Project 33

C1 — Folding-fin mechanism model

Field	Value
Status	CONTRADICTED — Current evidence contradicts the claim or one of its requirements.
Strongest accepted evidence	MODEL ONLY
Evidence classes cited	IMPLEMENTATION, TEST PROCEDURE, ANALYTICAL
Gate reached	ANALYTICAL MODEL (next: SOFTWARE REPRODUCTION)
Last review	CURRENT — snapshot recorded 2026-09-28 by tooling snapshot (no human review)

Question. Can the specified four-bar linkage carry the fin from folded (0 deg) to 92 deg and hold it over-center?

Current statement. In the planar model, the specified baseline linkage (ground 25, coupler 60, input 15, output 15 mm) cannot close at any drive angle from 0 to 92 deg, and none of the 81 swept variants can. Transmission-angle and envelope requirements therefore cannot be evaluated, and over-center locking is not modeled.

Requirements

ID	Requirement	Check	Bound	Observed	Result
R-C1-CLOSURE	The baseline linkage closes (assembles) at every drive angle from 0 to 92 deg.	machine	= true	false	NOT SATISFIED (analytical)
R-C1-TRANSMISSION	The transmission angle stays within 40-140 deg throughout deployment.	machine	≥ 40 and ≤ 140 deg	artifact reports no value (null means no value exists)	NOT EVALUABLE (analytical)
R-C1-LOCK	The over-center toggle holds the fin at the deployed position against the design hinge moment.	physical measurement	none stated	NOT MEASURED	NOT MEASURED

Known contradictions

• R-C1-CLOSURE
• D-002
• D-004

Open questions

• Which topology and dimensions were intended? The recorded dimensions cannot form a closed loop (D-002).

Discrepancies

• D-002 (OPEN) The specified four-bar cannot be assembled
• D-004 (OPEN) Over-center locking is claimed but not modeled
• D-005 (OPEN) C1 CAD artifacts are illustrative bars, not the modeled mechanism
• D-001 (RESOLVED) Historical C1 note contradicts its own sweep
• D-003 (RESOLVED) C1 model revision 1 reported placeholders as results, and its tests passed on them

Assumptions

• The mechanism is a planar, pin-jointed four-bar loop.
• Link lengths are pin-centre distances in millimetres.
• The drive angle is measured from the folded position.

Limitations

• A planar model cannot tell whether a different topology or pivot layout was intended.
• Loop geometry says nothing about loads, clearance, compliance, or locking torque.
• Rendered or exported CAD of the links is not evidence that the mechanism assembles.

Measurement needed to close the next gate

• Reviewer confirmation of the intended link dimensions and topology.
• A revised, reviewed model; only then an inert, instrumented deployment test of a printed linkage.

Pre-registered experiments

• None.

What this claim does not establish

• Any inert physical measurement: none has been accepted for this claim.
• Physical performance of any hardware.
• Flight readiness or safety for live propulsion.

Evidence

Artifact	Class	SHA-256 (first 12)	What it is
mechanism/four_bar.py	IMPLEMENTATION	c29b5f1905d0	Planar four-bar kinematics, revision 2: loop closure by circle intersection; unassemblable poses report null.
docs/EVIDENCE/C1_four_bar_sweep.json	ANALYTICAL	b5db59c4d5fc	Baseline and 81-configuration sweep. Null values mean the linkage cannot close; no value exists.
docs/EVIDENCE/C1_four_bar_plot.png	ANALYTICAL	5097fb03a463	Rendered loop-closure check for the baseline. Pixels are not reproduced byte for byte; the JSON carries the values.
docs/assets/review/c1_loop_closure.svg	ANALYTICAL	6eaf21321a2c	Loop-closure diagram: the output circle never meets the coupler circles over the drive range.
tests/test_four_bar.py	TEST PROCEDURE	63215cc6d69d	Geometry and null-handling tests. Does not assert that the design meets a requirement.
CAD Files/FusionScripts/Project33FourBar/Project33FourBar.py	IMPLEMENTATION	135baaed83db	Fusion sketch and CadQuery export for the baseline links. Its own comment calls the assembly purely illustrative.
CAD Files/Four Bar Linkage.step	IMPLEMENTATION	7f4afad7b1d7	Illustrative STEP of four separate bars. It is not a closed or kinematically constrained mechanism.

Earlier versions (failure archive)

• evidence/archive/notes-v1/C1_four_bar.md — Historical C1 note. Its Grashof, transmission-angle, and over-center statements are not supported by its own sweep.
• evidence/archive/C1_four_bar_sweep.v1.json — Revision 1 sweep: every row reports 90 degrees and a 0.0 envelope, placeholders for linkages that cannot close.
• evidence/archive/test_four_bar.v1.py.txt — Revision 1 tests that passed on placeholder values.

A change to any of these files makes the last review insufficient

• CAD Files/Four Bar Linkage.step
• CAD Files/FusionScripts/Project33FourBar/Project33FourBar.py
• docs/EVIDENCE/C1_four_bar_plot.png
• docs/EVIDENCE/C1_four_bar_sweep.json
• docs/assets/review/c1_loop_closure.svg
• mechanism/four_bar.py
• tests/test_four_bar.py
• tools/review_figures.py

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