WO1983001681A1

WO1983001681A1 - Improved gyro-stabilized apparatus

Info

Publication number: WO1983001681A1
Application number: PCT/US1982/001547
Authority: WO
Inventors: Corporation Navidyne; Edmund S. Zavada; Laurence J. Mayer
Original assignee: Navidyne Corp
Priority date: 1981-11-09
Filing date: 1982-11-01
Publication date: 1983-05-11
Also published as: EP0093169A1

Abstract

A gyro-stabilized apparatus for a ship-board antenna (22) or the like includes an azimuth platform (18) stabilized by gyro assemblies (32, 34, 36 and 38) each gyro assembly having a housing (84) which serves as an end bell for a gyro motor (82) and which is pivotally supported on the platform by trunnions (106, 108) having bearings (118) thereon resiliently supported in a bearing housing (110). A coaxial bore through one trunnion passes electrical conductors (128) to the gyro motor from the platform without exerting extraneous torques on the gyro assembly during precession. The platform is supported on a support structure (14) by a gimbal assembly (150) which enables precise alignment of the gimbal axes intersection with the rotational axis of the platform, and enables precise alignment of the gimbal axes with respect to the pitch and roll axes of the ship. The gimbal assembly affords an unobstructed passage through the center thereof for cables. An elevation assembly (20), pivotally mounted on the azimuth platform (18) for supporting an antenna, is formed so that it can be rotated from horizon-to-horizon over zenith.

Description

TITLE: IMPROVED GYRO-STABILIZED APPARATUS

SPECIFICATION

Background of the Invention

The present invention relates to improved gyro- stabilized apparatus of the type employed on moving vehicles, for example, for providing a stabilized mounting platform for antennas, guns, optical devices, and the like.

The use of gyros for stabilizing movable plat¬ forms on ships or other vehicles, for example, is well known. Several stabilized platforms are available commercially for maintaining the position of a ship¬ board satellite antenna fixed in space. In some stabilized platforms, the gyros are mounted directly on the platform to provide short-term stabilization. Long-term azimuth stabilization is afforded by slaving the platform to the ship's gyrocompass, which provides steady-state or average direction or reference orien¬ tation of the platform.

It is the purpose of the present invention to provide improved stabilized platforms of the foregoing type, more particularly in the areas of improved gyro assemblies, improved caging mechanisms, improved gimbal assemblies, and improved platforms, which contribute to stabilized platforms that are better able to com¬ pensate for variations in the ship's motion.

OMPI Summary of the Invention

In accordance with one aspect, the invention provides a gyro assembly, adapted for use on a gyro- stabilized platform, comprising a rotor, a rotor housing, and a drive motor mounted on the housing for spinning the rotor, the housing being formed to serve as an end bell for the motor.

In accordance with another aspect, the invention provides a gyro assembly housing formed with a pair of trunnions extending therefrom for pivotally mounting the housing on a -stabilized platform, the trunnions defining a precession axes of the gyro assembly, and each trunnion having a bearing thereon supported within a bearing housing, attached to the platform, by a resilient material to provide vibration isolation between the gyro assembly and the platform.

•In accordance with a further aspect, the invention provides a caging apparatus for caging a gyro assembly pivotally mounted for precession on a rotable gyro- stabilized platform which comprises a caging lever pivotally mounted on the platform about an axis substantially parallel to the rotational axis of the platform, the caging lever having a portion engage- able with the gyro assembly for caging the gyro assembly and having a counter-balancing portion disposed with respect to the pivotal mounting of the caging lever so as to prevent a shift In the platform's center of gravity when the caging lever is pivoted.

In accordance with another aspect, the invention provides a gimbal assembly for supporting a gyro- stabilized platform on a support structure comprising

OMPI a first yoke connected to a platform, a second yoke connected to the support structure, a gimbal ring sized to enable the first and second yokes to be located within the gimbal ring, first means for pivotally connecting the first yoke to the gimbal ring for rotation about a first axis, second means for pivotally connecting the second yoke to the gimbal ring for rotation about a second axis substantially perpendicular to the first axis, each yoke having an aperature therethrough and the center of the gimbal ring being open to provide unobstructed access from the support structure to the platform through the yokes and the gimbal ring.

