| """Measure axle height variation while a STEP-derived wheel rolls on a floor.""" |
|
|
| 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("Wheel volume must be positive") |
| bounds = shape.BoundingBox() |
| inertia = props.MatrixOfInertia() |
| density = setup["material_density_kg_m3"] |
| outer = cq.Solid.makeCylinder(50, 10, cq.Vector(0, 0, -5)) |
| bore = cq.Solid.makeCylinder(10, 10, cq.Vector(0, 0, -5)) |
| hub = cq.Solid.makeCylinder(15, 10, cq.Vector(0, 0, -5)).cut(bore) |
| full_cylindrical_tread = any( |
| face.geomType() == "CYLINDER" |
| and abs(face.Area() - 2 * math.pi * 50 * 10) < 0.001 |
| and abs(face.BoundingBox().xlen - 100) < 1e-6 |
| and abs(face.BoundingBox().ylen - 100) < 1e-6 |
| and abs(face.BoundingBox().zlen - 10) < 1e-6 |
| for face in shape.Faces() |
| ) |
| 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(), |
| "bore_intrusion_mm3": shape.intersect(bore).Volume(), |
| "hub_missing_mm3": hub.cut(shape).Volume(), |
| "full_cylindrical_tread": full_cylindrical_tread, |
| "collision_vertices_mm": [[v.x, v.y, v.z] for v in vertices], |
| } |
|
|
|
|
| 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.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) |
| system.SetGravitationalAcceleration(ch.ChVector3d(0, -setup["gravity_m_s2"], 0)) |
| material = ch.ChContactMaterialNSC() |
| material.SetFriction(setup["contact_friction"]) |
| floor = ch.ChBodyEasyBox(3, 0.1, 0.3, 1000, False, True, material) |
| floor.SetPos(ch.ChVector3d(0, -0.05, 0)) |
| floor.SetFixed(True) |
| system.Add(floor) |
|
|
| axle = setup["initial_axle_m"] |
| wheel = (ch.ChBodyEasyCylinder(ch.ChAxis_Z, 0.05, 0.01, 1000, False, True, material) |
| if properties["full_cylindrical_tread"] else ch.ChBody()) |
| wheel.SetMass(properties["mass_kg"]) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(properties["inertia_tensor_kg_m2"]) |
| wheel.SetInertia(inertia) |
| wheel.SetPos(ch.ChVector3d(axle[0] + center[0], |
| axle[1] + center[1], axle[2] + 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])) |
| if not properties["full_cylindrical_tread"]: |
| wheel.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, points)) |
| wheel.EnableCollision(True) |
| system.Add(wheel) |
| planar = ch.ChLinkLockPlanar() |
| planar.Initialize(wheel, floor, ch.ChFramed(ch.ChVector3d(*axle))) |
| system.Add(planar) |
| drive = ch.ChForce() |
| wheel.AddForce(drive) |
| drive.SetMode(ch.ChForce.TORQUE) |
| drive.SetDir(ch.ChVector3d(0, 0, 1)) |
|
|
| dt = setup["time_step_s"] |
| steps = round(setup["duration_s"] / dt) |
| settle = round(setup["settling_s"] / dt) |
| if dt <= 0 or steps <= settle or abs(steps * dt - setup["duration_s"]) > 1e-12: |
| raise ValueError("Invalid simulation duration or time step") |
| heights = [] |
| spin_errors = [] |
| contact_steps = 0 |
| for i in range(steps): |
| t = i * dt |
| target = setup["target_spin_rad_s"] * min(1.0, t / setup["spin_ramp_s"]) |
| error = target - wheel.GetAngVelParent().z |
| command = setup["speed_controller_gain_N_m_s_rad"] * error |
| limit = setup["maximum_drive_torque_N_m"] |
| drive.SetMforce(max(-limit, min(limit, command))) |
| system.DoStepDynamics(dt) |
| if i >= settle: |
| heights.append(wheel.GetPos().y) |
| spin_errors.append(abs(wheel.GetAngVelParent().z / setup["target_spin_rad_s"] - 1)) |
| if floor.GetContactForce().Length() > 1e-8: |
| contact_steps += 1 |
| mean_height = sum(heights) / len(heights) |
| rms_height = math.sqrt(sum((value - mean_height) ** 2 for value in heights) |
| / len(heights)) |
| end = wheel.GetPos() |
| if not all(math.isfinite(value) for value in (rms_height, end.x, end.y)): |
| raise ValueError("Nonfinite wheel trajectory") |
| return { |
| "post_ramp_rms_axle_height_m": rms_height, |
| "mean_axle_height_m": mean_height, |
| "distance_m": end.x - axle[0], |
| "mean_relative_spin_error": sum(spin_errors) / len(spin_errors), |
| "floor_contact_fraction": contact_steps / len(heights), |
| "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_ramp_rms_axle_height_m"] |
| candidate = after["simulation_result"]["post_ramp_rms_axle_height_m"] |
| checks = { |
| "baseline_bump_measurable": baseline > 0.0005, |
| "axle_height_variation_reduced": candidate <= baseline * |
| (1 - setup["required_relative_axle_height_variation_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"], bp["bounds_mm"])), |
| "outer_radius_limited": ap["external_added_mm3"] |
| <= setup["maximum_external_added_mm3"], |
| "shaft_bore_clear": ap["bore_intrusion_mm3"] |
| <= setup["maximum_bore_intrusion_mm3"], |
| "hub_interface_intact": ap["hub_missing_mm3"] |
| <= setup["maximum_hub_missing_mm3"], |
| "both_roll_forward": all(result["simulation_result"]["distance_m"] |
| >= setup["minimum_rolling_distance_m"] |
| for result in (before, after)), |
| "spin_speed_held": all(result["simulation_result"]["mean_relative_spin_error"] |
| <= setup["maximum_relative_spin_error"] |
| for result in (before, after)), |
| "floor_contact_observed": all(result["simulation_result"]["floor_contact_fraction"] |
| >= setup["minimum_floor_contact_fraction"] |
| for result in (before, after)), |
| } |
| after["comparison_to_before"] = { |
| "relative_axle_height_variation_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"RMS axle height variation: {baseline} -> {candidate} m") |
| print(f"Task passed: {after['comparison_to_before']['passed']}") |
| if not after["comparison_to_before"]["passed"]: |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
