diff --git a/chassis/ASSEMBLY.md b/chassis/ASSEMBLY.md
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+# 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  FC mount (MAMBA F722S)
+1. Place silicone anti-vibration grommets onto nylon M3 standoffs.
+2. Lower FC onto standoffs; secure with M3×6 BHCS. Snug only — do not over-torque.
+3. Orient USB-C port 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 |
+| FC hole pattern | 30.5 × 30.5 mm | ±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.
diff --git a/chassis/BOM.md b/chassis/BOM.md
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--- /dev/null
+++ b/chassis/BOM.md
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+# SaltyBot Chassis — Bill of Materials
+**Task:** bd-1iy5
+**Rev:** A — 2026-02-28
+**Agent:** sl-mechanical
+
+---
+
+## Structural / Fabricated Parts
+
+| # | Part | Qty | Material | Notes |
+|---|------|-----|----------|-------|
+| 1 | Main deck plate | 1 | 6mm 5052 aluminium plate, 640×220mm | CNC router or waterjet; all holes per `chassis_frame.scad` |
+| 2 | Longitudinal rib (front) | 1 | 4mm 5052 aluminium, 600×40mm | Laser-cut; press-fit into deck slots |
+| 3 | Longitudinal rib (rear)  | 1 | 4mm 5052 aluminium, 600×40mm | Same file, symmetric |
+| 4 | Motor fork bracket (L) | 1 | 8mm 6061 aluminium | CNC mill or FDM PETG @100% infill for prototyping |
+| 5 | Motor fork bracket (R) | 1 | 8mm 6061 aluminium | Mirror of item 4 |
+| 6 | Battery tray | 1 | 3mm PETG FDM or 3mm aluminium fold | `chassis_frame.scad` — `battery_tray()` module |
+| 7 | FC mount plate / standoffs | 1 set | PETG or nylon FDM | Includes 4× M3 nylon standoffs, 6mm height |
+| 8 | Jetson Nano mount plate | 1 | 4mm 5052 aluminium or 4mm PETG FDM | B01 58×58mm hole pattern |
+| 9 | Front bumper bracket | 1 | 5mm PETG FDM | Saddle clamps for 22mm EMT conduit |
+| 10 | Rear bumper bracket | 1 | 5mm PETG FDM | Mirror of item 9 |
+
+---
+
+## Motors
+
+| # | Part | Qty | Source / Spec | Notes |
+|---|------|-----|---------------|-------|
+| 11 | Hoverboard hub motor | 2 | Generic 6.5" / 170mm OD, 36V nominal | ~350W each; 14mm flat axle; confirm exact OD before cutting fork slots |
+| 12 | Motor hall-sensor cable extension | 2 | 6-pin JST-PH 300mm | Route through deck cable slot |
+
+---
+
+## 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** |
diff --git a/chassis/chassis_frame.scad b/chassis/chassis_frame.scad
new file mode 100644
index 0000000..8c96c82
--- /dev/null
+++ b/chassis/chassis_frame.scad
@@ -0,0 +1,340 @@
+// =============================================================================
+// SaltyBot — Parametric Chassis Frame
+// Task: bd-1iy5
+// Agent: sl-mechanical
+// Date: 2026-02-28
+//
+// Self-balancing two-wheeled robot chassis
+// Requirements:
+//   - 600mm wheelbase
+//   - 2x hoverboard hub motors (170mm OD)
+//   - STM32 MAMBA F722S FC mount (30.5x30.5mm pattern)
+//   - Battery tray (24V 4Ah — ~180x70x50mm pack)
+//   - Jetson Nano B01 mount plate (100x80mm, M3 holes)
+//   - Front/rear bumper brackets
+// =============================================================================
+
+// ─── RENDER QUALITY ──────────────────────────────────────────────────────────
+$fn = 64;
+
+// =============================================================================
+// PARAMETERS — edit here to adjust the whole model
+// =============================================================================
+
+// ── Wheelbase / overall geometry ─────────────────────────────────────────────
