tiltrotor back-transition improvements:

- do not set zero throttle during the entire back-transition because otherwise
we need to make the back-transition really short
- added ramping up of throttle setpoint during backtransition to avoid
step inputs
- back-transition ends after back-transition time and not when motors are fully
rotated updwards. previously the vehicle would enter hover mode at high speed
which was not handled well by the mc position controller

Signed-off-by: Roman <bapstroman@gmail.com>

src/modules/vtol_att_control/tiltrotor.cpp

@@ -124,7 +124,9 @@ void Tiltrotor::update_vtol_state()
 			break;
 
 		case TRANSITION_BACK:
-			if (_tilt_control <= _params_tiltrotor.tilt_mc) {
+			float time_since_trans_start = (float)(hrt_absolute_time() - _vtol_schedule.transition_start) * 1e-6f;
+
+			if (_tilt_control <= _params_tiltrotor.tilt_mc && time_since_trans_start > _params->back_trans_duration) {
 				_vtol_schedule.flight_mode = MC_MODE;
 			}
 
@@ -303,18 +305,28 @@ void Tiltrotor::update_transition_state()
 		// tilt rotors back
 		if (_tilt_control > _params_tiltrotor.tilt_mc) {
 			_tilt_control = _params_tiltrotor.tilt_fw -
-					fabsf(_params_tiltrotor.tilt_fw - _params_tiltrotor.tilt_mc) * time_since_trans_start / _params->back_trans_duration;
+					fabsf(_params_tiltrotor.tilt_fw - _params_tiltrotor.tilt_mc) * time_since_trans_start / 1.0f;
 		}
 
-		// set zero throttle for backtransition otherwise unwanted moments will be created
-		_actuators_mc_in->control[actuator_controls_s::INDEX_THROTTLE] = 0.0f;
-
-		_mc_roll_weight = 0.0f;
+		_mc_yaw_weight = 1.0f;
 
+		// while we quickly rotate back the motors keep throttle at idle
+		if (time_since_trans_start < 1.0f) {
+			_mc_throttle_weight = 0.0f;
+			_mc_roll_weight = 0.0f;
+			_mc_pitch_weight = 0.0f;
+
+		} else {
+			_mc_roll_weight = 1.0f;
+			_mc_pitch_weight = 1.0f;
+			// slowly ramp up throttle to avoid step inputs
+			_mc_throttle_weight = (time_since_trans_start - 1.0f) / 1.0f;
+		}
 	}
 
 	_mc_roll_weight = math::constrain(_mc_roll_weight, 0.0f, 1.0f);
 	_mc_yaw_weight = math::constrain(_mc_yaw_weight, 0.0f, 1.0f);
+	_mc_throttle_weight = math::constrain(_mc_throttle_weight, 0.0f, 1.0f);
 
 	// copy virtual attitude setpoint to real attitude setpoint (we use multicopter att sp)
 	memcpy(_v_att_sp, _mc_virtual_att_sp, sizeof(vehicle_attitude_setpoint_s));
@@ -353,7 +365,7 @@ void Tiltrotor::fill_actuator_outputs()
 
 	} else {
 		_actuators_out_0->control[actuator_controls_s::INDEX_THROTTLE] =
-			_actuators_mc_in->control[actuator_controls_s::INDEX_THROTTLE];
+			_actuators_mc_in->control[actuator_controls_s::INDEX_THROTTLE] * _mc_throttle_weight;
 	}
 
 	_actuators_out_1->timestamp = hrt_absolute_time();

src/modules/vtol_att_control/vtol_type.cpp

@@ -124,6 +124,7 @@ void VtolType::update_mc_state()
 	_mc_roll_weight = 1.0f;
 	_mc_pitch_weight = 1.0f;
 	_mc_yaw_weight = 1.0f;
+	_mc_throttle_weight = 1.0f;
 }
 
 void VtolType::update_fw_state()