the Build
A slender survey torpedo, built to explore on her own. Here's what's inside — and what she can do.
Specs are design targets, refined as we test.
A 4-inch torpedo hull of four sealed, locking tubes — one for electronics, three for batteries — with a camera nose dome and a finned tail. ~2.1-2.3 m, ~37-40 kg, sized to carry to the water yourself.
Six thrusters (aft, lateral, vertical) on a custom ArduSub frame for efficient transit and precise hovering, with fixed X-tail fins for cruise stability — all active control via the thrusters, no fin servos.
A DIY oil + external-bladder buoyancy engine (VBS): a self-locking leadscrew pushes oil to an external bladder to change displacement — slow, efficient depth changes and soft landings, holding depth at zero power.
About 3.7 kWh across three battery banks, plus an independent survival battery, watched cell by cell — enough for multi-day missions with reserve to spare.
Three independent computers: a bare-metal Supervisor that owns the failsafes, a Pixhawk flight controller, and a Jetson AI brain for the mission and the cameras.
GPS doesn't work underwater, so she dead-reckons from motion, heading and depth, and zeroes the drift with a GPS fix each time she surfaces — with DVL bottom-lock and sonar/terrain matching stacking on for precision.
She runs herself within hard safety limits: an onboard plan with deterministic validators, a small local AI for in-the-moment calls, and Claude reviewing and re-planning at every surfacing. Layered recovery — drop-weights, a timer release and an acoustic pinger — brings her home if anything goes wrong.
Hull, propulsion, buoyancy and electronics architecture frozen.
Every system priced and sourced; parts arriving.
The dry bench build: assemble and bring up all the avionics, then power-on and prove every subsystem before anything gets wet.
16/16 steps · open checklist →Three 4S16P banks: 192 cells spot-welded, busbars in, BMS wired, balanced and capacity-checked. At 14 kg the pack is half the vehicle's mass and the number every other number is derived from.
0/9 steps · open checklist →Electronics and supervisor trays assembled and mounted — Jetson, Pixhawk, thruster-cut FETs, ESCs, comms and the supervisor, each in its tube with its real harness. This is where the bench becomes the vehicle.
First boot with no lab supply anywhere: the real packs, through the real busbars, regulators and rails, running the real trays. Everything up to this point has been on a bench supply.
0/1 steps · open checklist →LTE and Iridium, from the assembled sub rather than a bench. Danu reports its position over satellite and pushes data over cellular, on its own power and antennas.
The dry-fire on the flight article: both heartbeats cut, countdown expires, thrusters cut, burn wires fire into a test load, strobe on, Iridium position away. No READY, no dive.
0/1 steps · open checklist →~25 litres of syntactic foam shaped by hand into a two-piece clamshell. The thing that makes Danu neutrally buoyant and turns a bundle of tubes into a hull.
Tubes and every penetrator hold a vacuum, then submerge dry.
0/9 steps · open checklist →In the water, weighed and balanced: neutral with the drop weight attached, positive without it, level fore and aft. The buoyancy budget stops being a spreadsheet.
All six thrusters, trim, and self-righting proven in shallow water.
Sink, hover and rise on the VBS at shallow depth.
Reservoir: GPS/compass waypoints and return-to-home on her own.
Drift-bounded nav over a natural bottom.
Carried in and recovered from shore, solo.
Hull, dome and bladder hydrostatically proven past operating depth.
Near-shore, short, low-traffic — her first real water.
A self-directed run out and back over several days.
The whole point — eyes on a wreck, footage home.
Everything that can be tested on a table has been tested on a table. It's finally time to start working on the actual sub!
For months, Danu has been a plan — a requirements doc, a bill of materials, and a pile of carefully machined parts waiting on a bench. This week she s…
Card #02 in our requirements series is up — and it answers the first thing anyone asks about a submarine: how deep?
