| """Run a STEP-contact track shoe over a rigid rock at fixed speeds.""" |
|
|
| 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 track-shoe solid") |
| mount = cq.Solid.makeBox(100, 100, 10, cq.Vector(-50, -50, 20)) |
| envelope = cq.Solid.makeBox(300, 100, 30, cq.Vector(-150, -50, 0)) |
| vertices, faces = shape.tessellate(setup["cad_tessellation_tolerance_mm"]) |
| if len(vertices) < 8 or len(faces) < 12: |
| raise ValueError("Track-shoe tessellation is incomplete") |
| return { |
| "step_sha256": hashlib.sha256(step.read_bytes()).hexdigest(), |
| "volume_mm3": shape.Volume(), |
| "mount_missing_mm3": max(0.0, mount.Volume() - mount.intersect(shape).Volume()), |
| "envelope_excess_mm3": max(0.0, shape.Volume() - |
| shape.intersect(envelope).Volume()), |
| "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 |
|
|
| collision_mesh_ch = ch.ChTriangleMeshConnected() |
| vertices = [ch.ChVector3d(*point) for point in collision_mesh["vertices"]] |
| for a, b, c in collision_mesh["faces"]: |
| collision_mesh_ch.AddTriangle(vertices[a], vertices[b], vertices[c]) |
| results = {} |
| for speed in setup["drive_speeds_m_s"]: |
| system = ch.ChSystemSMC() |
| system.SetCollisionSystemType(ch.ChCollisionSystem.Type_BULLET) |
| system.SetGravitationalAcceleration( |
| ch.ChVector3d(0, 0, -setup["gravity_m_s2"])) |
| system.SetSolver(ch.ChSolverSparseLU()) |
| material = ch.ChContactMaterialSMC() |
| material.SetFriction(setup["contact_friction"]) |
| material.SetRestitution(0) |
| material.SetYoungModulus(setup["contact_young_modulus_Pa"]) |
| floor = ch.ChBodyEasyBox(2, 1, 0.1, 1000, False, True, material) |
| floor.SetPos(ch.ChVector3d(0, 0, -0.05)) |
| floor.SetFixed(True) |
| system.Add(floor) |
| rock = ch.ChBodyEasySphere(setup["rock_radius_m"], 1000, |
| False, True, material) |
| rock.SetPos(ch.ChVector3d(*setup["rock_center_m"])) |
| rock.SetFixed(True) |
| system.Add(rock) |
| shoe = ch.ChBody() |
| shoe.SetMass(setup["carrier_mass_kg"]) |
| shoe.SetInertiaXX(ch.ChVector3d(*setup["carrier_inertia_kg_m2"])) |
| shoe.SetPos(ch.ChVector3d(*setup["initial_position_m"])) |
| shoe.AddCollisionShape(ch.ChCollisionShapeTriangleMesh( |
| material, collision_mesh_ch, False, False, |
| setup["collision_thickness_m"])) |
| shoe.EnableCollision(True) |
| system.Add(shoe) |
| guide = ch.ChLinkMateGeneric() |
| guide.SetConstrainedCoords(False, True, False, True, True, True) |
| guide.Initialize(shoe, floor, ch.ChFramed(shoe.GetPos())) |
| system.Add(guide) |
| motor = ch.ChLinkMotorLinearSpeed() |
| motor.SetGuideConstraint(ch.ChLinkMotorLinear.GuideConstraint_FREE) |
| motor.Initialize(shoe, floor, ch.ChFramed( |
| shoe.GetPos(), ch.QuatFromAngleY(math.pi / 2))) |
| motor.SetMotorFunction(ch.ChFunctionConst(speed)) |
| system.Add(motor) |
| spring = ch.ChForce() |
| shoe.AddForce(spring) |
| spring.SetMode(ch.ChForce.FORCE) |
| spring.SetDir(ch.ChVector3d(0, 0, 1)) |
| 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 time grid") |
| peak_acceleration = 0.0 |
| peak_height = setup["initial_position_m"][2] |
| for index in range(steps): |
| position = shoe.GetPos() |
| velocity = shoe.GetPosDt() |
| spring.SetMforce( |
| setup["carrier_mass_kg"] * setup["gravity_m_s2"] + |
| setup["spring_stiffness_N_m"] * |
| (setup["spring_rest_height_m"] - position.z) - |
| setup["spring_damping_N_s_m"] * velocity.z) |
| system.DoStepDynamics(dt) |
| if index * dt >= 0.3: |
| peak_acceleration = max(peak_acceleration, |
| abs(shoe.GetPosDt2().z)) |
| peak_height = max(peak_height, shoe.GetPos().z) |
| if not all(math.isfinite(value) for value in ( |
| peak_acceleration, peak_height, shoe.GetPos().x)): |
| raise ValueError("Non-finite shoe trajectory") |
| results[str(speed)] = { |
| "peak_vertical_acceleration_m_s2": peak_acceleration, |
| "rock_climb_m": peak_height - setup["initial_position_m"][2], |
| "final_x_m": shoe.GetPos().x, |
| "motor_speed_m_s": motor.GetMotorPosDt(), |
| "collision_triangle_count": collision_mesh_ch.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"] |
| speeds = [str(speed) for speed in setup["drive_speeds_m_s"]] |
| baseline = [bs[speed]["peak_vertical_acceleration_m_s2"] for speed in speeds] |
| candidate = [gs[speed]["peak_vertical_acceleration_m_s2"] for speed in speeds] |
| reductions = [1 - a / b for a, b in zip(candidate, baseline)] |
| checks = { |
| "baseline_acceleration_measurable": min(baseline) >= |
| setup["minimum_baseline_peak_acceleration_m_s2"], |
| "acceleration_reduced_both_speeds": min(reductions) >= |
| setup["required_relative_peak_acceleration_reduction"], |
| "candidate_acceleration_below_limit": max(candidate) <= |
| setup["maximum_candidate_peak_acceleration_m_s2"], |
| "rock_climbed": all(gs[speed]["rock_climb_m"] >= |
| setup["minimum_rock_climb_m"] for speed in speeds), |
| "motor_speeds_met": all(abs(gs[speed]["motor_speed_m_s"] - float(speed)) |
| < 1e-6 for speed in speeds), |
| "course_traversed": all(gs[speed]["final_x_m"] > 0.25 |
| for speed in speeds), |
| "volume_fixed": abs(ap["volume_mm3"] / bp["volume_mm3"] - 1) <= |
| setup["maximum_relative_volume_change"], |
| "mount_fixed": ap["mount_missing_mm3"] <= |
| setup["maximum_mount_missing_mm3"], |
| "envelope_fixed": ap["envelope_excess_mm3"] <= |
| setup["maximum_envelope_excess_mm3"], |
| } |
| after["comparison_to_before"] = { |
| "relative_peak_acceleration_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 acceleration: {baseline} -> {candidate} m/s2") |
| print(f"Task passed: {all(checks.values())}") |
| if not all(checks.values()): |
| raise SystemExit(1) |
|
|
|
|
| if __name__ == "__main__": |
| main() |
|
|
