#4350 Bicycle: System Breakdown in SysML v2

#4350 Bicycle: System Breakdown in SysML v2

#4350 Break down a bicycle into subsystems, components and parts in SysML v2

In SysML v2, we shift from the "block-based" mindset of v1.x to a more precise Usage and Definition pattern. Using the new textual notation, we can decompose a bicycle into a clear hierarchy that maps directly to engineering requirements and manufacturing Bill of Materials (BOM).

Below is a breakdown of a bicycle using SysML v2 syntax, organized by hierarchical levels.

---

1. Top-Level System Definition

We start by defining the part def for the bicycle and its primary decomposition into major subsystems.

part def Bicycle {
    // Subsystem Usages
    part frameSubsystem: FrameSubsystem;
    part drivetrainSubsystem: DrivetrainSubsystem;
    part steeringSubsystem: SteeringSubsystem;
    part brakingSubsystem: BrakingSubsystem;
    part wheelSubsystem: WheelSubsystem[2]; // Front and Rear
}

---

2. Subsystem & Component Decomposition

Here, we break those subsystems down into specific components. In SysML v2, we often use part to represent the usage of a component within a larger assembly.

A. Frame Subsystem

Focuses on the structural integrity and rider interface.

part def FrameSubsystem {
    part mainFrame: MainFrame;       // The "Diamond" or "Step-through"
    part frontFork: FrontFork;
    part saddleAssembly: SaddleAssembly {
        part saddle: Saddle;
        part seatPost: SeatPost;
        part seatClamp: Clamp;
    }
}

B. Drivetrain Subsystem

The power transmission logic.

part def DrivetrainSubsystem {
    part crankset: Crankset;
    part bottomBracket: BottomBracket;
    part chain: Chain;
    part pedals: Pedal[2];
    part cassette: RearCassette;
    part derailleurSystem: DerailleurSystem {
        part frontDerailleur: Derailleur[0..1];
        part rearDerailleur: Derailleur;
        part shiftCables: Cable[1..*];
    }
}

C. Steering Subsystem

The directional control mechanism.

part def SteeringSubsystem {
    part handlebars: Handlebars;
    part stem: Stem;
    part headset: Headset;    // Bearings allowing the fork to rotate
    part grips: Grip[2];
}

---

3. Atomic Parts (The "BOM" Level)

At the lowest level, we define the individual parts. This is where you would link to specific mass properties or material requirements.

Subsystem	Component	Discrete Parts (Atomic)
Wheel	Hub Assembly	Axle, Bearings, Hub Shell, Flanges
Wheel	Rim Assembly	Rim, Spokes (e.g., 32x), Nipples, Rim Tape
Braking	Caliper	Brake Pads, Pistons, Return Spring, Mounting Bolts
Drivetrain	Chain	Inner Link, Outer Link, Roller, Pin

---

4. Defining Connections (Internal Block Diagram equivalent)

In SysML v2, we use connect statements to show how these parts interact. For example, how the Drivetrain provides torque to the Rear Wheel:

part bicycle_Instance : Bicycle {
    connect drivetrainSubsystem.cassette to wheelSubsystem[2].hub 
        indexed by torqueTransfer;
        
    connect steeringSubsystem.headset to frameSubsystem.frontFork 
        indexed by steeringInterface;
}

Key SysML v2 Concepts Used:

• part def: Defines the "blueprint" (Definition).

• part: Defines the "usage" of that blueprint in a specific context.

• Multiplicity [2]: Indicates there are two instances (e.g., wheels or pedals).

• Nesting: Visually represents the system-of-systems hierarchy.

Given your background in S&MA, this structure is particularly useful for Failure Mode and Effects Analysis (FMEA), as you can now attach attribute values (like MTBF or Material Stress limits) directly to the part def of the Braking or Drivetrain subsystems.

From <https://gemini.google.com/app/>  Google Gemini 3.0 (Fast)