Merge pull request 'feat: Prototype base plate — real hub motor axle measurements' (#11) from sl-mechanical/prototype-baseplate into main

chassis/BOM.md

@@ -1,24 +1,78 @@
 # SaltyBot Chassis — Bill of Materials
-**Task:** bd-1iy5
+**Task:** bd-1iy5 / prototype-baseplate
-**Rev:** A — 2026-02-28
+**Rev:** C — 2026-02-28 (vertical stem architecture; batteries on mast carousel)
 **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 C
+
+> Batteries are removed from the base plate. Plate is now compact (680×130mm).
+> Stem socket replaces battery tray. See Part B (stem clamp) below.
+
+| # | Part | Qty | Material | Cut size | Notes |
+|---|------|-----|----------|----------|-------|
+| 1 | Base plate | 1 | 6mm 5052-H32 Al **or** 8mm acrylic | 680×130mm blank | `RENDER="plate_2d"` → DXF |
+| 2 | Dropout clamp — lower | 2 | 8mm 6061-T6 Al | 90×70mm blank | Round bore Ø16.51mm; `RENDER="clamp_lower_2d"` |
+| 3 | Dropout clamp — upper | 2 | 8mm 6061-T6 Al | 90×70mm blank | D-cut bore; `RENDER="clamp_upper_2d"` |
+| 4 | Stem flange ring | 2 | 6mm Al or acrylic | Ø82mm disc | One above + one below plate; `RENDER="stem_flange_2d"` |
+| 5 | Vertical stem tube | 1 | 38.1mm OD × 1.5mm wall 6061-T6 Al | 1050mm length | 1.5" EMT conduit is a drop-in alternative |
+| 6 | FC standoff M3×6mm nylon | 4 | Nylon | — | MAMBA F722S vibration isolation |
+| 7 | Ø4mm × 16mm alignment pin | 8 | Steel dowel | — | Dropout clamp-to-plate alignment |
+
+### Battery Stem Clamp (`stem_battery_clamp.scad`) — Part B
+
 | # | 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` |
+| 8 | Collar half | 2 | PETG FDM (5 perimeters, 40% infill) | Print flat-side-down; mirror 2nd in slicer. Bore Ø38.6mm |
-| 2 | Longitudinal rib (front) | 1 | 4mm 5052 aluminium, 600×40mm | Laser-cut; press-fit into deck slots |
+| 9 | Radial arm | 4 | 4mm 5052-H32 Al (laser-cut) **or** PETG FDM | `RENDER="arm_2d"` for DXF with `ARM_THICK=4`; or print at 8mm |
-| 3 | Longitudinal rib (rear)  | 1 | 4mm 5052 aluminium, 600×40mm | Same file, symmetric |
+| 10 | Battery cradle | 4 | PETG FDM (4 perimeters, 30% infill) | U-channel, open top; holds 1 pack per cradle |
-| 4 | Motor fork bracket (L) | 1 | 8mm 6061 aluminium | CNC mill or FDM PETG @100% infill for prototyping |
+| 11 | M6×60 SHCS | 4 | SS | 2 collar clamping bolts × 2 sides |
-| 5 | Motor fork bracket (R) | 1 | 8mm 6061 aluminium | Mirror of item 4 |
+| 12 | M6 hex nut | 4 | SS | Captured in collar nut pockets |
-| 6 | Battery tray | 1 | 3mm PETG FDM or 3mm aluminium fold | `chassis_frame.scad` — `battery_tray()` module |
+| 13 | M6×12 set screw | 2 | SS, cup-point | 1 per collar half for height lock |
-| 7 | FC mount plate / standoffs | 1 set | PETG or nylon FDM | Includes 4× M3 nylon standoffs, 6mm height |
+| 14 | M4×20 SHCS | 8 (16 for 4) | SS | Arm-to-collar bolts (2 per arm) |
-| 8 | Jetson Nano mount plate | 1 | 4mm 5052 aluminium or 4mm PETG FDM | B01 58×58mm hole pattern |
+| 15 | M4×16 SHCS | 8 (16 for 4) | SS | Cradle-to-arm bolts (2 per cradle) |
-| 9 | Front bumper bracket | 1 | 5mm PETG FDM | Saddle clamps for 22mm EMT conduit |
+| 16 | M4 hex nut | 16 (32 for 4) | SS | Nuts for items 14 + 15 |
-| 10 | Rear bumper bracket | 1 | 5mm PETG FDM | Mirror of item 9 |
+| 17 | Velcro strap 25mm × 600mm | 4–8 | — | 1–2 per battery pack through cradle slots |
+
+### 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 |
 
 ---
 
@@ -26,8 +80,9 @@
 
 | # | 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 |
+| 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** |
-| 12 | Motor hall-sensor cable extension | 2 | 6-pin JST-PH 300mm | Route through deck cable slot |
+| 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 |
 
 ---
 
@@ -43,13 +98,27 @@
 
 ---
 
-## Battery
+## Battery (Vertical Stem Mount — Rev C)
+
+> Batteries mount VERTICALLY on the stem carousel, **not** on the base plate.
+> Each pack stands upright (420mm tall) in a cradle at the end of a radial arm.
 
 | # | 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 |
+| 18 | Battery pack | 2–4 | 24V, **420×88×56 mm** each (caliper-verified) | Snap into battery cradle from above |
-| 19 | Velcro strap 20mm wide | 2 | 300mm length | Route through tray strap slots |
+| 19 | BMS board | 1 | Matched to cell chemistry | Mount to stem or base plate underside; run wiring down stem |
-| 20 | BMS board | 1 | Matched to cell chemistry | Mount externally on rear inner face of tray wall |
+
+### Battery stem clamp — configuration guide
+
+| Config | Arm count | Carousel weight | Balance | Notes |
+|--------|-----------|-----------------|---------|-------|
+| 2-pack | 2 arms, 180° apart | ~1.4 kg | ✅ Symmetric | Minimum configuration |
+| 4-pack | 4 arms, 90° apart  | ~2.8 kg | ✅ Symmetric | Maximum practical config |
+| 3-pack | 3 arms, 120° apart | ~2.1 kg | ⚠ Asymmetric mass | Needs counter-balance or avoid |
+
+### CG height tuning
+
+Slide entire carousel up/down the stem with M6 collar bolts loosened. Tighten at desired height. Typical balance point (initial estimate): batteries centred at 450–600 mm above base plate. Adjust in ≈50 mm increments during commissioning.
 
