This ROS stack includes an Arduino sketch and a collection of ROS packages for controlling an Arduino-based robot using standard ROS messages and services.
Supported sensors currently include Ping sonar and Sharp GP2D12 infrared as well as generic analog and digital sensors (e.g bump switches, voltage sensors, etc.)
The package also includes a base controller for a differential drive that accepts ROS Twist messages and publishes odometry data back to the PC. In this version of the stack, the base controller requires the use of an Arduino Mega 2560 controller together with a Pololu motor controller shield (http://www.pololu.com/catalog/product/2502) and a Robogaia Mega Encoder shield (http://www.robogaia.com/two-axis-encoder-counter-mega-shield-version-2.html).
The current version of the stack requires an Arudino Mega controller + Pololu Dual VNH5019 Motor Driver Shield + Robogaia Encoder shield. If you do not have this hardware, you can still try the package for reading sensors and controlling servos using other Arduino-compatible controllers. See the NOTES section at the end of this document for instructions on how to do this.
To use the base controller you must also install the Polulu Arduino library found at:
https://github.com/pololu/Dual-VNH5019-Motor-Shield
and the Robogaia Encoder library found at:
http://www.robogaia.com/uploads/6/8/0/9/6809982/__megaencodercounter-1.3.tar.gz
These libraries should be installed in your standard Arduino sketchbook/libraries directory.
Finally, it is assumed you are using version 1.0 or greater of the Arduino IDE.
$ cd ~/ros_workspace
$ git clone https://github.com/hbrobotics/ros_arduino_bridge.git
$ cd ros_arduino_bridge
$ rosmake
The provided Arduino sketch is called MegaRobogaiaPololu and is located in the ros_arduino_firmware package. This sketch is specific to the hardware requirements above but it can also be used with other Arduino-type boards (e.g. Uno) by turning off the base controller as described in the NOTES section at the end of this document.
To install the MegaRobogaiaPololu sketch, follow these steps:
$ cd SKETCHBOOK_PATH
where SKETCHBOOK_PATH is the path to your Arduino sketchbook directory.
$ ln -s `rospack find ros_arduino_firmware`/src/libraries/MegaRobogaiaPololu MegaRobogaiaPololu
This last command creates a link in your sketchbook folder for the MegaRobogaiaPololu sketch that you must run on your Arduino Mega controller. By creating a link rather than copying the files, the sketch will get updated along with other files in the ros_arduino_bridge stack.
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Make sure you have already installed the DualVNH5019MotorShield and MegaEncoderCounter libraries into your Arduino sketchbook/libraries folder.
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Launch the Arduino 1.0 IDE and load the MegaRobogaiaPololu sketch. You should be able to find it by going to:
File->Sketchbook->MegaRobogaiaPololu
NOTE: If you don't have the Arduino Mega/Pololu/Robogaia hardware but still want to try the code, see the notes at the end of the file.
If you want to control PWM servos attached to your controller, change the two lines that look like this:
//#define USE_SERVOS #undef USE_SERVOS
to this:
#define USE_SERVOS //#undef USE_SERVOS
You must then edit the include file servos.h and change the N_SERVOS parameter as well as the pin numbers for the servos you have attached.
- Compile and upload the sketch to your Arduino.
Now that your Arduino is running the required sketch, you can configure the ROS side of things on your PC. You define your robot's dimensions, PID parameters, and sensor configuration by editing the YAML file in the directory ros_arduino_python/config. So first move into that directory:
$ roscd ros_arduino_python/config
Now copy the provided config file to one you can modify:
$ cp arduino_params.yaml my_arduino_params.yaml
Bring up your copy of the params file (my_arduino_params.yaml) in your favorite text editor. It should start off looking like this:
port: /dev/ttyUSB0
baud: 57600
timeout: 0.1
rate: 50
sensorstate_rate: 10
use_base_controller: False
base_controller_rate: 10
# === Robot drivetrain parameters
#wheel_diameter: 0.146
#wheel_track: 0.2969
#encoder_resolution: 8384 # from Pololu for 131:1 motors
#gear_reduction: 1.0
#motors_reversed: True
# === PID parameters
#Kp: 20
#Kd: 12
#Ki: 0
#Ko: 50
# === Sensor definitions. Examples only - edit for your robot.
# Sensor type can be one of the follow (case sensitive!):
# * Ping
# * GP2D12
# * Analog
# * Digital
# * PololuMotorCurrent
sensors: {
#motor_current_left: {pin: 0, type: PololuMotorCurrent, rate: 5},
#motor_current_right: {pin: 1, type: PololuMotorCurrent, rate: 5},
#ir_front_center: {pin: 2, type: GP2D12, rate: 10},
#sonar_front_center: {pin: 5, type: Ping, rate: 10},
arduino_led: {pin: 13, type: Digital, rate: 5, direction: output}
}
NOTE: Do not use tabs in your .yaml file or the parser will barf it back out when it tries to load it. Always use spaces instead. ALSO: When defining your sensor parameters, the last sensor in the list does not get a comma (,) at the end of the line but all the rest must have a comma.
Let's now look at each section of this file.
Port Settings
The port will likely be either /dev/ttyACM0 or /dev/ttyUSB0. Set accordingly.
The MegaRobogaiaPololu Arudino sketch connects at 57600 baud by default.
