🔧 Year 8 Design & Technology

CAD/CAM & Digital Fabrication

CAD (Computer-Aided Design)

• Software used to create precise 2D drawings and 3D models of products before they are made
• Advantages over hand drawing: easy to edit, scale, rotate, and mirror; automatic measurement; can be shared electronically; can be sent directly to CAM machines
• Types: 2D CAD (Inkscape, Adobe Illustrator — for laser cutting, vinyl cutting); 3D CAD (Fusion 360, TinkerCAD, SketchUp — for 3D printing, CNC milling)
• Parametric modelling: dimensions are driven by parameters — change one value and the model updates automatically. Professional approach used in engineering.
• Rendering: applying realistic materials, lighting, and shadows to a 3D model to produce a photorealistic image — used for visualisation and client presentation

CAM (Computer-Aided Manufacture)

• Software/process that uses the CAD file to control manufacturing machines automatically
• Removes much human error and produces consistent results
• The design workflow: CAD model → export as appropriate file format → CAM software generates tool paths → machine executes the cut/print/engrave

Digital Fabrication Technologies

• Laser cutter: a high-powered laser beam cuts or engraves 2D shapes from flat sheet materials (acrylic, plywood, cardboard, leather, fabric). Extremely precise. Requires a 2D CAD file.
• 3D printer (FDM — Fused Deposition Modelling): builds up objects layer by layer from molten plastic (PLA, ABS). Additive manufacturing — no waste material. Limited by print speed, resolution, and material properties.
• Vinyl cutter: cuts adhesive vinyl into shapes and letters — used for stickers, signage, and iron-on transfers for textiles
• CNC (Computer Numerically Controlled) router/mill: a computer-controlled cutting machine that removes material (subtractive) from wood, foam, or soft metals. Creates 3D contoured surfaces that 2D laser cutting cannot.

Prototyping and Iteration

• A prototype is an early model of a product used to test ideas and gather feedback before expensive final production
• Paper/card prototyping: quick, cheap, good for form and scale. Net (flat pattern) → fold into 3D form.
• Low-fidelity vs high-fidelity prototype: low-fi is rough and quick; high-fi closely resembles the final product
• Iterative design: test → evaluate → refine → test again. Each iteration improves the product.

Mechanisms & Structures

Levers

• A lever is a rigid bar that pivots around a fulcrum (pivot point). Used to multiply force or distance.
• Class 1 lever: fulcrum between effort and load (see-saw, scissors, pliers)
• Class 2 lever: load between fulcrum and effort (wheelbarrow, nutcracker) — always a mechanical advantage (load > 1)
• Class 3 lever: effort between fulcrum and load (tweezers, fishing rod) — increases speed/distance but requires greater effort
• Mechanical advantage (MA) = Load ÷ Effort. MA > 1 means a mechanical advantage (easier to move a larger load)
• Velocity ratio (VR) = effort distance ÷ load distance. If MA = 3, VR = 3 (you push 3 times further to move the load 1×)

Gears

• Gears transmit rotational motion and can change speed, direction, and torque
• Meshing gears rotate in opposite directions
• Gear ratio = teeth on driven gear ÷ teeth on driver gear
• Gear ratio > 1: the driven gear turns more slowly but with more torque (force) — used in low gears of bicycles and cars (climbing hills)
• Gear ratio < 1: the driven gear turns faster but with less torque — used in high gears (speed on flat roads)
• An idler gear between driver and driven gear reverses direction without changing speed
• Rack and pinion: converts rotary motion (pinion gear) to linear motion (rack) — used in car steering and rail systems
• Worm gear: a screw-like gear that meshes with a spur gear; large reduction ratio; can only drive in one direction (self-locking) — used in lifts and tuning pegs

