UWU PDB

SwimBladder

Power distribution board (PDB) project files for the SwimBladder project.

Silkscreen tag: SOAR UWU | 8 x T200 | V1.1

[!WARNING] This board is an unvalidated, untested work in progress (WIP). It has not completed electrical, thermal, or in-water system validation. Do not treat this design as production-ready hardware.

Project Status

• Current state: WIP (design in progress)
• Revision: V1.1
• Validation status: not electrically validated
• Test status: not thermally validated, not full-load validated, not field-tested
• Use at your own risk until formal verification is completed

Repository Contents

• KiCad Project Files v1.1/ - Canonical KiCad project, PCB, schematic, and the SwimBladder Custom Footprints library. Open KiCad Project Files v1.1/UWU PDB.kicad_pro.
• KiCad Project Files/ - Deprecated earlier project set, kept for history. Do not edit.
• SwimBladder PDB.kicad_sch (repo root) - Stale May snapshot, superseded by the schematic inside KiCad Project Files v1.1/. Do not use.
• Screenshots/ - Board and schematic screenshots. v1.1 *.png are current; the unprefixed files are the earlier V1.0 captures.
• SwimBladderV1.0.step - 3D board model (V1.0 geometry).
• Swim_Bladder_Doc_v3_0.pdf - Full engineering reference and calculations. Component values in this PDF predate the V1.1 schematic changes listed below.

Project Overview

This board is designed as a compact 8-thruster central star-node PDB for Blue Robotics T200 systems with 4S battery input. It is currently in a pre-validation state and should be treated as a reference design draft.

• System topology: battery -> cable-side main fuse -> optional e-stop/contactor -> dual XT90 input -> central high-current node -> 8 fused ESC branches -> XT60 outputs
• Nominal battery voltage: 14.8 V (4S), full charge: 16.8 V
• Thruster design current: about 25 A each
• Total design current: 200 A (with burst targets up to around 280-300 A)
• Per-branch fuse target: 30 A

Schematic Summary (V1.1)

Input / central node

• Dual XT90 input connectors (J1, J19) feeding one common +VBAT star node, symmetrical wiring for current sharing.
• Bulk capacitance at the node: C_MAIN1, C_MAIN2 = 4700 uF each.
• Input TVS: D1 (D_TVS), 22-24 V standoff class for 4S. Recommended part: SMDJ22A (unidirectional, 3 kW, DO-214AB / SMC footprint, Diode_SMD:D_SMC or D_SMC_HandSolder).
• Rail bleed / discharge: R_BLEED1 = 22 kOhm. Draws ~0.76 mA / ~13 mW continuously at full charge - trivial dissipation for a 0603, well within its power/voltage rating.
• Power/status LED: D2 (LED) with series resistor R_LED1 = 10 kOhm.

Per-ESC branch (x8)

• Branch fuse: F_ESC1..F_ESC8 = 30 A.
• Branch bulk cap: C_ESC1..C_ESC8 = 1000 uF.
• Branch high-frequency cap: C_HF1..C_HF8 = 1 uF.
• Output: J3..J10, XT60 per branch.
• Branch decoupling is now two caps (1000 uF + 1 uF). The earlier third per-branch cap (1 nF high-frequency) has been removed - on a high-current motor branch it contributes negligible benefit and can create anti-resonance with the larger caps.

PWM signal

• 16-pin IDC header J2 (Conn_02x08_Odd_Even, 2x8, 2.54 mm), alternating PWM / GND pins. Suggested part footprint: Connector_IDC:IDC-Header_2x08_P2.54mm_Vertical.
• Individual PWM channel inputs: J11..J18 (PWM1..PWM8).
• Per-channel series resistor: R_PWM1..R_PWM8 = 100 Ohm.
• Per-channel pulldown resistor: R_PD1..R_PD8 = 10 kOhm.

Passive Footprint Notes

• PWM channel series resistors (R_PWM*): 0402 hand-solder land pattern (Resistor_SMD:R_0402_1005Metric_Pad0.72x0.64mm_HandSolder) for IDC header pitch.
• All other signal passives (R_BLEED1, R_LED1, R_PD*) and branch HF caps: 0603 hand-solder (R_0603_1608Metric_Pad0.98x0.95mm_HandSolder / C_0603_1608Metric_Pad1.08x0.95mm_HandSolder).
• Custom / project-specific footprints live in KiCad Project Files v1.1/SwimBladder Custom Footprints.