Polling Rates
The main rate parameter (50 Hz by default) determines how fast the outside ROS loop runs. The default should suffice in most cases. In any event, it should be at least as fast as your fastest sensor rate (defined below).
The sensorstate_rate determines how often to publish an aggregated list of all sensor readings. Each sensor also publishes on its own topic and rate.
The use_base_controller parameter is set to False by default. Set it to True to use base control (assuming you have the required hardware.) You will also have to set the PID paramters that follow.
The base_controller_rate determines how often to publish odometry readings.
Defining Sensors
The sensors parameter defines a dictionary of sensor names and sensor parameters. (You can name each sensor whatever you like but remember that the name for a sensor will also become the topic name for that sensor.)
The four most important parameters are pin, type, rate and direction. The rate defines how many times per second you want to poll that sensor. For example, a voltage sensor might only be polled once a second (or even once every 2 seconds: rate=0.5), whereas a sonar sensor might be polled at 20 times per second. The type must be one of those listed (case sensitive!). The default direction is input so to define an output pin, set the direction explicitly to output. In the example above, the Arduino LED (pin 13) will be turned on and off at a rate of 2 times per second.
Setting Drivetrain and PID Parameters
To use the base controller, you will have to uncomment and set the robot drivetrain and PID parameters. The sample drivetrain parameters are for 6" drive wheels that are 11.5" apart. Note that ROS uses meters for distance so convert accordingly. The sample encoder resolution (ticks per revolution) is from the specs for the Pololu 131:1 motor. Set the appropriate number for your motor/encoder combination. Set the motors_reversed to True if you find your wheels are turning backward, otherwise set to False.
The PID parameters are trickier to set. You can start with the sample values but be sure to place your robot on blocks before sending it your first Twist command.
Take a look at the launch file arduino.launch in the ros_arduino_python/launch directory. As you can see, it points to a config file called my_arduino_params.yaml. If you named your config file something different, change the name in the launch file.
With your Arduino connected and running the MegaRobogaiaPololu sketch, launch the ros_arduiono_python node with your parameters:
$ roslaunch ros_arduino_python arduino.launch
You should see something like the following output:
process[arduino-1]: started with pid [6098]
Connecting to Arduino on port /dev/ttyUSB0 ...
Connected at 57600
Arduino is ready.
[INFO] [WallTime: 1355498525.954491] Connected to Arduino on port /dev/ttyUSB0 at 57600 baud
[INFO] [WallTime: 1355498525.966825] motor_current_right {'rate': 5, 'type': 'PololuMotorCurrent', 'pin': 1}
[INFO]
etc
If you have any Ping sonar sensors on your robot and you defined them in your config file, they should start flashing to indicate you have made the connection.
To see the aggregated sensor data, echo the sensor state topic:
$ rostopic echo /arduino/sensor_state
To see the data on any particular sensor, echo its topic name:
$ rostopic echo /arduino/sensor/sensor_name
For example, if you have a sensor called ir_front_center, you can see its data using:
$ rostopic echo /arduino/sensor/ir_front_center
You can also graph the range data using rxplot:
$ rxplot -p 60 /arduino/sensor/ir_front_center/range
Place your robot on blocks, then try publishing a Twist command:
$ rostopic pub -1 /cmd_vel geometry_msgs/Twist '{ angular: {z: 0.5} }'
The wheels should turn in a direction consistent with a counter-clockwise rotation (right wheel forward, left wheel backward). If they turn in the opposite direction, set the motors_reversed parameter in your config file to the opposite of its current setting, then kill and restart the arduino.launch file.
Stop the robot with the command:
$ rostopic pub -1 /cmd_vel geometry_msgs/Twist '{}'
To view odometry data:
$ rostopic echo /odom
or
$ rxplot -p 60 /odom/pose/pose/position/x:y, /odom/twist/twist/linear/x, /odom/twist/twist/angular/z
The ros_arduino_python package also defines a few ROS services as follows:
digital_set_direction - set the direction of a digital pin
$ rosservice call /arduino/digital_set_direction pin direction
where pin is the pin number and direction is 0 for input and 1 for output.
digital_write - send a LOW (0) or HIGH (1) signal to a digital pin
$ rosservice call /arduino/digital_write pin value
where pin is the pin number and value is 0 for LOW and 1 for HIGH.
servo_write - set the position of a servo
$ rosservice call /arduino/servo_write id pos
where id is the index of the servo as defined in the Arduino sketch (servos.h) and pos is the position in degrees (0 - 180).
servo_read - read the position of a servo
$ rosservice call /arduino/servo_read id
where id is the index of the servo as defined in the Arduino sketch (servos.h)
If you do not have the hardware required to run the base controller, follow the instructions below so that you can still use your Arduino-compatible controller to read sensors and control PWM servos.
First, you need to edit the MegaRobogaiaPololu sketch. At the top of the file, change the two lines that look like this:
#define USE_BASE //#undef USE_BASE
to this:
//#define USE_BASE #undef USE_BASE
You also need to comment out the line that looks like this:
#include "MegaEncoderCounter.h"
so it looks like this:
//#include "MegaEncoderCounter.h"
Compile the changes and upload to your controller.
Next, edit your my_arduino_params.yaml file and set the use_base_controller parameter to False. That's all there is to it.