MC-stabilized: rescale thrust input to hover thrust at zero stick input

Use hover thrust estimate in stabilized mode to rescale stick inputs. Prevents vehicle from losing/gaining altitude when switching from position to stabilized mode.

src/modules/mc_att_control/mc_att_control.hpp

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2013-2019 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2013-2025 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -47,6 +47,7 @@
 #include <uORB/topics/manual_control_setpoint.h>
 #include <uORB/topics/parameter_update.h>
 #include <uORB/topics/autotune_attitude_control_status.h>
+#include <uORB/topics/hover_thrust_estimate.h>
 #include <uORB/topics/vehicle_attitude.h>
 #include <uORB/topics/vehicle_attitude_setpoint.h>
 #include <uORB/topics/vehicle_control_mode.h>
@@ -98,9 +99,11 @@ private:
 
 	uORB::SubscriptionInterval _parameter_update_sub{ORB_ID(parameter_update), 1_s};
 
+	uORB::Subscription _hover_thrust_estimate_sub{ORB_ID(hover_thrust_estimate)};
+	uORB::Subscription _vehicle_attitude_setpoint_sub{ORB_ID(vehicle_attitude_setpoint)};
+	uORB::Subscription _v_control_mode_sub{ORB_ID(vehicle_control_mode)};
 	uORB::Subscription _autotune_attitude_control_status_sub{ORB_ID(autotune_attitude_control_status)};
 	uORB::Subscription _manual_control_setpoint_sub{ORB_ID(manual_control_setpoint)};
-	uORB::Subscription _vehicle_attitude_setpoint_sub{ORB_ID(vehicle_attitude_setpoint)};
 	uORB::Subscription _vehicle_control_mode_sub{ORB_ID(vehicle_control_mode)};
 	uORB::Subscription _vehicle_land_detected_sub{ORB_ID(vehicle_land_detected)};
 	uORB::Subscription _vehicle_local_position_sub{ORB_ID(vehicle_local_position)};
@@ -118,8 +121,10 @@ private:
 
 	matrix::Vector3f _thrust_setpoint_body; /**< body frame 3D thrust vector */
 
+	float _hover_thrust{NAN};
+
 	float _man_yaw_sp{0.f};				/**< current yaw setpoint in manual mode */
-	float _man_tilt_max;                    /**< maximum tilt allowed for manual flight [rad] */
+	float _man_tilt_max{0.f};			/**< maximum tilt allowed for manual flight [rad] */
 
 	SlewRate<float> _manual_throttle_minimum{0.f}; ///< 0 when landed and ramped to MPC_MANTHR_MIN in air
 	SlewRate<float> _manual_throttle_maximum{0.f}; ///< 0 when disarmed ramped to 1 when spooled up

src/modules/mc_att_control/mc_att_control_main.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2013-2018 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2013-2025 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -103,15 +103,31 @@ MulticopterAttitudeControl::throttle_curve(float throttle_stick_input)
 {
 	float thrust = 0.f;
 
+	{
+		hover_thrust_estimate_s hte;
+
+		if (_hover_thrust_estimate_sub.update(&hte)) {
+			if (hte.valid) {
+				_hover_thrust = hte.hover_thrust;
+			}
+		}
+	}
+
+	if (!PX4_ISFINITE(_hover_thrust)) {
+		_hover_thrust = _param_mpc_thr_hover.get();
+	}
+
+	// throttle_stick_input is in range [-1, 1]
 	switch (_param_mpc_thr_curve.get()) {
 	case 1: // no rescaling to hover throttle
 		thrust = math::interpolate(throttle_stick_input, -1.f, 1.f,
 					   _manual_throttle_minimum.getState(), _param_mpc_thr_max.get());
 		break;
 
-	default: // 0 or other: rescale such that a centered throttle stick corresponds to hover throttle
+	default: // 0 or other: rescale to hover throttle at 0 stick input
-		thrust = math::interpolateNXY(throttle_stick_input, {-1.f, 0.f, 1.f},
+		thrust = math::interpolateNXY(throttle_stick_input,
-		{_manual_throttle_minimum.getState(), _param_mpc_thr_hover.get(), _param_mpc_thr_max.get()});
+		{-1.f, 0.f, 1.f},
+		{_manual_throttle_minimum.getState(), _hover_thrust, _param_mpc_thr_max.get()});
 		break;
 	}