North Finding

© Brooke Clarke 2007 - 2016




Types
AG8
Wild Surveying Gyros
Patents
Related

Types

There are many ways to find true north. 

There is a fixed relationship between time and position on Earth that shows up in a number of ways.  Navigation, Surveying, Time and Frequency, Gyroscopes, Flywheels , Astronomy as well as North Finding are all interrelated.

Some crude ways are to use an analog wrist watch and point the minute hand to the Sun and then a North-South line is half way between the minute hand and 12:00, this is called the Boy Scout method.  Or that moss grows on the North side of tree trunks.

Following are some more accurate ways.

Magnetic Compass

Use a magnetic compass and correct for the local magnetic declination (Wiki), my sensors web page on magnetism.
A problem with this is applying the correction in the correct direction.
Another problem is that the compass needs to be level, if it's tipped there will be an error.
Another problem is using a compass that's accurate enough. 
The compass that's part of a surveying instrument, like the Leitz 115 transit, is good to better than one degree.
A compass with a single piece needle will tend to point more in the up-down direction than horizontally in most parts of the world and so needs to have a balancing weight added to keep the needle level and so will only work over a limited range of latitudes.

Noon Sun

There are a number of methods of using the fact that the Sun is at true South (or North for the southern hemisphere) at local noon (not clock noon).  
One way is to mark the path of the shadow cast by the tip of a vertical pole.  A line from the base of the pole to the closest point of the shadow path is on a North-South line.
Another way to to determine time when the Sun is due south (transit time) at:
http://aa.usno.navy.mil/data/docs/RS_OneDay.php
Using a vertical pole mark the shadow of the tip at the transit time.  A line from the base of the pole to the closest point of the shadow path in on a North-South line.

There are solar attachments for some transit surveying instruments that allow finding North based on the Sun's position.

The Dipleidscope is designed to tell you when it's exactly noon, but it could be used to find North if you know the time when the Sun transits (see above).

A Noon Mark (Wiki) is a type of Sundial (Wiki) that is constructed on a South facing vertical wall and incorporates the Equation Of Time (Wiki).
The EOT corrects Sundial time from being off by as much as 16 minutes to better than 1 minute of time based on the date.  Or, more accurately if the EOT is computed for the current year.
It can also be implemented as a ceiling dial by means of a small mirror.

Stars

Stars can be observed by knowing the time that they transit the local meridian just as was done for the Sun.  A problem is that you don't want to use a star that transits directly overhead, but rather one that transits not too far above the horizon.  For more on this and the limiting accuracy see my Stellar Timekeeping web page.  (Note: Astronomical "seeing" caused by atmospheric turbulence limits the precision of a single star observation to single digit milli arc seconds of angle.)

Theodolites have right angle eyepiece attachments to allow looking at stars that are high in the sky.  Also Pilot Balloon (PiBal) theodolites have the eyepiece at right angles to the telescope axis to allow looking skyward.  The Wild T16 91 arc minute) or T2 (1 arc second) will result in precision North is the hour angle of Polaris is taken into account.

North Star

The North Star (Wiki) is not at the celestial pole (Wiki) and so circles the celestial pole.  The error in finding North if you use the North star at a random time can be on the order of 3/4 of a degree.

One way to eliminate this error is to use a Polaris finderscope.  This is a small telescope with circular rings that are offset from the center line of the scope by the offset of Polaris.  When aligned with the center point at the celestial pole you will see Polaris on one of the rings.  As time goes by Polaris will stay on the same ring.  This is one way to align an astronomical telescope, but it can take some time since you need to wait for the sky to rotate.

Another way to eliminate the problem of Polaris not being due North is to determine when Polaris transits.  That happens two times every day, once when Polaris is directly above the celestial pole and again when it's below the pole.  If you follow the North star with a transit and stop tracking it when it transits then your have found North.

