# SaltyBot Chassis — Bill of Materials
**Task:** bd-1iy5 / prototype-baseplate
**Rev:** B — 2026-02-28 (updated with caliper-verified axle measurements)
**Agent:** sl-mechanical

---

## ⚠ 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.

---

## Structural / Fabricated Parts

### Prototype Base Plate (`prototype_baseplate.scad`) — Rev B

| # | Part | Qty | Material | Cut size | Notes |
|---|------|-----|----------|----------|-------|
| 1 | Prototype base plate | 1 | 6mm 5052-H32 aluminium **or** 8mm clear acrylic | 680×220mm blank | Laser or CNC; export DXF from `RENDER="plate_2d"` |
| 2 | Dropout clamp — lower (L+R) | 2 | 8mm 6061-T6 aluminium | 90×70mm blank each | Round bore Ø16.51mm; `RENDER="clamp_lower_2d"` |
| 3 | Dropout clamp — upper (L+R) | 2 | 8mm 6061-T6 aluminium | 90×70mm blank each | D-cut bore (Ø16.25mm, 13.6mm flat chord); `RENDER="clamp_upper_2d"` |
| 4 | FC standoff M3×6mm nylon | 4 | Nylon | — | MAMBA F722S vibration isolation |
| 5 | Ø4mm alignment pin | 8 | Steel dowel | 16mm length | Clamp-to-plate alignment (2 per clamp stack) |

### 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 Nano 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 |

---

## 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 |

---

## Electronics Mounts

| # | Part | Qty | Spec | Notes |
|---|------|-----|------|-------|
| 13 | STM32 MAMBA F722S 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 Nano B01 module | 1 | 69.6×45mm module + carrier | 58×58mm M3 carrier hole pattern |
| 17 | Nylon M3 standoff 8mm | 4 | F/F nylon | Jetson board standoffs |

---

## Battery

| # | Part | Qty | Spec | Notes |
|---|------|-----|------|-------|
| 18 | LiPo / LiFePO4 pack | 1 | 24V (6S LiPo or 8S LiFePO4), 4Ah, ≤185×72×52mm | Confirm dims before printing tray; add 2mm clearance |
| 19 | Velcro strap 20mm wide | 2 | 300mm length | Route through tray strap slots |
| 20 | BMS board | 1 | Matched to cell chemistry | Mount externally on rear inner face of tray wall |

---

## 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 |

---

## Fasteners

| # | Part | Qty | Spec |
|---|------|-----|------|
| 23 | M5×16 SHCS | 24 | ISO 4762, SS |
| 24 | M5 hex nut | 24 | ISO 4032, SS |
| 25 | M4×12 SHCS | 12 | ISO 4762, SS |
| 26 | M4 hex nut | 12 | ISO 4032, SS |
| 27 | M3×10 SHCS | 20 | ISO 4762, SS |
| 28 | M3 hex nut | 20 | ISO 4032, SS |
| 29 | M3×6 BHCS | 8 | FC + Jetson board bolts |
| 30 | M14×1.5 axle nut | 4 | One each side per motor, flanged | Confirm axle thread pitch on actual motors |
| 31 | Serrated washer M14 | 4 | Axle anti-rotation |
| 32 | Flat washer M5 | 48 | SS |

---

## 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

---

## 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** |