ROS Programming: Building Powerful Robots

Last year, the ROS web page was updated with a new design and a new organization of contents. The following is a screenshot of the web page:

In the menu, you can find information about ROS and whether ROS is a good choice for your system. You can also find blogs, news, and other features.

Instructions for ROS installation can be found under the Install tab in the Getting Started section.

ROS recommends that you install the system using the repository instead of the source code, unless you are an advanced user and you want to make a customized installation; in that case, you may prefer installing ROS using the source code.

To install ROS using the repositories, we will start by configuring the Ubuntu repository in our system.

In this section, you will learn the steps for installing ROS Kinetic in your computer. This process has been based on the official installation page, which can be found at http://wiki.ros.org/kinetic/Installation/Ubuntu.

We assume that you know what an Ubuntu repository is and how to manage it. If you have any doubts about it, refer to https://help.ubuntu.com/community/Repositories/Ubuntu.

Before we start the installation, we need to configure our repositories. To do that, the repositories need to allow restricted, universe, and multiverse. To check if your Ubuntu accepts these repositories, click on Ubuntu Software Center in the menu on the left-hand side of your desktop, as shown in the following screenshot:

Click on Edit | Software Sources and you will see the following window. Make sure that all the listed options are checked as shown in the following screenshot (choose the appropriate country for the server from which you download the sources):

Normally these options are marked, so you should not have any problem with this step.

In this step, you have to select your Ubuntu version. It is possible to install ROS Kinetic in various versions of the operating system. You can use any of them, but we recommend version 15.10 to follow the chapters of this section. Keep in mind that Kinetic works in the Wily Werewolf (15.10) and Xenial Xerus (16.04) versions of Ubuntu. Type the following command to add the repositories:

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -cs) main" > /etc/apt/sources.list.d/ros-latest.list'

Once you've added the correct repository, your operating system will know where to download programs to install them into your system.

This step is to confirm that the origin of the code is correct and that no one has modified the code or programs without the knowledge of the owner. Normally, when you add a new repository, you have to add the keys of that repository, so it's added to your system's trusted list.

$ wget http://packages.ros.org/ros.key -O - | sudo apt-key add -

Now we can be sure that the code came from an authorized site and has not been modified.

We are ready to start the installation now, but before we do that, we'd better make an update to avoid problems with the libraries and versions of software that are not ideal for ROS. This is done with the following command:

$ sudo apt-get update

ROS is huge; sometimes you will install libraries and programs that you will never use. Normally it has four different installations, but this depends on the final use. For 

example, if you are an advanced user, you might only need the basic installation for a robot without much space on the hard disk. For this section, we recommend you use the full installation because it will install everything necessary to practice the examples and tutorials.

It doesn't matter if you don't know what are you installing right now — rviz, simulators, navigation, and so on. You will learn everything in the upcoming chapters:

$ sudo apt-get install ros-kinetic-desktop-full

$ sudo apt-get install ros-kinetic-desktop

$ sudo apt-get install ros-kinetic-ros-base

$ sudo apt-get install ros-kinetic-PACKAGE

Before using ROS we need to initialize rosdep. The rosdep command-line tool helps with the installation of system dependencies for the source code that we are going to compile or install. For this reason, it is required by some of the core components in ROS, so it is installed by default with it. To initialize rosdep, you have to run the following commands:

$ sudo rosdep init
$ rosdep update

Congratulations! If you are at this step, you have an installed version of ROS on your system! To start using it, the system needs to know the location of the executable or binary files, as well as the other commands. To do this, normally you need to execute the next script; if you also install another ROS distro, you can work with both just by calling the script of the one you need each time, since this script simply sets your environment. Here, we use the one for ROS Kinetic, but just replace kinetic with indigo or jade, for example, if you want to try other distros:

$ source /opt/ros/kinetic/setup.bash

If you type roscore in the shell, you will see something starting up. This is the best test for finding out if you have ROS, and if it is installed correctly.

