Explore and validate joint design for PETG/PLA + TPU prints (5 candidate joints + OpenSCAD CAD + anchor-upset shape variants + Design F captive-core + Edison Phase-1/2/3/5 + Phase-4 submitted + lander-context reco + TPU-inside vs TPU-outside comparison...

cad/joint-design/A_anchor_bulb.scad

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+// =============================================================================
+// Design A — Anchor-bulb spherical node
+// =============================================================================
+// PETG sphere at each tensegrity vertex with through-holes; TPU cable threads
+// through and is terminated in a printed-in-place TPU bulb on the far side.
+// Per Edison Phase-3 ANALYSIS 19e0c868 §3 (CAD review) geometry, which
+// supersedes the earlier c38a2046 / ce84ddf8 numbers (raises bulb-to-bore
+// pull-through ratio from 1.38× to 1.71×):
+//   - Node OD ≈ 9.5 mm (was 9.0; cleanly encases the 2.8 mm bore while
+//     preserving perimeter thickness)
+//   - Through-bore Ø ≈ 2.8 mm (0.4 mm clearance over 2.4 mm cable)
+//   - Bulb OD ≈ 4.8 mm (printed-in-place TPU on the far side; 1.71× bore,
+//     full 1.0 mm radial TPU bearing against the PETG face)
+// One PETG strut enters the node from -Z; one TPU cable passes through it
+// horizontally along +X, terminated in a bulb on the +X side.
+// =============================================================================
+include <_common.scad>
+
+node_d  = 9.5;       // PETG node sphere outer diameter
+bore_d  = 2.8;       // through-hole diameter (cable_d + 0.4 mm clearance)
+bulb_d  = 4.8;       // TPU bulb outer diameter at far end of cable (1.71× bore)
+bulb_off = node_d/2 + 1.5;  // bulb center distance from node center along +X
+
+module designA_petg() {
+    difference() {
+        union() {
+            sphere(d=node_d);
+            translate([0, 0, -strut_l]) cylinder(h=strut_l, d=strut_d);
+        }
+        // Horizontal cable bore along +X (clear right through the node)
+        translate([-node_d, 0, 0]) rotate([0, 90, 0])
+            cylinder(h=2*node_d, d=bore_d);
+    }
+}
+
+module designA_tpu() {
+    // Cable on the entry (-X) side
+    translate([-cable_l, 0, 0]) rotate([0, 90, 0])
+        cylinder(h=cable_l, d=cable_d);
+    // Cable through the bore + a short stub past the bulb's near face
+    translate([-node_d/2 - 0.1, 0, 0]) rotate([0, 90, 0])
+        cylinder(h=node_d + 1.5, d=cable_d);
+    // Anchor bulb on the +X side
+    translate([bulb_off, 0, 0]) sphere(d=bulb_d);
+}
+
+module designA() {
+    petg() designA_petg();
+    tpu()  designA_tpu();
+}
+
+designA();

cad/joint-design/A_anchor_bulb_section_X.scad

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+// Section view of Design A — cut at the X=0 plane, keep +X half (cut at X=0).
+// Apply intersection per-color part so PETG/TPU colors survive the CSG.
+include <_common.scad>
+use <A_anchor_bulb.scad>
+
+module half_cube_X() { translate([0, -30, -40]) cube([60, 60, 60]); }
+
+petg() intersection() { designA_petg(); half_cube_X(); }
+tpu()  intersection() { designA_tpu();  half_cube_X(); }

cad/joint-design/A_anchor_bulb_section_Y.scad

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+// Section view of Design A — anchor-bulb spherical node cut at Y=0 (keep
+// -Y half so the camera at -Y sees the cut face). Apply intersection
+// per-color part so PETG/TPU colors survive the CSG operation.
+include <_common.scad>
+use <A_anchor_bulb.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA_petg(); half_cube_negY(); }
+tpu()  intersection() { designA_tpu();  half_cube_negY(); }

cad/joint-design/A_anchor_bulb_section_Z.scad

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+// Section view of Design A — cut at the Z=0 plane, keep +Z half above the joint mid-plane (cut at Z=-2).
+// Apply intersection per-color part so PETG/TPU colors survive the CSG.
+include <_common.scad>
+use <A_anchor_bulb.scad>
+
+module half_cube_Z() { translate([-30, -30, -2]) cube([60, 60, 60]); }
+
+petg() intersection() { designA_petg(); half_cube_Z(); }
+tpu()  intersection() { designA_tpu();  half_cube_Z(); }