In accordance with another aspect, the invention provides a gyro-stabilized apparatus comprising a support structure, a gyro-stabilized azimuth platform supported on the support structure by a gimbal assembly, the azimuth platform being rotatable in azimuth about a first axis, and an elevation assembly pivotally supported on the azimuth platform for rotation about a second axis substantially perpendicular to the first axis. The elevation assembly comprises a member having first and second depending portions located adjacent to peripheral regio-ns of the azimuth platform, the first and second depending portions being pivotally connected to the azimuth platform at the peripheral regions to define the second axis, and the first and second depending portions being sized to enable the elevation assembly to be rotated over zenith about said second axis.

Brief Description of the Drawings

Figure 1 is a perspective view of a gyro-stabilized apparatus in accordance with the invention;

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OMPI m Figure 2 is a transverse sectional view taken approximately along the line 2-2 of Figure 1 illus¬ trating a top view of an azimuth assembly of the stabilized apparatus; Figure 3 is a vertical sectional view of a gyro assembly;

Figure 4 is a vertical sectional view taken approximately along the line 4-4 of Figure 3;

Figure 5 is a perspective vi.ew of a caging lever;

Figure 6 Is a vertical sectional view, partially broken away, taken- approximately along the line 6-6 of Figure 2;

Figure 7 is a transverse sectional view of a gimbal assembly taken approximately along the line 7-7 of Figure 6;

Figure 8 is an exploded fragmentary perspective view of a portion of the gimbal assembly;

Figure 9 is an elevation view, partially broken away, illustrating an elevation assembly of the stabilized apparatus of Figure 1; and

Figure 10 is a diagrammatic view illustrating an over zenith movement of the elevation assembly. Description of the Preferred Embodiment The invention may be employed for gyro-stabilization of a wide variety of devices' such as antennas, guns, optical devices, and the like, particularly on moving vehicles, and for illustrative purposes will be de¬ scribed in connection with the stabilization of a ship-board platform for a satellite antenna.

Figure 1 illustrates a stabilized ship-board antenna system 12 embodying the invention. As shown, the antenna system may generally comprise a support structure 14, such as a post, mounted on a base 16, which may be supported on the deck or superstructure of a ship, a stabilized azimuth assembly 18 supported on support structure 14, an elevation assembly 20 pivotally mounted on the azimuth assembly, and a satellite antenna 22 mounted on the elevation assembly. As will be described in more detail hereinafter, the azimuth assembly is rotatably supported on support structure 14 for azimuth motion relative to the ship, and is pivotally supported on support structure 14 for pitch and roll movement relative to the ship by a gimbal assembly having orthogonal gimbal axes that may be aligned with the pitch and roll axes of the ship. As will also be described shortly, the azimuth assembly includes gyros for providing short-term stabilization .of the azimuth assembly. Thus, the orientation of the azimuth assembly in inertial space remains fixed as the ship rolls and pitches. Elevation assembly 20 is pivotally mounted on the azimuth assembly for rotation ^*• about a substantially horizontal axis through the azimuth assembly. As is apparent, antenna 22 may be pointed in any desired direction by a combined movement of the azimuth assembly and the elevation assembly, and may then be held fixed in inertial space by stabilization of the azimuth assembly. Azimuth assembly 18 is illustrated in more de¬ tail in Figure 2. As shown, the azimuth assembly may comprise an azimuth platform 30, which may be a casting of an aluminum/magnesium alloy, or the like, having generally the shape of a cross (as viewed from the top). Four gyro assemblies 32, 34, 36, and 38 may be pivotally supported (in a manner to be described shortly) on the azimuth platform for movement about precession axes to stabilize the azimuth platform about orthogonal horizontal axes. The gyro assemblies are connected to .depending brackets or platform extensions 40, 42 which project from the platform adjacent to the ends of the platform arms. In the preferred embodi- ment, the platform and the gyro assemblies themselves are pendulous . A caging lever 44 is provided for each gyro assembly, one caging lever being pivotally mounted on each platform extension 42. In addition,, the azimuth platform may support an azimuth drive motor 46 connected by a drive chain 48 to a stationary azimuth gear 50 mounted on the gimbal assembly for rotating the azimuth platform in azimuth, and may support an elevation drive motor 52 for rotating the elevation assembly 20 with respect to the azimuth platform..