GPS

The AG8 gyroscope North Finding System was replaced by the "Gun Laying" (Wiki) application in the PLGR and DAGR GPS receivers.
The accuracy is easily better than one mil (Wiki).
There are two Gun Laying (Azimuth Determination) methods that can be done with either the DAGR or Polaris:

A less accurate, but quick and easy way to find North with the DAGR or Polaris is to use it's internal magnetic compass.  Since the DAGR knows it's Lat and Lon and it has some version of the World Magnetic Model it can be setup to display true bearings by applying the WMM to the magnetic bearing.  Note:  You must hold the GPS horizontally level, best on a table or other surface.

There are other GPS methods but none of them come close the the Gun Laying System in accuracy.

North Seeking Gyroscope

When the axis of a gyroscope is parallel to the Earth's spin axis the gyro will be stable, but if the gyro axis is off a little it will precess. In this way a gyroscope can be used to determine North to high precision.  Note:  This is very different than a gyro compass where the gyro just maintains an azimuth that drifts with time.
Also see my gyroscope web page.

Wiki: Gyrotheodolite - Showing Wild GAK gyro mounted on a T16 theodolite. - Schuler tuning -

Pendulous

The key idea is that the center of mass if below the horizontal gyroscope spin axis.  That's so say that when the gyro is not spinning the weight pulls down on the gyro and brings the spin axis to a horizontal position.  This way when the spin axis is not parallel to the earth's spin axis then the gyro will precess in such a way as to cause the spin axis to tilt either up or down.  This tilt will raise the weight which will in turn produce torque forcing the gyro spin axis to move to the East or West, i.e. to come closer to being parallel with the earth's spin axis.  This system only works on land, in a vehicle any acceleration will effect the weight and cause problems.

Hunting

The gyroscope oscillates back and forth about true north with a period that depends on the rotational momentum of the gyro.  Large gyros, like used in early ship gyrocompass systems might have a period of oscillation about North on the order of a few hours.  A small earth based pendulous gyrocompass, like used for surveying, might have a period of a few minutes.  Since the hunting is continuous and the method of finding the center of the East and West excursions involves measuring over a number of cycles, i.e. tens of minutes either the bearings need to be exceptionally good or the flywheel needs to be powered.  This is way Foucault was not able to make this demonstration. 

Note for this undamped case if the spin axis starts at x degrees to the West of North it will oscillate between x degrees West and x degrees East of North forever.

The example on pg 87:
We = 72.9E-6 rad/sec (aprox 4 seconds per revolution)
M = 4E6 gm cm2/sec
Lat = 40 deg North
Mp = 80E3 dyne cm
Starting angle = 10 deg West of North
T = 0 when at 10 deg West
Period = 99 minutes

Gyroscopes: Theory and Design
, paragraph 5-8 Equations of Motion - Pendulum Gyro, pg 85

AG8

References

Lightweight Gyro Azimuth Theodolite (Lear North Seeking Gyro Model No. 11ng530a) by Robert T. Flowe
Engineering Test Report; Lightweight Gyro Azimuth Theodolite (Lear North-Seeking Gyro Model No. 11NG530A) 21 Feb 1963

Patents

3146530 Pendulous North Seeking Gyroscopic Assembly, Harry N. Eklund (Lear Siegler), Mar 9, 1965 -
                33/321
, 33/333, 33/363.00R, 33/275.00G, 33/327, 74/5.00R - North Seeking
                to determine the direction of geodetic North

3172213   North Seeking Gyroscope, Harry N. Eklund (Lear Siegler Inc), Mar 9, 1965 -Tripod & theodolite,
                  33/327, 33/324, 74/5.1, 74/5.5, 33/275.00G, 33/346, 336/135, 336/30
RE26370 North Seeking Gyroscope, H. N. Eklund (Lear Siegler Inc), Apr 9, 1968 -
 

3512264 MERIDIAN-SEEKING INSTRUMENT**, Ambrosini Leonard R (Lear Siegler Inc), May 19, 1970, 33/324, 74/5.60E, 33/320, 74/5.60R
2510068
Gyrocompass
Sperry
ship use
3172213
see above
Lear Siegler North Finding
3258976
see below
Gen Precision
Tripod mounted