cad/joint-design/A_variants/A0_sphere.scad

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+// =============================================================================
+// Design A0 — Reference: spherical bulb (the original Phase-3 geometry)
+// =============================================================================
+// Included here purely as the visual baseline so the four alternative upset
+// shapes (frustum, torus, countersunk, lobed, mushroom) have something to
+// be montaged against. Geometry is identical to `A_anchor_bulb.scad`.
+// =============================================================================
+include <_common_variants.scad>
+
+bulb_d   = upset_od;                // 4.8 mm sphere upset
+bulb_off = upset_x + bulb_d/2 - 0.5; // a little embedded into the +X face
+
+module designA0_petg() { nodeA_petg(); }
+
+module designA0_tpu() {
+    nodeA_tpu_cable();
+    translate([bulb_off, 0, 0]) sphere(d=bulb_d);
+}
+
+module designA0() {
+    petg() designA0_petg();
+    tpu()  designA0_tpu();
+}
+
+designA0();

cad/joint-design/A_variants/A0_sphere_section_Y.scad

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+// Section view (cut at Y=0) for variant A0_sphere. Keep -Y half so the camera
+// at -Y sees the cut face. Apply intersection per-color part so the
+// PETG/TPU colours survive the CSG operation.
+include <_common_variants.scad>
+use <A0_sphere.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA0_petg(); half_cube_negY(); }
+tpu()  intersection() { designA0_tpu();  half_cube_negY(); }

cad/joint-design/A_variants/A1_frustum.scad

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+// =============================================================================
+// Design A1 — Truncated cone / frustum (rivet-head) upset
+// =============================================================================
+// Replaces the spherical bulb of the reference design with a flat-topped
+// frustum so the TPU bears against the PETG/PLA face on a flat annulus
+// instead of a curved spherical cap. The flat top also lays down cleanly
+// under the H2D top-layer pass (no curved free surface).
+//
+// Shape parameters:
+//   - Base OD (against the PETG face) = upset_od (4.8 mm) → preserves the
+//     1.71× pull-through ratio of the reference geometry.
+//   - Top OD                          = 3.6 mm (75 % of base) → gentle 30°
+//     half-angle, self-supporting in TPU 85A on a Bambu H2D without supports.
+//   - Height                          = 2.4 mm → ~6 layers at 0.4 mm.
+// Bearing area (flat annulus between bore Ø 2.8 and base Ø 4.8) = 6.0 mm²
+// (vs. ≈3.4 mm² projected bearing on the reference sphere) → ~75 % more
+// load-spreading area at the same OD.
+// =============================================================================
+include <_common_variants.scad>
+
+base_d  = upset_od;        // 4.8 mm at the PETG face
+top_d   = 3.6;             // 75 % of base — 30° half-angle
+height  = 2.4;             // 6 layers at 0.4 mm
+base_x  = upset_x - 0.3;   // a touch embedded in the +X face for fusion
+
+module designA1_petg() { nodeA_petg(); }
+
+module designA1_tpu() {
+    nodeA_tpu_cable();
+    // Frustum aligned with the cable axis (+X).
+    translate([base_x, 0, 0]) rotate([0, 90, 0])
+        cylinder(h=height, d1=base_d, d2=top_d);
+}
+
+module designA1() {
+    petg() designA1_petg();
+    tpu()  designA1_tpu();
+}
+
+designA1();

cad/joint-design/A_variants/A1_frustum_section_Y.scad

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+// Section view (cut at Y=0) for variant A1_frustum. Keep -Y half so the camera
+// at -Y sees the cut face. Apply intersection per-color part so the
+// PETG/TPU colours survive the CSG operation.
+include <_common_variants.scad>
+use <A1_frustum.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA1_petg(); half_cube_negY(); }
+tpu()  intersection() { designA1_tpu();  half_cube_negY(); }

