"""Map STEP rocker bores to a sprung body-roll experiment.""" 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 shape = cq.importers.importStep(str(step)).val() if shape.ShapeType() != "Solid" or len(shape.Solids()) != 1 or not shape.isValid(): raise ValueError("Expected one valid suspension rocker solid") holes = [] expected_area = 2 * math.pi * 5 * 10 for face in shape.Faces(): if face.geomType() != "CYLINDER": continue bounds = face.BoundingBox() if (abs(face.Area() - expected_area) < 1e-3 and abs(bounds.zmin) < 1e-5 and abs(bounds.zmax - 10) < 1e-5): holes.append(face.Center().x) holes.sort() if len(holes) != 3: raise ValueError("Expected exactly three through bores of radius 5 mm") envelope = cq.Solid.makeBox(140, 30, 10, cq.Vector(-20, -15, 0)) return { "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), "volume_mm3": shape.Volume(), "pivot_x_mm": holes[0], "spring_pickup_x_mm": holes[1], "wheel_pickup_x_mm": holes[2], "envelope_excess_mm3": max(0.0, shape.Volume() - shape.intersect(envelope).Volume()), } def dynamics(properties: dict, setup: dict) -> dict: import pychrono as ch spring_arm = (properties["spring_pickup_x_mm"] - properties["pivot_x_mm"]) / 1000 wheel_arm = (properties["wheel_pickup_x_mm"] - properties["pivot_x_mm"]) / 1000 if spring_arm <= 0 or wheel_arm <= 0: raise ValueError("Rocker arm lengths must be positive") ratio = spring_arm / wheel_arm half_track = setup["track_width_m"] / 2 roll_stiffness = (2 * setup["spring_stiffness_N_m"] * ratio ** 2 * half_track ** 2) roll_damping = (2 * setup["spring_damping_N_s_m"] * ratio ** 2 * half_track ** 2) results = {} for acceleration in setup["lateral_acceleration_pulses_m_s2"]: system = ch.ChSystemSMC() system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) system.SetSolver(ch.ChSolverSparseLU()) ground = ch.ChBody() ground.SetFixed(True) system.Add(ground) body = ch.ChBody() body.SetMass(setup["body_mass_kg"]) inertia = setup["body_roll_inertia_kg_m2"] body.SetInertiaXX(ch.ChVector3d(inertia, 1000, 1000)) system.Add(body) hinge = ch.ChLinkLockRevolute() hinge.Initialize(body, ground, ch.ChFramed( ch.ChVector3d(0, 0, 0), ch.QuatFromAngleY(math.pi / 2))) system.Add(hinge) torque = ch.ChForce() body.AddForce(torque) torque.SetMode(ch.ChForce.TORQUE) torque.SetDir(ch.ChVector3d(1, 0, 0)) dt = setup["time_step_s"] steps = round(setup["duration_s"] / dt) if dt <= 0 or abs(steps * dt - setup["duration_s"]) > 1e-12: raise ValueError("Invalid simulation time grid") peak = 0.0 for index in range(steps): time = index * dt rotation = body.GetRot() roll = 2 * math.atan2(rotation.e1, rotation.e0) roll_rate = body.GetAngVelParent().x if setup["pulse_start_s"] <= time <= ( setup["pulse_start_s"] + setup["pulse_duration_s"]): phase = (time - setup["pulse_start_s"]) / setup["pulse_duration_s"] lateral_acceleration = acceleration * math.sin(math.pi * phase) else: lateral_acceleration = 0.0 external = (setup["body_mass_kg"] * lateral_acceleration * setup["roll_moment_arm_m"]) torque.SetMforce(external - roll_stiffness * roll - roll_damping * roll_rate) system.DoStepDynamics(dt) peak = max(peak, abs(roll)) if not math.isfinite(peak): raise ValueError("Non-finite body-roll response") results[str(acceleration)] = { "peak_roll_rad": peak, "effective_roll_stiffness_N_m_rad": roll_stiffness, "effective_roll_damping_N_m_s_rad": roll_damping, "available_wheel_travel_m": ( setup["available_spring_stroke_m"] / ratio), "spring_to_wheel_lever_ratio": ratio, } return results 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) 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, after = results["before"], results["after"] bp, ap = before["step_properties"], after["step_properties"] bs, gs = before["simulation_result"], after["simulation_result"] cases = [str(value) for value in setup["lateral_acceleration_pulses_m_s2"]] baseline = [bs[case]["peak_roll_rad"] for case in cases] candidate = [gs[case]["peak_roll_rad"] for case in cases] reductions = [1 - a / b for a, b in zip(candidate, baseline)] checks = { "peak_roll_reduced_both_pulses": min(reductions) >= setup["required_relative_peak_roll_reduction"], "candidate_roll_limit": max(candidate) <= setup["maximum_candidate_peak_roll_rad"], "wheel_travel_retained": all(gs[case]["available_wheel_travel_m"] >= setup["required_wheel_travel_m"] for case in cases), "spring_pickup_range": setup["spring_pickup_min_mm"] <= ap["spring_pickup_x_mm"] <= setup["spring_pickup_max_mm"], "pivot_fixed": abs(ap["pivot_x_mm"] - bp["pivot_x_mm"]) <= setup["maximum_pivot_error_mm"], "wheel_pickup_fixed": abs(ap["wheel_pickup_x_mm"] - bp["wheel_pickup_x_mm"]) <= setup["maximum_wheel_pickup_error_mm"], "volume_fixed": abs(ap["volume_mm3"] / bp["volume_mm3"] - 1) <= setup["maximum_relative_volume_change"], "envelope_fixed": ap["envelope_excess_mm3"] <= setup["maximum_envelope_excess_mm3"], } after["comparison_to_before"] = { "relative_peak_roll_reductions": reductions, "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"Peak roll: {baseline} -> {candidate} rad") print(f"Task passed: {all(checks.values())}") if not all(checks.values()): raise SystemExit(1) if __name__ == "__main__": main()