Notes · Design and TechnologyUK · A-Levels

Requirements for product design and development

This chapter sets out what makes a product succeed for real users: how products are developed and improved, how inclusive and user-centred design widens who a product serves, how ergonomics and anthropometric data make a product fit the human body, and - drawing on the broad Design and Technology title - how mechanical systems create and control the movement many products need, with the calculations that size them.

4 sections~16 min reading time3 competenciesLevel Standard 2 · Advanced 2

T·0777 / 18

Exam profile

AO4 · Explain product development and improvement, inclusive design, ergonomics and anthropometrics, and mechanical systemsAO2 · Apply anthropometric percentile data and mechanical calculations (mechanical advantage, velocity ratio, gear ratio) to a designAO3 · Analyse and evaluate how well a product fits its users and performs its function

Operators:explaincalculateapplyanalyseevaluatejustifycompare

basic level

AS-Level expects product development, inclusive design and the use of anthropometric data understood, with the basic idea of a mechanism.

higher level

The full A-Level expects anthropometric percentiles and mechanical calculations (mechanical advantage, velocity ratio, gear ratio, efficiency) applied, and design decisions justified against the user and the function. Mechanical devices feature most heavily in the Design Engineering title; here they support products that must create or control movement.

Depth

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Contents · 4 sections

Requirements for product design and development

Product development and improvement#

StandardAQA 7552 3.1.7DfE GCE D&T - product development

Influences on product development

Fig. 1Products are developed under two forces - technology push (a new capability seeking a use) and market pull (a need seeking a product) - and are improved by feedback; obsolescence, especially planned obsolescence, drives replacement but raises ethical questions.

Products rarely appear finished and unchanging; they are developed and improved over time in response to new needs, technologies and feedback. Development can be incremental - a series of small improvements to an existing product (each new phone adding features) - or radical, a leap to something genuinely new that redefines a category. Understanding how and why products evolve helps a designer position a new product and plan its future improvement.

New products are driven by two forces. Technology push is when a new technology or material makes a new product possible and the maker looks for a use for it (the transistor enabling portable radios, lithium batteries enabling cordless tools). Market pull is when a customer need or demand pulls a product into being (a demand for healthier food, for accessibility, for lower energy use). Most successful products combine both - a technology that answers a real market need - and recognising which force is at work explains why a product exists.

Obsolescence is when a product ceases to be useful or wanted. Planned obsolescence is the deliberate design of a product to have a limited life or to be superseded, so customers buy again - through fragile parts, non-replaceable batteries, or fashion-led restyling. Design obsolescence and technological obsolescence occur when a product is outdated by better designs or new technology. Planned obsolescence raises real ethical and environmental concerns, and the responsible-design chapter returns to the tension between commercial renewal and sustainability.

Improving a product starts from evidence: user feedback, testing, sales data and the analysis of competitor products all reveal shortcomings and opportunities. A designer improves a product by addressing a genuine weakness (a handle that is uncomfortable, a part that fails, a feature users want) rather than by change for its own sake, and evaluates each improvement against the specification and the user. Continuous, evidence-led improvement is how good products stay competitive and useful.

Worked example

Analysing what drives a product

Cordless power tools largely replaced corded ones over two decades. Explain the roles of technology push and market pull, and comment on obsolescence.

Technology push
Better lithium-ion batteries and efficient brushless motors made cordless tools powerful and long-lasting enough to rival corded ones - a technology enabling a new product.
Market pull
Users wanted the freedom and safety of no trailing cable on site and at home - a real demand pulling the product forward; the successful cordless tool answers this need with the new battery technology.
Comment on obsolescence
Frequent changes of battery format can make older tools obsolete even when working, a form of designed obsolescence that raises waste concerns; a responsible maker keeps a battery platform compatible across generations.

Result: Cordless tools were driven by both technology push (better batteries and motors) and market pull (demand for cordless freedom); changing battery formats illustrate how obsolescence can be designed in, with environmental consequences.

Typical mistakes

Confusing technology push (capability seeking a use) with market pull (need seeking a product).
Treating all product change as improvement - restyling for fashion or planned obsolescence is not the same as addressing a genuine weakness.

