system-create

name	system_create
description	Create and configure a PyChrono ChSystem, gravity, contact method, and solver.
compatibility	pychrono >= 8.0
metadata	{"domain":"mbs"}

Skill: MBS System Creation

Purpose

Create and configure a PyChrono multi-body simulation system (ChSystem), set gravity, choose contact method, and configure the solver.

When to Use

Use at the top of every MBS simulation script, before creating any bodies or links.

Key Concepts

ChSystemNSC vs ChSystemSMC

• ChSystemNSC (Non-Smooth Contact): rigid/impulsive impacts, fast, best for rigid-body scenes with discrete collisions
• ChSystemSMC (Smooth Contact Method): penalty-based, soft contacts, best for granular or compliant-contact scenarios

Gravity

sys.SetGravityY()                                          # shorthand: (0, -9.81, 0)
sys.SetGravitationalAcceleration(chrono.ChVector3d(0, -9.81, 0))  # explicit form
sys.SetGravitationalAcceleration(chrono.ChVector3d(0, 0, 0))       # disable gravity

Collision System

Call only when bodies have collision shapes and contact is needed. For pure MBS (joints and motors only, no contact), omit — it adds overhead and can cause instability.

# When contact/collision is needed:
sys.SetCollisionSystemType(chrono.ChCollisionSystem.Type_BULLET)

# Pure MBS (no contact): do NOT call SetCollisionSystemType

NSC Solver (tune for collision-heavy NSC scenes)

solver_max_iter = int  # max solver iterations
sys.SetSolverType(chrono.ChSolver.Type_PSOR)
sys.GetSolver().AsIterative().SetMaxIterations(solver_max_iter)
# Alternative:
solver = chrono.ChSolverPSOR()
solver.SetMaxIterations(solver_max_iter)
sys.SetSolver(solver)

Minimal Example

import pychrono.core as chrono
import pychrono.irrlicht as chronoirr

solver_max_iter = int  # max solver iterations

# NSC system with gravity and collision
sys = chrono.ChSystemNSC()
sys.SetGravityY()
sys.SetCollisionSystemType(chrono.ChCollisionSystem.Type_BULLET)
sys.SetSolverType(chrono.ChSolver.Type_PSOR)
sys.GetSolver().AsIterative().SetMaxIterations(solver_max_iter)

# SMC system (no gravity, for spring demo)
sys = chrono.ChSystemNSC()
sys.SetGravitationalAcceleration(chrono.ChVector3d(0, 0, 0))