Instead of trying to keep a vehicle type within the FirmwarePlugin instance, pass the vehicle to the function so it can query the type that way.

src/FirmwarePlugin/APM/ArduRoverFirmwarePlugin.cc

@@ -74,7 +74,7 @@ void ArduRoverFirmwarePlugin::guidedModeChangeAltitude(Vehicle* vehicle, double
     qgcApp()->showMessage(QStringLiteral("Change altitude not supported."));
 }
 
-bool ArduRoverFirmwarePlugin::supportsNegativeThrust(void)
+bool ArduRoverFirmwarePlugin::supportsNegativeThrust(Vehicle* /*vehicle*/)
 {
     return true;
 }

src/FirmwarePlugin/APM/ArduRoverFirmwarePlugin.h

@@ -50,7 +50,7 @@ public:
     void    guidedModeChangeAltitude                (Vehicle* vehicle, double altitudeChange) final;
     int     remapParamNameHigestMinorVersionNumber  (int majorVersionNumber) const final;
     const   FirmwarePlugin::remapParamNameMajorVersionMap_t& paramNameRemapMajorVersionMap(void) const final { return _remapParamName; }
-    bool    supportsNegativeThrust                  (void) final;
+    bool    supportsNegativeThrust                  (Vehicle *) final;
     bool    supportsSmartRTL                        (void) const override { return true; }
     QString offlineEditingParamFile                 (Vehicle* vehicle) override { Q_UNUSED(vehicle); return QStringLiteral(":/FirmwarePlugin/APM/Rover.OfflineEditing.params"); }
 

src/FirmwarePlugin/FirmwarePlugin.cc

@@ -50,11 +50,6 @@ FirmwarePluginFactoryRegister* FirmwarePluginFactoryRegister::instance(void)
     return _instance;
 }
 
-FirmwarePlugin::FirmwarePlugin(MAV_TYPE vehicleType)
-{
-    _vehicleType = vehicleType;
-}
-
 AutoPilotPlugin* FirmwarePlugin::autopilotPlugin(Vehicle* vehicle)
 {
     return new GenericAutoPilotPlugin(vehicle, vehicle);
@@ -132,7 +127,7 @@ bool FirmwarePlugin::supportsThrottleModeCenterZero(void)
     return true;
 }
 
-bool FirmwarePlugin::supportsNegativeThrust(void)
+bool FirmwarePlugin::supportsNegativeThrust(Vehicle* /*vehicle*/)
 {
     // By default, this is not supported
     return false;

src/FirmwarePlugin/FirmwarePlugin.h

@@ -49,8 +49,6 @@ public:
         TakeoffVehicleCapability =          1 << 4, ///< Vehicle supports guided takeoff
     } FirmwareCapabilities;
 
-    FirmwarePlugin(MAV_TYPE vehicleType = MAV_TYPE_GENERIC);
-
     /// Maps from on parameter name to another
     ///     key:    parameter name to translate from
     ///     value:  mapped parameter name
@@ -164,7 +162,7 @@ public:
 
     /// Returns true if the vehicle and firmware supports the use of negative thrust
     /// Typically supported rover.
-    virtual bool supportsNegativeThrust(void);
+    virtual bool supportsNegativeThrust(Vehicle *);
 
     /// Returns true if the firmware supports the use of the RC radio and requires the RC radio
     /// setup page. Returns true by default.
@@ -346,9 +344,6 @@ protected:
     // Returns regex QString to extract version information from text
     virtual QString _versionRegex() { return QString(); }
 
-protected:
-    MAV_TYPE _vehicleType = MAV_TYPE_GENERIC;
-
 private:
     QVariantList _toolBarIndicatorList;
     static QVariantList _cameraList;    ///< Standard QGC camera list

src/FirmwarePlugin/PX4/PX4FirmwarePlugin.cc

@@ -35,9 +35,8 @@ PX4FirmwarePluginInstanceData::PX4FirmwarePluginInstanceData(QObject* parent)
 
