diff --git a/guiTools/spawn_drones.sh b/guiTools/spawn_drones.sh
index 70a4ca4..48b4473 100644
--- a/guiTools/spawn_drones.sh
+++ b/guiTools/spawn_drones.sh
@@ -21,7 +21,7 @@ fi
 cd ./models/$DRONE_MODEL
 for (( j=0; j<$SIM_DRONE_COUNT; j++ ));
 do
-    xacro -v fdm_port_in:=$((9002 + ($j * 10))) model.xacro.sdf -o model.sdf
+    xacro -v fdm_port_in:=$(($FDM_PORT_IN + ($j * 10))) model.xacro.sdf -o model.sdf
     value=$(</home/gz-workspace/ardupilot_gazebo/models/$DRONE_MODEL/model.sdf)
     #-string is better than using -file option. File is not up to date in the next iteration.
     ros2 run ros_gz_sim create -world $WORLD_NAME -string "$value" -name spiri-$j -x $j  -y 0 -z 0.195