Pr port 4.5.7.5 rc1 rc2 to 4.6.3

[vigneshm-debug]

porting of ArduPlane 4.5.7.5 rc1 and rc2 features to the 4.6.3

https://www.notion.so/airbound/backporting-4-5-7-5-rc1-rc2-to-4-6-3-38321adf4be980d39735f1b0dd7ae18b?v=29721adf4be981d59032000c1dc9579e&source=copy_link

[greptile-apps]

Greptile Summary

This PR backports several ArduPlane 4.5.7.5 features onto the 4.6.3 base: a configurable land-detection timeout with a disarm watchdog, a redesigned pitch-relaxation controller with hysteresis, yaw-priority clamping in the tailsitter motor mixer, autobailout logic reworked around back-transition timing, and GPS switching improvements with dual sat/vacc hysteresis thresholds.

• AC_AttitudeControl: the old roll+pitch setpoint relaxation is replaced with a pitch-only LPF+hysteresis scheme; two new AP_Float params (RELX_LO/RELX_HI) replace RELX_ANG, and the thrust-error yaw reset threshold is widened from 2× to 3× AC_ATTITUDE_THRUST_ERROR_ANGLE.
• QuadPlane: land_detector() now uses the new Q_LND_DET_TIM parameter (default 200 ms, documented range 1000–4000 ms) instead of the old hardcoded 4000/6000 ms values; a disarm watchdog fires emergency GCS messages if the vehicle stays armed after final-landing detection starts.
• Lua scripts: autobailout.lua now triggers on back-transition completion rather than landing phase; ab_gps_mode.lua adds asymmetric switch-away/switch-back thresholds and extends VTOL phase detection into Auto mode.

Confidence Score: 3/5

Two behavioural changes need resolution before merge: the static LPF state in the attitude controller carries over across arm cycles, and the land-detector timeout default is 20-30× shorter than the values it replaced.

The attitude controller now stores relaxation state in static locals instead of member variables, so a flight that ends with relaxation active leaves non-zero state that immediately attenuates pitch commands on the next arming. Separately, Q_LND_DET_TIM defaults to 200 ms against a documented floor of 1000 ms and the old hardcoded 4–6 s thresholds, making premature landing completion significantly more likely. Both issues sit on frequently-executed control paths. The remaining changes — GPS hysteresis, yaw-priority clamping, autobailout rework, and hwdef expansion — look correct and self-consistent.

AC_AttitudeControl.cpp (static locals and orphaned RELX_TC param), quadplane.cpp (LND_DET_TIM default and range annotation).

