Skip to content

[WIP] Using RobotPreferences#

Overview#

In this section we will be going over

  1. Creating and using RobotPreferences in Elastic
  2. How to convert encoder counts to inches

What Are RobotPreferences#

  • On SmartDashboard or ShuffleBoard there is a widget called Robot Preferences that can store variables that can be quickly changed
  • For example you might have a variable that changes PID values which can be changed from Robot Preferences on SmartDashboard/ShuffleBoard
  • For this section of our tutorial we will create a robot preference called driveEncoderCountsPerFoot

Creating RobotPreferences#

1) Create a new empty class called RobotPreferences

  • This is where we store all of our RobotPreferences to access anywhere
  • If we want to use a RobotPreference we call RobotPreferences.preferenceName()

2) Inside the constructor type:

public static double driveEncoderCountsPerFoot(){
  return Preferences.getInstance().getDouble(“driveEncoderCountsPerFoot”, 1.0);
}
  • The format for creating a RobotPreference is
public static variableType preferenceName(){
  return Preferences.getInstance().getVariableType("preferenceName", value);
Example

Your full RobotPreferences.java should look like this

package frc.robot;

import edu.wpi.first.wpilibj.Preferences;

/**
* Add your docs here.
*/
public class RobotPreferences {
      // Drivetrain
      /**
      * Default value is 1.0
      */
      public static double driveEncoderCountsPerFoot() {
        return Preferences.getInstance().getDouble("driveEncoderCountsPerFoot", 1.0);
      }

}

Creating getDriveEncoderDistance Method#

  • We will use this RobotPreference to help us create a method that can keep track of the distance our robot has driven in inches

1) Create a method called getDriveEncoderDistance inside of Drivetrain

2) Inside type:

return (getDriveEncoderCount() / RobotPreferences.driveEncoderCountsPerFoot()) * 12;
  • This will divide the current encoder count by however many counts there are in a foot then multiply that number by 12 to give us the encoder distance in inches

Note

You may need to invert this value if your encoder counts backward when the robot is driving forward

Example

The code you typed should be this

public double getDriveEncoderDistance() {
 return (getDriveEncoderCount() / RobotPreferences.driveEncoderCountsPerFoot()) * 12;
}

3) Add the method to the update method in Telemetry

Using RobotPreferences#

  • After deploying the code to your robot, open Elastic from the Driver Station.
  • In the top menu go to File → Add Widget (or look in the left-side widget panel) and find the Robot Preferences widget, then drag it onto a tab.
  • Alternatively, right-click on an empty area of a tab and select Add Widget → Robot Preferences.

Once the widget is visible:

  • Click the + (Add) button inside the widget.
  • A dialog will appear. Enter the key name (the string you passed to Preferences.getInstance(), e.g. "driveEncoderCountsPerFoot") and select the matching type (Number for doubles and ints, String for text, Boolean for true/false).
  • The preference will appear in the widget with its default value.
  • Double-click the value field next to a preference to edit it — changes take effect immediately on the running robot without redeploying.
  • If you double click on the preference value you will notice that you can change its value
  • If you change a preference value it will update immediately

Tip

If you want to save your robot preference values that you've changed make sure you hardcode them in RobotPreferences.java later or take a picture if you want to use them again later

Measuring Distance Using Encoders#

  • Right now the encoders tell us distance in terms of encoder counts
  • We will use our driveEncoderCountsPerFoot preference to save how many counts there are when the robot drives 1 foot

1) Move the wheel on your robot with the Drivetrain encoder attached 1 foot or drive your robot 1 foot

2) Read how many counts your encoder has in the Drive Encoder Count window

  • If you want to measure again press the Reset Drive Encoder command button to reset the Drivetrain encoder count

3) Change the value of driveEncoderCountsPerFoot in the widget to this number

4) Reset the Drivetrain encoder and move the wheel 1 foot or drive the robot 1 foot again

5) Make sure your Drive Encoder Distance window reads approximately 12 (this is in inches)

  • If not repeat these steps again

6) Save your RobotPreferences widget with this value

7) Hardcode this value in RobotPreferences.java in the driveEncoderCountsPerFoot method incase you cannot recover your RobotPreferences save