ROS2 for Waveshare Alphabot2-Pi

This repo contains ROS2 packages for the Waveshare Alphabot2-Pi mobile robot:

• alphabot2: it contains the nodes used to manage Alphabot2 sensors and actuators.
• alphabot2_interfaces: it contains all the custom interfaces (ROS messages) designed for AlphaBot2.

The current implementation includes nodes to manage the motors, the IR obstacle sensors and the camera. There is also a node for QR-code detection.

Please, see here for the ROS2 nodes topology and TODO.

The code has been originally developed for the final project of the Robotics course, University of Brescia.

Requirements

• Robot: Waveshare Alphabot2-Pi mobile robot (see here), equipped a Raspberry Pi4 (8 GB).

• OS: Ubuntu Server 20.04 (Focal Fossa) x64.

Ubuntu and ROS2 setup

Install Ubuntu Server 20.04 x64 on the RPi4 (see here).

Connect the RPi4 to WiFi and add auto-connection at boot (see here).

Install ROS2 Foxy Fitzroy Base (reference) and the dependencies:

sudo apt update && sudo apt install curl gnupg2 lsb-release
sudo curl -sSL https://raw.githubusercontent.com/ros/rosdistro/master/ros.key  -o /usr/share/keyrings/ros-archive-keyring.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/ros-archive-keyring.gpg] http://packages.ros.org/ros2/ubuntu $(source /etc/os-release && echo $UBUNTU_CODENAME) main" | sudo tee /etc/apt/sources.list.d/ros2.list > /dev/null
sudo apt update && sudo apt install ros-foxy-ros-base

Install python dependencies:

sudo apt install python3-pip python3-colcon-common-extensions python3-rosdep2
pip3 install RPi.GPIO argcomplete

Initialize rosdep and source the ROS2 core environment:

rosdep update
source /opt/ros/foxy/setup.bash

Fix GPiO permission problem (reference):

sudo apt install rpi.gpio-common
sudo usermod -aG dialout ubuntu

Suggestions

Source the ROS2 core environment (underlay) and the ROS2 local workspaces (overlays) in the file .bashrc so that they are automatically sourced in every bash shell:

source /opt/ros/foxy/setup.bash
source /path_to_your_ros_ws/install/local_setup.bash

Plug an additional external network adapter and setup it as a WiFi Access Point to easily SSH into the RPi4. Please follow this guide and also these additional tricks:

• put optional: true for wlan0 in 50-cloud-init.yaml to prevent endless booting time.
• don't put After=network-online.target and Wants=network-online.target
• sudo systemctl enable dnsmasq

Camera node (v4l2_camera)

For the Raspberry Camera management we use the ROS2 implementation v4l2_camera (reference).

Install required tools:

sudo apt install v4l-utils
echo bcm2835-v4l2 | sudo tee -a /etc/modules

Add start_x=1 in /boot/config.txt

Clone the camera node and dependencies needed to compress images into the src folder of your ros workspace:

git clone -b foxy https://gitlab.com/boldhearts/ros2_v4l2_camera.git
git clone -b ros2 https://github.com/ros-perception/vision_opencv.git
git clone -b ros2 https://github.com/ros-perception/image_common.git                  
git clone -b ros2 https://github.com/ros-perception/image_transport_plugins.git 

To fix building errors, modify camera_info_manager.cpp:46 (in image_common/camera_info_manager/) to:

#include "rcpputils/get_env.hpp"

Source build:

cd your_ros_ws
rosdep install --from-paths src -r -y
colcon build

Build and usage

After you have all the requirements satisfied, clone this repo in your_ros_ws/src and build it:

git clone https://github.com/Mik3Rizzo/alphabot2-ros2
cd your_ros_ws
colcon build

I recommend to run all the nodes at once using the launch file:

ros2 launch alphabot2 alphabot2_launch.py

To move the robot, publish a Twist ROS2 message on the alphabot2/cmd_vel topic. For example:

ros2 topic pub --rate 1 alphabot2/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 1.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 5.0}}"

This command publishes every second a linear velocity of 1 m/s and an angular rate of 5 rad/s.

Please note that the maximum theoretical linear velocity is 1.65 m/s while the angular rate is 38.8 rad/s. These quantities are estimated with the robot suspended from the floor and supplied with two Sony US14500VR Li-ion 3.7V batteries at full charge. In these conditions the maximum wheel RPM is 750.

About

Michele Rizzo, Master's Degree Computer Engineering student at University of Brescia.

• Mail: [email protected].
• Github: Mik3Rizzo

Please, feel free to contact me for informations or problems.