Analyze FFF tendon print-angle impact across active test PRs

[Copilot]

Print-in-place tensegrity specimens (PR #35) deposit TPU tendons at a mix of 0°/45°/90° relative to the bead direction, which biases strength-dominated tests more than stiffness-dominated ones. This PR adds an analysis answering how much that affects the experiments planned across the open PRs.

Deliverable

• New reviews/tendon_print_angle_impact.md (style matches reviews/mock_reviews.md and literature/davami2025-analysis.md).

Contents

• Mechanism — why the geometry guarantees a 0°/45°/90° tendon population for any single build orientation; why slender tendons + TPU 85A + captive-core joints sharpen the effect vs. typical FFF coupons.
• Anisotropy bracket (FFF-TPU literature, not yet measured on our parts): σ_90°/σ_0° ≈ 0.3–0.6; E_90°/E_0° ≈ 0.7–0.9. Strength is the dominant concern; stiffness is mostly preserved.
• FoM-class effect — small for stiffness-like FoMs (initial Instron slope, low-f transfer function, F_pre), large for first-failure FoMs, medium and load-path-dependent for SEA / h_crit / peak-g.
• Per-PR severity table (L/M/H) with mitigations for 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, 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, 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... #39/Anchor-bulb pre-tensioning DOE: 15-specimen test plate (air gap × joint size, A3 countersunk, horizontal cable) #52, Edison query on strut material (PLA vs PETG vs HF/CF) — fetched + interpreted #45, Explore egg-drop demo via Edison LITERATURE_HIGH query (+ drag-free baseline / V·m benchmark, Brown-lab BEAR baseline, and SUPERball v2 actuator follow-ups) #47, Run initial instron tensile tests for stiffness testing #49/Edison LITERATURE_HIGH brief: ASTM standards & best practices for initial Instron stiffness tests (#49) #50, Add strut-curvature design-axis exploration synthesis #54, Add tensegrity build-kit & DIY-materials recommendations #56, Analyze Davami et al. 2025 (dynamic AM tensegrity) + Edison follow-up #58, Edison literature briefs: objectives / outcomes per drop-test data source + cross-modality ANALYSIS synthesis #60. Highlights:
  • H — 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 (build orientation is currently frozen in the Sobol batch generator) and generalization beyond PR Anchor-bulb pre-tensioning DOE: 15-specimen test plate (air gap × joint size, A3 countersunk, horizontal cable) #52's fixed-orientation DOE.
  • M — sim↔experiment validation in 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, egg-drop h_crit in Explore egg-drop demo via Edison LITERATURE_HIGH query (+ drag-free baseline / V·m benchmark, Brown-lab BEAR baseline, and SUPERball v2 actuator follow-ups) #47, the FFF-vs-SLA delta in Analyze Davami et al. 2025 (dynamic AM tensegrity) + Edison follow-up #58 (Davami used isotropic Tough 2000), and the cross-modality objective synthesis in Edison literature briefs: objectives / outcomes per drop-test data source + cross-modality ANALYSIS synthesis #60.
  • L — equipment/doc PRs (Document Lansmont M23 drop tower and Polytec QTec laser vibrometer #28, Edison query on strut material (PLA vs PETG vs HF/CF) — fetched + interpreted #45, Add tensegrity build-kit & DIY-materials recommendations #56) and the initial sub-densification Instron run (Edison LITERATURE_HIGH brief: ASTM standards & best practices for initial Instron stiffness tests (#49) #50).
• Five ranked mitigations, cheapest first:
  1. Per-tendon angle dump from the sliced gcode (extend 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's patch_mm_extruder.py).
  2. Sobol replicates at ≥2 build orientations.
  3. k_anisotropy(theta) scalar in simulations/printable_design.py.
  4. Promote build_orientation from frozen context to a categorical Ax design parameter (PRs Scaffold Bayesian-optimization script with honegumi + customized tensegrity campaign #30/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/Edison literature briefs: objectives / outcomes per drop-test data source + cross-modality ANALYSIS synthesis #60).
  5. Structural fix: post-print manual TPU threading via PR Anchor-bulb pre-tensioning DOE: 15-specimen test plate (air gap × joint size, A3 countersunk, horizontal cable) #52's noted alternative path — fully decouples tendon strength from slicer-decided angles.
• Near-term follow-ups assigned per 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 gcode log + unfreeze orientation; Edison LITERATURE_HIGH brief: ASTM standards & best practices for initial Instron stiffness tests (#49) #50 add "first-tendon-to-fail + angle bin" to the Instron metadata schema; Anchor-bulb pre-tensioning DOE: 15-specimen test plate (air gap × joint size, A3 countersunk, horizontal cable) #52 add a 3-cell × {0°,45°,90°} sanity sub-array; 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/Edison literature briefs: objectives / outcomes per drop-test data source + cross-modality ANALYSIS synthesis #60 plumb a single anisotropy_ratio knob).
• Scope guard — explicitly notes what is not invalidated: 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 captive-core joint, PR Edison query on strut material (PLA vs PETG vs HF/CF) — fetched + interpreted #45 strut-material recommendation, PR Edison LITERATURE_HIGH brief: ASTM standards & best practices for initial Instron stiffness tests (#49) #50 protocol, PR Document Lansmont M23 drop tower and Polytec QTec laser vibrometer #28 LDV resolution.