Every part and where it stands. No prices, just progress — grouped by build phase (what gets built when).
| Flight controller | Pixhawk 6C (aluminum case) | Arrived |
| AI computer | Jetson Orin Nano Super dev kit 8GB | Arrived |
| Supervisor MCU | ST Nucleo-F446RE (incl 1 spare) | Arrived |
| GPS | SparkFun NEO-M9N breakout + antenna | Arrived |
| Compass | RM3100 magnetometer — received FlyArm Meg_3D_3100 (generic breakout, bare header) | Arrived |
| LTE modem | Sixfab 4G/LTE kit, Quectel EG25-G | Arrived |
| Iridium | RockBLOCK 9603 (SMA antenna mode) | Arrived |
| Ethernet switch | BotBlox GigaBlox Nano (4x gigabit, 26mm, 5-60V) | Arrived |
| First thruster | T200 + Basic ESC | Arrived |
| Depth primary | Bar30XT (BARXT-VP, sealed) | Arrived |
| Depth backup | Bar30 | Arrived |
| Leak sensors | SOS leak sensor | Arrived |
| Camera primary | Arducam IMX678 4K STARVIS 2 USB 3.0 (bare module, NO enclosure) | Arrived |
| Camera secondary | DWE exploreHD (400m sealed, epoxy/potted cable) | Arrived |
| Bench charger | ISDT P30 | Arrived |
| Iridium antenna | Maxtena M1621HCT-P-SMA (passive Iridium helical, 1616-1626.5MHz, SMA-M, IP67) | Arrived |
| Iridium antenna feedthrough | SMA F-F bulkhead, epoxy-potted into M10 (depth-rated) + short internal SMA jumper | Arrived |
| Camera gimbal (pan/tilt) | Adafruit Mini Pan-Tilt bracket (#1967) + 2× MG90S metal-gear servos + printed camera adapter | Arrived |
| Power module | Holybro PM08-CAN (DroneCAN, 2-14S / 200A, dual 5.2V BEC) | Arrived |
| Switch connector board | BotBlox GigaBlox Nano Pico-Conn (PicoBlade->RJ45) | Arrived |
| Camera rear | DWE exploreHD (400m sealed, epoxy/potted cable) — rear-facing | Arrived |
| I2C splitter | I2C splitter board (bundled with the Pixhawk 6C kit, #1) — passive JST-GH fan-out | Arrived |
| Bench DC power supply | Adjustable bench PSU — e.g. 0–30V/10A (electronics) + a 16V/40A+ rail for thruster tests (or one 30V/30A) | Arrived |
| Jetson boot SSD | NVMe M.2 SSD 256–512GB | Arrived |
| microSD cards | microSD 64GB (Pixhawk logging) + spare | Arrived |
| Powered USB hub | Yahboom USB 3.0 HUB (VL817, 4x USB-A 3.0, 9-24V in, 5A) — 68.5x60.35x19.6mm, fits 4in bore | Arrived |
| Multimeter | Digital multimeter (true-RMS) | Arrived |
| Bench consumables | Dupont/jumper wires, USB-C/USB-A cables, XT60/XT90 leads, silicone wire, JST/ferrule crimp kit, heat-shrink, solder | Arrived |
| Vacuum pump | Mityvac MV8255 | Arrived |
| Vacuum plug | BR vacuum plug | Arrived |
| O-ring grease | Molykote 55, 100g | Arrived |
| O-ring kit | OSK 386pc metric Buna-N + exact-size spares | Arrived |
| Pick set | Hook & pick set | Arrived |
| Potting epoxy | MG Chemicals 832B 450ml kit | Arrived |
| Marine epoxy | West System 105/205 + mini pumps | Arrived |
| Field epoxy | Loctite Marine syringes | Arrived |
| JST crimper | Engineer PA-09 | Arrived |
| Ferrule kit | IWISS HSC8 6-4 + ferrules | Arrived |
| Heat shrink | Wirefy adhesive-lined 3:1 kit | Arrived |
| HDPE sheet | 1/2" × 24×48 (frame) | Arrived |
| Filament | PETG ×2 + ASA ×1 | Arrived |
| Chem kit | Loctite 243 + Permatex anti-seize + IPA | Arrived |
| Calipers | iGaging EZ-Cal 6" | Arrived |
| Torque driver | Wheeler FAT Wrench 10–65 in-lb | Arrived |
| Fasteners | 316 SS M3–M5 per-size boxes | Planned |
