feat: Add Issue #254 - CSI camera rain/sun shields

Add csi_rain_shield.scad with parametric visor-style protective
shields for all 4 Raspberry Pi CSI cameras (IMX219).

Features:
- Visor-style overhang (32mm forward extension) shields lens from
  rain and direct sunlight
- Drip edge prevents water from trickling back onto PCB
- Snap-fit tabs (4 per shield, no fasteners required)
- Ventilation slots prevent moisture condensation
- Optional transparent polycarbonate lens cover insert
- Radially symmetric design fits all 4 cameras

Includes comprehensive BOM with:
- Print settings and material specifications
- Assembly instructions for snap-fit installation
- Maintenance and troubleshooting guide
- Weather resistance performance notes
- Design variants for different conditions
- Post-print finishing recommendations

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

chassis/csi_rain_shield.scad

@@ -0,0 +1,221 @@
+// ============================================================
+// csi_rain_shield.scad — CSI Camera Rain/Sun Shield
+// Issue: #254  Agent: sl-mechanical  Date: 2026-03-02
+// ============================================================
+//
+// Parametric visor-style rain and sun shield for SaltyBot's
+// 4× Raspberry Pi CSI IMX219 cameras (32×32 mm PCB).
+//
+// Features:
+//   • Visor-style overhang — protects lens from rain & sun
+//   • Drip edge — prevents water from running back onto PCB
+//   • Snap-fit attachment — clips to camera housing, no fasteners
+//   • Transparent polycarbonate compatible — removable lens cover
+//   • Radial symmetry — same design fits all 4 cameras
+//
+// Design for IMX219:
+//   • Camera face plate: 38×38 mm (32 mm PCB + 3 mm frame per side)
+//   • Arm depth: 52 mm from sensor head centre to camera
+//   • 10° nose-down tilt on radial arms
+//
+// Assembly:
+//   1. Print shield body (flat-side-down, minimal supports)
+//   2. Optional: Insert clear polycarbonate sheet in front
+//   3. Snap shield onto camera housing (4 tabs lock into grooves)
+//   4. Repeat for all 4 cameras
+//
+// RENDER options:
+//   "shield"        single shield unit (default)
+//   "assembly"      4 shields on camera arms (visual reference)
+//   "lens_cover"    removable transparent polycarbonate insert
+// ============================================================
+
+RENDER = "shield";
+
+// ── Camera housing dimensions ──────────────────────────────
+// IMX219 camera with face-plate protection.
+CAM_PCB_SIZE    =  32.0;       // PCB square side
+CAM_FACE_SIZE   =  38.0;       // face plate (PCB + 3mm bezel each side)
+CAM_FACE_THICK  =   4.0;       // face plate thickness (front-to-back)
+
+// M2 hole pattern on PCB (for reference, not used in shield)
+M2_SPACING      =  24.0;       // hole pattern spacing
+
+// ── Radial arm geometry (from imx219_mount.scad) ───────────
+ARM_R           =  50.0;       // platform radius (used in assembly view)
+REACH_LEN       =  52.0;       // arm extension from sensor head
+ARM_TILT        =  10.0;       // nose-down tilt angle
+
+// ── Rain shield overhang ───────────────────────────────────
+// Visor extends forward and downward from camera housing.
+
+VISOR_OVERHANG  =  32.0;       // forward extension from camera face
+VISOR_H         =  18.0;       // overhang height (downward from top)
+VISOR_DROP      =  16.0;       // bottom lip drop (prevents water runoff)
+VISOR_THICK     =   3.0;       // wall thickness
+
+// Drip edge: curved lip at bottom to prevent water trickling back
+DRIP_RADIUS     =   3.0;       // radius of drip edge curve
+DRIP_HEIGHT     =   4.0;       // height of drip lip
+
+// ── Snap-fit attachment tabs ───────────────────────────────
+// Tabs clip into grooves on camera housing side walls.
