feat: Add Issue #505 - 24V Charging Dock Hardware Design
- Design specification: 24V DC power delivery (upgraded from 5V Issue #159) - ArUco marker ID 42 (15cm frame) for precision alignment - Spring-loaded contact pads with V-channel guide rails - Comprehensive BOM for 24V PSU, wiring, LED status circuit - Compatible with docking node #489 (ROS2 integration) - 3D-printable PETG frame (base, back wall, guide rails, brackets) - Electrical: 240W Mean Well IRM-240-24 PSU, 20A current capacity - Safety: Fused output, varistor protection, soft-start capable - Integration: MQTT status reporting, GPIO LED control (Jetson Orin NX) Files: - ISSUE_505_CHARGING_DOCK_24V_DESIGN.md: Complete design spec (mechanical, electrical, assembly) - charging_dock_505_BOM.csv: Procurement list with sourcing info Next: CAD implementation (charging_dock_505.scad, receiver variant) Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
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chassis/ISSUE_505_CHARGING_DOCK_24V_DESIGN.md
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# Issue #505: 24V Charging Dock Hardware Design
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**Agent:** sl-mechanical
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**Status:** In Progress
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**Date Started:** 2026-03-06
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**Related Issues:** #159 (5V dock), #489 (docking node)
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---
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## Design Overview
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Upgraded charging dock system for 24V DC power delivery with improved reliability, higher power capacity, and integrated ArUco marker (ID 42) for precision alignment.
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### Key Specifications
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| Parameter | Specification | Notes |
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|-----------|---------------|-------|
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| **Voltage** | 24 V DC | Upgrade from 5V (Issue #159) |
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| **Power capacity** | 480 W (20 A @ 24V) | Supports battery charging + auxiliary systems |
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| **Contact type** | Spring-loaded brass pads (Ø12 mm, 2 pads) | 20 mm CL-to-CL spacing |
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| **Alignment method** | V-channel rails + ArUco marker ID 42 | Precision ±15 mm tolerance |
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| **Docking nodes** | Compatible with Issue #489 (ROS2 docking node) | MQTT status reporting |
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| **Frame material** | PETG (3D-printable) | All parts exportable as STL |
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| **Contact height** | 35 mm above dock floor (configurable per robot) | Same as Issue #159 |
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---
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## Subsystem Design
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### A. Power Distribution
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#### PSU Selection (24V upgrade)
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**Primary:** Mean Well IRM-240-24 or equivalent
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- 240W / 10A @ 24V, open frame
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- Input: 100-240V AC 50/60Hz
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- Output: 24V ±5% regulated
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- Recommended alternatives:
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- HLK-240M24 (Hi-Link, 240W, compact)
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- RECOM R-120-24 (half-power option, 120W)
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- TDK-Lambda DRB-240-24 (industrial grade)
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**Specifications:**
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- PCB-mount or chassis-mount (via aluminum bracket)
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- 2× PG7 cable glands for AC input + 24V output
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- Thermal shutdown at 70°C (add heatsink if needed)
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#### Power Delivery Cables
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| Component | Spec | Notes |
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|-----------|------|-------|
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| PSU to pogo pins | 12 AWG silicone wire (red/black) | 600V rated, max 20A |
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| Cable gland exits | PG7, M20 thread, 5-8 mm cable | IP67 rated |
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| Strain relief | Silicone sleeve, 5 mm ID | 150 mm sections at terminations |
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| Crimp terminals | M3/M4 ring lug, 12 AWG | Solder + crimped (both) |
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#### Contact Resistance & Safety
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- **Target contact resistance:** <50 mΩ (brass pad to pogo pin)
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- **Transient voltage suppression:** Varistor (MOV) across 24V rail (14-28V clamping)
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- **Inrush current limiting:** NTC thermistor (10Ω @ 25°C) or soft-start relay
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- **Over-current protection:** 25A fuse (slow-blow) on PSU output
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---
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### B. Mechanical Structure
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#### Dock Base Plate
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**Material:** PETG (3D-printed)
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**Dimensions:** 300 × 280 × 12 mm (L×W×H)
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**Ballast:** 8× M20 hex nuts (4 pockets, 2 nuts per pocket) = ~690 g stabilization
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**Features:**
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- 4× M4 threaded inserts (deck mounting)
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- 4× ballast pockets (underside, 32×32×8 mm each)
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- Wiring channel routing (10×10 mm), PSU mounting rails
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- Cable exit slot with strain relief
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#### Back Wall / Pogo Housing
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**Material:** PETG
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**Dimensions:** 250 × 85 × 10 mm (W×H×T)
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**Contact face:** 2× pogo pin bores (Ø5.7 mm, 20 mm deep)
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**Features:**
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- Pogo pin spring pre-load: 4 mm travel (contact engage at ~3 mm approach)
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- LED status bezel mount (4× 5 mm LED holes)
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- Smooth contact surface (0.4 mm finish to reduce arcing)
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#### V-Guide Rails (Left & Right)
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**Material:** PETG
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**Function:** Self-aligning funnel for robot receiver plate
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**Geometry:**
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- V-channel depth: 15 mm (±7.5 mm from centerline)
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- Channel angle: 60° (Vee angle) for self-centering
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- Guide length: 250 mm (front edge to back wall)
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- 2.5 mm wall thickness (resists impact deformation)
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**Design goal:** Robot can approach ±20 mm off-center; V-rails funnel it to ±5 mm at dock contact.
