> 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/mechanisms/double-jointed-arm.md).

# DoubleJointedArm

**Package:** `yams.mechanisms.positional`\
**Extends:** `SmartPositionalMechanism`

`DoubleJointedArm` controls a serial two-joint arm: a lower link (shoulder) and an upper link (elbow). Each joint has its own `SmartMotorController`. The class provides both direct joint angle control and inverse kinematics to a Cartesian target.

**See also:** [ArmConfig](/api-reference/java-reference/config/arm-config.md)

***

## Constructor

```java
DoubleJointedArm(
    ArmConfig lowerConfig, SmartMotorController lowerSMC,
    ArmConfig upperConfig, SmartMotorController upperSMC
)
```

| Parameter     | Type                   | Description                                                        |
| ------------- | ---------------------- | ------------------------------------------------------------------ |
| `lowerConfig` | `ArmConfig`            | Configuration for the lower (shoulder) joint, including arm length |
| `lowerSMC`    | `SmartMotorController` | Motor controller for the lower joint                               |
| `upperConfig` | `ArmConfig`            | Configuration for the upper (elbow) joint, including arm length    |
| `upperSMC`    | `SmartMotorController` | Motor controller for the upper joint                               |

***

## State Queries

### `getLowerAngle()`

```java
public Angle getLowerAngle()
```

Returns the current lower joint (shoulder) angle.

**Returns:** `Angle`

***

### `getUpperAngle()`

```java
public Angle getUpperAngle()
```

Returns the current upper joint (elbow) angle.

**Returns:** `Angle`

***

### `getPosition()`

```java
public Translation2d getPosition()
```

Returns the current end-effector position in Cartesian space, computed from forward kinematics.

**Returns:** `Translation2d`

***

## Command Factories

### `setAngle(Angle lower, Angle upper)`

```java
public Command setAngle(Angle lower, Angle upper)
```

Drives both joints to the target angles simultaneously. Runs indefinitely until interrupted.

| Name    | Type    | Description                                 |
| ------- | ------- | ------------------------------------------- |
| `lower` | `Angle` | Target angle for the lower (shoulder) joint |
| `upper` | `Angle` | Target angle for the upper (elbow) joint    |

**Returns:** `Command`: runs until interrupted.

***

### `setPosition(Translation2d target, boolean allowMirror)`

```java
public Command setPosition(Translation2d target, boolean allowMirror)
```

Uses inverse kinematics to move the end-effector to `target` in Cartesian space. Runs indefinitely until interrupted.

| Name          | Type            | Description                                                                                                                             |
| ------------- | --------------- | --------------------------------------------------------------------------------------------------------------------------------------- |
| `target`      | `Translation2d` | Desired end-effector position                                                                                                           |
| `allowMirror` | `boolean`       | When `true`, the IK solver may choose either elbow-up or elbow-down configuration; when `false`, only the primary configuration is used |

**Returns:** `Command`: runs until interrupted.

***

### `runTo(Translation2d target, boolean allowMirror, Distance tolerance)`

```java
public Command runTo(Translation2d target, boolean allowMirror, Distance tolerance)
```

Uses inverse kinematics to move to `target`, ending when the end-effector is within `tolerance` of the target position.

| Name          | Type            | Description                                                                                                                             |
| ------------- | --------------- | --------------------------------------------------------------------------------------------------------------------------------------- |
| `target`      | `Translation2d` | Desired end-effector position                                                                                                           |
| `allowMirror` | `boolean`       | When `true`, the IK solver may choose either elbow-up or elbow-down configuration; when `false`, only the primary configuration is used |
| `tolerance`   | `Distance`      | Maximum acceptable distance between current and target position for the command to end                                                  |

**Returns:** `Command`: ends when within tolerance.

***

## Triggers

### `isNear(Translation2d position, Distance tolerance)`

```java
public Trigger isNear(Translation2d position, Distance tolerance)
```

True when the end-effector is within `tolerance` of `position`.

| Name        | Type            | Description                     |
| ----------- | --------------- | ------------------------------- |
| `position`  | `Translation2d` | Reference end-effector position |
| `tolerance` | `Distance`      | Maximum acceptable distance     |

**Returns:** `Trigger`

***

### `max()`

```java
public Trigger max()
```

True when either joint is at its upper hard limit.

**Returns:** `Trigger`

***

### `min()`

```java
public Trigger min()
```

True when either joint is at its lower hard limit.

**Returns:** `Trigger`

***

## Visualization & Simulation

The following methods share the same interface as the single-joint `Arm` class.

| Method                   | Returns                | Description                                                                          |
| ------------------------ | ---------------------- | ------------------------------------------------------------------------------------ |
| `simIterate()`           | `void`                 | Advances joint physics simulation one loop iteration; call in `simulationPeriodic()` |
| `updateTelemetry()`      | `void`                 | Publishes current joint angles and end-effector position to NetworkTables            |
| `visualizationUpdate()`  | `void`                 | Updates the Mechanism2d visualization                                                |
| `getMechanismLigament()` | `MechanismLigament2d`  | Returns the Mechanism2d ligament for the arm segments                                |
| `getMechanismRoot()`     | `MechanismRoot2d`      | Returns the Mechanism2d root for the arm                                             |
| `getMotor()`             | `SmartMotorController` | Returns the lower joint motor controller                                             |

***

## Examples

{% @github-files/github-code-block url="<https://github.com/Yet-Another-Software-Suite/YAMS/blob/master/examples/double_jointed_arm/java/frc/robot/subsystems/DoubleJointedArmSubsystem.java#L92-L145>" %}