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DART Sphere behaves like a Cube

asked 2020-12-21 06:39:55 -0600

awck gravatar image

updated 2020-12-21 06:43:34 -0600

Dear Gazebo Community,

when I spawn a sphere into an empty world using the ODE engine the sphere just stays where it is (as expected). When I spawn exactly the same sphere into a world simulated with the DART 6 engine, then the sphere first "wobbles" a little and ends up in a slightly different position (and orientation!) than where I spawned it. When I push the sphere around in the DART world (by applying forces in Gazebo 11) then the sphere doesn't roll, but rather behaves like a cube and lands on "one side", while it should execute a smooth rolling motion. Anyone have a clue what this is?

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answered 2020-12-21 12:43:46 -0600

azeey gravatar image

This is caused by the fact that DART, by default, uses the FCL collision library with a configuration that changes simple shapes like sphere into a mesh. In your case, the resulting mesh doesn't have enough resolution to correctly behave as a sphere. You can change the DART's collision detector to bullet and you should get better behavior in your example. You'd that by setting the dart_collision_detectorparameter (http://sdformat.org/spec?ver=1.7&elem...)

<?xml version="1.0" ?>
<sdf version="1.7">
  <world name="default">
    <physics type="dart">
      <dart>
         <collision_detector>bullet</collision_detector>
      </dart>
    </physics>
   ...
  </world>
</sdf>
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Hi azeey, thanks for your quick reply! Indeed, when I change the collision detector to bullet the sphere actually rolls - so it works much smoother now. However, with the bullet collision detector the sphere slowly starts rolling away from its launch position even though I am not applying any forces/torques. Can I increase the mesh resolution? I tried increasing the friction coefficients, inertia and mass values, but the problem persists and the sphere slowly rolls off upon launch. Thanks! :-)

awck gravatar imageawck ( 2020-12-23 05:54:20 -0600 )edit
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Asked: 2020-12-21 06:39:55 -0600

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Last updated: Dec 21 '20