turtlebot_gazebo demo questions

asked 2012-02-22 08:06:58 -0500

cassander
121 ●13 ●15 ●21

updated 2012-02-23 01:17:47 -0500

I have a few questions regarding the turtlebot_gazebo demo.

1 > Does the physics simulator gazebo limit the frame rate at 25 fps?

2 > What happens when a node publishes messages to a topic faster than they are being consumed? Do the messages wait in a queue to be consumed?

3 > And is it possible to have a computation graph where nodes are written using different client libraries?

4 > Could you also please tell what is the meaning of the term RMS Error in gazebo?

5 > How can a node consume and produce messages to the same topic? Is it some kind of closed feedback loop control for that particular node?

Thanks and regards.

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Shouldn't this be five questions?

Mac ( 2012-02-22 13:11:51 -0500 )edit

I agree! At least put the common topic of all questions in the title, e.g. "turtlebot_gazebo demo details".

bit-pirate ( 2012-02-22 13:50:25 -0500 )edit

@Marcus Thanks for pointing that out. Title changed )

cassander ( 2012-02-23 01:18:13 -0500 )edit

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answered 2012-02-22 08:39:02 -0500

DimitriProsser

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1) The "frame rate" of Gazebo (the rate at which it's drawn to screen) is based on your computer's hardware. Gazebo runs two threads, a physics thread and a render thread. The physics thread's update rate can be set in the .world file.

2) ROS queues all incoming messages until nodes are able to service those callbacks. This queue length is specified in the constructor of a subscriber.

3) If by "different client libraries" you mean, "can you use C++ and Python for different nodes in the same graph?", then the answer is yes. You may be some nodes in C++ and some in Python with no problem at all.

4) I will omit this for someone more with more Gazebo knowledge.

5) It is not recommended to have a node subscribe to and publish to the same topic. You should have two different topics for this. Since you cannot know which node publishes a certain message on a topic, you could cause a lot of confusion doing this.

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answered 2012-02-22 15:12:52 -0500

hsu
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4) RMS error displayed in gazebo (electric) is the root-mean-squared value of the change in Lagrange multipliers (Δλ) as described here. It's an approximate indicator of how much the constraint satisfaction step has converged under the quickstep algorithm.

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Im sorry but that just flew over my head. In any case, is this something that I have to be consciously aware while using ROS and gazebo?

cassander ( 2012-02-23 04:28:28 -0500 )edit

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