LoadFault Module Documentation

Toolbox: RflySim PHM

Introduction

One-sentence description: This module enables modeling of three common types of payload faults on UAVs, computing changes in total mass, inertia moments, and moments caused by faults, providing fault model inputs for UAV fault diagnosis and Prognostics and Health Management (PHM) simulation.

This module is the core component of the RflySim PHM interface library specifically designed for UAV payload fault simulation. It supports configuration and computation of three typical payload fault types: payload drop, payload shift, and payload leak. It automatically extracts corresponding fault parameters based on externally injected fault commands and updates the UAV rigid-body dynamics parameters under fault conditions.

Typically used in conjunction with the CopterSim rigid-body six-degree-of-freedom (6-DOF) simulation module in the RflySim toolchain, this module outputs the computed fault dynamics parameters to the dynamics model, enabling UAV flight simulation with payload faults. It can also integrate with RflySim3D for 3D visualization under fault conditions, and interface with PX4 flight controllers to conduct hardware-in-the-loop (HIL) fault simulation tests. It serves as a foundational module for UAV payload fault diagnosis and fault-tolerant control algorithm validation.

Port Descriptions

Input Ports

Port Name	Data Type	Dimension	Description
6DOF Bus1	Bus	-	Encapsulates output signals from a simplified environment model and a rigid-body 6-DOF model [to be confirmed]
ModelParam.uavMass	double	1×1	Total UAV mass
ModelParam.uavR	double	1×1	Specific reference radius/distance of the UAV, used to compute offset of moving mass
FaultIn	Bus	-	Fault input, containing fault type and corresponding fault parameters

Output Ports

Port Name	Data Type	Dimension	Description
Fail Model Bus1	Bus	-	Encapsulates output signals uavMass, uavJ, deltaM, and uavR after fault computation

Parameter Configuration

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
uavMass	double	1.0	(0, +∞)	Initial total UAV mass
uavR	double	0.1	(0, +∞)	UAV reference radius/distance, used to compute offset of moving mass
isLoadFall	bool	false	true/false	Flag indicating whether a payload drop fault occurs
LoadFallParams	double array	[0]	-	Parameter array for payload drop fault
isLoadShift	bool	false	true/false	Flag indicating whether a payload shift fault occurs
LoadShiftParams	double array	[0, 0, 0, 0]	-	Parameter array for payload shift fault
isLoadLeak	bool	false	true/false	Flag indicating whether a payload leak fault occurs
LoadLeakParams	double array	[0, 0]	-	Parameter array for payload leak fault
dcm	double	eye(3)	3×3 orthogonal matrix	Direction cosine matrix, used to transform forces generated by payload movement into the UAV body-fixed frame
uavlostJ	double matrix	zeros(3,3)	3×3 matrix	Inertia moment matrix lost by the UAV due to payload fault

Parameter Setting Notes

isLoadFall / isLoadShift / isLoadLeak

These three boolean parameters enable the corresponding payload fault types manually. If external FaultIn port injection is used, set the corresponding parameters to false, allowing external fault injection signals to control fault triggering.

Fault Parameter Descriptions

• LoadFallParams: The payload drop fault requires only one parameter—the proportion of dropped payload mass to total mass (range: 0 to 1).
• LoadShiftParams: The payload shift fault requires four parameters in order: proportion of shifted payload mass to total mass, x-axis shift factor, y-axis shift factor, z-axis shift factor.
• LoadLeakParams: The payload leak fault requires two parameters in order: maximum leaked mass proportion to total mass, leak rate factor.

Module Characteristics

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

Data Communication Protocol

This module does not involve network communication.

Related Modules

Module Name	Description
FaultParamsExtract	Extracts fault type and corresponding fault parameters from input fault information
PropellerFault	Propeller fault injection and fault model computation module, part of the RflySim PHM interface library
BatteryFault	Battery fault injection and fault model computation module, part of the RflySim PHM interface library
IMUFault	IMU sensor fault injection and fault model computation module, part of the RflySim PHM interface library

Notes and Common Issues

• Initialization Order: This module relies on the 6DOF Bus signal output by the six-degree-of-freedom model; therefore, the six-degree-of-freedom model module must be initialized before the LoadFault module. Otherwise, bus signal parsing errors will occur, preventing accurate calculation of mass and inertia moment changes after the fault.

• Fault ID Matching: The injected fault signal input must strictly match the fault IDs predefined by the module: 123452 corresponds to load drop fault, 123456 to load drift fault, and 123457 to load leak fault. If the ID does not match, the module cannot recognize the injected fault and will retain either the no-fault state or the fault state from the previous time step.

• Parameter Dimension Requirements: The dimensions of parameter arrays must conform to the specific fault type:

• Load drop fault: 1D (weight change ratio),
• Load drift fault: 4D (weight change ratio + drift factors in x, y, and z directions),

• Load leak fault: 2D (initial weight leak ratio + leak rate factor).
  Incorrect dimensions will lead to erroneous simulation calculations.

• Sampling Time Matching: The module’s output fault parameters remain unchanged at their previous state until a new fault injection occurs. Therefore, the module’s sampling time must match the sampling time of the six-degree-of-freedom flight control simulation; otherwise, fault state updates may be delayed or erroneous.

• Inertia Moment Matrix Format: The input lost inertia moment uavlostJ must be a 3×3 matrix, and the output torque change deltaM must be a 3×1 vector. Format mismatches will trigger Simulink signal dimension mismatch errors.

• Simultaneous Multi-Fault Triggering: The module supports triggering multiple load faults concurrently (by simultaneously setting isLoadFall, isLoadShift, and isLoadLeak to true), in which case it superimposes the effects of different faults on mass and inertia moments. If only a single fault is to be triggered, the enable boolean values for the other faults must be set to false.

Changelog

• v4.1.0 (2024-07-24): Initial release of the LoadFault module, supporting fault parameter extraction and fault impact calculation for three types of load faults: LoadFall, LoadShift, and LoadLeak.