# Multicopter SITL not receiving ROS2 messages

**URL:** <https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926>\
**Category:** PX4 Autopilot\
**Created:** [October 24, 2023, 8:41pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926 "2023-10-24T20:41:22Z")\
**Posts on this page:** 10\
**Page:** 1

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [October 24, 2023, 8:41pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/1 "2023-10-24T20:41:22Z")

</div>

Hi everybody!  
I’m currently working on a project in which I have to simulate multiple copters in an environment.  
Preliminary info: I’m working with **ROS2 Humble** , **Gazebo 7** and I’ve [forked PX4](https://github.com/slim71/PX4-Autopilot) with small changes.

I’ve started from the single case:

- execute PX4 with  
`PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_POSE='0,0' PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i 1`  
in order to get the `MAV_SYS_ID` equal to the istance number (if I got that correctly)
- start the Micro XRCE agent with `MicroXRCEAgent udp4 -p 8888`
- launch my **ROS2** code, which at the moment starts up the _Offboard mode,_ arm the vehicle and gives fixed setpoints such that the drone will hover at 5m (done following the offboard example)  
Here’s a snippet of the message sent:

```cpp
px4_msgs::msg::VehicleCommand msg {};
msg.param1 = param1;
msg.param2 = param2;
msg.command = command;
msg.target_system = 0;
msg.target_component = 0;
msg.source_system = 1;
msg.source_component = 1;
// msg.confirmation = 0;
msg.from_external = true;
msg.timestamp = this->gatherTime().nanoseconds() / 1000; // gatherTime() calls the node 'now()' function
this->pub_to_command_topic_->publish(msg);

```

Since it seems to do what I intend, I was also trying to do the same in the multi-vehicle simulation.  
Through some code I create a bash script which does the following

```bash
#!/bin/bash
gnome-terminal --tab -t 'Gazebo' -- bash -c 'source /home/slim71/Documents/git/SpartanLIFT/install/odst/share/odst/resource/include_px4_models.sh && gz sim -r tugbot_depot.sdf'
gnome-terminal --tab -t 'PX4 - x500' -- bash -c 'cd PX4-Autopilot; PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_POSE='0,0' PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i 1'
gnome-terminal --tab -t 'PX4 - X3' -- bash -c 'cd PX4-Autopilot; sleep 6; PX4_SYS_AUTOSTART=4242 PX4_GZ_MODEL_POSE='0,1' PX4_GZ_MODEL=X3 ./build/px4_sitl_default/bin/px4 -i 2'
gnome-terminal --tab -t 'PX4 - X3' -- bash -c 'cd PX4-Autopilot; sleep 7; PX4_SYS_AUTOSTART=4242 PX4_GZ_MODEL_POSE='0,2' PX4_GZ_MODEL=X3 ./build/px4_sitl_default/bin/px4 -i 3'
gnome-terminal --tab -t 'PX4 - emesent_hovermap' -- bash -c 'cd PX4-Autopilot; sleep 8; PX4_SYS_AUTOSTART=4007 PX4_GZ_MODEL_POSE='0,3' PX4_GZ_MODEL=emesent_hovermap ./build/px4_sitl_default/bin/px4 -i 4'
gnome-terminal --tab -t 'PX4 - typhoon_h480' -- bash -c 'cd PX4-Autopilot; sleep 9; PX4_SYS_AUTOSTART=6012 PX4_GZ_MODEL_POSE='0,4' PX4_GZ_MODEL=typhoon_h480 ./build/px4_sitl_default/bin/px4 -i 5'
gnome-terminal --tab -t 'Interactive shell' -- bash

```

Then, for now, I simply run the same ROS2 code manually in another terminal. I can see the messages flow through the correct topics (starting in `/px4_1/`, since they are for the agent 1), but nothing happens in the simulation.

So I have a couple of questions:

- is appending `-i <x>` the right way to link a PX4 model to a specific `MAV_SYS_ID` (since this is needed for the VehicleCommand messages)?
- is thera a way to launch PX4 as verbose to understand what’s happening differently in the two cases?
- any other stuff to check?

I can share mode code if needed, it’s all public anyway! I haven’t done that straight away because it’s a bit much.

