ROS and the Raspberry Pi

http://www.robopgmr.com/?page_id=3589

Arnold Bailey

+ROS

Contents

• The complexity of robotics

• What is ROS?

• Hardware and software options

• Creating an ROS user application.

• Conclusion

2

3

Can complex robotic systems be programmed on an RPi?

?

The Distributed Brain

• Manage diverse asynchronous activity

• Manage significant complexity.

• Device abstract

• Multi-language operation.

• Distribution of resources

5

Advanced robotic systems require:

6

The Challenge!Need to develop expertise

Cost Functionality

Industry Academic

Open Source

7

• A software framework for developing robotic systems in a meta-operating system environment.

• The primary goal of ROS is to support code reuse in robotics research and development

• ROS was originally developed in 2007 at the Stanford Artificial Intelligence Laboratory and development continued at Willow Garage

• Managed by the Open Source Robotics Foundation

What is ROS?

ROS Distributed Architecture

8

9

ROS MasterEnables ROS nodes to locate one another and provide parameter services.

Peer-to-Peer Messaging

• Master(roscore): Provides naming and registration services to the rest of the nodes in the system.

• Package: A virtual directory holding one or more executables (nodes)

• Messages: Defined in msg files. Basic data types.

• Node: An agent communicating with ROS and other nodes via messages.

• Topics (publish / subscribe) using typed messages

• Services: Request / Response, synchronism functionality, remote computation.

• Bag: Bags are a format for recording and playback of messages.

ROS Core Concepts

ArduinoUno

Pi Co-op

Raspberry Pi

ROS Application-ard01

ROS

PyMatalib

Firmatalib

GPIO

Motion Detector LED

Hardware abstraction, low-level device control

readpin 8

sensor

writepin 13

13

Multiple Languages

C++ Node: Map Building

Python Node: Laser Scanner

Topic: “Laser Data”

Subscribe Publish

ROS core Components

Middleware Robot Specific Features Tools

• Messaging Passing• Recording/Playback• Remote Procedure Calls• Distributed Parameters

• Standard Robot Messages• Robot Geometry Library• Robot Description Language• Pre-emptable RPC• Diagnostics• Pose Estimation • Localization• Navigation

• Command line tools• Integrated Tools

ROS

15

PCL OpenRave RQT TF actionlib gmapping gmapping

amcl move_base turtlesim PR2 Turtlebot RViz Navigation MoveIt!

Development Tools Integrated into ROS

16

rosbag rosbash roscd rosclean roscore rosdep rosed roscreate-pkg roscreate-stack rosrun roslaunch

roslocate rosmake rosmsg rosnode rospack rosparam rossrv rosservice rosstack rostopic rosversion

User Command Line Tools

Example Hardware• Raspberry Pi

• Model B

• 16 GB SD (Could use 8 GB)

• Pi Co-op Board

• Arduino Uno (resides on board)

• Parallax Motion Detecter

• Breadboard

17

18

Pymata/Firmata

Arduino Libraries

rosserial_arduino rosserial

Pi Co-op x

RPi to Arduino x x

RPI direct to device x

Hardware/software options

Pi Co-op Add-on Board• It’s a GPIO plug-in board that

houses an ATmega328p chip and female headers.

• Arduino Uno bootloader to make it easy to program.

• Pi communicates with the chip over UART (serial) protocol.

• uses a library called pyMata to control the analog inputs and digital inputs.

• Can attach power to the Pi Co-op

Pi Co-op connection to Motion Detecter

RPi and Arduino Connected Over Serial GPIO

RPi connected to LED using GPIO pins

Create a Package

23

$ source /opt/ros/indigo/setup.bash $ mkdir -p ~/catkin_ws/src $ cd ~/catkin_ws/src $ catkin_init_workspace $ cd ~/catkin_ws/ $ catkin_make

$ cd ~/catkin_ws $ source /opt/ros/indigo/setup.bash $ cd ~/catkin_ws/src $ catkin_create_pkg ard01 std_msgs rospy roscpp $ rospack depends1 ard01 $ roscd ard01 $ cat package.xml # view it $ rospack depends1 rospy # view $ pico package.xml

Create Workspace

Craete Package

24

Package ad01 Files

CMakeList.txt

packahages.xml

/catkin_ws

/scripts

/src

/msg

/srv

rb_motion_test

Communication GraphPackage: ard01

rb_motion_detect rb_blink_led

rb_motion_detect

rb_motion_detect

rb_blink_led

#!/usr/bin/env python # import rospy from PyMata.pymata import PyMata

subscriber = rospy.Subscriber("rb_motion_detect", String, scallback)

rospy.init_node('rb_motion_detect', anonymous=True)

