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Mechanical design

1. Mechanical design

Modeling strategy

In V0.1, the Fusion 360 file was large, making modeling history hard to track and edits difficult. In V0.2, the design has been split into separate components to make it easier to track history and make changes.

Ref: Fusion 360 Components and Assemblies Explained | Day 13 of Learn Fusion 360 in 30 Days
  1. Strategies
    • Top-Down Modeling: Design all parts within a single file using Internal Components for assemblies with 15–20 unique parts.
    • Bottom-Up Modeling: Use External Components (Xrefs) if you plan to reuse the same part across multiple different projects.
    • Container Hierarchy: Use Sub-assemblies by nesting components to manage complex designs and timeline organization.
    • Parametric Integrity: Always ensure the correct component is Active so its sketches and features are stored in its local timeline rather than the root.
  2. Tips
    • The Golden Rule: Always create, name, and activate a component before you start sketching.
    • Organization: Rename every sketch and component immediately to keep the browser and timeline legible.
    • Avoid Body-to-Component: Don’t wait until a body is finished to convert it; doing so leaves the design history in the top-level root folder.
    • Visual Focus: Use transparency or isolation to navigate crowded assemblies.
  3. Commands
    • New Component: Creates a fresh container for sketches and bodies.
    • Activate: Switches the parametric timeline to focus on a specific component.
    • Copy & Paste: Creates a linked duplicate; changes to one affect the other.
    • Paste New: Creates a completely independent copy of a component.
    • Isolate: Hides all other components except the one selected.
    • Break Link: Converts an external component into an internal one by severing the connection to the source file.
    • Get Latest: Updates an external component to its most recent saved version.

Component layout

  • 4 stepper motors directly drive wheels as before
  • The 6000 mAh battery at the center bottom between the stepper motors which lower the center of gravity
  • The PCB at the top
  • The minimum dimensions defined by the four motors and the battery
    Roughly W150 x L150 x H105 mm (excluding arm)
    (V0.1: W190 x L195 x H103 mm)

Topology optimization

Because I am interested in designing with optimization in addition to human intuition, I tried topology optimization using the plugin tOpos in Rhino Grasshopper.

Ref: formlabs | Topology Optimization 101: How to Use Algorithmic Models to Create Lightweight Design

Topology optimization (TO) uses algorithms to optimize material distribution inside a defined design space based on loads, constraints, and conditions. It removes unnecessary material to reduce weight and improve performance.

  • TO vs Generative Design
    • TO starts from a user-created CAD model and optimizes it
    • Generative design goes further by generating designs automatically from constraints without a starting model
  • How it works
    1. Designers define loads, materials, and constraints
    2. TO software, typically using finite element methods (FEM), simulates pressure/loads on the model
    3. Identifies redundant material, and outputs an optimized shape for evaluation
  • Software Tools
    • nTopology
    • SOLIDWORKS Simulation
    • Autodesk Fusion 360
  • Topology optimization paired with additive manufacturing unlocks efficient, high-performance designs that are otherwise difficult or impossible to produce with traditional methods.

tOpos settings:

  1. Set boundary
    1. Created a boundary that does not interfere with components
    2. Set Young module and Poisson number (Probably these values don't influence final results)
  2. Set Support
  3. Set Load
    1. Battery bottom: Surface load
    2. Mounting points for PCB, Servo etc.: Volume load
  4. Set Model
    1. Resolution:
    2. ...