+WHEELBASE          = 600;   // mm, center-to-center axle distance (lateral)
+FRAME_WIDTH        = 220;   // mm, front-to-back depth of main deck
+DECK_THICKNESS     = 6;     // mm, main deck plate thickness
+WALL_T             = 4;     // mm, general wall thickness for brackets/ribs
+
+// ── Hub motor parameters ─────────────────────────────────────────────────────
+MOTOR_OD           = 170;   // mm, motor housing outer diameter
+MOTOR_AXLE_D       = 14;    // mm, axle bolt diameter
+MOTOR_AXLE_FLAT    = 10;    // mm, axle flat-to-flat (for anti-rotation)
+MOTOR_FORK_WIDTH   = 24;    // mm, dropout slot width (fits 10-14mm axle + spacers)
+MOTOR_FORK_DEPTH   = 60;    // mm, dropout slot depth from fork tip
+MOTOR_FORK_H       = 80;    // mm, total height of motor fork bracket
+MOTOR_FORK_T       = 8;     // mm, fork plate thickness
+AXLE_HEIGHT        = 310;   // mm, axle CL above ground (motor radius + clearance)
+
+// ── FC mount (MAMBA F722S — 30.5 × 30.5 mm M3 pattern) ──────────────────────
+FC_MOUNT_SPACING   = 30.5;  // mm, hole pattern pitch
+FC_MOUNT_HOLE_D    = 3.2;   // mm, M3 clearance
+FC_STANDOFF_H      = 6;     // mm, standoff height
+FC_PAD_T           = 3;     // mm, mounting pad thickness
+
+// ── Battery tray (24V 4Ah LiPo / LiFePO4) ───────────────────────────────────
+BATT_L             = 185;   // mm, cell pack length
+BATT_W             = 72;    // mm, cell pack width
+BATT_H             = 52;    // mm, cell pack height
+BATT_WALL          = 3;     // mm, tray wall thickness
+BATT_FLOOR         = 4;     // mm, tray floor thickness
+BATT_STRAP_W       = 20;    // mm, Velcro strap slot width
+BATT_STRAP_T       = 2;     // mm, strap slot depth
+
+// ── Jetson Nano B01 mount plate ──────────────────────────────────────────────
+// B01 carrier board hole pattern: 58 x 58 mm M3 (inner) + corner pass-throughs
+JETSON_HOLE_PITCH  = 58;    // mm, M3 mounting hole pattern
+JETSON_HOLE_D      = 3.2;   // mm
+JETSON_PLATE_L     = 105;   // mm, plate length
+JETSON_PLATE_W     = 90;    // mm, plate width
+JETSON_PLATE_T     = 4;     // mm, plate thickness
+JETSON_STANDOFF_H  = 8;     // mm
+
+// ── Bumper bracket ────────────────────────────────────────────────────────────
+BUMPER_L           = WHEELBASE + 60; // mm, bumper rail length (overhangs wheel CL)
+BUMPER_H           = 40;    // mm, bracket vertical height
+BUMPER_T           = 5;     // mm, bracket plate thickness
+BUMPER_TUBE_OD     = 22;    // mm, 3/4" EMT conduit OD for bumper rail
+
+// ── Rib / gusset parameters ───────────────────────────────────────────────────
+RIB_W              = 20;    // mm, longitudinal rib width
+RIB_H              = 40;    // mm, rib height below deck
+RIB_T              = 4;     // mm, rib plate thickness (laser/router cut)
+
+// ── Fastener helpers ─────────────────────────────────────────────────────────
+M3_D    = 3.2;
+M4_D    = 4.3;
+M5_D    = 5.3;
+M6_D    = 6.5;
+
+// =============================================================================
+// MAIN ASSEMBLY — comment/uncomment parts as needed
+// =============================================================================
+
+color("Silver", 0.9) main_deck();
+color("DimGray")     motor_fork(side= 1);   // right (+X)
+color("DimGray")     motor_fork(side=-1);   // left  (-X)
+color("SteelBlue")   battery_tray();
+color("OliveDrab")   fc_mount_plate();
+color("DarkOrange")  jetson_mount_plate();
+color("Tomato")      bumper_bracket(front= 1);
