HKDSE DAT cheat sheet

Design process cycle: identify problem → research → specify criteria and constraints → generate ideas → develop and model → evaluate → realise. Evaluation feeds back into earlier stages rather than ending the cycle.

Design fixation is premature commitment to one solution type; countermeasures include brainstorming rules (defer judgement, build on others' ideas, encourage wild ideas) and morphological analysis.

Morphological chart: list independent design parameters as rows and possible options as columns, then combine options across rows to generate new solution variants.

Criteria types: must-have constraints are binary (pass/fail); desirable criteria are weighted and scored, typically on a 1–5 scale, then multiplied by weight and summed for comparison.

Function analysis expresses a product as a verb–noun pair (e.g. 'transmit torque'); it separates what the product must do from how it does it.

Ergonomic data to apply: anthropometric percentiles (5th percentile female to 95th percentile male for reach; limits for clearance), posture neutrality, and repetitive-strain avoidance.

Design for sustainability hierarchy: avoid/reduce material → reuse components → recycle materials → recover energy → dispose. Embodied energy and end-of-life are assessed across the whole life cycle.

Intellectual property: a patent protects a novel, inventive and industrially applicable functional invention for up to 20 years; a registered design protects appearance; copyright protects original works automatically.

Ferrous metals contain iron (steel, cast iron); non-ferrous metals include aluminium, copper, brass and titanium. Ferrous metals are magnetic and susceptible to rust unless alloyed or coated.

Hardness tests: Brinell uses a hardened steel or carbide ball (HB); Vickers uses a diamond pyramid (HV); Rockwell uses indentation depth (HRC). Tensile testing yields Young's modulus from the elastic gradient of a stress–strain curve.

Thermoplastics (PE, PP, PVC, ABS) soften on heating and can be remoulded; thermosetting plastics (epoxy, melamine, polyester resin) cross-link permanently and cannot be remelted.

Manufacturing process selection rules: injection moulding for high-volume complex thermoplastic parts; vacuum forming for large shallow shells; extrusion for constant cross-section; blow moulding for hollow containers.

Joining: soldering melts filler below ~450 °C without melting the workpiece; brazing is above that; welding fuses the parent material. Mechanical fasteners allow disassembly; adhesives spread load but resist peeling poorly.

Mechanisms: gear ratio = driven teeth ÷ driver teeth; velocity ratio of a pulley or gear train equals the ratio of input to output speed; a worm drive gives large reduction and resists back-driving.

Structures: a truss is rigid when triangulated; members carry tension or compression; bending moment is largest where shear is zero. Adding depth increases stiffness more efficiently than adding material thickness at the neutral axis.

Electrical/electronic basics: V = IR; series resistances add; parallel resistances combine as 1/RT = 1/R1 + 1/R2; a potential divider gives Vout = Vin × R2/(R1+R2). Logic gates: AND, OR, NOT, NAND, NOR, XOR.