Hardware design & fabrication

While not much forward progress has been made in the past month, we remain committed to our goal of a spring/summer maiden voyage. Part of the delay is due to hardware fabrication and purchasing. Purchasing at the hobbyist level can be difficult for certain specialty items because the few companies that have a product don't have the sales resources to deal with small fish clients. These companies typically rely on large orders and aren't in the business of web stores and one-offs. Hobbyist fabrication is undoubtedly more prevalent nowadays, but still remains expensive on a small scale for specialized parts. The lesson is to make friends with skilled machinists.

Despite delays, we're executing on a carefully crafted plan for hardware fabrication. Let's take a look at that plan in bullet point format:

1. Fabricate the acrylic viewing dome. This dome will be attached to the front of the sub, will hold the Point Grey computer vision camera used for visual navigation. We looked at two different manufacturers for this-- eMachineShop and CalPlastics. CalPlastics is the lower-cost option, despite a $400 minimum order on custom fabrications. They don't guarantee a uniform thickness throughout the dome, since they use a blowing process to form it, but for that price we were able to purchase three units. They also can't guarantee exact screw hole placement because they hand drill them. We compromised on a machined ring that they'd place overtop the dome's flange to guide the hand-drilled hole position. In hindsight, we should have first purchased the dome before the acrylic hull. CalPlastics sells domes for $30 each that comply to a different tube diameter, and acrylic tubes are available in an abundance of sizes.
2. Buy the cast acrylic hull tube. We already did this through US Plastics, who sells cast acrylic tubing in five foot minimum lengths, which they'll cut for $1 per cut. We chose cast acrylic, despite the price increase over extruded, because cast acrylic is typically clearer and lacks the striations present in extruded materials. Also keep in mind that the edge pieces of the original five foot piece are not flat! We didn't know this, and ended up with two unusable one foot pieces (until we can cut them). Further headache came from US Plastic's refusal to refund 20% of the cost for a one foot section that came deeply scratched. They eventually gave in, but not until after several heated emails. As I mentioned above, this step should have come second, due to the wide availability of differently-sized acrylic tubes. What can I say-- hindsight is 20/20.
3. Buy the external connectors. After a month+ wait, Seaconn sent to us quotes for a number of their underwater-mateable All-Wet connectors. They're pricey, to the tune of $1200 for connectors for six thrusters, two battery packs, six miscellaneous (lights, ballast tanks, etc), and a number of dummy connectors. Once we have these, we'll know how many, and what size, holes the aluminum endcap should have.
4. Fabricate the endcap and flange adaptors. The flange adaptor forms a seal to the inside of the acrylic hull and provides a surface onto which the endcap, and the dome on the other end, can screw onto. All of these parts are designed, barring the number and size of holes in the flat aluminum endcap. Given the possibility that the screw holes in the acrylic dome are not placed properly, we have not yet started the fabrication process on these parts. Add to that the fact that eMachineShop may take up to 35 days to manufacture.
5. Finishing the aluminum parts. eMachineShop charges an arm and leg for parts finishing. The most we can afford is a brushed finish. After that, we plan to use a local shop for hard anodizing. These processes together should smooth the pieces enough to form a solid seal with the o-rings.
6. Pot the batteries. We'll place the batteries, two each, into anodized aluminum tubes filled with thermally-conductive potting compound. This will protect the batteries from water and other damage, as well as provide a uniform metal exterior that is easily attached to sub's external frame.

Encap sans connector holes

flange adaptor

viewing dome