DRIVE ASSEMBLY COMPRISING TWO SHAFTS CONNECTED BY

DRIVE MEANS

The present patent application for industrial invention relates to a drive assembly comprising two shafts connected by drive means.

DE916740 discloses a transmission comprising a Maltese cross mechanism, suitable for transforming a continuous rotation into an intermittent rotation. A first shaft is connected to a drive shaft by means of gears. A feeler with pins is fixed at one end of the first shaft. A second shaft supports a Maltese cross driven wheel. The driven wheel is provided with eight protuberances that are separated by radial slots. During the rotation of the first shaft, the pins of the feeler, which is joined to the first shaft, are alternatively inserted into the slots of the driven wheel, making the driven wheel rotate by one step.

US2009/229391 discloses a power coupling device comprising a cam shaft provided with cam lobe which engages a first roller tappet mounted on a rocker arm. In such a way, a rotation of the cam shaft determines a rotation of the cam and consequently a movement of the rocker arm.

The rocker arm engages a second roller tappet, this one being affixed to the support at one end of a splined shaft. The end of the splined shaft opposite the support, is coupled to a coil spring. A worm is mounted on the splined shaft and is engaged with a cylindrical gear mounted on an output shaft of the power coupling device.

When the rocker arm is raised, the support translates vertically and the worm performs as a rack, causing the gear to rotate.

When the rocker arm is lowered, the coil spring is loaded, causing the worm to rotate. Such a rotation of the worm causes the gear to rotate also during the return travel of rocker arm to the initial position. The purpose of the present invention is to disclose a drive assembly that is simple, effective and reliable.

This purpose is achieved according to the invention with the characteristics of the appended independent claim 1.

Advantageous embodiments appear from the dependent claims.

The drive assembly of the invention is defined by claim 1.

For the sake of clarity, the description of the drive assembly according to the invention continues with reference to the appended drawings, which have a merely illustrative, not limiting value, wherein:

- Fig. 1 is a diagrammatic front view of a first shaft, a feeler and a propeller of a second shaft of the drive assembly according to the invention;

Fig. 1A is a front view of the feeler of Fig. 1 in two different time instants: one in contact with an initial section of a concave curved edge of a blade of the propeller, and one in contact with an ending section of the concave curved edge of the blade of the propeller;

Figs. 2 to 25 are diagrammatic front views that sequentially illustrate the movement of a feeler and of a propeller of the drive assembly according to the invention, during the rotation of the first and the second shaft;

Figs. 26 and 27 are diagrammatic views that illustrate the orientation of the feelers connected in series to the first shaft and the orientation of the propellers mounted in series on the second shaft, in two different time instants;

- Figs. 28 to 30 are diagrammatic front views that illustrate the movement of a propeller mounted on the second shaft and of three feelers connected to the first shaft and to a third and a fourth shaft in three different time instants, according to an alternative embodiment of the drive assembly of the invention;

- Figs. 31 to 33 are diagrammatic front views that illustrate the movement of a feeler connected to the first shaft and of three propellers mounted on the second shaft and on a third and a fourth shaft in three different time instants, according to an additional alternative embodiment of the drive assembly of the invention;

Fig. 34 is a diagrammatic view of the drive assembly of the invention which comprises multiple propellers mounted in series on the second shaft and multiple feelers connected in series to the first, third and fourth shaft;

Fig. 35 is a diagrammatic view of the drive assembly of the invention which comprises multiple feelers connected in series to the first shaft and multiple propellers mounted in series on the second, on the third and on the fourth shaft;

Fig. 36 is the same as Fig. 35, wherein the first shaft is rotated by 30° relative to the first shaft shown in Fig. 35.

With reference to Fig. 1 , a drive assembly according to a first embodiment of the invention is disclosed.

The drive assembly of the invention comprises a first shaft (A1 ) with an axis of rotation (X1 -X1 ) (not shown in Fig. 1 , but only in Figs. 26 and 27), and a feeler (T1 ) connected to the first shaft (A1 ).

The drive assembly of the invention also comprises a second shaft (A2) with an axis of rotation (X2-X2) (not shown in Fig. 1 ) parallel to the axis of rotation (X1 -X1 ) of the first shaft (A1 ).

