AR4 ROS Driver

ROS 2 driver of the AR4 robot arm from Annin Robotics. Tested with ROS 2 Iron on Ubuntu 22.04.

Supports:

• AR4 (Original version)
• AR4 MK2
• AR4 servo gripper

Features:

• Moveit control (GUI and Python interface example)
• Gazebo simulation
• Hand-Eye calibration

This is a refresh of ar3_core.

Video Demo:

Motion Planning using RViz and Moveit:

Startup, Calibration, and Servo Gripper Demo

Hand-Eye Calibration Demo

Overview

• ar_description
  • Hardware description of arm & servo gripper urdf.
• ar_hardware_interface
  • ROS interfaces for the arm and servo gripper drivers, built on the ros2_control framework.
  • Manages joint offsets, limits and conversion between joint and actuator messages.
  • Handles communication with the microcontrollers.
• ar_microcontrollers
  • Firmware for the microcontrollers, ie. Teensy and Arduino Nano.
• ar_moveit_config
  • MoveIt module for motion planning.
  • Controlling the arm and servo gripper through Rviz.
• ar_gazebo
  • Simulation on Gazebo.

Installation

• Install ROS 2 Iron for Ubuntu 22.04
• Clone this repository:

  git clone https://github.com/ycheng517/ar4_ros_driver

• Import required external repos:

  vcs import . --input ar_hand_eye/hand_eye_calibration.repos

• Install workspace dependencies:

  rosdep install --from-paths . --ignore-src -r -y

• Build the workspace:

  colcon build

• Source the workspace:

  source install/setup.bash

• Enable serial port access if you haven't already done so:

  sudo addgroup $USER dialout

  You will need to log out and back in for changes to take effect.

Firmware Flashing

The Teensy and Arduino Nano sketches provided in ar_microcontrollers are compatible with the default hardware. To flash it, follow the same procedure as specified in AR4 Robot Setup.

[Optional] Running in Docker Container

A docker container and run script has been provided that can be used to run the robot and any GUI programs. It requires an NVIDIA GPU, and the NVIDIA Container Toolkit to be installed. Then you can start the docker container with:

docker build -t ar4_ros_driver .
./run_in_docker.sh

Usage

There are two modules that you will always need to run:

1. Arm module - this can be for either a real-world or simulated arm

   • For controlling the real-world arm, you will need to run the ar_hardware_interface module
   • For the simulated arm, you will need to run the ar_gazebo module
   • Either of the modules will load the necessary hardware descriptions for MoveIt

2. MoveIt module - the ar_moveit_config module provides the MoveIt interface and RViz GUI.

The various use cases of the modules and instructions to run them are described below:

---

MoveIt Demo in RViz

If you are unfamiliar with MoveIt, it is recommended to start with this to explore planning with MoveIt in RViz. This contains neither a real-world nor a simulated arm but just a model loaded within RViz for visualisation.

The robot description, moveit interface and RViz will all be loaded in the single demo launch file

ros2 launch ar_moveit_config demo.launch.py

---

Control real-world arm with MoveIt in RViz

Start the ar_hardware_interface module, which will load configs and the robot description:

ros2 launch ar_hardware_interface ar_hardware.launch.py \
  calibrate:=True

Available Launch Arguments:

• calibrate: Whether to calibrate the robot arm (determine the absolute position of each joint).
• include_gripper: Whether to include the servo gripper. Defaults to: include_gripper:=True.
• serial_port: Serial port of the Teensy board. Defaults to: serial_port:=/dev/ttyACM0.
• arduino_serial_port: Serial port of the Arduino Nano board. Defaults to arduino_serial_port:=/dev/ttyUSB0.

⚠️📏 Note: Calibration is required after flashing firmware to the Teensy board, and power cycling the robot and/or the Teensy board. It can be skipped in subsequent runs with calibrate:=False.

Start MoveIt and RViz:

ros2 launch ar_moveit_config ar_moveit.launch.py

Available Launch Arguments:

• include_gripper: Whether to include the servo gripper. Defaults to: include_gripper:=True.
• use_sim_time: Make Moveit use simulation time. Should only be enabled when running with Gazebo. Defaults to: use_sim_time:=False.

You can now plan in RViz and control the real-world arm. Joint commands and joint states will be updated through the hardware interface.

---

Control simulated arm in Gazebo with MoveIt in RViz

Start the ar_gazebo module, which will start the Gazebo simulator and load the robot description:

ros2 launch ar_gazebo ar_gazebo.launch.py

Start Moveit and RViz:

ros2 launch ar_moveit_config ar_moveit.launch.py use_sim_time:=true include_gripper:=True

You can now plan in RViz and control the simulated arm.

---

Hand-Eye Calibration

See ar_hand_eye package's README