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...

[Copilot]

Extensively explore and validate joint design for PETG/PLA (struts) + TPU (cables) prints meant to mimic tensegrity.

Edison query batch

• Fetched + committed Edison trajectories 1400ca69 (commercial-tensegrity collaborators) and 3b9d76b5 (academic venues) → edison-trajectories/{1400ca69…,3b9d76b5…}.{md,json}.
• Surveyed existing joint context across the repo (issues Document Lansmont M23 drop tower and Polytec QTec laser vibrometer #28, Add runnable tensegrity simulation demos (MuJoCo, PyBullet, PyChrono, Newton, DiffPD, PolyFEM+IPC) + 3D animated renders + Edison survey + regime-aware sweeps + PLA/TPU 85A printable-design model + BO integration bridge + PR #35 Sobol T3-prism sweep ac... #33, Bambu Lab H2D TPU prints #37; PRs Add reference STL models for canonical tensegrity structures + Edison literature surveys (initial + design-gaps follow-up) #22, Explore TPU+PLA BO design variables and base structures (Edison literature result + PR #22 design-gaps synthesis, hierarchical search space) #24, Add T3-prism (3-strut tensegrity) parametric CAD with Bambu PETG .gcode.3mf slice + re-importable project .3mf (H2D-only, supports enabled, scale 1.5× / cable_d 4.5 mm) + PLA-cables and PLA-struts/TPU-cables MM variants (with modeled-in PLA scaffo... #35) and distilled 5 candidate joint design ideas grounded in the H2D PETG+TPU IDEX print stack and the in-progress single-piece T3-prism (PR Add T3-prism (3-strut tensegrity) parametric CAD with Bambu PETG .gcode.3mf slice + re-importable project .3mf (H2D-only, supports enabled, scale 1.5× / cable_d 4.5 mm) + PLA-cables and PLA-struts/TPU-cables MM variants (with modeled-in PLA scaffo... #35).
• Stage 1 — submitted one 1-credit LITERATURE Edison query per joint design idea (5 total) with proposal/CAD/literature/equipment context attached; all 5 fetched + committed (md+json):
  • A-anchor-bulb task 0b5d7ba2…
  • B-dovetail task ccb7b854…
  • C-tpu-sleeve-overmold task 5a7ffce4…
  • D-eyelet-loop task 727a449d…
  • E-tpu-rebar task ae373eb5…
• Stage 2 in tandem — LITERATURE_HIGH be6768ab… (prior-art ranking) + ANALYSIS c38a2046… (synthesis + design-for-test recommendation) — both fetched + committed (md+json).
• Submitted follow-up ANALYSIS ce84ddf8-5930-4c61-a6ce-65cf9ee3a6fa with all 5 Phase-1 outputs attached (the original c38a2046 only had C/D/E because A and B finished after submission). Fetched + committed: it inverts the recommendation to B (dovetail) primary + A (anchor-bulb) backup — the prior-art quantitative gap (Ermolai 2024 / Zhang 2021 reporting 6–24 MPa for FDM dovetails vs. Yavas 2022 1–2.7 MPa for the rebar-shear analog) outweighed E's theoretical simplicity.
• Synthesis edison-trajectories/joint-design/README.md links every artifact, contrasts the two Phase-2 rankings, and surfaces the original recommendation. task_manifest.json records every submitted task ID, its attachments, and its status.

OpenSCAD CAD models, renders, and visual prior-art comparison

• Authored OpenSCAD CAD models for all 5 candidate joints under cad/joint-design/: A_anchor_bulb.scad, B_dovetail.scad, C_tpu_sleeve_overmold.scad, D_eyelet_loop.scad, E_tpu_rebar.scad, plus per-design three-orthogonal-plane cutaway variants *_section_{X,Y,Z}.scad and a shared _common.scad parameter file. Initial geometry followed the Phase-2 ANALYSIS recommendations.
• cad/joint-design/render.sh produces iso + section PNG renders + STL exports for each design and assembles four contact-sheet montages: renders/all_iso_montage.png, renders/all_section_montage.png (Y-cut row), renders/all_compare_montage.png (CAD-vs-reference side-by-side), and renders/all_multiplane_section_montage.png (4×5 grid: iso + 3 orthogonal cuts × 5 designs).
• Curated public reference images for visual prior-art comparison at cad/joint-design/references/README.md — verified-200 Wikimedia Commons URLs (tensegrity 3-prism, finished dovetail joint, hose clamp, chain-link fence, rebar loop, anchor-bolt SVG, etc.) plus DOIs of the closest peer-reviewed prior-art papers (Pajunen 2019, Ermolai 2024, Zhang 2021, Khatri 2024, Yavas 2022, Mortensen 2025). 5 reference JPEGs downloaded locally and resized.

