Manually changing MAVLink system ID for PX4 SITL instances

alireza_ghaderi · July 15, 2023, 12:22pm

Hello,I am running PX4 SITL instances on separate VMware nodes (Ubuntu) and trying to connect to both instances on the ground on another instance on the network. I am using either JMAVSim or Gazebo for simulation. The problem I am facing is that QGroundControl seems to treat both instances as the same drone, and I suspect that the system ID or something else should specify that they are different.I have tried the following methods to set unique system IDs for each PX4 SITL instance:

Modifying the SYSID_THISMAV parameter in the ROMFS/px4fmu_common/init.d-posix/rcS file for each instance.
Setting the MAV_SYS_ID environment variable before starting each PX4 SITL instance on the separate VMware nodes.
Changing the Mavlink ID from paramteres also didnt work since it needed reboot and after reboot the SITL it still shows as 1

Unfortunately, none of these methods worked, and QGroundControl still shows the system ID and MAVLink ID as 1 for both instances.I would appreciate any help or suggestions on how to manually change the MAVLink system ID for PX4 SITL instances running on different systems so that QGroundControl can recognize them as separate drones.
Thank you!

Benja · July 15, 2023, 2:04pm

Hi @alireza_ghaderi , SYS_MAV_ID is set here

github.com

PX4/PX4-Autopilot/blob/327b7e611e4547a1d72a9cf38a03ec80a8905a98/ROMFS/px4fmu_common/init.d-posix/rcS#L131


      
          
          if param compare SYS_AUTOCONFIG 1
          then
          	# Reset params except Airframe, RC calibration, sensor calibration, flight modes, total flight time, and next flight UUID.
          	param reset_all SYS_AUTOSTART RC* CAL_* COM_FLTMODE* LND_FLIGHT* TC_* COM_FLIGHT*
          	set AUTOCNF yes
          fi
          
          # multi-instance setup
          # shellcheck disable=SC2154
          param set MAV_SYS_ID $((px4_instance+1))
          param set UXRCE_DDS_KEY $((px4_instance+1))
          
          if [ $AUTOCNF = yes ]
          then
          	param set SYS_AUTOSTART $SYS_AUTOSTART
          
          	param set CAL_ACC0_ID  1310988 # 1310988: DRV_IMU_DEVTYPE_SIM, BUS: 1, ADDR: 1, TYPE: SIMULATION
          	param set CAL_GYRO0_ID 1310988 # 1310988: DRV_IMU_DEVTYPE_SIM, BUS: 1, ADDR: 1, TYPE: SIMULATION
          	param set CAL_ACC1_ID  1310996 # 1310996: DRV_IMU_DEVTYPE_SIM, BUS: 2, ADDR: 1, TYPE: SIMULATION
          	param set CAL_GYRO1_ID 1310996 # 1310996: DRV_IMU_DEVTYPE_SIM, BUS: 2, ADDR: 1, TYPE: SIMULATION

using px4_instance.px4_instance is set by px4_alias.sh, who is generated by

github.com

PX4/PX4-Autopilot/blob/327b7e611e4547a1d72a9cf38a03ec80a8905a98/platforms/posix/src/px4/common/px4-alias.sh_in

#!/bin/sh

# File is auto-generated by cmake compilation, do not edit.
R="`pwd`/"

# Map the NuttX-style variable definition 'set <var> <value>' to something that
# bash and alternatives understand
# define _set first because sh (POSIX shell) does not like overwriting set directly
_set() {
	eval $1=\"$2\"
}
alias set=_set

# Don't stop on errors.
#set -e

# Arguments passed to this script:
# $1: optional instance id
px4_instance=0
[ -n "$1" ] && px4_instance=$1

This file has been truncated. show original

and is filled with the number passed with the -i option on the startup script. See for example the multi-vehicle sim guide for Gazebo

alireza_ghaderi · July 16, 2023, 2:33am

Thnks
If I understand correct, this command should be executed in the terminal:
export px4_instance 2
make px4_sitl gazebo

I did this but still doesn’t work. still, in parameters, MAV_SYS_ID shows as 1.
is there sth wrong?
can we manually hard code and change it from the startup code? or can we change the parameters that are auto-being loaded?

and can a similar technique be used with jmavsim?

alireza_ghaderi · July 17, 2023, 7:17am

After trying different methods to set unique system IDs for each PX4 SITL instance on separate VMware nodes, the solution that worked was to modify the rcS file in the build version of the PX4-Autopilot directory. The file path is
PX4-Autopilot/build/px4_sitl_default/etc/init.d-posix/rcS
, and the line to modify is
param set MAV_SYS_ID $((px4_instance+1))
. You can manually set a different system ID by changing the value of
MAV_SYS_ID to the desired number, for example,
param set MAV_SYS_ID 2

bclay1297 · July 18, 2023, 4:37pm

Supposivly we can set use a mavlink message to change SYSID_THISMAV. I have not been successful that one either

alireza_ghaderi · July 21, 2023, 5:57am

you might be able to do that in a real drone. but in SITL I don’t think since you need to reboot the sitl after changing this parameter and next time it loads, it is gonna read from rcs file again in build directory