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Should the odometry have better no speed or a calculated speed or cmd_vel?

asked 2014-11-16 23:56:13 -0500

ct2034 gravatar image

updated 2014-11-17 04:07:15 -0500

I am working on a robot. And currently I have no information about its actual speed, like from motors e. G. But the odom message has a field for twist. What will be the best thing to do:

  1. leave the twist with 0s
  2. calculate speed from past positions ... or
  3. use cmd_vel

Thanks for your help.

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answered 2014-11-17 02:02:32 -0500

ahendrix gravatar image

There are two places where the speed information in an odometry message is used:

navigation (move_base) uses the speed as the current speed of the robot, for computing the maximum commandable speed according to the acceleration limits. Setting a zero speed will confuse move_base and generally precent the local_planner from commanding the maximum velocity

A kalman filter (robot_pose_ekf, robot_localization) will usually use the velocity from the wheel encoders as one of the inputs to the kalman filter, which will integrate the velocity along with other measurements to produce an estimate of the robot's position. Again, using zeros here can cause the position estimates of your robot to be wrong.

If you can differentiate the wheel positions to produce a fairly clean, stable velocity estimate, that's probably more accurate than simply repeating the commanded velocity.

If there's a lot of noise in your differentiated wheel velocities, or if your wheel speed controller is not very accurate, using the calculated wheel velocities may cause the navigation controller to be unstable, and it may be wiser to repeat the commanded velocities.

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Asked: 2014-11-16 23:56:13 -0500

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Last updated: Nov 17 '14