cad/joint-design/A_variants/A2_torus.scad

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+// =============================================================================
+// Design A2 — Toroidal / donut upset
+// =============================================================================
+// Replaces the spherical bulb with a torus printed coaxially with the cable
+// so the PETG/PLA face bears on the inner curve of the torus. The torus
+// distributes the bearing load over a wider annulus than the spherical cap
+// of the reference design, giving a lower peak contact stress under the
+// repeated drops of the lander demo (#16).
+//
+// Shape parameters:
+//   - Major OD   = upset_od (4.8 mm) → preserves the 1.71× pull-through ratio
+//   - Tube Ø     = 1.8 mm → 3-perimeter wall in TPU at 0.4 mm nozzle
+//   - Major R    = (major_od - tube_d) / 2 = 1.5 mm
+// The cable shaft passes through the hole in the centre of the torus; the
+// inner radius of the torus (= 0.6 mm) is < cable radius (1.2 mm) so the
+// torus wraps around and grips the cable shaft — this is what closes the
+// load path against the PETG/PLA face.
+// =============================================================================
+include <_common_variants.scad>
+
+major_od = upset_od;            // 4.8 mm overall OD
+tube_d   = 1.8;                 // 3-perimeter wall at 0.4 mm nozzle
+major_r  = (major_od - tube_d)/2;
+torus_x  = upset_x + tube_d/2;  // bearing face flush against +X of node
+
+module torus(major_r, tube_d) {
+    rotate_extrude(convexity=4)
+        translate([major_r, 0, 0])
+            circle(d=tube_d);
+}
+
+module designA2_petg() { nodeA_petg(); }
+
+module designA2_tpu() {
+    nodeA_tpu_cable();
+    // Torus axis coincides with the cable axis (+X) — rotate the XY-plane
+    // torus 90° about Y so it sits with its hole facing -X.
+    translate([torus_x, 0, 0]) rotate([0, 90, 0])
+        torus(major_r, tube_d);
+}
+
+module designA2() {
+    petg() designA2_petg();
+    tpu()  designA2_tpu();
+}
+
+designA2();

cad/joint-design/A_variants/A2_torus_section_Y.scad

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+// Section view (cut at Y=0) for variant A2_torus. Keep -Y half so the camera
+// at -Y sees the cut face. Apply intersection per-color part so the
+// PETG/TPU colours survive the CSG operation.
+include <_common_variants.scad>
+use <A2_torus.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA2_petg(); half_cube_negY(); }
+tpu()  intersection() { designA2_tpu();  half_cube_negY(); }

cad/joint-design/A_variants/A3_countersunk.scad

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+// =============================================================================
+// Design A3 — Conical (countersunk) head — flush, self-centring
+// =============================================================================
+// Replaces the protruding bulb with a conical TPU head that mates a matching
+// countersink cut into the +X exit of the PETG/PLA bore. The result is a
+// flush far face (no protruding feature to snag on impact) and the cone
+// self-centres the cable in the bore as the joint loads up.
+//
+// Shape parameters (90° included angle, standard ANSI flat-head):
+//   - Countersink mouth Ø = upset_od (4.8 mm) at the +X face
+//   - Cone bottom Ø       = bore_d   (2.8 mm) where it meets the cable
+//   - Half-angle          = 45° → cone axial depth = (4.8-2.8)/2 = 1.0 mm
+//   - Total head height   = 1.6 mm (1.0 mm cone + 0.6 mm flat top, just so
+//                                   the head is clearly visible in the iso
+//                                   render — set to 0.0 for true flush)
+// Functional bearing area is the full conical wall = π·(R+r)·s ≈ 8.8 mm²
+// (vs. ≈3.4 mm² projected on the reference sphere) → ~2.6× more bearing
+// area at the same OD.
+// =============================================================================
+include <_common_variants.scad>
+
+cs_mouth_d = upset_od;          // 4.8 mm at the +X face
+cs_root_d  = bore_d;            // 2.8 mm where the cable shaft enters
+cs_depth   = (cs_mouth_d - cs_root_d) / 2;   // 45° → 1.0 mm
+head_top_h = 0.6;               // 0 = perfectly flush; nonzero for visibility
+
+module designA3_petg() {
+    difference() {
+        nodeA_petg();
+        // Cut a 45° countersink into the +X face: narrow (root) end deeper
+        // inside the node, wide (mouth) end at the +X face.
+        translate([upset_x - cs_depth, 0, 0]) rotate([0, 90, 0])
+            cylinder(h=cs_depth + 0.01, d1=cs_root_d, d2=cs_mouth_d);
+    }
+}
+
+module designA3_tpu() {
+    nodeA_tpu_cable();
+    // Conical head filling the countersink (root at -X, mouth at +X face),
+    // plus a thin flat top extending past the +X face for visibility.
+    translate([upset_x - cs_depth, 0, 0]) rotate([0, 90, 0])
+        cylinder(h=cs_depth, d1=cs_root_d, d2=cs_mouth_d);
+    translate([upset_x, 0, 0]) rotate([0, 90, 0])
+        cylinder(h=head_top_h, d=cs_mouth_d);
+}
+
+module designA3() {
+    petg() designA3_petg();
+    tpu()  designA3_tpu();
+}
+
+designA3();