 ---
 
@@ -64,18 +133,23 @@
 
 ## Fasteners
 
-| # | Part | Qty | Spec |
+| # | Part | Qty | Spec | Use |
-|---|------|-----|------|
+|---|------|-----|------|-----|
-| 23 | M5×16 SHCS | 24 | ISO 4762, SS |
+| 20 | M5×16 SHCS | 16 | ISO 4762, SS | Dropout clamp bolts (4 per clamp × 4) |
-| 24 | M5 hex nut | 24 | ISO 4032, SS |
+| 21 | M5×20 SHCS | 8  | ISO 4762, SS | Stem flange bolts (4 per flange × 2) |
-| 25 | M4×12 SHCS | 12 | ISO 4762, SS |
+| 22 | M5 hex nut | 24 | ISO 4032, SS | |
-| 26 | M4 hex nut | 12 | ISO 4032, SS |
+| 23 | M4×20 SHCS | 16 | ISO 4762, SS | Arm-to-collar (2 per arm × 4 arms × 2) |
-| 27 | M3×10 SHCS | 20 | ISO 4762, SS |
+| 24 | M4×16 SHCS | 16 | ISO 4762, SS | Cradle-to-arm (2 per cradle × 4 arms × 2) |
-| 28 | M3 hex nut | 20 | ISO 4032, SS |
+| 25 | M4 hex nut  | 32 | ISO 4032, SS | |
-| 29 | M3×6 BHCS | 8 | FC + Jetson board bolts |
+| 26 | M6×60 SHCS  | 4  | ISO 4762, SS | Collar clamping bolts |
-| 30 | M14×1.5 axle nut | 4 | One each side per motor, flanged | Confirm axle thread pitch on actual motors |
+| 27 | M6 hex nut  | 4  | ISO 4032, SS | Captured in collar pockets |
-| 31 | Serrated washer M14 | 4 | Axle anti-rotation |
+| 28 | M6×12 set screw | 2 | ISO 4026, SS cup-point | Stem height lock (1 per collar half) |
-| 32 | Flat washer M5 | 48 | SS |
+| 29 | M3×10 SHCS | 12 | ISO 4762, SS | FC mount + miscellaneous |
+| 30 | M3×6 BHCS  | 4  | ISO 4762, SS | FC board bolts |
+| 31 | Axle lock nut (match axle tip thread) | 4 | Flanged, confirm thread | 2 per motor |
+| 32 | Flat washer M5 | 32 | SS | |
+| 33 | Flat washer M4 | 32 | SS | |
+| 34 | Ø4×16 dowel pin | 8 | Steel | Dropout clamp alignment |
 