As shown in Figure 2, the precession axes of gyro assemblies 32 and 34 are parallel, and the pre¬ cession axes of gyro assemblies 36 and 38 are parallel and perpendicular to the precession axes of gyro assemblies 32 and 34. Gyro assemblies 32 and 34, and gyro assemblies 36 and 38, constitute, respectively, first and second pairs of gyros for stabilizing the platform with respect to the reference axes. Each gyro assembly has a nominally vertical spin axis, except when it precesses. As is well known, when external torques are supplied to the azimuth platform as a result of the ship's rolling and pitching motions, the gyro assemblies precess to absorb the torques in order to maintain the azimuth platform in a substantially horizontal plane. The ship's gyrocompass may be used as a long-term azimuth reference for the platform, and the azimuth drive motor may be slaved to the gyrocompass by a servo system (now shown) so that, in general, the orientation of the platform with respect to a meridian remains fixed as the ship yaws. Accordingly, azimuth platform 30 (and antenna 22) is stabilized so that its orientation in inertial space remains fixed as the ship rolls, pitches and yaws. Each caging lever 44 may be a casting, having the shape best illustrated in Figure 5, comprising a pair of spaced, horizontal (in Figure 5) planar members 54, each having a centrally located hole 55 for receiving - a bolt (as shown in Fugure 2) for pivotally connecting the caging lever to a platform extension 42. A vertically extending engaging por¬ tion 56, rounded about its vertical axes as shown, may be connected between the spaced members 54 adjacent to one end of the members, and another ver- tically extending counter-balancing portion 57 may be con¬ nected between the members on the side of the pivotal mounting axis opposite to the engaging por-^" tion 56. A pair of tabs 58 may be formed on each member 54 adjacent to engaging portion 56, as shown. One of the tabs (the top one, for example) may be connected to an operating rod or cable 60. The oper¬ ating rods are arranged in pairs and each pair is connected to the movable member 62 of a corresponding operating solenoid 64 mounted on the azimuth platform. As shown in Figure 5, the caging lever is preferably symmetrical about a transverse plane (horizontal in figure) so that the same casting may be employed for all caging levers. (It will be noted that the tab 58 that is used depends on whether the caging lever is used as a "left-hand" or "right-hand" lever.) As shown in Figure 2, a spring 66 engaging a tab 58 and a platform extension 42 may be employed for biasing each caging lever to a non-caging position (the positions of the caging levers at the bottom of Figure 2 associated with gyro assemblies 32 and 36) .

