sensor_combined Module Documentation

Toolbox: Sensors and Actuators

Introduction

One-sentence Description: Retrieves combined native sensor data from the PX4 flight controller for use in developing custom drone control algorithms in Simulink.

This module belongs to the Sensors and Actuators interface library of the RflySim toolchain. It interfaces with the underlying sensor data from the PX4 flight controller (Pixhawk hardware), supporting flexible selection of outputs including magnetometer, accelerometer, gyroscope, barometer data, and timestamp since gyroscope startup. All output data are aligned to the NED coordinate system and provided with standard units, enabling direct use in development and validation of custom flight control algorithms.

This module requires the PX4 hardware to run the px4io service to obtain valid sensor signals. It can be used either with a real PX4 flight controller for hardware-in-the-loop simulation, or paired with CopterSim or RflySim3D for software-in-the-loop simulation. It serves as a core sensor interface module in the RflySim toolchain for supporting user-defined control algorithm development.

Port Descriptions

Input Ports (Inputs)

This module has no input ports.

Output Ports (Outputs)

The output ports are determined by the configuration in the Output Selection region of the parameter dialog box. Enabling an option generates the corresponding output port:

Port Name	Data Type	Dimension	Description
Magnetometer	single/double [to be confirmed]	1×3	Magnetometer output: magnetic field data in the NED coordinate system, unit: Gauss
Accelerometer	single/double [to be confirmed]	1×3	Accelerometer output: linear acceleration data in the NED coordinate system, unit: m/s²
Gyroscope	single/double [to be confirmed]	1×3	Gyroscope output: angular velocity (p, q, r) in the body-fixed coordinate system, unit: rad/s
Barometer	single/double [to be confirmed]	1×1	Barometer output: temperature-compensated pressure value, unit: millibar; alternatively, altitude can be output
Timestamp	double	1×1	Timestamp output: elapsed time since gyroscope startup, unit: microseconds

Parameter Configuration (Parameters)

The following parameters can be configured in the Mask dialog box opened by double-clicking the module:

Parameter Name	Type	Default Value	Available Values/Range	Description
CopterID	int	1	1~255	Assigned drone ID, used to retrieve sensor data for the corresponding drone
Sample time	double	0.01	>0	Module sampling time, unit: seconds
Magnetometer(x,y,z)	bool	false	true/false	Whether to output magnetometer data
Accelerometer(x,y,z)	bool	false	true/false	Whether to output accelerometer data
Gyroscope(x,y,z)	bool	false	true/false	Whether to output gyroscope data
Barometer(Altitude)	bool	false	true/false	Whether to output barometer data
uORB and RunTime(timestamp)	bool	false	true/false	Whether to output runtime timestamp

Parameter Setting Notes

Output Selection Region

This region allows selecting the types of sensor data to be output. Each selected option automatically generates a corresponding output port, enabling flexible selection based on control algorithm requirements.

Sample time

This parameter sets the sampling frequency for reading sensor data. Typically, it should match the sensor output frequency of the PX4 flight controller. In simulation environments, the default value 0.01 can be retained.

CopterID

When multiple drones exist in the simulation scenario, this parameter specifies which drone’s sensor data the current module should retrieve. For single-drone simulations, the default value 1 is sufficient.

Module Characteristics (Block Characteristics)

Characteristic	Value
Supported Data Types	double, single
Direct Feedthrough	No
Sample Time	Discrete
Code Generation Support	No

Data Communication Protocol

The module communicates with the px4io service on the PX4 hardware side via UDP. It sends a sensor data request structure to port 20010 + drone ID on the remote IP. The request format follows the RflySim platform’s new VisionSensorReq protocol, with a fixed checksum of 12345 and a sensor type ID corresponding to the combined sensor identifier.

Related Modules

Module Name	Description
GPS_Recorder	Outputs raw GPS positioning data
rangefinder	Outputs distance measurement data from ranging sensors
airspeed	Outputs airspeed sensor measurement data
OpticalFlow	Outputs motion measurement data from optical flow sensors

Usage Examples

For relevant usage examples, refer to the following path:

``` [RflySim Installation Path]/RflySimAPIs/5.RflySimFlyCtrl/0.ApiExps/5.PSPOfficialExps/Readme.pdf

Please refer to Readme.pdf in the path above for complete example descriptions and operational steps.

Notes and Common Issues

• Initialization Dependency: This module requires the PX4 hardware to have the px4io service running before it can obtain valid sensor data. Before launching simulation, ensure the PX4 service has started normally; otherwise, the output will remain at the initial zero value.
• Multi-UAV Adaptation Note: When simulating multiple UAVs, this module automatically binds sensor data corresponding to the assigned ID. Ensure the target aircraft ID in the model configuration matches the actual PX4 flight controller number to avoid reading incorrect sensor data.
• Coordinate System Note: The magnetometer, accelerometer, and gyroscope data output by the module are all referenced to the NED coordinate system. When developing control algorithms, verify your algorithm’s coordinate system requirements to prevent control anomalies caused by coordinate system mismatches.
• Unit Consistency Note: Sensor output units conform to the native PX4 definitions: magnetometer units are in Gauss, acceleration units are in m/s², angular velocity units are in rad/s, barometric altitude corresponds to pressure units in millibars, and timestamp units are in microseconds. Do not perform additional unit conversions during use.
• Sampling Time Matching: The module’s sampling time should ideally match the actual sensor output frequency of the PX4 flight controller (e.g., the gyroscope typically outputs at 250 Hz, so the corresponding sampling time can be set to 0.004 s). Avoid excessively high sampling frequencies (which may cause redundant reads) or too low frequencies (which may introduce data delays and degrade control performance).
• Data Output Port Description: The number of module output ports is determined by the selections made in the Output Selection parameter interface. Output ports are generated only for the data types that are checked. If a required sensor output port is missing during use, verify the corresponding check state in the parameter configuration.

Changelog

• v4.10 (2024-08-12): Initial release. Supports acquisition of fused sensor data from PX4 hardware, with selectable outputs for magnetometer, accelerometer, gyroscope, barometer, and timestamp data.