saltylab-firmware/chassis/sensor_rail_BOM.md

Sensor Rail BOM — Issue #138

Agent: sl-mechanical | Date: 2026-03-01

Universal 2020 T-slot sensor mount rail system. Compatible with SaltyLab (stem), SaltyRover (square posts), SaltyTank (uprights).

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Purchased Hardware

#	Description	Spec	Qty (per robot)	Notes
H1	2020 T-slot aluminium extrusion	20×20 mm, 200 mm length	1–2	OpenBuilds V-Slot or MISUMI HFS5-2020. Order pre-cut or cut with mitre saw.
H2	M5×10 BHCS	Stainless	4	Rail-to-adapter attachment (M5 T-nuts in rail)
H3	M5 T-nut (drop-in)	For 2020 slot	4	Off-the-shelf; used for adapter attachment
H4	M3×16 SHCS	Stainless	N	One per sensor bracket (thumbscrew + clamping)
H5	M3 hex nut	DIN 934, stainless	N	One per bracket T-nut (press-fit in pocket)
H6	M3×6 BHCS	Stainless	2N	Bracket arm-to-base plate (2 per bracket)
H7	M4×30 SHCS	Stainless	2	Stem adapter clamping bolts
H8	M4 hex nut	DIN 934, stainless	2	Stem adapter nut pockets
H9	M4×12 BHCS	Stainless	4	Post adapter clamping
H10	M4×12 BHCS	Stainless	4	Tank clamp frame attachment
H11	M3×8 SHCS	Stainless	4	RPLIDAR platform bolts
H12	1/4-20 UNC hex nut	Zinc or SS	1	D435i tripod nut (captured in bracket)
H13	M2×6 SHCS	Stainless	4	IMX219 PCB mounting
H14	M3×8 SHCS	Stainless	4	UWB PCB mounting
H15	M5×6 set screw	Cup point, SS	2	Optional rail end cap retention

N = number of brackets installed; typical per robot: 3–5.

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Printed Parts (PETG unless noted)

Part	File	Qty	Print settings	Mass est.
T-nut base	sensor_rail_brackets.scad base_stl	N brackets	5 perims, 60% infill	~6 g
RPLIDAR bracket	sensor_rail_brackets.scad rplidar_stl	1	4 perims, 40% infill	~18 g
D435i bracket	sensor_rail_brackets.scad d435i_stl	1	4 perims, 40% infill	~14 g
IMX219 bracket	sensor_rail_brackets.scad imx219_stl	1–4	4 perims, 40% infill	~8 g
UWB bracket	sensor_rail_brackets.scad uwb_stl	1–4	4 perims, 40% infill	~10 g
Cable clip	sensor_rail_brackets.scad cable_clip_stl	6–10	3 perims, 20% infill	~2 g
Rail end cap	sensor_rail.scad end_cap_stl	2	5 perims, 40% infill	~3 g
Index pin set (×4)	sensor_rail.scad index_pin_stl	1 set	4 perims, 40% infill	~4 g
Thumbscrew wheel	sensor_rail.scad (thumbscrew_wheel)	N	4 perims, 30% infill	~1.5 g
Stem adapter half	sensor_rail.scad stem_adapter_stl	2	5 perims, 60% infill	~22 g
Post adapter	sensor_rail.scad post_adapter_stl	1–2	5 perims, 60% infill	~28 g
Tank clamp	sensor_rail.scad tank_clamp_stl	1–2	5 perims, 60% infill	~20 g

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Rail Length Reference

Robot variant	Recommended rail length	Notes
SaltyLab	200 mm	On Ø25 mm stem; 1 rail
SaltyRover	200 mm	On rear sensor mast posts
SaltyTank	150–200 mm	On tank side uprights or top bar

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Mass Summary (typical install: 1 rail + 3 brackets + 8 clips)

Item	Mass
200 mm 2020 Al extrusion	~110 g
3× bracket assemblies (base + arm)	~60 g
8× cable clips	~16 g
1× adapter (stem)	~44 g
Hardware (bolts/nuts)	~25 g
Total	~255 g

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Export Commands

# Rail profile DXF (spec for extrusion supplier)
openscad sensor_rail.scad -D 'RENDER="rail_2d"' -o sensor_rail_profile.dxf

# Printable rail section (prototype)
openscad sensor_rail.scad -D 'RENDER="rail_section_stl"' -o sensor_rail_200.stl

# Adapters
openscad sensor_rail.scad -D 'RENDER="stem_adapter_stl"' -o sensor_rail_stem_adapter.stl
openscad sensor_rail.scad -D 'RENDER="post_adapter_stl"' -o sensor_rail_post_adapter.stl
openscad sensor_rail.scad -D 'RENDER="tank_clamp_stl"'   -o sensor_rail_tank_clamp.stl
openscad sensor_rail.scad -D 'RENDER="end_cap_stl"'      -o sensor_rail_end_cap.stl
openscad sensor_rail.scad -D 'RENDER="index_pin_stl"'    -o sensor_rail_index_pins.stl

# Brackets
openscad sensor_rail_brackets.scad -D 'RENDER="base_stl"'        -o srb_tnut_base.stl
openscad sensor_rail_brackets.scad -D 'RENDER="rplidar_stl"'     -o srb_rplidar.stl
openscad sensor_rail_brackets.scad -D 'RENDER="d435i_stl"'       -o srb_d435i.stl
openscad sensor_rail_brackets.scad -D 'RENDER="imx219_stl"'      -o srb_imx219.stl
openscad sensor_rail_brackets.scad -D 'RENDER="uwb_stl"'         -o srb_uwb.stl
openscad sensor_rail_brackets.scad -D 'RENDER="cable_clip_stl"'  -o srb_cable_clip.stl

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Assembly Notes

1. Rail purchase: Order OpenBuilds V-Slot 2020 or MISUMI HFS5-2020 in desired length. Specify M5 tapped centre bore at both ends. Index holes optional (can drill manually at 25 mm pitch).
2. T-nut bases: Press M3 hex nut into pocket before inserting into rail. Insert T-nut tongue into T-groove from end of rail before fitting end caps.
3. Thumbscrew retention: Thread M3×16 SHCS through thumbwheel, then through bracket arm, into T-nut. Tighten hand-tight (¼ turn from snug). No tools required.
4. Indexed positioning: Insert Ø4.9 mm index pin through rail M5 cross-hole and bracket index pocket for repeatable 25 mm grid positioning.
5. Adapter installation:
   • Stem: clamp 2 halves around Ø25 mm stem with M4×30 bolts; torque 1.5 N·m.
   • Post: slide C-clamp around 20×20 post; tighten M4×12 bolts; torque 1.2 N·m.
   • Tank: slide clamp onto 6 mm frame plate edge; tighten M4×12 bolts.
6. Cable clips: Push cable into C-channel from front. Snap into T-groove. No fasteners needed.