It's very difficult or next to impossible to precisely control wheeled robot motion using open loop motor control. Many applications require accurately setting the pose or travel distance of a wheeled robot. Small continuous rotation micro servo motors are a great low cost solution to drive small robots but they lack the feedback control of larger servo motors.
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/tutorials/show/add-an-encoder-to-feetech-micro-360-degree-continuous-rotation-servo-fs90r