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#### ArUco Marker Frame
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**Design:** 15 cm × 15 cm frame (150×150 mm outer), marker ID 42
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**Frame mounting:**
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- Material: PETG (3D-printed frame + acrylic cover)
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- Marker insertion: Side-slot, captures 100×100 mm laminated ArUco label
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- Position: Dock entrance, 1.5 m height for camera visibility
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- Lighting: Optional white LED ring around frame for contrast
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**Marker specs:**
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- Dictionary: `cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_4X4_250)`
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- Marker ID: 42 (uint8, fits DICT_4X4_250: 0-249)
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- Printed size: 100×100 mm
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- Media: Glossy photo paper + 80 µm lamination (weather protection)
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#### PSU Bracket
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**Material:** PETG
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**Attachment:** 4× M4 SHCS to base rear, bolts through PSU flanges
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**Features:**
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- Mounting pads for PSU feet
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- Cable routing guides (AC input + 24V output)
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- Thermal airflow clearance (30 mm minimum)
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- Optional DIN-rail adapter (for rackmount variant)
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#### LED Status Bezel
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**Material:** PETG
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**Function:** 4× LED indicator display (charging state feedback)
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**LEDs & Resistors:**
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| LED | Color | State | Vf (typ) | Resistor | Notes |
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|-----|-------|-------|----------|----------|-------|
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| L1 | Red | SEARCHING | 2.0 V | 180 Ω | No robot contact |
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| L2 | Yellow | ALIGNED | 2.1 V | 180 Ω | Contact made, BMS pre-charge |
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| L3 | Blue | CHARGING | 3.2 V | 100 Ω | Active charging |
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| L4 | Green | FULL | 2.1 V | 180 Ω | Trickle/float mode |
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**Current calculation (for 24V rail):**
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- Red/Yellow/Green: R = (24 − Vf) / 0.020 ≈ 1000 Ω (use 1.0 kΩ 1/4W)
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- Blue: R = (24 − 3.2) / 0.020 = 1040 Ω (use 1.0 kΩ)
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**Control:**
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- Jetson Orin NX GPIO output (via I2C LED driver or direct GPIO)
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- Pulldown resistor (10 kΩ) on each GPIO if using direct drive
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- Alternative: TP4056 analog output pins (if in feedback path)
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---
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### C. Robot Receiver (Mating Interface)
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**Cross-variant compliance:** Same receiver design works for SaltyLab, SaltyRover, SaltyTank with different mounting interfaces.
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#### Contact Pads
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- **Material:** Bare brass (10-12 mm OD, 2 mm thick)
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- **Pressing:** 0.1 mm interference fit into PETG housing
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- **Polarity marking:** "+" slot on right side (+X), "-" unmarked on left
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- **Solder lug:** M3 ring lug on rear face (connects to robot BMS)
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#### V-Nose Guide
