Design Brief for an Aged-Care Mobility Aid
A Year 12 student is developing a major design project: a walking frame for a local aged-care facility. The brief requires it to fold for transport, weigh under 4 kg, support a 120 kg user, and cost under $180 to produce. The student has built a prototype from 25 mm aluminium tube with a single pivot bolt and a spring-loaded locking pin. In testing, the frame folds unexpectedly when a 90 kg load is applied off-centre, and the facility's physiotherapist says the grips are too small for arthritic hands. The student has eight weeks left, a $300 materials budget, and access to the school's metalwork room (welding, brazing, lathes) but no CNC or 3D printing. The folio currently contains sketches but no test data.
1. Evaluate the prototype failure and explain what the student should do next in the design process.
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The failure is a design and safety issue, not a manufacturing accident: a single pivot with a spring pin creates a single point of failure, and off-centre loading produces a moment that the pin cannot resist. The correct response is to return to research and testing rather than patching the prototype.
Specifically the student should:
- Define the load cases (vertical, off-centre, lateral) and the failure criterion (no folding below a stated safety factor, e.g. the frame must withstand well above 120 kg).
- Redesign the folding mechanism so the load path does not pass through the pin alone: for example a sleeve or brace that engages when unfolded, or a dual-pin arrangement, so a single pin failure does not collapse the frame.
- Re-test systematically and record the data, since the folio has no test evidence and the marking criteria reward documented evaluation.
- Address the ergonomic finding (grip diameter and material) as a separate design requirement derived from end-user research, not as an afterthought.
The judgement point is that the physiotherapist's feedback and the failed test are valuable design information; the student should treat them as inputs to a revised brief and specification, and document the iteration in the folio.
2. The student proposes welding the frame solid to eliminate the folding risk. Assess this proposal against the brief and constraints.
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Welding the frame solid removes the folding failure mode cheaply and uses equipment the student actually has, which is a genuine advantage. But it fails the brief: the frame must fold for transport, and a solid frame also becomes bulky to store in the facility and difficult for a user to lift into a car.
It also creates new problems:
- A welded aluminium frame needs appropriate filler and heat control; distortion and heat-affected-zone weakening are real risks in a school workshop, and the student may not have the skill to guarantee weld quality on thin tube.
- Welding removes adjustability, so the frame cannot be tailored to different user heights.
- It does not address the grip problem at all.
A better judgement is to keep the folding requirement and solve the locking problem properly, using the workshop's capability (machining a sleeve, brazing a reinforced joint) rather than abandoning a core brief requirement to avoid a difficult sub-problem. If time forces a compromise, the student should document the trade-off explicitly in the folio, showing awareness of the constraint rather than hiding it.