Enlighten Engineering

OMD For Simulink Users Guide

Introduction

OMD is partially written in Python and definning models is done using a python script. This document describes how each element is defined and includes a set of python commands that defines a model.

Body

Description

Defines a body to be included in the simulation. Bodies have mass and inertia and move in space in response to forces and interactions with other bodies to which they are joined through joints.
The following parameters need to be defined:

• Mass: 1 Scalar
• Inertia: 3x3 Matrix

Syntax

OMDPYTHONBODY = Body("name", Bool specifiying if body is fixed, mass, inertia)

Example

b1 = Body("body1",False,5,[[1,0,0],[0,1,0],[0,0,1]])
Instantiates a body b1, with the name "body1" (often the same string), which is not fixed, has a mass of 5 and the inertia isthe identity matrix.
The units are left to the user, just be consistent.

Joints

Revolute Joint

Description

Defines a kinematic connection between 2 bodies which only allows those two bodies to rotate relative to each other about a single axis.

Syntax

OMDREVJOINT = JointRev("name",Parent,Child,p2j,j2c,a,theta,omega)
where:

• name: name of the joint
• Parent: First Body of the Joint
• Child: Second Body in joint
• p2j: Vector defining the location from the Parent to the joint in the Parent's Coordinates
• j2c: Vector defining the location of the joint in the Parent's Coordinates
• a: Vector defining the axis of the joint in the Parent's Coordinates
• theta: Initial joint orientation
• omega: Initial joint angular velocity

Example

p2j = [0.,0,0]
j2c = [1,0,0.]
a = [0,1,0]
j1rev = JointRev("j1rev",irf,b1,p2j,j2c,a,0,0)

Translational Joint

Description

Defines a kinematic connection between 2 bodies which only allows those two bodies to translate relative to each other along a single axis.

Syntax

OMDTRANSJOINT = JointTrans("name",Parent,Child,p2j,j2c,a,x,xdot)
where:

• name: name of the joint
• Parent: First Body of the Joint
• Child: Second Body in joint
• p2j: Vector defining the location from the Parent to the joint in the Parent's Coordinates
• j2c: Vector defining the location of the joint in the Parent's Coordinates
• a: Vector defining the axis of the joint in the Parent's Coordinates
• x: Initial seperation
• xdot: Initial translational velocity

Example

p2j = [0.,0,0]
j2c = [1,0,0.]
a = [0,1,0]
j1trans = JointRev("j1trans",irf,b1,p2j,j2c,a,0,0)

6DOF Joint

Planer Joint

Spherical Joint

U Joint

Forces

1 Body Force

Description

A force and or torque on a body whose line of action and offset are both definable.

Syntax

f1 = Force1Body("f1",b1,fv,tv,coord)
where:

• f1: Name of the Force
• b1: Body on which the force is applies ( not the name of the body, which is a string)
• fv: The Force Vector in Body Coordinates
• tv: Torque Vector in Body Coordinates
• coord: Coordinates in Body coordintes relative to the center of mass on which the force and torque vector acts

Example

fv = [0.0,0.0,-9.81]
tv = [0,0,0]
coord = [0,0,0]
f1 = Force1Body("f1",b1,fv,tv,coord)

Revolute Joint Force

Description

Applies torque to a revolute joint, this joint is applied by the parent on the child. The Vector defining the force is applied to a child.
An equal and opposite force is applied to the parent.

Syntax

f3 = ForceRevJnt("f3",j1rev,torque)
where:

• f1: Name of the Force
• j1rev: Joint to which the torque is applied
• torque: Scalar defining the torque to be applied