RoNeX on Windows with Matlab

This tutorial shows how to interact with RoNeX from MATLAB with minimal prior knowledge of Linux and ROS. RoNeX drivers run on Ubuntu within a VirtualBox virtual machine (A pre-configured VM image is available for download) so a native Linux install is not required. We use the MATLAB ROS support package under MATLAB R2013a or R2013b to send/receive data from RoNeX and process it in MATLAB.

For this tutorial we used Windows 8 64 bit install as the host system, although it should work on other versions of Windows without issues. It is running on a Lenovo Notebook computer, with a RoNeX stack connected to the Ethernet port, and a Wifi card connected to a network using DHCP.

If you experience problems during this tutorial, please let us know!

Installing VirtualBox + RoNeX Image

First download + install VirtualBox. The latest install file can be downloaded from: https://www.virtualbox.org/wiki/Downloads

Next install a Virtual Machine image with Ubuntu, ROS and the RoNeX drivers.

Configure VirtualBox

Once installed, open VirtualBox, go to File > Import Appliance, then find the Ubuntu ROS_RoNeX.ova system image you’ve just downloaded. You can adjust the amount of resources available to the VM here if you like, otherwise click import.

The host machine has both Wired and Wireless network cards configured to obtain an IP address automatically using DHCP. Once you have imported the virtual machine, you will need to open Settings > Network for that machine, and update the settings for adapter 1 (wired) and adapter 2 (wireless). By default the network adapter names correspond to those on our test machine, so you will need to select the correct names for your machine from the drop-down list. Ensure both adapters are attached to: “Bridged Adapter”. You shouldn’t need to adjust the advanced settings.

Ensure the machine is connected to your wifi network and has obtained an IP address. If you don’t have a wireless or second wired card for a network connection, it is possible to set up static IPs for communication between MATLAB and VirtualBox, but that is beyond the scope of this tutorial.

Install MATLAB + ROS toolbox

To interact with ROS you will require MATLAB R2013a or R2013b. If you don’t have MATLAB already, you can head over to the Mathworks website to find out how to get it:

http://www.mathworks.com/

Once MATLAB is set up, you will need to set up ROS support by downloading it from here:

http://www.mathworks.com/hardware-support/robot-operating-system.html

Configure ROS inside Virtual Machine

With your network adapters correctly configured in VirtualBox, once Ubuntu has booted, it should have obtained a unique IP on your network. You can check this IP by opening a terminal window (ctrl+alt+t) and typing:

ifconfig

Under adapter eth1 - inet addr: you should see the IP assigned to the virtual machine, make a note of it. Now in the same terminal we’re going to set this IP in our ROS configuration. Open up the .bashrc config file by typing:

gedit ~/.bashrc

Scroll to the bottom of the file, and you should see the following lines：

export ROS_HOSTNAME=192.168.0.14
export ROS_MASTER_URI=http://192.168.0.14:11311

Change the IP address there to the one obtained from ifconfig. Be sure to leave the “http://” and ”:11311” on the ROS_MASTER_URI.

Hardware Configuration

As previously mentioned, RoNeX is connected to the wired Ethernet port on the Laptop, which should now be set as eth0 in the virtual machine.

Connect one of your pre-made RoNeX GIO cables, to the analogue port on the GIO node, then connect 5V, GND and Channel 0 to your potentiometer, preferably on a solderless breadboard.

MATLAB Code

The MATLAB code below starts a RoNeX node and subscriber to receive RoNeX data.

The first section should be copied to a new MATLAB script in your workspace, named rostest.m

rosinit('http://192.168.0.14:11311')
sub = rossubscriber('/ronex/general_io/12/state', @my_function, 'Buffersize', 10))

i = 'a';
while i ~= 'q'
    i = input('q to quit', 's')
end

rosshutdown
clear;

This code should be copied into a file named my_function.m, in the same directory as rostest.m

function my_function(~, message)
    mydata = message.Analogue;
    disp (mydata(1));
end

Modifying the MATLAB Code

You will need to change the first line of the MATLAB script, to ensure the IP address listed for the ROS master, matches that we obtained from Ubuntu in the ROS configuration step.

rosinit('http://192.168.0.14:11311')

The Code Explained

The MATLAB code we are running is fairly simple, you can find a PDF manual with more information on the various functions in the MATLAB ROS Support package you downloaded. We’ll start by looking at rostest.m:

rosinit('http://192.168.0.14:11311')
sub = rossubscriber('/ronex/general_io/12/state', @my_function, 'Buffersize', 10)

All of the ROS setup is done in these three lines. In the first a ROS node is defined (the user could choose an appropriate name), with the address of the ROS master.

Secondly a subscriber is defined to receive messages on the specified topic. The RoNeX message formats are included in the MATLAB ROS package by default, so we don’t have to worry about custom messages. We set the callback function for the subscriber, i.e. whenever a valid message is received on the topic, this function is executed.

Finally we set a queue size of 10, this may need to be increased on slower machines so they don’t miss messages.

i = 'a';
while i ~= 'q'
    i = input('q to quit', 's')
end

This code is to allow us to quit the program cleanly. It loops while waiting for keyboard input, if the received input character is a ‘q’, it will move on to shutdown the node.

rosshutdown
clear;

Once the quit message has been received, the node is shutdown and then everything is removed from the variable workspace using the clear command.

Next we will look at the my_function.m file:

function my_function(~, message)
    mydata = message.Analogue;
    disp (mydata(1));
end

This function is called every time a message is received on the corresponding topic, and is passed the message as an input argument. MATLAB allows to access the fields of the message but renames them to a camel case format instead of the lower case with underscores that is usual in ROS. The RoNeX state message has an analogue field, so we can access the Analogue field in the message (we could similarly access Digital).

Once we have the data, as the potentiometer is connected to channel 0, we are interested in the first value in the array, so we display this value then wait for the next message.

Execute Programs

First make sure ROS and the RoNeX driver are running in the virtual machine, as described in (see Launch driver ).

Next run the MATLAB script (Either by right clicking on it in the current folder window and clicking run, typing the name of the file in the command window, or pressing f5 in the rostest.m editor window)

You should see the data from the potentiometer displayed in the command window, as you turn the pot, the values will reflect the angle of the shaft. Press q then enter when you are ready to quit the program.