3817508 Circular connection bands for a suspended body, D Bergstrom, D Clark, (Lear Siegler Inc), Jun 18, 1974, 267/160
3863357
Power driven band clamp for pendulous north seeking gyroscopes, Clark David C, Knapp Ralph E (Lear Siegler, Inc.), Feb 4, 1975, 33/324

3863355 Power transfer assembly, Darryl K Bergstrom, David C Clark, Lear Siegler Inc, Feb 4, 1975, 33/324, 33/354            

3890718 Method for determining astronomic north by gyrocompass, Gregerson Leslie F, Symonds Gordon R, Jun 24, 1975, 33/301, 33/324, 74/5.5, 368/118
                 Uses light beam and photo sensors to time oscillations.


3988659 Meridian seeking instrument, Leonard R. Ambrosini (Lear Siegler, Inc.), Oct 26, 1976, 318/648, 318/623, 33/324, 33/275.00G, 318/624
               This is the AG8 (AG-8) North Finding (Seeking) gyroscope.

3997975 Calibration of a meridian seeking instrument, Ralph E. Knapp (Lear Siegler, Inc.), Dec 21, 1976, 33/324, 318/689, 318/648, 33/326
                AG8 Calibration in field

Fig 1 AG-8 theory of operation
AG8
                  North Seeking Gyroscope prototype Lear Sieglar
                  11NG530A
AG-8 Patent 3988659 Fig 2
AG-8
                  North Finding gyro patent 3988659 Fig 2
     



From the book "Surveying Instruments and their Operational Principles" Chapter 2.5.2 Gyroscopic TheodoliteGyro-thodolites from Surveying Instruments and their
        Operational Principles

Manuals

TM 5-6675-250-10 Survey Instrument: Azimuth, Gyro, Lightweight, Model AG-8, Type 1 (6675-00-062-5575)
TM 5-6675-250-10-HR Survey Instrument: Azimuth, Gyro, Lightweight,
                                        (Lear Siegler, Inc. Model AG-8), Type 1, NSN 6675-00-062-8579
TM 5-6675-250-20 Survey Instrument: Azimuth, Gyro, Lightweight, Model AG-8, Type 1 (6675-00-062-8579)
TM 5-6675-250-20P Survey Instrument: Azimuth, Gyro, Lightweight,
                                        (Lear Siegler, Inc. Model AG-8 and AG-8A) NSN 6675-00-062-8579 Jan 1976
TM 5-6675-250-34 Survey Instrument: Azimuth, Gyro, Lightweight,
                                        (Lear Siegler, Inc. Model AG-8 and AG-8A) NSN 6675-00-062-8579 Dec 1975
TM 5-6675-250-34P Survey Instrument: Azimuth, Gyro, Lightweight,
                                        (Lear Siegler, Inc. Model AG-8 and AG-8A) NSN 6675-00-062-8579 Jan 1976

Wild Surveying Gyros

There are two models that use identical gyro mechanisms made by Perkin Elmer.
The gyro never settles down to a single bearing but instead it continuously oscillates about true North.
So there's a number of ways to figure out where North is, one way is to note the left and right peak azimuth readings and then use the mean.  But this will not work with the T2 theodolite because it's fine motion screw can not track over the peak-to-peak oscillation range.  Other methods depend on timing various aspects of the oscillation.

GAK 1 Gyro Attachment

ARK 2 Gyro Aiming

Includes a built-in telescope

Auxiliary Equipment

GKK3 DC - AC Converter
GKB2 Battery
GKL3 Batt. Charger
GST10-2 Tripod
Wild T16 theodolite PN 560247 (maybe part of GG3-1 NSN: 6675-01-289-8481)

ARK 2 Aiming Circle
ARK2 Gyroscopic North Finding
GAK 1 Gyro Attachment
GAK1 North Seeking
                  Gyroscopic Theodolite accessory

2930240 Gyroscopic surveying compass, Dietrich Wartenberg, Otto Rellensmann, Mar 29, 1960, 74/5.00R, 33/327, 74/5.7, 33/275.00G, 356/149
3001290 Gyroscopic compass, Karl-Heinrich Stier, Otto Rellensmann (Lear Inc), Sep 26, 1961, 356/148, 33/285, 33/315, 33/275.00G