Active revision

Choose a product that has changed markedly over a decade. Explain whether technology push or market pull drove its development and evaluate whether any of its changes amount to planned obsolescence.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for design and technology (Department for Education) · AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Inclusive and user-centred design#

StandardAQA 7552 3.1.7DfE GCE D&T - inclusive design

User-centred design puts the needs, abilities and context of real users at the heart of every decision, rather than designing for an imagined 'average' person or for the designer's own convenience. It relies on researching and involving users throughout the process - observing them, testing prototypes with them, and iterating on their feedback - so the finished product genuinely works for the people who will use it.

Inclusive design (sometimes called design for all) goes further: it aims to make products usable by as many people as possible without the need for special adaptation, including older people, people with disabilities and people of different sizes, strengths and abilities. Rather than designing a 'normal' product and a separate 'special' version, inclusive design widens the mainstream product so it excludes as few people as possible - larger, clearer controls, easy-grip handles, level access, clear labelling.

Designing inclusively benefits everyone, not only those with specific needs - a principle sometimes seen in features that help a wide range of users (a low kerb helps wheelchair users, parents with pushchairs and delivery workers alike; a large, well-lit control helps someone with poor eyesight and someone in a hurry). It also widens the market for a product and increasingly meets legal and ethical expectations of accessibility, so inclusivity is both a social good and a commercial advantage.

In practice a designer applies inclusive and user-centred thinking by identifying the full range of intended users and their needs, involving them in research and testing, and evaluating the product against how well it serves that range - not just the middle of it. This connects directly to anthropometrics (fitting the range of body sizes) and to the iterative design process, where user feedback drives each cycle of improvement.

Worked example

Applying inclusive design

Redesign the controls of a microwave oven to be more inclusive. Identify three features and explain how each widens the range of users served.

Large, tactile controls
Replace small flush buttons with large, raised, well-spaced buttons with a tactile click, so users with limited dexterity, arthritis or poor eyesight can find and press them - and everyone benefits from easier use.
Clear, high-contrast display and labelling
Use a large, high-contrast display and simple symbols, so users with reduced vision can read settings; clarity helps every user work the microwave quickly.
Simple, forgiving operation
Offer a single large 'start with 30 seconds' control and clear feedback, reducing the cognitive load for users unfamiliar with complex menus while still allowing full control - inclusive without excluding advanced use.

Result: Large tactile buttons, a high-contrast display and simple forgiving operation make the microwave usable by people with reduced dexterity or vision while helping every user - inclusive design widens the mainstream product rather than creating a separate version.

Typical mistakes

Treating inclusive design as designing a separate 'special' product rather than widening the mainstream product for all.
Claiming a product is user-centred without any actual user research or testing to support it.

Active revision

A kitchen appliance is to be usable by older people and those with limited hand strength or eyesight, as well as everyone else. Identify three inclusive design features and explain how each widens who can use it.

Active recall

Recall the key points — then reveal.

Sources: AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Ergonomics and anthropometrics#

AdvancedAQA 7552 3.1.7DfE GCE D&T - ergonomics and anthropometrics

Anthropometric percentiles of stature (illustrative)

Fig. 2Illustrative adult stature at the 5th, 50th and 95th percentiles (mm). Designers use the extremes, not the average: the 95th percentile for clearances (so the tall fit) and the 5th for reaches (so the short can reach).

Ergonomics (human factors) is the study of designing products, systems and environments to fit the people who use them, so they are comfortable, safe and efficient. It covers physical fit (size, reach, posture, force), sensory factors (what users can see, hear and feel) and cognitive factors (how easily they understand and operate a product). A well-designed handle, seat, control panel or workspace all rest on ergonomic thinking.

Anthropometrics is the branch of ergonomics that measures the human body - heights, reaches, grips, widths - across a population. Because people vary, these measurements are given as statistical distributions, and designers work in percentiles: the 5th percentile value is exceeded by 95% of people (only 5% are smaller), and the 95th percentile value is exceeded by only 5% (95% are smaller). Designing to a single 'average' (50th percentile) fits almost no one well, because few people are average in every dimension.

