Scientists mostly ask why and how nature works. Engineers ask a different question: how can we solve this problem? The Canadarm, the robotic arm that flew on the US space shuttles from 1981, had to lift huge loads in space yet weigh little and fold neatly into the shuttle's cargo bay. Nobody got that right on the first try. Designers sketched, built test versions, found what failed, and improved them again and again. That loop of design, test and improve is the engineering design process, and you can use it for anything from a better phone stand to a bridge.
The design cycle
- Define the problem. Say who has the problem, what the solution must do (criteria) and what limits you must work within (constraints).
- Research. Find out how others have solved similar problems and what materials and science ideas apply.
- Brainstorm. Come up with many possible solutions without judging them yet.
- Choose and plan. Compare the ideas against the criteria and constraints, pick one, and make labelled sketches and a materials list.
- Build a prototype. A prototype is a first working model used for testing.
- Test. Measure how well the prototype meets each criterion, using fair, repeated tests.
- Evaluate and improve. Find what failed and why, change the design, and test again. Each round is called an iteration.
- Communicate. Share the final design, test results and what you learned.
Criteria and constraints
- Goals you can measure, used to judge success
- The bridge must hold at least 2 kg
- The bridge must span a 30 cm gap
- The bridge should be as light as possible
- Restrictions on materials, money, time, size or safety
- Use only 50 craft sticks and white glue
- Finish in two class periods
- Cost no more than the supplies provided
Good designs balance criteria against constraints. Making the bridge stronger usually means adding more sticks, but more sticks make it heavier and use up your limit. Giving up some of one thing to get more of another is called a trade-off. Engineers also expect early prototypes to fail. A failed test is data: it shows exactly where the design is weak. Just like in a fair test, change one thing at a time between iterations so you know which change made the difference.
| Scientific experimentation | Engineering design | |
|---|---|---|
| Starts with | A question about how nature works | A problem that people need solved |
| Main goal | Explain: find out what is true | Create: make something that works |
| What you test | A hypothesis, using variables | A prototype, against criteria |
| Typical result | A conclusion supported by data | An improved product, device or system |
Choosing between designs: a decision matrix
| Criterion (weight) | Design A: truss | Design B: arch | Design C: flat beam |
|---|---|---|---|
| Strength (× 3) | 4 → 12 | 3 → 9 | 5 → 15 |
| Low cost (× 2) | 2 → 4 | 5 → 10 | 1 → 2 |
| Easy to build (× 1) | 5 → 5 | 3 → 3 | 2 → 2 |
| Total | 21 | 22 | 19 |
STEM careers and the skilled trades
| Career | How it uses design and investigation |
|---|---|
| Electrician (skilled trade) | Plans and installs wiring to meet the electrical code, then tests circuits for safety |
| Millwright / industrial mechanic (skilled trade) | Installs and repairs factory machines; diagnoses faults by testing one part at a time |
| Heating, ventilation and air conditioning (HVAC) technician (skilled trade) | Sizes and installs systems for a building, measures airflow and temperature, and adjusts |
| Civil engineer | Designs bridges, roads and water systems against criteria such as load and cost |
| Environmental technologist | Samples water, soil and air, records data, and checks results against standards |
| Agricultural technician | Runs field trials of crops or growing methods with controlled variables |
Canada has a long record of design. Elsie MacGill designed the Maple Leaf Trainer II airplane in the late 1930s and then led the engineering work to mass-produce Hawker Hurricane fighters at a factory in Fort William (now Thunder Bay), Ontario. Engineer John Hopps helped build one of the first heart pacemakers at the National Research Council in Ottawa around 1950. The Canadarm was built by the Canadian company Spar Aerospace. More recently, a Montréal team led by Mohamed Hage founded Lufa Farms and opened what is described as the world's first commercial rooftop greenhouse in 2011, designing a way to grow vegetables on city roofs year-round.