which coordinate system is mass_center of body defined in?

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ruoshi wen
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Joined: Sat Jun 17, 2017 7:44 pm

which coordinate system is mass_center of body defined in?

Post by ruoshi wen » Fri Sep 15, 2017 2:16 am

Hi, all!
I want to know which coordinate system is mass_center defined in.

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				<Body name="r_humerus">
					<mass>1.864572</mass>
					<mass_center> 0 -0.180496 0</mass_center>
					<inertia_xx>0.01481</inertia_xx>
					<inertia_yy>0.004551</inertia_yy>
					<inertia_zz>0.013193</inertia_zz>
					<inertia_xy>0</inertia_xy>
					<inertia_xz>0</inertia_xz>
					<inertia_yz>0</inertia_yz>
					<!--Joint that connects this body with the parent body.-->
Also, I want to know the axis of SpatialTransform is defined in which coordinate system.
e.g.<axis>-0.05889802 0.0023 0.99826136</axis> of coordinates "r_shoulder_elev"

Code: Select all

<Joint>
						<CustomJoint name="r_shoulder">
							<!--Defines how the child body moves with respect to the parent as a function of the generalized coordinates.-->
							<SpatialTransform>
								<!--3 Axes for rotations are listed first.-->
								<TransformAxis name="rotation1">
									<!--Names of the coordinates that serve as the independent variables         of the transform function.-->
									<coordinates>r_shoulder_elev</coordinates>
									<!--Rotation or translation axis for the transform.-->
									<axis>-0.05889802 0.0023 0.99826136</axis>
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Dimitar Stanev
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Joined: Fri Jan 31, 2014 5:14 am

Re: which coordinate system is mass_center of body defined in?

Post by Dimitar Stanev » Fri Sep 15, 2017 7:22 am

I want to know which coordinate system is mass_center defined in.
Body's local frame.
Also, I want to know the axis of SpatialTransform is defined in which coordinate system.
e.g.<axis>-0.05889802 0.0023 0.99826136</axis> of coordinates "r_shoulder_elev"
viewtopicPhpbb.php?f=91&t=6619&p=17217& ... 20da3eb962
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ruoshi wen
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Joined: Sat Jun 17, 2017 7:44 pm

Re: which coordinate system is mass_center of body defined in?

Post by ruoshi wen » Sun Sep 17, 2017 6:08 pm

Body's local frame.
How to define Body's local frame?
Thanks.
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Dimitar Stanev
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Re: which coordinate system is mass_center of body defined in?

Post by Dimitar Stanev » Sun Sep 17, 2017 11:26 pm

Each body moves wrt to a parent body. So the position and orientation of body's local frame depends on its predecessors. Essentially you need to specify the joint type.

https://simtk-confluence.stanford.edu/p ... ew/3376228
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