YAML schema for Chrono model specification

Model specification

A YAML model file model.yaml defines the mechanical system for the simulation. It defines:

1. Bodies: rigid bodies that carry mass and inertia and, optionally, collision and visualization geometry
2. Joints: connection between a pair of bodies, specified either as a kinematic (ideal) joint or as a bushing
3. Passive force elements: translational and rotational linear or non-linear spring-damper force elements acting between two rigid bodies
4. Motors and actuators:
   • translational and rotational motors acting between two rigid bodies at the position (displacement or angle), velocity (linear or angular speed), or force (force or torque) levels. Motors are specified through a time function for the control input (position, velocity, or force)
   • external actuators

Bodies

Each body represents a physical object in the simulation with the following properties:

Property	Description	Required	Default
name	Unique identifier for the body	Yes
fixed	Indicates if body fixed relative to global frame	No	false
mass	Mass in kg	Yes, if body not fixed
com	Center of Mass, relative to body reference frame	No	same as body reference frame
inertia->moments	Moments of inertia [Ixx, Iyy, Izz] relative to centroidal frame	Yes, if body not fixed
inertia->products	Products of inertia [Ixy, Iyz, Izx] relative to centroidal frame	No	[0, 0, 0]
location	Origin of the body reference frame, relative to model frame	Yes
orientation	Orientation of the body reference frame relative to model frame	No	identity rotation

Joints

Joints connect two bodies and constrain their relative motion. They can be represented through constraints (kinematic joints) or through stiff compliance (bushings).

Property	Description	Required
type	Joint type (revolute, prismatic, spherical, etc.)	Yes
name	Unique identifier for the joint	Yes
body1	Name of the first body to connect	Yes
body2	Name of the second body to connect	Yes
bushing_data	Bushing compliance data; if not present, the joint is kinematic	No

Passive spring-damper force elements

Spring-damper elements apply forces between bodies.

Property	Description	Required
type	Spring-damper type type (TSDA, RSDA)	Yes
name	Unique identifier for the force element	Yes
body1	Name of the first body to connect	Yes
body2	Name of the second body to connect	Yes

For linear spring-dampers, use the spring_coefficient and damping_coefficient properties. For example:

spring_dampers:
  - name: linear_spring_damper
    type: TSDA
    body1: first_body
    body2: second_body
    point1: [6.5, 0, 0]
    point2: [5.5, 0, 0]
    spring_coefficient: 50.0
    damping_coefficient: 5.0
    free_length: 1.0
    visualization:
      type: SPRING
      radius: 0.05
      resolution: 80
      turns: 15

For nonlinear behavior, use spring_curve_data and/or damping_curve_data and/or the pair deformation/map_data. These properties allow specification of spring-damper characteristics as tabular data (which will be linearly interpolated by Chrono at run-time). For example:

spring_dampers:
  - name: nonlinear_spring_damper
    type: TSDA
    body1: first_body
    body2: second_body
    point1: [6.5, 0, 0]
    point2: [5.5, 0, 0]
    deformation: [ 0.273304, 0.278384, 0.283464, 0.288544, 0.293624, 0.324104, 0.343002, 0.361899, 0.380797, 0.399694, 0.418592, 0.423672, 0.428752, 0.433832, 0.438912 ],
    map_data: [
      [ -0.666667, -5691.62, -5691.62, -5691.62, -5691.62, -5691.62, -9690.35, -9690.35, -9690.35, -9690.35, -9690.35, -9690.35, -5691.62, -5691.62, -5691.62, -5691.62 ],
      [ -0.333333, -2845.81, -2845.81, -2845.81, -2845.81, -2845.81, -4845.17, -4845.17, -4845.17, -4845.17, -4845.17, -4845.17, -2845.81, -2845.81, -2845.81, -2845.81 ],
      [ 0.0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ],
      [ 0.333333, 21307.1, 21307.1, 21307.1, 21307.1, 21307.1, 11675.1, 11675.1, 11675.1, 11675.1, 11675.1, 11675.1, 21307.1, 21307.1, 21307.1, 21307.1 ],
      [ 0.666667, 42614.2, 42614.2, 42614.2, 42614.2, 42614.2, 23350.2, 23350.2, 23350.2, 23350.2, 23350.2, 23350.2, 42614.2, 42614.2, 42614.2, 42614.2 ]
    ]

Motors

YAML schema