Important Files Changed

Filename	Overview
ArduPlane/quadplane.cpp	Adds configurable land-detector timeout (LND_DET_TIM, default 200 ms — inconsistent with documented range 1000–4000 ms and 20-30× shorter than old hardcoded values), a disarm watchdog (DARM_WDG_T), weathervane gain override during VTOL position hold, and exposes tailsitter_in_vtol_transition to scripting.
ArduPlane/quadplane.h	Adds AP_Float timeout_ms, wdg_timeout_s, and wdg_start_ms to landing_detect struct; moves Log_Write_AttRate to private; adds tailsitter_in_vtol_transition public accessor.
libraries/AC_AttitudeControl/AC_AttitudeControl.cpp	Replaces the old roll+pitch attitude relaxation with a pitch-only hysteresis LPF; introduces two static locals that won't reset across arm cycles; reindexes RELX_ANG→RELX_LO/RELX_HI which breaks EEPROM backward compatibility; leaves RELX_TC as an orphaned parameter.
libraries/AC_AttitudeControl/AC_AttitudeControl.h	Replaces _max_tilt_relax/_relax_time_constant with _high_tilt_relax/_low_tilt_relax/_tc_tilt_relax; removes _relaxed_roll/pitch member state and _ts_back_transition_done flag; _relax_time_constant is now a dead member.
ArduPlane/tailsitter.cpp	Removes the call to set_tailsitter_back_transition_done(true) on VTOL transition complete, consistent with the removal of that flag from the attitude controller.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/scripts/autobailout.lua	Replaces landing-phase trigger with a proper in_vtol_flight() check using back-transition timing; renames MODE_DLY to BTRN_DLY with a longer default (2500 ms); increases loop rate to 20 Hz; leaves is_vehicle_landing() as dead code.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/scripts/ab_gps_mode.lua	Adds hysteresis to GPS switching (dual SAT/VACC thresholds), extends VTOL phase detection to Auto mode with loiter nav commands, and fixes the return interval to use milliseconds correctly.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/defaults.parm	Tunes several flight parameters (pitch limits, roll/yaw P gains halved, RELX_EN enabled by default, LAND_ALTCHG increased 5× to 1.5 m, TRIM_THROTTLE reduced); adds new params Q_LND_DET_TIM and Q_DARM_WDG_T.
libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C-bdshot/hwdef.dat	Enables FORCE_APJ_DEFAULT_PARAMETERS and increases AP_PARAM_MAX_EMBEDDED_PARAM to 16384 to embed the expanded defaults.parm in firmware.
libraries/AP_Motors/AP_MotorsTailsitter.cpp	Adds yaw priority clamping for tilt servos: constrains yaw thrust to the headroom left after pitch, sets limit.yaw flag when clamped, preventing pitch+yaw from exceeding servo range.
libraries/AP_Scripting/docs/docs.lua	Adds Lua binding documentation stub for quadplane:tailsitter_in_vtol_transition().
libraries/AP_Scripting/generator/description/bindings.desc	Registers tailsitter_in_vtol_transition as a Lua-accessible singleton method on QuadPlane.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[QPOS_LAND_DESCEND] --> B[check_land_final]
    B -->|land_detector passes ≥200ms + 1000ms| C[QPOS_LAND_FINAL]
    C --> D[check_land_complete]
    D --> E{motors armed?}
    E -->|No| F[return false]
    E -->|Yes| G{lower_limit_start_ms != 0 and wdg_start_ms == 0?}
    G -->|Yes| H[Start DISARM_WDG timer]
    H --> I{elapsed >= wdg_timeout_s?}
    I -->|Yes| J[MAV_SEVERITY_EMERGENCY message + restart timer]
    I -->|No| K[land_detector check]
    G -->|No| K
    K -->|passes| L[QPOS_LAND_COMPLETE]
    K -->|fails| M[return false]
    N[set_armed=true] -->|reset wdg_start_ms=0| D
    subgraph AC_AttitudeControl
        O[attitude_controller_run_quat] --> P{_ts_enabled and _att_relax_enabled and not _ts_in_transition?}
        P -->|Yes| Q[Compute pitch_tilt from attitude_body]
        Q --> R{pitch_tilt > RELX_HI?}
        R -->|Yes| S[_att_relax_active = true]
        R -->|No: pitch_tilt < RELX_LO?| T[_att_relax_active = false]
        S --> U[LPF: relaxation_factor_lpf toward 1]
        T --> V[LPF: relaxation_factor_lpf toward 0]
        U & V --> W[euler_sp.y *= 1 - relaxation_factor_lpf]
        W --> X[thrust_heading_rotation_angles]
    end