| 3D printer (Bambu H2C) | Bambu Lab H2C (Vortek hot-end swap; no laser) + filament dryer (AMS optional) | Arrived |
| Thermal coupling | Thermal pad/copper-shim kit + flat tinned copper braid straps (couple Jetson/regulators/ESCs to the hull) | Arrived |
| Thrusters | T200 (5 more, 6 total) | Arrived |
| ESCs | Basic ESC R3 | Arrived |
| Pressure tubes | WTE Locking Tube 4in aluminum - 1x 300mm (electronics) + 3x 400mm (battery banks) | Arrived |
| End caps | WTE 4" alu end caps (mixed hole patterns) | Arrived |
| Dome | 4" polycarbonate dome BR-107201 (1000m) | Arrived |
| O-ring flanges | WTE 4" O-ring flange | Arrived |
| Clamps | Enclosure clamp 4" | Arrived |
| Penetrators | WetLink M10 (assorted seal sizes) | Arrived |
| Penetrator blanks | WLP blank M10 | Arrived |
| Vent/vacuum/PRV | Vents ×3 + vacuum plug + PRV ×3 + backfill | Arrived |
| Power switch | M10 switch 5A | Arrived |
| Lights | Lumen R4 set of 4 | Arrived |
| Echosounder | Ping2 sonar altimeter | Arrived |
| Flotation foam | R-3318 large block | Arrived |
| Water temp | Celsius sensor | Arrived |
| BR sundries | Molykote 111, picks, desiccant, WLP wrenches, O-rings | Arrived |
| X-tail fins (fixed) | Fixed X-tail fin set — fabricated HDPE/3D-printed (passive, no servos) | Planned |
| Lights — zone 2 | Lumen R4 pre-connected set of 4 (500m) — outer/wide zone | Arrived |
| Echosounder (forward) | Ping2 sonar — forward-facing (basic forward collision warning) | Arrived |
| Thruster guards | T200 intake guards/screens — 3D-printed (tough filament), 6× | Planned |
| Sacrificial anode | US Marine Products MAGNESIUM anode (freshwater) — bolt-on, bonded to hull | Arrived |
| VBS leadscrew | ACME leadscrew + anti-backlash bronze/Delrin nut (~8mm, ~300mm stroke, small lead) | Arrived |
| VBS motor | NEMA23 stepper (or geared BLDC), >=1 N·m | Arrived |
| VBS motor driver | Stepper driver (DM542-class) or BLDC ESC | Arrived |
| VBS cylinder + piston | ~20mm bore x ~300mm stroke, Al/Delrin; rolling-diaphragm or O-ring piston (oil side only) | Planned |
| VBS external bladder | Reinforced TPU/rubber bladder ~0.2 L + perforated shroud | Planned |
| VBS hydraulic oil | Light mineral/hydraulic oil + fill/bleed port | Planned |
| VBS oil penetrator | High-pressure bulkhead fitting (dry module -> external bladder line) | Planned |
| VBS position sensor | Linear pot / encoder + end-limit switches | Planned |
| VBS pump module + mounts | Dedicated dry pump-module housing + printed/HDPE mounts | Planned |
| Mast antenna feedthroughs | SMA bulkheads + potting for GPS / LTE / AIS-VHF mast antennas (design TBD with mast) | Planned |
| Battery cells | Samsung INR21700-58E — 5330 mAh min, 10.7 A cont, flat top. 4S16P per bank x3 = 192 cells + 6 spares; ~3.7 kWh total. See docs/POWER-BUDGET.md. | Arrived |
| BMS | 4S 60/80A Li-ion BMS, 61x42mm (Create idea, 2-pack) | Ordered |
| Survival battery | Bioenno BLF-1206A 12V 6Ah LiFePO4 | Arrived |
| Spot welder | Glitter 801D capacitive | Arrived |
| Nickel strip | Pure nickel strip 0.15mm x 8mm (~15m needed) | Ordered |
| Pack materials | Pack materials — fish/barley paper, Kapton tape, cell-top insulator rings (cell holders are 3D-PRINTED, not purchased) | Arrived |
| Connectors/wire | XT90-S anti-spark (pack/bus trunk) + XT60 (thruster & accessory branches); silicone 10 AWG trunk + 12-14 AWG branches + 16-22 AWG signal; JST-GH | Arrived |
