sl-mechanical
beb0af7ce6
Protects expensive sensors when robot tips over during testing.
Files added:
chassis/bumper_frame.scad — roll cage (25 mm stem collar + 4 inclined
posts + crown ring + TPU snap pad). Posts at
45/135/225/315° between cameras. Crown at
Z=148 mm above cage collar, 18 mm above RPLIDAR
top. RPLIDAR FOV unobstructed.
chassis/base_bumper.scad — clip-on bumper ring for 270×240 mm base plate.
50 mm tall, 15 mm standoff, rounded corners.
4× corner + 4× side clip brackets. TPU snap
edge caps. FC status LEDs remain visible.
chassis/stem_protector.scad — split TPU sleeve for 25 mm stem. Snap-fit
closure (no hardware). Install 3–4 sleeves
along stem at ~200 mm intervals.
chassis/bumper_BOM.md — full BOM, print settings, install heights,
mass estimate (~500 g total, balanced).
All parts print without supports. Fully removable (clip/snap/clamp).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
170 lines
6.4 KiB
Markdown
170 lines
6.4 KiB
Markdown
# SaltyBot Bumper & Crash Protection — BOM + Assembly Notes
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**Rev A — 2026-03-01 — sl-mechanical**
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---
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## System Overview
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Three independent protection layers:
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| Layer | File | Protects |
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|-------|------|----------|
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| Sensor head roll cage | `bumper_frame.scad` | RPLIDAR, RealSense, 4× IMX219 |
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| Base plate bumper ring | `base_bumper.scad` | FC, motors, wiring, wheels |
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| Stem impact sleeves | `stem_protector.scad` | 25 mm stem tube along length |
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---
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## Design Constraints Met
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| Constraint | How addressed |
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|-----------|---------------|
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| RPLIDAR 360° FOV | Roll cage posts at 45°/135°/225°/315° (between cameras). At RPLIDAR scan-plane height (~105 mm from cage collar), posts are ~78 mm from stem CL — well outside RPLIDAR body (35 mm radius). Crown ring sits at Z=148 mm, above RPLIDAR top. |
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| Camera views | Posts avoid all four camera directions (0°/90°/180°/270°). |
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| FC status LEDs | Base bumper clips below plate edge — does not cover plate top face or sides. LEDs remain visible. |
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| Removable | All parts clip or clamp; no permanent fasteners into robot structure. |
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| No supports | All parts print flat-face-down (collar halves, posts, crown ring, brackets, sleeves). |
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| Lightweight | PLA frame + TPU pads only where needed; crown ring is hollow, brackets are thin-wall. |
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---
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## Part A — Sensor Head Roll Cage (`bumper_frame.scad`)
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### Printed parts
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| # | RENDER | Qty | Material | Settings | Notes |
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|---|--------|-----|----------|----------|-------|
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| 1 | `collar_front` | 1 | PETG | 5 perims, 40% infill | Flat-face-down |
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| 2 | `collar_rear` | 1 | PETG | 5 perims, 40% infill | Flat-face-down; mirror of front |
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| 3 | `post` | 4 | PETG or PLA | 4 perims, 25% infill | Lay flat on narrow face |
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| 4 | `crown` | 1 | PETG or PLA | 4 perims, 30% infill | Flat (natural print orientation) |
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| 5 | `tpu_pad` | 1 | TPU 95A | 3 perims, 20% infill, 25 mm/s | Snap-on crown impact ring |
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### Fasteners
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| 6 | M4×25 SHCS | 2 | Cage collar clamping bolts |
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| 7 | M4 hex nut | 2 | Captured in collar rear half |
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| 8 | M4×10 set screw | 1 | Height/rotation lock (front collar) |
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| 9 | M4×20 SHCS | 8 | Post-to-collar (2 per post, through boss) |
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| 10 | M4×16 SHCS | 8 | Post-to-crown (2 per post, through crown top) |
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| 11 | M4 hex nut | 8 | Under collar for post bolts |
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| 12 | M4 flat washer | 16 | All M4 bolt heads |
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### Cage installation — height reference
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```
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Z from cage collar base:
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Z = 0 mm — cage collar bottom (clamp to stem here)
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Z = 24 mm — cage collar top
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Z = 54 mm — sensor-head collar bottom (≈30 mm above cage collar)
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Z = 90 mm — sensor-head collar top + platform
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Z = 100 mm — RPLIDAR base (above anti-vibration ring)
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Z = 130 mm — RPLIDAR top
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Z = 148 mm — cage crown ring (12 mm clear of RPLIDAR)
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```
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> **Install the cage collar ~30 mm BELOW the sensor-head collar on the same 25 mm stem.**
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> Slide collar down stem, position posts, attach crown ring, then tighten collar clamp bolts.
