quadchute: introduced parameter to specify maximum height

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

src/modules/vtol_att_control/vtol_att_control_params.c

@@ -248,6 +248,21 @@ PARAM_DEFINE_INT32(VT_FW_QC_P, 0);
  */
 PARAM_DEFINE_INT32(VT_FW_QC_R, 0);
 
+/**
+ * Quadchute maximum height.
+ *
+ * Maximum height above the ground (if available, otherwhise above home if available, otherwise above the local origin) where triggering a quadchute is possible.
+ * Triggering a quadchute always means transitioning the vehicle to hover flight in which generally a lot of energy is consumed.
+ * At high altitudes there is therefore a big risk to deplete the battery and therefore crash. Currently, there is no automated
+ * re-transition to fixed wing mode implemented and therefore this parameter serves and an intermediate measure to increase safety.
+ *
+ * @unit m
+ * @increment 1
+ * @decimal 1
+ * @group VTOL Attitude Control
+ */
+PARAM_DEFINE_FLOAT(VT_FW_QC_HMAX, 200.0f);
+
 /**
  * Airspeed less front transition time (open loop)
  *

src/modules/vtol_att_control/vtol_type.cpp

@@ -214,7 +214,21 @@ bool VtolType::can_transition_on_ground()
 
 bool VtolType::isQuadchuteEnabled()
 {
-	return _v_control_mode->flag_armed && !_land_detected->landed;
+	float dist_to_ground = 0.f;
+	const float home_position_z = _attc->get_home_position_z();
+
+	if (_local_pos->dist_bottom_valid) {
+		dist_to_ground = _local_pos->dist_bottom;
+
+	} else if (PX4_ISFINITE(home_position_z)) {
+		dist_to_ground = -(_local_pos->z - home_position_z);
+
+	} else {
+		dist_to_ground = -_local_pos->z;
+
+	}
+
+	return _v_control_mode->flag_armed && !_land_detected->landed && dist_to_ground < _param_quadchute_max_height.get();
 }
 
 bool VtolType::isMinAltBreached()

src/modules/vtol_att_control/vtol_type.h

@@ -314,6 +314,7 @@ protected:
 					(ParamFloat<px4::params::VT_FW_ALT_ERR>) _param_vt_fw_alt_err,
 					(ParamInt<px4::params::VT_FW_QC_P>) _param_vt_fw_qc_p,
 					(ParamInt<px4::params::VT_FW_QC_R>) _param_vt_fw_qc_r,
+					(ParamFloat<px4::params::VT_FW_QC_HMAX>) _param_quadchute_max_height,
 					(ParamFloat<px4::params::VT_F_TR_OL_TM>) _param_vt_f_tr_ol_tm,
 					(ParamFloat<px4::params::VT_TRANS_MIN_TM>) _param_vt_trans_min_tm,