OMPI When either solenoid 64 is operated, its caging levers are pivoted^" to a caging position (the position of the two caging levers at the top of Figure 2 associated with gyro assemblies 34 and 38) , at which the engaging portion of each caging lever engages a striker plate 68, preferably of steel, which is positioned on an adjacent surface 70 (see Figure 4) of the housing of an associated gyro assembly. This pivots the gyro assembly about its precession axis and forces the spin axis of the gyro assembly to become parallel with the rotational axis of the platform. When the solenoids are de-energized, springs 66 pivot the engaging levers to their non-caging positions. Stops 72, which may comprise pins depending from the azimuth platform, limit the travel of the movable members of the solenoids and establish the non-caging positions of the caging levers.. In the - non-caging positions, engaging portions 56 of the cag¬ ing levers serve as precession limits (stops) for the gy^ro assemblies. Portion 57 of the caging lever serves as a counterbalance for equalizing the weight of the caging lever about its pivotal axis so that the center of gravity of the azimuth assembly does not change during caging. Figure 3 illustrates one of the gyro assemblies (all of. which may be the same) in detail. As shown, the gyro assembly may comprise a rotor 80, preferably of cast iron and having a generally H-shaped cross section, an electrical motor 82 for rotating the rotor and a^*. ousing 84 which covers the top and sides of the rotor and provides a mounting surface for the motor. Housing 84 is preferably a cup-shaped casting having an upper surface which includes an annular, substantially horizontal (in the figure) peripheral portion 86 and a central depression 88 in which motor 82 is mounted. The motor shaft 90 may extend through an opening in the housing, and rotor 80 may be connected to the shaft by a taperlock bushing 92 and a screw 94 threaded Into the shaft, as shown.

Significantly, housing 84 may be formed to serve as the end bell of the motor. As shown, the housing may be formed with a circular groove 96 for receiving the edge of .the cylindrical motor housing 98, and may be formed with a bearing boss 100 for receiving a ball bearing 102 for supporting motor shaft 90. Housing 84 may also have tapped holes (not shown) for receiving elongated bolts 104 (see Figure 2 also) which pass through the motor for connecting the motor to the housing. Forming the housing to serve as the motor end bell reduces the cost of the motor since it is unnecessary to purchase a motor with an end bell on it. Moreover, this simplifies the attachment of the motor to the housing and avoids the necessity of pro¬ viding pivots on the motor for pivotally mounting the gyro assembly to the azimuth platform, as will now be described.

To pivotally mount the gyro assembly to the azimuth platform, housing 84 may be cas with a pair of projecting, large diameter, stepped trunnions 106 and 108. Each trunnion may be received within a bearing housing 110 having holes 112 therethrough to enable attachment of the bearing housing to a platform exten- sion 40 or 42, as by bolts 114 and nuts 116, as shown in Figiire 2. A precision ball bearing 118 may be located on the end of each trunnion by a locking ring 120. Bearings 118 are preferably supported within

OMPI * housings 110 by a resilient material 122, such as a high durometer polyurethane compound, to isolate the gyro assembly from vibrations transmitted to the azimuth platform. The large diameter trunnions 106 and 108 provide sufficient strength for supporting the gyro assembly on the azimuth platform, and the precision ball bearings 118 substantially reduce friction so that the gyro assembly may precess easily about its pivotal axis. The large diameter trunnions also have another advantage. As shown in Figures 3 and 4, trunnion 108 may have a hole 124 through its center coaxial with the pivotal axis of the gyro assembly. The hole may be lined with tubular insulating material 126, and electrical conductors 128 supplying power to motor 82 may be passed from the azimuth platform through the hole to the interior of housing 84. As shown in Figure 3, the electrical conductors may then pass through a grommet 130 located in peripheral surface portion 86 of the housing and be connected to a term¬ inal strip 132. Preferably, electrical conductors 128 comprise very flexible wire, and by feeding the electrical conductors to the gyro assembly along its precession axis (through hole 124)., the extraneous torques and forces which would otherwise be applied to the gyro assembly by the wires when the gyro assembly precesses are virtually eliminated.

Peripheral surface portion 86 of the gyro housing also provides a convenient mounting surface for a mounting bracket 133 for a motor starting capacitor 134, and a motor start relay 136 (see Figure 2) ; and terminal strip 132 provides a con¬ venient electrical interconnection point for wires running between the capacitor, the relay, and the motor. Moreover, this arrangement eliminates the requirement for more than two wires to be supplied to the gyro assembly from the azimuth platform, and conveniently enables the spin direction of the gyro rotor to be established by merely moving wires on the terminal strip.

