[control_allocation] centralize the definition of minimum yaw margin

src/modules/control_allocator/ControlAllocation/ControlAllocationSequentialDesaturation.cpp

@@ -219,7 +219,7 @@ ControlAllocationSequentialDesaturation::mixYaw()
 	// Change yaw acceleration to unsaturate the outputs if needed (do not change roll/pitch),
 	// and allow some yaw response at maximum thrust
 	ActuatorVector max_prev = _actuator_max;
-	_actuator_max += (_actuator_max - _actuator_min) * 0.15f;
+	_actuator_max += (_actuator_max - _actuator_min) * MINIMUM_YAW_MARGIN;
 	desaturateActuators(_actuator_sp, yaw);
 	_actuator_max = max_prev;
 

src/modules/control_allocator/ControlAllocation/ControlAllocationSequentialDesaturation.hpp

@@ -57,6 +57,10 @@ class ControlAllocationSequentialDesaturation: public ControlAllocationPseudoInv
 	void allocate() override;
 
 	void updateParameters() override;
+
+	// This is the minimum actuator yaw granted when the controller is saturated.
+	// In the yaw-only case where outputs are saturated, thrust is reduced by up to this amount.
+	static constexpr float MINIMUM_YAW_MARGIN{0.15f};
 private:
 
 	/**

src/modules/control_allocator/ControlAllocation/ControlAllocationSequentialDesaturationTest.cpp

@@ -325,13 +325,18 @@ TEST(ControlAllocationSequentialDesaturationTest, AirmodeDisabledReducedThrustAn
 	allocator.allocate();
 
 	const auto &actuator_sp = allocator.getActuatorSetpoint();
-	// In the case of yaw saturation, thrust per motor will be reduced by the hard-coded
-	// magic-number yaw margin of 0.15f.
-	constexpr float YAW_MARGIN{0.15f}; // get this from a centralized source when available.
-	constexpr float YAW_DIFF_PER_MOTOR{1.0f + YAW_MARGIN - DESIRED_THRUST_Z_PER_MOTOR};
+	// In the case of yaw saturation, thrust per motor will be reduced by
+	// ControlAllocationSequentialDesaturation::MINIMUM_YAW_MARGIN.
+	constexpr float YAW_DIFF_PER_MOTOR{1.0f +
+					   ControlAllocationSequentialDesaturation::MINIMUM_YAW_MARGIN - DESIRED_THRUST_Z_PER_MOTOR};
 	// At control set point, there will be 2 different actuator values.
-	constexpr float HIGH_THRUST_Z_PER_MOTOR{DESIRED_THRUST_Z_PER_MOTOR + YAW_DIFF_PER_MOTOR - YAW_MARGIN};
-	constexpr float LOW_THRUST_Z_PER_MOTOR{DESIRED_THRUST_Z_PER_MOTOR - YAW_DIFF_PER_MOTOR - YAW_MARGIN};
+	constexpr float HIGH_THRUST_Z_PER_MOTOR{
+		DESIRED_THRUST_Z_PER_MOTOR + YAW_DIFF_PER_MOTOR
+		- ControlAllocationSequentialDesaturation::MINIMUM_YAW_MARGIN};
+	constexpr float LOW_THRUST_Z_PER_MOTOR{
+		DESIRED_THRUST_Z_PER_MOTOR - YAW_DIFF_PER_MOTOR
+		- ControlAllocationSequentialDesaturation::MINIMUM_YAW_MARGIN};
+
 	EXPECT_NEAR(actuator_sp(0), HIGH_THRUST_Z_PER_MOTOR, EXPECT_NEAR_TOL);
 	EXPECT_NEAR(actuator_sp(1), HIGH_THRUST_Z_PER_MOTOR, EXPECT_NEAR_TOL);
 	EXPECT_NEAR(actuator_sp(2), LOW_THRUST_Z_PER_MOTOR, EXPECT_NEAR_TOL);