"""Solve STEP-derived steering arms and measure tire scrub in a turn.""" 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 steering knuckle solid") holes = {} for face in shape.Faces(): if face.geomType() != "CYLINDER": continue bounds = face.BoundingBox() if abs(bounds.zmin + 5) > 1e-5 or abs(bounds.zmax - 5) > 1e-5: continue if abs(face.Area() - 2 * math.pi * 20 * 10) < 1e-3: holes["hub"] = [face.Center().x, face.Center().y] elif abs(face.Area() - 2 * math.pi * 8 * 10) < 1e-3: holes["tie"] = [face.Center().x, face.Center().y] if set(holes) != {"hub", "tie"}: raise ValueError("Expected one hub bore and one tie-rod bore") envelope = cq.Solid.makeBox(250, 200, 10, cq.Vector(-200, -150, -5)) return { "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), "volume_mm3": shape.Volume(), "hub_center_mm": holes["hub"], "tie_pickup_mm": holes["tie"], "envelope_excess_mm3": max(0.0, shape.Volume() - shape.intersect(envelope).Volume()), } def dynamics(properties: dict, setup: dict) -> dict: import pychrono as ch arm_x = (properties["tie_pickup_mm"][0] - properties["hub_center_mm"][0]) / 1000 arm_y = (properties["tie_pickup_mm"][1] - properties["hub_center_mm"][1]) / 1000 system = ch.ChSystemSMC() system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) system.SetSolver(ch.ChSolverSparseLU()) ground = ch.ChBody() ground.SetFixed(True) system.Add(ground) rack = ch.ChBody() rack.SetMass(1) rack.SetInertiaXX(ch.ChVector3d(0.1, 0.1, 0.1)) system.Add(rack) rack_guide = ch.ChLinkMateGeneric() rack_guide.SetConstrainedCoords(True, False, True, True, True, True) rack_guide.Initialize(rack, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) system.Add(rack_guide) motor = ch.ChLinkMotorLinearPosition() motor.SetGuideConstraint(ch.ChLinkMotorLinear.GuideConstraint_FREE) motor.Initialize(rack, ground, ch.ChFramed( ch.ChVector3d(0, 0, 0), ch.QuatFromAngleX(-math.pi / 2))) motor.SetMotorFunction(ch.ChFunctionRamp( 0, setup["rack_travel_m"] / setup["rack_travel_duration_s"])) system.Add(motor) knuckles = [] for side in (1, -1): knuckle = ch.ChBody() knuckle.SetMass(1) knuckle.SetInertiaXX(ch.ChVector3d(0.1, 0.1, 0.1)) knuckle.SetPos(ch.ChVector3d( 0, side * setup["front_track_m"] / 2, 0)) system.Add(knuckle) kingpin = ch.ChLinkLockRevolute() kingpin.Initialize(knuckle, ground, ch.ChFramed(knuckle.GetPos())) system.Add(kingpin) tie_rod = ch.ChLinkDistance() tie_rod.Initialize( knuckle, rack, True, ch.ChVector3d(arm_x, side * arm_y, 0), ch.ChVector3d(setup["rack_x_m"], side * setup["rack_half_width_m"], 0)) system.Add(tie_rod) knuckles.append(knuckle) dt = setup["time_step_s"] steps = round(setup["rack_travel_duration_s"] / dt) if dt <= 0 or abs(steps * dt - setup["rack_travel_duration_s"]) > 1e-12: raise ValueError("Invalid steering time grid") target_steps = { round(abs(displacement / setup["rack_travel_m"]) * steps): str(displacement) for displacement in setup["evaluation_rack_displacements_m"] } results = {} for index in range(steps): system.DoStepDynamics(dt) if index + 1 not in target_steps: continue angles = [2 * math.atan2(body.GetRot().e3, body.GetRot().e0) for body in knuckles] if min(angles) <= 0: raise ValueError("Both front wheels must steer into the left turn") turn_radius = (setup["wheelbase_m"] / math.tan(sum(angles) / 2)) half_track = setup["front_track_m"] / 2 ideal = [ math.atan(setup["wheelbase_m"] / (turn_radius - half_track)), math.atan(setup["wheelbase_m"] / (turn_radius + half_track)), ] errors = [angle - target for angle, target in zip(angles, ideal)] work = sum( setup["tire_friction_limit"] * setup["tire_normal_load_N"] * math.tanh(setup["lateral_slip_stiffness"] * abs(error)) * setup["maneuver_distance_m"] * abs(math.sin(error)) for error in errors ) if not all(math.isfinite(value) for value in ( *angles, turn_radius, *errors, work)): raise ValueError("Non-finite steering solution") results[target_steps[index + 1]] = { "inner_steer_rad": angles[0], "outer_steer_rad": angles[1], "turning_radius_m": turn_radius, "tire_slip_angle_errors_rad": errors, "scrub_work_J": work, "rack_displacement_m": rack.GetPos().y, } if len(results) != len(target_steps): raise ValueError("Steering run missed a requested rack displacement") 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["evaluation_rack_displacements_m"]] baseline = [bs[case]["scrub_work_J"] for case in cases] candidate = [gs[case]["scrub_work_J"] for case in cases] reductions = [1 - a / b for a, b in zip(candidate, baseline)] checks = { "scrub_reduced_both_turns": min(reductions) >= setup["required_relative_scrub_work_reduction"], "turning_radius_met": ( gs[cases[0]]["turning_radius_m"] <= setup["maximum_turning_radius_m_at_15mm"] and gs[cases[1]]["turning_radius_m"] <= setup["maximum_turning_radius_m_at_20mm"]), "rack_positions_met": all(abs(gs[case]["rack_displacement_m"] - float(case)) < 1e-5 for case in cases), "tie_clearance": setup["minimum_tie_pickup_y_mm"] <= ap["tie_pickup_mm"][1] <= setup["maximum_tie_pickup_y_mm"], "hub_fixed": max(abs(a - b) for a, b in zip( ap["hub_center_mm"], bp["hub_center_mm"])) <= setup["maximum_hub_center_error_mm"], "tie_x_fixed": abs(ap["tie_pickup_mm"][0] - bp["tie_pickup_mm"][0]) <= setup["maximum_tie_pickup_x_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_scrub_work_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"Tire scrub work: {baseline} -> {candidate} J") print(f"Task passed: {all(checks.values())}") if not all(checks.values()): raise SystemExit(1) if __name__ == "__main__": main()