# `BB.Igniter.Transmission`
[🔗](https://github.com/beam-bots/bb/blob/main/lib/bb/igniter/transmission.ex#L6)

Shared Igniter upgrade logic for lifting actuator-driver `reverse?` options
into per-attachment `transmission` blocks.

Used by the upgrade tasks in each driver package (Feetech, Robotis,
PCA9685, Pigpio). The transformation is:

Before:

    joint :shoulder do
      type :revolute
      limit do
        lower(~u(-10 degree))
        upper(~u(190 degree))
        effort(~u(10 newton_meter))
        velocity(~u(180 degree_per_second))
      end
      actuator :motor, {BB.Servo.Feetech.Actuator,
        servo_id: 1, controller: :feetech, reverse?: true
      }
      link :arm
    end

After (with `lift_offset?: true`):

    joint :shoulder do
      type :revolute
      limit do
        lower(~u(-10 degree))
        upper(~u(190 degree))
        effort(~u(10 newton_meter))
        velocity(~u(180 degree_per_second))
      end
      actuator :motor, {BB.Servo.Feetech.Actuator,
        servo_id: 1, controller: :feetech
      } do
        transmission do
          offset(~u(90.0 degree))
          reversed? true
        end
      end
      link :arm
    end

The `offset` is computed as `(lower + upper) / 2`, preserving the
auto-centering behaviour the Feetech/Robotis drivers used to derive
internally. `lift_offset?: false` skips the offset computation — used by
the PCA9685 and Pigpio upgraders, which never auto-centered.

Also handles re-running on code that was previously upgraded to put the
`transmission` block at the joint level: such blocks are removed and
merged into the actuator's own block.

# `lift_reverse_question`

```elixir
@spec lift_reverse_question(Igniter.t(), module(), keyword()) :: Igniter.t()
```

Lift `reverse?` opts on the given driver's actuator child-specs into
per-attachment `transmission` blocks across the project.

Options:

  * `:lift_offset?` (default `false`) — when true, also compute and emit
    an `offset(...)` value derived from the enclosing joint's `lower` and
    `upper` limits, preserving the implicit centering that Feetech and
    Robotis drivers used to do internally.

---

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