Air or Gas Bearing

This is an improved version of the Pendulous.  It's more complicated in exchange for a much shorter period of oscillation.
3173215 uses air bearing gyro like: 2925736, 2926530, 2938157

Torquer & Pickup

are described in 2926530 AUTOMATIC CONTROL SYSTEM FOR A PIVOTED PLATFORM - inertial platform

Gyrocompass

A one degree of freedom gyro rotor that has drift typically used in ships and aircraft since it's more accurate than a simple magnetic compass.
The magnetic compass has a big error if it's not held horizontally or near metal or wires carrying electrical currents.  Totally inoperable in a metal submarine or armored tank.

Inertial Navigation Systems (INS) Wiki

First generation systems used an inertial platform, i.e. a plate that is maintained level and pointing to true North.  On that platform accelerometers measure X, Y & Z accelerations that are integrated to determine position.

The next generation anchors the gyros and accelerometers to the frame of the vehicle.  Called "Strap Down" INS.  A computer figures out where the vehicle is.  This eliminates a lot of error sources associated with the mechanical platform and is much simpler in terms of hardware.

The problem is all gyros have some long term drift rate (depends on the physical volume of the gyro, see table) so the error goes up as the time since last fix.  This is why some other form of navigation is needed to update the INS.

Rate Gyros

Rate gyros are used to measure turning about a single axis.  These are not gimbled and are similar to a motor, i.e. just a cylindrical can that contains the gyro and some type of pickoff mechanism that can put out a signal if the can moved in such a way as the long cylindrical axis is tipped relative to where it was.  If the cylindrical axis is translated so that the new vector is parallel to the old vector, not output will result.

Patents

Class 33/327 Geometrical Instruments/ 318 .Gyroscopically controlled or stabilized  324..Gyroscopic compass 327...Fluid, suspension or control

Class 356/149: Optics Measuring and Testing
            .138 Angle Measuring or Angular Axial Alignment
                ..148 Artificial reference
                    ...149 Gyroscope or pendulum stabilized optical element


1074771 Gyroscope-compass, Theodor Bruger (Hartmann & Braun Ag), Oct 7, 1913, 33/327, 33/324, 33/326 -Foculat meridian finding
1136566 Gyro-compass, Hans Usener, Apr 20, 1915, 33/324, 33/344, 74/5.46 - meridian type

