| """Measure STEP-mesh wheel drawbar pull at fixed commanded slip.""" |
|
|
| 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 wheel solid") |
| hub = cq.Solid.makeCylinder(100, 10, cq.Vector(0, -5, 0), |
| cq.Vector(0, 1, 0)).cut( |
| cq.Solid.makeCylinder(30, 10, cq.Vector(0, -5, 0), cq.Vector(0, 1, 0))) |
| bore = cq.Solid.makeCylinder(30, 80, cq.Vector(0, -40, 0), |
| cq.Vector(0, 1, 0)) |
| envelope = cq.Solid.makeBox(600, 80, 600, cq.Vector(-300, -40, -300)) |
| vertices, faces = shape.tessellate(setup["cad_tessellation_tolerance_mm"]) |
| if len(vertices) < 8 or len(faces) < 12: |
| raise ValueError("Wheel tessellation is incomplete") |
| return { |
| "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), |
| "volume_mm3": shape.Volume(), |
| "hub_missing_mm3": max(0.0, hub.Volume() - hub.intersect(shape).Volume()), |
| "bore_overlap_mm3": bore.intersect(shape).Volume(), |
| "envelope_excess_mm3": max(0.0, shape.Volume() - |
| shape.intersect(envelope).Volume()), |
| "radius_error_mm": abs(max(math.hypot(point.x, point.z) |
| for point in vertices) - 300), |
| "collision_mesh": { |
| "vertices": [[axis / 1000 for axis in point.toTuple()] |
| for point in vertices], |
| "faces": faces, |
| }, |
| } |
|
|
|
|
| def dynamics(collision_mesh: dict, setup: dict) -> dict: |
| import pychrono as ch |
| import pychrono.vehicle as veh |
|
|
| mesh = ch.ChTriangleMeshConnected() |
| vertices = [ch.ChVector3d(*point) for point in collision_mesh["vertices"]] |
| for a, b, c in collision_mesh["faces"]: |
| mesh.AddTriangle(vertices[a], vertices[b], vertices[c]) |
| results = {} |
| for offset in setup["starting_x_offsets_m"]: |
| system = ch.ChSystemSMC() |
| system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) |
| system.SetGravitationalAcceleration( |
| ch.ChVector3d(0, 0, -setup["gravity_m_s2"])) |
| system.SetSolver(ch.ChSolverSparseLU()) |
| ground = ch.ChBody() |
| ground.SetFixed(True) |
| system.Add(ground) |
| wheel = ch.ChBody() |
| wheel.SetMass(setup["wheel_mass_kg"]) |
| wheel.SetInertiaXX(ch.ChVector3d(*setup["wheel_inertia_kg_m2"])) |
| wheel.SetPos(ch.ChVector3d(offset, 0, setup["wheel_initial_height_m"])) |
| system.Add(wheel) |
| material = ch.ChContactMaterialSMC() |
| material.SetFriction(0.8) |
| material.SetRestitution(0) |
| wheel.AddCollisionShape(ch.ChCollisionShapeTriangleMesh( |
| material, mesh, False, False, 0.002)) |
| wheel.EnableCollision(True) |
| terrain = veh.SCMTerrain(system, False) |
| terrain.Initialize(setup["terrain_length_m"], setup["terrain_width_m"], |
| setup["terrain_grid_m"]) |
| terrain.SetSoilParameters( |
| setup["soil_Kphi"], setup["soil_Kc"], setup["soil_n"], |
| setup["soil_cohesion_Pa"], setup["soil_friction_angle_deg"], |
| setup["soil_Janosi_m"], setup["soil_elastic_stiffness_Pa_m"], |
| setup["soil_damping_Pa_s_m"]) |
| dt = setup["time_step_s"] |
| settle_steps = round(setup["settling_duration_s"] / dt) |
| drive_steps = round(setup["drive_duration_s"] / dt) |
| sample_start = round(setup["measure_after_drive_s"] / dt) |
| if (abs(settle_steps * dt - setup["settling_duration_s"]) > 1e-12 or |
| abs(drive_steps * dt - setup["drive_duration_s"]) > 1e-12 or |
| abs(sample_start * dt - setup["measure_after_drive_s"]) > 1e-12): |
| raise ValueError("Invalid simulation time grid") |
| for _ in range(settle_steps): |
| system.DoStepDynamics(dt) |
| linear = ch.ChLinkMotorLinearSpeed() |
| linear.SetGuideConstraint(ch.ChLinkMotorLinear.GuideConstraint_FREE) |
| linear.Initialize(wheel, ground, ch.ChFramed( |