+
+SNAP_TAB_H      =   6.0;       // tab height (above housing)
+SNAP_TAB_W      =   8.0;       // tab width
+SNAP_TAB_D      =   2.0;       // tab depth (into groove)
+SNAP_CLEARANCE  =   0.4;       // clearance for easy snap/unsnap
+
+NUM_TABS        =   4;         // 4 tabs around perimeter
+
+// ── Lens cover (polycarbonate insert) ──────────────────────
+// Optional transparent front cover — slides into grooves.
+
+LENS_COVER_T    =   2.0;       // polycarbonate sheet thickness
+LENS_COVER_W    =  CAM_FACE_SIZE + 6.0;  // cover width (with edge flanges)
+LENS_COVER_FLANGE = 3.0;       // flange width on each side
+
+// ── Ventilation ────────────────────────────────────────────
+// Small vent slots prevent moisture condensation inside shield.
+
+VENT_SLOT_W     =   3.0;       // vent slot width
+VENT_SLOT_H     =   2.0;       // vent slot height
+NUM_VENTS       =   3;         // slots per side (3 on left, 3 on right)
+
+// ── General ────────────────────────────────────────────────
+$fn = 64;
+e   = 0.01;
+
+// ─────────────────────────────────────────────────────────────
+// csi_rain_shield()
+//   Single shield unit — visor with snap-fit tabs.
+//   Print flat-side-down (visor facing down).
+//
+// Coordinate system:
+//   X = left-right (camera width direction)
+//   Y = front-back (camera pointing direction)
+//   Z = up-down
+//   Camera face at Y=0, lens center at origin.
+// ─────────────────────────────────────────────────────────────
+module csi_rain_shield() {
+    // Main visor body — asymmetric overhang
+    difference() {
+        union() {
+            // Visor base plate (behind camera, attaches to housing)
+            translate([-CAM_FACE_SIZE/2 - 4, -CAM_FACE_THICK - 2, 0])
+                cube([CAM_FACE_SIZE + 8, 6, VISOR_THICK]);
+
+            // Forward overhang — curved top for water runoff
+            translate([-VISOR_H/2, -CAM_FACE_THICK, 0]) {
+                difference() {
+                    // Main overhang volume
+                    cube([VISOR_H, VISOR_OVERHANG, VISOR_THICK]);
+
+                    // Curved top surface (water sheds outward)
+                    translate([VISOR_H/2, 0, -e])
+                        rotate([90, 0, 0])
+                            cylinder(r = VISOR_H/2 + 2, h = VISOR_OVERHANG + 2*e);
+                }
+            }
+
+            // Side flanges (stabilize against wind, provide snap-tab base)
+            for (sx = [-1, 1])
+                translate([sx * (CAM_FACE_SIZE/2 + 2), -CAM_FACE_THICK, 0])
+                    cube([4, CAM_FACE_THICK + VISOR_OVERHANG/2, VISOR_THICK]);
+
+            // Drip edge — bottom lip curves downward & forward
+            translate([-(VISOR_H-2)/2, -CAM_FACE_THICK + VISOR_OVERHANG - 2, -DRIP_HEIGHT])
+                rotate([0, 90, 0])
+                    cylinder(r = DRIP_RADIUS, h = VISOR_H - 4);
+        }
+
+        // Lens opening — lets camera see through (frame around camera face)
+        translate([-(CAM_FACE_SIZE-2)/2, -CAM_FACE_THICK - 2, -e])
+            cube([CAM_FACE_SIZE-2, 2, VISOR_THICK + 2*e]);
+
+        // Vent slots (prevent condensation) — left side
+        for (i = [0 : NUM_VENTS-1]) {
+            vent_y = -CAM_FACE_THICK + (VISOR_OVERHANG * (i+1) / (NUM_VENTS+1));
+            translate([-(CAM_FACE_SIZE/2 + 8), vent_y, VISOR_THICK/2 - VENT_SLOT_H/2])
+                cube([2, VENT_SLOT_W, VENT_SLOT_H]);
+            translate([(CAM_FACE_SIZE/2 + 6), vent_y, VISOR_THICK/2 - VENT_SLOT_H/2])
+                cube([2, VENT_SLOT_W, VENT_SLOT_H]);
+        }
+    }
+
+    // Snap-fit tabs — clip into camera housing grooves
+    for (i = [0 : NUM_TABS-1]) {
+        angle = (360 / NUM_TABS) * i - 45;  // 4 tabs at 90° intervals, rotated -45°
+        translate([-CAM_FACE_SIZE/2 - 3, -CAM_FACE_THICK/2, 0])
+            rotate([0, 0, angle])
+                translate([CAM_FACE_SIZE/2 + 3 + SNAP_TAB_D/2, 0, -SNAP_TAB_H/2])
+                    cube([SNAP_TAB_W, SNAP_TAB_D + SNAP_CLEARANCE, SNAP_TAB_H], center=true);
+    }
+
+    // Lens cover groove — retains transparent polycarbonate insert
+    translate([-(LENS_COVER_W/2 + 1), -CAM_FACE_THICK - 1.5, -e])
+        cube([LENS_COVER_W + 2, 1.5, LENS_COVER_T + 0.5]);
+}
+
+// ─────────────────────────────────────────────────────────────
+// csi_lens_cover()
+//   Removable transparent polycarbonate insert.
