Modelling Methods & Evaluating a Design Outcome
Why Model a Design?
A model allows a designer to test and refine a design idea at relatively low cost before committing to expensive tooling or full manufacture. Models can test proportions (is the product the right size visually?), scale (does it fit in the intended space?), and function (do the moving parts work correctly? does the electronic circuit perform as designed?). The type of model chosen depends on what needs to be tested: a rough card model is made in minutes and reveals shape; a 3D-printed prototype takes hours but reveals surface quality and assembly fit; a virtual 3D CAD model takes longer to build but can be tested digitally for strength and interference before any material is used.
Virtual 3D CAD Modelling
Virtual modelling uses 3D CAD modelling software to build a digital representation of the design. Equipment required: a computer with 3D parametric CAD software (such as SolidWorks, Fusion 360 or Creo). Stages: create 2D sketches of cross-sections, extrude or revolve them to form 3D solids, add features (holes, fillets, chamfers), apply materials and simulate loading. The information obtained includes: visual appearance and proportions, mass and centre of gravity, stress concentration under load (FEA), assembly clearances, and interference between parts. Advantage: no material is consumed; changes are instant. Limitation: cannot test real-world surface feel, assembly by hand, or robustness under actual use conditions.
The five modelling methods in the specification are: virtual 3D CAD, card, block, breadboarding and 3D printing. Each provides different information: CAD gives digital analysis; card and block give proportions and scale; breadboarding tests electronic function; 3D printing produces a near-prototype-quality physical model.
Card Modelling
Card modelling involves cutting, folding and gluing sheets of card (or foam board) to produce a quick, low-cost physical representation of a design. Equipment required: card or foam board, scalpel or scissors, steel rule, cutting mat, adhesive. Stages: draw out the net of the form on card, cut and score fold lines, fold and glue to produce the 3D shape, add detail features with additional pieces. The information obtained is primarily proportions and visual scale — the model shows whether the product is the right size in three dimensions and can be placed in its intended context (e.g. on a desk or in a user's hand). Advantage: very fast and cheap to produce; no specialist skills required. Limitation: it is not suitable for testing structural strength or final surface finish; card has very different material properties to the final product.
Block Modelling
A block model is carved or shaped from a solid block of material — commonly modelling foam (such as polyurethane foam), balsa wood, clay or MDF. Equipment required: the block material, cutting tools (craft knife, rasp, sandpaper), and finishing materials (filler, paint). Stages: rough out the overall shape, refine the form with rasps and sandpaper, apply filler and primer, paint to represent the final appearance. The information obtained includes external form, ergonomics (how the product feels in the hand), surface curves and aesthetic quality. Block models are used to test the ergonomic feel of products such as hand tools, telephones and medical devices. Advantage: produces a realistic model of the final form. Limitation: time-consuming to produce; cannot test internal mechanisms or function.
A breadboard is a reusable plastic board with a grid of holes connected by metal strips that allow electronic components to be inserted and wired without soldering. Equipment required: breadboard, electronic components (resistors, LEDs, ICs, etc.), jumper wires, power supply. Stages: place components in the appropriate rows, connect them with jumper wires according to the circuit diagram, power the circuit and test its function. The information obtained is whether the electronic circuit works as designed — component values, switching behaviour and signal levels can all be tested and adjusted rapidly. Advantage: components can be reused; the circuit can be modified without desoldering. Limitation: not suitable for high-frequency circuits; connections are less secure than soldered joints; layout bears no resemblance to the final PCB.
3D printing (additive manufacture) builds a physical object layer by layer from a 3D CAD file (typically STL format), using materials such as PLA or ABS plastic. Equipment required: a 3D printer, CAD software to produce the STL file, and slicing software to generate the print toolpaths. Stages: produce the 3D CAD model, export as STL, slice the file to generate G-code, load material filament, print layer by layer, remove support material and finish the surface. The information obtained includes: dimensional accuracy, surface quality, assembly fit between parts, weight, and visual appearance very close to the final product. Advantage: high geometric complexity is possible; much faster than traditional machining for one-off models; can be used to assess dimensional accuracy and assembly fit. Limitation: layer-by-layer construction can leave visible surface ridges; material properties (strength, flexibility) of PLA/ABS differ from production materials; large parts require long print times.
Evaluating a Design Outcome
Once a prototype or final product has been produced, the design must be evaluated as an outcome — not just as an idea. Quantitative comparison involves measuring the product against numerical criteria in the specification: dimensions are measured using vernier callipers, micrometers, steel rules or CMM (coordinate measuring machine); electrical performance is measured with a multimeter or oscilloscope; mass is measured on a balance. Each measured value is compared against the specification tolerance — pass or fail is determined objectively.
Methods of evaluating a design outcome include: measuring dimensions and functionality (quantitative comparison against the specification), user testing, and identifying potential modifications and improvements. These differ from methods of evaluating design ideas — they are applied after manufacture, not before.
User Testing and Identifying Modifications
User testing involves giving the product to representative users and observing how they interact with it, or gathering structured feedback through questionnaires, interviews or observation checklists. User testing reveals ergonomic issues, misunderstandings in the interface, assembly difficulties and safety concerns that cannot be found through dimensional measurement alone. The feedback is compared with the qualitative criteria in the specification — for example, whether the product is perceived as comfortable, attractive or easy to use. Following evaluation, the designer identifies potential modifications and improvements: features that fail a quantitative check must be redesigned to bring them within tolerance; features that fail user testing may need form changes, material changes or instruction redesign. Identifying modifications and improvements is not a failure — it is the expected output of a properly conducted evaluation and drives the next iteration of the design.
For comparison questions, know each method's key information, equipment, stages, advantage and limitation. Virtual 3D CAD: digital, no material used, tests mass/stress/clearance; limitation — no physical feel. Card: cheap and fast, tests proportions and scale; limitation — no function or strength testing. Block: tests external form and ergonomics; limitation — slow to produce, no function. Breadboarding: tests electronic circuit function; limitation — not suitable for high-frequency signals. 3D printing: near-prototype quality, high complexity, directly from CAD; limitation — layer ridges, material properties differ from production. Always select the modelling method that matches what the designer needs to find out — this is a common exam question structure.