> 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/exponential-profile-pid-controller.md).

# ExponentialProfilePIDController

**Package:** `yams.math`

`ExponentialProfilePIDController` wraps a `PIDController` with an `ExponentialProfile` to produce smooth, physically-motivated setpoints. The exponential profile models a first-order system response; unlike the trapezoidal profile, it does not have a constant-velocity segment, so it tends to feel more natural for arm and flywheel mechanisms.

## Constructors

```java
ExponentialProfilePIDController(PIDController controller, ExponentialProfile.Constraints constraints)
ExponentialProfilePIDController(double kP, double kI, double kD, ExponentialProfile.Constraints constraints)
```

## Constraints Factory Methods

These static methods produce `ExponentialProfile.Constraints` suited to specific mechanism types:

| Method                                                                                                                                    | Description                                                    |
| ----------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------- |
| `static Constraints createElevatorConstraints(Voltage maxVolts, DCMotor motor, Mass mass, Distance drumRadius, MechanismGearing gearing)` | Constraints for an elevator (linear system).                   |
| `static Constraints createArmConstraints(Voltage maxVolts, DCMotor motor, MomentOfInertia moi, MechanismGearing gearing)`                 | Constraints for an arm using MOI directly.                     |
| `static Constraints createArmConstraints(Voltage maxVolts, DCMotor motor, Mass mass, Distance length, MechanismGearing gearing)`          | Constraints for an arm; computes MOI from mass and length.     |
| `static Constraints createFlywheelConstraints(Voltage maxVolts, DCMotor motor, MomentOfInertia moi, MechanismGearing gearing)`            | Constraints for a flywheel using MOI.                          |
| `static Constraints createFlywheelConstraints(Voltage maxVolts, DCMotor motor, Mass mass, Distance radius, MechanismGearing gearing)`     | Constraints for a flywheel; computes MOI from mass and radius. |
| `static Constraints createConstraints(Voltage maxVolts, AngularVelocity maxVelocity, AngularAcceleration maxAcceleration)`                | Generic constraints from physical limits.                      |

## Control Methods

| Method                                                                                    | Returns  | Description                                                                          |
| ----------------------------------------------------------------------------------------- | -------- | ------------------------------------------------------------------------------------ |
| `calculate(double measurementPosition, double setpointPosition)`                          | `double` | Advances the profile by one timestep and returns PID output. Uses FPGA clock for dt. |
| `calculate(double measurementPosition, double setpointVelocity, double setpointPosition)` | `double` | Same, but also provides an explicit velocity setpoint for feedforward.               |
| `reset(State measurement)`                                                                | `void`   | Resets the profile and PID to the given state. Call on enable.                       |
| `reset(double position, double velocity)`                                                 | `void`   | Resets with position and velocity scalars.                                           |

## State Query Methods

| Method                         | Returns                 | Description                                                                   |
| ------------------------------ | ----------------------- | ----------------------------------------------------------------------------- |
| `atSetpoint()`                 | `boolean`               | True when the measurement is within the configured tolerance of the setpoint. |
| `getSetpoint()`                | `double`                | The current profile position target.                                          |
| `getCurrentState()`            | `State`                 | The current profile state (position + velocity).                              |
| `getCurrentAngle()`            | `Angle`                 | Current profile position as an `Angle`.                                       |
| `getNextAngle()`               | `Angle`                 | Next profile position (one timestep ahead).                                   |
| `getCurrentVelocitySetpoint()` | `AngularVelocity`       | Current velocity setpoint from the profile.                                   |
| `getNextVelocitySetpoint()`    | `AngularVelocity`       | Next velocity setpoint.                                                       |
| `getNextState()`               | `Optional<State>`       | The next profile state, or empty if not yet calculated.                       |
| `getConstraints()`             | `Optional<Constraints>` | The configured constraints, or empty.                                         |

## PID Tuning Methods

| Method                                                            | Description                                         |
| ----------------------------------------------------------------- | --------------------------------------------------- |
| `setTolerance(double tolerance)`                                  | Sets the position tolerance for `atSetpoint()`.     |
| `getPositionTolerance()`                                          | Returns the current tolerance.                      |
| `getP()`, `setP(double kP)`                                       | Proportional gain.                                  |
| `getI()`, `setI(double kI)`                                       | Integral gain.                                      |
| `getD()`, `setD(double kD)`                                       | Derivative gain.                                    |
| `setConstraints(Constraints constraints)`                         | Updates the profile constraints at runtime.         |
| `enableContinuousInput(double minimumInput, double maximumInput)` | Enables continuous input (for wrapping mechanisms). |

## Example

```java
ExponentialProfile.Constraints constraints =
    ExponentialProfilePIDController.createArmConstraints(
        Volts.of(12),
        DCMotor.getNEO(1),
        Kilograms.of(2), Meters.of(0.5),
        new MechanismGearing(GearBox.fromTeeth(14, 72))
    );

ExponentialProfilePIDController controller =
    new ExponentialProfilePIDController(0.5, 0.0, 0.0, constraints);
controller.setTolerance(0.05); // radians
```

## Examples

{% @github-files/github-code-block url="<https://github.com/Yet-Another-Software-Suite/YAMS/blob/master/examples/exponential_arm/java/frc/robot/subsystems/ExponentiallyProfiledArmSubsystem.java#L157-L171>" %}

{% @github-files/github-code-block url="<https://github.com/Yet-Another-Software-Suite/YAMS/blob/master/examples/exponential_elevator/java/frc/robot/subsystems/ExponentiallyProfiledElevatorSubsystem.java#L134-L146>" %}