saltylab-firmware/chassis/rover_BOM.md

SaltyRover Chassis — BOM + Assembly Notes

Rev A — 2026-03-01 — sl-mechanical Issue: #73

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Overview

SaltyRover is the stable 4-wheel variant of SaltyLab. Low CG, wide track — designed not to tip over. Reuses the 25 mm vertical stem, sensor head, RPLIDAR, RealSense, IMX219 camera mounts, and roll cage from SaltyLab without modification.

Top view (schematic):

          Forward (+Y)
               │
   ◉─────────────────────◉   ← front axle (AXLE_BASE/2 = 170 mm forward)
   │     [Orin NX]       │
   │     [battery]       │   ← flat packs below deck (low CG)
   │     [battery]       │
   │       [FC]          │
   ◉─────────────────────◉   ← rear  axle
           │
       stem (centre)

Dimensions (approx):
   Robot width (tyre-to-tyre):  ~810 mm  (TRACK_W=540 + 2×TIRE_W/2)
   Robot length (axle-to-axle): ~340 mm  (AXLE_BASE)
   Deck width:                   480 mm
   Deck length:                  500 mm
   Ground clearance:             ~50 mm  (deck bottom to ground)
   Overall height (with 550 mm stem + sensor head): ~800 mm

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Height Stack

Z from ground:
  Z =   0 mm  — ground
  Z =  50 mm  — chassis bottom (battery tray floor)
  Z = 109 mm  — deck bottom face
  Z = 117 mm  — deck top face  (Z=0 in SCAD coords)
  Z = 127 mm  — motor axle CL  (+10 mm above deck top)
  Z = 139 mm  — deck stem collar top  (117+22)
  Z = 145 mm  — stem adapter flange top (139+6)
  Z = 173 mm  — stem clamp top  (145+28)
  Z = 723 mm  — stem top with 550 mm rover stem

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File Index

File	Description	RENDER
saltyrover_chassis.scad	Main deck plate, stem collar, standoffs	assembly / deck / deck_2d
rover_motor_mount.scad	L-bracket + axle clamp plate, 4×	assembly / bracket / clamp_plate / bracket_2d
rover_battery_tray.scad	Slide-out battery tray, 2–4 packs	assembly / tray / rail / latch / tray_2d
rover_stem_adapter.scad	Flange + split clamp, locks stem to deck	assembly / base_flange / clamp_front / clamp_rear

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Part A — Deck Plate (saltyrover_chassis.scad)

Structural parts

#	RENDER	Qty	Material	Process	Notes
1	deck_2d	1	8 mm 5052-H32 Al	Waterjet or CNC router	480×500 mm blank
—	—	—	or 8 mm PETG FDM	Print in sections, bolted lap joints	Prototype only

Fasteners (deck to motor brackets)

#	Spec	Qty	Use
2	M5×20 SHCS	16	Motor bracket flange to deck (4 per corner × 4)
3	M5 hex nut	16	Captured on deck underside
4	M4×16 SHCS	4	Stem adapter flange to deck collar
5	M4 flat washer	4	Under bolt head

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Part B — Motor Brackets (rover_motor_mount.scad)

Print or CNC 4×. Each bracket handles one drive motor.

Printed parts

#	RENDER	Qty	Material	Settings	Notes
6	bracket	4	PETG or PC	5 perims, 60% infill	Print flange face down; add M5 inserts or use nuts
7	clamp_plate	4	PETG	4 perims, 40% infill	Axle retention; print flat

CNC alternative: bracket_2d → DXF, CNC route from 10 mm 6061-T6 Al plate.

Fasteners

#	Spec	Qty	Use
8	M4×20 SHCS	8	Axle clamp plate to bracket (2 per motor × 4)
9	M4 hex nut	8	Captured in bracket
10	Axle lock nut	4	Axle tip retention — verify axle thread before ordering (BOM.md: Ø≈10 mm tip)
11	M5×20 SHCS	16	Bracket flange to deck (from item 2 above)

⚠ Axle note: BOM.md caliper values: base OD 16.11 mm, D-cut OD 15.95 mm, flat chord 13.00 mm. Verify AXLE_D / AXLE_FLAT / BEARING_OD in rover_motor_mount.scad before printing.

