F0RM2
THEPATENT ACT, 1970
(39 of 1970)
COMPLETESPECIFICATION
Title:
A PLANETARY GEARBOX WITH GROOVED FLEX PIN AND DOUBLE
CANTILEVER ARRANGEMENT FOR LOAD DISTRIBUTION

(a) Applicant Name: Elecon Engineering Company Ltd.
(b) Nationality: Indian
(C) Address- Elecon Engineering Co. Ltd.
Anand Sojitra Road
Vallabh Vidyanagar - 388120
Gujarat, India.
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes and ascertains the nature of this
invention and the manner in which it is to be performed.
√ COMPLETE

Technical Field
[0001] The present patent application relates to a Planetary Gearbox with grooved flex pin and double cantilever arrangement for load distribution. More particularly present invention provides effective means by use of flexpin and bush pin to reduce misalignment and improve gear life span.
Background
[0002] Planetary gear box are well known. The basic planetary gear set includes a centrally located Sun gear Surrounded by a Series of planetary gears that mesh with the Sun gear. A ring gear meshes with the planetary gears. The Sun gear is rotatably fixed to a shaft and rotation of the shaft drives the Sun gear, which in turn drives the planetary gears, which drive the ring gear. Typically, the planetary gears are mounted to carrier shafts and are freely rotatable about their respective carrier Shaft. The carrier shafts are either captured between a pair of carrier decks, thus enclosing the planetary gear box, or the carrier Shafts extend from a single gear carrier. Generally, a bearing member is located between each planetary gear and the carrier shaft that carries the planetary gear. When the planetary gear Set is placed under torque, a load acts on the carrier shaft in a direction that is generally perpendicular to the longitudinal axis of the carrier shaft.
[0003] This load causes wear of the bearing member and the carrier shaft. In planetary gear Sets comprising only a single deck carrier wherein one end of the carrier shaft is free the load produced by torque causes a deflection of the carrier pin because the carrier shaft acts as a cantilevered member. This causes further wear of the bearing member and the carrier shaft. Additionally, planetary gears are typically designed Such that the teeth of the gear have a crowned shape to them. This crowned shape is necessary in order to aid in proper meshing of the planetary gear with the Sun gear when the planetary gear System is under a torque load and also to keep the planetary gear centered on its carrier Shaft. This crowning is difficult and expensive to use.

[0004] Planetary gear systems are widely used in a variety of industrial environments. In such arrangements, the rotational input is usually in the form of a sun gear. A plurality of planetary gears is mounted about the sun gear for receiving rotational force from the sun gear through intermeshing of respective teeth. Conventionally, planetary gears are mounted on a rotating planetary gear area, and the output element is usually in the form of a ring gear.
[0005] A typical epicyclic gear or planetary gear system in addition to sun gear and a plurality of planet gears uses a ring gear provided with internal teeth. The sun gear is located in the carrier, with the planet gear engaged to the sun and ring gear going around both the planetary gears and the sun gear. The ring gear is typically engaged with all the planet gears. Thus each planet gear is engaged with both the sun and the ring gear, and to none of the other planets, while the ring and sun are each engaged with all the planets. The planets are all mounted to the shafts in a parallel relationship, which relationship would ideally be retained during rotation. Of these three sets of items, sun, planets mounted on the carrier, and the ring gear, one will typically be held fixed and the other to rotate, with power to rotate fed to one rotating component, at a given angular speed and torque, and power taken from the other rotating component at a changed torque and speed related linearly or inversely to the first by the gear ratio.
[0006] A common problem in all gear systems both planetary and non-planetary is misalignment of the two gears as their teeth mesh. When the axes of rotation of the gears are not perfectly parallel the partial contacts of the teeth cause expanding and contact stresses to one end of a tooth. Theoretically, potential power loss of the gear assembly output due to misalignment can be 30 percent or higher. The out-of-parallel condition causes significant problems in excessive wear, added friction, added noise, and higher stress in the gear teeth, which causes metal fatigue.
[0007] Another issue created in planetary gear assemblies with four or more gears is the load distribution between the load gears. In order to better approximate uniform loading, one of the suggested methods is to allow plastic deformation of planet gear shafts and provide "flexible mounts." Still another problem arises due to deflection of the carrier under load, which will introduce the most misalignment when

