Prototype Construction, cont'd.

I've actually kept quite busy for the last week. I've been sourcing and producing parts for the first working model, which is quite exciting. For this first model, whose primary purpose is to ensure everything in the design works as expected, I've chosen to use advanced production techniques not available in Ghana. This is mostly to reduce cost and effort, but also for the important fact that this prototype is meant to validate the design, and deviations in dimensions and quality could affect those results. If the design works with everything precisely in tolerance and properly assembled, I can start replacing high-tech parts with simpler ones, and start looking into what in the system can be replaced in the field with whatever's around.

So far, I've produced the large gear, both cams, and the two bearing mounts using 3-D printing, from an ABS plastic honeycomb. They're all within +-0.003" tolerance, according to the machine and measurements. I've also sent all sheet metal part blueprints to the water-jet, which has about a one week lead time, with a +-0.012" tolerance. I've also acquired all hardware and miscellaneous bits from McMaster-Carr, including a 6ft section of 7/16" Al-6061 rod which I'll machine six axles from.

Many of the parts -- specifically, the nuts, bolts, axle, and a few others -- are best purchased in quantity and amortized across multiple units. I've yet to put together an exact price estimation per unit, but I expect below $50 -- the sheet metal is the biggest unknown expense for production, and may drive costs up.

Below in Fig. 7 you can see the collection of 3-D printed parts -- anything which I've printed can just as easily be made from wood or even aluminum with only a bandsaw, file, and drill, which should ease production in the field. I understand the large gear may also be available from the same company which supplies our coin mechanisms, which would improve lifespan over a plastic or wooden component -- the necessary equipment to machine the specific pitch and modulus of gear needed is very uncommon, and not available in the easy-to-get-to shops.

Figure 7: 3-D Printed Parts and hardware (Bearings visible on the right)

More to come over the coming weeks, particularly once the water-jet parts are returned -- from there, assembly should take only a day or two. I'm hopeful for a working device by the first of November. From there, I can start determining which parts can easily be made in the field, and playing with different methods of manufacturing the system in less-than-optimal conditions.