A rotating imaging system has a rotating portion, an idler, at least one sensor, a tilt sensor and a processor. The rotating portion has a diameter and rotates about a central axis. The idler rotates about an axis parallel to the central axis, and has a second diameter that is smaller than the diameter of the rotating portion. The rotating portion and the idler engage with each other such that both rotate simultaneously. The at least one sensor detects flags on the idler as the idler rotates. The tilt sensor is mounted to the rotating portion and determines a rotation angle of the rotating portion within a range of one revolution, and the processor determines an absolute rotation of the rotating portion based on at least a signal from the at least one sensor and the rotation angle determined by the tilt sensor.