An omnidirectional borehole
navigation system comprising a housing for traversing a borehole; an outer
gimbal connected to said housing and at least two or more stacked inner gimbals that are nested in and connected to said outer
gimbal, said inner gimbals each having an axis parallel to one another and perpendicular to the outer
gimbal; at least one inertial sensor located on each inner gimbal, the at least one inertial sensor including at least one gyro or
accelerometer, the gyros having input axes that span
three dimensional space and the accelerometers having input axes that span
three dimensional space; one or more gyro circuits within the housing and responsive to the at least one gyro to produce the inertial angular rate about each gyro input axis; one or more
accelerometer circuits within the housing and responsive to the at least one
accelerometer to produce the non-
gravitational acceleration along each accelerometer input axis; a processor responsive to said gyro circuits and said accelerometer circuits for determining the attitude and the position of said housing in the borehole; an outer gimbal drive
system with complete rotary freedom; and an inner gimbal drive
system for controlling the orientation of each of the inner gimbals. The drive
system that controls the stacked inner gimbals may be a
rack and pinion gear, or a
gear train such as a bicycle chain gear rotating the inner gimbals in parallel between stops while maintaining the input axis orthogonality of gyro triads and the input axis orthogonality of accelerometer triads. The inner gimbal stops may be elastic to allow for small misalignments in the inner gimbal drive system.