EC-15.2 Capstone I: Design, Plan and Feasibility

What this is and why it exists

The first stage exists to answer one question. Is this buildable, by these people, in this time?

That is why the feasibility demonstration is on the riskiest element rather than the simplest. It is also why lead times appear here rather than being discovered later.

The hours for this topic are larger than anywhere else in the area, because a capstone stage is a term of work. An estimate pretending otherwise would be the one figure in the area that lies.

The vocabulary

• Feasibility demonstration — the smallest build that proves the risky part works.
• Bill of materials — the list of every part, with cost, source and lead time.
• Lead time — how long a part takes to arrive after it is ordered.
• Critical path — the sequence of tasks that decides the earliest finish.
• Slack — spare time in a schedule, placed where it may be needed.
• Approval — permission required before certain work may proceed.
• Stage review — the meeting that decides whether the project continues as planned.

The mental model

The first stage turns a proposal into a design somebody could build from. Architecture, interfaces, component choices, and the calculations showing that the design meets its requirements.

The test is whether a second person could start building from what you have written. If the answer needs a conversation with you, the design is still in your head rather than on paper, and it is not finished.

The feasibility demonstration is the heart of the stage. Build the smallest thing that proves the frightening part works.

Not the easiest part, which you already know will work and which produces a satisfying photograph. The part you are least sure about. Doing this in the first stage turns an unknown into either a solved problem or a changed plan. It does so while the plan can still change.

Leaving it until the second stage is how a project discovers in week nine that its central assumption was wrong.

The bill of materials is where projects die quietly. Every part, its cost, where it comes from, and how long it takes to arrive.

A component with an eight-week lead time, discovered in the second stage, has ended more projects than any technical difficulty. Checking lead times takes an afternoon and it is the cheapest insurance available. Note an alternative for anything critical, so that a supply problem is an inconvenience rather than a redesign.

The schedule needs tasks, dependencies, and an honest view of which tasks cannot start until others finish. That chain is the critical path, and it is the only part of the schedule that decides the finish date.

Where the slack goes matters more than how much there is. Put slack next to the uncertain tasks rather than saving it all for the end. Slack at the end is consumed by the first thing that overruns and protects nothing after that.

Safety, ethics and approvals belong in this stage rather than the next. Mains voltages, radio transmission, anything involving people or their data, and anything that could injure someone.

Whatever permission is needed takes time to obtain, and the first stage is when to find out what is needed. Discovering an approval requirement in the second stage usually means the project cannot proceed as designed.

Finally, the stage review, which has three possible conclusions and only three. The project is feasible as planned. It needs a stated change. Or it should be replaced with something achievable.

A review that concludes only that progress has been made has not done its job, and it leaves everyone comfortable until the deadline arrives.

What you should now be able to explain or do

• Take a proposal to a design a second person could build from.
• Choose the riskiest element and demonstrate its feasibility first.
• Build a bill of materials with costs, sources, lead times and alternatives.
• Identify the critical path and place slack next to the uncertain tasks.
• Identify what approvals a project needs, early enough to obtain them.
• Run or attend a stage review that reaches one of its three real conclusions.

Check yourself