 ---
 

chassis/prototype_baseplate.scad

@@ -0,0 +1,348 @@
+// =============================================================================
+// SaltyBot — Prototype Base Plate  (Rev C — compact, stem-mount)
+// Agent: sl-mechanical  |  2026-02-28
+//
+// Laser-cut or CNC-routed flat plate (6 mm Al / 8 mm acrylic).
+// Uses CALIPER-VERIFIED hub motor axle measurements (see PR #7 / #11).
+//
+// ARCHITECTURE CHANGE (Rev C):
+//   Batteries are NO LONGER on the base plate.
+//   They stand vertically on a central stem via stem_battery_clamp.scad.
+//   The base plate is now compact — only axle dropouts + stem socket + FC mount.
+//
+// ── AXLE PROFILE (stepped D-cut, caliper-verified) ───────────────────────────
+//  Zone   │ Feature          │ Ø / Width          │ Length
+//  ───────┼──────────────────┼────────────────────┼──────────
+//  Base   │ Round (near hub) │ Ø 16.11 mm         │ 15.00 mm
+//  D-cut  │ Round OD         │ Ø 15.95 mm         │ 43.35 mm
+//         │ Flat chord       │   13.00 mm         │
+//  Tip    │ Shoulder/end     │ —                  │  3.00 mm
+//  Total  │ Hub face → tip   │ —                  │ 65.50 mm
+//  Bearing seat collar:  Ø 37.8 mm
+//  Tire:  10 × 2.125" pneumatic (Ø 254 mm, 35 PSI)
+// =============================================================================
+
+$fn = 128;
+
+// =============================================================================
+// AXLE PARAMETERS — caliper-verified
+// =============================================================================
+
+AXLE_BASE_DIA   = 16.11;
+AXLE_BASE_LEN   = 15.00;
+AXLE_DCUT_DIA   = 15.95;
+AXLE_DCUT_FLAT  = 13.00;
+AXLE_DCUT_LEN   = 43.35;
+AXLE_TIP_LEN    =  3.00;
+AXLE_TOTAL      = 65.50;
+BEARING_SEAT_OD = 37.80;
+TIRE_OD         = 254.0;
+AXLE_CL_HEIGHT  = TIRE_OD / 2;   // 127 mm above ground
+
+// =============================================================================
+// PLATE PARAMETERS
+// =============================================================================
+
+WHEELBASE       = 600.0;  // mm  axle C/L to axle C/L
+// Plate depth now driven only by structural + FC needs (no battery footprint).
+PLATE_DEPTH     = 130.0;  // mm  front-to-rear
+PLATE_OVERHANG  =  40.0;  // mm  plate past axle C/L each side
+PLATE_THICK     =   6.0;  // mm
+
+// Fork slot
+FORK_W          = AXLE_BASE_DIA + 0.4;   // 16.51 mm
+FORK_DEPTH      =  50.0;
+
+// Dropout clamp (two-piece sandwich)
+CLAMP_L         =  80.0;
+CLAMP_H         =  60.0;
+CLAMP_THICK     =   8.0;
+CLAMP_BOLT_D    =   5.3;   // M5
+CLAMP_BOLT_DX   =  22.0;
+CLAMP_BOLT_DY   =  22.0;
+CLAMP_ALIGN_D   =   4.1;   // Ø4 pin
+
+// D-cut bore clearance
+DCUT_CL         =  0.3;
+
+// FC mount — MAMBA F722S 30.5 × 30.5 mm M3
+FC_PITCH        = 30.5;
+FC_HOLE_D       =  3.2;
+// FC is offset toward front of plate (away from stem)
+FC_X_OFFSET     = -40.0;  // mm from plate centre (negative = front/motor side)
+
+// =============================================================================
+// STEM SOCKET PARAMETERS
+// =============================================================================
+
+STEM_OD         = 38.1;   // mm  1.5" EMT conduit OD
+STEM_BORE       = STEM_OD + 0.5;   // 38.6 mm with clearance
+// Flange ring (laser-cut, bolts above + below plate to grip tube):
+STEM_FLANGE_OD  = 82.0;   // mm  flange outer diameter
+STEM_FLANGE_BC  = 66.0;   // mm  bolt circle diameter (4× M5 at 90°)
+STEM_FLANGE_T   =  6.0;   // mm  = PLATE_THICK (flush-mount)
+// Stem position: at plate centre (X=0, Y=0)
+
+// =============================================================================
+// UTILITIES
+// =============================================================================
+
+M3 = 3.2; M4 = 4.3; M5 = 5.3;
+PLATE_X_HALF = WHEELBASE/2 + PLATE_OVERHANG;   // ± 340 mm
+DCUT_R  = (AXLE_DCUT_DIA + 2*DCUT_CL) / 2;
+DCUT_FC = AXLE_DCUT_FLAT + 2*DCUT_CL;
+
+// =============================================================================
+// RENDER CONTROL
+// =============================================================================
+//
+//  "assembly"        full 3-D preview
+//  "plate_2d"        DXF — base plate
+//  "clamp_lower_2d"  DXF — lower dropout clamp  (× 2)
+//  "clamp_upper_2d"  DXF — upper dropout clamp  (× 2)
+//  "stem_flange_2d"  DXF — stem flange ring      (× 2, one above + one below plate)
+
+RENDER = "assembly";
+
+if (RENDER == "assembly") {
+    assembly();
+} else if (RENDER == "plate_2d") {
+    projection(cut=true) translate([0,0,-PLATE_THICK/2]) base_plate();
+} else if (RENDER == "clamp_lower_2d") {
+    projection(cut=true) translate([0,0,-CLAMP_THICK/2]) clamp_lower();
+} else if (RENDER == "clamp_upper_2d") {
+    projection(cut=true) translate([0,0,-CLAMP_THICK/2]) clamp_upper();
+} else if (RENDER == "stem_flange_2d") {