+//   This is a phantom/visual-only part; actual cover is cut from
+//   2.0 mm clear polycarbonate sheet and trimmed to size.
+// ─────────────────────────────────────────────────────────────
+module csi_lens_cover() {
+    // Clear lens cover — sits in grooves on shield front edge
+    difference() {
+        union() {
+            // Main cover plate (represents polycarbonate insert)
+            translate([-(LENS_COVER_W/2), -CAM_FACE_THICK - 2, 0])
+                cube([LENS_COVER_W, 2, LENS_COVER_T]);
+
+            // Side flanges (grip in shield grooves)
+            for (sx = [-1, 1])
+                translate([sx * (LENS_COVER_W/2 - LENS_COVER_FLANGE/2),
+                          -CAM_FACE_THICK - 2, 0])
+                    cube([LENS_COVER_FLANGE, 2, LENS_COVER_T]);
+        }
+
+        // Lens opening (clear aperture in front of camera)
+        translate([-(CAM_FACE_SIZE-4)/2, -CAM_FACE_THICK - 3, -e])
+            cube([CAM_FACE_SIZE-4, 4, LENS_COVER_T + 2*e]);
+    }
+}
+
+// ─────────────────────────────────────────────────────────────
+// assembly_4x_shields()
+//   All 4 shields mounted on radial arms (reference visualization).
+// ─────────────────────────────────────────────────────────────
+module assembly_4x_shields() {
+    // 4 shields at 90° intervals (matches 4x CSI cameras)
+    for (angle = [0, 90, 180, 270]) {
+        color("LightSteelBlue", 0.85)
+            rotate([0, 0, angle])
+                translate([ARM_R, 0, 0])
+                    rotate([ARM_TILT, 0, 0])
+                        csi_rain_shield();
+
+        // Phantom camera face (reference only)
+        color("DarkGray", 0.5)
+            rotate([0, 0, angle])
+                translate([ARM_R, 0, 0])
+                    rotate([ARM_TILT, 0, 0])
+                        translate([-(CAM_FACE_SIZE/2), 0, -CAM_FACE_THICK/2])
+                            cube([CAM_FACE_SIZE, 1, CAM_FACE_SIZE], center=false);
+    }
+}
+
+// ─────────────────────────────────────────────────────────────
+// Render selector
+// ─────────────────────────────────────────────────────────────
+if (RENDER == "shield") {
+    csi_rain_shield();
+
+} else if (RENDER == "assembly") {
+    assembly_4x_shields();
+
+} else if (RENDER == "lens_cover") {
+    csi_lens_cover();
+}

chassis/csi_rain_shield_BOM.md

@@ -0,0 +1,294 @@
+# CSI Camera Rain/Sun Shield — BOM + Assembly
+**Rev A — 2026-03-02 — sl-mechanical**
+
+---
+
+## System Overview
+
+Protective visor-style rain and sun shields for all 4 Raspberry Pi CSI cameras (IMX219) on SaltyBot's sensor head.
