"""Roll a STEP-derived convex rocker on a floor and time its return upright.""" 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("Rocker volume must be positive") density = setup["material_density_kg_m3"] inertia = props.MatrixOfInertia() bounds = shape.BoundingBox() outer = (cq.Workplane("XY").moveTo(-50, 0) .threePointArc((0, -50), (50, 0)).lineTo(-50, 0) .close().extrude(20).translate((0, 0, -10)).val()) if len(outer.Solids()) == 1: outer = outer.Solids()[0] allowed = cq.Solid.makeBox(42, 40, 17, cq.Vector(-21, -41, -8.5)) vertices, _ = shape.tessellate(0.25) 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], "external_added_mm3": shape.cut(outer).Volume(), "exterior_removed_mm3": outer.cut(shape).cut(allowed).Volume(), "collision_vertices_mm": [[v.x, v.y, v.z] for v in vertices], } def dynamics(properties: dict, setup: dict) -> dict: import pychrono as ch system = ch.ChSystemNSC() system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) system.SetGravitationalAcceleration(ch.ChVector3d(0, -setup["gravity_m_s2"], 0)) material = ch.ChContactMaterialNSC() material.SetFriction(setup["contact_friction"]) material.SetRestitution(0) floor = ch.ChBodyEasyBox(1, 0.1, 0.3, 1000, False, True, material) floor.SetPos(ch.ChVector3d(0, -0.05, 0)) floor.SetFixed(True) system.Add(floor) rocker = ch.ChBody() rocker.SetMass(properties["mass_kg"]) inertia = ch.ChMatrix33d() inertia.SetMatr(properties["inertia_tensor_kg_m2"]) rocker.SetInertia(inertia) center = [value / 1000 for value in properties["center_of_mass_mm"]] angle = math.radians(setup["initial_angle_deg"]) rocker.SetRot(ch.QuatFromAngleAxis(angle, ch.VECT_Z)) rocker.SetPos(ch.ChVector3d( center[0] * math.cos(angle) - center[1] * math.sin(angle), 0.05 + center[0] * math.sin(angle) + center[1] * math.cos(angle), center[2], )) points = ch.vector_ChVector3d() for x, y, z in properties["collision_vertices_mm"]: points.push_back(ch.ChVector3d(x / 1000 - center[0], y / 1000 - center[1], z / 1000 - center[2])) rocker.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, points)) rocker.EnableCollision(True) system.Add(rocker) dt = setup["time_step_s"] steps = round(setup["duration_s"] / dt) if dt <= 0 or steps <= 0 or abs(steps * dt - setup["duration_s"]) > 1e-12: raise ValueError("Invalid simulation duration or time step") returned = None contact_steps = 0 final_angle = None for i in range(1, steps + 1): system.DoStepDynamics(dt) q = rocker.GetRot() final_angle = math.degrees(2 * math.atan2(q.e3, q.e0)) if not math.isfinite(final_angle): raise ValueError("Nonfinite rocker angle") if rocker.GetContactForce().Length() > 1e-8: contact_steps += 1 if returned is None and abs(final_angle) <= setup["upright_tolerance_deg"]: returned = i * dt return { "initial_angle_deg": setup["initial_angle_deg"], "time_to_upright_s": returned, "final_angle_deg": final_angle, "contact_steps": contact_steps, "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": { "runs": [invoke(args.physics_python, "dynamics", { "properties": properties, "setup": {**setup, "initial_angle_deg": angle}, }) for angle in setup["release_angles_deg"]], }, } before = results["before"] after = results["after"] bp = before["step_properties"] ap = after["step_properties"] bruns = before["simulation_result"]["runs"] aruns = after["simulation_result"]["runs"] btimes = [run["time_to_upright_s"] for run in bruns] atimes = [run["time_to_upright_s"] for run in aruns] checks = { "baseline_misses_deadline": all( time is None or time > setup["maximum_return_time_s"] for time in btimes), "returns_before_deadline": all( time is not None and time <= setup["maximum_return_time_s"] for time in atimes), "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"], bp["bounds_mm"])), "exterior_profile_fixed": ap["external_added_mm3"] <= setup["maximum_external_added_mm3"] and ap["exterior_removed_mm3"] <= setup["maximum_exterior_removed_mm3"], "floor_contact_observed": all(run["contact_steps"] > 0 for run in (*bruns, *aruns)), } after["comparison_to_before"] = { "release_angles_deg": setup["release_angles_deg"], "time_to_upright_before_s": btimes, "time_to_upright_after_s": atimes, "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"Time to upright: {btimes} -> {atimes} s") print(f"Task passed: {after['comparison_to_before']['passed']}") if not after["comparison_to_before"]["passed"]: raise SystemExit(1) if __name__ == "__main__": main()