saltylab-firmware/chassis/sensor_head_assembly.md
sl-mechanical 23f2daa3cd feat: sensor head mounts — stem collar, RPLIDAR, RealSense, 4× IMX219
Part of Phase 2 sensor mount designs for SaltyBot 25 mm mast.

Files added:
  chassis/sensor_head.scad        — split collar (25 mm OD stem) + octagonal platform
  chassis/rplidar_mount.scad      — anti-vibration ring for RPLIDAR A1M8 (Ø58 mm BC)
  chassis/realsense_mount.scad    — RealSense D435i arm bracket, 10° tilt, 1/4-20 nut
  chassis/imx219_mount.scad       — 4× IMX219 radial arms, 10° tilt, CSI ribbon slot
  chassis/sensor_head_assembly.md — assembly diagram + fastener BOM + print settings

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
2026-02-28 22:53:18 -05:00

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# SaltyBot Sensor Head — Assembly Diagram
**Rev A — 2026-02-28 — sl-mechanical**
---
## Overview
The sensor head mounts on top of the 25 mm OD vertical stem.
Five printed/machined parts stack on a split collar platform.
---
## TOP VIEW (schematic)
```
FRONT (+X)
[IMX219 arm] | [IMX219 arm]
90° | 0°
↑ +---------+ ↑
| | | |
[IMX219]←----[•]---| RPLIDAR |---[•]----→[IMX219]
270° | | Ø70mm | | 90°
↓ | | ↓
+---------+
| PLAT |
| Ø120mm |
| (octag) |
+---------+
↑ | | ↑
[RS arm]---[•]---| COLLAR |---[•]
| Ø52mm |
+---------+
|
25mm stem
```
---
## SIDE VIEW (section through front, to scale)
```
Z
│ RPLIDAR A1M8 (Ø70 × 30 mm)
│ ┌────────────────────┐ ← Z ≈ 52 mm (top of RPLIDAR)
│ │ ██████████████ │
│ │ ██ A1M8 ██ │ ← Z ≈ 22 mm (bottom of RPLIDAR)
│ └────────────────────┘
│ │ │ │ │ ← M3×30 bolts (4 off)
│ ┌────┴────┴────┴────┐
│ │ rplidar_ring.scad│ ← Z = 14..18 mm (4 mm ring)
│ │ [silicone gromm]│ ← grommets 8 mm below ring
│ └───────────────────┘
│ ┌───────────────────┐
│ │ P L A T F O R M │ ← Z = 36..44 mm
│ │ (octag, Ø120mm) │
│ └───────────────────┘
│ │ COLLAR │
│ ┌────┴────────┴────┐
│ │ COLLAR FRONT │ ← Z = 0..36 mm
│ │ │ stem bore │ │
│ │ COLLAR REAR │
│ └──────────────────┘
│ │
│ 25 mm STEM
└─────────────────────────────────────── X
```
> **Note on Z references:** Z=0 is the bottom of the collar.
> Stem clamp bolts lock the sensor head at chosen height on the mast.
---
## IMX219 Arm (side view — one arm shown)
```
Platform edge Camera PCB
│ │
─────┤══════════════════════════════════════╗
│ ←── 52 mm arm ──────────────────► ║ IMX219
─────┤══════════════════════════════════════╝ ← 10° nose down
│ 2× M4 4× M2
│ base bolts PCB bolts
│ [slot: CSI ribbon through arm length]
```
---
## RealSense Arm (side view)
```
Platform edge
│ 2× M4
─────┤
│ Base ←── 75 mm arm ──────────────────►
─────┤ plate
│ (flat) ══════════════════════════════════╗
║ ← 10° nose down
║ D435i
║ 90×25×25
1/4-20 nut (captured)
```
---
## Assembly Sequence
| Step | Action |
|------|--------|
| 1 | Print 2× `collar_half` (flat-face-down; mirror one in slicer) |
| 2 | Print 1× `platform` |
| 3 | Print 1× `rplidar_ring` |
| 4 | Print 1× `realsense_bracket` |
| 5 | Print 4× `imx219_arm` (one per direction) |
| 6 | Seat 4× M3 silicone anti-vibration grommets in platform holes |
| 7 | Place rplidar_ring on grommets; pass 4× M3×30 SHCS from platform bottom up through ring |
| 8 | Set RPLIDAR A1M8 on ring; tighten M3×30 into RPLIDAR tapped holes (fingertight) |
| 9 | Thread 1/4-20 hex nut into realsense_bracket pocket; bolt D435i onto bracket |
| 10 | Bolt realsense_bracket to platform front with 2× M4×16 SHCS |
| 11 | Bolt 4× imx219_arm to platform with 2× M4×16 SHCS each |
| 12 | Snap IMX219 PCBs onto arm face plates with 4× M2×6 BHCS each |
| 13 | Route CSI ribbon cables through arm slots toward platform centre |
| 14 | Assemble collar halves around stem (flat faces mating); tighten M4×30 clamping bolts |
| 15 | Tighten M4 set screw in front collar half to lock height |
| 16 | Torque RPLIDAR M3 bolts: 0.5 N·m |
---
## Fastener Summary
| Qty | Size | Use |
|-----|------|-----|
| 2 | M4×30 SHCS | Collar clamping bolts |
| 1 | M4×10 set screw | Collar height / rotation lock |
| 2 | M4×16 SHCS | RealSense bracket to platform |
| 8 | M4×16 SHCS | IMX219 arms to platform (2 per arm) |
| 4 | M2×6 BHCS | IMX219 PCB to face plate (per arm; ×4 arms = 16 total) |
| 4 | M3×30 SHCS | RPLIDAR ring to platform (through grommet) |
| 4 | M3 anti-vibration grommet | Silicone, M3, Ø6 | Between platform and RPLIDAR ring |
| 1 | 1/4-20 hex nut | Captured in RealSense bracket |
| 2 | M4 hex nut | Captured in collar rear half |
| 8 | M4 flat washer | Under head of all M4 bolts |
---
## Print Settings
| Part | Material | Infill | Perimeters | Notes |
|------|----------|--------|-----------|-------|
| collar_half (×2) | PETG | 40% | 5 | Flat-face-down; print support-free |
| platform | PETG or PLA | 30% | 4 | Top-face-up |
| rplidar_ring | PETG | 30% | 3 | Flat |
| realsense_bracket | PETG | 35% | 4 | Base on bed; arm horizontal |
| imx219_arm (×4) | PETG or PLA | 30% | 3 | Flat, arm along X |