the gears are subject to maximum load. At such time the carrier torsional deformation introduces the largest misalignment due to the deformation. A significant part of the large percentage of derating of all gears due to misalignment is directly attributable to this fact.
[0008] One of the solutions offered by the industry is to use a pair of spaced-apart rigidly connected plates to function as the planet carrier. The double-pate design allows to significantly reduce deflection of the planet shaft and misalignment. However, the double-plate design is significantly heavier than the one plate, and more costly to construct. Such designs are not well suited to the use of flexible mountings for the planets, which in turn makes them poorly suited to use of more than three planets. Also out-of-tolerance issues will tend to be aggravated by the stiffness of those designs.
[0009] It is assumed that the planetary gearbox arrangement offers many advantages over traditional gearbox arrangements. One advantage is its unique combination of both compactness and outstanding power transmission efficiencies. Typical efficiency losses in a planetary gearbox arrangement are only 3% per stage. This type of efficiency ensures that a high proportion of the energy being input through the sun gear into the gearbox is multiplied and transmitted into torque, rather than being wasted on mechanical losses inside the gearbox. Another advantage of the planetary gearbox arrangement is load distribution. Because the load being transmitted is shared between multiple planets, or planetary gear sets 36 torque capability is greatly increased. The more planets in the system the greater load ability and the higher the torque density. The planetary gearbox arrangement also creates greater stability and increased rotational stiffness. However, as stated above, such engineering solutions are not without problems, such as the design complexity and gaps between the meshing teeth during rotation of the sun gear 34.
[00010] In state of the art some disclosure was observed including Pat. No. 6,994,651 issued to G. P. Fox and E. Jallat, where an epicyclic gear system that has a sun gear, a ring gear located around the sun gear and planet gears located between and engaged with the sun and ring gears is disclosed.. A carrier flange is

offset axially from the planet gear and a carrier pin projects from it into the planet gear. Each carrier pin, being cantilevered from the carrier flange, has a double taper and is said to deflect relative to the flange under the torque. The inner race, being cantilevered from the pin at its opposite end where the deflection of the pin is the greatest, deflects in the opposite direction so as to compensate for the deflection caused by the pin. As a consequence of the two deflections, the axis Y for the planet gear remains essentially parallel to the center axis X, and the planet gear remains properly meshed with the sun gear and ring gear. A groove in the pin is said to facilitate the flexure of the pin.
OBJECT OF INVENTION
[00011] The prime object of the present invention is to a Planetary Gearbox with grooved flex pin with double cantilever arrangement for load distribution.
[00012] An object of the present invention is to provide a planetary gear box that includes self-aligning flex pin for the planetary gears that greatly reduces the wear to the carrier shaft caused by torque-induced loads on the planetary gear box.
[00013] A further object of the invention is to provide an effective means by use of flexpin and bush pin to reduce misalignment and improve gear life span.
[00014] Another object of the present invention is to provide gearbox that is intended to better accommodate shaft misalignment relative to the central shaft, to more evenly distribute the force along the planet gear tooth width, and to more evenly share the loading among the various planet gears.
[00015] Yet another object of the present invention is to provide double cantilever arranged flexpin and bush pin that gives floating type assembly for shaft pin that compensate load bearing.
[00016] Further object of the present invention is to minimize the deviation of the supporting pin axes, and therefore of the respective planet gear axes with respect to the ring gear and Sun gear axes that results in uneven load distribution on the meshing teeth of the planet, Sun and ring gears, and on the bearings, thus impairing operation of the gear system and normally significantly reducing the working life of its component parts.