The key principle is to design to the appropriate percentile for the type of dimension. For a clearance - a space everyone must pass through or fit into (a doorway, a seat width, legroom) - design for the largest user, the 95th (or 99th) percentile, so the biggest fit and everyone smaller fits too. For a reach - something everyone must be able to reach or operate (a shelf, a control, a brake lever) - design for the smallest user, the 5th percentile, so the shortest can reach and everyone taller can too. Where one size cannot serve the range, make the dimension adjustable to span the 5th to 95th percentile (a car seat, an office chair).

Applying anthropometric data means choosing the right dimension, the right percentile and a sensible allowance (for clothing, shoes, movement and comfort), then checking the design against the range of users. Designing to the average, or to the designer's own size, is the classic error - it produces doorways the tall must stoop through and shelves the short cannot reach. Percentile-based design, with adjustability where needed, is how a product is made to fit a diverse population.

Worked example

Choosing a percentile and sizing a clearance

A designer must set the height of a doorway so that virtually everyone can walk through without stooping. Using the illustrative data (5th percentile stature 1600 mm, 50th 1740 mm, 95th 1880 mm), determine the percentile to design to and a suitable door height.

Identify the type of dimension
A doorway is a clearance - a space everyone must pass through - so it must accommodate the largest user; smaller users then fit automatically.
Choose the percentile
Design to the 95th percentile stature (1880 mm), so 95% of people are shorter and fit easily; designing to the 50th percentile (1740 mm) would leave many taller people stooping.
Add allowances
Add an allowance for shoes (about 25 mm) and clearance for headroom, hats and comfortable movement (about 100 mm): 1880 + 25 + 100 = 2005 mm.
State the result
A door height of about 2000 mm (2 m) accommodates the 95th percentile plus allowances - close to the standard internal door height - so almost everyone passes through without stooping.

Result: Design the doorway to the 95th percentile stature (1880 mm) plus about 125 mm of allowances, giving roughly 2000 mm - a clearance is sized to the largest user so that everyone smaller fits too.

Typical mistakes

Designing to the 50th percentile 'average' - it fits almost no one well because few people are average in every dimension.
Choosing the wrong extreme - designing a doorway to the 5th percentile (too low) or a shelf reach to the 95th (too high).

Active revision

A public-transport grab rail must be reachable by standing passengers of all sizes. State which percentile you would design its height to, justify the choice, and describe one allowance you would add.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for design and technology (Department for Education) · AQA A-level Design and Technology: Product Design (7552) specification (AQA)

Mechanical systems and movement in products#

AdvancedAQA 7552 3.3DfE GCE D&T - mechanical devices

A lever: effort, load and fulcrum

Fig. 3A lever multiplies force: the effort on the long arm balances a larger load on the short arm. Mechanical advantage = load / effort, and for a lever the velocity ratio = effort arm / load arm.

Many products must create or control movement, and mechanical devices (mechanisms) do this by transmitting and transforming force and motion. There are four basic types of motion: linear (in a straight line), rotary (turning about an axis), reciprocating (back and forth in a straight line) and oscillating (swinging back and forth about a pivot). A mechanism typically converts one type of motion or force into another - turning a handle (rotary) to raise a load (linear), or rotary motion into reciprocating motion in an engine.

Levers multiply force and are described by mechanical advantage (MA), the ratio of load to effort: MA = load / effort. A lever with an MA greater than 1 lets a small effort move a large load (a crowbar, bottle opener, wheelbarrow). Its geometry is captured by the velocity ratio (VR), the distance moved by the effort divided by the distance moved by the load, which for a lever equals the effort arm divided by the load arm. In an ideal machine MA equals VR; in a real one friction makes MA less than VR, and the efficiency = MA / VR x 100% measures the losses.

Pulleys and gears transmit rotary motion and also trade speed for force. A pulley system's velocity ratio equals the number of rope sections supporting the load, letting a small effort raise a heavy weight over a longer distance. Gears mesh toothed wheels; the gear ratio = teeth on the driven gear / teeth on the driver gear. A large driven gear (more teeth) turns more slowly than the driver but with more torque - so gears change both speed and turning force, as in a bicycle or a hand drill.

