Introduction to SimCreator and Multi-Body Dynamics  April 25, 2005

What is SimCreator?  GUI Based System Modeling Package  Similar to Simulink, SystemBuild, EASY5  Specialized for Realtime System Modeling: Driving Simulation, Flight Simulation, Games, Embedded Control  Modeling Constructs also Support Complex Off- Line Simulation

Typical SimCreator Session

SimCreator Capabilities  Support for Single and Double Precision Models  Easy Editing of User Coded Components  Component Connectors Include a Description and Units  Vector Connections  Variable Width Components  Enhanced Metafile Based Icons  HTML Based Help Files  Sub Models

SimCreator Capabilities  Easy Access to and Setting of Initial Conditions  State Values Can be Overridden Inside User Code  Automatic C Code Generation  Multiprocessing with Multirate Integration  Generated C Code Uses Datafile Based Constants and Initial Conditions  Multiple Inputs and Outputs for User Coded Components  External Code Hooks to Inputs, Outputs, and Initial Conditions

SimCreator Capabilities  Highly Efficient Realtime Code  Mixed Continuous and Algebraic Inputs to Same User Code Block  Multiple Connections Can Be Made Between Components with a Single Mouse Click  Generates Embedded Code  Parallel and Distributed Build and Execution Environment  Highly Efficient Execution Interpretor

Standard Library

Math Library

Altia Interface for GUIs

GUI Plotting Dialog

Driving Simulator

Distributed Simulator

Multi-Body Dynamics  SimCreator’s multi-body dynamics component library is based on Composite Rigid Body Methods (CRBM) (recursive method)  CRBM method is used for open kinematic chains  For closed kinematic chains, constraint equations with corresponding Lagrange multipliers are introduced and are used to augment the mass matrix

Recursive Multi-Body Approach Revolute LinAccel1 LinVel1 LinPos1 AngAccel1 AngVel1 TM1 Force1 Moment1 LinAccel3 LinVel3 LinPos3 AngAccel3 AngVel3 TM3 Force3 Moment3 JointAng JointAngRate ExternalJointTorque LinkNumber1 LocalJointAxis LinkNumber3 OffsetMB LinAccel1 LinVel1 LinPos1 AngAccel1 AngVel1 TM1 Force1 Moment1 Offset LinAccel3 LinVel3 LinPos3 AngAccel3 AngVel3 TM3 Force3 Moment3 LinkNumber1LinkNumber3

Mass Matrix  To maintain real-time must select the appropriate joints to minimum the number of equations in the mass matrix Joint Type# of Equations Revolute1 Prismatic1 Cylindrical2 Universal2 Screw1 Spherical3 Cut Spherical3 Distance Constraint1

Double Pendulum Example

Double Pendulum Results  Z in SimCreator is –Y in DADS

4 Bar Example

4 Bar Results

MTVR Model (Working with John Weller and Steve Schultz)

MTVR Corner Module

Lateral Displacement vs Roll Angle (DADS vs. SimCreator)

Realtime Performance  The MTVR had the following complexity:  66 equations in the augmented mass matrix  36 equivalent joints  25 equivalent bodies  115 states  Full powertrain  2nd order Runge-Kutta method at 500 Hz.  Using a computer with a 1.7 GHz Pentium M  MTVR model took 22 seconds to perform a 60 second simulation.

Powertrain  Vehicle subsystems are also broken down into reusable modules  Lowest level components are C code

MTVR Powertrain

SimCreator Conversion (Phase I SBIR)  DADS is a Cartesian multi-body modeling approach. Several steps are required to translate a Cartesian model into a recursive (CRBM) model, needed for real-time simulation in SimCreator. These steps include:  Determine weighting factors for each joint  Determine the best joints to cut  Determine the optimal base body  Build a recursive spanning tree  Minimize mass matrix size  Minimize tree length

Advantage Of GUI  Structured Framework to Build C Code Components  Causality  Unified Integration Algorithm  Built in Data Management and Plotting  Greater Insight Into the Model  Hierarchical Viewing  Model and Component Reuse