Preferred methods and systems generate a control input based on a periodically-varying characteristic associated with the rotation of a drill string. The periodically varying characteristic can be correlated with the magnetic tool face and gravity tool face of a rotating component of the drill string, so that the control input can be used to initiate a response in the rotating component as a function of gravity tool face.
Pursuant to 35 U.S.C. .sctn. 202(c), it is acknowledged that the U.S. government may have certain rights to the invention described herein, which was made in part with funds from the U.S. Department of Energy National Energy, Grant No. DE-FG02-02ER83368.