Moving Joints

There are two ways to move joints in the simulation: the Joint GUI (graphical, interactive) and the move_joints CLI node (scriptable, one-shot commands).

Both publish JointTrajectory messages to the joint_trajectory_controller.

Joint GUI (interactive)

The Joint GUI launches automatically with the simulation. It provides sliders for each joint discovered from the robot’s URDF.

Controls

Button	Action
Send	Publishes the current slider positions as a trajectory command
Sync	Reads current joint positions from /joint_states and moves sliders to match
Reset	Zeros all sliders

You can also:

• Change the Duration (seconds) for how long the trajectory takes
• Select which Topic to publish on (auto-discovered from available JointTrajectory topics)
• Click Refresh to re-scan for topics

How it works

1. On launch, the GUI parses the URDF file for all revolute joints, reading their lower and upper limits
2. It subscribes to /joint_states to discover which joints are actually active and their starting positions
3. When you hit Send, it publishes a JointTrajectory message to the selected topic with positions offset by each joint’s origin angle

Tip

If the GUI shows “Discovering joints from /joint_states…” for a long time, the joint controllers may not have started yet. Wait for Gazebo to fully load.

move_joints node (CLI)

The move_joints node sends a single trajectory command and exits. It’s useful for scripting or quick tests.

Usage

Inside devcontainer

ros2 run sim_common move_joints --ros-args \
    -p joints:="['shoulder_1', 'elbow_1', 'wrist_1', 'wrist_2']" \
    -p positions:="[0.5, 0.5, 0.2, 0.0]" \
    -p duration:=2.0

Parameters

Parameter	Required	Default	Description
joints	Yes	—	List of joint names to move
positions	Yes	—	Target positions (radians), one per joint
duration	No	2.0	Seconds to reach the target
topic	No	See below	Trajectory topic to publish on

Default topic: /joint_trajectory_controller/joint_trajectory

Behavior

The node:

1. Creates a publisher on the trajectory topic
2. Waits (polling every 0.5s) until at least one subscriber is connected
3. Publishes the trajectory message
4. Logs the command and exits

This means the joint trajectory controller must be running before move_joints can send its command. If you run it right after launching the simulation, it will wait automatically until the controller is ready.

Example: move two joints

Inside devcontainer

ros2 run sim_common move_joints --ros-args \
    -p joints:="['shoulder_1', 'elbow_1']" \
    -p positions:="[1.0, -0.5]" \
    -p duration:=3.0

Example: move a single joint slowly

Inside devcontainer

ros2 run sim_common move_joints --ros-args \
    -p joints:="['wrist_1']" \
    -p positions:="[0.8]" \
    -p duration:=5.0