| """Measure yaw caused by a fixed push through a STEP-derived chassis.""" |
|
|
| 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("Chassis volume must be positive") |
| bounds = shape.BoundingBox() |
| inertia = props.MatrixOfInertia() |
| density = setup["material_density_kg_m3"] |
| pad = cq.Solid.makeBox(5, 10, 10, cq.Vector(-50, -5, -5)) |
| 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], |
| "push_pad_missing_mm3": pad.cut(shape).Volume(), |
| } |
|
|
|
|
| def dynamics(properties: dict, setup: dict) -> dict: |
| import pychrono as ch |
|
|
| center = [value / 1000 for value in properties["center_of_mass_mm"]] |
| system = ch.ChSystemNSC() |
| system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) |
| chassis = ch.ChBody() |
| chassis.SetMass(properties["mass_kg"]) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(properties["inertia_tensor_kg_m2"]) |
| chassis.SetInertia(inertia) |
| chassis.SetPos(ch.ChVector3d(*center)) |
| system.Add(chassis) |
| push = ch.ChForce() |
| chassis.AddForce(push) |
| push.SetMode(ch.ChForce.FORCE) |
| push.SetAlign(ch.ChForce.WORLD_DIR) |
| push.SetDir(ch.ChVector3d(1, 0, 0)) |
| push.SetVrelpoint(ch.ChVector3d(*[ |
| point / 1000 - coordinate |
| for point, coordinate in zip(setup["push_point_mm"], center) |
| ])) |
| push.SetMforce(setup["push_force_N"]) |
|
|
| dt = setup["time_step_s"] |
| steps = round(setup["duration_s"] / dt) |
| pulse_steps = round(setup["push_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") |
| for i in range(steps): |
| if i == pulse_steps: |
| push.SetMforce(0) |
| system.DoStepDynamics(dt) |
| q = chassis.GetRot() |
| yaw = math.degrees(2 * math.atan2(q.e3, q.e0)) |
| if not math.isfinite(yaw): |
| raise ValueError("Nonfinite yaw angle") |
| return {"absolute_yaw_deg": abs(yaw), "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"]["absolute_yaw_deg"] |
| candidate = after["simulation_result"]["absolute_yaw_deg"] |
| inertia_before = bp["inertia_tensor_kg_m2"][2][2] |
| inertia_after = ap["inertia_tensor_kg_m2"][2][2] |
| checks = { |
| "baseline_yaw_measurable": baseline > 1, |
| "yaw_reduced": candidate <= baseline * (1 - setup["required_relative_yaw_reduction"]), |
| "mass_fixed": abs(ap["mass_kg"] / bp["mass_kg"] - 1) |
| <= setup["maximum_relative_mass_change"], |
| "footprint_and_height_fixed": all( |
| abs(a - b) <= setup["maximum_envelope_change_mm"] |
| for a, b in zip(ap["bounds_mm"], bp["bounds_mm"])), |
| "polar_inertia_in_band": abs(inertia_after / inertia_before - 1) |
| <= setup["maximum_relative_polar_inertia_change"], |
| "push_pad_intact": ap["push_pad_missing_mm3"] |
| <= setup["maximum_push_pad_missing_mm3"], |
| "planar_center": abs(ap["center_of_mass_mm"][2]) |
| <= setup["maximum_center_z_offset_mm"], |
| "planar_inertia": all(abs(ap["inertia_tensor_kg_m2"][i][2]) |
| <= setup["maximum_out_of_plane_cross_inertia_kg_m2"] |
| for i in (0, 1)), |
| } |
| after["comparison_to_before"] = { |
| "relative_yaw_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"Absolute yaw: {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() |
|
|
