> ## Documentation Index
> Fetch the complete documentation index at: https://bedrockdynamics.studio/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Drone (ArduPilot)

> ArduPilot-based quadcopter with GUIDED mode velocity control and 4-channel WASM interface.

## Simulation Container

```bash theme={null}
docker pull bedrockdynamics/substrate-sim:ardupilot-gazebo
```

The container bundles ArduPilot SITL, Gazebo Harmonic, and the MAVLink gRPC bridge.

| Port | Protocol | Purpose                                                   |
| ---- | -------- | --------------------------------------------------------- |
| 9090 | gRPC     | ros2-bridge (telemetry streaming + MAVLink command relay) |

## Differences from PX4

ArduPilot and PX4 are both MAVLink-based autopilots, but they differ in several ways that affect the bridge implementation:

| Aspect                | PX4                                                | ArduPilot                                                  |
| --------------------- | -------------------------------------------------- | ---------------------------------------------------------- |
| Velocity control mode | OFFBOARD                                           | GUIDED                                                     |
| Mode switching        | `COMMAND_LONG` with `MAV_CMD_DO_SET_MODE`          | `SET_MODE` message with ArduPilot mode numbers             |
| MAVLink dialect       | Standard MAVLink 2                                 | `ardupilotmega` dialect with extra messages                |
| Setpoint message      | `SET_POSITION_TARGET_LOCAL_NED`                    | `SET_POSITION_TARGET_LOCAL_NED` (same)                     |
| Arming                | `COMMAND_LONG` with `MAV_CMD_COMPONENT_ARM_DISARM` | Same, but may require arming checks to be disabled in SITL |

The flight sequence is similar but uses GUIDED mode instead of OFFBOARD:

<Steps>
  <Step title="ARM">
    Send the arm command. ArduPilot enables the motors.
  </Step>

  <Step title="TAKEOFF">
    Command takeoff. ArduPilot handles the climb in its current mode.
  </Step>

  <Step title="GUIDED">
    Switch to GUIDED mode. ArduPilot accepts external velocity setpoints.
  </Step>

  <Step title="Velocity Control">
    WASM controllers write body velocity commands at 100Hz. The bridge relays these as MAVLink setpoint messages.
  </Step>

  <Step title="LAND">
    Switch to LAND mode. ArduPilot handles descent and motor disarm.
  </Step>
</Steps>

## WASM Channels

ArduPilot drones use the same `ChannelManifest::quadcopter()` manifest as PX4 drones — 4 body velocity command channels and 4 position state channels at 100Hz.

### Command Channels (4)

| Index | Name              | Unit  | Limits        |
| ----- | ----------------- | ----- | ------------- |
| 0     | `body/velocity.x` | m/s   | -5.0 to 5.0   |
| 1     | `body/velocity.y` | m/s   | -5.0 to 5.0   |
| 2     | `body/velocity.z` | m/s   | -3.0 to 3.0   |
| 3     | `body/yaw_rate`   | rad/s | -pi/2 to pi/2 |

### State Channels (4)

| Index | Name              | Unit | Type     |
| ----- | ----------------- | ---- | -------- |
| 0     | `body/position.x` | m    | Position |
| 1     | `body/position.y` | m    | Position |
| 2     | `body/position.z` | m    | Position |
| 3     | `body/yaw`        | rad  | Position |

The NED frame negation applies here too — the bridge negates `vz` so that positive values in the WASM controller mean "go up."

<Warning>
  ArduPilot support is less tested than PX4. The SITL simulation and bridge integration have had less validation. If you encounter issues, please report them at [github.com/BedrockDynamics/roz-oss](https://github.com/BedrockDynamics/roz-oss/issues).
</Warning>

## Source Code

* Channel manifest: [`crates/roz-core/src/channels.rs`](https://github.com/BedrockDynamics/roz-oss/blob/main/crates/roz-core/src/channels.rs) (`ChannelManifest::quadcopter()`)
* MAVLink bridge: [`crates/roz-worker/`](https://github.com/BedrockDynamics/roz-oss/tree/main/crates/roz-worker)