> For the complete documentation index, see [llms.txt](https://yagsl.yassrobotics.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://yagsl.yassrobotics.com/how-to-guides/use-a-custom-gyro.md).

# Use a custom gyro

{% hint style="info" %}
If your gyro is one of the [supported types](/reference/hardware/gyroscopes.md#supported-gyroscope-types) (Pigeon 2, Canandgyro, NavX3-CAN), you don't need this page — just set `gyro.type` normally in `swervedrive.json`.
{% endhint %}

Use a `custom` gyro when your hardware isn't one the parser builds for you. The most common case is the older roboRIO SPI/I2C/USB-serial [Studica AHRS](https://www.studica.com/navx2-micro) (the classic NavX2) — only the CAN-based NavX3 is supported directly, so an AHRS on the MXP/SPI port needs this escape hatch. The same approach works for any other IMU, a simulated/composited heading source, or a heading fused from multiple sensors.

## 1. Set `gyro.type` to `custom`

In `swervedrive.json`, set the gyro's `type` to `custom`. The `id`/`canbus` fields are unused for a custom gyro (leave them at `0`/`""`), and — this is the part that catches people out — `gyroAxis` and `gyroInvert` are **also ignored**. The parser sees `custom` and skips gyro configuration entirely.

```json
{
  "gyro": { "type": "custom", "id": 0, "canbus": "" },
  "gyroAxis": "yaw",
  "gyroInvert": false,
  "modules": ["frontleft.json", "frontright.json", "backleft.json", "backright.json"]
}
```

## 2. Construct the gyro and supply it yourself

Because the parser never calls `SwerveDriveConfig.withGyro()` for a `custom` gyro, you call it yourself on the `SwerveDriveConfig` you build **before** handing it to `SwerveParser.createSwerveDrive(...)`. Everything else — modules, motor controllers, encoders — is still built normally from the rest of the JSON.

```java
import com.studica.frc.AHRS;
import static edu.wpi.first.units.Units.Degrees;

// Onboard MXP SPI port is the common mounting for a roboRIO AHRS.
private final AHRS gyro = new AHRS(AHRS.NavXComType.kMXP_SPI);

public SwerveDriveSubsystem() {
  SwerveDriveConfig cfg = new SwerveDriveConfig()
      .withSubsystem(this)
      .withTelemetry(TelemetryVerbosity.HIGH)
      .withGyro(() -> Degrees.of(gyro.getAngle()));

  drive = new SwerveParser(new File(Filesystem.getDeployDirectory(), "swerve/base"))
      .createSwerveDrive(cfg);
}
```

{% hint style="danger" %}
If you forget to call `withGyro()` before `createSwerveDrive()`, YAMS has no heading supplier to build the drive with — expect a `NoSuchElementException`/`RuntimeException` at startup, not a silent fallback.
{% endhint %}

## 3. Handle inversion yourself

Since `gyroInvert` is ignored, do any inversion directly in the `Supplier<Angle>` you pass to `withGyro()`, then call `withGyroInverted()` yourself to keep it in sync with anything else in YAMS that reads that flag:

```java
.withGyro(() -> Degrees.of(-gyro.getAngle())) // AHRS reports CW+; YAGSL/YAMS expect CCW+
.withGyroInverted(false)
```

## 4. Verify it

Follow the normal [gyro CCW+ check](/how-to-guides/determine-inversion.md#2-confirm-the-gyro-reads-ccw) — `Mechanisms/swerve/gyro` in NetworkTables should still populate and behave exactly like a parser-built gyro, since from YAMS's perspective a `Supplier<Angle>` is a `Supplier<Angle>` regardless of where it came from. If it increases while the robot rotates counter-clockwise, you're done; if not, negate the supplier as in step 3 rather than flipping `gyroInvert` (which, again, is ignored).

## Optional: angular velocity for skew correction

If you also want gyro-based angular-velocity skew correction (see [Swerve Drive Drift](/reference/swerve-drift-causes.md)), a `custom` gyro needs its angular velocity supplied the same way the heading was — the parser doesn't build this for you either, custom or not:

```java
.withGyroVelocity(() -> DegreesPerSecond.of(-gyro.getRate()))
.withGyroAngularVelocityScaleFactor(1.0)
```

{% hint style="warning" %}
`AHRS.getRate()` and `getAngle()` follow the same sign convention (both CW+ on Studica hardware) — if you negated one to get CCW+, negate the other too, or your skew correction will fight the heading it's supposed to be correcting.
{% endhint %}


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