SUMMARY
The present invention provides to a Planetary Gearbox with grooved flex pin and double cantilever arrangement for load distribution. More particularly present invention provides effective means by use of flexpin and bush pin to reduce misalignment and improve gear life span. The invention are achieved through a provision of an epicyclic gear assembly that has a central toothed sun gear unit mounted on a carrier plate and plurality of planetary gear sets Surrounding the central Sun gear in torque-transmitting relationship. Each of said planetary gear sets has a toothed planetgear Supported by a flex pin and bush pin, the first end of which is cantilevered from the carrier plate. A second end of the planet shaft supports the planet gear. A double-tapered concave middle portion of the planet shaft allows flexing of the shaft so as to facilitate elastic deflection of the planet shaft while distributing loads between the planet gear sets.
BRIEF DESCRIPTION OF THE DRAWINGS
[00017] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate disclosed embodiments and, together with the description, serve to explain the disclosed embodiments. In the drawings:
[00018] FIG. 1 illustrates perspective side view of planetary gearbox
according to present invention
[00019] Fig. 2 illustrates perspective side view of gear carrier according to
present invention [00020] Fig. 3 illustrates perspective side view of gearbox without internal gear to
understand internal arrangement of the planet
[00021] Fig. 4 illustrates perspective sectional side view of the gearbox
showcasing arrangement between flex pin, pin bush, planet rings
[00022] Fig. 5 illustrates sectional side view of pin bush, flex pin, planet gear and
internal gear
[00023] Fig. 6 illustrates sectional enlarged view of portion described in Fig. 5 [00024] Fig. 7 illustrates sectional side view of grooved flex pin according to
present invention

[00025] Fig. 8 illustrates section view and side view of bush pin according to the present invention
[00026] Fig. 9 shows a loading and boundary condition of simplified model of a Grooved Flex11 with Pin Bush 12.
[00027] Fig. 10 shows von-misses stresses acting on simplified model of a Grooved Flex Pin 11 with Pin Bush 12.
[00028] Fig. 11 shown total deformation on simplified model of a Grooved Flex Pin 11 with Pin Bush 12.
DETAILED DESCRIPTION
[00029] Reference will now be made in detail to the disclosed embodiments, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
[00030] The present specification provides certain definitions and methods to better define the embodiments and aspects of the invention and to guide those of ordinary skill in the art in the practice of its fabrication. Provision, or lack of the provision, of a definition for a particular term or phrase is not meant to imply any particular importance, or lack thereof; rather, and unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.
[00031] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs. The terms "first", "second", and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item, and the terms "front", "back", "bottom", and/or "top", unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation. If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and independently combinable.

[00032] The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described inventive features may be combined in any suitable manner in the various embodiments.
[00033] As discussed above, on any sort of planetary gearbox application, one significant issue is load sharing among the planet gears. Many effects can cause misdistribution of loads between planet gears. These would include, but are not limited to tolerance errors in the manufacture of components of the gearbox, side loads introduced to the carrier in the case of a jacking system, storm loads causing deflections of the jacking pinion shaft, the rig leg chord walking off center of the jack case if the leg guides are worn excessively, a wind turbine seeing eccentric loads on the rotor due to the wind speed being higher above the centerline of the rotor than below. Any of these sorts of issues can cause some planet gear meshes to see significantly higher loads that the others, and to deal with this, a softer (more deflection per unit load) flex pin help by allowing the more loaded planet to deflect more and so push the load via the carrier to other planets is desirable. The present invention solves these problems through the structural aspects of the gear box assembly described below.
[00034] Fig. 1 illustrates planetary gearbox (1) according to the present invention. Referring now to the drawings and initially to FIG. 1, a perspective side view of a planetary gear set and is shown generally by numeral (1). Planetary gear set (1) includes a the planet carrier (5). A Sun gear (2) is centrally mounted on the planet carrier (5) and is Surrounded by a plurality of planetary gears (3). Planetary gears (3) mesh with Sun gear (2). An internal ring gear (4) surrounds planetary gears (3) and meshes with planetary gears (3). Each of the planetary gears (3) are mounted to the planet carrier (5) with the help of flex pin (11). The said arrangement is described in details in later para. A bush pin (12) is located between each carrier and its respective