+    projection(cut=true) translate([0,0,-STEM_FLANGE_T/2]) stem_flange();
+}
+
+// =============================================================================
+// ASSEMBLY
+// =============================================================================
+
+module assembly() {
+    color("Silver",       0.85) base_plate();
+
+    for (side = [-1, 1]) {
+        color("SteelBlue",    0.80)
+            translate([side * WHEELBASE/2, 0, PLATE_THICK])
+                clamp_lower();
+        color("CornflowerBlue", 0.80)
+            translate([side * WHEELBASE/2, 0, PLATE_THICK + CLAMP_THICK])
+                clamp_upper();
+    }
+
+    // Stem flange rings (above and below plate)
+    color("DimGray", 0.70)
+        translate([0, 0, -STEM_FLANGE_T])
+            stem_flange();
+    color("DimGray", 0.70)
+        translate([0, 0, PLATE_THICK])
+            stem_flange();
+
+    // Reference ghosts
+    %color("Orange", 0.25)
+        translate([0, 0, PLATE_THICK + STEM_FLANGE_T])
+            cylinder(d=STEM_OD, h=800);   // vertical stem
+    %for (side = [-1, 1])
+        color("Tomato", 0.2)
+            translate([side * WHEELBASE/2, 0, 0])
+                rotate([0, side*90, 0])
+                    axle_ghost();
+}
+
+// =============================================================================
+// BASE PLATE  (Part A — compact)
+// =============================================================================
+
+module base_plate() {
+    R = 12;   // corner radius
+    difference() {
+        // ── Outer profile ──
+        linear_extrude(PLATE_THICK)
+            minkowski() {
+                square([2*(PLATE_X_HALF - R), PLATE_DEPTH - 2*R], center=true);
+                circle(r=R);
+            }
+
+        // ── Fork slots (open at ±X edges, semicircular tip) ──────────────
+        for (side = [-1, 1]) {
+            translate([side*(PLATE_X_HALF - FORK_DEPTH), -FORK_W/2, -1])
+                cube([FORK_DEPTH + 1, FORK_W, PLATE_THICK + 2]);
+            translate([side*(PLATE_X_HALF - FORK_DEPTH), 0, -1])
+                cylinder(d=FORK_W, h=PLATE_THICK + 2);
+        }
+
+        // ── Bearing seat relief (prevents Ø37.8 mm collar binding on edge) ─
+        for (side = [-1, 1])
+            translate([side*PLATE_X_HALF - side*(BEARING_SEAT_OD/2 + 1),
+                       -BEARING_SEAT_OD/2, -1])
+                cube([BEARING_SEAT_OD/2 + 2, BEARING_SEAT_OD, PLATE_THICK + 2]);
+
+        // ── Dropout clamp bolt through-holes ─────────────────────────────
+        for (side = [-1, 1])
+        for (dx = [-CLAMP_BOLT_DX, CLAMP_BOLT_DX])
+        for (dy = [-CLAMP_BOLT_DY, CLAMP_BOLT_DY])
+            translate([side*WHEELBASE/2 + dx, dy, -1])
+                cylinder(d=CLAMP_BOLT_D, h=PLATE_THICK + 2);
+
+        // ── Alignment pin holes (Ø4) ──────────────────────────────────────
+        for (side = [-1, 1])
+        for (dy = [-CLAMP_BOLT_DY + 8, CLAMP_BOLT_DY - 8])
+            translate([side*WHEELBASE/2, dy, -1])
+                cylinder(d=CLAMP_ALIGN_D, h=PLATE_THICK + 2);
+
+        // ── Stem socket bore ──────────────────────────────────────────────
+        translate([0, 0, -1])
+            cylinder(d=STEM_BORE, h=PLATE_THICK + 2);
+
+        // ── Stem flange bolt holes (4× M5, 90° pattern on STEM_FLANGE_BC) ─
+        for (a = [0, 90, 180, 270])
+            rotate([0, 0, a])
+                translate([STEM_FLANGE_BC/2, 0, -1])
+                    cylinder(d=M5, h=PLATE_THICK + 2);
+
+        // ── FC mount (MAMBA F722S 30.5 × 30.5 M3) ────────────────────────
+        for (x = [FC_X_OFFSET - FC_PITCH/2, FC_X_OFFSET + FC_PITCH/2])
+        for (y = [-FC_PITCH/2, FC_PITCH/2])
+            translate([x, y, -1])
+                cylinder(d=FC_HOLE_D, h=PLATE_THICK + 2);
+
+        // ── Wiring / cable pass-through slots (2×, flanking stem) ─────────
+        for (dy = [-30, 30])
+            hull() {
+                translate([15, dy, -1])  cylinder(d=14, h=PLATE_THICK + 2);
+                translate([-15, dy, -1]) cylinder(d=14, h=PLATE_THICK + 2);
+            }
+
+        // ── Lightening slots (between FC zone and dropout zones) ──────────
+        for (sx = [-1, 1]) {
+            // One slot each side of stem, in the structural corridor
+            lx = sx * (WHEELBASE/4);
+            hull() {
+                translate([lx, -(PLATE_DEPTH/2 - 22), -1]) cylinder(d=18, h=PLATE_THICK+2);
+                translate([lx,  (PLATE_DEPTH/2 - 22), -1]) cylinder(d=18, h=PLATE_THICK+2);
+            }
+        }
+    }
+}
+
+// =============================================================================
+// STEM FLANGE RING  (laser-cut, qty 2 — one above, one below plate)
+// =============================================================================
+
+module stem_flange() {
+    difference() {