cad/joint-design/A_variants/A3_countersunk_section_Y.scad

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+// Section view (cut at Y=0) for variant A3_countersunk. Keep -Y half so the camera
+// at -Y sees the cut face. Apply intersection per-color part so the
+// PETG/TPU colours survive the CSG operation.
+include <_common_variants.scad>
+use <A3_countersunk.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA3_petg(); half_cube_negY(); }
+tpu()  intersection() { designA3_tpu();  half_cube_negY(); }

cad/joint-design/A_variants/A4_lobed.scad

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+// =============================================================================
+// Design A4 — Star / lobed / knurled head (rotational keying)
+// =============================================================================
+// Replaces the spherical bulb with a 6-lobed star head so the upset can't
+// rotate relative to the bore under repeated drops. This is what the lander
+// demo (#16) Bruceton n≥20 reuse case actually wants — every drop
+// reseats the joint at a slightly different angle, and a smooth bulb just
+// spins; a lobed head torsionally keys against the bore exit.
+//
+// Shape parameters:
+//   - Bounding OD            = upset_od (4.8 mm) → preserves 1.71× ratio
+//   - Lobe count             = 6
+//   - Lobe Ø (each)          = 1.6 mm → 4-perimeter feature in TPU at 0.4 mm
+//   - Lobe centre radius     = 1.4 mm from cable axis
+//   - Head thickness         = 1.6 mm along +X
+// The PETG/PLA bore is left round (Ø 2.8 mm); the lobes engage the +X face
+// of the node when the cable pulls in -X. Optionally one could match the
+// bore mouth with a 6-lobe profile to fully constrain rotation; here we
+// leave the bore round so the joint stays drop-in compatible with the
+// reference geometry and only change the head.
+// =============================================================================
+include <_common_variants.scad>
+
+bound_d   = upset_od;           // 4.8 mm bounding circle
+lobes     = 6;
+lobe_d    = 1.6;
+lobe_r    = (bound_d - lobe_d) / 2;   // 1.6 mm centre offset → 4.8 mm bound
+head_th   = 1.6;                // 4 layers at 0.4 mm
+head_x    = upset_x - 0.3;      // a touch embedded in the +X face
+
+module star_head(thickness, lobes, lobe_d, lobe_r, hub_d) {
+    // 2D star + central hub, then linear-extruded along +Z.
+    linear_extrude(height=thickness, convexity=8) {
+        union() {
+            circle(d=hub_d);
+            for (i = [0:lobes-1]) {
+                rotate([0, 0, i * 360 / lobes])
+                    translate([lobe_r, 0, 0])
+                        circle(d=lobe_d);
+            }
+        }
+    }
+}
+
+module designA4_petg() { nodeA_petg(); }
+
+module designA4_tpu() {
+    nodeA_tpu_cable();
+    // Lobed disc on the cable axis (+X). Hub Ø ≥ bore so the head fully
+    // covers the bore exit; lobes radiate outward in the Y-Z plane.
+    translate([head_x, 0, 0]) rotate([0, 90, 0])
+        star_head(thickness=head_th, lobes=lobes, lobe_d=lobe_d,
+                  lobe_r=lobe_r, hub_d=bore_d + 0.6);
+}
+
+module designA4() {
+    petg() designA4_petg();
+    tpu()  designA4_tpu();
+}
+
+designA4();

cad/joint-design/A_variants/A4_lobed_section_Y.scad

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+// Section view (cut at Y=0) for variant A4_lobed. Keep -Y half so the camera
+// at -Y sees the cut face. Apply intersection per-color part so the
+// PETG/TPU colours survive the CSG operation.
+include <_common_variants.scad>
+use <A4_lobed.scad>
+
+module half_cube_negY() { translate([-30, -30, -40]) cube([60, 30, 60]); }
+
+petg() intersection() { designA4_petg(); half_cube_negY(); }
+tpu()  intersection() { designA4_tpu();  half_cube_negY(); }