Structural Principles

• Triangulation: triangles are the strongest shape because they cannot deform without changing the length of a side. Trusses use triangles. Bridges, roof trusses, cranes all rely on triangulation.
• Load types: tension (pulling/stretching), compression (squashing), shear (sliding layers), torsion (twisting), bending
• Beam: a horizontal structural member; experiences compression on the top and tension on the bottom under a central load. An I-beam cross-section maximises strength with minimal material.
• Shell structures: strength comes from the shape/skin rather than the material thickness (egg, dome, car body)
• Stiffening: ribbing, corrugating, and folding flat sheet materials increases rigidity dramatically without adding much material (like corrugated cardboard)

Textiles Technology

Types of Fabric

• Natural fibres: cotton (comfortable, breathable, absorbent; wrinkles; from the cotton plant), wool (warm, absorbent, elastic; from sheep), silk (smooth, lustrous, strong; from silkworm cocoons), linen (strong, cool, crisp; from flax plant)
• Synthetic fibres: polyester (durable, crease-resistant, quick-drying, but not breathable; made from petroleum), nylon (strong, elastic, moisture-wicking; first synthetic fibre), acrylic (wool-like but cheaper; not breathable), Lycra/elastane (very elastic; used in sportswear)
• Blended fabrics: two or more fibres combined to get the best properties of each. Poly-cotton (80/20) is durable and comfortable. Wool-polyester suits resist wrinkling while maintaining warmth.
• Smart/technical fabrics: Gore-Tex (waterproof yet breathable — micropores too small for water droplets but large enough for water vapour), Kevlar (bullet-resistant), PCM fabrics (phase-change materials that regulate body temperature)

Fabric Construction

• Weaving: warp threads (running lengthwise) and weft threads (running crosswise) interlace. Plain weave (simple over/under), twill weave (diagonal ribbing, e.g. denim), satin weave (smooth, lustrous surface)
• Knitting: interlocking loops of yarn. More stretchy than woven fabrics. Weft knitting (rows, e.g. T-shirts, jumpers) vs warp knitting (columns, e.g. tights, some sportswear)
• Non-woven fabrics: fibres bonded by heat, adhesive, or needling (felt, interfacing, paper towels). Cheaper and quicker to make but less durable.

Construction Techniques

• Pattern: a template (paper or digital) used to cut fabric pieces accurately. Includes seam allowance (typically 1.5 cm)
• Seams: the join where two pieces of fabric are stitched. Plain seam (basic), French seam (enclosed edges, no fraying), flat-felled seam (strong, neat on both sides; used in jeans)
• Hems: the finished edge of a garment. Single hem (one fold), double hem (two folds for strength), blind hem (almost invisible from the front)
• Fastenings: zips, buttons/buttonholes, velcro, press studs, hooks and eyes, ties
• Embellishment: embroidery, appliqué (applying fabric shapes), beading, screen printing, dye-sublimation printing

Advanced Food Technology

Food Science: Raising Agents

• Raising agents introduce gas bubbles into a mixture, making it rise during cooking
• Baking powder: a mixture of bicarbonate of soda and an acid (cream of tartar). The acid-alkali reaction produces CO₂ without needing liquid acid. Used in cakes and scones.
• Bicarbonate of soda (baking soda): an alkali. Requires an acidic ingredient (buttermilk, yoghurt, lemon juice, vinegar) to produce CO₂. Produces more CO₂ than baking powder but can taste soapy if excess.
• Yeast: a living organism that ferments sugars and produces CO₂ and alcohol. Used in bread making. Requires warmth (28–38°C) and time (proving). Killed above 60°C.
• Steam: water in the mixture turns to steam during cooking; particularly important in choux pastry (profiteroles, eclairs) and flaky/puff pastry.
• Whisked egg: beating eggs (especially egg whites) incorporates air. Meringues, soufflés, and fatless sponges rely on this.