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [October 25, 2023, 7:55pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/2 "2023-10-25T19:55:52Z")

</div>

I think I’ve found something: it all goes well when I launch PX4 on its own (which actually opens up Gazebo too, of course), but when I open up Gazebo manually with `gz sim -r <world>.sdf` as I do in the script, I get some warnings of Preflight checks failed:

```bash
slim71@slim71-Ubuntu:~/Documents/git/SpartanLIFT/PX4-Autopilot$ PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_POSE='0,0' PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i 1
INFO [px4] instance: 1
INFO [px4] working directory /home/slim71/Documents/git/SpartanLIFT/PX4-Autopilot/build/px4_sitl_default/roo
________  _____ 
| ___ \ \ \ / / / |
| |_/ / \ V / / /| |
| __/ / \ / /_| |
| | / /^\ \ \___ |
\_| \/ \/ |_/

px4 starting.

INFO [px4] startup script: /bin/sh etc/init.d-posix/rcS 1
env SYS_AUTOSTART: 4001
INFO [param] selected parameter default file parameters.bson
INFO [param] importing from 'parameters.bson'
INFO [parameters] BSON document size 443 bytes, decoded 443 bytes (INT32:16, FLOAT:6)
INFO [param] selected parameter backup file parameters_backup.bson
INFO [dataman] data manager file './dataman' size is 7866640 bytes
INFO [init] gazebo already running world: world_demo
INFO [init] PX4_GZ_MODEL_POSE set, spawning at: 0,0
INFO [gz_bridge] world: world_demo, model name: x500_1, simulation model: x500
INFO [gz_bridge] Requested Model Position: 0,0
INFO [lockstep_scheduler] setting initial absolute time to 27310000 us
INFO [commander] LED: open /dev/led0 failed (22)
WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing
WARN [health_and_arming_checks] Preflight Fail: ekf2 missing data
INFO [tone_alarm] home set
INFO [mavlink] mode: Normal, data rate: 4000000 B/s on udp port 18571 remote port 14550
INFO [tone_alarm] notify negative
INFO [mavlink] mode: Onboard, data rate: 4000000 B/s on udp port 14581 remote port 14541
INFO [mavlink] mode: Onboard, data rate: 4000 B/s on udp port 14281 remote port 14031
INFO [mavlink] mode: Gimbal, data rate: 400000 B/s on udp port 13031 remote port 13281
INFO [logger] logger started (mode=all)
INFO [logger] Start file log (type: full)
INFO [logger] [logger] ./log/2023-10-25/19_49_51.ulg	
INFO [logger] Opened full log file: ./log/2023-10-25/19_49_51.ulg
INFO [mavlink] MAVLink only on localhost (set param MAV_{i}_BROADCAST = 1 to enable network)
INFO [mavlink] MAVLink only on localhost (set param MAV_{i}_BROADCAST = 1 to enable network)
INFO [px4] Startup script returned successfully
pxh> INFO [uxrce_dds_client] synchronized with time offset 1698263363654153us
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/failsafe_flags data writer, topic id: 80
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/position_setpoint_triplet data writer, topic iINFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/sensor_combined data writer, topic id: 168
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/timesync_status data writer, topic id: 190
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_attitude data writer, topic id: 207
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_control_mode data writer, topic id: 21INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_gps_position data writer, topic id: 21INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_local_position data writer, topic id: INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_odometry data writer, topic id: 225
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_status data writer, topic id: 230
WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing
INFO [uxrce_dds_client] successfully created rt/px4_1/fmu/out/vehicle_global_position data writer, topic id:WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing
WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing
WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing
INFO [tone_alarm] notify negative
WARN [health_and_arming_checks] Preflight Fail: barometer 0 missing

```

Since the commander is never ready for takeoff, nothing happens…  
Any feedback about this?

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [October 26, 2023, 8:16pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/3 "2023-10-26T20:16:29Z")

</div>

Maybe my first idea was wrong…  
I’ve tried dividing the Gazebo launch in server and GUI with `gz sim -r -s` and `gz sim -g` both manually and through the script, but I had no luck with my issue…  
It just seems that sometimes the sensor are OK and sometimes not. Most of the time I end up with all PX4 instances complaining about missing sensors, even though they work out great on their own… I might inspect more and open another topic, with the correct title and info, if I find something more insightful

---

<div class="post-metadata">

**Author:** ![iftahnaf](https://discuss.px4.io/user_avatar/discuss.px4.io/iftahnaf/32/5894_2.png) [@iftahnaf](https://discuss.px4.io/u/iftahnaf)\
**Post date:** [October 27, 2023, 5:27am UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/4 "2023-10-27T05:27:58Z")

</div>

Hi @slim71,

I created a ROS 2 launch file that loads `gz`, PX4 instances, and offboard node for each instance, maybe you could find it useful.