Phase-3 follow-up Edison ANALYSIS (CAD review against published prior art) — fetched + applied

• Submitted Edison ANALYSIS 19e0c868-3587-440d-ba4a-07da4dddf99a attaching the zipped cad/joint-design/ directory (5 SCAD + section variants + 13 PNG renders + 5 STL + 3 montages + references README + 5 reference JPEGs), the ce84ddf8 followup, the joint-design synthesis README, and task_manifest.json.
• Submission script committed at scripts/edison/submit_joint_cad_review.py; submission record (task ID + every attached data_entry: URI) at edison-trajectories/joint-design/PHASE3-cad-review-SUBMITTED.json.
• Phase-3 result fetched + committed at edison-trajectories/joint-design/PHASE3-cad-review-19e0c868-3587-440d-ba4a-07da4dddf99a.{md,json}. task_manifest.json phase3.cad_review updated to success.
• Applied Phase-3 dimensional refinements to B_dovetail.scad (uni-axial primary):
  • node_d 9.0 → 12.0 mm (≥2-perimeter PETG cheek)
  • slot_mouth 6.4 → 5.4 mm, slot_inner 7.4 → 7.06 mm, slot_height 3.6 → 4.0 mm, slot_depth 5.0 → 6.0 mm
  • flank_deg 25 → 22.5° (Wang 2026 shear optimum)
  • Differential clearance: clear_lat 0.20 mm (Y, load-bearing), clear_roof 0.30 mm (Z, bridge sag) — Ermolai 2024
  • mouth_fillet 0.5 mm (Frascio 2024 TPU de-notch)
• Applied Phase-3 refinements to A_anchor_bulb.scad (lander/egg-drop primary; uni-axial backup):
  • node_d 9.0 → 9.5 mm, bore_d 2.9 → 2.8 mm, bulb_d 4.0 → 4.8 mm (raises pull-through ratio 1.38× → 1.71×)
• Re-ran cad/joint-design/render.sh → updated iso + section PNGs, STLs, and all four contact-sheet montages to reflect the refined B and A geometry.
• Updated synthesis README (edison-trajectories/joint-design/README.md) with a Phase-3 row + parameter-change tables.

Multi-plane cross-section pass + visualization bug fixes (per PR review feedback)

• Added per-design orthogonal cross-section .scad files at three cut planes (Y=0, X=0, Z=−2): A_anchor_bulb_section_{X,Y,Z}.scad, B_dovetail_section_{X,Y,Z}.scad, C_tpu_sleeve_overmold_section_{X,Y,Z}.scad, D_eyelet_loop_section_{X,Y,Z}.scad, E_tpu_rebar_section_{X,Y,Z}.scad.
• Generating these cuts surfaced two non-physical visualizations in the prior CAD, which were fixed:
  • B_dovetail.scad: TPU cable was emerging at z=0 while the dovetail head was centered at z=−3.5 — cable was floating in air, disconnected from the head. Cable now exits the +X face of the node along the slot centerline and is mechanically continuous with the head.
  • D_eyelet_loop.scad: refactored designD() into designD_petg() / designD_tpu() modules and clarified the eyelet-center geometry (eyelet_center_z constant) so the chain-link topology (linking number ±1) is visibly unambiguous from any of the three cut planes.
• New cad/joint-design/renders/all_multiplane_section_montage.png assembles iso + 3 cuts × 5 designs into a 4×5 grid for at-a-glance topology verification.

