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08 — Mechanical Concept

Source of truth: 00-architecture-decisions.md (ADR Baseline v0.3, 2026-09-27: no built-in cellular modem (confirmed final, D1); magnesium AZ91D die-cast chassis-heatsink with machined AZ31B / thixomolded AZ91D prototypes (D4); 190 × 96 × 38 mm final (D3 — 36 mm option closed, CFast kept); two-slat articulated shutter approved unchanged (D11); 850 g target with a bottom-up ~828 g; passive cooling for EVT with the fan envelope reserved and the fan decision at EVT exit (D5); 4 mm slot gaps with a 163 mm slot row and 170 mm shutter, Wi-Fi antennas in the front frame's upper band, BLE chip antenna at the bottom-left, service-replaceable battery behind a screw-down door). This document is aligned to that revision; §3.4 records the reasoning behind the 38 mm thickness and the closed 36 mm option; §4.1 carries the magnesium DFM, coating and galvanic rules. Related: 06-thermal.md (heat path, gap pads), 07-rf-antenna.md (window sizes/materials), 09-pcb-architecture.md (board outlines, mezzanine), 05-power-budget.md (pack electricals), 11-certification.md (MIL-STD-810H / IP54 lab plan). Drawings: ../drawings/top-view.svg, ../drawings/front-view.svg, ../drawings/side-view.svg, ../drawings/exploded-view.svg (all 1 mm = 4 px, rev C, 2026-09-27 — material callouts updated to magnesium, no dimensional change). See §15.

1. Design intent in one paragraph

A bag-proof brick, not a gadget. The device is a rigid magnesium chassis-heatsink (AZ91D die-cast, conversion-coated and powder-coated light matte grey) that forms the rear and bottom skins and carries every connector load, wrapped on the front and ends by a glass-filled polycarbonate frame whose upper band doubles as the only RF window (the two Wi-Fi antennas flank the OLED; a small window at the bottom-left covers the BLE chip antenna; the end caps carry only the shutter rail grooves and drains and have no RF requirement; the rear face is all metal), with thermoplastic-urethane bumpers on every corner and edge. All five card slots sit in a single recessed channel along the top edge and are covered by a two-slat sliding hard-anodized aluminum shutter that runs in acetal rails and parks against the rear face. The battery pack sits behind a gasketed screw-down door in the front frame so a service centre can replace it (EU Battery Regulation 2023/1542). Nothing sticks out when the shutter is closed; the only openings are three sealed USB-C receptacles, one RJ45 behind a latched door, the sealed button and reset pinhole, and a vent membrane (ADR §3.4; the v0.1 SIM tray is gone).

2. Envelope, mass budget and CG

2.1 Envelope

Dimension	ADR target	This document	Note
Length (L, along slot row)	190 mm	190 mm	163 mm slot row + 170 mm shutter, leaving 10 mm at each end for the end-cap rail grooves and drains (ADR §7; no RF requirement on the end caps)
Height (H, front face)	96 mm	96 mm	40 mm reader band + 44 mm battery band + ~12 mm port band
Thickness (T)	38 mm	38 mm — final (D3)	21700 cell (21 mm) stacked in Z with the main board + a uniform 6.5 mm rear-face budget; the tallest rear-face parts are the SoM stack (~4.5 mm) and the NVMe 2280 in its socket (~4.7 mm), and the ~2 mm slack goes to SoM boss height and thicker gap pads (§3.2, §10); derivation in §3.4 (the 36 mm option is closed)
Top-edge recess depth	6 mm	6 mm	inserted cards ≥ 1 mm below shutter plane
Corner radius (plan)	—	R8 (chassis) under R10 TPU
Top-rear edge radius	—	R10 (shutter track corner R14 at pin centres)	see §6

Volume ≈ 0.69 L. For scale: a 190 × 96 × 38 mm brick is roughly two iPhone Pro Max stacked, or a thick trade paperback. It stands on its bottom (port) edge with the top edge and slots up, which is how it lives on a DIT cart.

2.2 Mass budget

Item	Mass (g)	Basis
4 × 21700 cells	276	69 g each (Samsung 50E class)
Pack: PC+GF cradle, pack PCB, nickel strips, wiring, foam wrap	45
Magnesium AZ91D die-cast chassis, 1.6 mm walls (rear skin + bottom/side walls), ribs, bosses, coating	143	~76 cm³ × 1.81 g/cm³ ≈ 138 g casting + ~5 g conversion coat / powder coat / Al–Zn-Ni inserts (verify). v0.2: 6061 CNC at 2.0 mm walls, 250 g
PC+30 % GF front frame incl. end caps, Wi-Fi window band, lens bezel, battery door + 6 screws	74	~52 cm³ × 1.43 + door hardware
TPU Shore 80A overmold (corners + edges + button + RJ45 door)	45
Shutter: 2 × hard-anodized 6061 slats 2.0 × 20 × 170 mm	37	13.6 cm³
Shutter hardware: 2 POM rails, hinge pin, 8 pins/rollers, 2 detent cartridges, magnets, seals	22
Main board 165 × 80 × 1.6 (10 L) + components + SoM	82	PCB 40, SoM 25, rest 17 (v0.1: rest 20 incl. the M.2 Key-B socket, the 5 A modem buck and the SIM connector/TVS — all deleted)
Reader daughterboard 172 × 38 × 1.6 (8 L) + 5 card connectors + controllers	45
M.2 module (Wi-Fi 2230)	6	NVMe 2280 on Pro SKU adds 8
OLED module + lens	10
Antennas (2 Wi-Fi flex + cables, BLE chip antenna)	4
External connectors (USB-C ×3, RJ45), gaskets, vent, screws, thermal pads, EMI gasket	39	v0.1: 42 incl. the nano-SIM tray, its gasket and chassis bore (−3 g)
Total, base SKU, magnesium chassis	828	~828 g (ADR §2); 22 g under the 850 g target without any of the reserve trims below (v0.2 aluminum: 935 g; v0.1: 957 g)
EVT/DVT machined AZ31B chassis	≈ +5–10 g	thicker machined walls / no draft on prototype parts → ≈ 833–838 g (ADR §2: 830–840 g); verify on the first EVT casting-equivalent

Reconciliation to the ADR target (850 g, ADR §2): the magnesium baseline meets it with ~22 g of margin. The former trims are held in reserve, not baseline:

Measure	Saving (g)	Cost / risk
Walls 1.6 → 1.2 mm (AZ91D casts to ~1.0–1.2 mm; ribs retained for stiffness)	−25	only if the EVT drop matrix shows margin; 1.6 mm is kept in the baseline for drop (§4.1)
Shutter slats 2.0 → 1.6 mm	−8	plate stiffness ∝ t³; keep 2.0 unless drop tests pass
TPU trimmed to corners + top/bottom edges only	−12	grip and drop impact still on corners
Delete one cell row (2S1P, 36 Wh)	−160	halves runtime — not recommended

Plan (D4): production chassis in AZ91D hot-chamber die-cast with 1.6 mm walls → ~828 g; EVT/DVT units in machined AZ31B (or thixomolded AZ91D if faster/cheaper) so the thermal data reflects production — not CNC aluminum. AZ31B conducts ~30 % better than AZ91D (k ≈ 96 vs ≈ 72 W/m·K, verify), so EVT thermal results on AZ31B must be corrected to AZ91D, or DVT must run on thixomolded / T0 AZ91D shots, before the fan gate is called (06-thermal.md §3, ADR §12). Aluminum (~935 g) is no longer planned. The 1.2 mm wall, 1.6 mm slat and reduced-TPU options are reserve only; they remain available if the EVT drop tests or the die-cast wall tolerance push the mass back up.

