# GoPro 3-Prong T-Slot Sensor Rail Mount — BOM + Assembly
**Rev A — 2026-03-02 — sl-mechanical**

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## System Overview

Universal GoPro HERO 5+ camera mount for sensor_rail.scad (T-slot 20×20 mm).

| Feature | Spec |
|---------|------|
| Camera interface | Standard GoPro 3-prong (HERO 5+) |
| Rail system | T-slot 2020 OpenBuilds / MISUMI compatible |
| Tilt range | 0° – 90° from horizontal |
| Tilt detents | 15° increments (0°, 15°, 30°, 45°, 60°, 75°, 90°) |
| Retention | M3 thumbscrew clamp (T-nut to rail) + M5 index pin (angle lock) |
| Weight | ~85 g (printed) + ~45 g (fasteners) |

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## Design Features

- **Top mount:** Standard GoPro 3-prong interface — no custom adapters, works with any GoPro HERO 5+ compatible accessory.
- **Bottom clamp:** Integrated T-nut slides into rail T-groove; single M3 thumbscrew locks clamp to rail (no tools required).
- **Tilt mechanism:** Rotating bracket + M5 hinge pin; camera tilts 0°–90° and locks at 15° steps via M5 index holes.
- **Printability:** Both parts print flat-face-down, no support material required.
- **Compatibility:** Works with all SaltyLab / SaltyRover sensor_rail.scad mounts; positions camera anywhere along rail.

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## Part A — Printed Components

### 1. Base Clamp (gopro_mount.scad, RENDER="base_stl")

**Purpose:** Holds T-nut in rail T-groove; provides rotation axis for camera bracket.

| Parameter | Value | Notes |
|-----------|-------|-------|
| Qty | 1 | Single part per mount |
| Material | PETG | 5 perimeters, 40% infill (gyroid) |
| Print size | ~45 × 35 × 28 mm | Flat-face-down (rail-side down) |
| Orientation | Rail bore facing DOWN | Supports natural bed adhesion |
| Support | None | Design allows direct print |
| Wall thickness | 4–5 mm minimum | Ensure M3 threads cut cleanly |

**Key features:**
- Integrated T-nut pocket (friction-fit to rail T-groove)
- M3 thumbscrew bore (perpendicular to T-nut, from outside rail face)
- M5 hinge-pin bore (passes through to camera bracket)
- 7 index holes (one for each tilt angle: 0°, 15°, 30°, 45°, 60°, 75°, 90°)
- Vent slots for weight reduction

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### 2. Camera Bracket (gopro_mount.scad, RENDER="camera_bracket")

**Purpose:** Holds GoPro camera via 3-prong mount; rotates about M5 hinge pin.

| Parameter | Value | Notes |
|-----------|-------|-------|
| Qty | 1 | Single part per mount |
| Material | PETG | 4 perimeters, 30% infill |
| Print size | ~35 × 25 × 51 mm | Flat-face-down (prong-side down) |
| Orientation | GoPro prongs facing DOWN | Minimal post-processing |
| Support | None | Design supports printing without supports |
| Wall thickness | 3–4 mm | Adequate for M5 through-bore |

**Key features:**
- 3 cylindrical prong sockets (GoPro standard spacing)
- M5 hinge-pin bore (receives bolt from base)
- 1 index hole (aligns with base index holes at tilt angle)
- Lightweight design

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## Part B — Fasteners & Hardware

All fasteners are stainless steel or zinc-plated for corrosion resistance.

| # | Spec | Qty | Use | Notes |
|---|------|-----|-----|-------|
| 1 | M3 × 12 SHCS | 1 | Thumbscrew — clamps T-nut to rail | or M3 cap screw with printed knob |
| 2 | M3 washer | 1 | Under thumbscrew head | standard flat washer |
| 3 | M5 × 25 SHCS | 1 | Hinge pin — camera bracket rotation axis | or M5 cap screw + lock washer |
| 4 | M5 washer | 2 | Hinge pin lock washers (each end) | prevents backlash |
| 5 | M5 lock nut | 1 | Hinge pin lock nut | nylon-insert preferred |
| 6 | M5 × 8 roll pin | 7 | Index pins — lock tilt angle | one for each 15° detent (0°–90°) |

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## Installation & Assembly

### Step 1: Prepare T-slot Rail

1. Verify rail is clean (no burrs, chips).
2. Slide base clamp assembly onto rail from above (rail face toward clamp bore).
3. Align T-nut pocket with T-slot T-groove (groove faces inward).

### Step 2: Clamp Base to Rail

1. Insert M3 thumbscrew through rail outer face, through the T-nut pocket.
2. Tighten **finger-tight** first (do not overtighten — rail will deform).
3. Verify clamp is centered on rail (equal gap on both sides).
4. Tighten to **hand-tight** (≈2 N·m for M3).

### Step 3: Assemble Hinge & Camera Bracket

1. Slide M5 × 25 bolt through base clamp hinge bore (horizontal, perpendicular to rail).
2. Mount camera bracket on bolt (prong-side facing camera direction).
3. Add M5 washers at both bolt ends.
4. Tighten M5 lock nut to **hand-tight** (≈5 N·m).
   - Bolt should rotate smoothly but without play.
   - If bracket binds, loosen slightly; if too loose, add second lock washer.