Lander/egg-drop (#16) and PLA (#45) integration

• Added a "Lander-context recommendation" section to the synthesis README: for the omnidirectional-impact, n≥20-Bruceton-drop egg-drop / planetary-lander demo (issue Submit Edison literature query tying tensegrity MRG framework to NASA space priorities, and commit fetched results #16), the recommended joint is A (anchor-bulb) with the Phase-3-refined geometry. B (co-printed dovetail / T-slot) remains the recommended joint for the uni-axial crutch-tip print.
• Documented that the strut material is now planned to be PLA per Edison query on strut material (PLA vs PETG vs HF/CF) — fetched + interpreted #45, not PETG.

Phase-4 Edison submissions (per PR review feedback) — non-blocking, fetch next session

• LITERATURE_HIGH f9804247-51f3-43de-a676-94b4b008b886 — project-context single-joint pick. Asks Edison to recommend one joint design (A–E) given the full project context: PLA struts per Edison query on strut material (PLA vs PETG vs HF/CF) — fetched + interpreted #45, TPU 85A tendons, lander/egg-drop demo per Submit Edison literature query tying tensegrity MRG framework to NASA space priorities, and commit fetched results #16 (Bruceton n≥20, omnidirectional impact, reusability), Bambu H2D IDEX print stack, and the Phase-3-refined geometry for A and B.
• ANALYSIS e9a1f4cc-7509-41b4-89e7-3f63ef406333 — per-design vision review with individual tiles. Attaches 27 individual files (5 .scad sources + 5 iso PNGs + 15 section_{X,Y,Z} PNGs + _common.scad + the joint-design README) — explicitly no mosaics — and specifically asks for confirmation of B-dovetail slot-axis cable continuity and D-eyelet chain-link topology.
• Submission script: scripts/edison/submit_joint_phase4.py. Submission records (task IDs + every attached data_entry: URI): edison-trajectories/joint-design/PHASE4-{context,vision}-SUBMITTED.json. task_manifest.json extended with a phase4 section.

Anchor-upset shape variants (per PR review feedback)

In response to the question of why design A uses a sphere, authored CAD + visualizations for 5 alternative TPU upset shapes for design A, all preserving the Phase-3 1.71× pull-through ratio (only the upset shape changes):

• A0 — spherical (reference baseline; matches A_anchor_bulb.scad)
• A1 — truncated cone / frustum (rivet head; flat bearing face for cleaner top-layer finish)
• A2 — torus / donut (distributes bearing load over a wider annulus, lower peak contact stress)
• A3 — conical countersunk head (flush, self-centering, ~8.8 mm² conical wall)
• A4 — 6-lobed / star / knurled head (rotational keying for Bruceton n≥20 reuse)
• A5 — mushroom / tee-head with 0.4 mm radiused undercut (Frascio 2024; maximum mechanical interlock per gram of TPU)

Design F — captive TPU core inside PETG/PLA outer shell

New Design F (cad/joint-design/F_captive_core.scad) — a non-feed-through anchor in which the TPU "knot" lives entirely inside a PETG/PLA outer shell:

• Ø7 mm TPU captive core inside Ø12 mm shell (Ø8 mm cavity, 0.5 mm radial print-in-place gap) — pull-out ratio 2.5× vs. 1.71× for Phase-3 A.
• Teardrop strut→shell fillet via convex hull — smooth blend, no stress riser.
• Layer-interlock teeth (per @achris0520) — two staggered rings of 8 radial teeth (PETG inward at z=+0.6 mm, TPU outward at z=−0.6 mm, 22.5° rotational stagger) so the captive core cannot translate ±Z without relying on PETG/PLA-TPU chemical adhesion.

Proposal correction — removed unverified Ye et al. tensegrity attribution

Edison Phase-5 ANALYSIS (28d942ea) confirmed that the ye2023multimaterial citation (Ye et al. 2023, Nature Communications — thick-panel origami metamaterials) does not describe a tensegrity core-wrapping strategy, and the DOI previously associated with the claim resolved to an unrelated paper (Filla et al., fibrin-fibre networks). Additionally, the description was topologically inverted relative to the actual project design (which uses a captive TPU core inside a PLA shell, not PLA struts encapsulated by TPU skins).