Note that if you open another terminal you also have to source the setup.bash file to set the environment variables to detect the ROS packages installed on your system. Otherwise, roscore or other ROS commands will not work. This is because the script must be sourced again to configure the environment variables, which include the path where ROS is installed, as well as other packages and additional paths for compiling new code properly.

It is very easy to solve this; you just need to add the script at the end of your .bashrc script file so that when you start a new shell, the script will execute and you will have the environment configured.

The .bashrc file is within the user home (/home/USERNAME/.bashrc). It has the configuration of the shell or terminal, and each time the user opens the terminal, this file is loaded. That way, you can add commands or configuration to make the user's life easy. For this reason, we will add the script at the end of the .bashrc file to avoid keying it in each time we open a terminal. We do this with the following command:

$ echo "source /opt/ros/kinetic/setup.bash" >> ~/.bashrc

To see the results, you have to execute the file using the following command, or close the current terminal and open another:

$ source ~/.bashrc

Some users need more than a single ROS distribution installed in their system, so you'll have several distros living in the same system and may need to switch between them. Your ~/.bashrc file must only source the setup.bash file of the version you are currently using, since the last call will override the environment set by the others.

For example, you might have the following lines in your .bashrc file:

…
source /opt/ros/indigo/setup.bash
source /opt/ros/jade/setup.bash
source /opt/ros/kinetic/setup.bash
…

The ROS Kinetic version will be executed in this case. Make sure that the version you are running is the last one in the file. It's also recommended to source a single setup.bash.

If you want to check the version used in a terminal, you can do so easily running the echo $ROS_DISTRO command.

Now the next step is to install a command tool that will help us install other packages with a single command. This tool is based in Python, but don't worry, you don't need to know Python to use it. You will learn how to use this tool in the  upcoming chapters:

To install this tool on Ubuntu, run the following command:

$ sudo apt-get install python-rosinstall

And that's it! You have a complete ROS system installed in your system. When I finish a new installation of ROS, I personally like to test two things: that roscore and turtlesim both work.

If you want to do the same, type the following commands in different shells:

$ roscore
$ rosrun turtlesim turtlesim_node

If everything is okay, you will see the following screenshot:

The first step is to download the VirtualBox installation file. The latest version at the time of writing this section is 4.3.12; you can download the Linux version of it from http://download.virtualbox.org/virtualbox/4.3.12/. If you're using Windows, you can download it from http://download.virtualbox.org/virtualbox/4.3.12/VirtualBox-4.3.12-93733-Win.exe.

Once installed, you need to download the image of Ubuntu; for this tutorial we will use a copy of Ubuntu 15.10 from OSBOXES found at http://www.osboxes.org/ubuntu/; then we will simply install ROS Kinetic following the same instructions described in the previous section. In particular, the Ubuntu 15.10 image can be downloaded from http://sourceforge.net/projects/osboxes/files/vms/vbox/Ubuntu/15.10/Ubuntu_15.10-64bit.7z/download.

This would download a .7z file. In Linux, it can be uncompressed with the following:

$ 7z x Ubuntu_15.10-64bit.7z

If the .7z command is not installed, it can be installed with the following:

$ sudo apt-get install p7zip-full

The virtual machine file will go into the 64-bit folder with the name: Ubuntu 15.10 Wily (64bit).vdi

Creating a new virtual machine with the downloaded file is very easy; just proceed with the following steps. Open VirtualBox and click on New. We are going to create a new virtual machine that will use the Ubuntu 15.10 Wily (64bit).vdi file downloaded before, which is a hard disk image with Ubuntu 15.10 already installed.

Set the name, type, and version of the virtual machine as shown in the following screenshot:

You can configure the parameters of the new virtual machine in the windows that follow. Keep the default configuration and change only the name for the virtual system. This name is how you distinguish this virtual machine from others. For the RAM, we advise that you use as much as possible, but 8 GB should be enough.