planetary gear (3). Thus, Sun gear (2) is rotatably fixed to Sun shaft. Rotation of Sun Shaft rotates Sun gear (2), planetary gears (3) and ring gear (4), The planetary gear set or box (1), shown in FIG. 1, is highly schematic and serves only to illustrate the basic components of a planetary gear box. As will be understood by one of ordinary skill in the art, in actual practice planetary gear set (1) would include numerous other components not shown in FIG. 1.
[00035] Planetary gearbox (1) has potential to transmit high torque at several speed ranges. Centrally mounted sun gear rotates multiple planet gears (3), which further meshes to internal gear (4). The planet gears (3) are mounted over the flex pin (11) and bush pin (12), which supported on the planet carrier (5). The arrangement offers high torque transmission ratio. When planet wheels are supported over the planet pins with rigid support, it provide fluctuations in load transmission due large torque involved.
[00036] FIG. 2 illustrates planet carrier (5) wherein two planet rings (6,7) were connected together using support pin (8). The sun gear (2) centrally mounted and meshed with set of planet gears (3) which are mounted on planet carrier (5). The planet carrier (5) consists of corresponding holes to accommodate the flex pin (11) and bush pin (12). The present invention utilizes specially designed planet carrier (5) where double cantilever support structure of bush pin (12) and flex pin (11) collectively engaged to accommodate planet gear (3) between two rings (6, 7). The ring (6) specifically contains hole to accommodate grub screw (13). The detailed arrangement of flex pin (11), bush pin (12), grub screw (13) and rings (6, 7) described in detailed in following description.
[00037] Fig. 3 discloses perspective side view of planetary gear box (9) without internal gear (4) just to understand internal arrangement of plant wheel gear (3), sun gear (2). The arrangement provides clear view of interacting or intermeshing components in the present gear box. In state of the art gear, wear and tear is major problem with frequent down time for maintenance and replacement of shaft. The present invention provides inventive feature where easy replacement or opening of the system plays vital role to achieve object of the present invention.

[00038] Fig. 4 discloses perspective side sectional view of present invention where actual arrangement of flex pin (11), bush pin (12), bearing (15), planet gear (3) and external gear (4). As depicted in the figure one end of the grooved flex pin (11) is mounted over the ring (6) of the gear carrier (5) by grub screw (13). The said arrangement provides easy removal of particular flex pin from side by just accessing grub screw (13) from the top.
[00039] The sun gear (2) centrally mounted and meshed with set of planet wheel (3) which are mounted on planet carrier (5). The Planet carrier (5) consist of ring (6) and ring (7) connected together using connecting pin (8). Planet wheels (3) further meshes with internal gear (4) to transmit the torque. Planet wheel assembly (9) combines the sun gear (2), planet wheel (3) carried together by planet carrier (5). The Planet wheel (3) are mounted over flex pin (11).
[00040] Perspective cross-sectional view 10 of grooved flex pin design for the planetary gearbox. One end of grooved flex pin 11 is mounted over a ring 6 of planet carrier using grub screws 13 used to fix the grooved. Pin bush 12 is mounted on the other end of flex pin, however the pin bush 12 is kept free to make it a cantilever support, moreover known as double cantilever support between 11 & 12. A pair of cylindrical roller bearings 15 is placed over the pin bush 12, an external circlip 16, distance piece 17 and internal circlip 18 are placed in between for locking purpose. Planet wheels 3 are fixed over the bearings 15, which allows it to rotate. Planet wheel 3 meshes with internal teeth gear 4.
[00041] It is submitted that in conventional gear box the heavy loads tend to distort the carrier and its pins and skew the axis about which the planet pinions rotate. Under such conditions, the planet gear does not mesh properly with the sun and ring gears. This causes excessive wear in the planet pinions and the sun and ring gears, generates friction and heat, and renders the entire system overly noisy.
[00042] The deviation of the supporting flex pin axes, and therefore of the respective planet gear axes with respect to the ring gear and Sun gear axes, results in uneven load distribution on the meshing teeth of the planet, Sun and ring gears, and on the bearings, thus impairing operation of the gear system and normally significantly reducing the working life of its component part.

