Tumble gyro surveyor

1. A gimbal sensor platform positionable in a tool body having a longitudinal axis, the gimbal sensor platform comprising:

an outer gimbal, the outer gimbal rotatably coupled to the tool body;

an outer angular positioning device coupled to the outer gimbal to rotate the outer gimbal relative to the tool body about an outer gimbal axis of rotation;

an inner gimbal, the inner gimbal rotatably coupled to the outer gimbal;

an inner angular positioning device coupled to the inner gimbal to rotate the inner gimbal relative to the outer gimbal about an inner gimbal axis of rotation; and

a gyro coupled to the inner gimbal, the gyro having a sensitive axis substantially orthogonal to the inner gimbal axis of rotation.

2. The gimbal sensor platform of claim 1 , wherein the outer gimbal axis of rotation is substantially parallel to the longitudinal axis of the tool body.

3. A gimbal sensor platform positionable in a tool body having a longitudinal axis, the gimbal sensor platform comprising:

an outer gimbal, the outer gimbal rotatably coupled to the tool body;

an outer angular positioning device coupled to the outer gimbal to rotate the outer gimbal relative to the tool body about an outer gimbal axis of rotation, the outer gimbal axis of rotation canted to the longitudinal axis of the tool body;

an inner gimbal, the inner gimbal rotatably coupled to the outer gimbal;

an inner angular positioning device coupled to the inner gimbal to rotate the inner gimbal relative to the outer gimbal about an inner gimbal axis of rotation; and

a gyro coupled to the inner gimbal.

4. The gimbal sensor platform of claim 1 , wherein the inner gimbal axis of rotation is canted to the outer gimbal axis of rotation.

5. The gimbal sensor platform of claim 4 , wherein the inner gimbal axis of rotation is substantially perpendicular to the outer gimbal axis of rotation.

6. The gimbal sensor platform of claim 5 , further comprising an inner limit stop, the inner limit stop positioned to restrict rotation of the inner gimbal between a first cant angle and a second cant angle relative to the outer gimbal axis of rotation.

7. The gimbal sensor platform of claim 6 , wherein the first cant angle and second cant angle are in opposite directions of the outer gimbal axis of rotation.

8. The gimbal sensor platform of claim 1 , further comprising one or more accelerometers coupled to the inner gimbal.

9. The gimbal sensor platform of claim 1 , further comprising one or more magnetometers coupled to the inner gimbal.

10. A gimbal sensor platform positionable in a tool body having a longitudinal axis, the gimbal sensor platform comprising:

an outer gimbal, the outer gimbal rotatably coupled to the tool body;

an outer angular positioning device coupled to the outer gimbal to rotate the outer gimbal relative to the tool body about an outer gimbal axis of rotation;

an inner gimbal, the inner gimbal rotatably coupled to the outer gimbal;

an inner angular positioning device coupled to the inner gimbal to rotate the inner gimbal relative to the outer gimbal about an inner gimbal axis of rotation;

a gyro coupled to the inner gimbal; and

one or more accelerometers coupled to the outer gimbal; magnetometers coupled to the outer gimbal; or a positioning gyro coupled to the outer gimbal, the positioning gyro having a sensitive axis substantially parallel to the outer gimbal axis of rotation.

11. The gimbal sensor platform of claim 1 , further comprising one or more accelerometers coupled to the tool body.

12. The gimbal sensor platform of claim 1 , further comprising one or more magnetometers coupled to the tool body.

13. The gimbal sensor platform of claim 1 , further comprising an outer angular position measuring device coupled between the outer gimbal and the tool body.

14. The gimbal sensor platform of claim 1 , further comprising an inner angular position measuring device coupled between the inner gimbal and the outer gimbal.

15. The gimbal sensor platform of claim 1 , wherein the gimbal sensor platform is coupled to a drill string or a wireline system.

16. The gimbal sensor platform of claim 1 , further comprising an outer limit stop, the outer limit stop positioned to restrict rotation of the outer gimbal relative to the tool body.

17. A method comprising:

providing a gimbal sensor platform positioned in a tool body, the gimbal sensor platform including:

an outer gimbal, the outer gimbal rotatably coupled to the tool body;

an outer angular positioning device coupled to the outer gimbal to rotate the outer gimbal relative to the tool body about an outer gimbal axis of rotation;

an inner gimbal, the inner gimbal rotatably coupled to the outer gimbal;

an inner angular positioning device coupled to the inner gimbal to rotate the inner gimbal relative to the outer gimbal about an inner gimbal axis of rotation;

an inner limit stop, the inner limit stop positioned to constrain the rotation of the inner gimbal; and

a gyro coupled to the inner gimbal;

taking a first measurement with the gyro with the outer gimbal in a first position relative to the tool body and the inner gimbal in a first position relative to the outer gimbal, the first position of the inner gimbal in contact with the restraints of rotation of the inner gimbal;

rotating the inner gimbal to a second position relative to the outer gimbal;

taking a second measurement with the gyro;

rotating the outer gimbal to a second position relative to the tool body, the position of inner gimbal defining a third position, the second position of the inner gimbal in contact with the restraints of rotation of the inner gimbal; and

taking a third measurement with the gyro.

18. The method of claim 17 , further comprising determining an azimuth or a gyro toolface of the tool body.

19. The method of claim 17 , further comprising determining the orientation of the gyro at each of the first, second, and third measurements relative to the tool body.

20. The method of claim 18 , further comprising:

identifying gyro mass unbalance or error based at least in part on the first, second, and third measurements.

21. The method of claim 18 , wherein the gimbal sensor platform further comprises one or more accelerometers coupled to one or more of the inner gimbal, outer gimbal, or tool body, and the azimuth of the tool body is determined at least partially based on the readings of the accelerometers.

22. The method of claim 18 , wherein the gimbal sensor platform further comprises one or more magnetometers coupled to one or more of the inner gimbal, outer gimbal, or tool body, and the azimuth of the tool body is determined at least partially based on the readings of the magnetometers.

23. The method of claim 18 , wherein the gimbal sensor platform further comprises one or both of an inner angular position measuring device coupled between the inner gimbal and the outer gimbal or an outer angular position measuring device coupled between the outer gimbal and the tool body, and the azimuth of the tool body is determined at least partially based on the readings of any angular position measuring device.

24. The method of claim 17 , wherein the gimbal sensor platform further comprises one or more accelerometers coupled to one or both of the inner gimbal or outer gimbal, and the method further comprises:

taking a first acceleration measurement with an accelerometer at the first, second, or third position; and

determining an azimuth or inclination of the tool body.

25. The method of claim 24 , further comprising:

taking a second acceleration measurement with the accelerometer at a different position of the first, second, or third positions; and

identifying accelerometer error or bias based on the first and second acceleration measurements.

26. The method of claim 17 , wherein the gimbal sensor platform further comprises one or more magnetometers coupled to one or both of the inner gimbal or outer gimbal, and the method further comprises:

taking a first magnetometer measurement with a magnetometer at the first position, second position, or third position; and

determining an azimuth or inclination of the tool body.

27. The method of claim 26 , further comprising:

taking a second magnetometer measurement with the magnetometer at a different position of the first position, second position, or third position; and

identifying magnetometer error or bias based on the first and second magnetometer measurements.