A propeller (S1 ) is mounted on the second shaft (A2) and comprises curved blades (20) that protrude radially from the second shaft (A2). Each blade (20) comprises a concave curved edge (21 ) and a convex curved edge (22) disposed in such a way that the concave curved edge (21 ) of a blade (20) is joined to the convex curved edge (22) of the adjacent blade (20) in a point of inflection. Advantageously, the concave curved edge (21 ) of each blade (20) has a parabolic shape.

A linear actuator (1 ) is connected to the first shaft (A1 ) and to the feeler (T1 ) in order to push the feeler (T1 ), in such a way that said feeler (T1 ) slides along the concave curved edge (21 ) of one of the blades (20) of the propeller (S1 ), causing the second shaft (A2) to rotate. It must be noted that, according to alternative embodiments, the drive assembly of the invention can be provided with a plurality of identical feelers (T1 , T2, T3, T4, T5, T6, T7, T8) and of a plurality of identical blades (S1 , S2, S3, S4, S5, S6, S7, S8). In such a case, the feelers (T1 , T2, T3, T4, T5, T6, T7, T8) are connected in series to the first shaft (A1 ) and the propellers (S1 , S2, S3, S4, S5, S6, S7, S8) are mounted in series along the second shaft (A2), as shown in Figs. 26 and 27. Alternatively, the drive assembly according to the invention can be provided with a third and a fourth shaft (A3, A4; A5, A6), as shown in Figs. 28 to 33.

In any case, regardless of the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8), of propellers (S1 , S2, S3, S4, S5, S6, S7, S8) or of shafts (A1 , A2, A3, A4, A5, A6) of the drive assembly according to the invention, the modes in which each feeler (T1 , T2, T3, T4, T5, T6, T7, T8) cooperates with one of the blades (20) of a propeller (S1 , S2, S3, S4,

S5, S6, S7, S8) are the same as the ones shown in Figs. 2 to 25.

The drive assembly of the invention comprises gear reduction means that connect the first shaft (A1 ) to the second shaft (A2).

The gear reduction means define a transmission ratio between the first shaft (A1 ) and the second shaft (A2), in such a way that the propeller (S1 ) rotates until it is disposed in the desired position in order to correctly cooperate with the feeler (T1 ), as shown in Figs. 2 to 25.

Therefore, said gear reduction means perform as synchronization means for the two shafts (A1 , A2).

More precisely, the propeller (S1 ) is to move in such a way that the convex curved edge (22) of each blade (20) does not prevent the feeler (T1 ) from moving closer to the concave curved edge (21 ), against which said feeler (T1 ) is to exert its thrust.

Figs. 2 to 5 sequentially illustrate the sliding of the feeler (T1 ) connected to the first shaft, along the concave curved edge (21 ) of the blade (20) of the propeller (S1 ) mounted on the second shaft. The sliding of the feeler (T1 ) along the concave curved edge (21 ) of the blade (20) of the propeller (S1 ) causes a rotation of the second shaft (A2), whereon the propeller (S1 ) is fixed, in such a way that the concave curved edge (21 ) of the blade (20) of the propeller is always positioned correctly relative to the position of the feeler (T1 ) following to the rotation of the first shaft (A1 ).

In order to correctly position the concave curved edge (21 ) of the blade (20) of the propeller relative to the position of the feeler (T1 ), the number of blades (20) mounted on the second shaft (A2) is to coincide with the transmission ratio between the first shaft (A1 ) and the second shaft (A2).

According to a preferred embodiment of the invention, the blades (20) mounted on the second shaft (A2) are in a number of three and the transmission ratio is 3:1 , i.e. the first shaft (A1 ) has an angular speed equal to three times the angular speed of the second shaft (A2).

Advantageously, the gear reduction means of the drive assembly according to the invention comprise a first toothed wheel connected to the first shaft (A1 ), and a second toothed wheel connected to the second shaft (A2), which are not shown in the appended figures.

When the feeler (T1 ) is in contact with the concave curved edge (21 ) of one of the blades (20) of the propeller (S1 ), the feeler (T1 ) exerts a thrust on the propeller (S1 ) by means of the linear actuator (1 ).

The drive assembly of the invention comprises an actuation means for said linear actuator (1 ). Said actuation means moves the linear actuator (1 ) between a forward position and a backward position.