+
+| Feature | Spec |
+|---------|------|
+| Application | Protects IMX219 cameras from rain, dust, and direct sunlight |
+| Camera interface | Snap-fit to camera housing (32×32 mm PCB with 38×38 mm face plate) |
+| Material | PETG (printed) or polycarbonate (lens cover) |
+| Coverage | All 4 cameras (radial arms at 0°/90°/180°/270°) |
+| Visor overhang | 32 mm forward extension |
+| Installation | Tool-free snap-fit (no fasteners required) |
+| Optional | Clear polycarbonate lens cover insert |
+
+---
+
+## Design Features
+
+- **Visor-style overhang:** 32 mm forward extension shields lens from rain and sun glare
+- **Drip edge:** Curved bottom lip (3 mm radius) prevents water from running back onto PCB
+- **Snap-fit tabs:** 4 flexible tabs clip into grooves on camera housing sides (no fasteners)
+- **Ventilation slots:** 3 vent slots per side prevent moisture condensation inside shield
+- **Lens cover groove:** Optional slot accepts removable 2.0 mm clear polycarbonate sheet
+- **Minimal weight:** ~8–10 g per shield (4 shields ≈ 32–40 g)
+- **No supports needed:** Flat-print orientation; minimal bridging
+
+---
+
+## Part A — Printed Shields
+
+### Single Shield Unit (csi_rain_shield.scad, RENDER="shield")
+
+**Purpose:** Protective visor for one CSI camera lens; clips onto camera housing.
+
+| Parameter | Value | Notes |
+|-----------|-------|-------|
+| Qty | 4 | One per camera (front, back, left, right) |
+| Material | PETG | 4 perimeters, 25% infill (speed-optimized) |
+| Print size | ~45 × 55 × 8 mm | Flat-face-down orientation |
+| Print time | ~25–35 min per shield | Total ~2 hours for all 4 |
+| Support | Minimal | Small bridging over drip edge only |
+| Wall thickness | 3 mm nominal | Adequate for snap-tab rigidity |
+
+**Key features:**
+- Curved top surface sheds water outward
+- 4 snap-fit tabs (one per side) with 0.4 mm clearance for easy on/off
+- Vent slots (3 on left, 3 on right) for air circulation
+- Integrated groove for optional lens cover
+- Drip edge prevents water from trickling back
+
+**Post-print finishing:**
+- Remove minimal support (drip edge underside)
+- Smooth any rough edges with 220-grit sandpaper
+- Test snap-tabs fit snugly (should click into place with light pressure)
+- Verify vent slots are open (clear with compressed air if needed)
+
+---
+
+## Part B — Optional Lens Cover
+
+### Clear Polycarbonate Insert (csi_rain_shield.scad, RENDER="lens_cover")
+
+**Purpose:** Optional removable transparent lens cover; protects optics while allowing light transmission.
+
+| Parameter | Value | Notes |
+|-----------|-------|-------|
+| Qty | 4 | One per camera (optional) |
+| Material | Polycarbonate sheet, clear | 2.0 mm thickness; cut from larger stock |
+| Size | ~44 × 44 mm (with flanges) | Trimmed to fit shield groove |
+| Optical quality | >90% transmission | Standard transparency grade; no special optics required |
+| Source | Cut from 2.0 mm clear polycarbonate sheet | Order stock, cut to size, sand edges smooth |
+
+**Installation:**
+1. Measure shield opening: approx. 38×38 mm (camera face size)
+2. Cut polycarbonate sheet to ~44×44 mm (includes 3 mm flange on each side)
+3. Sand edges smooth with 220+ grit (prevent scratching during insertion)
+4. Slide into groove on shield front (flanges grip in shield channels)
+5. Can be removed/cleaned without tools
+
+**Note:** Lens cover is **optional** — shields work fine without it. Use for:
+- Extreme weather (heavy rain, salt spray)
+- Coastal/sandy environments (dust protection)
+- High-temperature environments (reduces direct solar heating on sensor)
+
+---
+
+## Assembly Instructions
+
+### Installation on Camera Housing
+
+1. **Prepare shield:** Remove any support material; verify snap-tabs are flexible.
+2. **Position shield:** Orient visor away from camera (forward overhang extends away).
+3. **Align tabs:** Match snap-tab positions with grooves on camera housing sides.
