diff --git a/docker-compose.yml b/docker-compose.yml
index 37d83e6..5e94ec7 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -52,7 +52,7 @@ services:
       - -c
       - |
         ./Tools/autotest/sim_vehicle.py $ARDUPILOT_VEHICLE --no-rebuild \
-        --no-mavproxy --enable-dds --sysid $DRONE_SYS_ID -I$TRACKER_INSTANCE
+        --no-mavproxy --enable-dds --sysid $DRONE_SYS_ID -I$INSTANCE
     profiles:
       - uav-sim
     stdin_open: true
diff --git a/sim_drone.py b/sim_drone.py
index e6eb46c..14d40f4 100644
--- a/sim_drone.py
+++ b/sim_drone.py
@@ -86,7 +86,7 @@ def modified_environ(*remove, **update):
 
 
 # @app.command()
-def start(tracker_instance: int = 0, sys_id: int = 1):
+def start(instance: int = 0, sys_id: int = 1):
     """Starts the simulated drone with a given sys_id,
     each drone must have it's own unique ID.
     """
@@ -96,12 +96,12 @@ def start(tracker_instance: int = 0, sys_id: int = 1):
     with logger.contextualize(syd_id=sys_id):
         env = os.environ
         with modified_environ(
-            SERIAL0_PORT=str(int(env["SERIAL0_PORT"]) + 10 * tracker_instance),
-            MAVROS2_PORT=str(int(env["MAVROS2_PORT"]) + 10 * tracker_instance),
-            MAVROS1_PORT=str(int(env["MAVROS1_PORT"]) + 10 * tracker_instance),
-            FDM_PORT_IN=str(int(env["FDM_PORT_IN"]) + 10 * tracker_instance),
-            SITL_PORT=str(int(env["SITL_PORT"]) + 10 * tracker_instance),
-            TRACKER_INSTANCE=str(tracker_instance),
+            SERIAL0_PORT=str(int(env["SERIAL0_PORT"]) + 10 * instance),
+            MAVROS2_PORT=str(int(env["MAVROS2_PORT"]) + 10 * instance),
+            MAVROS1_PORT=str(int(env["MAVROS1_PORT"]) + 10 * instance),
+            FDM_PORT_IN=str(int(env["FDM_PORT_IN"]) + 10 * instance),
+            SITL_PORT=str(int(env["SITL_PORT"]) + 10 * instance),
+            INSTANCE=str(instance),
             DRONE_SYS_ID=str(sys_id),
         ):
             logger.info("Starting drone stack, this may take some time")
@@ -126,7 +126,7 @@ def start_group():
     """Start a group of robots"""
     for i in range(sim_drone_count):
         logger.info(f"start robot {i}")
-        start(tracker_instance=i, sys_id=i + 1)
+        start(instance=i, sys_id=i + 1)
         # if i == 0:
         #     wait_for_gazebo()