Weird sphere movement

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Original report (archived issue) by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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Pull request #51 adds an example world which has a sphere on top of a large box representing the ground plane. I'd expect the sphere, which has no link, visual, collision or inertia poses, to sit still on top of the floor, but instead it sways back and forth as if its CoM wasn't centered or its collision shape a smooth sphere:

I'm ticketing this here because I'm not sure if the issue is coming from ign-physics or the integration.

[osrf-migration]

Original comment by Michael Grey (Bitbucket: mxgrey, GitHub: mxgrey).

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One possibility that jumps to mind is that dartsim by default will mesh-ify primitives when using FCL as a collision detector, because it used to have known issues with primitive shapes. This was fixed as of version 0.4, but the the Xenial repo distributes 0.3 (although Bionic distributes 0.5, so maybe we can start to avoid this problem). If the sphere is being converted into a mesh, then it might be bouncing back and forth between two corners of that mesh.

But I'm just speculating about this being the cause. I'll take a deep dive into this example and see if I can identify the real issue.

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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That does look like a meshified sphere. +1 to using the version in Bionic if that solves the issue.

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Original comment by Michael Grey (Bitbucket: mxgrey, GitHub: mxgrey).

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A potential fix for this issue can be found here: https://osrf-migration.github.io/ignition-gh-pages/#!/ignitionrobotics/ign-physics/pull-requests/36/

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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@chapulina , did the above PR fix this issue for you?

[osrf-migration]

Original comment by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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• changed state from "new" to "resolved"

Yes, the problem is solved, thanks @mxgrey !