"""Measure rotor tilt after a torque pulse on a free spherical gimbal.""" import argparse import hashlib import json import math import subprocess import sys from pathlib import Path ROOT = Path(__file__).resolve().parent def measure(step: Path, setup: dict) -> dict: import cadquery as cq from OCP.BRepGProp import BRepGProp from OCP.GProp import GProp_GProps shape = cq.importers.importStep(str(step)).val() if shape.ShapeType() != "Solid" or not shape.isValid() or len(shape.Solids()) != 1: raise ValueError(f"Expected one valid solid: {step}") props = GProp_GProps() BRepGProp.VolumeProperties_s(shape.wrapped, props) if props.Mass() <= 0: raise ValueError("Rotor volume must be positive") bounds = shape.BoundingBox() inertia = props.MatrixOfInertia() density = setup["material_density_kg_m3"] half_length = setup["half_length_mm"] shaft = cq.Solid.makeCylinder(setup["shaft_radius_mm"], 2 * half_length, cq.Vector(0, 0, -half_length)) return { "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), "volume_mm3": props.Mass(), "mass_kg": props.Mass() * density * 1e-9, "center_of_mass_mm": list(props.CentreOfMass().Coord()), "inertia_tensor_kg_m2": [ [inertia.Value(i, j) * density * 1e-15 for j in (1, 2, 3)] for i in (1, 2, 3) ], "bounds_mm": [bounds.xmin, bounds.xmax, bounds.ymin, bounds.ymax, bounds.zmin, bounds.zmax], "shaft_interface_missing_mm3": shaft.cut(shape).Volume(), } def dynamics(properties: dict, setup: dict) -> dict: import pychrono as ch system = ch.ChSystemNSC() system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) ground = ch.ChBody() ground.SetFixed(True) system.Add(ground) rotor = ch.ChBody() rotor.SetMass(properties["mass_kg"]) inertia = ch.ChMatrix33d() inertia.SetMatr(properties["inertia_tensor_kg_m2"]) rotor.SetInertia(inertia) rotor.SetAngVelParent(ch.ChVector3d(0, 0, setup["initial_spin_rad_s"])) system.Add(rotor) gimbal = ch.ChLinkLockSpherical() gimbal.Initialize(rotor, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) system.Add(gimbal) torque = ch.ChForce() rotor.AddForce(torque) torque.SetMode(ch.ChForce.TORQUE) torque.SetAlign(ch.ChForce.WORLD_DIR) torque.SetDir(ch.ChVector3d(1, 0, 0)) torque.SetMforce(setup["pulse_torque_N_m"]) dt = setup["time_step_s"] steps = round(setup["duration_s"] / dt) pulse_steps = round(setup["pulse_duration_s"] / dt) if dt <= 0 or steps <= pulse_steps or abs(steps * dt - setup["duration_s"]) > 1e-12: raise ValueError("Invalid simulation duration or time step") tilt_squared = 0.0 peak = 0.0 count = 0 for i in range(steps): if i == pulse_steps: torque.SetMforce(0) system.DoStepDynamics(dt) if i < pulse_steps: continue axis = rotor.GetRot().Rotate(ch.ChVector3d(0, 0, 1)) tilt = math.acos(max(-1.0, min(1.0, axis.z))) if not math.isfinite(tilt): raise ValueError("Nonfinite rotor tilt") tilt_squared += tilt * tilt peak = max(peak, tilt) count += 1 return { "post_pulse_rms_tilt_deg": math.degrees(math.sqrt(tilt_squared / count)), "post_pulse_peak_tilt_deg": math.degrees(peak), "steps": steps, } def invoke(python: str, phase: str, payload: dict) -> dict: run = subprocess.run( [python, str(Path(__file__).resolve()), "--phase", phase], input=json.dumps(payload), text=True, capture_output=True, check=False, ) if run.returncode: raise RuntimeError(f"{phase} failed:\n{run.stderr[-1600:]}") return json.loads(run.stdout) def main() -> None: parser = argparse.ArgumentParser() parser.add_argument("--cad-python", default=sys.executable) parser.add_argument("--physics-python", default=sys.executable) parser.add_argument("--phase", choices=("measure", "dynamics")) args = parser.parse_args() if args.phase: payload = json.load(sys.stdin) result = (measure(Path(payload["step"]), payload["setup"]) if args.phase == "measure" else dynamics(payload["properties"], payload["setup"])) print(json.dumps(result)) return setup = json.loads((ROOT / "setup.json").read_text()) results = {} for name in ("before", "after"): properties = invoke(args.cad_python, "measure", { "step": str(ROOT / f"{name}.step"), "setup": setup, }) results[name] = { "step_properties": properties, "simulation_result": invoke(args.physics_python, "dynamics", { "properties": properties, "setup": setup, }), } before = results["before"] after = results["after"] bp = before["step_properties"] ap = after["step_properties"] baseline = before["simulation_result"]["post_pulse_rms_tilt_deg"] candidate = after["simulation_result"]["post_pulse_rms_tilt_deg"] envelope = [-setup["outer_radius_mm"], setup["outer_radius_mm"], -setup["outer_radius_mm"], setup["outer_radius_mm"], -setup["half_length_mm"], setup["half_length_mm"]] checks = { "baseline_tilt_measurable": baseline > 0.1, "rms_tilt_reduced": candidate <= baseline * (1 - setup["required_relative_rms_tilt_reduction"]), "mass_fixed": abs(ap["mass_kg"] / bp["mass_kg"] - 1) <= setup["maximum_relative_mass_change"], "envelope_fixed": all(abs(a - b) <= setup["maximum_envelope_change_mm"] for a, b in zip(ap["bounds_mm"], envelope)), "shaft_interface_intact": ap["shaft_interface_missing_mm3"] <= setup["maximum_interface_missing_mm3"], "centered": max(abs(value) for value in ap["center_of_mass_mm"]) <= setup["maximum_center_offset_mm"], "principal_spin_axis": all(abs(ap["inertia_tensor_kg_m2"][i][2]) <= setup["maximum_cross_inertia_kg_m2"] for i in (0, 1)), } after["comparison_to_before"] = { "relative_rms_tilt_reduction": 1 - candidate / baseline, "checks": checks, "passed": all(checks.values()), } for name, result in results.items(): (ROOT / f"{name}.results.json").write_text(json.dumps(result, indent=2) + "\n") print(f"Post-pulse RMS tilt: {baseline:.4f} -> {candidate:.4f} deg") print(f"Task passed: {after['comparison_to_before']['passed']}") if not after["comparison_to_before"]["passed"]: raise SystemExit(1) if __name__ == "__main__": main()