+        cylinder(d=STEM_FLANGE_OD, h=STEM_FLANGE_T);
+        // Stem bore (tight fit — tube presses into flange)
+        translate([0, 0, -1])
+            cylinder(d=STEM_BORE, h=STEM_FLANGE_T + 2);
+        // 4× M5 flange bolts
+        for (a = [0, 90, 180, 270])
+            rotate([0, 0, a])
+                translate([STEM_FLANGE_BC/2, 0, -1])
+                    cylinder(d=M5, h=STEM_FLANGE_T + 2);
+    }
+}
+
+// =============================================================================
+// DROPOUT CLAMP — LOWER (round bore, base-section diameter)
+// =============================================================================
+
+module clamp_lower() {
+    difference() {
+        hull() {
+            translate([-CLAMP_L/2 + CLAMP_H/2, 0, 0]) cylinder(d=CLAMP_H, h=CLAMP_THICK);
+            translate([ CLAMP_L/2 - CLAMP_H/2, 0, 0]) cylinder(d=CLAMP_H, h=CLAMP_THICK);
+        }
+        // Round bore (base zone)
+        translate([0, 0, -1]) cylinder(d=AXLE_BASE_DIA + 0.4, h=CLAMP_THICK + 2);
+        // Slide-in slot (open toward wheel side)
+        translate([-CLAMP_L/2 - 1, -FORK_W/2, -1])
+            cube([CLAMP_L/2 + 1, FORK_W, CLAMP_THICK + 2]);
+        // Clamp bolts
+        for (dx = [-CLAMP_BOLT_DX, CLAMP_BOLT_DX])
+        for (dy = [-CLAMP_BOLT_DY, CLAMP_BOLT_DY])
+            translate([dx, dy, -1]) cylinder(d=CLAMP_BOLT_D, h=CLAMP_THICK + 2);
+        // Alignment pins
+        for (dy = [-CLAMP_BOLT_DY + 8, CLAMP_BOLT_DY - 8])
+            translate([0, dy, -1]) cylinder(d=CLAMP_ALIGN_D, h=CLAMP_THICK + 2);
+    }
+}
+
+// =============================================================================
+// DROPOUT CLAMP — UPPER (D-cut bore, anti-rotation)
+// =============================================================================
+
+module clamp_upper() {
+    dcut_r = DCUT_R;
+    dcut_d = sqrt(pow(dcut_r, 2) - pow(DCUT_FC/2, 2));
+
+    difference() {
+        hull() {
+            translate([-CLAMP_L/2 + CLAMP_H/2, 0, 0]) cylinder(d=CLAMP_H, h=CLAMP_THICK);
+            translate([ CLAMP_L/2 - CLAMP_H/2, 0, 0]) cylinder(d=CLAMP_H, h=CLAMP_THICK);
+        }
+        // D-cut bore
+        translate([0, 0, -1])
+            linear_extrude(CLAMP_THICK + 2)
+                dcut_profile_2d(dcut_r, dcut_d);
+        // Slide-in slot
+        translate([-CLAMP_L/2 - 1, -FORK_W/2, -1])
+            cube([CLAMP_L/2 + 1, FORK_W, CLAMP_THICK + 2]);
+        // Clamp bolts
+        for (dx = [-CLAMP_BOLT_DX, CLAMP_BOLT_DX])
+        for (dy = [-CLAMP_BOLT_DY, CLAMP_BOLT_DY])
+            translate([dx, dy, -1]) cylinder(d=CLAMP_BOLT_D, h=CLAMP_THICK + 2);
+        // Alignment pins
+        for (dy = [-CLAMP_BOLT_DY + 8, CLAMP_BOLT_DY - 8])
+            translate([0, dy, -1]) cylinder(d=CLAMP_ALIGN_D, h=CLAMP_THICK + 2);
+        // Orientation emboss
+        translate([0, dcut_d + 1.5, CLAMP_THICK - 0.8])
+            linear_extrude(1)
+                polygon([[0,0],[-3,-5],[3,-5]]);
+    }
+}
+
+// ── D-cut 2D profile helper ───────────────────────────────────────────────────
+module dcut_profile_2d(r, flat_d) {
+    intersection() {
+        circle(r=r);
+        translate([-r - 1, -r - 1])
+            square([2*(r+1), r + 1 + flat_d]);
+    }
+}
+
+// =============================================================================
+// AXLE GHOST (visualisation only)
+// =============================================================================
+
+module axle_ghost() {
+    cylinder(d=BEARING_SEAT_OD, h=12);
+    translate([0,0,12]) cylinder(d=AXLE_BASE_DIA, h=AXLE_BASE_LEN);
+    translate([0,0,12+AXLE_BASE_LEN]) cylinder(d=AXLE_DCUT_DIA, h=AXLE_DCUT_LEN);
+}
+
+// =============================================================================
+// DXF EXPORT
+// =============================================================================
+//
+//  Part 1 — Base plate:
+//    openscad prototype_baseplate.scad -D 'RENDER="plate_2d"' -o baseplate.dxf
+//
+//  Part 2 — Dropout clamp, lower (× 2):
+//    openscad prototype_baseplate.scad -D 'RENDER="clamp_lower_2d"' -o clamp_lower.dxf
+//
+//  Part 3 — Dropout clamp, upper (× 2):
+//    openscad prototype_baseplate.scad -D 'RENDER="clamp_upper_2d"' -o clamp_upper.dxf
+//
+//  Part 4 — Stem flange ring (× 2, one each side of plate):
+//    openscad prototype_baseplate.scad -D 'RENDER="stem_flange_2d"' -o stem_flange.dxf
+//
+//  Materials:
+//    Plate + flanges : 6 mm 5052-H32 aluminium  (preferred)
+//                      8 mm clear acrylic         (quick proto)
+//    Dropout clamps  : 8 mm 6061-T6 aluminium
+//  Stem tube         : 38.1 mm OD × 1.5 mm wall 6061-T6  (or 1.5" EMT)
+//    Cut stem to ~1050 mm — allows batteries from ~100 mm to ~950 mm height.
+// =============================================================================