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Part C — Battery Tray (rover_battery_tray.scad)

Printed parts

#	RENDER	Qty	Material	Settings	Notes
12	tray	1	PETG	4 perims, 30% infill	Print open-top face up; no supports
13	rail	2	PETG	5 perims, 40% infill	T-slot slide rail; print top-face down
14	latch	1	PETG or TPU 95A	4 perims, 30% infill	Spring retention clip; TPU gives better snap feel

Fasteners

#	Spec	Qty	Use
15	M4×12 FHCS	6	Slide rail to deck underside (3 per rail, countersunk)
16	M4 T-nut or nyloc	6	Captured under deck for rail bolts
17	M3×10 SHCS	2	Spring latch to tray end
18	Velcro strap 25 mm × 500 mm	4–8	Battery pack retention (1–2 per pack through tray floor slots)

Batteries

#	Part	Qty	Spec
19	Battery pack	2–4	24 V, 420×88×56 mm (BOM.md caliper-verified)
20	BMS board	1	Matched to cell chemistry; mount to deck underside near Y+ wall

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Part D — Stem Adapter (rover_stem_adapter.scad)

#	RENDER	Qty	Material	Settings	Notes
21	base_flange	1	PETG	5 perims, 40% infill	Print flat; add M4 brass inserts or use through-bolts
22	clamp_front	1	PETG	5 perims, 40% infill	Flat-face down
23	clamp_rear	1	PETG	5 perims, 40% infill	Mirror; flat-face down

Fasteners

#	Spec	Qty	Use
24	M4×20 SHCS	2	Stem clamp clamping bolts
25	M4 hex nut	2	Captured in clamp rear half
26	M4×8 set screw	1	Rotation lock (front half)
27	M4×16 FHCS	4	Flange to deck collar (countersunk)

Stem tube

#	Part	Qty	Spec	Notes
28	Vertical stem	1	25 mm OD × 1.5 mm wall 6061-T6 Al, 550 mm length	Cut from 1 m stock; SaltyLab uses 1000 mm

Sensor head, RPLIDAR, cameras, and roll cage from SaltyLab mount directly onto this 25 mm stem — no modifications required.

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Motors

Same hoverboard hub motors as SaltyLab. 4× required for rover.

#	Part	Qty	Spec
29	Hub motor	4	10×2.125" tire, 36V nominal, ~350W; axle OD 16.11mm (caliper)
30	Motor cable extension	4	6-pin JST-PH 300 mm hall sensor + 3-phase power

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Mass Estimate

Assembly	Est. mass
Al deck plate	~1.4 kg
Motor brackets × 4 (PETG)	~0.5 kg
Hub motors × 4	~7.2 kg
Battery packs × 2	~1.4 kg
Battery tray (PETG)	~0.3 kg
Stem + sensor head (from SaltyLab)	~1.5 kg
Electronics (FC + Orin + wiring)	~0.6 kg
Stem adapter + hardware	~0.2 kg
Fasteners	~0.3 kg
Total estimate	~13.4 kg

Wide 540 mm track + low 117 mm deck height → tip-over angle > 45°. CG is at approximately Z = 200 mm with packs flat and full payload.

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Assembly Sequence

1. Deck plate: Cut or print deck_2d. Waterjet preferred for Al.
2. Motor brackets: Print (or CNC) 4× bracket + 4× clamp_plate.
   • Test-fit axle D-cut bore before assembling to deck.
3. Slide rails: Print 2× rail. Bolt to deck underside.
4. Stem adapter: Print base_flange + clamp_front + clamp_rear.
   • Insert stem through deck collar bore; seat flange on collar top.
   • Bolt flange with 4× M4×16 FHCS.
   • Slide clamp halves on stem above flange; tighten M4 clamping bolts (1.5 N·m).
   • Tighten M4 set screw.
5. Motor brackets: Slide flange into deck edge slot; 4× M5×20 bolts.
   • Do not torque until axle alignment is confirmed.
6. Motors: Drop axle into bracket dropout slot. Install clamp plate.
   • Tighten clamp M4 bolts. Axle lock nut finger-tight + ¼ turn.
7. Battery tray: Slide tray in from +X with packs loaded.
   • Latch snaps at full insertion.
8. Sensor head + stem accessories: Install from SaltyLab as-is.
   • Recommend 550 mm stem for rover (sensor head at ~720 mm, stable).

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Tools Required

• M3/M4/M5 hex drivers
• Torque wrench: M5 structural bolts 4 N·m, M4 clamp bolts 1.5 N·m
• Thread locker (Loctite 243 blue) on axle lock nuts and stem clamp set screw
• Dial caliper — verify axle dimensions before bracket print/CNC