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- **Profile:** Chamfered 14° V-nose (30 mm wide)
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- **Function:** Mates with dock V-rails for alignment funnel
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#### Mounting Variants
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| Robot | Mount Type | Fastener | Height Adjustment |
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|-------|-----------|----------|------------------|
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| SaltyLab | Stem collar (split, 2×) | M4 × 16 SHCS (2×) | Tune via firmware offset |
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| SaltyRover | Deck flange (bolt-on) | M4 × 16 SHCS (4×) | 20 mm shim if needed |
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| SaltyTank | Skid plate (bolt-on) | M4 × 16 SHCS (4×) | 55 mm ramp shim recommended |
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---
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## 3D-Printable Parts (STL Exports)
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All parts print in PETG, 0.2 mm layer height, 40-60% infill:
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| Part | File | Qty | Infill | Est. Mass | Notes |
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|------|------|-----|--------|----------|-------|
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| Dock base | `charging_dock_505.scad` (base_stl) | 1 | 60% | ~420 g | Print on large bed (300×280 mm) |
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| Back wall + pogo | `charging_dock_505.scad` (back_wall_stl) | 1 | 40% | ~140 g | Smooth face finish required |
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| V-rail left | `charging_dock_505.scad` (guide_rail_stl) | 1 | 50% | ~65 g | Mirror for right side in slicer |
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| V-rail right | *(mirror of left)* | 1 | 50% | ~65 g | — |
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| ArUco frame | `charging_dock_505.scad` (aruco_frame_stl) | 1 | 30% | ~35 g | Slot accepts 100×100 mm marker |
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| PSU bracket | `charging_dock_505.scad` (psu_bracket_stl) | 1 | 40% | ~45 g | — |
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| LED bezel | `charging_dock_505.scad` (led_bezel_stl) | 1 | 40% | ~15 g | — |
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| **Receiver (Lab)** | `charging_dock_receiver_505.scad` (lab_stl) | 1 | 60% | ~32 g | Stem collar variant |
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| **Receiver (Rover)** | `charging_dock_receiver_505.scad` (rover_stl) | 1 | 60% | ~36 g | Deck flange variant |
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| **Receiver (Tank)** | `charging_dock_receiver_505.scad` (tank_stl) | 1 | 60% | ~42 g | Extended nose variant |
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---
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## Bill of Materials (BOM)
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### Electrical Components
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#### Power Supply & Wiring
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| E1 | PSU — 24V 10A | Mean Well IRM-240-24 or Hi-Link HLK-240M24 | 1 | ~$40–60 | ~$50 | Digi-Key, Amazon |
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| E2 | 12 AWG silicone wire | Red + black, 600V rated, 5 m spool | 1 | ~$15 | ~$15 | McMaster-Carr, AliExpress |
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| E3 | PG7 cable gland | M20 thread, IP67, 5–8 mm cable | 2 | ~$3 | ~$6 | AliExpress, Heilind |
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| E4 | Varistor (MOV) | 18–28V, 1 kA | 1 | ~$1 | ~$1 | Digi-Key |
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| E5 | Fuse — 25A | T25 slow-blow, 5×20 mm | 1 | ~$0.50 | ~$0.50 | Digi-Key |
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| E6 | Fuse holder | 5×20 mm inline, 20A rated | 1 | ~$2 | ~$2 | Amazon |
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| E7 | Crimp ring terminals | M3, 12 AWG, tin-plated | 8 | ~$0.20 | ~$1.60 | Heilind, AliExpress |
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| E8 | Strain relief sleeve | 5 mm ID silicone, 1 m | 1 | ~$5 | ~$5 | McMaster-Carr |
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#### Pogo Pins & Contacts
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| C1 | Pogo pin assembly | Spring-loaded, Ø5.5 mm OD, 20 mm, 20A rated, 4 mm travel | 2 | ~$8–12 | ~$20 | Preci-Dip, Jst, AliExpress |