As shown in Figure 4, surfaces 70 may be formed on housing 84 on opposite sides of trunnion 108 such that they are parallel to the spin axis of the gyro assembly, i.e., motor shaft 90. Striker plate 68, which may be U-shaped as shown in Figure 4, may be attached to these surfaces to provide an .engagement surface for the engaging portion 56 of a caging lever 44, as previously described. By forming the housing with surfaces 70 on opposite sides of trunnion 108, and by employing a U-shaped striker plate, the same housing design can be used for all gyro assemblies. The gyro assembly construction has advantages other than those noted above. For example, a stamped steel plate 140 may be used at the bottom of housing

84 for completely enclosing rotor 80 within the housing, thereby preventing contact with the spinning rotor. Furthermore, the circular trough around motor 82 (within central depression 88) provides a convenient location for counterweights, such as lead shot, for balancing the gyro assembly about its pivotal axis and for equalizing the weights^' of all of the gyro assemblies.

As previously mentioned, azimuth assembly 18 is pivotally supported on support structure 14 by a gimbal assembly. The details of a gimbal assembly 150 in accordance with the invention which may be employed for this purpose are illustrated in Figure 6-8. As shown, the gimbal assembly comprises a lower yoke 152

OMPI and an upper yoke 154. The legs of the yokes are positioned within a gimbal ring 156 and are pivotally connected to the ring for rotation about substantially perpendicular gimbal axes. The lower yoke is connected to support structure 14 (in a manner to be described shortly) and the upper yoke rotatably supports azimuth platform 30 about a central hub 157 by means of bear¬ ings 158 so that the azimuth platform can rotate ^"about the longitudinal axis of the upper yoke (a vertical axis through both yokes in Figure 6) . A grease seal 160 may be included for sealing a lubricant for the bearings within tire hub.

Yokes 152 and 154 may be standard industrial yokes that are precision machined to enable precision ball bearings 162 to be employed for pivotally mounting the yokes to the gimbal ring and to afford precise con¬ trol of the alignment of the gimbal axis intersection with the rotational axis of the azimuth assembly. As shown in -Figures 7 and 8, a ball bearing 162 may be fitted into a recess 164 in the end of each leg of each yoke. An internally threaded cylindrical member 166 having a head 168 on one end thereof and an outer diameter sized to mate with the inner diameter of bearing 162 may be passed through the bearing and re- ceived in a hole 170 in the gimbal ring for supporting the bearing on the gimbal ring. The portion 172 of the hole at the outer surface of the gimbal ring preferably has a slightly enlarged diameter to pro¬ vide a recess sized to receive a plurality of annular shims 174 formed to be located on member 166, and a washer 176 which abuts the end of the member 166, as shown in Figure 7. A retainer bolt 178 is then threaded into member 166 to complete the assembly. Each leg of the yokes is connected to the gimbal ring in the same manner. The gimbal ring connects the yokes together, and the cylindrical members 166 define substantially perpendicular _ pivotal axes for the yokes. By varying the number of shims 174 which are used on each side of a yoke, the center line of the yoke may be shifted laterally along its pivotal axis, thereby enabling precise alignment of the rotational axis of the azimuth platform. ith the gimbal axes,. The pre¬ cision ball bearings 162 minimize friction and preferably employ -a rather light grease for lubri¬ cation, thereby minimizing the starting torque re¬ quired to rotate the bearings. In addition, the con- struction of gimbal assembly 150 provides an unobstructed passageway through the center of the lower yoke 152, the gimbal ring 156_., and the upper yoke 154 (which does not exist with conventional X-type gimbal assemblies) for cables (not shown) running to the azimuth platform. Preferably, a tube 180, sized to confine the cables, is positioned within the tubular portion of the upper yoke 154, as shown. Confining the cables substantially reduces extraneous torques .and forces which would otherwise be applied to the azimuth platform by the cables, and avoids a possible shift in the platform's center of gravity.