For the hard drive, use the existing virtual hard drive file Ubuntu 15.10 Wily (64bit).vdi downloaded before, as shown in the following screenshot:

After this, you can start your virtual machine by clicking on the Start button. Remember to select the right machine before you start it. In our case, we only have one, but you could have more:

Once the virtual machine starts, you should see another window, as seen in the following screenshot. It is the Ubuntu 15.10 OS with ROS installed (use osboxes.org as the password to log in):

When you finish these steps, install ROS Kinetic as you would on a regular computer following the steps of the previous sections, and you will have a full copy of ROS Kinetic that can be used with this section.

In order to install it in Ubuntu, you only have to run the following:

$ sudo apt-get install docker.io

Docker images are like virtual machines or systems already set up. There are servers that provide images like this, so the users only have to download them. The main server is Docker hub, found at https://hub.docker.com. There, it is possible to search for Docker images for different systems and configurations. In our case, we are going to use ROS Kinetic images already available. All ROS Docker images are listed in the official ROS repo images on the web at https://hub.docker.com/_/ros/. The ROS container image is pulled down with the following command:

$ docker pull ros

There's a possibility that you may see this error:

You should either update your system or try adding your user to the docker group to resolve this:

$ sudo usermod -a -G docker $(whoami)

You should see multiple Docker images getting downloaded simultaneously. Each image has a different hash name. This will take some time, especially on slow networks. You will see something like the following once it is done:

The ROS Kinetic distribution can be pulled down using the corresponding tag, using the following command:

$ docker pull ros:kinetic-robot

Although you do not need to know it, the images and containers are stored by Docker in /var/lib/docker by default.

Once the container is downloaded, we can run it interactively with the following command:

$ docker run -it ros

This will be like entering a session inside the Docker container. This command will create a new container from the main image. Inside it we have a full Ubuntu system with ROS Kinetic already installed. We can install additional packages and run ROS nodes, as in a regular system. With docker ps -a, you can check all the containers available and the image they come from.

We have to set up the ROS environment inside the container in order to start using ROS. That is, we have to run the following command:

$ source /opt/ros/kinetic/setup.bash

Docker containers can be stopped from other terminals using docker stop, and they can also be removed with docker rm. Docker also allows you to configure the container to expose the network, as well as mounting a host folder as volumes into it. In addition to this, it also supports a Python API, and has many other features. All this can be found in the official documentation at https://docs.docker.com. However, in principle, docker run should be enough, and we can even SSH into a running Docker container, as a regular machine, using its name. We can also open another terminal for a running container with the following command (where NAME is the name of the Docker container, that you can fine using docker ps -a):

$ docker exec -it NAME bash

You can also create your own Docker images using docker build and specify what should be installed in them in Dockerfile. You can even publish them online with docker push, contributing them to the community or simply sharing your working setup. This section comes with a working Docker image and Dockerfile to build it, and you can find this by running docker build from the same folder where Dockerfile is. This Docker image is basically an extension of the ROS Kinetic one with the code of the section. The instructions to download and install it would be on the GitHub repository with the rest of the code. 

Before installing ROS on BeagleBone Black, we have to achieve some prerequisites. As this section is focused on ROS, we will list them without going into detail. There is a lot of information about BeagleBone Black and Ubuntu ARM available on websites, forums, and books that you can check out.

First, we have to install an Ubuntu ARM distribution compatible with ROS, so an image of Ubuntu ARM is needed. You can obtain an Ubuntu 16.04 Xenial armhf using wget with the following command:

$ wget https://rcn-ee.com/rootfs/2016-10-06/elinux/ubuntu-16.04.1-console-armhf-2016-10-06.tar.xz

From the URL https://rcn-ee.com/rootfs you can look for newer versions too. This version is the one mentioned in the official documentation at http://elinux.org/BeagleBoardUbuntu.