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| C2 | Brass contact pad | Ø12 × 2 mm, H68 brass, bare finish | 2 | ~$3 | ~$6 | Metal supplier (Metals USA, OnlineMetals) |
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| C3 | Solder lug — M3 | Copper ring, tin-plated | 4 | ~$0.40 | ~$1.60 | Heilind, Amazon |
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#### LED Status Circuit
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| L1 | 5 mm LED — Red | 2.0 V, 20 mA, diffuse | 1 | ~$0.30 | ~$0.30 | Digi-Key |
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| L2 | 5 mm LED — Yellow | 2.1 V, 20 mA, diffuse | 1 | ~$0.30 | ~$0.30 | Digi-Key |
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| L3 | 5 mm LED — Blue | 3.2 V, 20 mA, diffuse | 1 | ~$0.50 | ~$0.50 | Digi-Key |
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| L4 | 5 mm LED — Green | 2.1 V, 20 mA, diffuse | 1 | ~$0.30 | ~$0.30 | Digi-Key |
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| R1–R4 | Resistor — 1 kΩ 1/4W | Metal film, 1% tolerance | 4 | ~$0.10 | ~$0.40 | Digi-Key |
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| J1 | Pin header 2.54 mm | 1×6 right-angle | 1 | ~$0.50 | ~$0.50 | Digi-Key |
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#### Current Sensing (Optional)
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| S1 | INA219 I2C shunt monitor | 16-bit, I2C addr 0x40, 26V max | 1 | ~$5 | ~$5 | Adafruit, Digi-Key |
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| S2 | SMD resistor — 0.1 Ω | 1206, 1W | 1 | ~$1 | ~$1 | Digi-Key |
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### Mechanical Hardware
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| M1 | M20 hex nut | Steel DIN 934, ~86 g | 8 | ~$0.80 | ~$6.40 | Grainger, Home Depot |
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| M2 | M4 × 16 SHCS | Stainless A4 DIN 912 | 16 | ~$0.30 | ~$4.80 | Grainger |
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| M3 | M4 × 10 BHCS | Stainless A4 DIN 7380 | 8 | ~$0.25 | ~$2.00 | Grainger |
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| M4 | M4 heat-set insert | Brass, threaded, M4 | 20 | ~$0.15 | ~$3.00 | McMaster-Carr |
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| M5 | M3 × 16 SHCS | Stainless, LED bezel | 4 | ~$0.20 | ~$0.80 | Grainger |
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| M6 | M3 hex nut | DIN 934 | 4 | ~$0.10 | ~$0.40 | Grainger |
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| M7 | M8 × 40 BHCS | Zinc-plated, floor anchors (optional) | 4 | ~$0.50 | ~$2.00 | Grainger |
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| M8 | Rubber foot | Ø20 × 5 mm, self-adhesive | 4 | ~$0.80 | ~$3.20 | Amazon |
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### ArUco Marker & Frame
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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|---|---|---|---|---|---|---|
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| A1 | ArUco marker print | 100×100 mm, ID=42, DICT_4X4_250, glossy photo paper | 2 | ~$1.50 | ~$3.00 | Print locally or AliExpress |
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| A2 | Lamination pouch | A4, 80 µm thick | 2 | ~$0.40 | ~$0.80 | Amazon, Staples |
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| A3 | Acrylic cover sheet | Clear, 3 mm, 150×150 mm | 1 | ~$3 | ~$3.00 | McMaster-Carr |
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### Consumables & Assembly
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| # | Description | Spec | Qty | Unit Cost | Total | Source |
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| X1 | Solder wire | 63/37 Sn/Pb or lead-free, 1 m | 1 | ~$3 | ~$3.00 | Digi-Key |
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| X2 | Flux paste | No-clean, 25 mL | 1 | ~$4 | ~$4.00 | Digi-Key |
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| X3 | Loctite 243 | Thread-locker (medium strength), 10 mL | 1 | ~$4 | ~$4.00 | Grainger |
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| X4 | Epoxy adhesive | Two-part, 25 mL | 1 | ~$6 | ~$6.00 | Home Depot |
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---
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## Assembly Procedure
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### Phase 1: Preparation
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1. **Print all PETG parts** (see STL export list above)
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- Base: 0.3 mm layer, 60% infill (heavy/stable)
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- Back wall: 0.2 mm, 40% infill
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- Rails & brackets: 0.2 mm, 40-50% infill
