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14 Simulation

Simulate & Optimise

Run stress tests, find weak points with FEA, and let generative design create shapes you'd never imagine.

14. Simulation & Generation

Simulation predicts how parts behave under real-world conditions before manufacturing. Topology optimization and generative design let algorithms propose lighter, stronger geometry than hand-design.

Finite Element Analysis (FEA)

FEA divides a solid model into thousands of elements (a mesh), solves physics equations on each, and predicts how the part responds to forces, pressures, and temperatures.

  • What It Is: A numerical method that meshes geometry into small elements and solves physics equations on each to predict real-world behavior.
  • Mesh: Use finer mesh in high-stress areas (fillets, holes) and coarser mesh elsewhere to balance accuracy and solve time.
  • Fixtures: Define part constraints — fixed, pinned, or frictionless. Incorrect fixtures are the most common source of meaningless results.
  • Loads: Apply forces, pressures, and moments at the exact locations and directions they occur in real life.
  • Interpreting Results: Stress plots show blue (low) to red (near yield). Check that the safety factor (yield strength / max stress) meets your target — typically 1.5+ for static loads.

Challenge

Find the minimum beam thickness that keeps the safety factor above 2.0 under a 500N load.

⚠ Predict First

Where do you think the highest stress will appear on a cantilever beam loaded at the tip?

FEA (Finite Element Analysis) divides a part into small elements and solves stress/strain equations for each.

Safety Factor = Material Yield Strength / Max Stress. Values > 1.0 mean the part survives. > 2.0 is typical for robotics.

Key inputs: material, loads, constraints (fixed faces), mesh size.

Red = high stress. Blue = low stress. Concentrate on the transition zones.

Guided Exploration
  1. Apply a 200N load. Note where peak stress appears and the safety factor.
  2. Double the force to 400N. Did the safety factor halve exactly? Why or why not?
  3. Find the minimum beam thickness that keeps safety factor above 2.0 at 500N.
Topology Optimization

Topology optimization carves away non-load-bearing material from a solid block, leaving an organic structure that is as light as possible while meeting stiffness and strength requirements.

  • Preserve & Obstacle Regions: Mark areas that must remain solid (bolt holes, mounts) and areas where material cannot exist (clearance zones).
  • Load Cases: Apply the same fixtures and loads as FEA — multiple cases can be optimized simultaneously.
  • Optimization Goals: Typically minimize mass while maintaining a target stiffness or safety factor.
  • Post-Processing: The organic output must be smoothed and adapted for your manufacturing method (3D printing, CNC, casting).
Generative Design

Generative design extends topology optimization by generating dozens of alternatives, each tailored to a specific manufacturing process and material.

  • How It Differs: Runs optimizations in parallel across processes (3D printing, CNC, casting) to compare weight, cost, and performance trade-offs.
  • Manufacturing Constraints: Each result respects its target process rules — no undercuts for CNC, draft angles for casting — so geometry is born manufacturable.
  • Exploring Results: Designs ranked by mass, stress, and cost let you filter, compare, and export the best candidate.
Thermal & Modal Analysis

Heat Transfer: Thermal FEA simulates conduction, convection, and radiation to verify electronics stay within operating temperature and size heat sinks.

Modal Analysis: Calculates natural frequencies and mode shapes. Keep the first natural frequency at least 20% away from operating frequencies to avoid resonance.

Simulation Workflow

Follow this process for any simulation study.

1
Define Study & Materials

Choose the analysis type (static, modal, thermal) and assign accurate material properties to every body.

1 Experience
2 Reflect
3 Theorize
4 Apply
Quick Review Opportunity

Revisit
2
Apply Fixtures & Loads

Constrain the model as held in reality and apply all forces, pressures, and moments.

3
Generate Mesh & Solve

Create the element mesh, refine in critical areas, and run the solver.

4
Analyze Results

Review stress, displacement, and safety-factor plots to identify problem areas.

5
Iterate

Modify the design based on results and re-run until all requirements are met with minimum weight.

Interpreting Results

Knowing what to look at and what the numbers mean is critical for sound engineering decisions.

Result Type What It Shows Key Guidelines
Stress Color Map Blue = low stress, green = moderate, yellow = approaching yield, red = at or above yield strength Focus on red zones. If red appears only at a sharp corner or point load, it may be a stress singularity (a mesh artifact) -- refine the mesh and re-check.
Displacement Plot How much each point of the part moves under load (shown exaggerated for visibility) Check that maximum deflection is within your tolerance. For robot arms, even 0.5mm of tip deflection can affect accuracy.
Safety Factor Ratio of yield strength to actual stress at each point Minimum 1.5 for static loads on well-understood parts. 3-4 for dynamic, impact, or fatigue loads. Below 1.0 means the part will yield (permanent deformation).
Convergence Check Whether the solution has stabilized as mesh density increases Run at least 2-3 mesh refinement levels. If peak stress changes more than 5-10% between levels, the mesh is too coarse and results are unreliable.
Mode Shapes (Modal) The deformation pattern at each natural frequency Ensure the first natural frequency is at least 20% away from any motor or drivetrain operating frequency to avoid resonance.
Simulation Reality Check: FEA results are only as good as your boundary conditions — incorrect fixtures or materials produce precise but meaningless numbers. Always validate critical designs with physical testing.

Planetary Gear Set — sun gear, three planet gears on a carrier, and a ring gear with internal teeth. A compact, high-torque-density transmission common in servo gearboxes.

Stage 2 Pause and Reflect
✓ Your reflections are saved automatically
Stage 4 Apply What You Learned

Optimize a robot arm bracket for weight using topology optimization or manual lightening.

  • Define the load cases: what forces act on the bracket during operation?
  • Set constraints: which surfaces are fixed? Which are loaded?
  • Run FEA and identify areas with very low stress (candidates for material removal)
  • Iterate: remove material from low-stress regions and re-simulate
  • Validate: does the optimized design still meet the safety factor requirement?
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