[00043] The present invention discloses the planetary system in which the planet gears (3) are supported on and rotate flexpins mitigates the skewing. In this regard, a flexpin for a planet pinion at one end is anchored in and cantilevered from the wall of a carrier of which it is a fixed. The other end of the flexpin has a sleeve fitted to it, with the sleeve extending back over, yet otherwise spaced from the flexpin. The sleeve supports the planet gear in that it serves as a component of a bearing for the pinion.
[00044] Fig.6 is the detailed view of the arrangement shown in Fig. 5. An external circlip 16, distance piece 17 and internal circlip 18 are used for locking and suspension purpose. The radial space (14) between bore of planet carried ring 7 and outer diameter of pin bush 12. During operation the load transmission is supported by double cantilever arrangement of grooved flex pin 11 and pin bush 12. The grooved flex pin 11 deflects due to its cantilever support and gives flexibility, which provides uniform load distribution between planet wheels 3 and internal teeth gear 4 and reduces shock loads. The contact pattern between the planet wheel and internal teeth gear is at the midst over the face width.
[00045] If the load carried by the double cantilever arrangement of grooved flex pin and pin bush exceeds the threshold value of deflection of grooved flex pin, the radial space (14) between pin bush (12) and bore of planet carrier ring 7 came into action and the pin bush get supported over the bore of planet carrier ring 7. This provides additional safety to the planetary drive for high torque transmission, increasing the life of the flex pin arrangement and planetary gearbox.
[00046] Fig. 7 depicts stepped cut grooved flex pin according to the preferred embodiment of the present invention. The Grooved flex pin 11 is supported on 6 at one end, which consists of cylindrical portion 24, conical portion 25, cylindrical portion 26, conical portion 27, and cylindrical portion 28. A pin bush 12 is the cylindrical portion 30 with hollow portion 32, 33, upper extended cylindrical portion 29. 22 is the contact portion of 3 &4. The flexpin is fixed with carrier wall (6) by using grub screw (13) and opposite end 24 is accommodated in carrier ring 7.
[00047] The present specification provides certain definitions and methods to better define the embodiments and aspects of the invention and to guide those of ordinary skill in the art in the practice of its fabrication. Provision or lack of the provision,

of a definition for a particular term or phrase is not meant to imply any particular importance, or lack thereof; rather, and unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art.
[00048] Various embodiments of the invention are intended to more evenly distribute the force along the planet gear tooth width and to more evenly share the loading among the various planet gears. The planet gears can be secured more centrally, allowing the planet pins to flex to a greater degree. If this centralized support is connected to support segments, for example, bearings, which are then attached to the carrier walls, it will create two more narrowed regions which will allow the pivoting of the centralized region to be enhanced. Also, choosing the correct axial position in which to secure the planet gears to the planet pins will allow the planet gears to self align and distribute their force more evenly along the planet gear tooth width. For planet gears that have an overturning moment, a sliding flattened interface between the planet pins and the planet gears can be fashioned to resist such a moment. The flattened region will resist the overturning moment while sliding in the tangential direction. The planet pins can be designed to have a non-circular cross-section in order to be stiffer in the overturning moment direction than the tangential direction. These segments can be attached by interference or bolted.
[00049] One end of grooved flex pin 11 is mounted over a ring 6 of planet carrier using grub screws 13 used to fix the grooved. Pin bush 12 is mounted on the other end of flex pin, however the pin bush 12 is kept free to make it a cantilever support, moreover known as double cantilever support between 11 &12. The unique stepped cut design provides maximum flexibility for the shock absorbance in the gear box.
[00050] Fig. 8 depicts pin bush in a preferred embodiment of the present invention. The said pin bush (12) includes flange (29), tubular portion 30 and groove 31. The opposite end of bush pin contains tubular ring arrangement to accommodate flexpin (11) at part (24). Further the whole assembly will accommodated into the ring (7) of carrier (5).
[00051] The softness of the flex pin as a spring will allow small misalignments to correct themselves as force introduced by the misalignment on the gear tooth can be seen as a generally small additional moment added or subtracted to the moment and

