>AC: reset_I() on yaw PID
    end
    AC->>AC: "_ang_vel_body = ang_vel_body [overwrites .z]"
    Note over Motors: output_armed_stabilizing()
    Motors->>Motors: constrain pitch_thrust
    Motors->>Motors: "yaw_headroom = 1 - abs(pitch_thrust)"
    Motors->>Motors: limit yaw to headroom, set limit.yaw
    Motors->>Motors: "tilt_left/right = pitch +/- yaw_limited"

Loading

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sequenceDiagram
    participant Lua as autobailout.lua
    participant QP as QuadPlane (C++)
    participant AC as AC_AttitudeControl
    participant Motors as AP_MotorsTailsitter

    Note over Lua: update() every 50ms
    Lua->>QP: tailsitter_in_vtol_transition()
    QP-->>Lua: bool (new binding)
    Lua->>QP: in_vtol_mode()
    QP-->>Lua: bool
    Note over Lua: in_vtol_flight() guards monitoring
    alt in_vtol_flight() and armed and delay elapsed
        Lua->>Lua: check pitch vs AUTOB_PIT_LIM
        alt "pitch bad for > AUTOB_PIT_TOUT ms"
            Lua->>QP: vehicle:set_mode(QLOITER)
        end
    end
    Note over QP: vtol_position_controller() QRTL path
    QP->>QP: weathervane set_gain(wvane_max_gain/3)
    Note over AC: attitude_controller_run_quat()
    AC->>AC: compute local ang_vel_body
    alt "thrust_error > 2x threshold"
        AC->>AC: "_ang_vel_body.z = get_gyro().z [BUG: overwritten]"
        AC->>AC: reset_I() on yaw PID
    end
    AC->>AC: "_ang_vel_body = ang_vel_body [overwrites .z]"
    Note over Motors: output_armed_stabilizing()
    Motors->>Motors: constrain pitch_thrust
    Motors->>Motors: "yaw_headroom = 1 - abs(pitch_thrust)"
    Motors->>Motors: limit yaw to headroom, set limit.yaw
    Motors->>Motors: "tilt_left/right = pitch +/- yaw_limited"

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_{Reviews (1): Last reviewed commit: "ported hf4 anf hf5" | Re-trigger Greptile}

[greptile-apps]

Assignment to member variable is immediately overwritten

The change writes _ang_vel_body.z = _ahrs.get_gyro().z to the member, but line 969 unconditionally does _ang_vel_body = ang_vel_body, which replaces the entire struct — including .z — with the local ang_vel_body that was never updated in this branch. The intended gyro-passthrough for yaw during large thrust errors is silently discarded, so the rate controller receives the error-derived yaw target instead of the raw gyro value. The original code correctly wrote to ang_vel_body.z (the local variable), which was then picked up by the final assignment. The fix should use ang_vel_body.z = _ahrs.get_gyro().z; so the gyro value survives to line 969.

Suggested change

	_ang_vel_body.z = _ahrs.get_gyro().z;
	get_rate_yaw_pid().reset_I();
	ang_vel_body.z = _ahrs.get_gyro().z;
	get_rate_yaw_pid().reset_I();

[greptile-apps]

Dead code: is_vehicle_landing() is no longer called

The refactor replaced the is_vehicle_landing() guard in update() with in_vtol_flight(), but is_vehicle_landing() itself was left defined. It is now dead code and can be removed to avoid confusion.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!