chassis/stem_battery_clamp.scad

@@ -0,0 +1,378 @@
+// =============================================================================
+// SaltyBot — Battery Stem Clamp  (Part B)
+// Agent: sl-mechanical  |  2026-02-28
+//
+// HEIGHT-ADJUSTABLE battery carousel that slides on the central vertical stem.
+// 2–4 battery packs stand UPRIGHT, arranged radially around the mast.
+//
+// HOW IT WORKS
+//   1. Two collar halves clamp around the stem at the desired height.
+//   2. Radial arms project outward from the collar (one per battery pack).
+//   3. Each arm tip has a battery cradle — an upward-open U-channel that
+//      the pack slides into from above.
+//   4. Velcro straps thread through cradle slots and cinch around the pack.
+//   5. Loosen the M6 collar bolts → slide up/down for CG tuning.
+//      Tighten → locks in place.
+//
+// BATTERY (each pack, standing vertically):
+//   420 mm tall × 88 mm wide × 56 mm deep  (verified)
+//
+// ANGULAR LAYOUT
+//   BATT_COUNT = 2 → arms at  90° and 270°   (±Y, balanced front/rear)
+//   BATT_COUNT = 4 → arms at  45°, 135°, 225°, 315°  (each collar half owns 2)
+//   BATT_COUNT = 3 → arms at  90°, 210°, 330°
+//
+// PARTS (set RENDER= to export each)
+//   collar_half   — 3D print × 2   (mirror pair, RENDER="collar_half")
+//   arm           — laser-cut or print × BATT_COUNT  (RENDER="arm_2d" for DXF)
+//   battery_cradle — 3D print × BATT_COUNT  (RENDER="cradle")
+//
+// STEM
+//   38.1 mm OD × 1.5 mm wall 6061-T6 aluminium tube (or 1.5" EMT conduit).
+//   Cut to ~1050 mm.  Clamp can sit anywhere from 150 mm to 850 mm height.
+// =============================================================================
+
+$fn = 64;
+
+// =============================================================================
+// STEM
+// =============================================================================
+
+STEM_OD         = 38.1;
+STEM_BORE       = STEM_OD + 0.5;   // collar bore clearance
+
+// =============================================================================
+// COLLAR
+// =============================================================================
+
+COLLAR_H        = 80.0;   // mm  taller = more grip / less slip risk
+COLLAR_OD       = 84.0;   // mm  outer diameter  (wall = (84−38.6)/2 ≈ 22.7 mm)
+
+// Split plane: Y = 0  (each half is the +Y or −Y side)
+// Clamping bolts go through both halves at (±COLLAR_BOLT_X, 0, Z)
+COLLAR_BOLT_X   = 24.0;   // mm  bolt ±X from stem axis
+COLLAR_BOLT_D   =  6.5;   // M6 clearance
+COLLAR_NUT_D    = 11.0;   // M6 hex nut AF + 0.5 mm tolerance (point-to-point ≈ 10.4, use 11)
+COLLAR_NUT_H    =  5.2;   // M6 standard nut height + 0.2 mm
+
+// Height-lock / anti-rotation set screw (M6 thread on outer face of each half)
+SETSCREW_D      =  6.1;   // through-hole for M6 set screw
+
+// Arm attachment pads on collar exterior (flat boss, one per arm)
+ARM_PAD_W       = 32.0;   // mm  pad width (tangential)
+ARM_PAD_H       = 18.0;   // mm  pad height
+ARM_PAD_T       =  4.0;   // mm  pad protrusion from collar surface
+ARM_BOLT_D      =  4.3;   // M4 clearance  (arm-to-collar bolt)
+ARM_BOLT_SPAN   = 16.0;   // mm  C/L-to-C/L of two arm attachment bolts
+
+// =============================================================================
+// ARMS & BATTERIES
+// =============================================================================
+
+BATT_COUNT      = 4;      // 2, 3, or 4
+BATT_L          = 420.0;  // mm  pack height (vertical)
+BATT_W          =  88.0;  // mm  pack width  (tangential)
+BATT_D          =  56.0;  // mm  pack depth  (radial, into stem)
+BATT_CL         =   0.8;  // mm  all-round clearance in cradle
+
+ARM_REACH       =  55.0;  // mm  collar surface → battery near face
+ARM_W           =  28.0;  // mm  arm width
+ARM_THICK       =   8.0;  // mm  arm thickness (3D-print); 4 mm if laser-cut Al
+ARM_CRADLE_D    =  4.3;   // M4 clearance (cradle-to-arm bolt)
+
+// =============================================================================
+// BATTERY CRADLE
+// =============================================================================
+
+CRADLE_H        =  80.0;  // mm  cradle height (pack extends BATT_L-CRADLE_H above)
+CRADLE_WALL     =   4.5;  // mm  wall thickness
+CRADLE_STRAP_W  =  25.0;  // mm  Velcro strap slot width
+CRADLE_STRAP_T  =   6.0;  // mm  slot height
+
+// =============================================================================
+// ANGULAR PLACEMENT
+// =============================================================================
+
+// First arm angle chosen so all arms are clear of the Y=0 split plane
+ARM_START = (BATT_COUNT == 2) ? 90  :
+            (BATT_COUNT == 4) ? 45  :
+            /* 3 */              90  ;
+
+// Helper: is arm i on the +Y half (side=+1) or −Y half (side=−1)?
+// side = +1  →  sin(angle) >= 0
+// side = -1  →  sin(angle) <  0
+function arm_angle(i) = ARM_START + i * (360 / BATT_COUNT);
+function arm_on_side(i, side) =
+    (side > 0) ? (sin(arm_angle(i)) >= -0.001) :
+                 (sin(arm_angle(i)) <=  0.001);
+
+// =============================================================================
+// RENDER CONTROL
+// =============================================================================
+
+// "assembly"     — full 3-D preview with ghosts
+// "collar_half"  — single collar half for printing  (print 2, one mirrored)
+// "arm"          — single arm for printing or laser-cut
+// "arm_2d"       — 2-D DXF projection of arm
+// "cradle"       — single battery cradle for printing
+
+RENDER = "assembly";
+
+if (RENDER == "assembly") {
