Budget Trade-off in a Small Engineering Project
A graduating student team must build a working prototype of a solar-powered water pump controller for a capstone exhibition in 6 weeks with a budget of 25,000 AFN. The design has three subsystems: a charge controller (estimated 9,000 AFN in parts), a pump driver (8,000 AFN), and a sensor/display unit (6,000 AFN), totaling 23,000 AFN, leaving 2,000 AFN contingency. Week 3 testing reveals that the chosen charge controller overheats above 40°C and needs either a heatsink and fan (1,500 AFN, 3 days) or a replacement module (4,000 AFN, 5 days, but more efficient). The pump driver has not been tested. The exhibition requires a live demonstration, and the team has one soldering station and two members who can use it.
1. Compare the two charge-controller options against the budget, schedule, and risk, and recommend one.
Read the worked answer
Option 1 - heatsink and fan: cost 1,500 AFN, fits within the 2,000 AFN contingency, takes 3 days, keeps the existing module. Risk: the fix may not fully solve overheating if ambient temperatures exceed the tested range; the fan adds a moving part that can fail during the demo.
Option 2 - replacement module: cost 4,000 AFN, which exceeds the 2,000 AFN contingency by 2,000 AFN, so the team must cut elsewhere (e.g., trim the sensor/display budget). Takes 5 days and is more efficient, reducing heat at the source.
Recommendation: option 1 first, because it preserves contingency and time for the untested pump driver, which is a larger unknown. But set a checkpoint: if testing after the heatsink fix still shows overheating near 40°C, switch to option 2 immediately. Keep the 500 AFN remaining contingency untouched for the pump driver. The untested pump driver is the bigger schedule risk, so spending the contingency on a controller fix before that driver is tested is premature.
2. The pump driver has not been tested and there are 3 weeks left. How should the team sequence testing given one soldering station and two skilled members?
Read the worked answer
Treat the untested pump driver as the critical path. Sequence:
- Week 4, days 1–3: bench-test the pump driver alone, using the soldering station for any rework. One member tests while the second prepares instrumentation and records results. Do not start integrated testing until the driver runs reliably on the bench.
- Week 4, days 4–5: integrate driver with the fixed charge controller and run a load test.
- Week 5: full-system test including the sensor/display; fix faults; freeze hardware by end of week 5.
- Week 6: rehearse the live demonstration, including a fallback (battery-only or manual mode) in case the solar input is weak on the day.
The single soldering station is a bottleneck: schedule all rework in one block rather than interleaving, and have the second member handle non-soldering tasks in parallel. A fallback demonstration mode protects against a failure that cannot be fixed on exhibition day.
3. Halfway through week 5 the sensor/display fails and cannot be repaired within budget. What should the team do, and how should they present the prototype?
Read the worked answer
The sensor/display is a monitoring feature, not the core function (pumping water). The team should not sacrifice the working pump and controller to chase a display. Options: (a) remove the display and report sensor readings through a simple indicator (LED thresholds) if parts allow; (b) drop the display and document the intended design, showing measured data collected before the failure.
Presentation: demonstrate the working pump and controller live, state plainly that the display subsystem failed and was removed to protect the core function, and show the test data that was collected. Explain the decision as a deliberate trade-off - preserving the live demonstration of the main function over a secondary feature - rather than presenting a partial system as complete. Examiners generally reward honest reporting of a failure and a reasoned recovery over an unacknowledged gap.