This is part of the launch file:

```python
    px4_procs = []
    followers_nodes = []
    for i in range(number_of_instances):
        px4_launch_command = f'{mode} PX4_SYS_AUTOSTART=4001 ' + f'PX4_GZ_MODEL_POSE="0,{2*i}" ' + f'PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i {i}'
        sleep_time_s = 0 if i == 0 else 5 + i
        px4_procs.append(
        ExecuteProcess(
                cmd=['bash', '-c', f'sleep {sleep_time_s} && cd /workspaces/test/PX4-Autopilot && {px4_launch_command}'],
                output='screen',
                emulate_tty=True
            )
        )

        if i > 0:
            followers_nodes.append(
                Node(
                    package='px4_offboard',
                    executable='offboard_control_follower',
                    output='screen',
                    name=f'offboard_control_follower_{i}',
                    parameters=[{'id': i}],
                    emulate_tty=True
                )
            )

...
...
    elements_to_launch = [node_leader, node_dds_agent, node_rosbridge, sys_shut_down] + px4_procs + followers_nodes

    ld = LaunchDescription(elements_to_launch)
    return ld

```

I added a delay (`sleep_time_s`) between instances so that all instances connect to the same `gz`.

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [October 29, 2023, 8:34am UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/5 "2023-10-29T08:34:53Z")

</div>

I have something similar, so that should be the way, thank you! 🙂  
it seems there’s something else for me, still trying to understand what

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [October 30, 2023, 6:07pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/6 "2023-10-30T18:07:51Z")

</div>

It seems I’ve found the issue!  
I double checked the airframe files and found that the barometer sensor simulation was off!  
So I just set `param set-default SENS_EN_BAROSIM 1` and they worked fine. I still don’t really understand why manually launching a model worked while this way it didn’t, but maybe it’s because of some background stuff difference… 🤷🏾‍♂️

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [February 6, 2024, 9:25pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/7 "2024-02-06T21:25:35Z")

</div>

After a long time, I’ve encountered this again!  
Needing to activate a sensor to be able to solve this didn’t make sense at the time, but I wasn’t complaining… Turns out, since I don’t really clean the build files of PX4 a lot (not much changes in my project, PX4-wise), it was indeed something else and I just wasn’t seeing it.

In the PX4 tag I have checked out, the **/fmu/out/vehicle\_command\_ack** topic was not among the enabled ones in the [dds\_topics.yaml file](https://github.com/PX4/PX4-Autopilot/blob/3576d513cd15bfddb96e7a9a2f2dcc6eb941b4df/src/modules/uxrce_dds_client/dds_topics.yaml). After manually adding it (and _doing only that_ between two subsequent runs), I can confirm that without it no movements is initialized. Then I guess the policy is “_no ack, no start_”, so to speak! 😂

---

<div class="post-metadata">

**Author:** ![mrh](https://discuss.px4.io/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@mrh](https://discuss.px4.io/u/mrh)\
**Post date:** [December 6, 2024, 2:00am UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/8 "2024-12-06T02:00:11Z")

</div>

i have the same problem ,i found that the vehicle\_odometry topic send out x=0，y=0for all drones，should be y=3 6 9for drone 1 2 3,i can see all topics with namespace /px4\_instance do u know how to solve this？

---

<div class="post-metadata">

**Author:** ![slim71](https://discuss.px4.io/user_avatar/discuss.px4.io/slim71/32/13489_2.png) [@slim71](https://discuss.px4.io/u/slim71)\
**Post date:** [December 6, 2024, 8:46pm UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/9 "2024-12-06T20:46:20Z")

</div>

if you get actual data in the topics, I’d say there’s something else… or maybe you either specify the wrong spawn point or don’t do that at all…

maybe try opening a new question with more details? 🤷🏾‍♂️

---

<div class="post-metadata">

**Author:** ![mrh](https://discuss.px4.io/letter_avatar_proxy/v4/letter/m/3ab097/32.png) [@mrh](https://discuss.px4.io/u/mrh)\
**Post date:** [December 7, 2024, 2:17am UTC](https://discuss.px4.io/t/multicopter-sitl-not-receiving-ros2-messages/34926/10 "2024-12-07T02:17:11Z")

</div>

I found that when i use gazebo instead of gazebo-classic the output data is correct,thank u so much