This robot, code-named Blink-192, uses the Robot Operating System (ROS) to do two things: first, it reacts to keystrokes on a computer and drives around; second, it streams video from a raspberry pi camera back to said computer.
Blink-192 is a great example of how ROS can help with any robotics project. ROS connects Blink-192 to a desktop to stream video and receive steering commands with minimal setup and networking.
Blink-192 uses the following hardware:
- Raspberry Pi 3
- Waveshare Alphabot – Waveshare
- Raspberry Pi Camera 2
- 7.4V LiPo Battery
This specific Ubuntu image isn’t required, but it comes with ROS pre-installed a creates a wifi access point automatically.
ROS has become a nearly ubiquitous part of any serious robotics project. I first learned about it as part of the Udacity Robotics Engineer Nanodegree program last Summer, and I couldn’t wait to get started on my own project.
Despite its name, ROS isn’t actually an operating system; it runs on Ubuntu. It’s more of a messaging system that sends messages between different parts of a robot. Let’s take a deeper look at how to develop a project using ROS.
A node is defined as any executable that uses ROS to communicate. ROS will manage the lifecycle and messaging of any python script that’s run as a node, so using ROS will easily allow you to run multiple scripts simultaneously.
A topic is a messaging bus that ROS nodes use to exchange messages. Topics follow the publish/subscribe pattern (similar to Rx and Kafka), so each node can subscribe to any data topics it requires, and then publish whatever it wants.
Blink-192 ROS Setup
Blink-192 works using four different nodes:
keyboard_driver– Reads keystrokes and publishes them to the
keys_to_twist– Subscribes to
/keysand publishes a velocity command to
motors– Subscribes to
/cmd_veland controls motors
raspicam_node– Publishes video stream to
Every node except
keyboard_driver runs on Blink-192;
keyboard_driver runs on the desktop.
In order to control Blink-192, ROS needs to know to network between two computers. Since Blink-192 has its own wifi access point, this is relatively straightforward.
- Connect to wifi access point, my SSID starts with blink-192 – Ubiquity
- Get desktop ip address using
ip addr show
export ROS_IP=<ip address>
roslaunch blink-192 desktop.launch
- Ssh into Blink-192, and run
roslaunch blink-192 robot.launch
- Start driving!
ROS_MASTER_URI variable tells the desktop where to find the ROS master node that it should use, and
ROS_IP tells the ROS master how to connect back to it. Launch files are a convenient way of running multiple nodes at once.
That’s it! ROS handles all of the communication back-and-forth between Blink-192 and the desktop.
This is just one example of how ROS can make robotics projects easier. ROS also includes tools for simulation, visualization, parameters, and much much more. Because ROS uses common message types, you can easily add nodes that other people have written as well.
For more info, check out http://www.ros.org/is-ros-for-me/