| """Index a STEP-derived wheel tooth past a radial pawl in both directions.""" |
|
|
| 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"] |
| disk = cq.Solid.makeCylinder(100, 20, cq.Vector(0, 0, -10)) |
| bore = cq.Solid.makeCylinder(10, 20, cq.Vector(0, 0, -10)) |
| envelope = cq.Solid.makeCylinder(130, 20, cq.Vector(0, 0, -10)) |
| tooth_vertices = [[v.X, v.Y, v.Z] for v in shape.Vertices() |
| if v.Y >= 94 and abs(v.X) <= 80] |
| if len(tooth_vertices) < 8: |
| raise ValueError("Wheel needs a STEP-resolved indexing tooth") |
| tip = max(tooth_vertices, key=lambda v: v[0] ** 2 + v[1] ** 2) |
| if math.hypot(tip[0], tip[1]) < 110: |
| raise ValueError("Indexing tooth must extend beyond the base disk") |
| 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(envelope).Volume(), |
| "base_missing_mm3": disk.cut(bore).cut(shape).Volume(), |
| "bore_intrusion_mm3": shape.intersect(bore).Volume(), |
| "tip_angle_rad": math.atan2(tip[1], tip[0]), |
| "tooth_collision_vertices_mm": tooth_vertices, |
| } |
|
|
|
|
| def dynamics(properties: dict, setup: dict) -> dict: |
| import pychrono as ch |
|
|
| ch.ChCollisionModel.SetDefaultSuggestedEnvelope(1e-5) |
| ch.ChCollisionModel.SetDefaultSuggestedMargin(1e-5) |
| material = ch.ChContactMaterialNSC() |
| material.SetFriction(setup["contact_friction"]) |
| center = [value / 1000 for value in properties["center_of_mass_mm"]] |
| 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 duration or time step") |
| results = {} |
| for direction, name in ((1, "forward"), (-1, "reverse")): |
| system = ch.ChSystemNSC() |
| system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) |
| system.SetGravitationalAcceleration(ch.ChVector3d(0, 0, 0)) |
| ground = ch.ChBody() |
| ground.SetFixed(True) |
| system.Add(ground) |
| wheel = ch.ChBody() |
| wheel.SetMass(properties["mass_kg"]) |
| inertia = ch.ChMatrix33d() |
| inertia.SetMatr(properties["inertia_tensor_kg_m2"]) |
| wheel.SetInertia(inertia) |
| angle = (math.pi / 2 - direction * setup["initial_tip_gap_rad"] |
| - properties["tip_angle_rad"]) |
| wheel.SetRot(ch.QuatFromAngleAxis(angle, ch.VECT_Z)) |
| wheel.SetPos(ch.ChVector3d( |
| center[0] * math.cos(angle) - center[1] * math.sin(angle), |
| center[0] * math.sin(angle) + center[1] * math.cos(angle), center[2])) |
| base_points = ch.vector_ChVector3d() |
| for i in range(64): |
| theta = 2 * math.pi * i / 64 |
| for z in (-0.01, 0.01): |
| base_points.push_back(ch.ChVector3d( |
| 0.1 * math.cos(theta) - center[0], |
| 0.1 * math.sin(theta) - center[1], z - center[2])) |
| tooth_points = ch.vector_ChVector3d() |
| for x, y, z in properties["tooth_collision_vertices_mm"]: |
| tooth_points.push_back(ch.ChVector3d( |
| x / 1000 - center[0], y / 1000 - center[1], z / 1000 - center[2])) |
| wheel.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, base_points)) |
| wheel.AddCollisionShape(ch.ChCollisionShapeConvexHull(material, tooth_points)) |
| wheel.EnableCollision(True) |
| system.Add(wheel) |
| hinge = ch.ChLinkLockRevolute() |
| hinge.Initialize(wheel, ground, ch.ChFramed(ch.ChVector3d(0, 0, 0))) |
| system.Add(hinge) |
|
|
| radius = setup["pawl_radius_m"] |
| reference_y = setup["pawl_reference_y_m"] |
| pawl = ch.ChBodyEasySphere(radius, setup["pawl_density_kg_m3"], |
| False, True, material) |
| pawl.SetPos(ch.ChVector3d(0, reference_y, 0)) |
| system.Add(pawl) |
| guide = ch.ChLinkLockPrismatic() |
| guide.Initialize(pawl, ground, ch.ChFramed( |
| ch.ChVector3d(0, reference_y, 0), |
| ch.QuatFromAngleAxis(-math.pi / 2, ch.VECT_X))) |
| system.Add(guide) |
| spring = ch.ChForce() |
| pawl.AddForce(spring) |
| spring.SetMode(ch.ChForce.FORCE) |
| spring.SetDir(ch.ChVector3d(0, 1, 0)) |
| drive = ch.ChForce() |
| wheel.AddForce(drive) |
| drive.SetMode(ch.ChForce.TORQUE) |
| drive.SetDir(ch.ChVector3d(0, 0, 1)) |
| drive.SetMforce(direction * setup["wheel_drive_torque_N_m"]) |
| damping = ch.ChForce() |
| wheel.AddForce(damping) |
| damping.SetMode(ch.ChForce.TORQUE) |
| damping.SetDir(ch.ChVector3d(0, 0, 1)) |
|
|
| rotation = 0.0 |
| peak_pawl_y = reference_y |
| for _ in range(steps): |
| spring.SetMforce(-setup["pawl_preload_N"] - |
| setup["pawl_spring_stiffness_N_m"] * |
| (pawl.GetPos().y - reference_y)) |
| damping.SetMforce(-setup["wheel_viscous_damping_N_m_s_rad"] * |
| wheel.GetAngVelParent().z) |
| system.DoStepDynamics(dt) |
| rotation += wheel.GetAngVelParent().z * dt |
| peak_pawl_y = max(peak_pawl_y, pawl.GetPos().y) |
| if not math.isfinite(rotation + peak_pawl_y): |
| raise ValueError("Nonfinite ratchet trajectory") |
| results[name] = {"rotation_rad": rotation, |
| "peak_pawl_y_m": peak_pawl_y} |
| 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, 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"] |
| bs = before["simulation_result"] |
| gs = after["simulation_result"] |
| checks = { |
| "baseline_stalls_forward": abs(bs["forward"]["rotation_rad"]) |
| <= setup["maximum_baseline_forward_rotation_rad"], |
| "indexes_forward": gs["forward"]["rotation_rad"] |
| >= setup["minimum_forward_rotation_rad"], |
| "holds_reverse": abs(gs["reverse"]["rotation_rad"]) |
| <= setup["maximum_reverse_rotation_rad"], |
| "pawl_contact_observed": gs["forward"]["peak_pawl_y_m"] |
| >= setup["minimum_pawl_lift_y_m"], |
| "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"], |
| "base_disk_intact": ap["base_missing_mm3"] |
| <= setup["maximum_base_missing_mm3"], |
| "shaft_bore_clear": ap["bore_intrusion_mm3"] |
| <= setup["maximum_bore_intrusion_mm3"], |
| } |
| after["comparison_to_before"] = {"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"Forward rotation: {bs['forward']['rotation_rad']} -> " |
| f"{gs['forward']['rotation_rad']} rad") |
| print(f"Reverse rotation: {gs['reverse']['rotation_rad']} rad") |
| print(f"Task passed: {after['comparison_to_before']['passed']}") |
| if not after["comparison_to_before"]["passed"]: |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