shear load applied to the flex pin. A flex pin of this invention tends to deflect in a way that minimizes the eccentric loading due to misalignment, and the softer (more deflection per given load) the flex pin, the less the misalignment will matter in the operation of the gear assembly of this invention.
[00052] The present study objective is to analyse the grooved flex pin for a planetary gear box. The structural analysis of the grooved flex pin for the possible load due to operation is considered and simulated. For simplified simulation, only the grooved flex pin 11 with bush pin 12. Figure 9 shows the stage assembly of the planetary gearbox with grooved flex pin design.
[00053] In order to conduct present analysis applicant has relied on advanced FEA static structural tool Ansys 14.5 was used.
[00054] This present analysis is based on standard procedure of Finite Element Analysis based staticstructural analysis. The margin of the graph has not considered the influence at actual field response.
[00055] Figure 10 describes result of Von-misses stresses acting on simplified model of a Grooved Flex Pin 11 with PinBush 12. The Grooved Flex pin is subjected to stresses quite higher than the Pin Bush, so itfound to be critical component for design of planetary drive gearbox.Fig. 10 shows Von-misses stresses acting on simplified model of a Grooved Flex Pin 11 with Pin Bush 12.
[00056] Figure 11 Total deformation on simplified model of a Grooved Flex Pin 11 with Pin Bush 12.The Pin Bush end is subjected to higher deformation compared to the Grooved Flex pin, so it necessary care to be taken during design of it in planetary drive gearbox.
[00057] In elevated stress study the total deformation on simplified model of a Grooved Flex Pin 11 with Pin Bush 12 is shown in Fig. 11.
[00058] The instant invention allows as much elastic deflection of the planet under load as possible to distribute load between the planets. Additionally, the alignment of the planet gear with respect to the sun and ring gears is maintained due to the flexing abilities of the planet shafts.

[00059] Many changes and modifications can be made in the present invention without departing from the spirit thereof. I, therefore, pray that my rights to the present invention be limited only by the scope of the appended claims.
[00060] Moreover, while illustrative embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations or alterations based on the present disclosure. The elements in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the steps of the disclosed methods can be modified in any manner, including by reordering steps or inserting or deleting steps. It is intended, therefore, that the specification and examples be considered as example only, with a true scope and spirit being indicated by the following claims and their full scope of equivalents.

We claim,
1. A Planetary Gearbox (1) with grooved flex pin (11) with double cantilever
arrangement for load distribution, comprising:
at least one sun gear (2) configured to mount at central position in planet carrier (5) and
plurality of planetary gear sets surrounding the central gear in torque-transmitting
relationship, at least one ring gear (4) configured to intermesh with periphery of planet gear (3), at least one grooved flex-pin (11) configured to accommodate by one end of said planet
carrier (5) through grub screw (13); at least one planet carrier (5) configured to receive one or more planet gears (3), at
least one flex pin (11), at least one cylindrical roller bearings (15) and at least
one bush pin (12), at least one cylindrical roller bearings (15) configured to position between planet gear
and bush pin to reduce friction between the components, at least one bush pin (12) positioned between said planet carrier (5) and said flex pin
(11), wherein,
the planet carrier (5) contains grove to accommodate flex pin and bush pin,
the bush pin contains flange at the proximate end of the planet sleeve carries an outwardly extending flange to flexibly attach with planet carrier (5), the said bush pin contains groove at distal end that abut the planet carrier assembly and also provides radial space between planet carrier ring (7) and bush pin (12),
each of said planet gear (3) accommodated with a cylindrical roller bearings (15) interposed between the planet sleeve and the planet gear,
each flex pin contains concave middle portion having oppositely tapering parts which unitary connect at a smallest diameter center part of the middle portion.
2. The Planetary Gearbox (1) with grooved flex pin (11) with double cantilever
arrangement for load distribution as claimed in claim 1, comprising each of said
planetary gear sets comprising a toothed planet gear (3) supported by a flex pin
(11), the flex pin cantilevered from the carrier ring (7) at one end, and wherein

said middle portion of flex pin (11) has an outer circumference provided with at least one outwardly convex circumferential protrusion formed between the first end and the second end, said middle portion facilitating flexing of the planet shaft so as to allow elastic deflection of the planet shaft while distributing load betwe'en the planet gear sets.
3. The Planetary Gearbox (1) with grooved flex pin (11) with double cantilever arrangement for load distribution as claimed in claim 1, comprising flex pin tends to deflect in a way that minimizes the eccentric loading due to misalignment.
4. The Planetary Gearbox (1) with grooved flex pin (11) with double cantilever arrangement for load distribution as claimed in claim 1, each of the said flex pin retained in a generally parallel relationship to a central axis of the central sun gear during torque transmission between the sun gear and the planet gear sets.