# `BB.IK.TestRobots.PlanarBaseArm`
[🔗](https://github.com/beam-bots/bb_ik_fabrik/blob/main/test/support/test_robots.ex#L10)

A 2-DOF arm on a planar base, for solving chains that contain a multi-DoF joint.

Structure:
- odom
  - base (planar, Z surface normal) — three degrees of freedom
    - base_link
      - shoulder_joint (revolute, Z-axis)
        - link1
          - elbow_joint (revolute, Z-axis, 0.25m out)
            - link2
              - tip_joint (fixed, 0.25m offset)
                - tip

The arm alone reaches 0.5m from the base, so a target further out is only
reachable by driving the base as well — which is what makes this a test of the
planar joint rather than of the arm. Two revolute joints rather than one, so
the arm's own workspace is a disc rather than a circle and a chain scoped below
the base is still a solvable problem.

# `child_spec`

```elixir
@spec child_spec(Keyword.t()) :: Supervisor.child_spec()
```

Returns a child specification for starting this robot under a supervisor.

# `robot`

```elixir
@spec robot() :: BB.Robot.t()
```

Returns the optimised robot representation.

This struct is built at compile-time from the DSL definition and contains:
- All physical values converted to SI base units (floats)
- Flat maps for O(1) lookup of links, joints, sensors, and actuators
- Pre-computed topology metadata for efficient traversal

## Examples

    robot = Elixir.BB.IK.TestRobots.PlanarBaseArm.robot()
    {:ok, link} = BB.Robot.get_link(robot, :base_link)
    {:ok, joint} = BB.Robot.get_joint(robot, :shoulder)

# `start_link`

```elixir
@spec start_link(Keyword.t()) :: Supervisor.on_start()
```

Starts the robot's supervision tree.

## Options

All options are passed through to sensor and actuator child processes.

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*Consult [api-reference.md](api-reference.md) for complete listing*