1486261 Gyroscopic and other rotors, Carl L Norden, Mar 11, 1924, 74/5.7 - cast rotor spins because of air currents
1857736  Apparatus for use in combination or in conjunction with alpha sextant adapted for use as an artificial horizon and direction indicator, May 10, 1932, 356/147 - combines compass and gyroscope
1998948 Gyrocompass, Herbert H Thompson, Bruno A Wittkuhns, Sperry Gyroscope Co Inc, Apr 23, 1935, 33/327, 33/360, 74/5.60R - East-West type (not classical North-South)
1240872 Gyro Comapss, J. Perry & G. Brown, Sep 25, 1917 - shipboard meridian finding
2419948 Gyrocompass, T=2 * PI * SQRT(R/g) [R= radius of Earth, g=accel of gravity] = about 85 minutes - period of gyro changes depending on acceleration
2432613 Gyroscope sighting system having a fixed line of sight (gun sight?)
2510068 Gyrocompass, L. F. CARTER (Sperry Corp.) - ship use this patent adds inverted pendulum.
2752790 (Universal) Gyroscopic apparatus, Charles S Draper, Research Corp, Jul 3, 1956, 74/5.4 -
2752791 Gyroscopic apparatus, Jr William W Dunnell, Clarence A Haskell, John J Jarosh, Research Corp, Jul 3, 1956, 74/5.60D, 73/504.9, 74/5.5
2752792 Gyroscopic apparatus, Charles S Draper, Roger B Woodbury (Research Corp), Jul 3, 1956, 74/5.34, 244/191, 33/317.00R, 244/3.2, 33/321, 74/5.00R, 701/507 - Navigation
2771799
thread rolling tool
2852943 GYROSCOPIC APPARATUS (Sperry Corp.) - better mounting of gyro to lower wander and precession - for use in navigation, not north finding
2887783 Azimuth reference device, Blizard Robert B (Sperry Rand Corp), May 26, 1959, 33/301, 74/5.41, 33/324 - a few minutes to find meridian by measuring the rate of tilt.
                "Unfortunately, the standard gyro-compass can not be used successfully lfor this purpose because it requires between one and two hours or more
                 to settle on the meridian after starting up at a random position."
2902772 Gyroscopic compass, Ciscel Benjamin H, Honeywell Regulator Co, Sep 8, 1959, 33/321, 33/326, 74/5.00R, 33/317.00R, 33/322 - non pendulus
2919585 WIRE-SUPPORTED GYRO WHEEL (Sperry Rand Corp)- 0.06 deg/hr drift with 50E6 gm-cm^2/sec wheel - 0.020" piano wire suspension, separation of wheel from motor elements allows for less changes due to temp.  24,000 RPM  clutch spin up then disengages.
2925736 GYROSCOPIC ACCELEROMETER, Feb 23 1960, - air (gas) bearing
2926530 AUTOMATIC CONTROL SYSTEM FOR A PIVOTED PLATFORM - inertial platform
2930240 Gyroscopic surveying compass, Dietrich Wartenberg, Otto Rellensmann, Mar 29, 1960, 74/5.00R, 33/327, 74/5.7, 33/275.00G, 356/149 -
                Calls:
                1180815 Gyroscopic compass, Hermann Anschuetz-Kaempfe, Apr 25, 1916, 3/327, 74/5.00R, 74/5.95, 310/57
                - maybe the first surveying type North finder using a gyroscope.
2966744 Gyroscopic Theodolite Assembly, F.K. Mueller, Jan 3 1961 -
Calls:
1541775 BALL-CONTROLLED MARITIME AND SCIENTIFIC INSTRUMENT
1743533 GYROSCOPE SUPPORTING AND CENTERING APPARATUS
2972195 Gyro Compass (North American Aviation Inc)- Tripod Mounted, Basic Theory and diagrams.
Referenced by:
Patent Number Title Issue date
3997975 Calibration of a meridian seeking instrument Dec 21, 1976
5115570 Method for eliminating gyro errors May 26, 1992
2976618 MERIDIAN PLAN NORMAL TO EARTHS SPIN VECTOR PLANE TANGENT TO THE GEOID
3001290 Gyroscopic compass
3018142 Control apparatus, Jr Lyle F Warnock (Honeywell Regulator Co), Jan 23, 1962, 384/110, 384/905, 73/496, 74/5.00R
3146530 PENDULOUS NORTH SEEKING GYROSCOPIC ASSEMBLY, Harry N. Eklund (Lear Sieglar), Mar 9, 1965 -
                33/321
, 33/333, 33/363.00R, 33/275.00G, 33/327, 74/5.00R - North Seeking

3172213   North Seeking Gyroscope, Eklund -Tripod & theodolite, Mar 9, 1965, 33/327, 33/324, 74/5.1, 74/5.5, 33/275.00G, 33/346, 336/135, 336/30
RE26370 North Seeking Gyroscope

3173215 APERIODIC NORTH-SEEKING GYRO,
3173216 NORTH-SEEKING GYRO - non oscillating
3222795 ACCELERATED NORTH-SEEKING GYROCOMPASSING SYSTEM - pointing East the rate of precession is measured, then pointed West (180 deg move) and the rate is again measured, then north is calculated.  Uses a 3 axis INS type gyro.
3229376 Pendulous Gyrocompass - tripod mounted with theodolite
3222937 Gyroscope, (Special Devices Labs) - airborne navigation
3222795 Accelerated north-seeking gyrocompassing system, James C Gevas (Gen Precision Inc), Dec 14, 1965, 33/301, 33/321, 33/323, 701/505
3231984 AUTOMATIC NORTH SEEKING RATE GYRO COMPASS, (American Bosch)
3258976 Azimuth Alignment Sensor, Krupick et al. (Gen Precision), - Tripod mounted many drawings
                        Calls:
                        2746301 Gyroscopic devices (rate gyro)
                       
