Key Idea: A prototype exists to answer a question. Build it for the question, not for the photograph. Low fidelity early — cheap, disposable, honestly criticised. High fidelity late — tests function and materials, but hard to change. Drawings explore (sketch), communicate (isometric) and specify (orthographic, exploded). Physical for what the body judges. Virtual for many variants and internal forces.
Paper 1 — multiple choice
- Classify a prototype as low or high fidelity
- Match a drawing type to a stated purpose
- Identify which of the five a prototype tests
- Pick the rapid technique that suits a requirement
Paper 2 — analysing a product
- Justify a fidelity for a stage of development
- Outline the drawing type at four stages
- Explain how physical prototypes develop a product
- Justify a rapid prototyping technique by its properties
Carried into the design project
- Criterion C — ideation and modelling, 6 marks
- Criterion D — designing a solution, 6 marks
- Every prototype you build must state what it tested
Every statement in this topic is a list. Memorised as a list, none of them is usable under exam pressure. Each becomes usable once you attach it to the decision it answers.
| The list | The decision it serves | The giveaway in the question |
|---|---|---|
| Low / high fidelity | How much to commit at this stage | A stage or a deadline is named |
| Sketch / isometric / orthographic / exploded | Who the drawing is for and what they must do with it | A purpose — explore, present, manufacture, assemble |
| Scale / aesthetics / materials / function / performance | What this prototype is built to find out | A prototype is described, or a test is named |
| SLA / FDM / SLS | Which property the part must have | Finish, strength, cost, or a complex internal geometry |
A prototype answers one question. Build it for that question and leave out everything else. A function prototype should look rough on purpose — a finished shell makes testers comment on the colour.
Cost rises with fidelity and willingness to change falls. That pair of curves is the argument for low early, high late.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
| SLA | FDM | SLS | |
|---|---|---|---|
| Material | Liquid resin, laser-cured | Filament, melted and extruded | Powder, laser-fused |
| Finish | Best — finest detail | Worst — visible layers | Grainy and matt |
| Strength | Brittle, degrades in sun | Weak across the layers | Strong, near-isotropic |
| Supports | Needed; leave marks | Needed for overhangs | NONE — powder supports it |
| Choose it for | Appearance models | Cheap, fast, many prints | Parts that must work |
Important: Treating high fidelity as better. It is slower, dearer, and it makes everyone reluctant to change the design. Answering with an acronym. SLA earns nothing; "SLA, for the finest surface finish" earns the mark. Describing what a drawing looks like rather than what it is for.
Start from the question. If the body judges it, build it; if it is many variants or internal forces, model it.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
A company has twelve weeks to develop a child's scooter. Justify the prototyping approach it should take in week 1, week 5 and week 10.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A manufacturer of surgical instruments needs a prototype handle to be photographed for a catalogue, and another to be gripped and twisted by surgeons in a trial. Explain which rapid prototyping technique suits each and why.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A team designing a wheelchair-mounted drinks holder has produced forty CAD variants and no physical models. Analyse what this tells you about their process and what they still cannot know.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
What does fidelity mean?
Give the disadvantage of high fidelity that most students miss.
Which drawing would you manufacture from, and why?
Name the five things a physical prototype tests.
Name three virtual tools and what each answers.
Why does SLS need no supports?
Why is a printed prototype not equivalent to the production part?
Exam tips
- A prototype answers one question. Say which, then say what you would build.
- High fidelity is not better. Name its costs — slow, dear, and hard to change.
- For rapid prototyping, give the property, never just the acronym.
- Say what a drawing is for, not what it looks like.
- Anything the body judges — weight, grip, fatigue — needs a physical prototype.
- For justify, the reason carries the mark. The label on its own is half an answer.