As is apparent from the foregoing, the gimbal assembly provides two substantially perpendicular gimbal axes about which the azimuth assembly may pivot. It is very important that the gimbal axes be parallel to the reference axes of the ship's gyrocompass. Otherwise, when the azimuth platform is tilted in combined pitch and roll motion, an azimuth error will be introduced. For example, for

OMPI a platform tilt of 30 degrees about an axis 45 degrees to the gimbal axes, there is a four degree azimuth error, which can result in a significant antenna pointing error. When the axes of the gimbal assembly are aligned with the reference axes of the ship's gyrocompass, such errors do not exist. To permit alignment of the gimbal axes with the reference axes of the ship's gyrocompass, the lower yoke 152 is connected to support structure 14 in a manner which enables the yoke to be rotated with respect to the support structure so that align¬ ment can be easily-achieved. This is accomplished in the following manner.

As shown in Figure 6, the top portion of support structure 14 is formed with a tapered hole 184 sized to receive a standard taperlock bushing 186, and the tubular portion of the lower yoke 152 Is sized to match the inner bore of the taperlock bushing. The tubular portion of the yoke and the taperlock bushing are positioned in the tapered hole. Upon tightening bolts 188, which extend through the taperlock bushing and are threaded into the support structure, the taper¬ lock bushing causes the yoke to be clamped to the support structure. Upon^* loosening the bolts, the lower yoke may be rotated plus or minus 45 degrees to enable alignment of the gimbal axes with the reference axes of the gycrocompass. This is an important advantage of the invention in that it significantly simplifies the installation of the stabilized apparatus, since there is no need to align the supporting structure with the reference axes upon installation. Furthermore, the gimbal assembly is perfectly symmetrical, and there Is no distinction between the pitch and roll gimbal axes Each gimbal axes has the same degree of angular free¬ dom. Abutment between a circular depending projection 192 on the lower surface of the azimuth platform and a rubber bumper 194 at the top of support structure 14 limits the amount the azimuth assembly can pivot about the gimbal axes .

Figure 6 also illustrates the azimuth assembly drive arrangement in more detail. As shown, stationary azimuth gear 50 may ^*be bolted-to a gear spacer 196 threaded onto the top end of the tubular portion of upper yoke 154. When azimuth drive motor 46 is ener¬ gized, drive chain-48 causes the azimuth assembly to rotate about the longitudinal axis of upper yoke 154, i.e., a substantially vertical axis. A mechanical stop 198 having a projection (not shown) adapted to abut a corresponding projection on the the azimuth platform (also not shown) may be attached to gear 196 to limit the rotation of the azimuth assembly.

To establish a reference azimuth for the azimuth assembly, a marker 200 may be attached to ^"stationary azimuth gear 50 and an optical sensor 202 may be attached to the azimuth platform (see Figure 2 also) and positioned to intercept marker 200 (as illustrated in phantom lines in Figure 6) when the azimuth plat- form is rotated to a predetermined reference azimuth. A similar arrangement may be employed for establishing a reference elevation for the elevation assembly 20. As shown in Figure 9, an elevation marker 204 may be located on an elevation drive gear 206 attached to the elevation assembly 20, and another optical sensor 208 (shown in phantom in Figure 9) may be attached to the azimuth platform for producing a signal when the ele¬ vation assembly is located at the reference elevation. As shown in Figures 1 and 9, elevation assembly 20 may comprise an elevation platform 210, upon which antenna 22 is mounted, and a pair of rectangularly shaped depending members 212, formed from sheet metal, for example, adapted to be located adjacent to peripheral regions of the azimuth platform. The elevation assembly may be pivotally mounted to the azimuth platform (in the manner illustrated in Figures 6 and 9) by bearings 214 and, preferably, such that the pivotal axis of the elevation assembly intersects the intersection of the pitch and roll gimbal axes. This makes the weight of any devices attached to the elevation assembly irrelevant to the characteristics of the platform in that they cannot change its pen- dulosity. As shown in phantom lines in Figure 9, an enclosure 216 housing electrical printed circuit boards and the like may be connected to each depending member 212.