2951374 Position and rate sensitive gyro (Aircraft)
                       
2968956  Gyro compass (ships, planes, etc)
                       GB886063 fixed position gyrocompasses, Jan 3 1962 - survey instrument North Finding

3276267 GYROSCOPIC APPARATUS (Univ Match Corp) - missile guidance
3279086 Compensated gyroscopic directional reference, Bell Aerospace Corp, Oct 18, 1966, 33/324, 33/303, 74/5.47 - tripod mounted or missile navigation system
3283408 MERIDIAN AND LATITUDE INDICATOR
3307412 North-Seeking Gyro System (AGA Aktiebolag) -
Calls:
2552132 GIMBAL TYPE GYROSCOPES (GE)
2981113 Precision Directional Reference (Litton Sys) -
3311326 FORCE DIRECTION INDICATOR AND APPARATUS AND METHOD EMPLOYING SAME
3320819 GYRO INDEXING MECHANISM
3330945 ACCELERATED NORTH-SEEKING GYRO-COMPASSING SYSTEM
3346966 GYRO COMPASS MISALIGNMENT MEASURING APPARATUS AND METHOD
3379862 DEVICE FOR INDICATING THE ANGULAR VELOCITY OF A SYSTEM
3386179 GYROCOMPASS
3417474 Gyrocompass, Evans John L, Riordan Hugh E (Gen Precision Systems Inc), Dec 24, 1968, 33/275.00R, 33/324, 74/5.5 - quick to settle at North
3419967 Gyrocompasses, Rocks Eugene S, Smith Harry J, Jan 7, 1969, 33/327, 33/275.00G
3442143 Gyroscope - for INS
3452444 Meridian Detector, Takeshi HoJo (Kabushikikaisba), - Tripod Mounted
1240872
Gyro-Compass
1917
2139558
Followup System for Gyro Compass
1938
2142018
Ball Gyrocompass (Sperry Gyro)
1938
2972195
(see above)

3283408
(see above)


3509765 INERTIAL NAVIGATION SYSTEM
3512264 MERIDIAN-SEEKING INSTRUMENT**, L. R. AMBROSINI (Lear Siegler),
2510068
see above

3172213
see above

3258976
see above


3518771 NORTH-SEEKING GYROSCOPE (Teldix) - land based North Finding
3545092 METHOD FOR ALIGNING A NAVIGATION SYSTEM
3561129 NORTH-SEEKING SYSTEM
3569716 Opto-Electronic Liquid Level Sensor for Maintaining a Stable Platform (Army) - milliradian sensitivity Mercury pool
3619905 Gyro compasses, Stier Karl Heinrich, Nov 16, 1971, 33/285, 74/5.4, 33/275.00G - band suspension gyro for north finding
3619906 OSCILLATING NORTH-SEEKING PLATFORM (Army), Nov 16, 1971, 33/324, 318/649 - for inertial platform
3637032 Directional Drilling Apparatus
RE29526 Directional Drilling Apparatus 1978

3727466 Gyro noise reduction, G Kraus, J Rupert (Honeywell Inc), Apr 17, 1973, 74/5.00R, 74/5.7 - shroud reduces Reynolds number
3748912 Gyroscope with universally mounted rotor, Gec Wilmington, Jul 31, 1973, 74/5.00F -
3750300 NORTH-SEEKING GYRO PENDULUM (German)
Calls:
2110766 Gyrocompass (UK)
2802279 Gyrocompass (American Bosch) - ship nav
2970382 Gyro-Compass (Tokyo)
3229376 Pendulous Gyrocompass (N Am Aviation) - tripod mounted theodolite
Calls:
2599124 GYROMAGNETIC COMPASS APPARATUS (Kevin & Hughes, Scotland)
2735731 Three Element Flexture Pivot (N American Aviation)
2797580 Gyroscope Suspension (Am Bosch)
2887784 MINIATURE GYRO COMPASS (Sperry Rand) - ship
2970382 see above
2972195 see above
2976618 see above
3119607 FLEXURAL SUSPENSION BEARING (N American Aviation)