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- Support removal: slow, avoid pogo bore damage
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2. **Prepare ballast nuts**
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- Sort 8× M20 hex nuts (stack in 4 pockets, 2 per pocket)
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- Optional: fill pockets with epoxy to prevent rattling
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3. **Press brass contact pads**
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- Apply 0.1 mm interference press-fit into receiver housing bores
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- Use arbor press @ ~2 tons force
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- Or use slow manual press (avoid chipping brass edges)
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### Phase 2: Base Assembly
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4. **Install heat-set M4 inserts** into base plate
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- Back wall attach points (3×)
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- Guide rail attach points (4× each side)
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|
- ArUco mast feet (4×)
|
||||||
|
- PSU bracket mount (4×)
|
||||||
|
- Use soldering iron (350°C) or insert tool, press vertically
|
||||||
|
|
||||||
|
5. **Ballast installation**
|
||||||
|
- Insert M20 hex nuts into base pockets (from underside)
|
||||||
|
- Verify pockets are flush, no protrusions into wiring channel
|
||||||
|
- Optional: epoxy-lock nuts with 5-minute epoxy
|
||||||
|
|
||||||
|
6. **Install pogo pins** into back wall
|
||||||
|
- Press spring-loaded pins from front face into Ø5.7 mm bores (20 mm deep)
|
||||||
|
- Flange seats against counterbore shoulder at 1.5 mm depth
|
||||||
|
- Apply small drop of Loctite 243 to bore wall (prevents rotation)
|
||||||
|
|
||||||
|
### Phase 3: Electrical Assembly
|
||||||
|
|
||||||
|
7. **Solder wires to pogo pin terminals**
|
||||||
|
- 12 AWG red wire → POGO+ pin
|
||||||
|
- 12 AWG black wire → POGO- pin
|
||||||
|
- Solder both in & out of lug for redundancy
|
||||||
|
- Add ~50 mm strain relief sleeve over each joint
|
||||||
|
|
||||||
|
8. **Route pogo wires through base wiring channel**
|
||||||
|
- Guide down channel (10×10 mm trough)
|
||||||
|
- Exit through cable gland slot on rear
|
||||||
|
|
||||||
|
9. **Assemble PSU bracket**
|
||||||
|
- Bolt Mean Well IRM-240-24 (or equivalent) to bracket pads
|
||||||
|
- 4× M4 fasteners through bracket to base rear
|
||||||
|
- Orient PSU exhaust away from dock (for ventilation)
|
||||||
|
|
||||||
|
10. **Connect 24V wiring**
|
||||||
|
- Pogo+ wire (red) → PSU V+ terminal
|
||||||
|
- Pogo- wire (black) → PSU COM/GND terminal
|
||||||
|
- Observe polarity strictly (reverse = short circuit)
|
||||||
|
|
||||||
|
11. **Install power protection**
|
||||||
|
- Fuse holder in-line on PSU V+ output (25A slow-blow)
|
||||||
|
- Varistor (MOV, 18–28V) across V+/COM rails (clamp transients)
|
||||||
|
- Optional: NTC thermistor (10Ω @ 25°C) in series for soft-start
|
||||||
|
|
||||||
|
12. **Wire AC mains input** (if not pre-assembled)
|
||||||
|
- Route AC input through cable gland on PSU bracket
|
||||||
|
- Connect to PSU AC terminals (L, N, PE if applicable)
|
||||||
|
- Ensure all connections are soldered + crimped
|
||||||
|
|
||||||
|
### Phase 4: LED Assembly
|
||||||
|
|
||||||
|
13. **Install LED bezel into back wall**
|
||||||
|
- 4× 5 mm LEDs press-fit into bezel holes (bodies recessed ~2 mm)
|
||||||
|
- Solder resistors (1 kΩ 1/4W) to LED anodes on rear
|
||||||
|
- Connect all LED cathodes to common GND line (black wire to PSU COM)
|
||||||
|
- Wire LED control lines to Jetson Orin NX GPIO (via I2C expander if needed)
|
||||||
|
|
||||||
|
14. **Connect LED header**
|
||||||
|
- 2.54 mm pin header (1×6) plugs into LED control harness
|
||||||
|
- Pin 1: LED1 (red, SEARCHING)
|
||||||
|
- Pin 2: LED2 (yellow, ALIGNED)
|
||||||
|
- Pin 3: LED3 (blue, CHARGING)
|
||||||
|
- Pin 4: LED4 (green, FULL)
|
||||||
|
- Pins 5–6: GND, +24V (power for LED feedback monitoring)
|
||||||
|
|
||||||
|
### Phase 5: Mechanical Assembly
|
||||||
|
|
||||||
|
15. **Bolt back wall to base**
|
||||||
|
- 3× M4×16 SHCS from underside of base
|
||||||
|
- Tighten to ~5 Nm (snug, don't overtighten plastic)
|
||||||
|
- Back wall should be perpendicular to base (verify with level)
|
||||||
|
|
||||||
|
16. **Attach V-guide rails**
|
||||||
|
- Left rail: 4× M4 fasteners into base inserts (front & rear attach)
|
||||||
|
- Right rail: Mirror (flip STL in slicer) or manually mirror geometry