2.3 Centre of gravity

Battery (321 g) sits in the middle band, centered in L; the Wi-Fi/NVMe M.2 slots and the RJ45 sit to the right (the v0.1 modem, which was the heaviest part of that right-side stack, is gone and its area is now power-section spread and bulk capacitance, ADR §9); the battery door adds ~4 g to the front. Predicted CG: ~2 mm right of centre (v0.1: 3 mm), ~3–4 mm below mid-height, ~5 mm forward of mid-thickness (v0.2: 3 mm — the magnesium rear skin is ~107 g lighter, so the CG moves toward the battery). Acceptable; the 26-drop matrix covers every face, edge and corner regardless.

3. Internal layout

3.1 Zoning (front view, viewed from the front, X from left, Y from top)

Band (Y)	Contents (front→rear in Z)
0–40 mm "reader band"	LED bar (Y 3–6, over the slot row) and OLED (centred, active X 66.5–123.5, Y 10–40) in the front frame, flanked by the two Wi-Fi antenna flexes (X 12–52 and X 130–170, Y 30–38, centres 118 mm apart, bonded to the inner face of the PC frame with only air and the card-connector zone behind them); card connectors and inserted cards; reader daughterboard (vertical, parallel to main board, 172 × 38, X 9–181); its controllers; mezzanine to main board; main board upper region (rear face: ASM2812 switch, RTL8126 + magnetics under the top-left of the rear skin)
40–88 mm "battery band"	battery door (PC+GF panel X 18–172, Y 42–92, 6 × M2.5 screws, own gasket) in the front frame; battery pack (2 rows × 2 cells end-to-end, 144 × 44 mm footprint, X 23–167) directly behind it; main board (rear face: SoM, PD/charger, bucks; front face limited to ≤ 1.0 mm parts). No antenna may sit on the door: the cell cans are 2.4 mm behind it
88–96 mm "port band"	main board bottom edge with the three mid-mount USB-C receptacles (rear face, X 20–70) and PD controllers; RJ45 is a tall part and lives on the main-board front face at X 167–186 where there is no battery shadow
Right strip X 104–188 (rear face, Y 14–92)	two vertical M.2 slots: Wi-Fi 2230 (X 140–162) and NVMe 2280 (X 166–188, socket present but empty on the base SKU). The former modem area X 104–134 is now power-section spread and bulk capacitance plus the spare PCIe Gen2 test header (ADR §9, `09-pcb-architecture.md` §1.1). The M.2 modules (≤ 4.7 mm in their sockets) and the SoM stack (~4.5 mm) are the tallest rear-face parts; both sit inside the retained 6.5 mm budget (§3.2)
Left/right 10 mm end zones	PC end caps (part of the frame moulding): shutter rail grooves (inner 3 mm, X 7–10 and 180–183) and the two drain exits below the rails. No RF requirement — the v0.1 cellular antenna flexes and the right-end SIM tray are deleted, so the end caps may be opaque or painted and, as an EVT option, cast in magnesium as part of the chassis for drop stiffness (ADR §8). The 170 mm aluminum shutter stops 10 mm short of each end so the slats never run onto the end caps
Bottom-left corner X 11–18, Y 74–88	BLE chip antenna on the nRF5340 EC at the main board's lower-left corner, 6 × 12 mm copper-free keep-out (X 12–18, Y 75–87) to the board edge, behind a 7 × 14 mm PC window in the front frame between the left end cap and the battery door, clear of the corner bumper arm (Y ≥ 89) and of Port A's bracket (`07-rf-antenna.md` §5, `09-pcb-architecture.md` §1.1)

The main board (165 × 80 mm) spans Y 12–92 and overlaps the reader band in Y; the two boards are on different Z planes (see §3.2) so the overlap is deliberate — the reader board hangs on the main board's front face through the mezzanine.

3.2 Z-stack at the battery band (section A-A, worst case)

Front → rear, in mm:

#	Layer	mm	Cumulative
1	TPU texture + PC front frame wall	2.5	2.5
2	Closed-cell PU/silicone foam (battery float)	0.8	3.3
3	Pack cradle front wall (PC+GF)	0.8	4.1
4	21700 cell	21.0	25.1
5	Pack cradle rear wall	0.8	25.9
6	Clearance / foam	1.0	26.9
7	Main board front-face components in battery shadow (≤ 1.0 mm: passives, 0402/0603, low-profile FETs)	1.0	27.9
8	Main board (10-layer)	1.6	29.5
9	Rear-face component budget, uniform across the board and fixed at 6.5 mm — final (D3, ADR §13 item 13): the tallest parts are the SoM stack (~4.5 mm incl. gap pad) and the NVMe 2280 in its M.2 socket (~4.7 mm: 2.25 mm socket stand-off + 1.5 mm double-sided module + 1.0 mm thermal pad). The ~1.8–2 mm of slack is spent on a +2 mm SoM boss and thicker gap pads (§10). (v0.1: the modem's 4.2 mm socket + 1.8 mm parts/shield + 0.5 mm pad set the 6.5 mm)	6.5	36.0
10	Magnesium AZ91D rear skin, 1.6 mm cast wall (D4) + 0.4 mm rib root inside the envelope; the rest of the 1.5 mm ribs is outside it (drawings keep the 2.0 mm section envelope — no dimensional change)	2.0	38.0

The SoM (Firefly Core-3588J: 3 × B2B connectors at ~1.5 mm mated + 1.2 mm SoM PCB + 1.0 mm SoC + 0.8 mm gap pad ≈ 4.5 mm) sits inside the 6.5 mm budget with room for the magnesium boss on the skin behind it; the ~2 mm slack raises that boss by +2 mm and allows thicker pads on the switch and PHY (§10, 06-thermal.md §5). With the modem gone no rear-face part needs the full 6.5 mm; the owner nevertheless kept 38 mm (D3), so the slack is spent thermally rather than on a thinner device (§3.4).

