TurtleBots 3 Burger: Multi robot SLAM IRL

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Hello,

I have a fleet of 4 TurtleBots and I want to make a multi robot SLAM mapping. I know that it is possible in Gazebo that each robots create a map and a higher program merge the maps but I want to do it with my real robots, do you know how to do that ?

Ps: I used ROS Noetic and already set up namespace for each robots

Thank you for any information!

Edit: I don't even manage to launch a slam program on one robot so I ask for your help too.

To set up my robots, i followed the following tutorial so basically when i launch the following command on my Tb:

ROS_NAMESPACE=tb3_1 roslaunch turtlebot3_bringup turtlebot3_robot.launch multi_robot_name:=tb3_1 set_lidar_frame_id:=tb3_1/base_scan

I get the following tf tree, node graph and topics:

After i launch on my computer:

ROS_NAMESPACE=tb3_1 roslaunch turtlebot3_slam turtlebot3_slam.launch multi_robot_name:=tb3_1

and a tf problem appear, the map tf connect to odom tf and not to tb3_1/odom and a warning message tell me that there is a problem with odom (logic because it should be tb3_1/odom):

[WARN ] [1654781371.592635721]: MessageFilter [target=odom ]: Dropped 100.00% of messages so far.

I tried to do it step by step to find the problem by launching on my computer:

ROS_NAMESPACE=tb3_1 roslaunch turtlebot3_bringup turtlebot3_remote.launch multi_robot_name:=tb3_1

and after:

ROS_NAMESPACE=tb3_1 roslaunch turtlebot3_slam turtlebot3_gmapping.launch set_odom_frame:=tb3_1/odom

and i got a nice tf but still warning message and no data in the map topics: with the warning message:

[WARN ] [1654783298.853778784]: MessageFilter [target=odom ]: Dropped 100.00% of messages so far.

From there i tried a lot of thing like edit the parameters in the config files (create save of the originals and replace modified one by the saved one after test), removing ROS_NAMESPACE or modifying parameters but nothing work

Do you have any idea ?

Ps: I don't why but now i can't launch the slam program even without namespace.