+4. **Apply light pressure:** Snap shield onto housing with gentle thumb pressure.
+   - You should hear/feel a "click" as each tab engages.
+   - All 4 tabs should seat simultaneously (indicate correct orientation).
+5. **Verify fit:** Tug gently on shield — it should not move relative to housing.
+
+### Installation of Lens Cover (Optional)
+
+1. **Prepare cover:** Sand edges smooth; verify 44×44 mm dimension.
+2. **Align flanges:** Position cover so flanges align with groove channels on shield.
+3. **Slide into groove:** Insert cover from front, sliding flanges into shield grooves.
+4. **Check seating:** Cover should sit flush with shield front (no gaps).
+5. **Removal:** Gently pry from one corner to remove for cleaning.
+
+### Removal (For Cleaning/Replacement)
+
+1. **Lens cover:** Pop out with fingernail or plastic lever (takes 10 seconds).
+2. **Shield:** Flex one snap-tab up slightly while pulling shield forward.
+   - Repeat on opposite side if needed.
+   - Once one tab releases, shield pulls free easily.
+3. **Clean:** Wipe interior with dry cloth; use lens cleaner on polycarbonate if needed.
+4. **Reinstall:** Reverse steps above.
+
+---
+
+## Fastener List
+
+| # | Item | Qty | Notes |
+|---|------|-----|-------|
+| 1 | Printed shield (PETG) | 4 | See Part A specs above |
+| 2 | Polycarbonate lens cover | 4 | Optional; see Part B above |
+| – | **No fasteners required** | — | Shields attach via snap-fit tabs only |
+
+---
+
+## Mounting Configuration
+
+All 4 shields mount to radial arms of sensor_head.scad camera arms:
+
+```
+Top-down view (looking down at sensor head):
+
+        Camera 1 (0°, front)
+               ▲
+               │
+      Shield   │  Shield
+        (270°) │    (90°)
+         ◄────-●─────►
+               │
+               │
+        Camera 3 (180°, back)
+               ▼
+
+Each camera has a 32×32 mm PCB with 38×38 mm face plate.
+All 4 shields use identical design (radially symmetric).
+```
+
+---
+
+## Print Settings (Recommended)
+
+| Parameter | Value | Reason |
+|-----------|-------|--------|
+| **Nozzle temp** | 215–220 °C (PETG) | Prevent stringing; avoid over-heating |
+| **Bed temp** | 80 °C | Good adhesion for PETG |
+| **Print speed** | 40 mm/s | Normal speed; snapt-tabs need clean layers |
+| **Infill** | 25% | Sufficient for rigidity; saves weight & time |
+| **Perimeters** | 4 | Ensures solid snap-tabs |
+| **Supports** | Minimal (tree/linear) | Only under drip edge if needed |
+| **Orientation** | Flat-side-down | Visor face toward bed for best surface finish |
+| **Layer height** | 0.2 mm | Standard; 0.1 mm for improved surface finish |
+
+---
+
+## Mass Estimate
+
+| Component | Qty | Material | Est. mass |
+|-----------|-----|----------|-----------|
+| Rain shield (printed) | 4 | PETG | 8–10 g each (32–40 g total) |
+| Polycarbonate cover | 4 | PC sheet | 3–5 g each (12–20 g total, optional) |
+| **Subtotal (shields only)** | | | **32–40 g** |
+| **Total (with covers)** | | | **44–60 g** |
+
+**Impact on robot:** Negligible — <60 g added weight distributed symmetrically on sensor head.
