Motor Programming

[LFRobotics]

Okay - I want to have a motor that - when button 4 is pressed on the joystick the motor moves in one direction until he button is released - when button 5 is pressed the motor moves in the other direction until the button is released.

Here is the code I wrote:

Subsystem for the "ForkMotor":

package edu.wpi.first.LFRobot2014.subsystems;

import edu.wpi.first.LFRobot2014.RobotMap;
import edu.wpi.first.wpilibj.Jaguar;
import edu.wpi.first.wpilibj.SpeedController;
import edu.wpi.first.wpilibj.command.Subsystem;

/**
*
* @author FrankyMonezz
*/
public class ForkMotor extends Subsystem {
// Put methods for controlling this subsystem
// here. Call these from Commands.
SpeedController motor = new Jaguar(RobotMap.ForkMotorPort);

public void initDefaultCommand() {
// Set the default command for a subsystem here.
//setDefaultCommand(new MySpecialCommand());
}

public void up() {
motor.set(1);
}

public void down() {
motor.set(-1);
}
}


Command to move motor in one direction.

package edu.wpi.first.LFRobot2014.commands;


/**
*
* @author FrankyMonezz
*/
public class LiftForks extends CommandBase {

public LiftForks() {
// Use requires() here to declare subsystem dependencies
// eg. requires(chassis);
requires(ForkMotor);
}

// Called just before this Command runs the first time
protected void initialize() {
}

// Called repeatedly when this Command is scheduled to run
protected void execute() {
ForkMotor.up();
}

// Make this return true when this Command no longer needs to run execute()
protected boolean isFinished() {
return false;
}

// Called once after isFinished returns true
protected void end() {
}

// Called when another command which requires one or more of the same
// subsystems is scheduled to run
protected void interrupted() {
}
}

Command to move the motor in the other direction:

package edu.wpi.first.LFRobot2014.commands;

/**
*
* @author FrankyMonezz
*/
public class LowerForks extends CommandBase {

public LowerForks() {
// Use requires() here to declare subsystem dependencies
// eg. requires(chassis);
requires(ForkMotor);
}

// Called just before this Command runs the first time
protected void initialize() {
}

// Called repeatedly when this Command is scheduled to run
protected void execute() {
ForkMotor.down();
}

// Make this return true when this Command no longer needs to run execute()
protected boolean isFinished() {
return false;
}

// Called once after isFinished returns true
protected void end() {
}

// Called when another command which requires one or more of the same
// subsystems is scheduled to run
protected void interrupted() {
}
}

All ports are already set correctly in RobotMap and buttons are correctly assigned using whileHeld() in OI - noting this will the above code work?

THANKS for the help!

[Domenic Rodriguez]

In the constructor for each of your commands, you should pass the instance variable from CommandBase instead of the Subsystem class name:


public LiftForks() {
// Use requires() here to declare subsystem dependencies
// eg. requires(chassis);
requires(forkMotor); // or whatever you named the instance variable
}

instead of

public LiftForks() {
// Use requires() here to declare subsystem dependencies
// eg. requires(chassis);
requries(ForkMotor);
}


Another potential issue is that you don't appear to ever be stopping the motor. Even when the commands end, the motor will continue to spin (at least until the motor safety kicks in). One way to solve this issue would be to add a stop() method to your Subsystem, and then calling that method in each command's end() method.

[LFRobotics]

My Subsystem name is the same as the name in commandbase.

I did not end the command because I will use the button.whileHeld(new command) and should it shut the motor/command down when I release the button so I don't have to tell it to stop. Right now I am not having any issues with it - I haven't been able to test it though because I am having DS issues.

THANKS!

[Domenic Rodriguez]

My Subsystem name is the same as the name in commandbase.

I would recommend against using the same capitalization for the class name and the instance variable; it creates ambiguity as to which you are referring to. Common practice is to use headless camel case for variable names:

ForkMotor forkMotor = new ForkMotor();


I did not end the command because I will use the button.whileHeld(new command) and should it shut the motor/command down when I release the button so I don't have to tell it to stop...

Correct me if I'm wrong (it's been a while since I've worked with the command-based robot template), but just because your command is canceled doesn't mean the motor will shut off by itself. You need to explicitly tell it to stop moving with "motor.set(0)", otherwise it will just keep moving at the previous value it received (in your case either 1.0 or -1.0). This is why I recommend adding a ForkMotor#stop() method that get's called when your commands exit:


public class ForkMotor extends Subsystem {
....
// Existing subsystem code
...

public void stop() {
motor.set(0.0);
}
}


public class LiftForks extends CommandBase {
public LiftForks() {
// Use requires() here to declare subsystem dependencies
// eg. requires(chassis);
requires(ForkMotor);
}

// Called just before this Command runs the first time
protected void initialize() {
}

// Called repeatedly when this Command is scheduled to run
protected void execute() {
ForkMotor.up();
}

// Make this return true when this Command no longer needs to run execute()
protected boolean isFinished() {
return false;
}

// Called once after isFinished returns true
protected void end() {
ForkMotor.stop();
}

// Called when another command which requires one or more of the same
// subsystems is scheduled to run
protected void interrupted() {
end();
}
}

[LFRobotics]

Okay - yeah your right - THANKS a ton!