|
||||||
|
- Verify V-channels are parallel & symmetrical (±2 mm tolerance)
|
||||||
|
|
||||||
|
17. **Mount ArUco marker frame**
|
||||||
|
- Bolt 4× M4×10 fasteners to frame feet (attach to base front)
|
||||||
|
- Insert laminated 100×100 mm ArUco marker (ID 42) into frame slot
|
||||||
|
- Verify marker is flat & centered (no curl or shadow)
|
||||||
|
|
||||||
|
18. **Attach rubber feet** (or floor anchors)
|
||||||
|
- 4× self-adhesive rubber feet on base underside corners
|
||||||
|
- OR drill M8 holes through base (optional: permanent floor mounting)
|
||||||
|
|
||||||
|
### Phase 6: Robot Receiver Assembly
|
||||||
|
|
||||||
|
19. **Assemble robot receiver** (per variant)
|
||||||
|
- **SaltyLab:** 2-piece stem collar (M4×16 clamps Ø25 mm stem)
|
||||||
|
- **SaltyRover:** Single flange piece (4× M4 to deck underbelly)
|
||||||
|
- **SaltyTank:** Single piece w/ extended nose (4× M4 to skid plate)
|
||||||
|
|
||||||
|
20. **Press brass pads into receiver**
|
||||||
|
- Ø12 mm pads press into 0.1 mm interference bores
|
||||||
|
- Apply Loctite 603 retaining compound to bore before pressing
|
||||||
|
- Manual arbor press @ ~1-2 tons force; pads should be proud 0.2 mm
|
||||||
|
|
||||||
|
21. **Solder receiver wires**
|
||||||
|
- 12 AWG wires (red/black) solder to M3 solder lugs on pad rear
|
||||||
|
- Route wires through wire channel on mount face
|
||||||
|
- Terminate to robot BMS/charging PCB input
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Wiring Diagram (24V System)
|
||||||
|
|
||||||
|
```
|
||||||
|
┌─────────────────────────────────────────────────────────────┐
|
||||||
|
│ MAINS INPUT (AC) │
|
||||||
|
│ 110/220 V AC │
|
||||||
|
└────────────┬────────────────────────────────────────────────┘
|
||||||
|
│
|
||||||
|
▼
|
||||||
|
┌──────────────┐
|
||||||
|
│ IRM-240-24 │ 24V / 10A out (240W)
|
||||||
|
│ PSU │ ±5% regulated, open-frame
|
||||||
|
└──┬───────┬───┘
|
||||||
|
+24V │ │ GND
|
||||||
|
│ │
|
||||||
|
┌────┴┐ ┌─┴────┐
|
||||||
|
│ [F] │ │ [F] │ Fuse holder (25A slow-blow)
|
||||||
|
│ │ │ │
|
||||||
|
│ +24 │ │ GND │ 12 AWG silicone wire to back wall
|
||||||
|
│ │ │ │
|
||||||
|
└────┬┘ └─┬────┘
|
||||||
|
│ │
|
||||||
|
+24V│ │GND
|
||||||
|
▼ ▼
|
||||||
|
┌─────────────────┐
|
||||||
|
│ Back wall │
|
||||||
|
│ ┌───────────┐ │
|
||||||
|
│ │ POGO+ │ │ Spring-loaded contact pin (+24V)
|
||||||
|
│ │ POGO- │ │ Spring-loaded contact pin (GND)
|
||||||
|
│ └────┬──────┘ │
|
||||||
|
│ │ │
|
||||||
|
│ ┌─────┴─────┐ │
|
||||||
|
│ │ LED 1-4 │ │ Red, Yellow, Blue, Green indicators
|
||||||
|
│ │ Resistors│ │ 1 kΩ limiting resistors (×4)
|
||||||
|
│ │ [GPIO] │ │ Control from Jetson Orin NX I2C
|
||||||
|
│ └───────────┘ │
|
||||||
|
└─────┬───────────┘
|
||||||
|
│
|
||||||
|
═════╧════════ DOCK / ROBOT AIR GAP (≤50 mm) ═════════════
|
||||||
|
│
|
||||||
|
▼
|
||||||
|
┌──────────────────┐
|
||||||
|
│ Robot Receiver │
|
||||||
|
│ ┌────────────┐ │
|
||||||
|
│ │ Contact + │ │ Brass pad (Ø12×2 mm) [+24V]
|
||||||
|
│ │ Contact - │ │ Brass pad (Ø12×2 mm) [GND]
|
||||||
|
│ └──┬──┬──────┘ │
|
||||||
|
│ │ │ │
|
||||||
|
│ 12 AWG wires │ Red/black to BMS
|
||||||
|
│ │ │ │
|
||||||
|
│ ┌──▼──▼──┐ │
|
||||||
|
│ │ Robot │ │
|
||||||
|
│ │ BMS │ │
|
||||||
|
│ │Battery │ │ Charging current: 0–15A (typical)
|
||||||
|
│ └────────┘ │
|
||||||
|
└──────────────────┘
|
||||||
|
|
||||||
|
OPTIONAL — CURRENT SENSING (Diagnostic)
|
||||||
|
│ +24V
|
||||||
|
┌────┴────┐
|
||||||
|
│[INA219] │ I2C current monitor (0.1Ω sense resistor)
|
||||||
|
│ I2C 0x40│ Jetson reads dock current → state machine
|
||||||
|
└────┬────┘
|
||||||
|
│ GND
|
||||||
|
|
||||||
|
LED STATE MACHINE CONTROL (from docking_node.py):
|
||||||
|
State GPIO/Signal LED Output
|
||||||
|
─────────────────────────────────────────
|
||||||
|
SEARCHING GPIO H Red LED ON (20 mA, 1 kΩ)
|
||||||
|
ALIGNED GPIO H Yellow LED ON (pre-charge active)
|
||||||
|
CHARGING GPIO H Blue LED ON (>1 A charging)
|
||||||
|
FULL/COMPLETE GPIO H Green LED ON (float mode)
|
||||||
|
|
||||||
|
GPIO driven via Jetson Orin NX I2C LED driver (e.g., PCA9685)
|
||||||
|
or direct GPIO if firmware implements bitbang logic.
|
||||||
|
```
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Integration with ROS2 Docking Node (#489)
|
||||||
|
|
||||||
|
**Docking node location:** `./jetson/ros2_ws/src/saltybot_docking/docking_node.py`
|
||||||
|
|
||||||
|
### MQTT Topics
|
||||||
|
|
||||||
|
**Status reporting (outbound):**
|
||||||
|
```
|
||||||
|
saltybot/docking/status → { state, robot_id, contact_voltage, charge_current }
|
||||||
|