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---
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## Part B — Base Plate Bumper (`base_bumper.scad`)
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### Printed parts
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| # | RENDER | Qty | Material | Notes |
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|---|--------|-----|----------|-------|
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| 13 | `corner` | 4 | PETG | Print upright (Z = tall dimension); 4 perims, 40% infill |
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| 14 | `side` | 4 | PETG | Same orientation; 4 perims, 40% infill |
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| 15 | `tpu_cap` | ~14 | TPU 95A | 40 mm segments; install end-to-end along all rails |
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### Rails (straight sections between clips)
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Rails can be 3D-printed from SCAD profile or procured:
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| # | Description | Qty | Size | Alternative |
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|---|-------------|-----|------|-------------|
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| 16 | Front rail | 1 | 8×50×270 mm PLA/PETG extrusion | 25×8 mm aluminium flat bar |
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| 17 | Rear rail | 1 | 8×50×270 mm | same |
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| 18 | Left side rail | 1 | 8×50×240 mm | same |
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| 19 | Right side rail | 1 | 8×50×240 mm | same |
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> **DXF export:** `RENDER="rail_2d"` gives the 8×50 mm cross-section. Extrude to required length in CAM software.
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### Fasteners
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| # | Spec | Qty | Use |
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|---|------|-----|-----|
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| 20 | M4×16 SHCS | 16 | Rail to corner bracket (2 heights × 2 rails per corner = 4 per corner × 4) |
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| 21 | M4×16 SHCS | 8 | Rail to side bracket (2 per side bracket × 4) |
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| 22 | M3×8 set screw | 16 | Bracket lock to plate edge (2 per clip × 8 clips) |
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| 23 | M4 hex nut | 24 | All M4 rail bolts |
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### Installation — clip orientation
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```
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TOP VIEW of base plate corner:
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plate edge (Y direction)
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│
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───────────┤
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│◄── corner_bracket arm sits here, M3 set screw bites plate edge
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plate │
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───────────┘
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↑
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plate edge (X direction)
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```
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The clip slot engages the BOTTOM face of the plate. Slide bracket onto corner from below; tighten M3 set screws finger-tight → hand-tight.
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---
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## Part C — Stem Protector (`stem_protector.scad`)
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### Printed parts
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| # | RENDER | Qty | Material | Notes |
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|---|--------|-----|----------|-------|
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| 24 | `front` | 3–4 | TPU 95A | Flat-face-down; qty = no. of stem zones to protect |
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| 25 | `rear` | 3–4 | TPU 95A | Mirror; snap together around stem |
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### Recommended placement (25 mm stem, ~1000 mm total stem)
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| Position | Z from base plate | Purpose |
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|----------|-----------------|---------|
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| Sleeve 1 | 50–130 mm | Lowest zone — hit first in a side-fall |
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| Sleeve 2 | 300–380 mm | Mid stem (near battery carousel) |
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| Sleeve 3 | 600–680 mm | Upper stem |
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| Sleeve 4 | 850–930 mm | Below sensor head collar |
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### No fasteners required
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Sleeves snap closed around stem. For extra security on smooth aluminium stem: wrap one loop of 25 mm Velcro strap over each sleeve before snapping closed.
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---
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## Tools Required for Assembly
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- M2.5 / M3 / M4 hex drivers
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- Torque wrench: M4 cage-collar bolts 2 N·m, M3 set screws 0.8 N·m
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- Thread locker (Loctite 243 blue) on cage crown M4 bolts
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---
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## Mass Estimate
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| Part | Material | Est. mass |
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|------|----------|-----------|
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| Roll cage collar (×2 halves) | PETG | ~60 g |
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| Roll cage posts (×4) | PETG | ~80 g |
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| Crown ring | PETG | ~45 g |
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| TPU crown pad | TPU | ~15 g |
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| Base bumper (×4 corners + ×4 sides) | PETG | ~160 g |
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| Base bumper TPU caps | TPU | ~40 g |
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| Stem sleeves (×8 halves) | TPU | ~60 g |
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| Fasteners | SS | ~40 g |
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| **Total** | | **~500 g** |
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> **Balance note:** All protection hardware is symmetric about the robot's fore-aft axis. Roll cage is symmetric about all axes. Net CG shift is negligible (<5 mm vertical, <2 mm lateral).
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