PX4 Multirotor Client (cl_px4_mr)

SMACC2 client library for PX4 multirotor control via ROS 2 XRCE-DDS.

Architecture

The cl_px4_mr follows a pure component-based architecture where the client orchestrates seven specialized components:

ClPx4Mr (Client - Orchestrator)
├── CpVehicleCommand        - Sends vehicle commands (arm, disarm, mode, land, takeoff)
├── CpVehicleStatus         - Monitors arming state, landing, and nav mode
├── CpVehicleLocalPosition  - Tracks vehicle position in NED frame
├── CpTrajectorySetpoint    - Publishes position setpoints for offboard control
├── CpOffboardKeepAlive     - Maintains offboard mode via periodic heartbeat
├── CpVehicleCommandAck     - Monitors command acknowledgement responses
└── CpGoalChecker           - Detects when vehicle reaches target position

Components

CpVehicleCommand

Responsibility: Sends PX4 vehicle commands via /fmu/in/vehicle_command

• arm() / forceArm() / disarm() - Vehicle arming control
• setOffboardMode() - Switch to offboard control mode
• takeoff(altitude) / land() - Flight commands
• sendCommand(...) - Generic 7-parameter command interface

Signals: None

CpVehicleStatus

Responsibility: Monitors vehicle state from /fmu/out/vehicle_status_v1

• Tracks arming state and navigation mode transitions
• Detects armed/disarmed and landed state changes

Signals: onArmed_, onDisarmed_, onModeChanged_, onLanded_

CpVehicleLocalPosition

Responsibility: Tracks position from /fmu/out/vehicle_local_position

• Provides NED position (x, y, z) and heading
• Thread-safe accessors with validity checking

Signals: onPositionReceived_

CpTrajectorySetpoint

Responsibility: Publishes position commands to /fmu/in/trajectory_setpoint

• setPositionNED(x, y, z, yaw) - Set target position
• hold() - Hold current position
• republishLast() - Re-send last setpoint
• Thread-safe with cached last setpoint

Signals: None

CpOffboardKeepAlive

Responsibility: Publishes offboard control mode heartbeat to /fmu/in/offboard_control_mode

• Inherits from ISmaccUpdatable for periodic ~20Hz updates
• enable() / disable() - Toggle heartbeat publishing
• PX4 requires continuous offboard heartbeat to stay in offboard mode

Signals: None

CpVehicleCommandAck

Responsibility: Monitors command responses from /fmu/out/vehicle_command_ack

• Tracks last command ID and result code

Signals: onAckReceived_

CpGoalChecker

Responsibility: Monitors position and fires when goal is reached

• Inherits from ISmaccUpdatable for periodic distance checking
• setGoal(x, y, z, xy_tolerance, z_tolerance) - Set target with tolerances
• clearGoal() - Deactivate goal checking
• Default tolerances: 0.5m XY, 0.3m Z

Signals: onGoalReached_

CpTfBroadcaster (opt-in)

Responsibility: Publishes PX4’s state estimate as a ROS TF tree so sensors on the airframe can be placed in RViz: map -> base_link (translation from CpVehicleLocalPosition, rotation from /fmu/out/vehicle_attitude, converted NED/FRD -> ENU/FLU), a translation-only map -> base_link_follow (an RViz orbit target that does not spin with yaw) and a static base_link -> lidar_link from TfBroadcasterParams. Not created by ClPx4Mr; an orthogonal adds it with createClient<ClPx4Mr>()->createComponent<CpTfBroadcaster>(params). map is the FMU’s local NED origin expressed ENU (x east, y north, z up).

Signals: None

CpForwardObstacleGuard

Responsibility: Watches a sensor_msgs/PointCloud2 (from a CpTopicSubscriber<PointCloud2> on the same client, e.g. cl_generic_sensor::ClGenericSensor<PointCloud2>) for returns inside a forward cone about the sensor +x axis and raises / clears an obstacle flag with hysteresis (ForwardObstacleGuardParams: half angle, trigger / clear ranges, hit count, cloud debounce).

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