+    assembly();
+} else if (RENDER == "collar_half") {
+    collar_half(side=1);
+} else if (RENDER == "arm") {
+    arm();
+} else if (RENDER == "arm_2d") {
+    projection(cut=true) translate([0, 0, -ARM_THICK/2]) arm();
+} else if (RENDER == "cradle") {
+    battery_cradle();
+}
+
+// =============================================================================
+// ASSEMBLY
+// =============================================================================
+
+module assembly() {
+    // Collar halves
+    color("LightSlateGray", 0.88)  collar_half(side= 1);
+    color("SlateGray",      0.88)  collar_half(side=-1);
+
+    // Arms + cradles at each battery position
+    for (i = [0 : BATT_COUNT - 1]) {
+        a = arm_angle(i);
+        rotate([0, 0, a]) {
+            // Arm: originates at collar surface, runs along +X
+            color("DimGray", 0.90)
+                translate([COLLAR_OD/2, 0, (COLLAR_H - ARM_THICK) / 2])
+                    arm();
+
+            // Cradle: at arm tip
+            color("SteelBlue", 0.85)
+                translate([COLLAR_OD/2 + ARM_REACH,
+                           -(BATT_W/2 + BATT_CL + CRADLE_WALL),
+                           (COLLAR_H - CRADLE_H) / 2])
+                    battery_cradle();
+
+            // Battery ghost (not for export)
+            %color("DarkGoldenrod", 0.30)
+                translate([COLLAR_OD/2 + ARM_REACH + CRADLE_WALL,
+                           -(BATT_W/2 + BATT_CL),
+                           (COLLAR_H - CRADLE_H) / 2])
+                    cube([BATT_D + 2*BATT_CL, BATT_W + 2*BATT_CL, BATT_L]);
+        }
+    }
+
+    // Stem ghost
+    %color("Gray", 0.20)
+        translate([0, 0, -(COLLAR_H * 2)])
+            cylinder(d=STEM_OD, h=COLLAR_H * 14);
+}
+
+// =============================================================================
+// COLLAR HALF
+// =============================================================================
+// Printed flat-side-down (split face = print bed).
+// Print TWO: one as-is (side=+1), one mirrored in slicer (side=−1).
+// They are identical; the mirror instruction handles orientation.
+//
+// Bolt pattern:
+//   4× M6 through the flat face (2 per half at ±COLLAR_BOLT_X)
+//   M6 hex nut pockets on the flat face (captured before assembly)
+//   1× M6 set screw on the outer curved surface (height lock)
+//
+// Arm attachment:
+//   Raised pad on outer curved surface at each arm angle for this half.
+//   2× M4 through-holes per pad; M4 hex nut pocket on inside of collar wall.
+
+module collar_half(side = 1) {
+    mid_z   = COLLAR_H / 2;
+    wall_t  = (COLLAR_OD - STEM_BORE) / 2;
+    // Half of collar: the Y≥0 half (side=+1) or Y≤0 half (side=−1)
+
+    difference() {
+        union() {
+            // ── Half-cylinder body ──────────────────────────────────────
+            intersection() {
+                cylinder(d=COLLAR_OD, h=COLLAR_H);
+                // Keep only the appropriate half
+                translate([-COLLAR_OD/2 - 1,
+                           (side > 0) ? 0 : -COLLAR_OD - 1,
+                           -1])
+                    cube([COLLAR_OD + 2, COLLAR_OD + 1, COLLAR_H + 2]);
+            }
+
+            // ── Arm attachment pads ──────────────────────────────────────
+            for (i = [0 : BATT_COUNT - 1]) {
+                if (arm_on_side(i, side)) {
+                    a = arm_angle(i);
+                    rotate([0, 0, a])
+                        translate([COLLAR_OD/2, -ARM_PAD_W/2,
+                                   mid_z - ARM_PAD_H/2])
+                            cube([ARM_PAD_T, ARM_PAD_W, ARM_PAD_H]);
+                }
+            }
+        }
+
+        // ── Stem bore ────────────────────────────────────────────────────
+        translate([0, 0, -1])
+            cylinder(d=STEM_BORE, h=COLLAR_H + 2);
+
+        // ── Clamping bolt holes (2× through flat split face) ─────────────
+        // Bolt axis: along Y (perpendicular to split plane)
+        // Holes at (±COLLAR_BOLT_X, 0, COLLAR_H/3) and (±COLLAR_BOLT_X, 0, 2*COLLAR_H/3)
+        for (bx = [-COLLAR_BOLT_X, COLLAR_BOLT_X])
+        for (bz = [COLLAR_H/3, 2*COLLAR_H/3])
+            translate([bx, -1, bz])
+                rotate([-90, 0, 0])
+                    cylinder(d=COLLAR_BOLT_D, h=COLLAR_OD/2 + 2);
+
+        // ── M6 nut pockets on outer flat face of each half ───────────────
+        // Pocket depth = COLLAR_NUT_H from the far curved side inward.
+        // This allows pre-installing the nuts before bolting the halves together.
+        for (bx = [-COLLAR_BOLT_X, COLLAR_BOLT_X])
+        for (bz = [COLLAR_H/3, 2*COLLAR_H/3])
+            translate([bx, side * (COLLAR_OD/2 - COLLAR_NUT_H), bz])
+                rotate([-90, 0, 0])
+                    cylinder(d=COLLAR_NUT_D, h=COLLAR_NUT_H + 1, $fn=6);
+
+        // ── Set screw hole (M6, on curved outer surface at mid-height) ────
+        translate([0, side * (COLLAR_OD/2 + 1), COLLAR_H/2])
+            rotate([90, 0, 0])
+                cylinder(d=SETSCREW_D, h=COLLAR_OD/2 + 2);
+
+        // ── Arm bolt holes + nut pockets (through collar wall per arm) ────
+        for (i = [0 : BATT_COUNT - 1]) {
+            if (arm_on_side(i, side)) {
+                a = arm_angle(i);
+                for (dy = [-ARM_BOLT_SPAN/2, ARM_BOLT_SPAN/2])
+                    rotate([0, 0, a])
+                        translate([STEM_BORE/2 - 1, dy, mid_z])
+                            rotate([0, 90, 0]) {
+                                // Through-hole (M4 clearance all the way)
+                                cylinder(d=ARM_BOLT_D,