Once the image is downloaded, the next step is installing it on a microSD card. First, unpack the image with the following commands:

$ tar xf ubuntu-16.04.1-console-armhf-2016-10-06.tar.xz
$ cd ubuntu-16.04.1-console-armhf-2016-10-06

Insert a microSD of 2 GB or more on the card reader of your computer and install the Ubuntu image on it with the following setup script:

$ sudo ./setup_sdcard.sh --mmc DEVICE --dtb BOARD

In the preceding script, DEVICE is the device where the microSD appears on the system, for example /dev/sdb, and BOARD is the board name. For the BeagleBone Black it would be beaglebone. So, assuming the microSD is in /dev/mmcblk0, and you are using a BeagleBone Black, the command would be as follows:

$ sudo ./setup_sdcard.sh --mmc /dev/mmcblk0 --dtb beaglebone

If you do not know the device assigned to the microSD, you can use the following command:

$ sudo ./setup_sdcard.sh --probe-mmc

Once we have Ubuntu ARM on our platform, the BeagleBone Black network interfaces must be configured to provide access to the network, so you will have to configure the network settings, such as the IP, DNS, and gateway.

Remember that the easiest way could be mounting the SD card in another computer and editing /etc/network/interfaces.

Another easy way consists on using an Ethernet cable and running the DHCP client to obtain an IP address.

$ sudo dhclient eth0

For this, you need to boot up the BeagleBone Black with the microSD. For that, you need to keep the S2 button press before you power on the board, either with the DC or USB connector. After some minutes the system will show the login prompt. Log in with the user ubuntu and password temppwd (default ones) and then run the DHCP client command shown above with the Ethernet cable connected. Then, you can check the IP address assigned using (look at the inet addr: value):

$ ifconfig eth0

In our setup, we have connected to the BeagleBone Black the following devices (as shown in the image below):

After setting up the network, we should install the packages, programs, and libraries that ROS will need. Now that the network is up, we can also SSH into the board with (assuming the IP address assigned to it is 192.168.1.6):

$ ssh ubuntu@192.168.1.6

We are going to follow the instructions in http://wiki.ros.org/indigo/Installation/UbuntuARM, but with the changes required so they work for ROS kinetic (note they are still for indigo on the web). The first step consists on setting up the repository sources so we can install ROS.

$ sudo vi /etc/apt/sources.list

And add restricted to the sources, so you have something like this:

deb http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted universe multiverse
#deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial main restricted universe multiverse
deb http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main restricted universe multiverse
#deb-src http://ports.ubuntu.com/ubuntu-ports/ xenial-updates main restricted universe
multiverse
#Kernel source (repos.rcn-ee.com) : https://github.com/RobertCNelson/linux-stable-rcn-ee
#
#git clone https://github.com/RobertCNelson/linux-stable-rcn-ee
#cd ./linux-stable-rcn-ee
#git checkout `uname -r` -b tmp
#
deb [arch=armhf] http://repos.rcn-ee.com/ubuntu/ xenial main
#deb-src [arch=armhf] http://repos.rcn-ee.com/ubuntu/ xenial main

Then, update the sources running:

$ sudo apt-get update

The operating system for BeagleBone Black is set up for micro SD cards with 1-4 GB. This memory space is very limited if we want to use a large part of the ROS Kinetic packages. In order to solve this problem, we can use SD cards with more space and expand the file system to occupy all the space available with re-partitioning.

So if we want to work with a bigger memory space, it is recommended to expand the BeagleBone Black memory file system. This process is further explained at http://elinux.org/Beagleboard:Expanding_File_System_Partition_On_A_microSD.

Although the following steps are not needed in general, they are here in case you need them in your particular case. You can proceed by following these commands:

$ sudo su

$ fdisk /dev/mmcblk0

$ p

$ d
$ 2

$ n
$ p
$ 2

$ w

$ reboot

$ sudosu

$ resize2fs /dev/mmcblk0p2

Now we should be ready to install ROS. At this point, the process of installation is pretty similar to the PC installation previously explained in this chapter, so we should be familiar with it. We will see that the main difference when installing ROS on BeagleBone Black is that we can't install the ROS full-desktop; we must install it package by package.