With reference to Figs. 1 and 1A, the concave curved edge (21 ) of each blade (20) comprises an initial portion (211 ) and a final portion (212).

When the feeler (T1 ) is in contact with the initial portion (211 ) of the concave curved edge (21 ) of one of the blades (20) of the propeller (S1 ), the linear actuator (1 ) is in backward position and the feeler (T1 ) has an initial distance (d) relative to the axis (X1 -X1 ) of the first shaft (A1 ). When the feeler (T1 ) is in contact with the final portion (212) of the concave curved edge (21 ) of one of the blades (20) of the propeller (S1 ), the linear actuator (1 ) is in forward position and the feeler (T1 ) has a final distance (D) relative to the axis (X1 -X1 ), said distance (D) being higher than the initial distance (d).

Advantageously, the difference between the final distance (D) and the distance (d) (which is equivalent to the travel of the linear actuator (1 )) is comprised between 1.8-2.2 mm, preferably 2 mm.

Preferably, the linear actuator (1 ) comprises a piston and a spring. The spring pushes the linear actuator (1 ) on one side and the piston pushes the linear actuator (1 ) on the other side. More precisely, the spring pushes the linear actuator (1 ) away from the axis (X1 -X1 ) of the first shaft (A1 ), whereas the piston pushes the linear actuator (1 ) closer to the axis (X1 -X1 ) of the first shaft (A1 ).

Preferably, said linear actuator (1 ) also comprises stop means that prevent the linear actuator (1 ) from going beyond the backward position or the forward position.

Still with reference to Fig. 1A, between the time instant in which the feeler (T1 ) is in the initial portion (211 ) of the concave curved edge (21 ) of one of the blades (20) of the propeller (S1 ) and the time instant in which the feeler (T1 ) is in the final portion (212) of said concave curved edge (21 ), the first shaft (A1 ) rotates by a gamma angle (y), whereas the second shaft (A2) rotates by a delta angle (d).

The gamma angle (y) is three times the delta angle (d).

With reference to Figs 26 and 27, the drive assembly according to a preferred embodiment of the invention is disclosed, which provides for using two or more feelers (T1 , T2, T3, T4, T5, T6, T7, T8) connected to the first shaft (A1 ), and two or more propellers (S1 , S2, S3, S4, S5, S6, S7, S8) fixed to the second shaft (A2). Each feeler (T1 , T2, T3, T4, T5, T6, T7, T8) is suitable for cooperating with a corresponding propeller (S1 ,

S2, S3, S4, S5, S6, S7, S8). More precisely, the number of propellers (S1 , S2, S3, S4, S5, S6, S7, S8) disposed in series along the second shaft (A2) is equal to the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8) connected in series to the first shaft (A1 ).

The number of propellers (S1 , S2, S3, S4, S5, S6, S7, S8) and the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8) depend on the configuration and on the number of the blades (20). As a matter of fact, the number of propellers (S1 , S2, S3, S4, S5, S6, S7, S8) and, consequently, the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8), is calculated in such a way that during the rotation of the two shafts (A1 , A2) there is always at least one feeler (T1 , T2, T3, T4, T5, T6, T7, T8) in contact with the concave curved edge (21 ) of one of the blades (20) of a propeller (S1 , S2, S3, S4, S5, S6, S7, S8).

In order for at least one feeler (T1 , T2, T3, T4, T5, T6, T7, T8) to be in contact with one propeller (S1 , S2, S3, S4, S5, S6, S7, S8), the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8) must be equal to or higher than the ratio between a round angle and the gamma angle (y) (shown in Fig. 1A). Moreover, said feelers (T1 , T2, T3, T4, T5, T6, T7, T8) must be angularly spaced by an alpha angle (a) having a value that is lower than or equal to a round angle divided by the number of feelers (T1 , T2, T3, T4, T5, T6, T7, T8). Accordingly, the propellers (S1 , S2, S3, S4, S5, S6, S7, S8) must be staggered by a beta angle (b) with width equal to one third of the width of the alpha angle (a). More specifically, the propellers (S1 , S2, S3, S4, S5, S6, S7, S8) must be staggered in such a way that as soon as a feeler (T1 , T2, T3, T4, T5, T6, T7, T8) completes its contact and thrust step against the final portion (212) of the concave curved edge (21 ) of one of the blades (20) of a propeller (S1 ,

