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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
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