### Step 4: Mount GoPro Camera

1. Rotate camera bracket to desired tilt angle (0°, 15°, 30°, etc.).
2. Align index hole on bracket with corresponding hole on base clamp.
3. Insert M5 × 8 roll pin into aligned holes (pushes in snugly, no tools needed).
4. Verify pin locks camera position (should not rotate when pin is seated).
5. Slide GoPro onto 3 prongs until camera contacts mount.

### Step 5: Cable Management

- Route camera USB/HDMI cable down rail (behind robot).
- Use cable tie on thumbscrew pocket if additional restraint needed.

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## Tilt Angle Detents

The 15° step gives 7 fixed positions within 0°–90° range:

| Tilt Index | Angle | Use case |
|------------|-------|----------|
| 1 | 0° | Horizontal (level with horizon) |
| 2 | 15° | Slight upward tilt |
| 3 | 30° | Moderate upward tilt |
| 4 | 45° | Balanced forward-up tilt |
| 5 | 60° | Steep upward tilt |
| 6 | 75° | Nearly vertical forward |
| 7 | 90° | Straight vertical (zenith) |

To change tilt:
1. Push on camera bracket to rotate (index pin will pop out if at end of rotation).
2. Align new index hole.
3. Re-insert index pin.

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## Fastener Torque Spec

| Fastener | Size | Torque | Note |
|----------|------|--------|------|
| M3 thumbscrew | M3 × 12 | 2 N·m | Hand-tight; over-tightening deforms rail |
| M5 hinge pin | M5 × 25 | 5 N·m | Smooth rotation, no play |
| M5 lock nut | M5 | 2.5 N·m | After initial tightening, verify free rotation |

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## Post-Print Finishing

### Base Clamp
- **Support removal:** No supports needed.
- **Bore prep:** If M3 bore is rough, ream with M3 hand reamer (¼ turn only).
- **T-nut pocket:** Smooth with fine sandpaper if needed (must slide smoothly into groove).

### Camera Bracket
- **Support removal:** No supports needed.
- **Prong sockets:** Clean with compressed air; verify no strands block GoPro prongs.
- **Index hole:** Verify M5 bore is clear (small drill bit can clear if needed).

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## Mass Estimate

| Component | Material | Est. Mass |
|-----------|----------|-----------|
| Base clamp | PETG | ~35 g |
| Camera bracket | PETG | ~28 g |
| M3 thumbscrew | Stainless | ~2 g |
| M5 hinge bolt + nut | Stainless | ~6 g |
| M5 index pins (×7) | Steel | ~4 g |
| **Total (without camera)** | | **~75 g** |
| **Total (with GoPro HERO)** | | **~250 g** |

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## Mounting Position Recommendations

### On sensor_rail.scad vertical rail

| Position | Z height | Use |
|----------|----------|-----|
| Below sensor head | 700–800 mm | Forward-facing wide-angle view |
| Mid-rail | 400–500 mm | Side-looking perspective |
| Above base plate | 100–200 mm | Ground-level or low-angle view |

Index holes on rail face every 25 mm; position bracket at any height (friction-fit with T-nut + thumbscrew).

### On payload_bay_rail.scad (horizontal rail)

Mount horizontally by:
1. Rotate entire assembly 90° (rail runs front-to-back).
2. Tilt camera bracket 0°–90° to point downward or forward.
3. Good for payload bay documentation (downward view) or forward obstacle detection.

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## Storage & Maintenance

- **Store bracket vertical** (prongs up) to avoid stress on sockets.
- **Clean prongs** after each field session (dust prevents secure seating).
- **Verify index pin seating** before each deployment (pin can loosen if rattled).
- **Check thumbscrew** monthly (re-tighten if rail has shifted).

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## Design Notes for Future Revisions

- **Optional:** Add detent detents (spring-loaded ball bearing pockets) at index holes for positive clicks.
- **Optional:** Add strap attachment points on base clamp for secondary safety line.
- **Alternative bracket:** Straight vertical bracket (0° fixed) for weight-optimized variant.
- **Camera variants:** Compatibility with GoPro Session (action cam) and DJI Osmo Action (different prong patterns) would require bracket redesign.

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## Files

| File | Purpose |
|------|---------|
| `gopro_mount.scad` | OpenSCAD parametric model (3 RENDER variants) |
| `gopro_mount_BOM.md` | This document |
| `sensor_rail.scad` | Parent T-slot rail system (dependency) |
| `sensor_rail_brackets.scad` | Additional rail bracket options |

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## Assembly Checklist

- [ ] Print base clamp (PETG, 45 × 35 × 28 mm, flat-side-down)
- [ ] Print camera bracket (PETG, 35 × 25 × 51 mm, flat-side-down)
- [ ] Inspect prong sockets on bracket (no strands, smooth)
- [ ] Ream or smooth M3 thumbscrew bore in base clamp
- [ ] Test T-nut pocket (slides in/out of rail groove smoothly)
- [ ] Assemble: M3 thumbscrew + washer
- [ ] Assemble: M5 × 25 bolt + 2 washers + lock nut
- [ ] Mount bracket on hinge pin (hand-tight fit)
- [ ] Insert one M5 × 8 index pin at 0° (test fit)
- [ ] Mount GoPro camera (prongs snap in)
- [ ] Final check: camera level in 0° position
- [ ] Stow extra index pins in camera bag