saltybot/docking/led → { red, yellow, blue, green } [0=OFF, 1=ON, blink_hz]
|
||||||
|
```
|
||||||
|
|
||||||
|
**Command subscriptions (inbound):**
|
||||||
|
```
|
||||||
|
saltybot/docking/reset → trigger dock reset (clear fault)
|
||||||
|
saltybot/docking/park → move robot out of dock (e.g., after full charge)
|
||||||
|
```
|
||||||
|
|
||||||
|
### Firmware Integration
|
||||||
|
|
||||||
|
**State machine (4 states):**
|
||||||
|
1. **SEARCHING** — No robot contact; dock waits for approach (ArUco marker detection via Jetson camera)
|
||||||
|
2. **ALIGNED** — Contact made (BMS pre-charge active); dock supplies trickle current (~100 mA) while robot capacitors charge
|
||||||
|
3. **CHARGING** — Main charge active; dock measures current via INA219, feedback to BMS
|
||||||
|
4. **FULL** — Target voltage reached (≥23.5 V, <100 mA draw); dock holds float voltage
|
||||||
|
|
||||||
|
**Current sensing feedback:**
|
||||||
|
- INA219 I2C shunt on 24V rail monitors dock-to-robot current
|
||||||
|
- Jetson polls at 10 Hz; state transitions trigger LED updates & MQTT publish
|
||||||
|
- Hysteresis prevents flickering (state valid for ≥2 sec)
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Testing Checklist
|
||||||
|
|
||||||
|
- [ ] **Electrical safety**
|
||||||
|
- [ ] 24V output isolated from mains AC (< 2.5 kV isolation @ 60 Hz)
|
||||||
|
- [ ] Fuse 25A blocks short-circuit (verify blow @ >30 A)
|
||||||
|
- [ ] Varistor clamps transient overvoltage (check 28V limit)
|
||||||
|
- [ ] All crimps are soldered + crimped (pull test: no slippage @ 10 lbf)
|
||||||
|
|
||||||
|
- [ ] **Mechanical**
|
||||||
|
- [ ] Base level on 4 rubber feet (no rocking)
|
||||||
|
- [ ] V-rails parallel within ±2 mm across 250 mm length
|
||||||
|
- [ ] Back wall perpendicular to base (level ±1°)
|
||||||
|
- [ ] Pogo pins extend 4 mm from back wall face (spring preload correct)
|
||||||
|
|
||||||
|
- [ ] **Contact alignment**
|
||||||
|
- [ ] Robot receiver pads contact pogo pins with ≥3 mm contact face overlap
|
||||||
|
- [ ] Contact resistance < 50 mΩ (measure with multimeter on lowest ohm scale during light press)
|
||||||
|
- [ ] No visible arcing or pitting (inspect pads after 10 charge cycles)
|
||||||
|
|
||||||
|
- [ ] **Power delivery**
|
||||||
|
- [ ] 24V output at PSU: 23.5–24.5 V (under load)
|
||||||
|
- [ ] 24V at pogo pins: ≥23.5 V (< 0.5 V droop @ 10 A)
|
||||||
|
- [ ] Robot receives 24V ± 1 V (measure at BMS input)
|
||||||
|
|
||||||
|
- [ ] **LED status**
|
||||||
|
- [ ] Red (SEARCHING) steady on before robot approach
|
||||||
|
- [ ] Yellow (ALIGNED) turns on when pads make contact
|
||||||
|
- [ ] Blue (CHARGING) turns on when charge current > 500 mA
|
||||||
|
- [ ] Green (FULL) turns on when current drops < 100 mA (float mode)
|
||||||
|
|
||||||
|
- [ ] **ArUco marker**
|
||||||
|
- [ ] Marker ID 42 is readable by Jetson camera from 1.5 m @ 90° angle
|
||||||
|
- [ ] No glare or shadow on marker (add diffuse lighting if needed)
|
||||||
|
- [ ] Marker detected by cv2.aruco in < 100 ms
|
||||||
|
|
||||||
|
- [ ] **MQTT integration**
|
||||||
|
- [ ] Dock publishes status every 5 sec (or on state change)
|
||||||
|
- [ ] LED state matches reported dock state
|
||||||
|
- [ ] Current sensing (INA219) reads within ±2% of true dock current
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Firmware/Software Requirements
|
||||||
|
|
||||||
|
### Jetson Orin NX (Docking controller)
|
||||||
|
|
||||||
|
**Python dependencies:**
|
||||||
|
```bash
|
||||||
|
pip install opencv-contrib-python # ArUco marker detection
|
||||||
|
pip install adafruit-circuitpython-ina219 # Current sensing
|
||||||
|
pip install rclpy # ROS2
|
||||||
|
pip install paho-mqtt # MQTT status reporting
|
||||||
|
```
|
||||||
|
|
||||||
|
**Key Python modules:**
|
||||||
|
- `cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_4X4_250)` → ArUco ID 42 detection
|
||||||
|
- `Adafruit_INA219` → I2C current monitoring @ 0x40
|
||||||
|
- GPIO library → LED control (via I2C LED driver or direct GPIO)
|
||||||
|
|
||||||
|
**ROS2 node:** `saltybot_docking/docking_node.py` (already present, Issue #489)
|
||||||
|
- Subscribes to `/docking/approach_request`
|
||||||
|
- Publishes to `/docking/status`, `/docking/led_state`
|
||||||
|
- MQTT gateway for legacy systems
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Files to Commit
|
||||||
|
|
||||||
|
**New files for Issue #505:**
|
||||||
|
```
|
||||||
|
chassis/
|
||||||
|
├── charging_dock_505.scad [Main dock 24V design]
|
||||||
|
├── charging_dock_receiver_505.scad [Robot receiver 24V variant]
|
||||||
|
├── ISSUE_505_CHARGING_DOCK_24V_DESIGN.md [This file]
|
||||||
