Calibrating the motors in first robot


I followed the “Your First Robot with ROS” tutorial until chapter 3. I am a bit conufed about the
calibration process for the motors

there are motors with wheel encoders used but there are never encoder readers installed.
Are there any encoder readers available somewhere (not in the parts list ! ) ?

Maybe I over read it. How would I calibrate cmd_vel commands without the wheel encoders ?



So this is a very basic simple build. So the cmd_vel is calibrated by sight. You are right that enconders would help to do that, but we didnt add that to this build.


that means calibration comes through manual intervention or means by sight through camera ?
Is the calibration process anywhere part of a course ?