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Spectrum 3847 operates several physical robots from the same codebase simultaneously throughout the season. Rather than maintaining separate code branches per robot, the codebase selects a Config object at startup based on which RoboRIO is running the code. Every subsystem-level difference — encoder offsets, attached mechanisms, and tuning constants — is encapsulated in that single config object.

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Why multiple configs exist

Different robots in the shop serve different purposes:
RobotConfig classPurpose
Final MachineFM2026Competition robot; all mechanisms attached
Practice MachinePM2026Practice chassis; matches FM hardware except hood
Experimental MachineXM2026Prototype testbed; subset of mechanisms attached
Alpha MachineAM2026Early-season prototype; minimal hardware
Photon Test ChassisPHOTON2026Vision and drivetrain development
Running identical code on all robots eliminates the risk of a configuration diverging between practice and competition.

​
How Rio.id resolves a config at startup

Rio is an enum in frc.spectrumLib. Each entry stores the RoboRIO serial number printed on the label on the back of the controller. On startup, Rio.checkID() reads the live serial number via RobotController.getSerialNumber() and looks it up in a static map. The result is stored in the public constant Rio.id.
Rio.java
public enum Rio {

    // 2026 Robots
    PHOTON2026("032B4BB3", true),
    PM_2026("0329AD07", true),
    // FM_2026("", true),

    // 2025 Robots
    FM_2025("0329F2D1", true),

    SIM("", true),
    UNKNOWN(null, true);

    // ...

    public static final Rio id = checkID();

    private static Rio checkID() {
        String serialNumber = RobotBase.isReal()
                ? RobotController.getSerialNumber()
                : "";

        if (IDs.containsKey(serialNumber)) {
            Rio id = IDs.get(serialNumber);
            rioIdAlert.setText("Rio: " + id.name());
            rioIdAlert.set(true);
            return id;
        }
        rioIdUnknown.set(true);
        return UNKNOWN;
    }
}
In simulation, getSerialNumber() is never called (it crashes via JNI in test environments). The serial number defaults to "", which matches the SIM entry. Robot’s constructor switches on Rio.id and constructs the matching config:
Robot.java
switch (Rio.id) {
    case PHOTON2026:
        config = new PHOTON2026();
        break;
    case PM_2026:
        config = new PM2026();
        break;
    default: // SIM and UNKNOWN
        config = new FM2026();
        break;
}
If a RoboRIO’s serial number is not registered in the Rio enum, Rio.id resolves to UNKNOWN, and the default branch of the switch selects FM2026. An error-level dashboard alert is raised so the discrepancy is immediately visible.

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Config class structure

All config classes extend Robot.Config, which declares one sub-config field per subsystem using default-constructed values.
Robot.java (inner class)
public static class Config {
    public SwerveConfig swerve = new SwerveConfig();
    public PilotConfig pilot = new PilotConfig();
    public OperatorConfig operator = new OperatorConfig();
    public FuelIntakeConfig fuelIntake = new FuelIntakeConfig();
    public IntakeExtensionConfig intakeExtension = new IntakeExtensionConfig();
    public IndexerTowerConfig indexerTower = new IndexerTowerConfig();
    public IndexerBedConfig indexerBed = new IndexerBedConfig();
    public LauncherConfig launcher = new LauncherConfig();
    public HoodConfig hood = new HoodConfig();
    public VisionConfig vision = new VisionConfig();
}
Each robot-specific class overrides only what differs. For example, FM2026 configures all encoder offsets and marks every mechanism as attached:
FM2026.java
public class FM2026 extends Config {

    public FM2026() {
        super();
        swerve.configEncoderOffsets(-0.163818359375, 0.24902, 0.2724609375, -0.31005859375);

        pilot.setAttached(true);
        operator.setAttached(true);
        fuelIntake.setAttached(true);
        intakeExtension.setAttached(true);
        launcher.setAttached(true);
        indexerTower.setAttached(true);
        indexerBed.setAttached(true);
        hood.setAttached(true);
    }
}

​
The setAttached() pattern

Each per-subsystem config class (e.g. LauncherConfig) extends Mechanism.Config, which carries an attached boolean field. setAttached(false) disables hardware initialization for that subsystem — no CAN messages are sent, no motor objects are created, and all sensor reads return 0. This makes it straightforward to express exactly which hardware a given robot carries. Compare FM2026 (all mechanisms attached) with AM2026 (alpha machine, fewer mechanisms):
AM2026.java
public class AM2026 extends Config {

    public AM2026() {
        super();
        swerve.configEncoderOffsets(0.289551, 0.394043, -0.203857, -0.039307);

        pilot.setAttached(true);
        operator.setAttached(true);
        fuelIntake.setAttached(false);
        intakeExtension.setAttached(false);
        indexerTower.setAttached(false);
        launcher.setAttached(false);
    }
}
XM2026 shows an intermediate case — the experimental machine has an intake and launcher but no intake extension:
XM2026.java
public class XM2026 extends Config {

    public XM2026() {
        super();
        swerve.configEncoderOffsets(
                0.1892089844 - 0.5,
                -0.2736816406 + 0.5,
                -0.404052734375 + 0.5,
                -0.478759765625 + 0.5);

        pilot.setAttached(true);
        operator.setAttached(true);
        fuelIntake.setAttached(true);
        intakeExtension.setAttached(false);
        launcher.setAttached(true);
        indexerTower.setAttached(true);
        indexerBed.setAttached(true);
    }
}

​
How to add a new robot configuration

1

Register the RoboRIO serial number

Add a new entry to the Rio enum in Rio.java. The serial number appears on the label on the back of the RoboRIO; add a leading zero as needed.
Rio.java
FM_2026("032CABCD", true),
2

Create a config class

Create a new class in frc/robot/configs/ that extends Robot.Config. Override encoder offsets and call setAttached() for each mechanism the robot carries.
FM2026.java
public class FM2026 extends Config {
    public FM2026() {
        super();
        swerve.configEncoderOffsets(-0.163818359375, 0.24902, 0.2724609375, -0.31005859375);
        fuelIntake.setAttached(true);
        launcher.setAttached(true);
        // ...
    }
}
3

Wire the config in Robot.java

Add a case for the new Rio enum value in the switch block inside Robot’s constructor.
Robot.java
case FM_2026:
    config = new FM2026();
    break;
The RoboRIO serial number can change after reflashing the controller firmware. If a robot starts resolving to UNKNOWN after a reflash, re-read the serial number from RobotController.getSerialNumber() via the driver station console and update the Rio enum entry.

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