ROS2 Actions#

The WMX ROS2 application exposes one action server for trajectory execution, compatible with MoveIt2 and any FollowJointTrajectory action client. No custom .action files are defined – the system uses the standard control_msgs action type.

Action Summary#

Action Name

Type

Server Node

Status

/movensys_manipulator_arm_controller/follow_joint_trajectory

control_msgs/action/FollowJointTrajectory

follow_joint_trajectory_server

Active

FollowJointTrajectory#

Action Name

/movensys_manipulator_arm_controller/follow_joint_trajectory

Action Type

control_msgs/action/FollowJointTrajectory

Server Node

follow_joint_trajectory_server

Configurable

Name set via joint_trajectory_action parameter

Source File

follow_joint_trajectory_server.cpp

This action server receives a joint-space trajectory (a sequence of waypoints with timestamps) and executes it on the physical robot using the WMX AdvancedMotion::StartCSplinePos() cubic spline interpolation engine.

Goal#

The goal uses the standard trajectory_msgs/msg/JointTrajectory message:

Field

Type

Description

trajectory.joint_names

string[]

Joint names (joint1 through joint6)

trajectory.points[]

JointTrajectoryPoint[]

Ordered list of waypoints (maximum 1000 points)

trajectory.points[].positions

float64[]

Target joint positions in radians for each waypoint

trajectory.points[].time_from_start

duration

Timestamp relative to trajectory start

Note

Only the positions and time_from_start fields of each trajectory point are used. The velocities, accelerations, and effort fields are logged for diagnostics but not passed to the WMX engine – the cubic spline interpolation is computed internally by WMX.

Result#

Field

Type

Description

error_code

int32

0 on success; WMX error code on failure

error_string

string

Not set by the server (default empty)

Feedback#

No intermediate feedback is published during execution. The action server blocks on CoreMotion::Wait() until the spline motion completes or an error occurs.

Execution Details#

The server processes the trajectory as follows:

  1. Goal acceptance – All incoming goals are accepted unconditionally (ACCEPT_AND_EXECUTE). No goal validation beyond point count is performed.

  2. Thread dispatch – The execute() callback runs in a detached thread spawned from handle_accepted(), allowing the action server to remain responsive.

  3. Validation – Rejects goals with more than 1000 waypoints (aborts immediately with a warning). If the adjusted point count is 0, the server succeeds immediately without commanding motion.

  4. Timing adjustment – The first point’s time_from_start is forced to zero. If the last point has a time interval less than 1 ms from the previous point, it is dropped to prevent interpolation errors.

  5. Spline construction – For each trajectory point, positions are packed into a CSplinePosData structure and timestamps are converted to milliseconds. The dimensionCount and axis[] array are set to the joint_number parameter (typically 6).

  6. Execution – AdvancedMotion::StartCSplinePos(0, ...) begins the interpolated motion on buffer index 0 across all joints simultaneously.

  7. Wait – The server blocks on CoreMotion::Wait() for all axes in the selection.

  8. Result – On success, error_code = 0 and the goal succeeds. On failure, the WMX error code is returned and the goal is aborted.

Note

Cancel requests are accepted by the handle_cancel() callback, but the blocking Wait() call does not currently check goal_handle->is_canceling(). A TODO in the source code notes this limitation.

Example Usage#

Send a simple two-point trajectory via the command line:

ros2 action send_goal \
  /movensys_manipulator_arm_controller/follow_joint_trajectory \
  control_msgs/action/FollowJointTrajectory \
  "{trajectory: {
    joint_names: ['joint1', 'joint2', 'joint3', 'joint4', 'joint5', 'joint6'],
    points: [
      {positions: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
       time_from_start: {sec: 0, nanosec: 0}},
      {positions: [0.5, -0.3, 0.2, 0.0, 0.1, 0.0],
       time_from_start: {sec: 3, nanosec: 0}}
    ]
  }}"

Check that the action server is available:

ros2 action list

Expected:

/movensys_manipulator_arm_controller/follow_joint_trajectory

Inspect the action interface:

ros2 action info /movensys_manipulator_arm_controller/follow_joint_trajectory

Warning

This action moves real motors. Ensure the robot workspace is clear and all safety precautions are in place before sending trajectory goals.

MoveIt2 Integration#

MoveIt2 connects to this action server as a trajectory execution controller. The typical workflow is:

  1. MoveIt2 reads the current robot state from /joint_states

  2. The planner computes a collision-free trajectory

  3. MoveIt2 sends the trajectory as a FollowJointTrajectory goal

  4. The follow_joint_trajectory_server executes it via WMX cubic spline

  5. The manipulator_state node publishes real-time encoder feedback back to /joint_states at 500 Hz

The action server name must match the controller configuration in MoveIt2. The default name /movensys_manipulator_arm_controller/follow_joint_trajectory is set via the joint_trajectory_action parameter in the config YAML.

See Also#