wmx_ros2_message#

Overview#

The wmx_ros2_message package defines custom ROS2 message and service interfaces used by all nodes in the WMX ROS2 application. It contains no executable nodes – only interface definitions that are compiled into C++ and Python bindings by rosidl.

Package Structure#

wmx_ros2_message/
├── CMakeLists.txt
├── package.xml
├── msg/
│   ├── AxisPose.msg
│   ├── AxisState.msg
│   └── AxisVelocity.msg
└── srv/
    ├── SetAxis.srv
    ├── SetAxisGearRatio.srv
    └── SetEngine.srv

Dependencies#

Dependency

Type

Purpose

ament_cmake

buildtool

CMake build system

rclcpp

build + exec

ROS2 C++ client library

rosidl_default_generators

build

Message/service code generation

rosidl_default_runtime

exec

Runtime message type support

ament_lint_auto

test

Automated linting

ament_lint_common

test

Common lint rules

The package is a member of the rosidl_interface_packages group, which allows other packages to discover its generated interfaces at build time.

Message Definitions#

AxisPose#

Used for absolute and relative position motion commands. Published to /wmx/axis/position and /wmx/axis/position/relative.

int32[]   index       # Axis indices to command
float64[] target      # Target positions (radians)
string    profile     # Motion profile type (reserved for future use)
float64[] velocity    # Motion velocity per axis (rad/s)
float64[] acc         # Acceleration per axis (rad/s²)
float64[] dec         # Deceleration per axis (rad/s²)

All array fields are parallel – element i in each array corresponds to the same axis. The profile field is currently unused by the subscriber nodes.

Used by:

  • wmx_core_motion_node – subscribes on /wmx/axis/position and /wmx/axis/position/relative

  • wmx_core_motion_node – publishes position and relative position commands

AxisVelocity#

Used for continuous velocity motion commands. Published to /wmx/axis/velocity.

int32[]   index       # Axis indices to command
string    profile     # Motion profile type (reserved for future use)
float64[] velocity    # Target velocity per axis (rad/s)
float64[] acc         # Acceleration per axis (rad/s²)
float64[] dec         # Deceleration per axis (rad/s²)

Used by:

  • wmx_core_motion_node – subscribes on /wmx/axis/velocity

  • wmx_core_motion_node – publishes velocity commands

AxisState#

Comprehensive per-axis status feedback published at 100 Hz by the wmx_core_motion_node on /wmx/axis/state.

# Status flags (per axis)
int32[]   amp_alarm        # Amplifier alarm active (1 = fault)
int32[]   servo_on         # Servo enabled (1 = on)
int32[]   home_done        # Homing completed (1 = done)
int32[]   in_pos           # At target position (1 = in position)
int32[]   negative_ls      # Negative limit switch (1 = triggered)
int32[]   positive_ls      # Positive limit switch (1 = triggered)
int32[]   home_switch      # Home switch (1 = triggered)

# Command and feedback values (per axis)
float64[] pos_cmd          # Commanded position (radians)
float64[] velocity_cmd     # Commanded velocity (rad/s)
float64[] actual_pos       # Actual encoder position (radians)
float64[] actual_velocity  # Actual velocity (rad/s)
float64[] actual_torque    # Actual torque (Nm)

The status flags use int32 (not bool) to match the WMX CoreMotionStatus structure directly.

Used by:

  • wmx_core_motion_node – publishes on /wmx/axis/state at 100 Hz

Service Definitions#

SetEngine#

Controls the WMX engine lifecycle (device creation and communication).

# Request
bool   data      # true = create/start, false = close/stop
string path      # WMX3 device path (e.g., "/opt/lmx/")
string name      # Device name identifier
---
# Response
bool   success   # true if operation succeeded
string message   # Human-readable result description

Used by service:

  • /wmx/engine/set_device (on wmx_core_motion_node)

SetAxis#

Generic per-axis control operations. The meaning of the data field depends on which service uses this type.

# Request
int32[] index    # Axis indices (e.g., [0, 1, 2, 3, 4, 5])
int32[] data     # Per-axis values (meaning varies by service)
---
# Response
bool   success   # true only if ALL axes succeeded
string message   # Concatenated per-axis result messages

Used by services:

  • /wmx/axis/set_on – data: 1 = enable, 0 = disable

  • /wmx/axis/clear_alarm – data: not used (pass zeros)

  • /wmx/axis/set_mode – data: 0 = position, 1 = velocity

  • /wmx/axis/set_polarity – data: 1 = normal, -1 = reversed

  • /wmx/axis/homing – data: not used (pass zeros)

SetAxisGearRatio#

Configures the encoder gear ratio for each axis, mapping encoder counts to physical units (radians).

# Request
int32[]   index         # Axis indices
float64[] numerator     # Gear ratio numerators
float64[] denumerator   # Gear ratio denominators
---
# Response
bool   success          # true only if ALL axes succeeded
string message          # Concatenated per-axis result messages

The effective gear ratio per axis is numerator / denumerator.

Used by service:

  • /wmx/axis/set_gear_ratio (on wmx_core_motion_node)

Building the Package#

This package must be built before wmx_ros2_package because the main package depends on the generated message headers:

cd ~/wmx_ros2_ws
colcon build --packages-select wmx_ros2_message
source install/setup.bash

Verify the interfaces are registered:

ros2 interface list | grep wmx

Expected:

wmx_ros2_message/msg/AxisPose
wmx_ros2_message/msg/AxisState
wmx_ros2_message/msg/AxisVelocity
wmx_ros2_message/srv/SetAxis
wmx_ros2_message/srv/SetAxisGearRatio
wmx_ros2_message/srv/SetEngine

Inspect a specific interface:

ros2 interface show wmx_ros2_message/msg/AxisState