 }
 
-PX4FirmwarePlugin::PX4FirmwarePlugin(MAV_TYPE vehicleType)
-    : FirmwarePlugin(vehicleType)
-    , _manualFlightMode     (tr("Manual"))
+PX4FirmwarePlugin::PX4FirmwarePlugin()
+    : _manualFlightMode     (tr("Manual"))
     , _acroFlightMode       (tr("Acro"))
     , _stabilizedFlightMode (tr("Stabilized"))
     , _rattitudeFlightMode  (tr("Rattitude"))
@@ -591,7 +590,7 @@ QString PX4FirmwarePlugin::_versionRegex() {
     return QStringLiteral("v([0-9,\\.]*) Stable");
 }
 
-bool PX4FirmwarePlugin::supportsNegativeThrust(void)
+bool PX4FirmwarePlugin::supportsNegativeThrust(Vehicle* vehicle)
 {
-    return _vehicleType == MAV_TYPE_GROUND_ROVER;
+    return vehicle->vehicleType() == MAV_TYPE_GROUND_ROVER;
 }

src/FirmwarePlugin/PX4/PX4FirmwarePlugin.h

@@ -23,7 +23,7 @@ class PX4FirmwarePlugin : public FirmwarePlugin
     Q_OBJECT
 
 public:
-    PX4FirmwarePlugin   (MAV_TYPE vehicleType);
+    PX4FirmwarePlugin   ();
     ~PX4FirmwarePlugin  () override;
 
     // Overrides from FirmwarePlugin
@@ -69,7 +69,7 @@ public:
     QString             autoDisarmParameter             (Vehicle* vehicle) override { Q_UNUSED(vehicle); return QStringLiteral("COM_DISARM_LAND"); }
     uint32_t            highLatencyCustomModeTo32Bits   (uint16_t hlCustomMode) override;
     bool                supportsTerrainFrame            (void) const override { return false; }
-    bool                supportsNegativeThrust          (void) override;
+    bool                supportsNegativeThrust          (Vehicle *vehicle) override;
 
 protected:
     typedef struct {

src/FirmwarePlugin/PX4/PX4FirmwarePluginFactory.cc

@@ -29,11 +29,11 @@ QList<MAV_AUTOPILOT> PX4FirmwarePluginFactory::supportedFirmwareTypes(void) cons
     return list;
 }
 
-FirmwarePlugin* PX4FirmwarePluginFactory::firmwarePluginForAutopilot(MAV_AUTOPILOT autopilotType, MAV_TYPE vehicleType)
+FirmwarePlugin* PX4FirmwarePluginFactory::firmwarePluginForAutopilot(MAV_AUTOPILOT autopilotType, MAV_TYPE /*vehicleType*/)
 {
     if (autopilotType == MAV_AUTOPILOT_PX4) {
         if (!_pluginInstance) {
-            _pluginInstance = new PX4FirmwarePlugin(vehicleType);
+            _pluginInstance = new PX4FirmwarePlugin();
         }
         return _pluginInstance;
     }

src/Vehicle/Vehicle.cc

@@ -2871,9 +2871,9 @@ bool Vehicle::supportsThrottleModeCenterZero(void) const
     return _firmwarePlugin->supportsThrottleModeCenterZero();
 }
 
-bool Vehicle::supportsNegativeThrust(void) const
+bool Vehicle::supportsNegativeThrust(void)
 {
-    return _firmwarePlugin->supportsNegativeThrust();
+    return _firmwarePlugin->supportsNegativeThrust(this);
 }
 
 bool Vehicle::supportsRadio(void) const

src/Vehicle/Vehicle.h

@@ -854,7 +854,7 @@ public:
     bool sub(void) const;
 
     bool supportsThrottleModeCenterZero (void) const;
-    bool supportsNegativeThrust         (void) const;
+    bool supportsNegativeThrust         (void);
     bool supportsRadio                  (void) const;
     bool supportsJSButton               (void) const;
     bool supportsMotorInterference      (void) const;