Basic continuous rotation servo calibration.
When making a continuous rotation servo, one should "calibrate" the servo for best positioning. One way is to send the servo a 90 1500us position command and then carefully take the servo apart for the mod and secure the pot shaft with out moving the shaft. Another way is when the servo is apart, power it up and send it a 1500us command, then carefully adjust the pot until the motor stops, then secure the pot shaft in place.