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A link has invalid inertia

asked 2021-10-19 15:31:25 -0600

nealtanner gravatar image

What (and where) are the constraints that are checked when loading a model to decide if a link's inertia matrix is valid or not?

In my specific example, I am trying to model a 50 kg cylinder that is 1.5 m long with a 0.2 m radius. According to this online moment of inertia calculator, I come up with Ixx=10, Iyy=10, Izz=1, which loads and runs fine. However, when I slightly change Ixx and Iyy to model a somewhat squashed (elliptical) cylinder, I receive the following error.

[Err] [Server.cc:183] Error Code 18: Msg: A link named hull has invalid inertia.

The snipped from my .sdf file is below.

  <inertial>
    <mass>50.24</mass>
    <inertia>
      <ixx>12.0</ixx>
      <ixy>0</ixy>
      <ixz>0</ixz>
      <iyy>8.0</iyy>
      <iyz>0</iyz>
      <izz>1.0</izz>
    </inertia>
  </inertial>
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answered 2021-11-11 23:34:36 -0600

azeey gravatar image

The principal moments of the inertia must satisfy the triangle inequality. In your case iyy + izz < ixx, which is invalid.

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Asked: 2021-10-19 15:31:25 -0600

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Last updated: Nov 11