3.3 Z-stack at the reader band (section B-B)

Layer	mm	Cumulative
PC front frame + OLED lens (PC, hard-coated, 1.5 mm, recessed 0.5 mm)	2.5	2.5
OLED module (2.42", 1.8 mm) + FPC, LED bar flex 0.5	2.3	4.8
Air gap / card-connector housing front wall	2.2	7.0
Card + connector zone (CFe B connector housing ~7 mm incl. 3.8 mm card)	7.0	14.0
Reader daughterboard	1.6	15.6
Reader board rear-face controllers (GL9755/GL9750/ASM1064, eFuses)	1.5	17.1
Mezzanine (Samtec ADM6/ADF6, 5 mm stack) → main board front face	10.8	27.9
Main board + rear-face budget + skin (as §3.2)	10.1	38.0

The reader band has ~4 mm of slack that is used by the 6 mm slot recess (the top face steps down; the connectors sit 6 mm below the shutter plane).

3.4 Why the thickness is 38 mm (derivation behind ADR §2) — final; the 36 mm option is closed (D3, ADR §13 item 13)

An earlier draft paired a 34 mm thickness with the 2S2P 21700 pack; the ADR specifies 38 mm for the reasons below. The 21 mm cell must sit in Z in front of the main board because the board (165 × 80), the reader board (172 × 38) and the pack (144 × 44) cannot coexist in one plane inside a 186 × 92 mm interior. The unavoidable stack is cell (21) + two cradle walls (1.6) + board (1.6) + rear-face parts (≈ 4.5–4.7 with the SoM stack and the Wi-Fi/NVMe M.2 modules in their sockets; v0.1 needed 6.5 for the modem) + skin (2.0) + front frame (2.5) + clearances (≥ 1.8) ≈ 35 mm minimum, 38.0 mm with the uniform 6.5 mm rear budget that let any M.2 module go anywhere. Options:

Option	T (mm)	Energy	Consequence
A. 4 × 21700, 2S2P (as ADR), uniform 6.5 mm rear budget retained	38	72 Wh	ADR v0.3 baseline — final (D3); off-the-shelf UN 38.3-certified cells; simplest pack; drawings, shutter and pack unchanged from v0.1; the ~2 mm rear-budget slack goes to SoM boss height (+2 mm) and thicker gap pads (§10).
B. 4 × 21700 with a uniform ≈ 4.7 mm rear budget (SoM stack 4.5; Wi-Fi 2230 and NVMe 2280 in H2.25 sockets ≤ 4.7)	36	72 Wh	CLOSED — rejected by owner decision D3 (ADR §13 item 13). It became feasible when the v0.1 modem (the only rear-face part needing 6.5 mm) was deleted, but it would have cost a redraw of all four drawings, a 2 × 19 mm slat shutter, a thinner SoM boss and a re-check of the R14 track corner for 2 mm that is invisible in use. Row kept for history; not to be reopened.
C. 4 × 18650, 2S2P (3.5 Ah, e.g. LG MJ1 / Samsung 35E)	35	50 Wh	−30 % runtime; would nearly meet the earlier 34 mm draft
D. Custom Li-Po pouch pack, 2S2P, ~145 × 85 × 14 mm	30–31	72 Wh	custom pack certification (UN 38.3 + IEC 62133-2 on the pack, +$25–40 k, +8–10 weeks), swelling allowance, worse drop robustness, single-source pack vendor

Option A at 38 mm is the ADR v0.3 baseline and is final (D3) — the 2 mm is not worth a redraw and 38 mm keeps pre-certified cells. All four drawings are at T = 38 and stay so; rev C changes material callouts only. Option B is closed. Option D remains the only route to ≤ 34 mm at 72 Wh should a future variant ever require it; it would push a pack-certification delta into 05-power-budget.md and 11-certification.md.

4. Materials

Part	EVT / DVT	PVT / MP	Finish & notes
Chassis (rear + bottom skins, side walls, bosses, ribs)	Machined AZ31B magnesium (or thixomolded AZ91D if faster/cheaper) — not CNC aluminum, so thermal data reflects production	AZ91D magnesium, hot-chamber die-cast (D4)	Finish per D4.3 (§4.1): chromate-free conversion coat (Gardobond X 4707 / Alodine 5200 class) over the whole casting + light matte grey powder coat or e-coat 40–60 µm on external surfaces (ε ≈ 0.9, solar load); masked bare-conversion pads at the SoM/ASM2812/RTL8126 gap-pad bosses and the EMI-gasket lands; PEO (Keronite/Tagnite class) as the alternate for a later salt-fog claim. Walls 1.6 mm, draft ≥ 1°, ribs 1.2 mm — full DFM list in §4.1. Material data (verify): AZ91D k ≈ 72 W/m·K, cp ≈ 1.02 J/g·K, ρ 1.81; AZ31B k ≈ 96 W/m·K (~30 % better — EVT thermal results corrected to AZ91D or DVT on AZ91D). EVT option (ADR §8): cast the two 10 mm end caps as part of the chassis instead of the PC frame for drop stiffness — possible because the end caps have no RF requirement
Front frame + end caps (Wi-Fi RF window band, BLE window, lens bezel, rail grooves)	SLS PA12-GF then CNC PC	PC + 30 % GF (Sabic Lexan 3413 / Covestro Makrolon 9415), 2.0 mm nominal wall	textured MT-11020 grip; the Wi-Fi window band and the BLE window are the same material at 1.8 mm (Dk ≈ 3.2, tan δ ≈ 0.01 — acceptable per `07-rf-antenna.md` §3.2); an LDS-capable grade is no longer a baseline requirement (LDS Wi-Fi elements are only an optional PVT cost-down, `04-component-selection.md`)
Bumpers, button cap, RJ45 door	cast urethane	TPU Shore 80A (BASF Elastollan / Lubrizol Estane), 2-shot overmold onto the PC frame with mechanical interlocks	UV-stabilized, black
Shutter slats	6061-T6 CNC	6061-T6 stamped + machined edges	Type III hard anodize 40 µm, PTFE-impregnated (low friction against POM, scratch-resistant), laser-etched icons
Shutter rails	POM (Delrin 500P) machined	POM-C injection-moulded	self-lubricating, −40…+100 °C, low water absorption
Hinge pin, slide pins, detent balls, detent springs	304 stainless	304/316 stainless	pins Ø2.0 h6; balls Ø3.0; all run in POM parts or the anodized slats — no stainless-to-magnesium contact (§4.1)
Magnets	N52 NdFeB Ø4 × 2, Ni-Cu-Ni	same	2 pcs in slat 2, potted
Gaskets (frame perimeter, shutter perimeter, port collars)	cast silicone	silicone 40 Shore A compression gaskets (moulded) and 60 Shore A wiper lip	−55…+200 °C, low compression set
EMI/ground gasket (frame ↔ chassis)	fabric-over-foam strip	conductive fabric-over-foam (Laird/Parker) 1.5 mm	keeps chassis + PC-frame shield coherent for FCC Part 15B; contacts only the masked conversion-coated lands (§4.1; verify contact resistance)
OLED lens	PC 1.5 mm	PC, hard-coat (≥ 3H) + AR both sides	recessed 0.5 mm below frame surface
Thermal pads	Bergquist/Laird gap pads 1.0–3.0 W/m·K	same	on masked bare-conversion bosses; thicknesses in §10, `06-thermal.md` §5
Vent	Gore PolyVent (or Nitto Temish) Ø8 membrane	same	IP67-class membrane, pressure equalisation
Foam	closed-cell silicone / PORON	same	battery float + board isolation

4.1 Magnesium: castability, coating and galvanic isolation (D4.3 / D4.6)

Magnesium is anodic to every other material in the assembly and casts thinner than aluminum; both facts drive rules that the CAD, the coating spec and the fastener list must obey. All figures "(verify)" against the die-caster's and coater's datasheets before EVT.

DFM rules for the AZ91D die-casting (D4.6):

Feature	Rule	Note
Walls	1.6 mm nominal	AZ91D casts to ~1.0–1.2 mm; 1.6 kept for the 1.22 m drop (reserve trim to 1.2 mm in §2.2)
Draft	≥ 1° general, 1.5° on deep walls (side walls, shutter pocket step)	hot-chamber tool, no slides
Ribs	1.2 mm thick × ≤ 3× wall (≤ 4.8 mm) tall, R0.5 root fillets	external rear-skin ribs 1.5 mm tall, 20 mm pitch (§8, §10)
Bosses	≥ 2.5 mm wall, R0.5–1.0 fillets; thermal boss faces (SoM, ASM2812, RTL8126) machined after casting to 0.10 mm flatness	§14 CTQ; gap-pad compression 20–40 %
Undercuts	none in the rear skin; pocket step and rail lands pull straight
Threads	none tapped in magnesium — press-in or wire-thread inserts in every threaded hole, aluminum or Zn-Ni-plated (never stainless), per the galvanic table below
Prototypes	machined AZ31B (or thixomolded AZ91D) with the same wall/boss geometry; machined parts may carry slightly thicker walls (≈ +5–10 g, §2.2)	thermal correction AZ31B → AZ91D (`06-thermal.md` §3)
Machining fire safety	Mg machining fire-safety note for the CNC vendor: fine Mg chips and dust ignite — dry or mineral-oil (never water-miscible) coolant per the vendor's Mg practice, sharp tooling, chip evacuation, Class D extinguishing media at the machine; call it out on the RFQ and the prototype drawings	applies to all EVT/DVT machined AZ31B parts and to any post-cast boss machining

Coating stack (D4.3):

Layer	Spec	Thickness	Where	Thermal / electrical note
Conversion coat	chromate-free (Gardobond X 4707 / Alodine 5200 class)	~1 µm	whole casting, inside and out	thermally negligible; provides adhesion + first corrosion barrier; electrically conductive enough for EMI/ground contact — verify contact resistance on coupons
Top-coat	light matte grey powder coat or e-coat	40–60 µm	all external surfaces (rear face, bottom, side walls, ribs)	ε ≈ 0.9 helps radiation; light colour limits solar load (ADR §2); a 60 µm organic coat under an 8 W boss would add ~5 K, hence the masks below (verify)
Masked bare-conversion pads	masked during top-coat, conversion coat only	0 µm top-coat (§14 CTQ)	SoM / ASM2812 / RTL8126 gap-pad bosses; EMI-gasket lands (frame perimeter strip, card-cage grounding points, shield-frame screw lands)	thermal pads and the conductive gasket sit on bare conversion coat, never on powder
Alternate	plasma electrolytic oxidation (Keronite / Tagnite class), 15–25 µm ceramic, under the same top-coat	15–25 µm	if a later salt-fog / marine claim is needed	harder, better barrier; costlier; not baseline
Not coated	POM shutter tracks (separate mouldings)	—	—	no coating requirement

Galvanic pairs (magnesium is anodic to everything else):

Contact with the Mg chassis	Material choice	Isolation	Test
Screws (frame ×14, board standoffs, SoM ×4, pack ×4, USB-C brackets, end caps)	zinc-nickel-plated steel or 5056/6061 aluminum screws with aluminum washers	screw heads in coated pockets; no bare stainless on Mg	torque retention + coupon salt fog
Threaded inserts (all threads, incl. the ¼"-20 anchor)	aluminum or Zn-Ni-plated inserts — no stainless helicoils	pressed into cast pilots; conversion coat runs into the bore	pull-out ≥ spec after salt fog
Detent balls and springs (stainless)	stay stainless	housed in the POM detent cartridges — never touch Mg	dry/wet cycling (§6.4)
Shutter slats (hard-anodized 6061)	unchanged	run in POM T-tracks, rest on silicone seals; the rear-pocket step is powder-coated and the parked slats sit 1–2 mm off it on the track pins	shutter cycle test + inspection
EMI / ground gasket (Ni/Cu fabric-over-foam)	unchanged	contacts only masked conversion-coated lands; the powder top-coat everywhere else keeps the gasket off bare Mg	contact resistance ≤ target on coupons (verify)
Thermal gap pads	unchanged (non-conductive silicone)	on bare conversion-coated bosses; no galvanic couple	—
Steel keeper (magnets), Hall/magnet parts	unchanged	laminated behind the PC recess wall, not on Mg	—
USB-C receptacle brackets, RJ45 frame	Zn-Ni-plated steel (or aluminum) brackets; aluminum rivets	brackets screwed to coated pockets with Zn-Ni/Al screws	drop + salt fog
Coupon programme	500 h neutral salt fog (ASTM B117 / ISO 9227) on coated AZ91D (and AZ31B) coupons carrying each fastener/insert type and a gasket land, at EVT (verify)	—	no red/white corrosion at the joints; contact resistance and thermal-pad land condition re-measured after exposure

5. Top-edge slot arrangement

Order left→right viewed from the front: CFast 2.0 | CFexpress B | CFexpress A | SD UHS-II | microSD. Rationale: the two thick, hot cards (CFast, CFe B) sit at the left where the rear-skin ribs and the Ethernet PHY are not; CFe B is second from left so that the thumb naturally lands on the most-used slot; the thin SD/microSD share the right end, next to the OLED so slot icons and screen status read together.

Slot	Card (W × H × T mm)	Housing width	X start	X end	Opening (L × W mm)	Insertion depth	Card protrusion after push-push seat
CFast 2.0	42.8 × 36.4 × 3.6	45	13.5	58.5	44 × 6	34	2–3 mm, still ≥ 3 mm below shutter plane
CFexpress B	38.5 × 29.6 × 3.8	40	62.5	102.5	40 × 6	27	3 mm
CFexpress A	20.0 × 28.0 × 2.8	22	106.5	128.5	21.5 × 5	25	3 mm
SD UHS-II	24.0 × 32.0 × 2.1	27	132.5	159.5	25 × 4	26	6 mm → design requirement: a deep-insertion connector, or the recess floor lowered locally to 8 mm under this slot, so the seated card stays ≥ 1 mm below the shutter plane
microSD	11.0 × 15.0 × 1.0	13	163.5	176.5	12 × 3	13	2 mm

Row length 163 mm (45+40+22+27+13 + 4 × 4), centred, leaving 13.5 mm to each end of the 190 mm top edge; the 170 mm shutter covers X 10–180 and the outer 10 mm at each end belongs to the end caps (rail grooves + drain exits; no RF requirement). Gaps are 4 mm — enough for a 1.2 mm rib between connector housings in the recess floor and a fingertip on a single card, and the minimum that keeps the CFast and CFe B eject springs from interfering.

Orientation: cards insert downward from the top edge, card plane parallel to the main board (label side facing the user/front). Connectors are standard right-angle push-push types mounted on the front face of the vertical reader daughterboard; the reader board's top edge is 8 mm below the shutter plane.
Recess: a 6 mm deep channel, 22 mm wide (Z 8–30 of the 38 mm face), from X 12 to X 178 between the end caps. The shutter closes over the channel, so a seated card can protrude up to 5 mm from its connector and still clear the slats by ≥ 1 mm. Channel walls are drafted 5° so grit does not sit on a ledge.
Debris and drain: the channel floor slopes 3° toward two Ø2.5 mm drain slots at the channel ends that exit through the end caps below the rails. Each connector housing has a lip 0.8 mm above the floor. No blind pockets: the region under the shutter is either connector face or drain path.
Eject: push-push on all five (spring eject on CFast is 4.5 N; CFe B connectors from Molex/Amphenol/Hirose are specified with ≥ 10,000 insertions and a metal cage that is screwed to the reader board and pinned to the chassis rib so insertion force (≤ 15 N) never loads the solder joints).
Marking: slot icons and names laser-etched on the shutter's front slat (visible when closed) and moulded into the recess wall (visible when open). The LED bar segment under each slot doubles as the position marker in the dark.

6. Sliding shutter

The two-slat roll-top is approved unchanged (D11); only its thermal side-effect is new: when parked open, the two slats sit over the top ~40 mm band of the rear face with a 1–2 mm air gap on the track pins, which lowers the passive conductance a few per cent (06-thermal.md §3; ADR §2 open-shutter figures).

6.1 The geometric problem and the chosen mechanism

A single rigid plate wide enough to cover the 38 mm top face has nowhere to go when it slides: moving along the length needs 163 mm of travel (impossible), moving rearward leaves it cantilevered 38 mm behind the device, and a rigid plate cannot "drop into a rear pocket" because it cannot turn the corner. The ADR therefore specifies a two-slat articulated slider: two 2.0 mm hard-anodized 6061 slats, each 20 × 170 mm (X 10–180, centred), joined along their common long edge by a full-length Ø2.0 stainless piano-hinge pin in staked bushings. The slats stop 10 mm short of each end so their pins can enter the end-cap tracks and the slats never overrun the end caps. Each slat carries two Ø2.0 stainless pins per end (8 total) that project 3 mm into a T-profile POM track moulded into the inner 3 mm of each PC end cap (X 7–10 and 180–183). The track runs flat along the top face, turns a R14 (pin-centre) quarter circle at the top-rear edge and continues 40 mm down the rear face. Travel of the front edge: 36 mm.

State	Slat 1 (front)	Slat 2 (rear)	Notes
Closed	flat on top face, Z 0–20	flat on top face Z 20–38 + 2 mm wrapping onto the R10 top-rear radius	perimeter gasket compressed; magnets over Hall sensor; detent engaged
Open	Z 36–38 on top, then on the corner arc and 14 mm down the rear face	20–40 mm down the rear face, flat in the pocket	slot channel (Z 8–30) fully exposed; detent engaged; wiper lip parked

Because each slat is only 20 mm deep, the chord it forms while on the R14 arc has a sagitta of 4.2 mm; with the pins at slat mid-thickness the body corner must be ≤ R8.3 from the track centre — i.e. an ordinary R10 top-rear edge radius, which is also the ergonomic edge the palm wraps around. The rear-face pocket is a 2.5 mm step in the rear skin over the top 42 mm (behind the reader band, where rear-face components are only 1.5 mm tall, so the step costs nothing).

Rejected alternatives:

Alternative	Why rejected
Single rigid plate sliding rearward, parked cantilevered on end-cap fins	38 mm lever behind the device when open; fins snap in a 1.2 m drop with the shutter open (a common state during card handling); sand collects under the parked plate
Two half-length plates sliding to each end	~82 mm travel each; plates would extend past the ends and park as exposed metal levers outboard of the bumpers — a drop hazard and a snag point
Hinged lid (flip) with slide-latch	not "slide back and forth"; hinge line along the top-rear edge is a drop-impact line; open lid is a lever
Roll-top tambour (≥ 6 slats)	many hinge joints to seal, poor stiffness, sand ingestion between slats, cost
Rotating curved cover on a cylindrical top face	forces a curved top face; card slots at different insertion angles

6.2 Detents, latching and sensing

Detents: one stainless ball-spring cartridge (Ø3 ball, 0.5 N/mm spring, preload 6 N) per track, engaging a hemispherical dimple in slat 1's rear pin carrier at closed and at open. Combined detent force 8–12 N to break out, ≤ 4 N to run, with gloves. The detent is in the POM rail so wear is on a replaceable insert.
Closed hold: 2 × N52 Ø4 × 2 mm magnets potted in slat 2 pull onto a 0.8 mm steel keeper laminated behind the recess wall; holding force ≈ 3 N each, so the shutter does not creep open in a bag in transit and the Hall sensor (on the reader board, X = 95, under the rear rim) sees a clean > 10 mT step. Firmware treats "Hall = closed" as the IP54 state and shows a lock glyph.
End stops: the track has hard stops at both ends 0.5 mm beyond the detent positions; the slats cannot leave the track without removing the two end-cap screws.

6.3 Sealing (closed state only)

Perimeter compression gasket: silicone 40 A, 1.5 mm section, in a groove around the top face rim; slat 1's front edge and slat 2's rear wrap compress it 0.4 mm at closed (pulled by the magnets + detent). The slat-to-slat joint is covered by an overlapping 1.0 mm silicone strip bonded to slat 1 that lies on slat 2 (a "shingle") so water runs rearward off the joint.
Wiper lip: a 60 A silicone lip along slat 1's front edge wipes the front rim as the shutter closes and pushes grit forward and off.
Brush seals: nylon brush strips at both rail entries (top and rear) exclude sand from the T-track; the track is open at the bottom of the rear pocket so anything that gets in falls out.
Open state: the channel is exposed, so the device is only IP52 (dust-protected, dripping water) with the shutter open — stated on the label and in 01-requirements.md.

6.4 Wear, life and abuse

Life target 10,000 cycles (≈ 5 per day for 5 years). Wear couple: PTFE-impregnated hard anodize (HV ≈ 400) on POM-C; expected wear < 50 µm on the POM after 10 k cycles at 4 N. Test plan: 3 units on a pneumatic cycler at 0.5 Hz, dust-loaded (Arizona test dust A2, 5 g per 1,000 cycles), measure break-out force every 1,000 cycles (limit 6–15 N) and Hall margin.
Grit: all channels are open-ended; no blind pockets; the rail can be flushed with tap water. Pins are stainless; slats are anodized; magnets nickel-plated and potted.
Glove operation: a 1.5 mm raised ridge along slat 1's front edge, 170 mm long, gives the thumb purchase; the slat top is also lightly knurled (laser).
Anti-pinch: the leading edge of slat 1 is radiused R1 and the channel wall has 1.2 mm clearance; the closing force is < 4 N except at the final detent so a trapped finger tip is not injured.
Failure modes: bent slat after a shutter-open drop → each slat is retained by 4 screws through its pin carriers and is field-replaceable (service part); contaminated rail → flush with water; broken detent spring → cartridge is a press-in insert in the POM rail; lost magnet → Hall reports open, firmware warns "shutter sensor" and uploads continue.

7. Ports and protection (bottom end face unless noted)

Port	Connector	Sealing	Strain relief
Port A "PD / PHONE" (USB-C, PD sink, gadget)	IP67 mid-mount USB-C receptacle with integrated O-ring (Amphenol / JAE DX07 IPX7 series)	receptacle nose seals against a moulded collar in the chassis wall; O-ring compresses when the connector shell is screwed to a 1.5 mm Zn-Ni-plated steel (or aluminum) bracket — no stainless on the magnesium (§4.1)	the bracket, not the PCB, takes cable side-load; shell-to-bracket screws M1.6 ×2; PCB tails see only compliant solder joints
Port B "SSD / TETHER" (USB-C host for external SSDs, USB-tethered phones and USB cellular adapters; 5 V/3 A source)	same	same	same
Port C "USB4 FAST" (Pro SKU only; blanked plug on Base)	same, 40 Gbps-rated variant	same	same; on the Base SKU the hole is filled with a moulded TPU plug bonded in the collar. On Pro the same receptacle is now also a PD sink (D7: third TPS25750 + priority mux, `05-power-budget.md`) — a PCB population change, no mechanical change
RJ45 5GBASE-T	shielded, chassis-mounted shroud (Amphenol/Bel MagJack with metal frame)	hinged TPU door with over-center latch, living hinge in the overmold + stainless pin; door gasket lip seals to a raised rim; door open = not rated	jack frame riveted to chassis wall; PCB tails compliant; cable latch tab protected by the rim
Power / action button (front face, X 30, Y 12)	IP67 sealed tactile switch (C&K KSC/ Omron B3F-IP) under a TPU cap moulded into the frame	cap is part of the overmold	1.5 N actuation, 0.5 mm travel, illuminated ring via light pipe
Reset (bottom face, near Port A)	recessed Ø1.5 pinhole, sealed tact behind a TPU membrane	membrane	needs a Ø1 mm pin tool (paper clip)
Vent	Ø8 Gore membrane in the bottom face, under a labyrinth cap	membrane IP67	—

Port A, B, C are 18 mm apart (X = 25, 43, 61) so three cables can be inserted simultaneously with over-moulded connectors up to 12 mm wide. Ports face down when the device stands on a cart shelf, which is undesirable; the strap slots (§13) allow standing it on its rear face with ports facing the operator instead. The "PD" label on Port A is moulded in relief and etched white so it can be found by touch and in the dark.

8. Drop design — MIL-STD-810H Method 516.8, Procedure IV

Requirement: 26 drops (6 faces, 12 edges, 8 corners) from 1.22 m onto 5 cm of concrete over 2 in. plywood… the standard allows the drops to be distributed over up to 5 samples; we will use 5 samples, 26 drops each (130 drops) in DVT, shutter closed, and additionally 8 corner drops with the shutter open on 2 samples as a design-margin test. Pass = all functions, IP54 retained (re-run IP54 after drop).

Design features:

TPU corner bumpers 7 mm thick, edge bumpers 4 mm over an R8 chassis corner. Peak deceleration estimate for an ~830 g body onto concrete with 7 mm of 80 A TPU: ~250–350 g (crush ~4 mm). Board-mounted BGAs survive 1,500 g pulses; the concern is the cell pack and the connectors, handled below.
Floating battery pack: cells in a PC+GF cradle, wrapped in 0.8 mm closed-cell foam on all faces, cradle located by 4 TPU-bushed screws; pack connector is a 6-pin JST-GH with a 40 mm service loop. Cells are held by the cradle, not by the nickel strips.
Board mounting: main board on 8 M2.5 standoffs machined into the chassis, with PORON shock washers; reader board on 6 standoffs plus its 5 card cages pinned to the chassis rib; mezzanine has a 3 mm float in Z absorbed by the Samtec ADM6/ADF6's specified mated range.
Connector anchoring: every external connector's shell is screwed or riveted to the chassis (see §7). The SoM's three B2B connectors are additionally retained by 4 M2 screws into chassis bosses through the SoM's mounting holes.
Shutter in the drop: the slats are captive in the T-track with hard end stops; the hinge pin is staked; in the closed state the magnets and detent keep it from sliding under a 300 g pulse (mass 62 g × 300 g = 18 N, versus 8–12 N detent + 6 N magnets + friction — marginal, so the closed detent dimple is deeper (0.8 mm) and rated for 20 N). Shutter-open drops are a margin test, not a requirement.
Lens and OLED: lens recessed 0.5 mm; OLED glass on a 0.3 mm PORON gasket, bonded to the lens with OCA so the glass is supported over its whole area.
Card connectors: cards inside the recess cannot be struck; the cage/chassis pinning keeps insertion axis loads off the solder.
Chassis: ribs on the rear skin (1.2 mm × 1.5 mm, 20 mm pitch, longitudinal) triple its bending stiffness; bosses are ≥ 2.5 mm wall for M2.5 threads (aluminum or Zn-Ni-plated inserts in the magnesium — no tapped Mg, no stainless helicoils, §4.1).

Analysis plan: explicit dynamic FEA (LS-DYNA/Abaqus Explicit) on the corner drop in EVT using measured TPU stress–strain; instrument two EVT units with tri-axial accelerometers on the main board and the pack for correlation.

9. Sealing strategy (IP54)

IP5x (dust-protected) + IPx4 (splashing water from any direction) covers rain, spilled coffee, dusty locations and beach sand in a bag in transit, without the cost and thermal penalty of a fully immersible enclosure. Paths and closures:

Interface	Closure
PC front frame ↔ magnesium chassis (perimeter, ~560 mm)	moulded silicone 40 A gasket in a groove in the frame, 25 % compression, 14 M2.5 screws at ≤ 45 mm pitch; conductive fabric-over-foam strip inboard of it for EMI, on a masked conversion-coated land (§4.1)
Battery door ↔ front frame (perimeter ~410 mm)	second moulded silicone gasket in a groove around the door aperture, 6 × M2.5 captive screws, door lip overlaps the frame by 1.5 mm; door is opened only by service
Top face rim ↔ shutter (closed)	perimeter compression gasket + shingle strip + wiper lip (§6.3)
End caps ↔ frame	end caps are part of the frame moulding (one piece); in the optional magnesium-end-cap variant (§4) they become part of the chassis and the perimeter gasket path runs around them
USB-C ×3, button, reset	integrated O-rings / gaskets (§7); the v0.1 SIM tray penetration is deleted
RJ45	TPU door with gasket lip; rating requires the door closed
Rear-face shutter pocket	drains to the bottom; the pocket is outside the sealed volume
Vent	Gore membrane, prevents pumping of humid air through gaskets over altitude/temperature cycles (a 0.69 L sealed volume sees ±20 kPa across a flight; the membrane also lets the pack's internal pressure-relief work)

Test: IEC 60529 dust chamber (category 2, 8 h) and oscillating-tube splash; performed on 3 DVT units before and after the drop matrix; leak indicator paper inside.

10. Thermal interfaces (coordination with `06-thermal.md`)

Rear skin (magnesium, D4) is the primary heat spreader; bosses cast and then machined to 0.10 mm flatness under the SoM, ASM2812 and RTL8126 only (no modem boss), masked bare conversion coat on the boss faces (no powder under a pad, §4.1). The ~2 mm rear-budget slack (D3, ADR §13 item 13) is spent as: SoM boss +2 mm taller than the 06-thermal.md §5 local boss, with the SoM pad kept at 2.0 mm (3 W/m·K); ASM2812 and RTL8126 pads 1.0 → 1.5 mm to absorb boss/board tolerance at lower pressure; the standard 1.5 mm M.2 pad on the NVMe (Pro). Gap-pad count: SoM, switch, PHY, CFe B cage, CFast cage = 5.
Longitudinal external ribs on the rear skin (20 mm pitch, 1.5 mm tall) add ~18 % area; they also form the grip texture of the rear face.
CFe B and CFast cages are bridged to a chassis rib with a 1.5 mm pad so card heat (3 W) does not stay in the reader band.
Battery band is thermally isolated from the rear skin by the main board and foam; cell temperature is monitored by two NTCs on the pack PCB and is the charge-rate limiter.
Passive cooling for EVT (D5). The sealed tunnel-fan envelope stays reserved: a 25 × 25 × 10 mm tunnel zone in the bottom band, through the chassis bottom wall and the PC frame (component keep-out on the main board, no cast features yet). Whether the fan is designed into DVT is decided at the EVT-exit gate on measured magnesium (AZ91D-corrected) data against the ADR §12 pass criteria; a pass keeps the envelope empty, any fail designs the fan in for DVT.

11. Serviceability

Task	Access
Battery pack replacement (service centre; EU Battery Regulation 2023/1542 replaceability)	remove the 6 captive M2.5 screws of the screw-down battery door in the front frame → lift door → 4 pack screws → JST-GH connector → new pack, new door gasket. ~4 minutes, no FPCs disturbed, radios and frame untouched so no re-certification impact.
Shutter slat replacement	2 end-cap screws per end → slide slats out of track → 4 screws per slat. Field-serviceable.
Reader daughterboard swap (variant or repair)	frame off → 6 standoff screws + 5 cage pins → unplug mezzanine.
M.2 Wi-Fi/NVMe swap	frame off → battery out → M.2 screw. Service operation, not a user one: the two Wi-Fi MHF4 cables are rated for ~30 mating cycles and the antenna/module pairing is part of the radio grant (`07-rf-antenna.md`).
Gaskets	frame gasket and shutter gasket are separate service parts.

12. Assembly sequence (DFA)

Chassis prep: incoming coated AZ91D casting (conversion coat + powder/e-coat, masking verified: bare conversion coat on the three thermal bosses and the EMI-gasket lands, 0 µm top-coat, §14), press-fit aluminum / Zn-Ni-plated inserts (no stainless helicoils, no tapped Mg — §4.1), install vent membrane, RJ45 door pin, conductive gasket strip on the masked land.
Main board sub-assembly: SoM, M.2 modules (Wi-Fi 2230 with its 2 MHF4 cables; NVMe 2280 on Pro), TPM, all bench-tested before installation. The BLE chip antenna is an SMD part on the board — nothing to fit.
Apply gap pads to the masked chassis bosses (SoM 2.0 mm, switch and PHY 1.5 mm, §10); drop in main board; 8 screws + SoM 4 screws (Zn-Ni-plated steel or Al screws with Al washers per the §4.1 galvanic table); plug in and screw down the Zn-Ni/Al USB-C brackets and the RJ45 frame.
Route the 2 Wi-Fi antenna cables along the chassis top rail toward the front frame's upper band, clipped every 30 mm (captured by the frame at the reader band). Nothing is routed into the end caps.
Reader board sub-assembly (connectors, Hall sensor, LED bar flex); mate mezzanine; 6 screws; pin cages to rib; apply CFe B/CFast cage pads.
PC frame sub-assembly: OLED (OCA-bonded to lens), button switch, light pipe, Wi-Fi antenna flexes on the upper band either side of the OLED, LED bar light guide. The end caps receive only the POM rails (step 9).
Marry frame to chassis over the perimeter gasket; connect OLED/LED/button FPCs; 14 Zn-Ni-plated / aluminum screws (§4.1) in a torque pattern (0.35 N·m).
Battery pack (tested, fuel gauge programmed) into cradle with foam through the door aperture; 4 screws; connect JST-GH; fit battery door with its gasket, 6 captive screws (0.35 N·m).
Shutter: insert slats into end-cap tracks, fit end caps' detent cartridges, 2 screws per end.
Function test (all slots, all ports, radios via coupler), Hall calibration, IP leak test on sample basis (1 in 20 units, air-decay method through the vent port with the membrane masked).
Labels (bottom face laser-etched: regulatory, serial, UN 38.3 Wh), packaging.