+
+---
+
+## Weather Resistance
+
+| Condition | Protection | Notes |
+|-----------|-----------|-------|
+| **Light rain** | Excellent | Visor prevents direct water contact |
+| **Heavy rain** | Good | Drip edge minimizes runoff; vent slots allow drainage |
+| **Salt spray** | Good | PETG resists corrosion; rinsable with fresh water |
+| **Direct sunlight** | Excellent | Reduces lens heating; improves image contrast in bright conditions |
+| **Dust** | Very good | Visor blocks most airborne dust; lens cover optional for sandy environments |
+| **Snow/ice** | Fair | Shields prevent accumulation on lens; may require occasional wiping |
+
+---
+
+## Maintenance & Cleaning
+
+### Weekly (or after rain/dust storm)
+
+- **Wipe exterior:** Soft cloth, no cleaners (PETG safe with water only)
+- **Check vent slots:** Clear any debris with compressed air
+- **Verify snap-tabs:** Ensure shield hasn't loosened (retighten if needed)
+
+### Monthly (or as needed)
+
+- **Clean lens:** Remove polycarbonate cover; clean with lens cleaner + microfiber cloth
+- **Inspect for cracks:** Check snap-tabs and drip edge for damage
+- **Reattach cover:** Reinstall lens cover if removed
+
+### Seasonal (before extended operations)
+
+- **Deep clean:** Soak shields in warm soapy water; dry thoroughly
+- **Inspect material:** Check for UV degradation (yellowing, brittleness)
+- **Test fit:** Verify snap-tabs still grip firmly; replace if worn
+
+---
+
+## Troubleshooting
+
+| Issue | Cause | Solution |
+|-------|-------|----------|
+| Shield won't snap on | Tabs too tight | Sand snap-tabs lightly; verify groove alignment |
+| Shield rattles | Tabs too loose | Shim with thin tape; or reprint with tighter tolerance |
+| Water pooling inside | Vent slots blocked | Clear vents with compressed air |
+| Condensation on lens | Poor ventilation | Increase fan speed on sensor head or add desiccant packet |
+| Lens cover stuck | Flanges swollen | Let air-dry in sun for 1 hour; gently pry corner |
+| Drip edge cracked | Impact damage | Replace shield; or reinforce with epoxy + fiber tape |
+
+---
+
+## Design Variants
+
+### Variant 1: Enhanced Rain Protection (HEAVY WEATHER)
+- Extend visor overhang to 40 mm
+- Add full-width drip lip (vs. curved edge)
+- Thicken walls to 4 mm for durability
+- **Cost:** +10% weight, +5% print time
+
+### Variant 2: Minimal Sun Shield (LIGHTWEIGHT)
+- Reduce visor overhang to 20 mm
+- Thinner walls (2.5 mm)
+- Fewer vent slots (1 per side)
+- **Weight savings:** ~15%; best for dry climates
+
+### Variant 3: 360° Camera Protection (ADVANCED)
+- Add full-wrap shroud (not just visor)
+- Integrated housing covers (larger print)
+- Requires more support material
+- **Print time:** ~3 hours per shield
+
+---
+
+## Storage & Replacement
+
+**Shelf life:** PETG shields have indefinite shelf life if stored dry.
+
+**Replacement schedule:** Replace if:
+- Snap-tabs become loose or brittle
+- UV degradation visible (yellowing, embrittlement)
+- Cracks develop in visor
+- Polycarbonate cover becomes cloudy (clean first; replace if cloudiness persists)
+
+**Spares to keep:** 1–2 extra shields (in case of damage during field operations).
+
+---
+
+## Files & References
+
+| File | Purpose |
+|------|---------|
+| `csi_rain_shield.scad` | OpenSCAD parametric model (3 RENDER variants) |
+| `csi_rain_shield_BOM.md` | This document |
+| `imx219_mount.scad` | CSI camera housing reference (dependency) |
+| `sensor_head.scad` | Radial arm assembly reference |
+
+---
+
+## Assembly Checklist
+
+- [ ] Print all 4 shields (PETG, flat-face-down)
+- [ ] Remove support material (minimal)
+- [ ] Sand edges smooth (220 grit)
+- [ ] Test snap-tabs (should click into place with finger pressure)
+- [ ] Verify vent slots are open
+- [ ] *Optional:* Cut polycarbonate lens covers to size
+- [ ] *Optional:* Sand polycarbonate edges smooth
+- [ ] Mount shields on all 4 cameras (starting with front)
+- [ ] Verify all snap-tabs engaged
+- [ ] *Optional:* Install polycarbonate lens covers
+- [ ] Inspect for water shedding (test with water spray if available)
+- [ ] Label shields if needed (mark front/back camera positions)
+- [ ] Store spares in dry location