ros2_control Waveshare servo hardware interface

The ros2_control implementation for Waveshare ST series servo motors.

Specifically designed for Waveshare ST3025 servo motors and their Bus Servo Adapter, but should work with all of their ST series motors and controllers.

Set Up

This hardware interface is developed for ros2 Humble.

Testing was done with the bus servo adapter plugged into a Jetson Orin Nano via USB.

The Jetson runs ros2 Humble and Isaac ros insidie a Docker container.

It should work with any system using ros2_control.

1. Ensure the container can control the USB port

   sudo chmod 666 /dev/ttyACM0

   sudo usermod -a -G dialout admin

2. Clone the package into your src directory:

   git clone https://github.com/htchr/waveshare_servos.git

3. Build your workspace.

4. Source your workspace.

Usage

Reference the example.launch.py, example_controllers.yaml, and example.ros2_control.xacro files to reference how to use this hardware interface in another robot system.

To verify your installation works, launch the example launch file:

ros2 launch waveshare_servos example.launch.py

Move a position-controlled servo with:

ros2 topic pub --once /joint_trajectory_position_controller/joint_trajectory \
  trajectory_msgs/msg/JointTrajectory \
  "{header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, joint_names: ['<joint_name>'], points: [{positions: [<position>], time_from_start: {sec: 1, nanosec: 0}}]}"

Move a velocity-controlled servo with:

ros2 topic pub --once /joint_trajectory_velocity_controller/joint_trajectory \
  trajectory_msgs/msg/JointTrajectory \
  "{header: {stamp: {sec: 0, nanosec: 0}, frame_id: ''}, joint_names: ['<joint_name>'], points: [{velocities: [<velocities>], time_from_start: {sec: 1, nanosec: 0}}]}"

Additional Tools

Also included are some helper functions wrapped in ros2 nodes for ease-of-use.

Change Motor ID

To control multiple motors, they will need different IDs.

To set a new ID, plug in 1 motor at a time (make sure to turn off power in between), and run:

ros2 run waveshare_servos set_id --ros-args -p start_id:=<old> -p new_id:=<new>

Set Midpoint

The following command will set the middle position (tick 2048, pi radians, 180 degrees) of a given motor:

ros2 run waveshare_servos calibrate_midpoint --ros-args -p id:=<id>

TODO

• software tests
• hardware tests with multiple motors

License

Most of the servo code is from the SCServo_Linux package available on their website. Waveshare does not include a license in the example files. When asked, they said to use the GPLv3 license.

Some of the servo code is from adityakamath on github.