VTOL backtransition improvements

* vtol_type: only allow positive pitch setpoints during backtransition

* vtol params: set default of VT_B_DEC_FF to 0, as for most frames a FF is not necessary

* Tiltrotor: fix throttle during first part of back transition

* Tiltrotor: only enable all motors in second phase of backtransition (tilting phase)

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/vtol_att_control/tiltrotor.cpp

@@ -380,8 +380,6 @@ void Tiltrotor::update_transition_state()
 		_v_att_sp->thrust_body[0] = _thrust_transition;
 
 	} else if (_vtol_schedule.flight_mode == vtol_mode::TRANSITION_BACK) {
-		// turn on all MC motors
-		set_all_motor_state(motor_state::ENABLED);
 
 		// set idle speed for rotary wing mode
 		if (!_flag_idle_mc) {
@@ -403,13 +401,18 @@ void Tiltrotor::update_transition_state()
 			_v_att_sp->pitch_body = update_and_get_backtransition_pitch_sp();
 		}
 
-		// while we quickly rotate back the motors keep throttle at idle
 		if (time_since_trans_start < BACKTRANS_THROTTLE_DOWNRAMP_DUR_S) {
+			// blend throttle from FW value to 0
 			_mc_throttle_weight = 1.0f;
 			const float target_throttle = 0.0f;
-			blendThrottleDuringBacktransition(time_since_trans_start, target_throttle);
+			const float progress = time_since_trans_start / BACKTRANS_THROTTLE_DOWNRAMP_DUR_S;
+			blendThrottleDuringBacktransition(progress, target_throttle);
 
 		} else if (time_since_trans_start < timeUntilMotorsAreUp()) {
+			// while we quickly rotate back the motors keep throttle at idle
+
+			// turn on all MC motors
+			set_all_motor_state(motor_state::ENABLED);
 			_mc_throttle_weight = 0.0f;
 			_mc_roll_weight = 0.0f;
 			_mc_pitch_weight = 0.0f;
@@ -511,7 +514,7 @@ void Tiltrotor::blendThrottleAfterFrontTransition(float scale)
 
 void Tiltrotor::blendThrottleDuringBacktransition(float scale, float target_throttle)
 {
-	_v_att_sp->thrust_body[2] = -(scale * target_throttle + (1.0f - scale) * _last_thr_in_fw_mode);
+	_thrust_transition = -(scale * target_throttle + (1.0f - scale) * _last_thr_in_fw_mode);
 }
 
 

src/modules/vtol_att_control/vtol_att_control_params.c

@@ -329,10 +329,10 @@ PARAM_DEFINE_FLOAT(VT_FW_DIFTHR_SC, 0.1f);
  * @min 0
  * @max 0.2
  * @decimal 1
- * @increment 0.05
+ * @increment 0.01
  * @group VTOL Attitude Control
  */
-PARAM_DEFINE_FLOAT(VT_B_DEC_FF, 0.12f);
+PARAM_DEFINE_FLOAT(VT_B_DEC_FF, 0.f);
 
 /**
  * Backtransition deceleration setpoint to pitch I gain.

src/modules/vtol_att_control/vtol_type.cpp

@@ -231,14 +231,14 @@ float VtolType::update_and_get_backtransition_pitch_sp()
 	float integrator_input = _params->dec_to_pitch_i * accel_error_forward;
 
 	if ((pitch_sp_new >= pitch_lim && accel_error_forward > 0.0f) ||
-	    (pitch_sp_new <= -pitch_lim && accel_error_forward < 0.0f)) {
+	    (pitch_sp_new <= 0.f && accel_error_forward < 0.0f)) {
 		integrator_input = 0.0f;
 	}
 
 	_accel_to_pitch_integ += integrator_input * _transition_dt;
 
-
-	return math::constrain(pitch_sp_new, -pitch_lim, pitch_lim);
+	// only allow positive (pitch up) pitch setpoint
+	return math::constrain(pitch_sp_new, 0.f, pitch_lim);
 }
 
 bool VtolType::can_transition_on_ground()