Key Engineering Notes (from the PDF)

• Architecture: single compact central +VBAT node, not dual banks, for a roughly 90 mm x 90 mm board.
• Safety: main fuse should be upstream on the battery cable (recommended 225-250 A), close to the battery.
• Copper strategy: use a short, wide, via-stitched central polygon (L1 + L3 for +VBAT), and strong common ground return (L2 + L4).
• Copper thickness for the 200 A / 300 A rating: 1 oz (35 um) is not sufficient. Spec 2 oz (70 um) minimum on the outer layers, 3 oz preferred, and carry +VBAT and GND on two layers each in parallel (~4 oz-equivalent per net) with dense inter-layer via stitching. Treat the central node as a plane, not a trace, and size pours/vias for <= 20-30 C rise. Per-branch (~25 A): 2 oz outer with ~10-15 mm pour width is adequate.
• Via stitching: use two via classes - large power vias (~1.2 mm pad / 0.6 mm drill or bigger) for the +VBAT node and ground return, and a smaller class (~0.6-0.8 mm pad / 0.3-0.4 mm drill) for signal-ground / thermal stitching around the PWM header.
• Branch geometry: practical branch widths around 12-15 mm (8-10 mm absolute compact minimum for very short sections).
• Connectors: dual XT90 input for current sharing (symmetrical wiring), XT60 per ESC branch preferred.
• Protection/passives: 22-24 V standoff TVS class for 4S input, bulk capacitance near input/node plus branch-level capacitors.
• Signal: 16-pin IDC PWM header with alternating PWM/GND and per-channel series + pulldown resistors.

Known Issues / TODO (V1.1)

• No outstanding items. TVS placement, input HF cap grouping, indicator LEDs, and the R_BLEED1 value (now 22 kOhm) have all been resolved.

Quick Calculation Snapshot

• Per thruster power at 16 V and 25 A: 400 W
• System power for 8 thrusters: 3200 W
• Example central copper section in the doc (50 mm width, 140 um thickness, 25 mm length, one layer):
  • Estimated R ~= 0.0616 mOhm
  • Vdrop at 200 A ~= 0.012 V
  • Copper loss at 200 A ~= 2.46 W

For complete assumptions, formulas, BOM guidance, and test plan, see Swim_Bladder_Doc_v3_0.pdf.

Screenshots (V1.1)

_{Earlier V1.0 captures (Schematic.png, PCB Editor View.png, 3D View.png) remain in Screenshots/ for reference.}

Getting Started

1. Install KiCad (recommended version 8+).
2. Open the project from KiCad Project Files v1.1/UWU PDB.kicad_pro.
3. Review schematic, layout, and engineering assumptions from the PDF before fabrication, noting the V1.1 changes and open TODO items above.

Changelog

V1.1 (in progress)

• Canonical project files moved to KiCad Project Files v1.1/; earlier KiCad Project Files/ and the repo-root SwimBladder PDB.kicad_sch are deprecated.
• Added SwimBladder Custom Footprints library.
• Main bulk capacitance specified as C_MAIN1/2 = 4700 uF each.
• Removed the 1 nF per-branch decoupling cap; branches now use 1000 uF + 1 uF only.
• PWM front-end defined: R_PWM* = 100 Ohm series, R_PD* = 10 kOhm pulldown, inputs J11..J18.
• Added rail bleed resistor R_BLEED1 (value still a placeholder) and status LED D2 / R_LED1.
• Input TVS D1 present; placement correction pending (see Known Issues).

V1.0

• Initial 8-branch central star-node PDB layout.

Procurement (2-board build)

Bare PCB via JLCPCB; most components via LCSC (SwimBladder_LCSC_BatchBOM_v1.1.csv); full reference BOM in SwimBladder_BOM_v1.1.csv. JLCPCB and LCSC ship separately even though they're sister companies - no combined-box option outside of paying for JLC's PCBA assembly service.

Still need to source separately (not in the LCSC batch order)

• R_BLEED1, 22k Ohm, 0603 (LCSC C114065) - MOQ is Min:100/Mult:100, not worth it for ~3 pieces; ask around for spares or buy loose.
• R_LED1 + R_PD1..R_PD8, 10k Ohm, 0603 (LCSC C98220) - same MOQ issue, ~23 pieces needed.
• 30 A mini blade fuse elements (x16) for F_ESC1..F_ESC8 - these plug into the Keystone 3568 holder (which is in the LCSC order) but the fuse element itself isn't an LCSC/electronics- distributor item; source from an automotive parts store or RC supplier.
• F_ESC1..F_ESC8 fuseholders, Keystone 3568 (x8) - LCSC C5249699 was out of stock, dropped from the batch order; source from Digi-Key/Mouser instead.

Already owned, not in the order

• D2 status LED
• J2 IDC 2x08 header
• R_PWM1..R_PWM8, 100 Ohm, 0402 (from sample book)

License

This project is licensed under the MIT License. See the LICENSE file for details.