Introduction: Raspberry Pi and ROS (Robotic Operating System)
Now just so that you are not confused about the potentials of the Raspberry Pi as a robotic processor/controller, it has great potential for small computation and can run Linux and all the great features that come along with it. But this is a Arm processor and not a typical PC cpu so it is limited by its architecture and power capabilities. Some portions of Linux code have not been completely ported to ARM processors so you will be limited at the moment to what programs you can install. But for most of ROS and the programs I am going to cover in this tutorial, Pi is functional and can be useful depending on the demands of your project. But if you are planning to do any 3d/2d mapping/navigation with a Kinect/laser scanner at the moment I am not sure its possible utilizing just the Raspberry Pi but with time who knows. In the future I will also include another tutorial that connects the Raspberry Pi to a small robot to act as controller. So lets begin..
Step 1: Parts List
We are going to need the following items :
Micro USB power supply
USB keyboard and mouse
Monitor with HDMI input
SD Card with at least 8GB (Check this list of compatible cards )
And a computer with either Windows or Linux installed
Step 2: Writing the Image to the SD Card
Now there are a couple of different ways to get Linux and ROS working on Raspberry PI. One way is to write the Linux image to the SD card then download and install ROS form within the Raspberry Pi. This can become difficult and time consuming for the beginner, but it is useful when creating a custom ROS installation. These steps can be found here on the ROS WIKI
However we are going to be using a Linux image that has ROS pre-installed. Thanks to Jeremy Nicola for providing the image in the form of a zip file which can be found here
Rosberry PI Image
And in order to get our Linux image on to the SD Card we are going to use Image Writer for Windows, which can be downloaded here
FOR WINDOWS :
Insert the SD card into your SD card reader, then locate and remember what drive letter the SD card was assigned.
Format the card and make sure there is only one partition (FAT32 is a good choice), otherwise
Win32DiskImager can corrupt your SD card!
Extract the Raspbian-ROS-full.img.7z file somewhere.
Install and run Win32DiskImager utility as Administrator.
Select the Raspbian-ROS-full.img image file
Select the drive letter of the SD card in the device box. Make sure you select the correct drive, if you select the wrong drive you can corrupt your data on that assigned drive.
Click Write and wait for the write to complete.
Exit the program and eject the SD card.
If all goes well you should have a bootable image on your SD card.
FOR LINUX :
Use DD in the terminal to write the image to the SD card
copy and paste this after replacing the correct paths to your SD card and Raspberry Pi image
sudo dd if=/path/to/Download/img/file of=/path/to/SDcard
sudo dd if=/home/username/Downloads/Raspbian-ROS-full.img of=/dev/sdc
Wait for the command to return. This may take some time so be patient .If all goes well you should have a bootable image on your SD card.
Step 3: Starting Our Rosberry for the First Time
Insert the SD card into the Raspberry Pi's card slot. Connect the Raspberry PI to the HDMI monitor, keyboard, mouse and power supply. Before you can get into the desktop screen you will have to enter your username and password
And once Linux has booted to the desktop open a terminal screen [ Ctrl + Alt + t ] and enter the following :
The roscore is now running and we are now ready to start the tutorials.
If you want some background on ROS commands and Syntax look to this Cheat Sheet for help.
or the ROS Start Guide .
Step 4: ROS Tutorials
We are going to go over how to publish a message to the roscore then subscribe to that message. This concept is the basics behind the ROS system which gives us a dynamic way to publish/receive data to control our robot projects and get data from them.
With roscore running in one terminal open another terminal and copy and paste
rosrun roscpp_tutorials talker
This should start publishing something like this
[ INFO] [1358365440.794845809]: hello world 0
[ INFO] [1358365440.895024702]: hello world 1
[ INFO] [1358365440.995006238]: hello world 2
[ INFO] [1358365441.095000473]: hello world 3
[ INFO] [1358365441.195000082]: hello world 4
Then open another terminal and copy and paste
rosrun roscpp_tutorials listener
This should output the same data that the first terminal is displaying
Now lets get an idea of what is happening inside the roscore by using rxgraph to display the nodes and messages that are running in our system. Open a new terminal then copy and paste
Now you should see the running nodes and their respective messages with arrows to point out there output orientation, if you select all topics in the window you can see all the topics that are published and subscribed within the roscore.
For more ROS tutorials check out the ROS Tutorials page.