URDF compositional complexity

asked 2015-02-06 14:37:55 -0500

Freyr
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updated 2015-02-06 16:43:16 -0500

I'm in the process of creating a URDF description for my quadruped robot. I have a bunch of bioloids frames and motor models but if I define the leg chains using them I end up with a bunch of fixed joints that do nothing except allow me to define geometries and visuals. Is that to be expected? Should I try to 'bake' the models into single shapes? How do the fixed joints affect KDL chains generated from the description? Does the performance suffer?

Are there any best practices in this regards?

answered 2015-02-07 05:39:55 -0500

Stefan Kohlbrecher

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Note you can specify multiple collision geometries per link since introduction of this feature about a year ago or so and most tools (rviz, gazebo, moveit to name a few) support this. This way, you can get rid of most fixed frames. I'm actually not sure if this also works for visual geoms. In most cases, a few fixed frames won't hurt performance too badly though. What is more important for many applications (motion planning, simulation) is that you have simplified collision geometries for your model (low poly meshes or primitive based).

A example of the use of multiple collision geoms per link is https://bitbucket.org/osrf/drcsim/src...

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That is certainly useful to know. I'll try it out for visuals and see what happens.

Freyr ( 2015-02-07 07:01:47 -0500 )edit

Multiple visuals work in rviz but seem to pick up the material of the first visual element defined. Not sure if that is a bug or just not supported. Anyway I can define fewer links and joints which was the point.

Freyr ( 2015-02-07 19:04:14 -0500 )edit

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