Python Script Snippets

Libraries

Register node

Subscribe to topic

27

rospy.loginfo("Message is %s",data.data)

DETECT = 8 # Pin 8 is the detect on/off

# Configure the pins SERIAL_PORT = "/dev/ttyS0" # Create an instance of PyMata. firmata = PyMata( SERIAL_PORT, max_wait_time=5 )

setup

Logging

Python Script Snippets

28

pub = rospy.Publisher('rb_blink_led', String, queue_size=10) str = "1 0" # message to reset blinking pub.publish(str)

rospy.spin

time.sleep(.1)

firmata.close()

Publish a MWSSAGE

Delaying

Delaying

Wait until ROS caommand completes

Python Script Snippets

ExecutionTerminal session 1 Roscore

pi@raspberrypi ~ $ cd ~/catkin_ws pi@raspberrypi ~/catkin_ws $ source ./devel/setup.bash pi@raspberrypi ~/catkin_ws $ roscore ... logging to /home/pi/.ros/log/c4b68850-6434-11e4-a4b6-b827eb6d59e5/roslaunch-raspberrypi-2639.log

pi@raspberrypi ~/catkin_ws $ rosrun ard01 rb_motion_test.py Enter start/stop/exit motion detection:start [INFO] [WallTime: 1415119214.484039] motion_detect mode requested -start Enter start/stop/exit motion detection:

blepi@raspberrypi ~/catkin_ws $ rosrun ard01 rb_motion_detect.py [INFO] [WallTime: 1415119214.521525] Message is start

Terminal session 3 rb_motion_detect

^Cpi@raspberrypi ~/catkin_ws $ rosrun ard01 rb_blink_led.py [INFO] [WallTime: 1415119236.277651] Message is 1 5 [INFO] [WallTime: 1415119236.290445] Requested blink rate is 1, 5 Opening Arduino Serial port /dev/ttyS0 Please wait while Arduino is being detected. This can take up to 5 seconds ... Board initialized in 0 seconds Total Number of Pins Detected = 20 Total Number of Analog Pins Detected = 6 PyMata close(): Calling sys.exit(0): Hope to see you soon!

Terminal session 2 rb_motion_test

Terminal session 3 rb_blink_led

Conclusion

• ROS, on the Raspberry Pi is a very viable and easy to use approach to provide robotic system functionality at a very low cost.

• Because ROS is used industrywide and in many of the leading universities, ROS and RPi should be the method of choice to teach robotics in the advanced high school and university levels.

30

Attachments

• References

• Sample Arduino sketch

• Existing Systems vs ROS

31

References

• Installing ROS Indigo on the RPi

• Pi Co-OP video describes Pi Co-op

• Reference Pi Co-op and Arduino Software Installation – Notes for the detailed instructions.

• Installs PyMata (Python library)

• Loads Firmata (protocol used by Pymata to I/F with the Arquino)

32

33

// Sweep // by BARRAGAN <http://barraganstudio.com> // This example code is in the public domain #include <Servo.h>   Servo myservo;  // create servo object to control a servo                 // a maximum of eight servo objects can be created   int pos = 0;    // variable to store the servo position   void setup() {   myservo.attach(9);  // attaches the servo on pin 9 to the servo object }   void loop() {   for(pos = 0; pos < 180; pos += 1)  // goes from 0 degrees to 180 degrees   {                                  // in steps of 1 degree     myservo.write(pos);              // tell servo to go to position in variable 'pos'     delay(15);                       // waits 15ms for the servo to reach the position   }   for(pos = 180; pos>=1; pos-=1)     // goes from 180 degrees to 0 degrees   {                                     myservo.write(pos);              // tell servo to go to position in variable 'pos'     delay(15);                       // waits 15ms for the servo to reach the position   } }

Sample Arduino Code (IDE)

Existing Systems vs ROSGeneral Purpose ROS

Explicitly general purpose Exclusively for robotics programs

Native language programming Language independent

sequential architecture asynchronous distribyed

programming IDE sofyware framework

prprietary/open source opensource BSD license

heavily coded ROS frameworks are very light

programs nodes

communication messages

splintered usage industry-wide and academic usage