The Direct Solar DC Grinder worked. The prototype demonstrated that you could drive a grain mill directly from a solar panel with no battery buffer and no grid connection. The technical result was clean. The product was still two years away.
The gap between a working prototype and a shippable product is the most dangerous part of hardware development. It is where most hardware innovations stall. The technology works. The translation to a real operating environment surfaces requirements the prototype never had to satisfy.
What the Prototype Does Not Test
A prototype tests the core technical hypothesis. It does not test the service model. It does not test operating conditions at the tail of the distribution. It does not test what happens when a user who received no training tries to interact with it for the first time. It does not test what happens after 18 months in a dusty field in conditions no lab replicates.
These are not edge cases. They are the product. The prototype that works perfectly in a controlled environment and fails in the field after six months did not fail in the field. It failed in the gap between prototype and product, where nobody asked the right questions.
The Irrigation Valve Redesign
The wireless irrigation control system went through three significant valve redesigns between prototype and production. The first prototype valve was mechanically sound and required a trained operator. Three rounds of field interviews with farmers in three different states made clear that trained operators were not going to be available in the target operating environment.
The third design, the one that shipped, came directly from watching users interact with the second prototype in real field conditions. The interaction pattern they naturally used was different from the one the design assumed. None of this could have been discovered in a lab. Building the first two designs was not wasted effort. It was the process by which the product architecture became knowable.
Can someone with no technical background, in the actual operating environment, use this system effectively over its intended lifetime with the service support that will actually be available? The prototype answers a different question.
Closing the Gap Deliberately
The teams that navigate this gap well treat it as a distinct phase with its own deliverables. Not "continue development until the product is ready" but "answer the following specific questions before committing to production-intent design." Those questions cover the operating environment, the service model, the user, and the supply chain.
This phase has a name in the IIL methodology: the pre-production stage. Its purpose is not to build a better prototype. It is to gather the information that makes production-intent design decisions possible.