+color("Tomato")      bumper_bracket(front=-1);
+color("WhiteSmoke")  longitudinal_ribs();
+
+// =============================================================================
+// MODULES
+// =============================================================================
+
+// ─── Main deck plate ─────────────────────────────────────────────────────────
+module main_deck() {
+    difference() {
+        // Deck plate
+        translate([-WHEELBASE/2 - MOTOR_FORK_T, -FRAME_WIDTH/2, 0])
+            cube([WHEELBASE + 2*MOTOR_FORK_T, FRAME_WIDTH, DECK_THICKNESS]);
+
+        // Lightening holes — 3 rows × 4 cols
+        for (x = [-WHEELBASE/3, 0, WHEELBASE/3])
+        for (y = [-FRAME_WIDTH/4, FRAME_WIDTH/4])
+            translate([x, y, -1])
+                cylinder(d=50, h=DECK_THICKNESS+2);
+
+        // FC mount holes
+        fc_mount_holes(z_offset=-1, depth=DECK_THICKNESS+2);
+
+        // Battery tray floor cutout for wire pass-through
+        translate([-BATT_L/2 + 40, -BATT_W/2 + 40, -1])
+            cube([BATT_L - 80, BATT_W - 80, DECK_THICKNESS+2]);
+
+        // Cable routing slots
+        for (x = [-60, 60])
+            translate([x, -FRAME_WIDTH/2 - 1, -1])
+                cube([14, 18, DECK_THICKNESS+2]);
+    }
+}
+
+// ─── Longitudinal ribs (×2, symmetric F/R) ───────────────────────────────────
+module longitudinal_ribs() {
+    for (y = [-FRAME_WIDTH/2 + RIB_W/2 + WALL_T,
+               FRAME_WIDTH/2 - RIB_W/2 - WALL_T])
+        translate([-WHEELBASE/2, y - RIB_T/2, -RIB_H])
+            cube([WHEELBASE, RIB_T, RIB_H]);
+}
+
+// ─── Motor fork dropout bracket ──────────────────────────────────────────────
+// Mounts to deck edge; provides a CNC-milled or FDM dropout slot for the axle.
+// `side` = +1 (right/+X) or -1 (left/-X)
+module motor_fork(side = 1) {
+    x_pos = side * (WHEELBASE/2);
+
+    translate([x_pos, 0, 0]) {
+        difference() {
+            union() {
+                // Vertical fork body
+                translate([side*(DECK_THICKNESS/2), -MOTOR_FORK_WIDTH/2 - 4, -MOTOR_FORK_H])
+                    cube([side * MOTOR_FORK_T, MOTOR_FORK_WIDTH + 8, MOTOR_FORK_H + DECK_THICKNESS]);
+
+                // Gusset triangles
+                for (g = [-1, 1])
+                    translate([side*(DECK_THICKNESS/2), g*(MOTOR_FORK_WIDTH/2 + 2), -MOTOR_FORK_H])
+                        linear_extrude(height=MOTOR_FORK_T)
+                            polygon([[0,0],[0, g*20],[side*-30, 0]]);
+            }
+
+            // Axle dropout slot (open at bottom)
+            translate([side*(DECK_THICKNESS/2) - 1,
+                       -MOTOR_AXLE_FLAT/2,
+                       -MOTOR_FORK_DEPTH - MOTOR_AXLE_D/2])
+                cube([MOTOR_FORK_T + 2, MOTOR_AXLE_FLAT, MOTOR_FORK_DEPTH + 1]);
+
+            // Axle through-hole at slot top
+            translate([side*(DECK_THICKNESS/2) - 1, 0,
+                       -MOTOR_FORK_DEPTH - MOTOR_AXLE_D/2])
+                rotate([0, 90, 0])
+                    cylinder(d=MOTOR_AXLE_D + 1, h=MOTOR_FORK_T + 2);
+
+            // Bolt holes for deck attachment (M5 × 4)
+            for (y = [-20, 20])
+            for (z = [4, 12])
+                translate([side*(DECK_THICKNESS/2) - 1, y, z - MOTOR_FORK_H + MOTOR_FORK_H/2])
+                    rotate([0, 90, 0])
+                        cylinder(d=M5_D, h=MOTOR_FORK_T + 2);
+        }
+    }
+}
+
+// ─── Battery tray ─────────────────────────────────────────────────────────────
+// Positioned in centre of deck, recessed 10mm below deck surface
