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Orientation of mass moment of inertia

asked 2015-05-16 04:02:41 -0500

Tytteboevsen gravatar image

How should the orientation of the mass moment of inertia matrix be?

An example: Lets assume we have a cube and we are gonna make a joint angled 45 degrees on one of the sides. should i then calculate and orient the mass moment of inertia matrix according to this joint - angled 45 degrees. Or should i just calculate the Mass moment of inertia acoording to the initial reference frame?

Hope my question is clear.

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answered 2015-05-19 07:01:26 -0500

Tytteboevsen gravatar image

I think i get it now. To do what i want to I guess you have to:

First make sure where you initial reference frame is of the link. If you imported an stl or dae file this is the origo of you drawing.

Next find out where the COM is located acoording to this initial reference frame and use this in the link sdf under pose under xyz.

Then align the inertia axis as you wish and rotate them using the rpy of the same pose parameter.

You now have placed the COM according relative to the link reference frame and aligned the axis of the inertia matrix.

Now enter the inertia matrix according to the axis and through the COM. Link to example

Please note that the pose parameter is under the inertial parameter and this denotes the position of the COM relative to the link reference frame and that the rpy denotes the orientation of the inertia matrix.

Hope this helps someone else.

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answered 2015-05-17 07:13:05 -0500

scpeters gravatar image

I prefer to compute inertia in a frame aligned with the principal axes of the rigid body, and then use pose offsets to define the joint location. Can you describe your model a little further?

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Please see my website here for more info about my robot. Scroll down for images. The thing is my ankle is tilted 15 degrees and when i do the control of the robot i need the inertia calculated along this tilted axel. My hope was that i could use the same in gazebosim. Hope this clarifies it.

Tytteboevsen gravatar imageTytteboevsen ( 2015-05-17 14:59:57 -0500 )edit
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Asked: 2015-05-16 04:02:41 -0500

Seen: 809 times

Last updated: May 19 '15