saltylab-firmware/chassis/BOM.md

SaltyBot Chassis — Bill of Materials

Task: bd-1iy5 / prototype-baseplate Rev: C — 2026-02-28 (vertical stem architecture; batteries on mast carousel) Agent: sl-mechanical

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⚠ Axle Measurement Update (Rev B)

PR #7 (chassis_frame.scad) used placeholder values. The table below records the caliper-verified hub motor axle dimensions. All new designs must use these.

Feature	Measured	PR #7 placeholder	Delta
Axle base diameter (round, near hub)	16.11 mm	14 mm	+2.11 mm
D-cut shaft OD	15.95 mm	— (not modelled)	new
D-cut flat chord	13.00 mm	—	new
Total axle protrusion	65.5 mm	~60 mm est.	+5.5 mm
Base section length	15.0 mm	—	new
D-cut section length	43.35 mm	—	new
Tip / shoulder	3.0 mm	—	new
Bearing seat collar OD	37.8 mm	—	new
Tire OD	254 mm (10×2.125")	170 mm motor OD only	—
Axle CL height above ground	127 mm	310 mm (wrong)	−183 mm

chassis_frame.scad should be updated in a follow-on task to match Rev B values.

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Structural / Fabricated Parts

Prototype Base Plate (prototype_baseplate.scad) — Rev C

Batteries are removed from the base plate. Plate is now compact (680×130mm). Stem socket replaces battery tray. See Part B (stem clamp) below.

#	Part	Qty	Material	Cut size	Notes
1	Base plate	1	6mm 5052-H32 Al or 8mm acrylic	680×130mm blank	RENDER="plate_2d" → DXF
2	Dropout clamp — lower	2	8mm 6061-T6 Al	90×70mm blank	Round bore Ø16.51mm; RENDER="clamp_lower_2d"
3	Dropout clamp — upper	2	8mm 6061-T6 Al	90×70mm blank	D-cut bore; RENDER="clamp_upper_2d"
4	Stem flange ring	2	6mm Al or acrylic	Ø82mm disc	One above + one below plate; RENDER="stem_flange_2d"
5	Vertical stem tube	1	38.1mm OD × 1.5mm wall 6061-T6 Al	1050mm length	1.5" EMT conduit is a drop-in alternative
<<<<<<< HEAD
6	MCU standoff M3×6mm nylon	4	Nylon	—	ESP32 BALANCE / IO board isolation (dimensions TBD)

======= | 6 | FC standoff M3×6mm nylon | 4 | Nylon | — | ESP32-S3 BALANCE vibration isolation |

291dd68 (feat: remove all STM32/Mamba/BlackPill references — ESP32-S3 only) | 7 | Ø4mm × 16mm alignment pin | 8 | Steel dowel | — | Dropout clamp-to-plate alignment |

Battery Stem Clamp (stem_battery_clamp.scad) — Part B

#	Part	Qty	Material	Notes
8	Collar half	2	PETG FDM (5 perimeters, 40% infill)	Print flat-side-down; mirror 2nd in slicer. Bore Ø38.6mm
9	Radial arm	4	4mm 5052-H32 Al (laser-cut) or PETG FDM	RENDER="arm_2d" for DXF with ARM_THICK=4; or print at 8mm
10	Battery cradle	4	PETG FDM (4 perimeters, 30% infill)	U-channel, open top; holds 1 pack per cradle
11	M6×60 SHCS	4	SS	2 collar clamping bolts × 2 sides
12	M6 hex nut	4	SS	Captured in collar nut pockets
13	M6×12 set screw	2	SS, cup-point	1 per collar half for height lock
14	M4×20 SHCS	8 (16 for 4)	SS	Arm-to-collar bolts (2 per arm)
15	M4×16 SHCS	8 (16 for 4)	SS	Cradle-to-arm bolts (2 per cradle)
16	M4 hex nut	16 (32 for 4)	SS	Nuts for items 14 + 15
17	Velcro strap 25mm × 600mm	4–8	—	1–2 per battery pack through cradle slots

Full Chassis (chassis_frame.scad) — Rev A (placeholder values — pending Rev B update)

#	Part	Qty	Material	Notes
6	Main deck plate	1	6mm 5052 aluminium plate, 640×220mm	CNC router or waterjet; all holes per chassis_frame.scad
7	Longitudinal rib (front)	1	4mm 5052 aluminium, 600×40mm	Laser-cut; press-fit into deck slots
8	Longitudinal rib (rear)	1	4mm 5052 aluminium, 600×40mm	Same file, symmetric
9	Motor fork bracket (L)	1	8mm 6061 aluminium	Update fork slot to Ø16.51mm before cutting
10	Motor fork bracket (R)	1	8mm 6061 aluminium	Mirror of item 9
11	Battery tray	1	3mm PETG FDM or 3mm aluminium fold	chassis_frame.scad — battery_tray() module
12	FC mount plate / standoffs	1 set	PETG or nylon FDM	Includes 4× M3 nylon standoffs, 6mm height
13	Jetson Orin Nano Super mount plate	1	4mm 5052 aluminium or 4mm PETG FDM	B01 58×58mm hole pattern
14	Front bumper bracket	1	5mm PETG FDM	Saddle clamps for 22mm EMT conduit
15	Rear bumper bracket	1	5mm PETG FDM	Mirror of item 14

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Motors

#	Part	Qty	Source / Spec	Notes
16	Hoverboard hub motor	2	10×2.125" pneumatic tire, 36V nominal, ~350W	Axle: Ø16.11mm base / Ø15.95mm D-cut / 13mm flat; bearing seat Ø37.8mm — all caliper-verified
17	Motor hall-sensor cable extension	2	6-pin JST-PH 300mm	Route through deck cable slot
18	Axle lock nut	4	M16×1.5 or thread-matched to actual axle tip	Confirm thread at tip before ordering; calipers show Ø≈10mm at tip

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Electronics Mounts

⚠️ ARCHITECTURE CHANGE (2026-04-03): ESP32 BALANCE (ESP32) is retired. Replaced by ESP32 BALANCE + ESP32 IO. Board dimensions and hole patterns TBD — await spec from max.

#	Part	Qty	Spec	Notes
<<<<<<< HEAD
13	ESP32 BALANCE board	1	TBD — mount pattern TBD	PID balance loop; replaces ESP32 BALANCE
13b	ESP32 IO board	1	TBD — mount pattern TBD	Motor/sensor/comms I/O
14	Nylon M3 standoff 6mm	4	F/F nylon	ESP32 board isolation
15	Anti-vibration grommet M3	4	Ø6mm silicone	Under ESP32 mount pads
16	Jetson Orin module	1	69.6×45mm module + carrier	58×58mm M3 carrier hole pattern

======= | 13 | ESP32-S3 ESP32-S3 BALANCE FC | 1 | 36×36mm PCB, 30.5×30.5mm M3 mount | Oriented USB-C port toward front | | 14 | Nylon M3 standoff 6mm | 4 | F/F nylon | FC vibration isolation | | 15 | Anti-vibration grommet M3 | 4 | Ø6mm silicone | Under FC mount pads | | 16 | Jetson Orin Nano Super B01 module | 1 | 69.6×45mm module + carrier | 58×58mm M3 carrier hole pattern |

291dd68 (feat: remove all STM32/Mamba/BlackPill references — ESP32-S3 only) | 17 | Nylon M3 standoff 8mm | 4 | F/F nylon | Jetson board standoffs |

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Battery (Vertical Stem Mount — Rev C)

Batteries mount VERTICALLY on the stem carousel, not on the base plate. Each pack stands upright (420mm tall) in a cradle at the end of a radial arm.

#	Part	Qty	Spec	Notes
18	Battery pack	2–4	24V, 420×88×56 mm each (caliper-verified)	Snap into battery cradle from above
19	BMS board	1	Matched to cell chemistry	Mount to stem or base plate underside; run wiring down stem

Battery stem clamp — configuration guide

Config	Arm count	Carousel weight	Balance	Notes
2-pack	2 arms, 180° apart	~1.4 kg	✅ Symmetric	Minimum configuration
4-pack	4 arms, 90° apart	~2.8 kg	✅ Symmetric	Maximum practical config
3-pack	3 arms, 120° apart	~2.1 kg	⚠ Asymmetric mass	Needs counter-balance or avoid

CG height tuning

Slide entire carousel up/down the stem with M6 collar bolts loosened. Tighten at desired height. Typical balance point (initial estimate): batteries centred at 450–600 mm above base plate. Adjust in ≈50 mm increments during commissioning.

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Bumper Rail

#	Part	Qty	Spec	Notes
21	3/4" EMT conduit	2	22mm OD, 660mm length	Front and rear bumper rail; bent or straight
22	Conduit saddle clamp M4	6	3D-printed integral to bracket (items 9/10)	Back-up: standard pipe clamp 22mm

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Fasteners

#	Part	Qty	Spec	Use
20	M5×16 SHCS	16	ISO 4762, SS	Dropout clamp bolts (4 per clamp × 4)
21	M5×20 SHCS	8	ISO 4762, SS	Stem flange bolts (4 per flange × 2)
22	M5 hex nut	24	ISO 4032, SS
23	M4×20 SHCS	16	ISO 4762, SS	Arm-to-collar (2 per arm × 4 arms × 2)
24	M4×16 SHCS	16	ISO 4762, SS	Cradle-to-arm (2 per cradle × 4 arms × 2)
25	M4 hex nut	32	ISO 4032, SS
26	M6×60 SHCS	4	ISO 4762, SS	Collar clamping bolts
27	M6 hex nut	4	ISO 4032, SS	Captured in collar pockets
28	M6×12 set screw	2	ISO 4026, SS cup-point	Stem height lock (1 per collar half)
29	M3×10 SHCS	12	ISO 4762, SS	ESP32 mount + miscellaneous
30	M3×6 BHCS	4	ISO 4762, SS	ESP32 board bolts (qty TBD pending board spec)
31	Axle lock nut (match axle tip thread)	4	Flanged, confirm thread	2 per motor
32	Flat washer M5	32	SS
33	Flat washer M4	32	SS
34	Ø4×16 dowel pin	8	Steel	Dropout clamp alignment

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Tools Required for Assembly

• Torque wrench (M14 axle nuts: 35–40 N·m; M5: 4 N·m)
• M2.5 / M3 / M4 / M5 hex drivers
• Thread locker (Loctite 243 blue for all structural fasteners)
• Dial caliper — verify motor OD, axle flat before machining fork slot

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Estimated Masses

Assembly	Est. mass
Aluminium deck + ribs	~1.1 kg
Motor forks (×2 Al)	~0.4 kg
Motors (×2)	~3.6 kg
Battery (6S 4Ah LiPo)	~0.7 kg
Electronics (FC + Jetson + wiring)	~0.5 kg
Bumpers + brackets	~0.3 kg
Fasteners	~0.2 kg
Total estimate	~6.8 kg