Removed all three occurrences of the incorrect attribution from proposal.tex:

• Background ¶ — deleted the "wrapping-based strategy (rigid cores encapsulated by continuous soft skins)" sentence; retained the PLA–TPU energy-absorption claim citing khatri2024energy alone.
• Intro ¶ — dropped ye2023multimaterial from the multi-material fabrication citation.
• Section 1 — removed the "Following \citet{ye2023multimaterial}, the designs use a core-wrapping strategy (rigid PLA struts encapsulated by continuous TPU skins)…" sentence entirely.

proposal.pdf and proposal-diff.pdf rebuilt to reflect the correction.

[sgbaird-yolo]

@copilot pick back up from where you left off

[Copilot]

@copilot pick back up from where you left off

Picked back up in 9b235f2. Phase-2 results are in: LITERATURE_HIGH be6768ab (prior-art ranking) and ANALYSIS c38a2046 (synthesis) both fetched and committed under edison-trajectories/joint-design/. The original ANALYSIS only had C/D/E attached (A and B finished after submission), so I also fired a follow-up ANALYSIS ce84ddf8-5930-4c61-a6ce-65cf9ee3a6fa with all 5 Phase-1 outputs + the LITERATURE_HIGH reply attached — non-blocking, will fetch next session. Synthesis README contrasts the two rankings (they are nearly inverted: prior art favors B-dovetail; best-for-us favors E-barbed-rebar) and gives the concrete primary/backup recommendation, the 12-specimen drop-test screening matrix, and per-design simulator-assumption-violation corrections.

[sgbaird-alt]

@copilot fetch all artifacts from these various Edison queries and commit. Find images of these types so I can better visualization. Use QueryCAD or similar to model what this would actually look like. Compare your CAD models with what you find online, visually, to help you refine the model. Send a follow up Edison query. Wait and fetch the results

[Copilot]

@copilot fetch all artifacts from these various Edison queries and commit. Find images of these types so I can better visualization. Use QueryCAD or similar to model what this would ac...

Done in 21360bd.

Artifacts fetched + committed. Pre-fetched followup ANALYSIS ce84ddf8 is now on disk at edison-trajectories/joint-design/PHASE2-analysis-followup-ce84ddf8…. It inverts the recommendation: now B (dovetail) primary, A (anchor-bulb) backup (vs. the original E/A from c38a2046), driven by Ermolai 2024 + Zhang 2021 reporting 6–24 MPa for FDM dovetails while the rebar-shear analog Yavas 2022 only hits 1–2.7 MPa.

CAD modeled in OpenSCAD for all 5 designs at cad/joint-design/{A_anchor_bulb,B_dovetail,C_tpu_sleeve_overmold,D_eyelet_loop,E_tpu_rebar}.scad with section/cutaway variants, render.sh, STL+PNG renders, and contact-sheet montages (all_iso_montage.png, all_section_montage.png).

Compared visually against online references. Curated 5 verified-200 Wikimedia Commons images (tensegrity 3-prism, finished dovetail joint, hose clamp, chain-link fence, rebar loop) + DOIs at cad/joint-design/references/README.md, then built a side-by-side CAD-vs-reference montage:

Follow-up Edison query sent. ANALYSIS 19e0c868-3587-440d-ba4a-07da4dddf99a was submitted with the zipped cad/joint-design/ (CAD + renders + references), the ce84ddf8 followup, the synthesis README, and the manifest, asking for (1) per-design visual sanity check, (2) concrete dimensional refinements for B-dovetail (flank angle, clearance, print orientation, anti-warp), (3) refinements for A-anchor-bulb (bulb-to-bore-clear ratio), (4) drop-test matrix update, (5) bibliographic gaps. Status was in progress at session end (poll exceeded budget). Next session: fetch via EdisonClient.get_task('19e0c868-…'), commit PHASE3-cad-review-19e0c868-*.{md,json}, then apply any actionable CAD refinements and re-run render.sh. Submission script + manifest entry are committed at scripts/edison/submit_joint_cad_review.py and task_manifest.json phase3.cad_review.

