ROS 2 Interface Operation

SLATE Base Node

The SLATE interfaces with ROS 2 using the slate_base_node from the interbotix_slate_driver package.

Publishers

The slate_base_node publishes to the following topics:

  • odom
    • Type: nav_msgs/msg/Odometry
    • Description: The odometry of the base.
  • battery_state
    • Type: sensor_msgs/msg/BatteryState
    • Description: Battery state information including present voltage and state of charge.

Subscribers

The slate_base_node subscribes to the following topics:

  • cmd_vel
    • Type: geometry_msgs/msg/Twist
    • Description: Velocity commands

Services

The slate_base_node provides the following service servers:

  • set_text

    • Type: std_srvs/srv/SetString
    • Description: Sets the text on the SLATE screen.

  • set_motor_torque_status

    • Type: std_srvs/srv/SetBool
    • Description: If true, enables torque on the drive wheels. If false, disables torque on the drive wheels.

    Note

    Torque is enabled on the drive wheels by default.

  • enable_charging

    • Type: std_srvs/srv/SetBool
    • Description: If true, enables charging via the contact charger.

Parameters

The slate_base_node has the following parameters:

  • update_frequency:

    • Type: int
    • Description: The frequency in Hz of the SLATE update loop.

    This is the rate at which the SLATE updates based on the incoming data. * Default: 20

  • publish_tf:

    • Type: bool
    • Description: Setting this to true publishes the odom->base_link TF following REP 105.
    • Default: false

  • odom_frame_name:

    • Type: string
    • Description: The name of the odometry frame when publishing the odom->base_link TF.
    • Default: "odom"

  • base_frame_name:

    • Type: string
    • Description: The name of the base_link frame when publishing the odom->base_link TF.
    • Default: "base_link"

Examples

The slate_base_node is designed to be controlled by other user-written nodes that publish to the cmd_vel topic or call the services provided by the slate_base_node. Below are some examples of how to interact with the slate_base_node using ROS 2 command line tools.

Setting Parameters

You can set parameters for the slate_base_node when running it using the --ros-args flag.

# Set the update frequency to 20 Hz
$ ros2 run interbotix_slate_driver slate_base_node --ros-args -p update_frequency:=20

# Enable publishing of the odom->base_link TF
$ ros2 run interbotix_slate_driver slate_base_node --ros-args -p publish_tf:=true

# Set the odometry frame name to "my_odom"
$ ros2 run interbotix_slate_driver slate_base_node --ros-args -p odom_frame_name:="my_odom"

# Set the base frame name to "my_base"
$ ros2 run interbotix_slate_driver slate_base_node --ros-args -p base_frame_name:="my_base"

Calling Services

You can call services provided by the slate_base_node using the ros2 service call command.

# Disable charging
$ ros2 service call /enable_charging std_srvs/srv/SetBool "{data: false}"

# Set the lights to color BLUE
$ ros2 service call /set_light_state interbotix_slate_msgs/srv/SetLightState "{light_state: 4}"

# Set the text to "hello world" on the SLATE screen
$ ros2 service call /set_text interbotix_slate_msgs/srv/SetString "{data: 'hello world'}"

# Disable torque on the drive wheels
$ ros2 service call /set_motor_torque_status std_srvs/srv/SetBool "{data: false}"

Publishing Velocity Commands

You can publish velocity commands to the slate_base_node using the ros2 topic pub command. -r 10 sets the publishing rate to 10 Hz. -t 30 publishes the message 30 times. This has the effect of commanding the velocity to the base for three seconds.

Warning

These commands will move the base, so make sure the SLATE is in a safe location before running them. Press Ctrl+C to stop the command at any time.

# Publish a velocity command to move forward
$ ros2 topic pub -r 10 -t 30 /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.1, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.0}}"

# Publish a velocity command to rotate counter-clockwise
$ ros2 topic pub -r 10 -t 30 /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.1}}"