Cycle frequency relation between localization and navigation nodes

asked 2015-09-22 11:20:28 -0600

friufriu gravatar image

updated 2015-09-23 03:34:41 -0600

Hello all, I have a robot which is already set up and running with ROS. Everything seems to work fine most of the time, but any now and then I get a very weird behavior. Basically, the laser projection in Rviz does not completely overlay with the map as the robot moves (i.e. a map wall and the line seen by the laser should coincide as the robot moves). It is if I had the encoders incorrectly set, but this is not the case since this strange behavior happens only very few times.

Moreover, if I bring everything down and up again, it completely disappears. At first I could not make any sense of it, but now I suspect it only happens when I launch everything and leave the robot standing still for a while. I think it is this time -from launching to the first movement- that is producing some kind of lack of sync somewhere.

Now, everything in my robot runs at 30Hz (including odometry and move_base, where I set it up with the corresponding parameter) but the amcl, which runs at 40Hz, which is the hokuyo_node (and the laser itself) frequency.

My question is, could this difference in frequencies be affecting the correct pairing of the localization and navigation components of my system?

May be it is only after some time that the effect is visible e.g. accumulation of messages, lag, etc. This would explain why I only get this in these specific cases.

So, should everything run at the same frequency? Or can there be different frequency relations among the localization and navigation nodes?

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