3753374 Measuring instrument with gyro (Built into theodolite), Strassburg L, Aug 21, 1973, 74/5.7, 33/324 -

3769710 ELECTRONIC CELESTIAL NAVIGATION MEANS - star tracker see MD1
3806913 GYROSCOPIC NORTH-SEEKING DEVICE (French), Apr 23, 1974 - tripod mounted
3813788 DYNAMIC PENDULUM NORTH-SEEKING GYRO APPARATUS, Us Army, Jun 4, 1974, 33/321, 33/323 -
3849636 COMPUTER CIRCUIT - INS
3898744 CONSTANT PRECESSED GYROCOMPASS
3936948 Method for determining azimuthal direction relative to true north


3988659 Meridian seeking instrument, Leonard R. Ambrosini (Lear Siegler, Inc.), Oct 26, 1976, 318/648, 318/623, 33/324, 33/275.00G, 318/624
               This is the AG8 (AG-8) North Finding (Seeking) gyroscope.
               
3997975 Calibration of a meridian seeking instrument, Ralph E. Knapp (Lear Siegler, Inc.), Dec 21, 1976, 33/324, 318/689, 318/648, 33/326
               

4033045 Portable surveying gyrocompass apparatus, Willis G. Wing (Sperry Rand), Jul 5, 1977, 33/275.00G, 33/327, 33/326, 33/267 - looks like AG8
4033045 Portable
        surveying gyrocompass apparatus
4087919 Rate integrating gyroscopic aiming method and device therefor
4123849 Miniature north reference unit, Litton Systems, Inc., Nov 7, 1978, 33/320 -
4214482 Inertial instrument
4379365 Gyrocompass**
4433491 Azimuth determination for vector sensor tools
4442723 North seeking and course keeping gyro device
4461088 Survey apparatus and method employing canted tilt sensor
4461089 Instrument for the automatic determination of North direction, Bodenseewerk, 33/324
4559713 Azimuth determination for vector sensor tools
4635375 Vertical shaft system for gyroscopic theodolites with two degrees of freedom -
Patent Number Title Issue date
2000524 WELL SURVEYING INSTRUMENT May 1935
2852943 GYROSCOPIC APPARATUS Dec 1974
3162951 STATIONARY GYROSCOPIC COMPASS F
looks like AG8 with gyro below tripod hea   
Dec 1964
3619905 CYRO COMPASSES Nov 1971
4800501 Vehicle land navigating device

5060392 North finding system, Allied-Signal, 33/324 ; 33/318; 33/321 -
5115570 Method for eliminating gyro errors
5117559 Method of improving the north seeking result
5272922 Vibrating element angular rate sensor system and north seeking gyroscope (Watson Ind)
5349757 Tape-suspended meridian gyro
5566461 Method of determining the direction of north, Detlev J. Wick, Hans J. Senn, Bodenseewerk Geratechnik GmbH, Oct 22, 1996, 33/326, 33/324 
              
5752412
Process for scanning of gyroscopic instrument and a gyroscopic instrument using this process, Ulf Bey, Heino Hoffmann, Wolfgang Skerka (Raytheon), May 19, 1998
                74/5.60A, 74/5.60D, 74/5.60R
               

6621460 Instrument alignment devices and methods
6842153 Instrument alignment devices and methods
6968281 Method for calibrating an inertial measurement unit

8151475 North finding device, system and method, Mordechay Albo, Boris Bronshteyn (Azimuth Technologies Ltd.), Apr 10, 2012, 33/318, 33/324

20130238280 System and method for north finding, Israel Aerospace Industries Ltd., Sep 12, 2013, 702/150 - discusses a number of prior north finding systems
               

Related

Gyroscopes - YouTube Videos
Flywheels
DC PM Motors - Testing DC Motors

Book: Surveying Instruments  By Fritz Deumlich - section on gyro theodolites
web site of Nicoląs de Hilster - 1961 wild mil able t2

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page created July 28 2007.