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Arm Control

Until I am able to properly document the wiring I do not recommend working on this. Also, we've been told that the arm will be extra points and not required

Getting Started

It's assumed you already have built and properly wired the romi arm. It is also expected that you have a working command scheduler system. Also, make sure you've setup the stuff in the web config UI, however we will go over the web UI config in this doc.

Creating the subsystem

Like with the drive train, we need to make a subsystem that allows you to control the servos in the arm, if you've been able to drive your romi, you probably have a file structure that looks a bit like this.

- commands
- sensors
- subsystems
 - Drivetrain.java
- Constants.java
- main.java
- Robot.java
- RobotContainer.java

However we are missing the ability to control the external IO. Our arm is wired to the external IO which is what allows us to send signals and thus control it. However without the subsystem there is no code that defines that they exist or how the signals should be sent. To start, I recommend copying over the drivetrain subsystem and then removing everything but the basic boilerplate.

Todo: define "basic boilerplate" better
- commands
- sensors
- subsystems
 - Drivetrain.java
 + ExternalIO.java
- Constants.java
- main.java
- Robot.java
- RobotContainer.java

To save some time, these should be the main imports that you end up needing, along with the boilerplate imports that you already have in your file.

import edu.wpi.first.wpilibj.AnalogInput;
import edu.wpi.first.wpilibj.DigitalInput;
import edu.wpi.first.wpilibj.DigitalOutput;
import edu.wpi.first.wpilibj.DriverStation;
import edu.wpi.first.wpilibj.Servo;

Now we need to define what ports to use, this table shows the channel assigned to each EXT channel based on its configuration. This configuration must be performed using the web interface to the Romi. In the constructor, you must specify the configuration of each channel. This MUST match the configuration created using the web interface. (View Docs)

When wiring make sure that the black wire is on the pins marked as ground, and you can ignore the green one. I recommend finding some way to cable manage as it's easy for wires to get tangled in the wheel.

⚠️ I can NOT stress this enough, make sure this is 100% right
Channel DIO PWM Analog In
EXT0 8 2 -
EXT1 9 3 0
EXT2 10 4 1
EXT4 11 5 2
EXT5 12 6 3

After this, you have to code the subsystem, not much else to say. Here's bit of our code. You'd have to extend the switch statement and add one for each EXT that you are going to need. What you're trying to do is define what "settings" to use based on what EXT is being called. As you can see, we have a switch statement for each EXT, and then depending on what mode (DIO,PWM,AIN) is being requested, it defines what "settings" should be used. There of course is other ways to do this however, this is a pretty good solution and you can of course change it down the road if need be.

switch (ext0) {
  case DIO:
    if (modes[n++] == ChannelMode.INPUT)
      m_input8 = new DigitalInput(8);
    else
      m_output8 = new DigitalOutput(8);
    break;
    case PWM: m_servo2 = new Servo(2); break;
    /* i dont know if this derverstation error works 
     * !!!!!!!!!!!
     * this is only for ext0 because it does support analog in!!! Do not do this anywhere else!!!
     * !!!!!!!!!!!
     */
    case AIN: DriverStation.reportError("Cannot configure EXT0 as Analog Input", true); break;
}
switch (ext1) {
  case DIO:
    if (modes[n++] == ChannelMode.INPUT)
      m_input9 = new DigitalInput(9);
    else
      m_output9 = new DigitalOutput(9);
    break;
    case PWM:   m_servo3 = new Servo(3); break;
    case AIN:   m_analogInput0 = new AnalogInput(0); break;
}

Making the command

A subsystem is useless if it never gets used. Just make a new file in the commands folder and copy the biolerplate from some other command, you'll want to import the subsystem first.

- commands
 - SuperSecretCommands.java
 + ArmCommand.java
- sensors
- subsystems
- Constants.java
- main.java
- Robot.java
- RobotContainer.java

import frc.robot.subsystems.ExternalIO;

And from there you need to make your suppliers. Note: I am use jaws open/closed as a boolean here, for most people it makes sense to make it a double like the rest of them. So make sure to not blindly copy and paste code.

Make sure that you import the Java Supplier function as well.

import java.util.function.Supplier;
private final ExternalIO m_externalIO;
private final Supplier<Double> m_liftSupplier;
private final Supplier<Double> m_tiltSupplier;
private final Supplier<Boolean> m_jawsSupplier;

For the arm command method, just make sure you pass all of the suppliers and requirements for it. In the execute method we actually are using that subsystem we made to control the servo motors, my code ended up something like this.

@Override
public void execute() {
 // this is a boolean because its prob more simple when coding and we never need to have it half open or smth
 m_externalIO.m_servo2.set(m_jawsSupplier.get() ? 1.0 : 0.0);
 m_externalIO.m_servo3.set(m_liftSupplier.get());
 m_externalIO.m_servo4.set(m_tiltSupplier.get());
}

For isFinished you can just make it return false. isFinished() is a method that the command scheduler calls to determine whether or not the command should end. When isFinished() returns false, it is perpetual: it does not end (unless it is cancelled because another command that is scheduled requires the same subsystem.)
(Thank you David Muchow for this)

At this point you have a command that work's something like your arcade drive command. You'll have to make a second command that interfaces into this. Once you've made the second command you can use it in any schedule like any other command. I'll talk more about this later.