mini_servo

ROS 2 packages for viewing and planning with a mini hobby-servo robot arm.

The stack targets the small 6-axis hobby arms often sold as a "Mini Industrial Robotic Arm" or "ABB 6 Axis Robot Mechanical Arm". Older kits use 3 large and 3 small hobby servos; newer metal kits often use 6 large servos.

It is intended for ROS 2 Rolling (Ubuntu 24.04) and ROS 2 Lyrical (Ubuntu 26.04). On macOS, use Pixi + RoboStack Lyrical (see below).

Packages

• mini_servo_model — URDF/xacro, meshes, and RViz visualization
• mini_servo_moveit — MoveIt 2 planning config and demo launch
• mini_servo_gazebo — Gazebo sim with a feedforward position controller and ros_gz bridge
• mini_servo_hardware — real-robot serial hardware plugin plus the same feedforward controller
• mini_servo_firmware — Arduino sketch for an Adafruit PCA9685 PWM servo driver

Meshes were hand-built in Onshape and are included for gross visualization.

Build

Clone this repository into a colcon workspace src directory (or run colcon from the repo root):

cd ~/mini_servo_ws
rosdep install --from-paths src -y --ignore-src
colcon build --symlink-install
source install/setup.bash

macOS with Pixi + RoboStack

Pixi is already enough; no system ROS install is required. From this repo:

pixi install
pixi run build
pixi run visualize

That uses RoboStack Lyrical for osx-arm64. Other tasks: pixi run demo, pixi run gazebo, pixi run hardware. Gazebo on macOS is the least proven path; RViz visualization and MoveIt mock demo are the ones to try first.

Launch

Visualize the arm with a joint-state GUI:

ros2 launch mini_servo_model visualize_robot.launch.py

Plan in MoveIt 2 with mock ros2_control hardware:

ros2 launch mini_servo_moveit demo.launch.py

Run the arm in Gazebo with a feedforward position controller:

ros2 launch mini_servo_gazebo sim.launch.py

Command joint positions (radians) after the sim is up:

ros2 topic pub --once /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0]"

Drive the physical arm over serial (same feedforward command topic as Gazebo):

ros2 launch mini_servo_hardware hardware.launch.py serial_port:=/dev/ttyUSB0

The hardware plugin talks to mini_servo_firmware/mini_servo.ino at 500000 baud using comma-separated degrees. The Arduino firmware currently echoes commanded angles rather than encoder feedback.

Known issues

• Kinematics are approximate
• Joint limits may need calibration and might be flipped in direction