[sgbaird-yolo]

@copilot fetch all artifacts with the Edison query, incorporate feedback and recommendations (e.g., updated CAD models, new CAD models)

[Copilot]

@copilot fetch all artifacts with the Edison query, incorporate feedback and recommendations (e.g., updated CAD models, new CAD models)

Done in fb1f679.

Phase-3 ANALYSIS 19e0c868 fetched + committed at edison-trajectories/joint-design/PHASE3-cad-review-19e0c868-*.{md,json}. It flagged the original B_dovetail.scad as under-constrained (lateral PETG cheeks <2 perimeters; implied flank 15.5° vs. documented 25°) and the original A_anchor_bulb.scad as having only a 1.38× pull-through ratio.

Refinements applied to the CAD:

B_dovetail.scad (primary): node_d 9.0→12.0 mm, slot_mouth 6.4→5.4, slot_inner 7.4→7.06, slot_height 3.6→4.0, slot_depth 5.0→6.0, flank_deg 25→22.5° (Wang 2026 shear optimum), differential clearance 0.20 lateral / 0.30 roof (Ermolai 2024), and a 0.5 mm +X exit fillet (Frascio 2024).

A_anchor_bulb.scad (backup): node_d 9.0→9.5, bore_d 2.9→2.8, bulb_d 4.0→4.8 mm — pull-through ratio now 1.71× with a full 1.0 mm radial TPU bearing.

render.sh re-run; updated iso + section PNGs, STLs, and CAD-vs-reference comparison montage:

Synthesis README and task_manifest.json phase3.cad_review updated. New 2024–2026 references surfaced: Wang 2026, Frascio 2024, Mu 2024, Monti 2025.

[sgbaird]

@copilot design and make visualizations for these

• Truncated cone / frustum (rivet head) — flat bearing face → larger contact area at the same OD, and the TPU lays down on a flat top instead of a curved one (cleaner top-layer finish). Probably the best candidate.
• Toroidal/donut upset — distributes bearing load over a wider annulus, lower peak contact stress.
• Conical (countersunk) head that mates a matching countersink in the PETG/PLA bore exit → flush, self-centering, no protruding feature.
• Star/lobed/knurled head — adds rotational keying so the bulb can't spin in repeated drops (relevant for N_reuse).
• Mushroom / tee-head with a radiused undercut — maximum mechanical interlock per gram of TPU.

[Copilot]

@copilot design and make visualizations for these

• Truncated cone / frustum (rivet head) — flat bearing face → larger contact area at the same OD, and the TPU lays down ...

Done in 97dffa0.

Five alternative TPU upset shapes for Design A modeled in OpenSCAD at cad/joint-design/A_variants/, each preserving the Phase-3 1.71× pull-through ratio (node 9.5 / bore 2.8 / OD 4.8 mm) so only the upset shape changes:

• A0 sphere — reference (existing geometry)
• A1 truncated cone / "rivet head" — flat 6.0 mm² annular bearing (~75 % more area than A0 at the same OD), clean top-layer pass
• A2 torus / donut — distributed bearing on the inner curve, lower peak contact stress
• A3 countersunk — 90° cone mating a countersink in the +X face → flush, self-centring, ~8.8 mm² conical wall
• A4 6-lobed star / knurled — rotational keying so the upset can't spin through Bruceton n≥20 reuse
• A5 mushroom with 0.4 mm radiused undercut (Frascio 2024) — necks the cap base, not the bore lip

Iso + Y=0 cutaway grid (also added to the synthesis README; per-design *.png + *.stl and three contact-sheet montages are committed alongside):

Reproduce with bash cad/joint-design/A_variants/render.sh. Two open design-space axes (mating the bore mouth too; print-orientation tradeoff) are noted at the bottom of A_variants/README.md and are in scope for the pending Phase-4 f9804247 / e9a1f4cc results.