+module battery_tray() {
+    z_base = -BATT_FLOOR - BATT_H - 5;  // hang below deck
+    translate([-BATT_L/2 - BATT_WALL, -BATT_W/2 - BATT_WALL, z_base]) {
+        difference() {
+            // Outer tray body
+            cube([BATT_L + 2*BATT_WALL,
+                  BATT_W + 2*BATT_WALL,
+                  BATT_H + BATT_FLOOR]);
+
+            // Inner cavity
+            translate([BATT_WALL, BATT_WALL, BATT_FLOOR])
+                cube([BATT_L, BATT_W, BATT_H + 1]);
+
+            // Strap slots (2× longitudinal)
+            for (x = [BATT_L/2 - BATT_STRAP_W*2,
+                      BATT_L/2 + BATT_STRAP_W])
+                translate([x, -1, BATT_FLOOR + BATT_H/2 - BATT_STRAP_W/2])
+                    cube([BATT_STRAP_W, BATT_W + 2*BATT_WALL + 2, BATT_STRAP_W]);
+
+            // Ventilation slots bottom (3×)
+            for (i = [0:2])
+                translate([BATT_WALL + 20 + i*50, BATT_WALL + 10, -1])
+                    cube([30, BATT_W - 20, BATT_FLOOR + 2]);
+
+            // Mount holes to deck (M4 × 4 corners)
+            for (x = [10, BATT_L + BATT_WALL - 2])
+            for (y = [10, BATT_W + BATT_WALL - 2])
+                translate([x, y, BATT_H + BATT_FLOOR - 1])
+                    cylinder(d=M4_D, h=BATT_FLOOR + 2);
+        }
+    }
+}
+
+// ─── FC mount holes helper ────────────────────────────────────────────────────
+module fc_mount_holes(z_offset=0, depth=10) {
+    // MAMBA F722S: 30.5×30.5 mm M3 pattern, centred at origin
+    for (x = [-FC_MOUNT_SPACING/2, FC_MOUNT_SPACING/2])
+    for (y = [-FC_MOUNT_SPACING/2, FC_MOUNT_SPACING/2])
+        translate([x, y, z_offset])
+            cylinder(d=FC_MOUNT_HOLE_D, h=depth);
+}
+
+// ─── FC mount plate (raised 40mm above deck centre) ──────────────────────────
+module fc_mount_plate() {
+    fc_x = -50;   // offset toward front from deck centre
+    fc_y =  0;
+    plate_z = DECK_THICKNESS + FC_STANDOFF_H;
+
+    translate([fc_x, fc_y, 0]) {
+        difference() {
+            union() {
+                // Mount pads with standoffs
+                for (x = [-FC_MOUNT_SPACING/2, FC_MOUNT_SPACING/2])
+                for (y = [-FC_MOUNT_SPACING/2, FC_MOUNT_SPACING/2]) {
+                    translate([x, y, DECK_THICKNESS])
+                        cylinder(d=8, h=FC_STANDOFF_H);  // standoff column
+                    translate([x - 5, y - 5, DECK_THICKNESS])
+                        cube([10, 10, FC_PAD_T]);          // pad base
+                }
+                // Base plate
+                translate([-FC_MOUNT_SPACING/2 - 8, -FC_MOUNT_SPACING/2 - 8, DECK_THICKNESS])
+                    cube([FC_MOUNT_SPACING + 16, FC_MOUNT_SPACING + 16, FC_PAD_T]);
+            }
+            // M3 through-holes in standoffs
+            fc_mount_holes(z_offset=DECK_THICKNESS - 1, depth=FC_STANDOFF_H + FC_PAD_T + 2);
+
+            // Deck anchor holes
+            fc_mount_holes(z_offset=-1, depth=DECK_THICKNESS + 2);
+        }
+    }
+}
+
+// ─── Jetson Nano B01 mount plate ─────────────────────────────────────────────
+// Positioned rear of deck, elevated on standoffs
+module jetson_mount_plate() {
+    jet_x =  60;   // offset toward rear
+    jet_y =  0;
+    plate_z = DECK_THICKNESS + JETSON_STANDOFF_H;
+
+    translate([jet_x, jet_y, 0]) {
+        difference() {
+            union() {
+                // Mounting plate
+                translate([-JETSON_PLATE_L/2, -JETSON_PLATE_W/2, DECK_THICKNESS + JETSON_STANDOFF_H])