+                                         h=COLLAR_OD/2 - STEM_BORE/2 + ARM_PAD_T + 2);
+                                // Nut pocket on bore interior face
+                                cylinder(d=10, h=4.5, $fn=6);
+                            }
+            }
+        }
+    }
+}
+
+// =============================================================================
+// ARM
+// =============================================================================
+// Flat bar, ARM_REACH × ARM_W × ARM_THICK.
+// Collar end: 2× M4 clearance holes at ±ARM_BOLT_SPAN/2 in Y.
+// Cradle end: 2× M4 clearance holes at ±(ARM_W/2 - 8) in Y.
+// Can be laser-cut from 4 mm Al plate (reduce ARM_THICK to 4 in RENDER="arm_2d").
+
+module arm() {
+    difference() {
+        translate([0, -ARM_W/2, 0])
+            cube([ARM_REACH, ARM_W, ARM_THICK]);
+
+        // Collar-end bolt holes (M4, match arm pad on collar)
+        for (dy = [-ARM_BOLT_SPAN/2, ARM_BOLT_SPAN/2])
+            translate([8, dy, -1])
+                cylinder(d=ARM_BOLT_D, h=ARM_THICK + 2);
+
+        // Cradle-end bolt holes (M4)
+        for (dy = [-(ARM_W/2 - 8), ARM_W/2 - 8])
+            translate([ARM_REACH - 10, dy, -1])
+                cylinder(d=ARM_CRADLE_D, h=ARM_THICK + 2);
+
+        // Lightening slot in centre (optional — reduces print material)
+        if (ARM_REACH > 40) {
+            slot_l = ARM_REACH - 34;
+            slot_w = ARM_W - 16;
+            translate([17, -slot_w/2, -1])
+                hull() {
+                    translate([slot_w/2, slot_w/2, 0]) cylinder(d=slot_w/2*0.8, h=ARM_THICK+2);
+                    translate([slot_l - slot_w/2, slot_w/2, 0]) cylinder(d=slot_w/2*0.8, h=ARM_THICK+2);
+                }
+        }
+    }
+}
+
+// =============================================================================
+// BATTERY CRADLE
+// =============================================================================
+// U-channel, open top for pack insertion from above.
+// Inner pocket: (BATT_D + 2*BATT_CL) radially × (BATT_W + 2*BATT_CL) tangentially.
+// Cradle height CRADLE_H — battery extends (BATT_L − CRADLE_H) above the cradle.
+//
+// Strap slots: 2× horizontal slots through front+rear walls (Velcro through-pass).
+// Base bolt holes: 2× M4 for arm attachment (arm bolts up through arm into cradle).
+
+module battery_cradle() {
+    cw  = CRADLE_WALL;
+    id  = BATT_D + 2*BATT_CL;  // inner depth  (radial, +X direction)
+    iw  = BATT_W + 2*BATT_CL;  // inner width  (tangential, Y direction)
+
+    difference() {
+        // Outer block
+        cube([id + 2*cw, iw + 2*cw, CRADLE_H]);
+
+        // Battery slot (open top: subtract from cw to top + 1)
+        translate([cw, cw, -1])
+            cube([id, iw, CRADLE_H + 2]);
+
+        // Strap slots — through left and right walls (Y faces), 2 heights
+        for (sz = [CRADLE_H * 0.30, CRADLE_H * 0.65])
+            translate([-1, cw + (iw - CRADLE_STRAP_W) / 2, sz])
+                cube([id + 2*cw + 2, CRADLE_STRAP_W, CRADLE_STRAP_T]);
+
+        // Arm attachment holes in floor (2× M4)
+        for (dy = [cw + iw/2 - ARM_BOLT_SPAN/2,
+                   cw + iw/2 + ARM_BOLT_SPAN/2])
+            translate([cw + id/2, dy, -1])
+                cylinder(d=ARM_CRADLE_D, h=cw + 2);
+
+        // Corner chamfers (front face — aids pack insertion)
+        chamfer_s = 5;
+        for (cy = [cw - 0.01, cw + iw - chamfer_s + 0.01])
+            translate([cw - 0.01, cy, CRADLE_H - chamfer_s])
+                rotate([0, 45, 0])
+                    cube([chamfer_s * 1.42, chamfer_s, chamfer_s * 1.42]);
+    }
+}
+
+// =============================================================================
+// DXF / PRINT EXPORT
+// =============================================================================
+//
+//  COLLAR HALF  (3D print × 2 — print one as-is, mirror second in slicer):
+//    openscad stem_battery_clamp.scad -D 'RENDER="collar_half"' -o collar_half.stl
+//    Print settings: PETG, 5 perimeters, 40% infill, 0.2 mm layer, no supports needed
+//    (flat split face sits on bed; overhangs ≤ 45°)
+//
+//  ARM  — 3D print or laser-cut × BATT_COUNT:
+//    Print:       openscad stem_battery_clamp.scad -D 'RENDER="arm"' -o arm.stl
+//    Laser (DXF): openscad stem_battery_clamp.scad \
+//                   -D 'RENDER="arm_2d"' -D 'ARM_THICK=4' -o arm.dxf
+//    Laser material: 4 mm 5052-H32 aluminium
+//
+//  BATTERY CRADLE  (3D print × BATT_COUNT):
+//    openscad stem_battery_clamp.scad -D 'RENDER="cradle"' -o cradle.stl
+//    Print settings: PETG, 4 perimeters, 30% infill, 0.25 mm layer
+//
+// =============================================================================
+//
+// ASSEMBLY SEQUENCE
+//   1. Print collar halves × 2, cradles × BATT_COUNT.
+//   2. Laser-cut (or print) arms × BATT_COUNT.
+//   3. Press M4 hex nuts into collar bore-face pockets.
+//   4. Wrap collar halves around stem; thread M6 bolts through both halves.
+//      Do not fully tighten yet — position to desired height.
+//   5. Bolt each arm to its collar pad (M4 × 20 SHCS from arm outward).
+//   6. Bolt each cradle to its arm tip (M4 × 16 SHCS from below).
+//   7. Drop battery packs into cradles from above; route Velcro straps.
+//   8. Tighten M6 collar bolts (≈ 6 N·m each).  Use M6 set screw for rotation lock.
+//
+// CG TUNING
+//   Loosen M6 collar bolts (do not fully remove). Slide entire carousel up/down.
+//   Re-tighten. Typical balance point: batteries at 400–600 mm above base plate.
+// =============================================================================