# SaltyBot Chassis — Assembly Notes
**Task:** bd-1iy5 — Rev A — 2026-02-28

---

## Overview

```
         [Front bumper rail — 22mm EMT]
         ├─ bumper_bracket(front=+1) ──────────────────────┐
         │                                                  │
 ┌───────┴──────────── Main Deck (640×220×6mm Al) ─────────┴───────┐
 │  ← Jetson mount plate (rear/+X)   FC mount (front/−X) →         │
 │          [Battery tray hanging below centre]                     │
 └───┬──────────────────────────────────────────────────────────┬───┘
     │                                                          │
 Motor fork (L)                                          Motor fork (R)
 Hub motor CL: ±300mm from deck centre                          │
 Axle height: 310mm above ground                                │
         ├─ bumper_bracket(front=-1) ──────────────────────┘
         [Rear bumper rail — 22mm EMT]
```

---

## Step-by-step Assembly

### 1  Fabricate / print parts
- Send deck plate DXF (export from OpenSCAD → DXF) to CNC router or waterjet cutter.
- Print motor fork brackets in PETG 5 perimeters / 40% gyroid for prototype, or send STEP to machine shop.
- Print battery tray, FC pad, Jetson plate, bumper brackets in PETG.
- Export STEP: OpenSCAD → Render (F6) → Export as STL, then convert with FreeCAD for STEP.

### 2  Verify motor axle dimensions
- Measure actual hoverboard motor axle: diameter and flat-to-flat.
- Adjust `MOTOR_AXLE_D` and `MOTOR_AXLE_FLAT` in `chassis_frame.scad`.
- Re-export fork dropout slot.

### 3  Motor forks → deck
1. Thread M5 T-nuts into underside of deck edge slots (or use M5 rivet nuts).
2. Align fork bracket to deck edge; fasten with 4× M5×16 SHCS + flat washer each side.
3. Apply Loctite 243 to threads. Torque to 4 N·m.

### 4  Motors into forks
1. Slide hub motor axle into dropout slot (flat side aligns with slot).
2. Fit flat washer then flanged M14 axle nut; torque to 35–40 N·m.
3. Feed motor phase wires and hall-sensor cable through deck cable slot.

### 5  Longitudinal ribs
1. Align ribs with edge grooves on deck underside.
2. Secure with M4×12 SHCS through pre-drilled holes; torque 2.5 N·m.

### 6  Battery tray
1. Pass any wiring harness through deck wire-pass hole before mounting tray.
2. Align tray mounting ears to deck M4 threaded inserts (or rivet nuts).
3. Fasten 4× M4×12 SHCS. Torque 2.5 N·m.
4. Insert battery pack; route Velcro straps through slots and cinch.

### 7  MCU mount (ESP32 BALANCE + ESP32 IO)

> ⚠️ **ARCHITECTURE CHANGE (2026-04-03):** ESP32 BALANCE retired. Two ESP32 boards replace it.
> Board dimensions and hole patterns TBD — await spec from max before machining mount plate.

1. Place silicone anti-vibration grommets onto nylon M3 standoffs.
2. Lower ESP32 BALANCE board onto standoffs; secure with M3×6 BHCS. Snug only.
3. Mount ESP32 IO board adjacent — exact placement TBD pending board dimensions.
4. Orient USB connectors toward front of robot for cable access.

### 8  Jetson Nano mount plate
1. Press or thread M3 nylon standoffs (8mm) into plate holes.
2. Bolt plate to deck: 4× M3×10 SHCS at deck corners.
3. Set Jetson Nano B01 carrier onto plate standoffs; fasten M3×6 BHCS.

### 9  Bumper brackets
1. Slide 22mm EMT conduit through saddle clamp openings.
2. Bolt bracket to deck edge: 4× M5×16 SHCS per bracket.
3. Position bumper rail flush with motor OD outer edge; tighten saddle clamp bolts.

### 10  Cable routing
- Route motor phase cables along longitudinal ribs; secure with cable clips.
- FC ↔ ESC/VESC harness exits through front cable slot.
- Jetson USB/UART ribbon exits through rear cable slot.
- Power harness (battery XT60 → BMS → 24V bus) runs under deck along centreline.

---

## Critical Dimensions (verify before machining)

| Dimension | Nominal | Tolerance |
|-----------|---------|-----------|
| Wheelbase (axle C/L to C/L) | 600 mm | ±1 mm |
| Motor fork slot width | 24 mm | +0.5 / 0 |
| Motor fork dropout depth | 60 mm | ±0.5 mm |
| ESP32 BALANCE hole pattern | TBD — await spec from max | ±0.2 mm |
| ESP32 IO hole pattern | TBD — await spec from max | ±0.2 mm |
| Jetson hole pattern | 58 × 58 mm | ±0.2 mm |
| Battery tray inner | 185 × 72 × 52 mm | +2 / 0 mm |

---

## OpenSCAD Rendering Notes

```bash
# Render full assembly preview (F5 in GUI)
openscad chassis_frame.scad

# Export individual part STL for slicing
openscad chassis_frame.scad -D "PART=\"motor_fork\"" -o motor_fork_right.stl

# Export deck DXF (set DECK_THICKNESS=0.01 for 2D projection)
openscad chassis_frame.scad -D "RENDER_2D=true" -o deck_plate.dxf
```

**Slicing profile (PETG, structural parts):**
- Nozzle: 0.4mm  |  Layer: 0.2mm
- Perimeters: 5  |  Infill: 40% gyroid
- Supports: Yes (motor fork dropout slot)
- Orientation: Fork bracket printed vertically (load axis = layer direction)

---

## Safety Notes

- Verify axle nut torque after first 10-minute ride — hub motors vibrate and may back off.
- Battery tray is rated for packs ≤185×72×52mm; confirm dimensions before ordering cells.
- Ground all aluminium chassis parts to power-common to avoid RF interference with FC.
- Do **not** run robot without bumpers fitted — uncontrolled runaway risk.