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Interpetting a stream of cmd_vels

asked 2018-08-15 10:40:39 -0600

pitosalas gravatar image

updated 2018-08-15 10:43:14 -0600

gvdhoorn gravatar image

Investigating weird observed behavior of my TurtleBot3 (previous question: #q300209) I monitored the cmd_vel topic during the observed behavior. The conditions are as follows:

  • turtlebot3 running kinetic
  • map made by gmapping followed by teleoping to visit the maze
  • I changed the resolution of the map from 0.05 to 0.01 (I don't think this matters)
  • Saved the map
  • Stopped gmapping
  • start navigation

The robot was able to navigate to a variety of corners of the maze relatively well (it did get confused often.) but when I set up a goal where it would try to drive in reverse (twist x < 0) it would exhibit the bucking behavior. And looking at the cmd_vel message stream I did indeed see negative cmd_vels right next to positive ones. I was not running any teleop at the time. Here is some of the data. I had to search for it but you see negative x's next to positive x's. The maximum linear speed specified for TurtleBot3 is 0.22 so -0.11 is about half the maximum.

Any comments on whether this is normal or weird? And whether this can explain the "bucking" (very intense shuddering motion) that I've reported seeing?

linear: 
  x: -0.113387688994
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -0.661418616772
---
linear: 
  x: -0.12927775085
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -0.976840138435
---
linear: 
  x: 0.126691520214
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -1.05274891853
---
linear: 
  x: -0.148515239358
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -0.77896797657
---
linear: 
  x: -0.127474233508
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -0.721023142338
---
linear: 
  x: 0.134267643094
  y: 0.0
  z: 0.0
angular: 
  x: 0.0
  y: 0.0
  z: -1.08932781219
---
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Comments

You should try to find which nodes are publishing on the /cmd_vel topic with rosnode info /cmd_vel (during run time). Or if you are using a cmd_vel mutliplexer simply echo the topic /cmd_vel_mux/active to know what are the inputs for the command.

Delb gravatar imageDelb ( 2018-08-16 04:37:47 -0600 )edit

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answered 2018-08-15 14:06:35 -0600

This is almost certainly to do with your local planner configuration. Have you started with the default parameters and slowly tuned from there?

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Comments

Interesting! Actually I didn't touch the default that came with the installs. Is there a certain file that I can look at and/or post? The one thing I changed was when I made the map I changed the resolution from 0.05 to 0.01. Could that be it?

pitosalas gravatar imagepitosalas ( 2018-08-15 14:15:58 -0600 )edit

I wouldnt think so, but you should try with 0.05 and report back

stevemacenski gravatar imagestevemacenski ( 2018-08-15 16:09:21 -0600 )edit

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Asked: 2018-08-15 10:40:39 -0600

Seen: 36 times

Last updated: Aug 15 '18