Tiltrotor:

- added open-loop transition time for airspeed-less flying
- added ramping down the back motors during forwards transition

src/modules/vtol_att_control/tiltrotor.cpp

@@ -35,6 +35,7 @@
  * @file tiltrotor.cpp
  *
  * @author Roman Bapst 		<bapstroman@gmail.com>
+ * @author Andreas Antener 	<andreas@uaventure.com>
  *
 */
 
@@ -68,6 +69,7 @@ Tiltrotor::Tiltrotor(VtolAttitudeControl *attc) :
 	_params_handles_tiltrotor.elevons_mc_lock = param_find("VT_ELEV_MC_LOCK");
 	_params_handles_tiltrotor.front_trans_dur_p2 = param_find("VT_TRANS_P2_DUR");
 	_params_handles_tiltrotor.fw_motors_off = param_find("VT_FW_MOT_OFFID");
+	_params_handles_tiltrotor.airspeed_mode = param_find("FW_ARSP_MODE");
 }
 
 Tiltrotor::~Tiltrotor()
@@ -128,6 +130,10 @@ Tiltrotor::parameters_update()
 	if (_params_tiltrotor.airspeed_trans < _params_tiltrotor.airspeed_blend_start + 1.0f) {
 		_params_tiltrotor.airspeed_trans = _params_tiltrotor.airspeed_blend_start + 1.0f;
 	}
+
+	/* airspeed mode */
+	param_get(_params_handles_tiltrotor.airspeed_mode, &l);
+	_params_tiltrotor.airspeed_mode = math::constrain(l, 0, 2);
 }
 
 int Tiltrotor::get_motor_off_channels(int channels)
@@ -201,16 +207,27 @@ void Tiltrotor::update_vtol_state()
 		case FW_MODE:
 			break;
 
-		case TRANSITION_FRONT_P1:
+		case TRANSITION_FRONT_P1: {
+				// allow switch if we are not armed for the sake of bench testing
+				bool transition_to_p2 = can_transition_on_ground();
 
-			// check if we have reached airspeed to switch to fw mode
-			// also allow switch if we are not armed for the sake of bench testing
-			if (_airspeed->indicated_airspeed_m_s >= _params_tiltrotor.airspeed_trans || can_transition_on_ground()) {
-				_vtol_schedule.flight_mode = TRANSITION_FRONT_P2;
-				_vtol_schedule.transition_start = hrt_absolute_time();
-			}
+				// check if we have reached airspeed to switch to fw mode
+				transition_to_p2 |= _params_tiltrotor.airspeed_mode != control_state_s::AIRSPD_MODE_DISABLED &&
+						    _airspeed->indicated_airspeed_m_s >= _params_tiltrotor.airspeed_trans &&
+						    (float)hrt_elapsed_time(&_vtol_schedule.transition_start) > (_params->front_trans_time_min * 1e6f);
 
-			break;
+				// check if airspeed is invalid and transition by time
+				transition_to_p2 |= _params_tiltrotor.airspeed_mode == control_state_s::AIRSPD_MODE_DISABLED &&
+						    _tilt_control > _params_tiltrotor.tilt_transition &&
+						    (float)hrt_elapsed_time(&_vtol_schedule.transition_start) > (_params->front_trans_time_openloop * 1e6f);
+
+				if (transition_to_p2) {
+					_vtol_schedule.flight_mode = TRANSITION_FRONT_P2;
+					_vtol_schedule.transition_start = hrt_absolute_time();
+				}
+
+				break;
+			}
 
 		case TRANSITION_FRONT_P2:
 
@@ -290,6 +307,8 @@ void Tiltrotor::update_fw_state()
 
 void Tiltrotor::update_transition_state()
 {
+	VtolType::update_transition_state();
+
 	if (!_flag_was_in_trans_mode) {
 		// save desired heading for transition and last thrust value
 		_flag_was_in_trans_mode = true;
@@ -308,19 +327,25 @@ void Tiltrotor::update_transition_state()
 						&_vtol_schedule.transition_start) / (_params_tiltrotor.front_trans_dur * 1000000.0f);
 		}
 
-		// do blending of mc and fw controls
-		if (_airspeed->indicated_airspeed_m_s >= _params_tiltrotor.airspeed_blend_start) {
-			_mc_roll_weight = 0.0f;
+		bool use_airspeed = _params_tiltrotor.airspeed_mode != control_state_s::AIRSPD_MODE_DISABLED;
 
