A gerotor and bearing apparatus for a whirling mass orbital vibrator which
generates vibration in a borehole. The apparatus includes a gerotor with
an inner gear rotated by a shaft having one less lobe than an outer gear.
A whirling mass is attached to the shaft. At least one bearing is
attached to the shaft so that the bearing engages at least one sleeve. A
mechanism is provided to rotate the inner gear, the mass and the bearing
in a selected rotational direction in order to cause the mass, the inner
gear, and the bearing to backwards whirl in an opposite rotational
direction. The backwards whirling mass creates seismic vibrations.