For rotating the elevation assembly with respect to the azimuth assembly, elevation drive gear 206 may be bolted to one of depending members 212 and connected to the elevation drive motor 52 mounted on the azimuth platform (see Figure 2) by a drive chain (not specifi¬ cally illustrated) in a manner similar to that in which azimuth drive motor 46 is connected to stationary azimuth gear 50. Energizing the elevation drive motor causes the elevation assembly to rotate with respect to the azimuth assembly about its pivot axis.

As illustrated diagrammatlcally in Figure 10, the•construction of the elevation assembly and its arrangement with respect to the azimuth assembly enables the elevation assembly to be rotated from horizon to horizon over zenith. This considerably simplifies a ■cable unwrap maneuver. Over a period of time, the cables running between support structure 14 and azimuth assembly 18 will acquire a cumulative twist as a result of the relative movement between the ship and the azimuth assembly. ■. Periodically, this cumulative twist must be relieved. In conventional antenna systems, this requires a 360 degree azimuth rotation of the antenna platform. During such an unwrap maneuver,- the antenna is unable to track the satellite and communications are interrupted. With the invention, however, a cable unwrap maneuver can be performed simply by rotating the azimuth assembly 180 degrees and by rotating the antenna over zenith through an angle equal to the complement of the elevation angle. This maneuver can be performed more rapidly than is possible with conventional antenna systems, and accordingly minimizes the time during, which communications are interrupted.

While a preferred embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that changes can be made in this emobodiment without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

OMPI ^y A , WIPO

Claims

CLAIMS :

1. A gyro assembly, adapted for use on a gyro- stabilized platform, comprising a rotor, a rotor housing, and a drive motor mounted on the housing for spinning the rotor, the housing being formed to serve as an end bell for the motor.

2. The gyro assembly of Claim 1, further comprising means for pivotally mounting the housing on the plat¬ form, the mounting means defining a precession axis for the gyro assembly.

3. The .gyro assembly of Claim 2, wherein the mounting means comprises trunnions formed_.on said housing, each trunnion having a bearing thereon sup¬ ported by resilient material in a bearing housing adapted to be attached to the platform.

4. The gyro assembly of Claim 3, wherein said resilient material comprises a high durometer poly- urethane compound.

5. The gyro assembly of Claim 2, wherein one trunnion has a coaxial bore therethrough to enable electrical conductors to be connected to the motor from the platform such that they do not exert undesir¬ able forces on the gyro assembly during precession.

6. The gyro assembly of Claim 2, wherein said housing has a surface parallel to a spin axis of the rotor and positioned to be engaged by caging means for causing the spin axis of the rotor to be aligned with a rotational axis of the platform.

7. The gyro assembly of Claim 1, further- comprising a cover plate for enclosing the rotor within the housing.

8. The gyro assembly of Claim 1, wherein the housing is formed with a centrally located depression having a circular groove for receiving the edge of a cylindrical housing of the motor and having a bear¬ ing boss for receiving a bearing for supporting a shaft of the motor.

9. A gyro assembly, adapted for use with a gyro- stabilized platform, comprising a rotor, a housing cov¬ ering the rotor, and a drive motor mounted on the housing and connected to the rotor, the housing being

• formed with a air of trunnions extending therefrom for pivotally mounting the housing on the platform, the trunnions defining a precession axis of the gyro assembly, and each trunnion having a bearing thereon supported within a bearing housing attached to the platform, the bearings being supported in the bearing housings by a resilient material to provide vibration isolation between the gyro assembly and the platform.

10. The gyro assembly of Claim 9, wherein one trunnion has a coaxial bore therethrough for passing electrical conductors supplying power to the motor.

11. A gyro-stabilized apparatus comprising a platform movable about a platform axis, the platform having the shape of a cross, and means for pivotally mounting gyro assemblies between the ends of the platform arms.

12. The apparatus of Claim 11, wherein the mounting means comprises means depending from each arm to enable the gyro assemblies to be mounted for precession between the arms.