52, S3, S4, S5, S6, S7, S8), another feeler (T1 , T2, T3, T4, T5, T6, T7, T8) starts pushing against the initial portion (211 ) of the concave curved edge (21 ) of one of the curved blades (20) of another propeller (S1 , S2,

53, S4, S5, S6, S7, S8). Every time a feeler (T1 , T2, T3, T4, T5, T6, 17, T8) makes a complete rotation, the corresponding propeller (S1 , S2, S3, S4, S5, S6, S7, S8) rotates by 120°, and the feeler (T1 , 12, T3, T4, T5, T6, 17, T8) is cyclically in contact with the concave curved edge (21 ) of each blade (20).

According to a preferred embodiment, the gamma angle (y) and the alpha angle (a) coincide, in such a way that as soon as a feeler (T1 , 12, T3, T4, T5, T6, 17, T8) completes its contact and thrust step against the concave curved edge (21 ) of one of the curved blades (20) of a propeller (S1 , S2, S3, S4, S5, S6, S7, S8), another feeler (T1 , 12, T3, T4, T5, T6, 17, T8) starts pushing against the concave curved edge (21 ) of one of the curved blades (20) of another propeller (S1 , S2, S3, S4, S5, S6, S7, S8).

According to a preferred embodiment of the invention, the alpha angle (a) and the gamma angle (y) have a width equal to 45° and, consequently, the number of feelers (T1 , 12, T3, T4, T5, T6, 17, T8) is equal to eight, which corresponds to 360°/45°.

With reference to Figs. 26 and 27, the feelers (T1 , 12, T3, T4, T5, T6, 17, T8) are staggered, as well as the propellers (S1 , S2, S3, S4, S5, S6, S7, S8); it can be easily understood that the purpose of such a staggered position is a continuous transfer of motion from the first shaft (A1 ) to the second shaft (A2).

Figs. 26 and 27 show two different time instants of the drive assembly according to the invention comprising eight propellers (S1 , S2, S3, S4, S5, S6, S7, S8) and eight feelers (T1 , 12, T3, T4, T5, T6, 17,

T8).

The eight propellers (S1 , S2, S3, S4, S5, S6, S7, S8) and the eight feelers (T1 , T2, T3, T4, T5, T6, T7, T8) are defined with the prefix “first, second, third, fourth, fifth, sixth, seventh, and eighth” in order to understand the cooperation between the first shaft (A1 ) and the second shaft (A2). With reference to Fig. 26, the drive assembly is shown in a first time instant, wherein the first feeler (T1 ) is disposed in the final portion (212) of the concave curved edge (21 ) of one of the curved blades (20) of the first propeller (S1 ). Simultaneously, the second feeler (T2), which is staggered by 45° relative to the first feeler (T1), comes in contact with the initial portion (211 ) of the concave curved edge (21 ) of one of the curved blades (20) of the second propeller (S2), whereas the following feelers (T3, T4, T5, T6, T7, T8) are not in contact with the relative propellers (S3, S4, S5, S6, S7, S8).

With reference to Fig. 26, the drive assembly is shown in a second time instant, wherein the first shaft (A1 ) is rotated by 45° and the second shaft (A2) is rotated by 15° relative to the first time instant. As shown in Fig. 26, in said second time instant, the first feeler (T1 ) is no longer in contact with the first propeller (S1 ). Instead, the second feeler (T2) is in contact with the final portion (212) of the concave curved edge (21 ) of one of the curved blades (20) of the second propeller (S2), and the third feeler (T3) is in contact with the initial portion (211 ) of the concave curved edge (21 ) of one of the curved blades (20) of the third propeller (S3).

Although not shown in the appended figures, it can be easily understood that, by continuing the rotation of the first shaft (A1 ) and of the second shaft (A2), at every time instant there is at least one feeler (T1 , T2, T3, T4, T5, T6, T7, T8) in contact with a propeller (S1 , S2, S3, S4, S5, S6, S7, S8) and, therefore, there is always a linear thrust action on a propeller (S1 , S2, S3, S4, S5, S6, S7, S8).