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[QPOS_LAND_DESCEND] --> B[check_land_final]
    B -->|land_detector passes ≥200ms + 1000ms| C[QPOS_LAND_FINAL]
    C --> D[check_land_complete]
    D --> E{motors armed?}
    E -->|No| F[return false]
    E -->|Yes| G{lower_limit_start_ms != 0 and wdg_start_ms == 0?}
    G -->|Yes| H[Start DISARM_WDG timer]
    H --> I{elapsed >= wdg_timeout_s?}
    I -->|Yes| J[MAV_SEVERITY_EMERGENCY message + restart timer]
    I -->|No| K[land_detector check]
    G -->|No| K
    K -->|passes| L[QPOS_LAND_COMPLETE]
    K -->|fails| M[return false]
    N[set_armed=true] -->|reset wdg_start_ms=0| D
    subgraph AC_AttitudeControl
        O[attitude_controller_run_quat] --> P{_ts_enabled and _att_relax_enabled and not _ts_in_transition?}
        P -->|Yes| Q[Compute pitch_tilt from attitude_body]
        Q --> R{pitch_tilt > RELX_HI?}
        R -->|Yes| S[_att_relax_active = true]
        R -->|No: pitch_tilt < RELX_LO?| T[_att_relax_active = false]
        S --> U[LPF: relaxation_factor_lpf toward 1]
        T --> V[LPF: relaxation_factor_lpf toward 0]
        U & V --> W[euler_sp.y *= 1 - relaxation_factor_lpf]
        W --> X[thrust_heading_rotation_angles]
    end

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Comments Outside Diff (2)

1. libraries/AC_AttitudeControl/AC_AttitudeControl.cpp, line 196-280 (link)

   Parameter index reordering breaks EEPROM backward compatibility

   The old RELX_ANG at group index 25 is replaced by RELX_LO at index 25, and the new RELX_HI takes index 26 (previously RELX_EN). On any vehicle upgrading from the prior firmware, the flash/EEPROM key for index 25 carries the old RELX_ANG value (typically 45.0) which will now be loaded into _low_tilt_relax. Worse, the old RELX_EN value stored at index 26 will overwrite _high_tilt_relax, setting the upper hysteresis threshold to 0 or 1 (the old enable flag). With _high_tilt_relax ≈ 0, the relaxation activates at essentially any pitch deviation. This does not affect clean deployments, but field operators must perform a full parameter reset on upgrade.

2. libraries/AC_AttitudeControl/AC_AttitudeControl.cpp, line 244 (link)

   RELX_TC / _relax_time_constant is an orphaned parameter

   RELX_TC (index 24, field _relax_time_constant) remains in the var_info table and in the header, but is no longer referenced anywhere in attitude_controller_run_quat(). The new time-constant used by the LPF is _tc_tilt_relax (exposed as RELX_TLT_TC). Leaving RELX_TC in the table consumes a parameter slot and will confuse operators — changes to it will have no effect.

_{Reviews (1): Last reviewed commit: "fix duplicate AP_GROUPINFO indices" | Re-trigger Greptile}

[greptile-apps]

Static locals persist across arm/disarm cycles

relaxation_factor_lpf and _att_relax_active are declared static inside a member function called at ~400 Hz. Static locals in C++ are initialized once at program load and never reset. If the vehicle lands with relaxation active (relaxation_factor_lpf > 0), disarms, then re-arms without a full power cycle, the filter state carries over and the attitude controller immediately applies pitch attenuation the moment the motors are armed again. These variables should be member fields of AC_AttitudeControl (initialized in the constructor and optionally reset on arm) so their lifecycle is tied to the object rather than to the process.

[greptile-apps]

LND_DET_TIM default (200 ms) is outside its documented range and 20-30× shorter than the previous hardcoded timeout

The @Range annotation says 1000–4000 ms, but the default is 200 ms. More critically, the old land_detector() was hardcoded to 4000 ms in check_land_complete() and 6000 ms in check_land_final(); now both use the same parameter that defaults to 200 ms. With a 200 ms timeout the landing condition clears in roughly 1.2 s (200 ms for land_start_ms + 1000 ms for lower_limit_start_ms), down from 5–7 s previously. Combined with the Q_LAND_ALTCHG increase to 1.5 m in defaults.parm, this dramatically lowers the bar for declaring a landing complete, risking premature disarm sequences. The documented range should be corrected to reflect the actual intended operating window, or the default should be raised to something within that range.

[greptile-apps]

is_vehicle_landing() is now dead code

The function is defined but no longer called anywhere in the script. The old call site in update() has been replaced by if in_vtol_flight(). The function 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!