13. The apparatus of Claim 11, further com¬ prising caging means pivotally mounted on the plat¬ form adjacent to each gyro assembly, and operating means for operating the caging means in pairs to cage pairs of gyro assemblies.

14. An apparatus for caging a gyro assembly pivotally mounted for precession on a rotatable gyro-stabilized platform, the gyro assembly having a spin axis normally parallel to a rotational axis of the platform, the apparatus comprising a caging lever pivotally mounted on the platform about an axis substantially parallel to the rotational axis of the platform, the caging lever having a portion engageable with the gyro assembly for caging the gyro assembly, and having a counter-balancing portion disposed with respect to the pivotal mounting of the caging lever so as to prevent a shift in the platform^rs center of gravity when the caging lever is pivoted.

15. The apparatus of Claim 14, wherein the engaging portion of the caging lever extends parallel to the pivotal mounting axis of the caging lever and serves as a precession limit for the gyro assembly when In a non-caging position.

16. The apparatus of Claim 14, wherein the caging lever is symmetrical with respect to a transverse plane perpendicular to its pivotal mounting axis.

17. The apparatus of Claim 14, further comprising spring means for biasing the caging lever to a non-caging position at which the engaging portion does not engage the gyro assembly, and solenoid means operable to pivot the caging lever to a caging position at which said engaging portion . engages the gyro assembly.

18. A gimbal assembly for supporting a gyro- stabilized platform on a support structure comprising a first yoke connected to the platform, a second yoke connected to the support structure, a gimbal ring sized to enable the first and second yokes to be located within the gimbal ring, first means for pivotally connecting the first yoke to the gimbal ring for rotation about a"first axis-, and second means for pivotally connecting the second yoke to the gimbal ring for rotation about a second axis substantially perpendicular to the first axis, each yoke having an aperature therethrough and the center of the gimbal ring being open to provide unobstructed access from the support structure to the platform through the yokes and the gimbal ring.

19. The gimbal assembly of Claim 19, wherein the first and second means for connecting the yokes to the gimbal ring include means enabling adjustment of the location of each yoke along its respective pivotal, axis.

20. The gimbal assembly of Claim 18, wherein each yoke comprises^* a tubular member having a pair of legs projecting axially from one end thereof, and wherein said first and^'second pivotal connecting means comprise a roller bearing located in each leg, a cylindrical member passing through the bearing and being received in a cylindrical hole in the gimbal ring, and a bolt threaded into the member for connecting the members to the gimbal ring, and wherein the adjust¬ ment enabling means comprises shims positioned on the member between the gimbal ring and the bolt.

21. The gimbal assembly of Claim 18, wherein the second yoke is connected to the support structure by means enabling rotation of the second yoke about an axis perpendicular to said second axis to enable the second axis to be aligned with a reference axis.

22. The gimbal assembly of Claim 21, wherein the second yoke has a tubular member coaxial with said axis perpendicular to the second axis, and wherein said means enabling rotation of the second yoke com¬ prises a taperlock bushing positioned on said tubular member, the tubular member and bushing being received within a tapered hole in the support structure, and means for causing said bushing to clamp said tubular member in the hole.

23. The gimbal assembly of Claim 18, wherein the yokes and the gimbal ring are sized to afford equal angular movements of the yokes with respect to the gimbal ring.

24. A gyro-stabilized apparatus comprising a support structure, a gyro-stabilized azimuth platform supported on said support structure by a gimbal assembly , the azimuth platform being rotatable in azimuth about a first axis, and an elevation assembly pivotally supported on the azimuth platform for rotation about a second axis substantially perpendicular to the first axis, the elevation assembly comprising a member having first and second depending portions located adjacent to peripheral regions of the azimuth platform, the first and second depending portions being pivotally connected to the azimuth platform at said peripheral regions, said pivotal connections defining said second axis, and the first and second depending portions being sized to enable the elevation assembly to be rotated over zenith about said second axis.