saltylab-firmware/chassis/ASSEMBLY.md

SaltyBot Chassis — Assembly Notes

Task: bd-1iy5 — Rev A — 2026-02-28

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Overview

         [Front bumper rail — 22mm EMT]
         ├─ bumper_bracket(front=+1) ──────────────────────┐
         │                                                  │
 ┌───────┴──────────── Main Deck (640×220×6mm Al) ─────────┴───────┐
 │  ← Jetson mount plate (rear/+X)   MCU 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]

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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-S3 BALANCE + ESP32-S3 IO)

⚠ Board hole patterns TBD — measure Waveshare Touch LCD 1.28 PCB with calipers and update FC_PITCH / FC_MOUNT_SPACING in all scad files before machining the mount plate. Reference: docs/SAUL-TEE-SYSTEM-REFERENCE.md.

1. Place silicone anti-vibration grommets onto M3 nylon standoffs.
2. Lower ESP32-S3 BALANCE board onto standoffs; secure M3×6 BHCS — snug only.
3. Mount ESP32-S3 IO board adjacent — exact layout TBD pending board dimensions.
4. Orient USB-C connectors toward accessible side for field programming/debug.

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.

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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-S3 BALANCE hole pattern	TBD — caliper Waveshare board	±0.2 mm
ESP32-S3 IO hole pattern	TBD — caliper bare board	±0.2 mm
Jetson hole pattern	58 × 58 mm	±0.2 mm
Battery tray inner	185 × 72 × 52 mm	+2 / 0 mm

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OpenSCAD Rendering Notes

# 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)

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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.