how to control kobuki accurately?

edit

I guess your "problem" lies in the "velocity_smoother" package. ( http://wiki.ros.org/yocs_velocity_smo... ) This package ramps the speeds up and down in order to provide smoother commands to the base. You can play around with the parameters of this package using dynamic reconfigure, e.g. change the acceleration and deceleration limits to ridiculously high values to see if that makes a difference, or skip the node all together by directly publishing on the control topic:

/mobile_base/commands/velocity

Otherwise, it could also be network latency or a time sync issue if you control the kobuki from a workstation pc and not directly from the laptop connected to the base. This is easy to check by directly running the code on the laptop without any network connection in between.