13. Industrial design notes

Colorway: matte black TPU + graphite PC frame + light matte grey powder-coated magnesium chassis (solar load, ADR §2/§8 — replaces the v0.2 dark-grey finish); shutter slats in hard-anodize natural grey with a single accent line in the product colour ("poppy" red-orange) along the thumb ridge so the open/closed state reads at a distance.
Grip: TPU on all handling edges; rear-face ribs; the front frame has a fine texture (MT-11020) that also hides scuffs.
Labeling: slot names on the slat and in the recess; port names in relief; regulatory on the bottom face (etched, 4 mm cap height for the UN 38.3 Wh statement), FCC/CE/ISED IDs, serial + QR.
Anchors: one 1/4"-20 insert (aluminum or Zn-Ni-plated steel — no stainless in the magnesium, §4.1) on the bottom face at X = 95 (centre) for arm/clamp mounting on a cart, and two strap slots (25 × 4 mm) moulded into the end caps at Y 80–88 so the device can be hung on a bag strap or a shoulder sling with the top edge (slots) upward. A lanyard hole (Ø3) in the right end cap.
Standing orientations: on the bottom face (ports down — for a shelf), or on the rear face (angled by the ribs, screen toward the operator) using the strap slots as feet.

14. Tolerances and CTQs

CTQ	Nominal	Tolerance	Verification
Card seated top ↔ shutter plane clearance	1.0 mm min (SD case)	+0.5 / −0	CMM on recess floor, gauge card set
Shutter track straightness (both ends, parallelism)	—	0.10 mm over 190 mm	fixture; otherwise binding
Shutter break-out force (closed / open)	10 N	8–12 N	force gauge, 100 % at EOL
Shutter running force	3 N	≤ 4 N	same
Hall field at closed	> 10 mT	margin ≥ 2× threshold	EOL test
Perimeter gasket compression	25 %	20–30 %	section cut, gasket ink transfer
Frame ↔ chassis gap (cosmetic)	0.15 mm	≤ 0.30 mm	visual
Lens recess	0.5 mm	±0.1	depth gauge
USB-C receptacle position to chassis hole	—	±0.15 mm (X/Y), ±0.20 (Z)	plug gauge; bracket tolerances
Slot pitch (connector centres to recess icons)	per §5	±0.20 mm	CMM on reader board + frame
Rear-skin flatness under SoM boss	—	0.10 mm	gap pad compression 20–40 %
Mass	828 g (AZ91D chassis, Base SKU)	±25 g	scale
Top-coat thickness on the three thermal bosses and the EMI-gasket lands	0 µm (masked; bare conversion coat)	0 / no powder; conversion coat present	eddy-current / visual on 100 % at incoming; contact resistance on gasket lands (verify limit)
Top-coat thickness elsewhere	50 µm	40–60 µm	eddy-current gauge
Salt-fog coupon (galvanic)	500 h neutral salt fog, coated coupons with each fastener/insert type and a gasket land	no corrosion at joints; contact resistance and pull-out within spec after exposure	EVT coupon programme (§4.1, verify)
Envelope	190 × 96 × 38	±0.5 mm plastics, ±0.3 mm castings	CMM
Wi-Fi antenna separation (centre to centre)	118 mm	≥ 60 mm	frame fixture
Shutter end clearance to end cap rail groove	10 mm each end	+0.5 / −0	CMM

15. Drawings (`../drawings/`, scale 1 mm = 4 px, rev C, 2026-09-27 — regenerated for ADR v0.3 by `../drawings/generate_drawings.py`)

Rev B → rev C changes labels only, no dimension, coordinate or geometry change (D3): title block "Rev: C (ADR v0.3)"; section A-A header reads "rear Mg (AZ91D) skin at right", its leader "Mg AZ91D rear skin + ribs" and the legend hatch "magnesium AZ91D (section)"; the exploded-view chassis callout and parts-list row 10 read "Magnesium AZ91D die-cast chassis (EVT/DVT machined AZ31B), 1.6 mm walls, masked bosses, conversion coat + light grey powder coat"; parts-list row 14 adds the Zn-Ni/aluminum fastener note. The shutter slats keep their "hard-anodized 6061 Al" callouts. The "2 skin" section dimension is unchanged (1.6 mm wall + rib root, §3.2).

File	Shows
`top-view.svg`	The 190 × 38 mm top face looking down: the 22 mm slot channel, the five slot openings with true widths and 4 mm gaps (163 mm row) and chain dimensions, the 10 mm end caps (rail groove + drain exit, no RF requirement), the 170 mm shutter drawn dashed in the closed position and translucent in the open (parked) position, detent positions, Hall sensor and magnet positions, LED bar at the front edge; overall dimensions 190 and 38 and the section mark A-A (battery band).
`front-view.svg`	The 190 × 96 mm front face: LED bar (5 segments over the slots), centred OLED window with its offsets, the two Wi-Fi antenna zones flanking the OLED in the upper band with their 118 mm separation (the only RF window band), plain PC end caps (no RF window, no SIM tray), the BLE chip-antenna window at the bottom-left, power button, TPU corner bumpers, the screw-down battery door outline with its six screws, strap slots, and the bottom-edge cut-outs for Ports A/B/C and the RJ45 door; the closed shutter's edge above the top face.
`side-view.svg`	Right-end profile (96 × 38) with the shutter closed, the rear pocket, the plain PC+GF end cap (lanyard hole, strap slot; no RF window, no SIM tray), plus section A-A through the battery band: front frame, foam, cradle, two 21 mm cells stacked in Y, main board with front/rear component budgets, the SoM stack (4.5) and the NVMe/Wi-Fi M.2 stack (≤ 4.7) inside the retained 6.5 mm rear budget with the unused slack shown dashed, rear skin with ribs, TPU bumpers, top recess and reader-board region; dimensions 96, 38, 6, 21, 2, 6.5.
`exploded-view.svg`	Isometric-style exploded stack front→rear: shutter slats (170 mm), rails, PC frame with lens, plain end caps, Wi-Fi zones, BLE window and battery-door aperture, battery door, OLED and LED flex, battery pack, reader daughterboard (172 × 38) with five connectors, mezzanine, main board with SoM, two M.2 modules (Wi-Fi 2230, NVMe 2280) and the power-spread area where the v0.1 modem slot was, switch, bridges and ports, thermal pads (SoM, switch, PHY), magnesium AZ91D chassis with ribs (no RF window; masked bosses), four TPU bumpers, two Wi-Fi antenna flexes plus the BLE chip antenna (3 antennas), gaskets and screws; balloon numbers with a parts list.

docs/08-mechanical.md