[sgbaird]

@copilot let's go with a design that has a ball on the outside with tpu on the inside (rather than a full feedthrough), sort of like an inner ball/mass surrounded by the outer ball, though of course it doesn't have to be an exact ball and stick model if we want to reduce stresses (e.g., filet the interface between the ball and stick slightly so it's a bit more like a tear drop)

Noting also comment from @achris0520 in vertical-cloud-lab/byu-vcl#82 (comment), which we're open to and you're welcome to try out

Materials that do not bond together when printing can be set to interlock beams on certain layers, which keeps them from sliding apart

Embed visualizations of what you did (isometric, cross section) directly in your comment reply

[Copilot]

@copilot design and make visualizations for these

• Truncated cone / frustum (rivet head) — flat bearing face → larger contact area at the same OD, and the TPU lays down ...

Done in 9d20e5e — new Design F at cad/joint-design/F_captive_core.scad (+ _section_{X,Y,Z}.scad, F_captive_core.md, render_F.sh):

• Captive TPU core inside PETG/PLA outer shell — Ø7 mm TPU "knot" lives entirely inside an Ø12 mm shell with an Ø8 mm cavity (0.5 mm radial print-in-place gap). Cable exits one Ø2.8 mm bore on +X only; the core is way too big to back out → pull-out ratio 2.5× vs. 1.71× for the Phase-3 A.
• Teardrop strut→shell fillet — generated as hull(shell_sphere, small_sphere_below) so the cylindrical strut blends smoothly into the spherical shell with no sharp re-entrant corner.
• Layer-interlock teeth (per @achris0520) — two staggered rings of 8 radial teeth at the cavity equator: PETG/PLA inward at z=+0.6 mm, TPU outward at z=−0.6 mm, rotated by half a sector (22.5°). They print past each other with no fused contact, but their radial overlap means the captive core can't translate ±Z relative to the shell unless the teeth shear through each other — an interlock that doesn't depend on PETG/PLA-TPU bond chemistry.

Iso + 3 orthogonal cuts (the section_Y mid-plane and section_Z equator both clearly show the captive-core cavity and the staggered interlock teeth ring):

The synthesis README (edison-trajectories/joint-design/README.md) has a new "Design F" section linking the artifacts. Three open knobs (tooth count/stagger sweep, prolate-spheroid cavity, toroidal core) are listed at the bottom of F_captive_core.md for the pending Phase-4 (f9804247 / e9a1f4cc) feedback.

[sgbaird]

@copilot apparently Ye et al. (see https://github.com/vertical-cloud-lab/tensegrity-optimization/pull/20/changes#r3383484706) had a TPU skin around a rigid PLA core. We've been printing a soft TPU core with a rigid PLA wrapping. Send an edison query - which is better and why, in the context of the project goals (see especially https://github.com/vertical-cloud-lab/tensegrity-optimization/blob/65d0d3f2b1d673f74755e1c8900af5af2500fc53/bo/t3_prism_sobol_batch.py and the current manuscript draft: https://github.com/vertical-cloud-lab/tensegrity-optimization/blob/90ba8469afe010997b80dcae98a613d5133c17e3/manuscript/manuscript-body.tex). Use edison analysis, making sure to upload the BO script, the manuscript, and the conversation from this PR (using GitHub MCP)

See also #35 for some additional context. Wait and fetch the edison results this session, then report back.

[sgbaird]

@copilot then remove from the paper

so the tensegrity attribution cannot be verified and should be removed from the manuscript.

[Copilot]

@copilot then remove from the paper

so the tensegrity attribution cannot be verified and should be removed from the manuscript.

Done in 2a644f5. Removed all three occurrences of the ye2023multimaterial attribution from proposal.tex:

1. Background ¶ (was lines 99–104) — deleted the "wrapping-based strategy (rigid cores encapsulated by continuous soft skins)" sentence; kept only the factual PLA–TPU energy-absorption claim, citing khatri2024energy alone.
2. Intro ¶ (was line 66) — dropped ye2023multimaterial from the multi-material fabrication citation.
3. Section 1 (was lines 135–137) — removed the "Following \citet{ye2023multimaterial}, the designs use a core-wrapping strategy (rigid PLA struts encapsulated by continuous TPU skins)…" sentence entirely.

The Ye et al. 2023 paper (origami metamaterials, Nature Communications) does not describe a tensegrity core-wrapping strategy, and the description was also factually wrong for this project (which uses TPU inside PLA, as in Design F).

Updated PDFs: proposal.pdf · proposal-diff.pdf