| 5V regulators | Pololu D24V50F5 | Arrived |
| 12V regulators | Pololu D36V50F12 | Arrived |
| Ideal diodes | LTC4357/LTC4359 modules (bank ORing) | Planned |
| Fuses & holders | Fuse kit — 4x ANL/MIDI holders (3 banks + main bus) + 6-8 way blade fuse block (low-current branches) + assorted ANL (60A, 80-100A) & blade (10A) fuses + spares | Arrived |
| Thruster-cut (solid state) | Solid-state high-side thruster disconnect — 4x IRFB7430 (40V ~1.3 mOhm) paralleled + high-side charge-pump gate driver (LTC7000/LTC7001 class) + TVS | Arrived |
| Magnetic arm switch | Waterproof magnetic reed switch (NO/NC, 2-pack) — external magnet arms/disarms through the hull | Arrived |
| Bus capacitors | 35V 1000uF low-ESR filter capacitor (XT-lead) — mount on the ESC bus | Arrived |
| Charge port | CNLINKO LP20 IP68 2-pin panel connector (20A) — surface charge interface | Arrived |
| 3.3V regulator (LDO) | 3.3 V LDO, 250-500 mA, fed from the 5 V rail — supplies the RM3100 compass (VDD + I2CEN) and any future 3.3 V logic | Arrived |
| Imaging sonar | Ping360 | Planned |
| Tube sensors | BME280 (temp/RH/baro) — seal integrity | Arrived |
| Power monitors | INA228 high-side I2C | Arrived |
| Thruster current | ACS724 30A hall sensor | Arrived |
| Light sensor | TSL2591 lux (behind dome) | Arrived |
| Hydrophone | Aquarian H2a + USB audio interface | Planned |
| Internal mic | SPH0645 I2S MEMS | Arrived |
| Leak probes | Extra SOS probes + tips | Arrived |
| Burn-wire sense | Continuity sense resistors | Planned |
| I2C mux | TCA9548A ×2 + Qwiic cables | Arrived |
| Engine room cam | 160° USB board cam + pan servo + LED strip | Planned |
| DVL | Water Linked DVL A50 (300m) — 1-yr-old unit, 25% off | Arrived |
| AIS receiver | dAISy 2+ USB AIS receiver + small VHF whip on the mast | Planned |
| Strobe (USCG) | Sirius Signal C-1003 SOS light | Arrived |
| Strobe (12V) | Waterproof LED beacon (supervisor-driven) | Arrived |
| Burn wire | Nichrome 80, 30 + 32 AWG spools | Arrived |
| Release hardware | 316 springs/pins + 25lb lead shot | Planned |
| Timer release | DIY: ATtiny + coin cells, potted | Planned |
| Recovery pinger | DIY: piezo + ATtiny, potted | Planned |
| Tether | Fathom Slim 100m (ROV-ready) | Planned |
| Tether interface | Fathom-X board pair | Planned |
| AIS recovery beacon | Ocean Signal rescueME MOB1 (AIS + DSC, 7-yr standby, 24h active) | Arrived |
| Acoustic recovery beacon | Commercial 37.5kHz ULB — RJE ULB-362PL (power-loss auto-activate, ~90-day) | Planned |
| Pinger receiver | Directional 37.5kHz diver/locator hydrophone (topside) | Planned |
| Hi-vis surface marker | Hi-vis flag/pennant on mast + retroreflective tape | Arrived |
| Manipulator — gripper | BlueRobotics Newton Subsea Gripper (300m, 62mm jaw, 97-124N) | Planned |
| Landing skids/feet | Landing gear — HDPE + 3D-printed feet, wide footprint | Planned |
| Sample caddy | Free-flooding sample basket — 3D-printed, multi-compartment + mesh + latch | Planned |
| Pack collectors | 0.5mm (24ga) C110 copper sheet, 300 x 600mm | Ordered |
| Cell checker | 1-8S LiPo/Li-ion balance-lead voltage checker | Ordered |
| Pack/joint temp | DS18B20 1-Wire sensors (TO-92) + 4.7k pull-up | Planned |
Videos coming soon — build vlogs, tank tests, and dives. Visit the channel →