×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

inertia properties

inertia properties

inertia properties

(OP)
Hello all,

I'm building a dynamical model of an exoskeleton. To determine the inertial properties Solid Works is used (version 2010).
If I look at the output in the mass properties section, something strange happens to my opinion.
If the rotation matrix is pre- and postmultiplied with the diagonal inertia matrix(Equation used: Iout = inv(R)*Iinert*R

), the solution does not correspond with the other output (numbers are correct but minus signs are wrong). An example is included below.
Can somebody help me?

Mass properties of selected components

Output  coordinate System: Coordinate System4

The center of mass and the moments of inertia are output in the coordinate system of 100_Exoskeleton-without motors-update_20sim_07022011

Mass = 146.3293 grams

Volume = 50645.2787 cubic millimeters

Surface area = 23236.8002 millimeters^2

Center of mass: ( millimeters )
    X = -48.3769
    Y = -0.8218
    Z = 82.9338

Principal axes of inertia and principal moments of inertia: ( grams * square millimeters )
Taken at the center of mass:
R: Ix = (-0.6466, 0.0162, 0.7627)       Iinert(diagonal matrix    with Px,Py and Pz on diagonal) :Px = 53372.2917
         Iy = (0.7625, 0.0442, 0.6455)                                     Py = 546886.0625
         Iz = (-0.0233, 0.9989, -0.0409)                       Pz = 560232.1085

Moments of inertia: ( grams * square millimeters )
Taken at the center of mass and aligned with the output coordinate system. Iout
    Lxx = 340561.7431    Lxy = -4846.6654    Lxz = -243381.0661
    Lyx = -4846.6654    Lyy = 560073.6574    Lyz = 6627.9462
    Lzx = -243381.0661    Lzy = 6627.9462        Lzz = 259855.0621
 

RE: inertia properties

I believe that is because your center of mass is located in two negative axis and one positive axis.

StrykerTECH Engineering Staff
Milwaukee, WI
http://www.stryker-tech.com/

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources