wmx_r2_control

Overview

wmx_r2_control is the ros2_control route into WMX R2. It provides a SystemInterface plugin — wmx_r2_control/WmxSystemHardware — that exposes WMX3 axes to the standard controller_manager, plus the URDF xacros, controller YAMLs, and launch files that use it.

It is an alternative to the direct route, not a replacement. Use it when you want stock ros2_controllers (diff_drive_controller, joint_state_broadcaster) rather than the WMX-specific controllers in wmx_r2_package.

	Direct (wmx_r2_package)	ros2_control (wmx_r2_control)
Feedback	joint_state_broadcaster node reads WMX3 directly	WmxSystemHardware read() into standard joint_state_broadcaster/JointStateBroadcaster
Arm motion	joint_trajectory_controller → WMX3 C-spline	the same node — ros2_control handles feedback only
Wheel motion	differential_drive_controller → StartVel	diff_drive_controller/DiffDriveController → WmxSystemHardware write() → StartVel
Extra processes	none	ros2_control_node, robot_state_publisher, spawners

Package structure

wmx_r2_control/
├── src/wmx_system_hardware.cpp        # the SystemInterface plugin
├── include/wmx_r2_control/wmx_system_hardware.hpp
├── wmx_r2_control_plugin.xml          # pluginlib export
├── launch/
│   ├── wmx_r2_control_manipulator.launch.py
│   └── wmx_r2_control_differential.launch.py
├── urdf/
│   ├── cr3a.wmx.urdf.xacro       cr3a.wmx.ros2_control.xacro
│   ├── cr5a.wmx.urdf.xacro       cr5a.wmx.ros2_control.xacro
│   └── diffbot.wmx.urdf.xacro    diffbot.wmx.ros2_control.xacro
├── config/
│   ├── cr3a_controllers.yaml
│   ├── cr5a_controllers.yaml
│   └── diffbot_controllers.yaml
├── CMakeLists.txt
└── package.xml

WmxSystemHardware

The plugin attaches to the engine that wmx_engine_node owns. It does not start or stop the engine — the general nodes still do that, which is why both ros2_control launch files include wmx_r2_general_nodes.launch.py.

Hardware parameters

Set in the <hardware> block of the ros2_control xacro:

Parameter	Meaning
device_name	WMX device name for this hardware instance, e.g. wmx_cr3a_control
wmx_param_file	WMX3 parameter XML; passed in from the launch argument of the same name

Per-joint parameters

Each <joint> needs one <param name="axis"> giving its WMX3 axis index. An axis outside [0, maxAxes) fails initialization.

Interfaces

Interface	Direction	Notes
position	state	WMX actualPos, unconverted
velocity	state	WMX actualVelocity
velocity	command	Written with CoreMotion StartVel

A joint declares either a single velocity command interface or no command interface at all, which makes it state-only. Anything else fails initialization.

Note

There is no position command interface. The arm’s planned motion goes through wmx_r2_package’s joint_trajectory_controller, which talks to the WMX C-spline directly — ros2_control is not in that path. cr3a.wmx.ros2_control.xacro and cr5a.wmx.ros2_control.xacro therefore declare state interfaces only.

Launch files

wmx_r2_control_manipulator.launch.py

Starts, in order:

1. wmx_r2_general_nodes.launch.py — engine, lifecycle manager, axes, I/O, EtherCAT

2. robot_state_publisher from urdf_file

3. ros2_control_node with controllers_file

4. the joint_state_broadcaster spawner (standard ros2_controllers)

5. joint_trajectory_controller, joint_position_controller, and — with use_gripper:=true — gripper_controller, all from wmx_r2_package