Cams, cranks and linkages convert between the types of motion. A cam rotating under a follower converts rotary motion into reciprocating or oscillating motion (as in an engine valve or a toy); a crank and slider converts rotary to reciprocating (an engine piston, a sewing machine); a rack and pinion converts rotary to linear (steering, a stairlift). A designer selects a mechanism by the input and output motion required, the force or speed change needed, and then sizes it with these ratios - so a product moves exactly as intended.

\text{MA} = \dfrac{\text{load}}{\text{effort}}

Mechanical advantage

The ratio of load to effort. An MA greater than 1 means a small effort moves a larger load.

\text{VR} = \dfrac{\text{distance moved by effort}}{\text{distance moved by load}} = \dfrac{\text{effort arm}}{\text{load arm}}

Velocity ratio (lever)

The geometry of the machine: for a lever it equals the effort arm divided by the load arm.

\text{Efficiency} = \dfrac{\text{MA}}{\text{VR}} \times 100\%

Efficiency

In an ideal machine MA equals VR (100% efficient); friction makes MA less than VR in a real machine, so efficiency is below 100%.

\text{Gear ratio} = \dfrac{\text{teeth on driven gear}}{\text{teeth on driver gear}}

Gear ratio

A gear ratio greater than 1 means the driven gear turns more slowly than the driver but with more torque (speed traded for force).

Mechanisms and types of motion

Fig. 4Mechanisms grouped by what they do: the four types of motion, force multipliers (levers, pulleys, gears) and motion converters (cam, crank and slider, rack and pinion). A mechanism is chosen by the input and output motion required.

Worked example

Lever and gear calculations

(a) A lever lifts a 300 N load with an effort of 120 N; the effort arm is 600 mm and the load arm is 200 mm. Find the mechanical advantage, velocity ratio and efficiency. (b) A 20-tooth driver gear drives a 60-tooth gear at 300 rpm. Find the gear ratio and output speed.

Lever: mechanical advantage
MA = load / effort = 300 / 120 = 2.5.
Lever: velocity ratio
VR = effort arm / load arm = 600 / 200 = 3.
Lever: efficiency
Efficiency = MA / VR x 100 = 2.5 / 3 x 100 = 83.3%, so friction loses about a sixth of the input.
$\text{Efficiency} = \dfrac{2.5}{3} \times 100 = 83.3\%$
Gears: gear ratio
Gear ratio = driven teeth / driver teeth = 60 / 20 = 3 (a 3:1 reduction).
Gears: output speed and torque
Output speed = input speed / gear ratio = 300 / 3 = 100 rpm; the driven gear turns three times slower than the driver but delivers about three times the torque.

Result: The lever has MA 2.5, VR 3 and efficiency 83.3%; the 3:1 gear reduces 300 rpm to 100 rpm and roughly triples the torque - the ratios size the mechanism to the required force and speed.

Typical mistakes

Inverting a ratio - gear ratio is driven teeth over driver teeth, and mechanical advantage is load over effort; swapping them gives the reciprocal.
Assuming a real machine is 100% efficient - friction makes MA less than VR, so efficiency is below 100%.

Active revision

A driver gear of 20 teeth drives a gear of 60 teeth at an input speed of 300 rpm. Calculate the gear ratio and the output speed, and state what happens to the torque.

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for design and technology (Department for Education) · AQA A-level Design and Technology: Product Design (7552) specification (AQA)

References & sources

Sources

Department for Education

GCE AS and A level subject content for design and technology

AQA

AQA A-level Design and Technology: Product Design (7552) specification

Requirements for product design and development

4 sections~16 min reading time3 competenciesLevel Standard 2 · Advanced 2

Requirements for product design and development

Key points

Analysing what drives a product

Key points

Applying inclusive design

Key points

Choosing a percentile and sizing a clearance

Key points

Lever and gear calculations

Sources

Requirements for product design and development

Key points

Analysing what drives a product

Key points

Applying inclusive design

Key points

Choosing a percentile and sizing a clearance

Key points

Lever and gear calculations

Sources