Slam_toolbox utilizing lidar odometry

General Support
1

Hello, I’m building my first mobile robot with raspberry pi in the hopes of solidifying my understanding with ROS2 and some packages, but also trying to lower the barrier of setting up a low cost slam robot.

I’ve gotten the RPlidar A1 to run on it and publishing laser scan just fine at 7 Hz.
I have a TF ros2 run tf2_ros static_transform_publisher 0 0 0 0 0 0 base_link laser

and I launched the slam_toolbox with ros2 run slam_toolbox async_slam_toolbox_node --ros-args --params-file ~/Desktop/my_custom_config.yaml

Below is my configuration:

slam_toolbox:
  ros__parameters:
    use_sim_time: false
    update_rate: 1.0
    publish_period: 0.1
    resolution: 0.05
    max_laser_range: 8.0
    scan_topic: /scan
    odom_frame: base_link  # since you don't have odometry, the map can be used as an odom frame
    base_frame: base_link
    mode: mapping
    map_update_interval: 5.0 # 8.0
    max_occupied_threshold: 0.65
    min_free_threshold: 0.196
    minimum_time_interval: 0.5
    transform_publish_period: 0.02
    linear_update: 0.1 # 0.5
    angular_update: 0.1 #0.436
    scan_buffer_size: 10
    scan_buffer_maximum_scan_distance: 8.0
    lookup_transform_timeout_sec: 0.5
    submap:
      number_of_cells: 3500

I’m only getting an initial map when I run the slam_toolbox… after that the /map topic is showing the same data and /map_updates isn’t publishing anything…

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I don’t have other forms of odometry, I thought slam_toolbox would know to utilize laser scan as lidar odometry when setting my odom_frame to base_link in the configuration?

2

Mapping or localization, which one you want to do?
You want to use lidar as odometry, right?
Then you should set odometry frame as /scan, but I never try it, so I don’t kown if it works.

4

my understanding is that the odom_frame setting as base_link would make the slam_toolbox estimate the motion as well… but I’m not too sure as the document is a bit lacking on the lidar portion…

5

Hello @Genozen ,

Have a look at this Open Class: https://app.theconstructsim.com/open-classes/33a5afd7-2ef2-4074-ab72-0c54aa48fc61

I think it might be helpful here.

6

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8

@MagicalBrain your response is not correct, you are confusing frame by topic. Usually /scan is the name of the topic that published lidar data. The lidar data is referenced to a frame in the robot, usually named laser.

So @Genozen you need another extra ROS node that computes odometry and publishes it in the /odom topic. If your robot is not publishing odometry (maybe because it doesn’t have encoders in the wheels), you can use the package GitHub - Adlink-ROS/rf2o_laser_odometry that does that computation.
Once you launch that node and the odometry is being published by it, then you can use slam_toolbox to create your map