NetworkTables¶

NetworkTables resource

http://robotpy.readthedocs.io/projects/pynetworktables/en/latest/api.html http://robotpy.readthedocs.io/projects/pynetworktables2js/en/stable/

Install NetworkTables

Type these commands in the terminal:

$ pip3 install pynetworktables
$ pip3 install pynetworktables2js

What is NetworkTables?

Joysticks give us an easy interface to control the robot, but what if we want to tell the robot where it’s starting in the autonomous period? We can’t use joysticks because we can’t touch the conrols during the autonomous period. We can do this by building a webpage that aloows us to select the starting location before the match begins. The link that allows us to communicate between the webpage and robot is called NetworkTables. NetworkTables sends and receives data to the different devices on the robot network.

NetworkTables on the robot

To use NetworkTables on the robot we must import it just like we do with wpilib:

from networktables import NetworkTables

Next we have to create a table. Tables contain the data we want to send back and forth between different devices during the match. For example, if we want to know where our robot is starting in autonomous mode, and if we’re scoring a gear or just moving forward, we create an autonomous table. If we want to tell the webpage our robot’s current heading and speed, we would have a sensor table:

autonomousTable = NetworkTables.getTable("autonomous")
sensorTable = NetworkTables.getTable("sensor")

To get the autonomous mode we would say:

mode = autonomousTable.getString('mode', 'do_nothing')

If we want to tell the robot our current speed we would say:

sensorTable.putNumber('speed', speed_sensor.getSpeed())

NetworkTables on a webpage

To use network tables on an HTML page we must have web server and a webpage. Go to where you have the robot repository in the terminal and type:

$ git pull
$ git checkout networktables_fun

Navigate to the networktables folder in the terminal by typing:

$ cd networktables/

To run the server enter this in the terminal:

$ python3 tornado_server.py

Now go to the browser and enter http://127.0.0.1:8888/ into the address bar. Open another tab and enter http://127.0.0.1:8888/example.html in the browser. These are the html pages in the networktables/www folder index.html and example.html. If you look in these files you will se we are including the Javascript version of NetworkTables:

Getting and putting values in the NetworkTables is a bit different in Javascript. You do not create a table but type in:

NetworkTables.putValue('/table name/key', value);
NetworkTables.getValue('/table name/key', default_value);