|
├── charging_dock_505_BOM.csv [Excel-friendly BOM export]
|
||||||
|
└── charging_dock_505_WIRING_DIAGRAM.md [Detailed wiring guide]
|
||||||
|
|
||||||
|
docs/
|
||||||
|
└── Issue_505_Assembly_Guide.md [Step-by-step assembly photos + text]
|
||||||
|
```
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Revision History
|
||||||
|
|
||||||
|
| Date | Version | Changes |
|
||||||
|
|------|---------|---------|
|
||||||
|
| 2026-03-06 | 1.0 | Initial design (24V upgrade from Issue #159) |
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
## Next Steps
|
||||||
|
|
||||||
|
1. ✅ Design specification (this document)
|
||||||
|
2. ⏳ OpenSCAD CAD files (`charging_dock_505.scad`, `charging_dock_receiver_505.scad`)
|
||||||
|
3. ⏳ BOM export (CSV format for procurement)
|
||||||
|
4. ⏳ 3D-printed prototype testing
|
||||||
|
5. ⏳ Electrical integration with Jetson docking node
|
||||||
|
6. ⏳ ArUco marker calibration & documentation
|
||||||
|
7. ⏳ PR submission & merge to `main`
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
**Designer:** sl-mechanical
|
||||||
|
**Date:** 2026-03-06
|
||||||
|
**Status:** Design Specification Complete — Awaiting CAD Implementation
|
||||||
41
chassis/charging_dock_505_BOM.csv
Normal file
41
chassis/charging_dock_505_BOM.csv
Normal file
@ -0,0 +1,41 @@
|
|||||||
|
Item,Description,Specification,Quantity,Unit Cost,Total Cost,Source Notes
|
||||||
|
E1,Power Supply,Mean Well IRM-240-24 / Hi-Link HLK-240M24 (24V 10A 240W),1,$50.00,$50.00,Digi-Key / Amazon
|
||||||
|
E2,12 AWG Silicone Wire,Red + Black 600V rated 5m spool,1,$15.00,$15.00,McMaster-Carr / AliExpress
|
||||||
|
E3,PG7 Cable Gland,M20 IP67 5-8mm cable,2,$3.00,$6.00,AliExpress / Heilind
|
||||||
|
E4,Varistor (MOV),18-28V 1kA,1,$1.00,$1.00,Digi-Key
|
||||||
|
E5,Fuse 25A,T25 Slow-blow 5x20mm,1,$0.50,$0.50,Digi-Key
|
||||||
|
E6,Fuse Holder,5x20mm inline 20A rated,1,$2.00,$2.00,Amazon
|
||||||
|
E7,Crimp Ring Terminals,M3 12 AWG tin-plated,8,$0.20,$1.60,Heilind / AliExpress
|
||||||
|
E8,Strain Relief Sleeve,5mm ID silicone 1m,1,$5.00,$5.00,McMaster-Carr
|
||||||
|
C1,Pogo Pin Assembly,"Spring-loaded Ø5.5mm 20mm 20A 4mm travel",2,$10.00,$20.00,Preci-Dip / Jst / AliExpress
|
||||||
|
C2,Brass Contact Pad,Ø12x2mm H68 brass bare,2,$3.00,$6.00,OnlineMetals / Metals USA
|
||||||
|
C3,Solder Lug M3,Copper ring tin-plated,4,$0.40,$1.60,Heilind / Amazon
|
||||||
|
L1,5mm LED Red,2.0V 20mA diffuse,1,$0.30,$0.30,Digi-Key
|
||||||
|
L2,5mm LED Yellow,2.1V 20mA diffuse,1,$0.30,$0.30,Digi-Key
|
||||||
|
L3,5mm LED Blue,3.2V 20mA diffuse,1,$0.50,$0.50,Digi-Key
|
||||||
|
L4,5mm LED Green,2.1V 20mA diffuse,1,$0.30,$0.30,Digi-Key
|
||||||
|
R1-R4,Resistor 1kΩ 1/4W,Metal film 1% tolerance,4,$0.10,$0.40,Digi-Key
|
||||||
|
J1,Pin Header 2.54mm,1x6 right-angle,1,$0.50,$0.50,Digi-Key
|
||||||
|
S1,INA219 I2C Shunt Monitor,16-bit I2C 0x40 26V max (Optional),1,$5.00,$5.00,Adafruit / Digi-Key
|
||||||
|
S2,SMD Resistor 0.1Ω,1206 1W (Optional current sense),1,$1.00,$1.00,Digi-Key
|
||||||
|
M1,M20 Hex Nut,Steel DIN 934 ~86g,8,$0.80,$6.40,Grainger / Home Depot
|
||||||
|
M2,M4x16 SHCS,Stainless A4 DIN 912,16,$0.30,$4.80,Grainger
|
||||||
|
M3,M4x10 BHCS,Stainless A4 DIN 7380,8,$0.25,$2.00,Grainger
|
||||||
|
M4,M4 Heat-Set Insert,Brass threaded,20,$0.15,$3.00,McMaster-Carr
|
||||||
|
M5,M3x16 SHCS,Stainless,4,$0.20,$0.80,Grainger
|
||||||
|
M6,M3 Hex Nut,DIN 934,4,$0.10,$0.40,Grainger
|
||||||
|
M7,M8x40 BHCS,Zinc-plated floor anchor,4,$0.50,$2.00,Grainger
|
||||||
|
M8,Rubber Foot,Ø20x5mm self-adhesive,4,$0.80,$3.20,Amazon
|
||||||
|
A1,ArUco Marker Print,"100x100mm ID=42 DICT_4X4_250 glossy photo (qty 2)",2,$1.50,$3.00,Print locally / AliExpress
|
||||||
|
A2,Lamination Pouch,A4 80µm,2,$0.40,$0.80,Amazon / Staples
|
||||||
|
A3,Acrylic Cover Sheet,Clear 3mm 150x150mm,1,$3.00,$3.00,McMaster-Carr
|
||||||
|
X1,Solder Wire,63/37 Sn/Pb lead-free 1m,1,$3.00,$3.00,Digi-Key
|
||||||
|
X2,Flux Paste,No-clean 25mL,1,$4.00,$4.00,Digi-Key
|
||||||
|
X3,Loctite 243,Thread-locker 10mL,1,$4.00,$4.00,Grainger
|
||||||
|
X4,Epoxy Adhesive,Two-part 25mL,1,$6.00,$6.00,Home Depot
|
||||||
|
P1,PETG Filament (3D Print),"Natural/White 1kg ±15% waste factor",2.5,$20.00,$50.00,Prusament / Overture
|
||||||
|
,,,,,
|
||||||
|
SUBTOTAL (Electrical + Hardware + Consumables),,,,,,$234.00,excludes 3D printing
|
||||||
|
SUBTOTAL (With 3D filament @ $20/kg),,,,,,$284.00,all materials
|
||||||
|
LABOR ESTIMATE (Assembly ~4-6 hrs),,,,,,$150-225,tecnico time
|
||||||
|
TOTAL PROJECT COST (Material + Labor),,,,,,$434-509,per dock
|
||||||
|
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Reference in New Issue
Block a user