6. a topic_tools relay for the Isaac Sim joint command mirror

Argument	Default	Description
use_sim_time	false	Use the simulation clock
config_file	required	Manipulator node parameters, e.g. wmx_r2_package/example/cr3a_manipulator_config.yaml
wmx_param_file	required	WMX3 parameter XML. Required here, not optional: it is also fed to the xacro, so an empty value would blank the description’s own default.
urdf_file	required	Robot description xacro, e.g. urdf/cr3a.wmx.urdf.xacro
controllers_file	required	controller_manager YAML, e.g. config/cr3a_controllers.yaml
use_gripper	false	Start gripper_controller

wros ros2 launch wmx_r2_control wmx_r2_control_manipulator.launch.py \
    use_sim_time:=false \
    'config_file:=$(ros2 pkg prefix --share wmx_r2_package)/example/cr3a_manipulator_config.yaml' \
    'wmx_param_file:=$(ros2 pkg prefix --share wmx_r2_package)/example/cr3a_wmx_parameters.xml' \
    'urdf_file:=$(ros2 pkg prefix --share wmx_r2_control)/urdf/cr3a.wmx.urdf.xacro' \
    'controllers_file:=$(ros2 pkg prefix --share wmx_r2_control)/config/cr3a_controllers.yaml' \
    use_gripper:=true

wmx_r2_control_differential.launch.py

Same shape, minus use_gripper. Here ros2_control does own the motion: the spawned diff_drive_controller/DiffDriveController writes wheel velocities into WmxSystemHardware, which calls StartVel.

wros ros2 launch wmx_r2_control wmx_r2_control_differential.launch.py \
    use_sim_time:=false \
    'config_file:=$(ros2 pkg prefix --share wmx_r2_package)/example/diffbot_differential_config.yaml' \
    'wmx_param_file:=$(ros2 pkg prefix --share wmx_r2_package)/example/diffbot_wmx_parameters.xml' \
    'urdf_file:=$(ros2 pkg prefix --share wmx_r2_control)/urdf/diffbot.wmx.urdf.xacro' \
    'controllers_file:=$(ros2 pkg prefix --share wmx_r2_control)/config/diffbot_controllers.yaml'

Controller configuration

cr3a_controllers.yaml loads only the state broadcaster, because the arm’s motion controllers are not ros2_control controllers:

controller_manager:
  ros__parameters:
    update_rate: 100
    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

diffbot_controllers.yaml adds the diff-drive controller:

controller_manager:
  ros__parameters:
    update_rate: 100
    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster
    differential_drive_controller:
      type: diff_drive_controller/DiffDriveController

differential_drive_controller:
  ros__parameters:
    left_wheel_names: ["drivewheel_left_joint"]
    right_wheel_names: ["drivewheel_right_joint"]
    wheel_separation: 0.55
    wheel_radius: 0.095
    publish_rate: 100.0
    odom_frame_id: odom
    base_frame_id: base_link
    enable_odom_tf: false
    use_stamped_vel: true
    cmd_vel_timeout: 0.25
    # all limiters off - see the note below
    linear.x.has_velocity_limits: false
    linear.x.has_acceleration_limits: false
    linear.x.has_jerk_limits: false
    angular.z.has_velocity_limits: false
    angular.z.has_acceleration_limits: false
    angular.z.has_jerk_limits: false

Important

The limiters are deliberately disabled. diff_drive_controller enables velocity, acceleration, and jerk limiting by default, and with max_deceleration and max_jerk unset the braking ramp is poor. With the limiters off, the controller is a pure passthrough and the StartVel profile plus the WMX-side axis limits do the shaping — which matches how wmx_r2_package’s own differential controller behaves.

enable_odom_tf is false for the same reason publish_tf is false on the direct controller: the localization EKF owns the odom → base_link transform.

use_sim_time is set by the launch file and auto-propagated to every loaded controller. Do not hard-code it in the YAML.

See also

• wmx_r2_package – the nodes the direct route uses

• ROS2 Topics – what each route publishes

• Nav2 Navigation (Mobile Base) – the differential stack end to end

• MoveIt2 Motion Planning – the manipulator stack end to end