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buoyancy neutral object goes up with hydrodynamics plugin

asked 2017-03-14 23:15:02 -0500

kalvik gravatar image

updated 2017-03-15 10:36:46 -0500

Hello, I made an object in gazebo. I am using the hydrodynamics plugin on it. The fluid density is 1000. Every part of the object has the same density 1000. Its total weight is 0.218 kgs. When I start the sim the object just keeps going up. Why is it doing this. Since the object has the same density as its surroundings doesn't my object have neutral buoyancy? When I increase my objects weight to a couple of kgs it stays at the bottom. Why is it doing this?

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It might be easier for someone to help you if you provide a simple example model which reproduces the problem you're having. The yellow submarine on the underwater.world example stays in place: http://gazebosim.org/tutorials?tut=hydrodynamics&cat=plugins

chapulina gravatar imagechapulina ( 2017-03-15 10:49:25 -0500 )edit

I am making a bluerobotics T200 thruster. It's relatively small and weighs 0.211 kgs. When I create it in gazebo it ends up going to the surface and floating at the top. I guess if I attach the thruster to a thruster then it won't have the same issue.A simpler example of my problem would be if I make a tube which weighs 0.211kgs but with the same density as water (along with the hydrodynamics plugin) it floats at the surface instead of staying in place.

kalvik gravatar imagekalvik ( 2017-03-15 15:07:20 -0500 )edit

Are you using the `<volume>` tag?

chapulina gravatar imagechapulina ( 2017-03-15 15:28:49 -0500 )edit

Are you using the `volume` tag?

chapulina gravatar imagechapulina ( 2017-03-15 15:29:07 -0500 )edit

I am using the model editor and I am not aware of a volume tag so no.

kalvik gravatar imagekalvik ( 2017-03-15 15:30:34 -0500 )edit

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answered 2017-03-15 15:59:26 -0500

So based on the comments, I think you might not be setting all the necessary parameters for the buoyancy plugin. I suggest you go through this tutorial, which explains the parameters for that plugin:

http://gazebosim.org/tutorials?tut=hy...

When attaching the plugin to the model using the model editor, be sure to add the <volume> tag under <link>. Otherwise, Gazebo will use the bounding box of the link by default. If you want a density of 1000 kg / m^3 for a mass of 0.218 kg, the volume should be voume = mass / density = 0.218 / 1000 = 0.00218 m^3.

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Asked: 2017-03-14 23:15:02 -0500

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Last updated: Mar 15