-		} else {
-			// at low speeds give full weight to mc
-			_mc_roll_weight = 1.0f;
+		// at low speeds give full weight to MC
+		_mc_roll_weight = 1.0f;
+		_mc_yaw_weight = 1.0f;
+
+		// reduce MC controls once the plane has picked up speed
+		if (use_airspeed && _airspeed->indicated_airspeed_m_s > ARSP_YAW_CTRL_DISABLE) {
+			_mc_yaw_weight = 0.0f;
 		}
 
-		// disable mc yaw control once the plane has picked up speed
-		_mc_yaw_weight = 1.0f;
+		if (use_airspeed && _airspeed->indicated_airspeed_m_s >= _params_tiltrotor.airspeed_blend_start) {
+			_mc_roll_weight = 0.0f;
+		}
 
-		if (_airspeed->indicated_airspeed_m_s > ARSP_YAW_CTRL_DISABLE) {
+		// without airspeed wait until half of open-loop time has passed
+		if (!use_airspeed
+		    && (float)hrt_elapsed_time(&_vtol_schedule.transition_start) > (_params->front_trans_time_openloop * 1e6f) / 2) {
+			_mc_roll_weight = 0.0f;
 			_mc_yaw_weight = 0.0f;
 		}
 
@@ -331,7 +356,16 @@ void Tiltrotor::update_transition_state()
 		_tilt_control = _params_tiltrotor.tilt_transition +
 				fabsf(_params_tiltrotor.tilt_fw - _params_tiltrotor.tilt_transition) * (float)hrt_elapsed_time(
 					&_vtol_schedule.transition_start) / (_params_tiltrotor.front_trans_dur_p2 * 1000000.0f);
+
 		_mc_roll_weight = 0.0f;
+		_mc_yaw_weight = 0.0f;
+
+		// ramp down rear motors (setting MAX_PWM down scales the given output into the new range)
+		int rear_value = (1.0f - (float)hrt_elapsed_time(&_vtol_schedule.transition_start) /
+				  (_params_tiltrotor.front_trans_dur_p2 *
+				   1000000.0f)) * (float)(PWM_DEFAULT_MAX - PWM_DEFAULT_MIN) + (float)PWM_DEFAULT_MIN;
+
+		set_rear_motor_state(VALUE, rear_value);
 
 		_thrust_transition = _mc_virtual_att_sp->thrust;
 
@@ -395,12 +429,12 @@ void Tiltrotor::fill_actuator_outputs()
 	}
 
 	_actuators_out_1->timestamp = _actuators_fw_in->timestamp;
-	_actuators_out_1->control[actuator_controls_s::INDEX_ROLL] = -_actuators_fw_in->control[actuator_controls_s::INDEX_ROLL]
-			* (1 - _mc_roll_weight);
+	_actuators_out_1->control[actuator_controls_s::INDEX_ROLL] =
+		-_actuators_fw_in->control[actuator_controls_s::INDEX_ROLL];
 	_actuators_out_1->control[actuator_controls_s::INDEX_PITCH] =
-		(_actuators_fw_in->control[actuator_controls_s::INDEX_PITCH] + _params->fw_pitch_trim) * (1 - _mc_pitch_weight);
-	_actuators_out_1->control[actuator_controls_s::INDEX_YAW] = _actuators_fw_in->control[actuator_controls_s::INDEX_YAW]
-			* (1 - _mc_yaw_weight);	// yaw
+		(_actuators_fw_in->control[actuator_controls_s::INDEX_PITCH] + _params->fw_pitch_trim);
+	_actuators_out_1->control[actuator_controls_s::INDEX_YAW] =
+		_actuators_fw_in->control[actuator_controls_s::INDEX_YAW];	// yaw
 	_actuators_out_1->control[4] = _tilt_control;
 }
 
@@ -409,7 +443,7 @@ void Tiltrotor::fill_actuator_outputs()
 * Set state of rear motors.
 */
 
-void Tiltrotor::set_rear_motor_state(rear_motor_state state)
+void Tiltrotor::set_rear_motor_state(rear_motor_state state, int value)
 {
 	int pwm_value = PWM_DEFAULT_MAX;
 
@@ -429,6 +463,11 @@ void Tiltrotor::set_rear_motor_state(rear_motor_state state)
 		pwm_value = _params->idle_pwm_mc;
 		_rear_motors = IDLE;
 		break;
+
+	case VALUE:
+		pwm_value = value;
+		_rear_motors = VALUE;
+		break;
 	}
 
 	int ret;
@@ -457,7 +496,9 @@ void Tiltrotor::set_rear_motor_state(rear_motor_state state)
 
 	ret = px4_ioctl(fd, PWM_SERVO_SET_MAX_PWM, (long unsigned int)&pwm_max_values);
 
-	if (ret != OK) {PX4_WARN("failed setting max values");}
+	if (ret != OK) {
+		PX4_WARN("failed setting max values");
+	}
 
 	px4_close(fd);
 }

src/modules/vtol_att_control/tiltrotor.h

@@ -72,6 +72,7 @@ private:
 		int elevons_mc_lock;			/**< lock elevons in multicopter mode */
 		float front_trans_dur_p2;
 		int fw_motors_off;			/**< bitmask of all motors that should be off in fixed wing mode */
+		int airspeed_mode;
 	} _params_tiltrotor;
 
 	struct {
@@ -85,6 +86,7 @@ private:
 		param_t elevons_mc_lock;
 		param_t front_trans_dur_p2;
 		param_t fw_motors_off;
+		param_t airspeed_mode;
 	} _params_handles_tiltrotor;
 
 	enum vtol_mode {
@@ -103,7 +105,8 @@ private:
 	enum rear_motor_state {
 		ENABLED = 0,
 		DISABLED,
-		IDLE
+		IDLE,
+		VALUE
 	} _rear_motors;
 
 	struct {
@@ -128,7 +131,7 @@ private:
 	/**
 	 * Adjust the state of the rear motors. In fw mode they shouldn't spin.
 	 */
-	void set_rear_motor_state(rear_motor_state state);
+	void set_rear_motor_state(rear_motor_state state, int value = 0);
 
 	/**
 	 * Update parameters.

src/modules/vtol_att_control/vtol_att_control_main.cpp

@@ -132,6 +132,8 @@ VtolAttitudeControl::VtolAttitudeControl() :
 	_params_handles.vtol_type = param_find("VT_TYPE");
 	_params_handles.elevons_mc_lock = param_find("VT_ELEV_MC_LOCK");
 	_params_handles.fw_min_alt = param_find("VT_FW_MIN_ALT");
+	_params_handles.front_trans_time_openloop = param_find("VT_F_TR_OL_TM");
+	_params_handles.front_trans_time_min = param_find("VT_TRANS_MIN_TM");
 
 	/* fetch initial parameter values */
 	parameters_update();
@@ -560,6 +562,16 @@ VtolAttitudeControl::parameters_update()
 	param_get(_params_handles.fw_min_alt, &v);
 	_params.fw_min_alt = v;
 
+	param_get(_params_handles.front_trans_time_openloop, &_params.front_trans_time_openloop);
+
+	param_get(_params_handles.front_trans_time_min, &_params.front_trans_time_min);
+
+	/*
+	 * Minimum transition time can be maximum 90 percent of the open loop transition time,
+	 * anything else makes no sense and can potentially lead to numerical problems.
+	 */
+	_params.front_trans_time_min = math::min(_params.front_trans_time_openloop * 0.9f,
+				       _params.front_trans_time_min);
 
 	// update the parameters of the instances of base VtolType
 	if (_vtol_type != nullptr) {

src/modules/vtol_att_control/vtol_att_control_main.h

@@ -210,6 +210,8 @@ private:
 		param_t vtol_type;
 		param_t elevons_mc_lock;
 		param_t fw_min_alt;
+		param_t front_trans_time_openloop;
+		param_t front_trans_time_min;
 	} _params_handles;
 
 	/* for multicopters it is usual to have a non-zero idle speed of the engines

src/modules/vtol_att_control/vtol_type.h

@@ -60,6 +60,8 @@ struct Params {
 	int vtol_type;
 	int elevons_mc_lock;		// lock elevons in multicopter mode
 	float fw_min_alt;			// minimum relative altitude for FW mode (QuadChute)
+	float front_trans_time_openloop;
+	float front_trans_time_min;
 };
 
 // Has to match 1:1 msg/vtol_vehicle_status.msg