> For the complete documentation index, see [llms.txt](https://yams.yassrobotics.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://yams.yassrobotics.com/api-reference/java-reference/math/lqr-controller.md).

# LQRController

**Package:** `yams.math`

`LQRController` wraps a `LinearSystemLoop` and provides type-safe `calculate()` overloads for different mechanism types.

## Constructors

```java
LQRController(LQRConfig config)   // Preferred
LQRController(LQRType type, LinearSystemLoop<?, ?, ?> loop, Time period)
```

## Methods

| Method                                              | Returns | Description                                                      |
| --------------------------------------------------- | ------- | ---------------------------------------------------------------- |
| `reset(Angle angle, AngularVelocity velocity)`      | `void`  | Resets the observer for arm or flywheel systems. Call on enable. |
| `reset(Distance distance, LinearVelocity velocity)` | `void`  | Resets the observer for elevator systems.                        |
| `updateConfig(LQRConfig config)`                    | `void`  | Replaces the underlying system loop at runtime.                  |

## Calculate Overloads

| Method                                                                     | For Mechanism                   | Returns   |
| -------------------------------------------------------------------------- | ------------------------------- | --------- |
| `calculate(Angle measured, Angle position, AngularVelocity velocity)`      | Arm                             | `Voltage` |
| `calculate(Distance measured, Distance position, LinearVelocity velocity)` | Elevator                        | `Voltage` |
| `calculate(AngularVelocity measured, AngularVelocity velocity)`            | Flywheel                        | `Voltage` |
| `calculate(LinearVelocity measured, LinearVelocity velocity)`              | Flywheel (linear surface speed) | `Voltage` |

## Getters

| Method        | Returns               | Description                                                                                     |
| ------------- | --------------------- | ----------------------------------------------------------------------------------------------- |
| `getType()`   | `LQRType`             | The mechanism type this controller was configured for.                                          |
| `getConfig()` | `Optional<LQRConfig>` | The `LQRConfig` used to construct this controller, or empty if constructed from raw components. |

## Usage with SmartMotorControllerConfig

```java
LQRConfig lqrCfg = new LQRConfig(DCMotor.getNEO(1), gearing, moi)
    .withArm(Degrees.of(5), DegreesPerSecond.of(10),
             Degrees.of(1), DegreesPerSecond.of(5), Degrees.of(0.5))
    .withControlEffort(Volts.of(12));

SmartMotorControllerConfig motorConfig = new SmartMotorControllerConfig()
    .withLQRController(lqrCfg);
```

## See Also

* [LQRConfig](/api-reference/java-reference/math/lqr-config.md)
* [C++ LQRController](/api-reference/c++-reference/math/lqr-controller.md)