Plane: TKOFF_THR_MIN is applied to SLT transitions

ArduPlane/quadplane.cpp

@@ -838,6 +838,10 @@ bool QuadPlane::setup(void)
     pilot_speed_z_max_dn.convert_centi_parameter(AP_PARAM_INT16);
     pilot_accel_z.convert_centi_parameter(AP_PARAM_INT16);
 
+    // Provisionally assign the SLT thrust type.
+    // It will be overwritten by tailsitter or tiltorotor setups.
+    thrust_type = ThrustType::THRUST_TYPE_SLT;
+
     tailsitter.setup();
 
     tiltrotor.setup();

ArduPlane/quadplane.h

@@ -76,6 +76,14 @@ class QuadPlane
     void control_auto(void);
     bool setup(void);
 
+    enum class ThrustType : uint8_t {
+        THRUST_TYPE_UNDEFINED=0, // Undefined. Means that no backend has configured it yet.
+        THRUST_TYPE_SLT, // Traditional quadplane, with a pusher motor and independent multicopter lift.
+        THRUST_TYPE_TAILSITTER,
+        THRUST_TYPE_TILTROTOR,
+    };
+    ThrustType get_thrust_type(void) {return thrust_type;}
+
     void vtol_position_controller(void);
     void setup_target_position(void);
     void takeoff_controller(void);
@@ -198,6 +206,9 @@ class QuadPlane
     AP_Enum<AP_Motors::motor_frame_class> frame_class;
     AP_Enum<AP_Motors::motor_frame_type> frame_type;
 
+    // Types of different "quadplane" configurations.
+    ThrustType thrust_type;
+
     // Initialise motors to allow passing it to tailsitter in its constructor
     AP_MotorsMulticopter *motors = nullptr;
     const struct AP_Param::GroupInfo *motors_var_info;

ArduPlane/servos.cpp

@@ -559,6 +559,14 @@ float Plane::apply_throttle_limits(float throttle_in)
         if (aparm.takeoff_throttle_max != 0) {
             max_throttle = aparm.takeoff_throttle_max.get();
         }
+
+        // Apply minimum throttle limits only for SLT thrust types.
+        // The other types don't support it well.
+        if (quadplane.thrust_type == QuadPlane::ThrustType::THRUST_TYPE_SLT) {
+            if (aparm.takeoff_throttle_min.get() != 0) {
+                min_throttle = MAX(min_throttle, aparm.takeoff_throttle_min.get());
+            }
+        }
     }
 #endif
 

ArduPlane/tailsitter.cpp

@@ -208,6 +208,8 @@ void Tailsitter::setup()
         return;
     }
 
+    quadplane.thrust_type = QuadPlane::ThrustType::THRUST_TYPE_TAILSITTER;
+
     // Set tailsitter transition rate to match old calculation
     if (!transition_rate_fw.configured()) {
         transition_rate_fw.set_and_save(transition_angle_fw / (quadplane.transition_time_ms/2000.0f));

ArduPlane/tiltrotor.cpp

@@ -106,6 +106,8 @@ void Tiltrotor::setup()
         return;
     }
 
+    quadplane.thrust_type = QuadPlane::ThrustType::THRUST_TYPE_TILTROTOR;
+
     _is_vectored = tilt_mask != 0 && type == TILT_TYPE_VECTORED_YAW;
 
     // true if a fixed forward motor is configured, either throttle, throttle left  or throttle right.