| """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() |
|
|