Food Preservation

• Food spoils due to: microorganisms (bacteria, moulds, yeasts), enzymes, oxidation
• Preservation methods slow or prevent spoilage by removing conditions microorganisms need (warmth, moisture, oxygen, nutrients, neutral pH)
• Refrigeration (1–4°C): slows microbial growth; does not kill bacteria
• Freezing (−18°C): halts microbial activity; does not kill bacteria — they revive on thawing
• Pasteurisation: heating to 72°C for 15 seconds (HTST) then rapid cooling — kills most pathogenic bacteria in milk without significantly changing flavour
• Sterilisation: heating to 132°C+ — kills all microorganisms and spores; longer shelf life (UHT milk) but alters flavour more
• Drying/dehydration: removes water — bacteria cannot multiply without moisture. e.g. dried fruit, jerky, pasta
• Pickling: acidic vinegar environment (pH <4.5) inhibits bacterial growth
• Salting/curing: salt draws water out of food (and bacteria) by osmosis — e.g. cured meats, salted fish
• Jam making: high sugar content + heat; sugar osmotically inhibits bacteria

Diet and Health

• Dietary Reference Values (DRVs): government guidelines on nutrient intake. Not the same as a diet — just reference amounts to ensure adequate nutrition.
• Non-communicable diet-related diseases: type 2 diabetes (linked to obesity and excessive sugar/refined carb intake); cardiovascular disease (saturated fat → raised LDL cholesterol); some cancers; osteoporosis (calcium and vitamin D deficiency)
• Plant-based diets: increasing evidence that diets rich in vegetables, legumes, wholegrains, and fruits (Mediterranean diet, DASH diet) reduce risk of many chronic diseases
• Food labelling: traffic light system in the UK shows whether fat, saturated fat, sugars, and salt are high (red), medium (amber), or low (green) per portion

Electronics & Programmable Systems

Electronic Components Recap and Advancement

• Capacitor: stores electrical charge and releases it slowly. Used in filters, timing circuits, and power supplies. Symbol: two parallel lines.
• Transistor: a semiconductor device used as an amplifier or switch. A small base current controls a larger collector-emitter current. The fundamental building block of all modern electronics. Billions in a single microprocessor chip.
• Diode: allows current in one direction only. Used to prevent reverse polarity, in rectifiers (AC to DC), and in signal detection.
• Light-emitting diode (LED): emits light when current flows. Different colours from different semiconductor materials.
• Relay: an electromagnetically operated switch. A small current in the coil controls a much larger current in the switch contacts — useful for controlling high-power devices safely from a microcontroller.
• Sensor inputs: LDR (light-dependent resistor — resistance changes with light), thermistor (resistance changes with temperature), potentiometer (variable resistor for manual control), PIR (passive infrared — detects body heat for motion sensing)

Microcontrollers and Programmable Systems

• A microcontroller is a small computer on a single chip. Contains CPU, RAM, ROM (with the programme), and input/output pins. Used to control physical devices in embedded systems.
• Arduino (open-source microcontroller board): widely used in schools, hobbyist projects, and prototyping. Programmed in C/C++ (simplified). Can control LEDs, motors, displays, and read sensors.
• Raspberry Pi: a full single-board computer running Linux. More powerful than Arduino; used for more complex projects, IoT (Internet of Things), and media centres. Programmed in Python.
• BBC micro:bit: designed specifically for education. Can be programmed with block-based code (MakeCode) or Python. Has LEDs, buttons, accelerometer, compass, Bluetooth, and edge connector for external components.

Simple Input–Process–Output Model

• All electronic systems can be described as: Input (sensor, button, switch) → Process (microcontroller reads input and runs programme logic) → Output (LED on/off, motor speed, display message, buzzer tone)
• Example: smart garden watering system. Input: soil moisture sensor. Process: if moisture < threshold, turn on pump; if moisture ≥ threshold, turn off pump. Output: water pump.
• Feedback loops: the output affects the environment, which is then measured by the input — the system responds continuously. Used in thermostats, cruise control, autopilots.