README.md

FRC Project 02

In this project, you are going to select a partner to be able to work with, and both of you will be creating an algorithm that does the following:

• The robot must be able to drive forward straightly at 0.3 speed for a given distance. For example, you can create a method called public void goStraight(double distance) where the function makes the robot go straight until the encoder values for both the sides have reached the value of distance.

Encoders

For this project, encoders are sensors that measure how much degrees a wheel has been rotated. So for example, if a wheel has gone through a full 360-degree rotation, the value of the encoder would be 360. If the wheel were stationary for the whole period, then the value of the encoder would be 0. Encoders are very useful to make sure our robot travels accurately autonomously, as they enable us to make turns accurate, and they also help us drive straight.

The way we use encoders in our program is by creating an Encoders class and making two objects: one object for the wheels on the left of the robot, and one object for the wheels for the right of the robot. In this case, the leftEncoder object represents the encoder on the left wheels of the robot, and the rightEncoder object represents the encoder on the right wheels of the robot:

import edu.wpi.first.wpilibj.Encoder;
public class Encoders 
{
	Encoder leftEncoder = new Encoder(0,1, false, Encoder.EncodingType.k4X);
	Encoder rightEncoder = new Encoder(4,5, false, Encoder.EncodingType.k4X);
}

After declaring the leftEncoder and rightEncoder objects in the Encoders class, we can use them in the Robot class by creating an Encoders Object:

public class Robot extends IterativeRobot 
{
	Encoders encodersObject;
	public void robotInit() 
	{
		encodersObject = new Encoders();
	}
}

The way we obtain the encoder values from each Encoder object is by calling the get() function. The following is the code on how to get encoder values from the Encoder class and how to use that in the Robot class assuming that you have already created both the leftEncoder and the rightEncoder objects in the Encoders class and that you have created the encodersObject object in the Robot class:

• Encoders.java

public class Encoders 
{
	//This function returns the value of the right encoder
	public double getRightEncoder()
	{
		return rightEncoder.get();
	}
  
	//This function returns the value of the left encoder
	public double getLeftEncoder()
	{
		return leftEncoder.get();
	}
}

• Robot.java

public class Robot extends IterativeRobot 
{	
	public void autonomousPeriodic() 
	{
		double leftEncoderValue = encodersObject.getLeftEncoder();
		double rightEncoderValue = encodersObject.getRightEncoder();
	}
}

Note: In our robot, the left encoder is not facing the correct direction, and thus we negative the value:

public double getLeftEncoder()
{
	return -leftEncoder.get();
}

We can also set encoder values to 0 by calling the reset() function:

• Encoders.java

public class Encoders 
{
	//This function sets the value of both the encoders to 0
	public void resetEncoders()
	{
		rightEncoder.reset();
		leftEncoder.reset();
	}
}

• Robot.java

public class Robot extends IterativeRobot 
{	
	public void autonomousInit() 
	{
		encodersObject.resetEncoders();
	}
}

Using Encoders With Motors

The way we would use motors with encoders is key to completing this project. Here are some examples assuming you have created the encodersObject object and have declared two static motor objects in the Motors class.

• Moving the left motor forward until it has reached one full rotation:

public void autonomousPeriodic() 
{
	if(encodersObject.getLeftEncoder()<360)
	{
		Motors.leftMotor.set(.4);
	}
	else
	{
		Motors.leftMotor.set(0);
	}
}

• Moving the right motor backward until it has reached one full rotation (towards the back):

public void autonomousPeriodic() 
{
	if(encodersObject.getRightEncoder()>-360)
	{
		Motors.rightMotor.set(.4); //this is positive because remember the right motor is facing in the negative direction (Read FRC Project_01)
	}
	else
	{
		Motors.rightMotor.set(0);
	}
}

Extra Notes for Completing the Exercise

• To make the robot straight, you would have to compare both the values of the getLeftEncoder() and getRightEncoder, and the motor values of each motor should depend on the difference of both the encoder values.
• You would have to call the resetEncoders() function in the autonomousInit(), so that encoder values reset every time, you start the robot.
• Use the speed variable in the Robot.java file. That should be the standard speed the robot moves at.
• If you would like to learn more about the Encoder class created by FIRST, please read the about the Encoder class from the FRC Java API.

Good luck on the project!