| wheel.GetPos(), ch.QuatFromAngleY(math.pi / 2))) |
| linear.SetMotorFunction(ch.ChFunctionConst(setup["forward_speed_m_s"])) |
| system.Add(linear) |
| angular_speed = (setup["forward_speed_m_s"] / |
| (setup["wheel_outer_radius_m"] * |
| (1 - setup["commanded_longitudinal_slip"]))) |
| rotary = ch.ChLinkMotorRotationSpeed() |
| rotary.SetSpindleConstraint(ch.ChLinkMotorRotation.SpindleConstraint_FREE) |
| rotary.Initialize(wheel, ground, ch.ChFramed( |
| wheel.GetPos(), ch.QuatFromAngleX(-math.pi / 2))) |
| rotary.SetMotorFunction(ch.ChFunctionConst(angular_speed)) |
| system.Add(rotary) |
| forces = [] |
| for index in range(drive_steps): |
| system.DoStepDynamics(dt) |
| if index >= sample_start: |
| forces.append(-linear.GetMotorForce()) |
| mean_force = sum(forces) / len(forces) |
| if not math.isfinite(mean_force): |
| raise ValueError("Non-finite drawbar reaction") |
| results[str(offset)] = { |
| "mean_drawbar_pull_N": mean_force, |
| "final_center_height_m": wheel.GetPos().z, |
| "motor_forward_speed_m_s": linear.GetMotorPosDt(), |
| "motor_angular_speed_rad_s": rotary.GetMotorAngleDt(), |
| "modified_terrain_node_count": len(terrain.GetModifiedNodes()), |
| "collision_triangle_count": mesh.GetNumTriangles(), |
| } |
| 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["collision_mesh"], 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}) |
| collision_mesh = properties.pop("collision_mesh") |
| results[name] = { |
| "step_properties": properties, |
| "simulation_result": invoke(args.physics_python, "dynamics", { |
| "collision_mesh": collision_mesh, "setup": setup}), |
| } |
| before, after = results["before"], results["after"] |
| bp, ap = before["step_properties"], after["step_properties"] |
| bs, gs = before["simulation_result"], after["simulation_result"] |
| offsets = [str(offset) for offset in setup["starting_x_offsets_m"]] |
| baseline = [bs[offset]["mean_drawbar_pull_N"] for offset in offsets] |
| candidate = [gs[offset]["mean_drawbar_pull_N"] for offset in offsets] |
| gains = [a - b for a, b in zip(candidate, baseline)] |
| expected_angular_speed = (setup["forward_speed_m_s"] / |
| (setup["wheel_outer_radius_m"] * |
| (1 - setup["commanded_longitudinal_slip"]))) |
| checks = { |
| "drawbar_gain_both_offsets": min(gains) >= |
| setup["minimum_drawbar_gain_N"], |
| "positive_candidate_drawbar_pull": min(candidate) >= |
| setup["minimum_candidate_drawbar_pull_N"], |
| "commanded_speeds_met": all( |
| abs(gs[offset]["motor_forward_speed_m_s"] - |
| setup["forward_speed_m_s"]) < 1e-4 and |
| abs(gs[offset]["motor_angular_speed_rad_s"] - |
| expected_angular_speed) < 1e-4 for offset in offsets), |
| "soil_contact_active": all(gs[offset]["modified_terrain_node_count"] > 0 |
| for offset in offsets), |
| "volume_fixed": abs(ap["volume_mm3"] / bp["volume_mm3"] - 1) <= |
| setup["maximum_relative_volume_change"], |
| "hub_fixed": ap["hub_missing_mm3"] <= |
| setup["maximum_hub_missing_mm3"], |
| "bore_open": ap["bore_overlap_mm3"] <= |
| setup["maximum_bore_overlap_mm3"], |
| "envelope_fixed": ap["envelope_excess_mm3"] <= |
| setup["maximum_envelope_excess_mm3"], |
| "radius_fixed": ap["radius_error_mm"] <= |
| setup["maximum_radius_error_mm"], |
| } |
| after["comparison_to_before"] = { |
| "drawbar_gains_N": gains, |
| "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"Mean drawbar pull: {baseline} -> {candidate} N") |
| print(f"Task passed: {all(checks.values())}") |
| if not all(checks.values()): |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