Now you will start setting up your local machine:

$ sudo update-locale LANG=C LANGUAGE=C LC_ALL=C LC_MESSAGES=POSIX

After this, we will configure the source lists depending on the Ubuntu version that we have installed in BeagleBone Black. The number of Ubuntu versions compatible with BeagleBone Black is limited, and only active builds can be found for Ubuntu 16.40 Xenial armhf, the most popular version of Ubuntu ARM. Run the following to install the Ubuntu armhf repositories:

$ sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -cs) main" > /etc/apt/sources.list.d/ros-latest.list'

As explained previously, this step is needed to confirm that the origin of the code is correct and that no one has modified the code or programs without the knowledge of the owner:

$ sudo apt-key adv --keyserver hkp://ha.pool.sks-keyservers.net --recv-key 0xB01FA116

Before the installation of ROS packages, we must update the system to see all the packages on the ROS repository just added:

$ sudo apt-get update

This part of the installation is slightly different for the BeagleBone Black. There are a lot of libraries and packages in ROS, and not all of them compile fully on an ARM, so it is not possible to make a full desktop installation. It is recommended that you install them package by package to ensure that they will work on an ARM platform.

You can try to install ROS-base, known as ROS Bare Bones. ROS-base installs the ROS package along with the build and communications libraries but does not include the GUI tools (press ENTER (Y) when prompted):

$ sudo apt-get install ros-kinetic-ros-base

We can install specific ROS packages with the following command:

$ sudo apt-get install ros-kinetic-PACKAGE

If you need to find the ROS packages available for BeagleBone Black, you can run the following command:

$ apt-cache search ros-kinetic

For example, the following packages are the basics (already installed as ros-base dependencies) that work with ROS and can be installed individually using apt-get install:

$ sudo apt-get install ros-kinetic-ros
$ sudo apt-get install ros-kinetic-roslaunch
$ sudo apt-get install ros-kinetic-rosparam
$ sudo apt-get install ros-kinetic-rosservice

Although, theoretically, not all the packages of ROS are supported by BeagleBone Black, in practice, we have been able to migrate entire projects developed on PC to BeagleBone Black. We tried a lot of packages, and the only one that we could not install was rviz, which is indeed not recommended to run on it.

The rosdep command-line tool must be installed and initialized before you can use ROS. This allows you to easily install libraries and solve system dependencies for the source you want to compile, and is required to run some core components in ROS. You can use the following commands to install and initialize rosdep:

$ sudo apt-get install python-rosdep
$ sudo rosdep init
$ rosdep update

If you have arrived at this step, congratulations, because you have installed ROS in your BeagleBone Black. The ROS environment variables can be added to your bash, so they will be added every time a shell is launched:

$ echo "source /opt/ros/kinetic/setup.bash" >> ~/.bashrc
$ source ~/.bashrc

We have to be careful if we have more than one version of ROS in our system. The bashrc setup must use the variables of the version being used only.

If we want to set up the environment in the current shell, we will run the following command:

$ source /opt/ros/kinetic/setup.bash

Rosinstall is a common command-line tool in ROS that helps us to install packages easily. It can be installed on Ubuntu with the following command:

$ sudo apt-get install python-rosinstall

As a basic example, you can run a ROS core on one terminal on the BeagleBone Black:

$ roscore

And from another terminal publish a pose message (note you can press TabTab after geometry_msgs/Pose and it'd autocomplete the message fields, that then you need to change since it'd have the default values):

$ rostopic pub /dummy geometry_msgs/Pose
Position:
x: 1.0
y: 2.0
z: 3.0
Orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0 -r 10

Now, from your laptop (in the same network), you can set ROS_MASTER_URI to point to the BeagleBone Black (IP 192.168.1.6 in our case):

$ export ROS_MASTER_URI=http://192.168.1.6:11311

And now you should be able to see the pose published from the BeagleBone Black on your laptop doing:

$ rostopic echo -n1 /dummy
Position:
x: 1.0
y: 2.0
z: 3.0
Orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
---

If you use a PoseStamped, you can even visualize it on rviz.

From this point, you can check multiple projects at http://wiki.ros.org/BeagleBone, as well as another installation option, which uses the Angstrom OS instead of Ubuntu, but it does not support ROS Kinetic at the moment.