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Gazebo model jittering

asked 2013-02-13 10:59:36 -0500

Vaibhav Kapoor gravatar image

Hi, I managed to finally catch up with all the great development happening. I have put my model on this repository in the alesdescription/models/alesrobot folder. https://bitbucket.org/TheLegace/ales_...

I had made joints for my four wheeled robot, but for some reason it seems to be moving or jitterring on its own. It's noticeable and I am assuming the pose is changing. There is no plug in enabled so I cannot for the life of me understand why the model is moving.

If you would like me to upload the model anywhere else please let me know.

Thank you.

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You could change the link to point directly to the model file, it's faster for others to look into it.

AndreiHaidu gravatar imageAndreiHaidu ( 2013-02-13 12:06:18 -0500 )edit

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answered 2013-02-17 18:51:49 -0500

Vaibhav Kapoor gravatar image

Hi I had started removing every single component until the jitterring had stopped. The very first link was even jitterring, I realized that maybe it's the inertia's that I had not setup yet. So I just put some reasonable values and it looks like the model is not jitterring any longer.

I also had to make sure the wheels had inertia as well, also the high friction coefficient that I got from the Golf Cart vehicle.

Thank you.

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answered 2013-02-18 00:32:38 -0500

PMilani gravatar image

Hi Vaibhav

You can get jittering if the model is pretty stiff, ie large joint forces for the masses of the links. Looking at your ales.urdf file, I think that this is your problem as your link masses are quite tiny. In its worst case it can destroy your model.

However you could try reducing the physics step size (the dt element of your physics attribute in your SDF file) or increasing the number of your quickstep iterations. Play around with these to get a good feel for their effect.

This will slow your sim to real time ratio but it will allow the effect of comparatively large forces on small inertias to be accurately modelled.

cheers

Peter

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answered 2013-02-13 12:04:22 -0500

AndreiHaidu gravatar image

Hi,

Maybe you have some collisions between the links, and the joints try to keep them together, so the model is jittering. Try to "debug" it by commenting out the joints one at a time to see if one of them is responsible for it.

Cheers

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Asked: 2013-02-13 10:59:36 -0500

Seen: 1,277 times

Last updated: Feb 18 '13