+                    cube([JETSON_PLATE_L, JETSON_PLATE_W, JETSON_PLATE_T]);
+
+                // Four standoff columns
+                for (x = [-JETSON_HOLE_PITCH/2, JETSON_HOLE_PITCH/2])
+                for (y = [-JETSON_HOLE_PITCH/2, JETSON_HOLE_PITCH/2])
+                    translate([x, y, DECK_THICKNESS])
+                        cylinder(d=6, h=JETSON_STANDOFF_H);
+            }
+
+            // B01 M3 hole pattern (58×58 mm)
+            for (x = [-JETSON_HOLE_PITCH/2, JETSON_HOLE_PITCH/2])
+            for (y = [-JETSON_HOLE_PITCH/2, JETSON_HOLE_PITCH/2])
+                translate([x, y, DECK_THICKNESS - 1])
+                    cylinder(d=JETSON_HOLE_D, h=JETSON_STANDOFF_H + JETSON_PLATE_T + 2);
+
+            // Ventilation / cable routing slots in plate
+            for (i = [-1, 0, 1])
+                translate([i*25 - 10, -JETSON_PLATE_W/2 + 10,
+                           DECK_THICKNESS + JETSON_STANDOFF_H - 1])
+                    cube([20, JETSON_PLATE_W - 20, JETSON_PLATE_T + 2]);
+
+            // Deck anchor holes (M3 × 4 corners of plate)
+            for (x = [-JETSON_PLATE_L/2 + 8, JETSON_PLATE_L/2 - 8])
+            for (y = [-JETSON_PLATE_W/2 + 8, JETSON_PLATE_W/2 - 8])
+                translate([x, y, -1])
+                    cylinder(d=M3_D, h=DECK_THICKNESS + 2);
+        }
+    }
+}
+
+// ─── Bumper bracket ───────────────────────────────────────────────────────────
+// `front` = +1 (front) or -1 (rear)
+module bumper_bracket(front = 1) {
+    y_pos = front * (FRAME_WIDTH/2);
+
+    translate([0, y_pos, 0]) {
+        difference() {
+            union() {
+                // Horizontal mounting rail plate
+                translate([-BUMPER_L/2, front*(BUMPER_T/2), 0])
+                    cube([BUMPER_L, BUMPER_T, BUMPER_H]);
+
+                // Vertical gussets at ends
+                for (x = [-BUMPER_L/2 + 5, BUMPER_L/2 - BUMPER_T - 5])
+                    translate([x, front*(BUMPER_T), 0])
+                        cube([BUMPER_T, 20, BUMPER_H]);
+
+                // Bumper tube saddle clamps (×3 evenly spaced)
+                for (x = [-BUMPER_L/3, 0, BUMPER_L/3])
+                    translate([x - BUMPER_TUBE_OD/2 - 2,
+                               front*(BUMPER_T + 15),
+                               BUMPER_H - BUMPER_TUBE_OD/2 - 5])
+                    difference() {
+                        cube([BUMPER_TUBE_OD + 4, BUMPER_TUBE_OD/2 + 4, BUMPER_TUBE_OD + 4]);
+                        translate([BUMPER_TUBE_OD/2 + 2, -1, BUMPER_TUBE_OD/2 + 2])
+                            rotate([-90, 0, 0])
+                                cylinder(d=BUMPER_TUBE_OD, h=BUMPER_TUBE_OD/2 + 6);
+                    }
+            }
+
+            // Deck mounting holes (M5 × 6 along length)
+            for (x = [-BUMPER_L/2 + 20, -BUMPER_L/6, BUMPER_L/6, BUMPER_L/2 - 20])
+                translate([x, y_pos * 0.001, -1])
+                    cylinder(d=M5_D, h=BUMPER_H + 2);
+        }
+    }
+}
+
+// =============================================================================
+// DIMENSIONS / ANNOTATIONS  (2D cross-section reference)
+// =============================================================================
+// Uncomment to render a side-view dimension guide:
+//
+// %translate([0, FRAME_WIDTH/2 + 30, 0]) {
+//     color("Blue") {
+//         cube([WHEELBASE, 1, 1]);        // wheelbase span
+//         translate([0,0,0]) text(str("Wheelbase: ", WHEELBASE, "mm"), size=12);
+//     }
+// }