So, as I was routing my way through a PVC sheet I started being concerned a single sheet would not be strong enough against pressure. Also the plan for sealing both front end back lids was flimsy, well I wasn't confident this would work at all. So I looked up T-Zero Systems' solution and realized a real cap would fit better. Now that I can design and print my own parts, I'm willing to double down on moving away from the original design. A better, more robust design:
- moves threaded rods outside the hull, making for more space inside the hull.
- uses o-rings to seal the water out the hull
- is printed and covered in epoxy, and is therefore too thick for the magnetic propulsion design
- involves screwing holes through the cap to let cables through
Internal motors are not an option, so they need to be located outside the hull now. Brushless motors work in water, so that`where Im going. Now I dug a little and found out that brushless motors, due their brushless design, require a specific controller called and ESC for Electronic Speed Controller. I don't understand why BL motors don't come with integrated ESC but I've found quite a variety of options and features to pick from when choosing the right ESC for a given BLDC, first one being to pick a bidirectional one 😅 (no need for that when building a plane for instance). An interesting feature is the BEC (Battery Eliminator Circuit), which seems to be a fancy name for a voltage regulator / step converter (as explained there). in other words, it's an integrated power cable coming out of the ESC, meant to power the Pi or whatever micro-controller is driving the motor.
Since the ESC is powering both engine & microcontroller, it's where the battery gets plugged.
ESC are handily rated X-YS where X and Y are lipo battery types (voltages)
and S is the... unit?
Shopping list:
- 2x BLDC motor. I picked a D2830 with 750KV and 2-4S, which requires (at least) a 30A ESC.
- 2x bidirectional ESC with a 5V3A BEC. The BLHeli seems alright, 40A with BEC 2-4S. I wish it came with XT-60 & banana plugs but I guess I can order connectors on my own :(
- 1x 4S battery, I found this one with an xt60 plug and rated at 7200maH
So all these changes causing new designs to accommodate for new material is what I assume is the price of my lack of experience with this type of project. I'm happy to learn, even though at times it feels like diving deeper and deeper with no guarantee to ever see the surface again. This metaphore is quite à-propos!
At the end of the day that's a few packages to wait for. I'll focus on the tube cap design in the meantime (and setting up a filament drybox :P)