A small, opinionated, human-readable language for describing robot intent.

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urml-chrono-runtime

High-fidelity validation reference runtime for URML — ChronoAdapter for Project Chrono multibody / multi-physics, via pychrono.

Project Chrono is an open high-fidelity multibody engine (Chrono::Vehicle ground dynamics, terramechanics for deformable terrain, Chrono::Sensor) from the University of Wisconsin-Madison and the University of Parma. This adapter mirrors MujocoAdapter / PX4Adapter: lazy pychrono, no ROS 2 dependency, a lazily-built cached ChSystem, failures returned not raised. Built against the frozen substrate Protocol per RFC-0014.

Chrono's distinctive role for URML is high-fidelity pre-deployment validation (RFC-0328): URML checks a program statically against the declared capability manifest and active safety envelope first, then drives the same validated intent through a short Chrono simulation segment so the dynamics come back as evidence. URML composes above Chrono; it never embeds it. The differentiator is the static capability-and-envelope check before the expensive multibody solver ever spins, so the high-fidelity run only ever exercises admissible programs.

The primitive → driver-input altitude follows Project Chrono lead Dan Negrut's feedback on issue #746: align each manifest entry to a concrete ChSystem configuration at the level of Chrono's motion primitives and driver inputs.

Method coverage

grasp/release, dock, detect, capture, speak, listen return not_supported_in_base_sim (a Chrono::Sensor or articulated-model companion supplies them under the unchanged program, manifest, and validator). The drone trio returns not_applicable_sim.

Install / use

PyChrono ships via conda-forge, not as a PyPI wheel. The [chrono] extra is intentionally empty (it documents the boundary); pychrono is imported lazily, so this module loads on every host without it.

conda install -c conda-forge pychrono            # the engine
pip install -e reference/chrono-runtime[chrono]   # the adapter

from urml_chrono_runtime import ChronoAdapter, ChronoConfig
from urml_chrono_runtime.adapter import DriverSegment
cfg = ChronoConfig(steps_per_command=200,
                   location_to_segment={"ridge_waypoint": DriverSegment(driver=[0.8, 0.1, 0.0])})
with ChronoAdapter(cfg) as sim:
    r = sim.send_navigation_goal(location="ridge_waypoint")
    assert r.success and r.final_pose["sim_time"] > 0.0

Without pychrono installed, ChronoAdapter() raises a clear error pointing at conda-forge.

Status

v0.1 (this release):

• ChronoAdapter + ChronoConfig (PyChrono, no ROS). chrono_vehicle_cell manifest + conformance/fixtures/home/21_chrono_vehicle_terrain_positive.yaml verified through the runner (hermetic against MockROSAdapter; adapter-agnostic against ChronoAdapter).
• Terramechanics scene (scene: terramechanics): a rig on Chrono SCM deformable terrain, selected by the manifest's validation.terrain_fidelity: deformable hint (RFC-0381). The validation-evidence payload gains sinkage, peak contact force, and a tip-stability margin alongside the base dynamics — the richer evidence Project Chrono lead Dan Negrut pointed at on #746. See terramechanics.py and chrono_adapter.terramechanics.yaml.
• Hermetic unit tests: navigation (configured + unmapped), the NSC/SMC system-type switch, measure (validation-evidence payload), scan-stub, lifecycle, the not-supported / not-applicable-sim sentinels, the missing-pychrono (conda-pointing) error, the conformance hook, and the terramechanics scene (sinkage / contact-force / tip-margin evidence, driver-force application, bare-path regression) — no pychrono install required (a fake pychrono, with a vehicle/SCM surface, is injected into sys.modules).
• Gated .github/workflows/chrono-integration.yml: chrono-smoke (real pychrono from conda-forge + the hermetic suite + the live smoke) and chrono-sitl-e2e against a real Chrono::Vehicle scene (first run is a calibration run by design — the established px4 / mujoco / opcua convention). The live SCM scene is that calibration target: its physics reads are version-sensitive, so each degrades to an honest unavailable note rather than crashing.
• SPEC-GAPS.md: the two manifest gaps the mapping surfaced (terrain-fidelity + simulator-target-class hints) shipped as RFC-0381; the terramechanics scene now reads the terrain-fidelity hint.

Follow-ups (not yet): a true sentence→motion validation video; a Chrono::Sensor companion for detect / capture; a full Chrono::Vehicle (HMMWV-class) model under the rig, pinned in CI.

Core Commitment

This runtime is Apache 2.0. It is outside the Core Commitment boundary (only ROS 2 + PX4 reference runtimes are named there) but carries the same no-vendor-coupling, no-cloud, no-enterprise-edition posture. PyChrono / Project Chrono is BSD-3-Clause (confirmed by the maintainers on #746); a validated-intent mapping carries no license entanglement.

Related documents

• /reference/mujoco-runtime/ — the zero-ROS simulator sibling whose structure this mirrors.
• /docs/rfcs/0328-project-chrono-outreach.md — the engagement and mapping this implements.
• /docs/rfcs/0014-substrate-conformance.md — the conformance contract this is built against.
• /conformance/ — the test suite that decides conformance.