The thrust of one of said feelers (T1 , T2, T3, T4, T5, T6, T7, T8) on one blade (20) of one of said propellers (S1 , S2, S3, S4, S5, S6, S7, S8) creates an angular moment that causes the second shaft (A2) to move.

With reference to Figs. 31 , 32, 33, an alternative embodiment of the drive assembly of the invention comprises a third shaft (A3) and a fourth shaft (A4), which are identical to the first shaft (A1 ). The third shaft (A3) and the fourth shaft (A4) are disposed at a distance from the second shaft (A2) that is equal to the distance between the first shaft (A1 ) and the second shaft (A2). Moreover, said third shaft (A3), said fourth shaft (A4) and said first shaft (A1 ) are equally spaced. More precisely, the first shaft (A1 ), the third shaft (A3) and the fourth shaft (A4) are disposed around said second shaft (A2) staggered by 120°.

According to an additional alternative embodiment of the invention, which is shown in Figs. 28, 29, 30, the drive assembly comprises a third shaft (A5) and a fourth shaft (A6) identical to the second shaft (A2) and disposed at a distance from the first shaft (A1 ) equal to the distance between the second shaft (A2) and the first shaft (A1 ). Moreover, said third shaft (A5), said fourth shaft (A6) and said second shaft (A2) are equally spaced. More precisely, the second shaft (A2), the third shaft (A5) and the fourth shaft (A6) are disposed around the first shaft (A1 ) staggered by 120°.

Although not shown in the figures, according to the two aforementioned alternative embodiments of the invention, the drive assembly comprises additional gear reduction means that connect the third and the fourth shaft (A3, A4; A5, A6) with the first shaft (A1 ) or with the second shaft (A2).

More precisely, according to the embodiment of the invention shown in Figs. 28, 29 and 30, said additional gear reduction means are configured in such a way to have an angular speed ratio between the first shaft (A1 ) and the third and the fourth shaft (A5, A6) of 3:1. Said additional gear reduction are configured in such a way that the first shaft (A1 ) has a triple speed than the angular speed of the third and fourth shaft (A5, A6), as well as of the second shaft (A2).

In the embodiment shown in Figs. 31 , 32 and 33, said additional gear reduction means are configured in such a way to have an angular speed ratio between the second shaft (A2) and the third and the fourth shaft (A3, A4) of 1 :3. Said additional gear reduction means are configured in such a way that the second shaft (A2) has an angular speed equal to one third of the angular speed of the third and fourth shaft (A3, A4).

Also in the latter two embodiments of the invention, the first shaft (A1 ), the second shaft (A2), the third shaft (A3; A5) and the fourth shaft

(A4; A6) can comprise multiple propellers (S1 , S2, S3, S4, S5, S6, S7, S8) and/or can be connected to multiple feelers (T1 , T2, T3, T4, T5, T6, T7, T8), in such a way to obtain a thrust and a continuous cooperation between the shafts (A1 , A2, A3, A4, A5, A6), as shown in Figs. 34, 35 and 36.

With reference to Fig. 34, the drive assembly of the invention comprises eight propellers (S1 , S2, S3, S4, S5, S6, S7, S8) mounted in series on the second shaft (A2), and eight feelers (T1 , T2, T3, T4, T5, T6, T7, T8) connected in series to the first shaft (A1 ), to the third shaft (A3) and to the fourth shaft (A4).

As shown in Fig. 34, in such a configuration, each one of the three feelers (T1 , T2, T3, T4, T5, T6, T7, T8) that cooperate with the same propeller (S1 , S2, S3, S4, S5, S6, S7, S8) is disposed in the same position, relative to the other two feelers, with reference to the concave curved edge (21 ) of the blade (20) that cooperates with it. Such a simultaneous cooperation can be especially appreciated with reference to the third feelers (T3) and to the second feelers (T2) shown in Fig. 34, wherein the third feelers (T3) are simultaneously in contact with the initial portion (211 ) of the concave curved edge (21 ) of each blade (20) of the third propeller (S3), whereas the second feelers (T2) are simultaneously in contact with the ending portion (212) of the concave curved edge (21 ) of each blade (20) of the second propeller (S2).

With respect to the solution shown in Figs. 26 and 27, the simultaneous symmetrical cooperation of the three feelers (T1 , T2, T3, T4, T5, T6, T7, T8) on a single propeller (S1 , S2, S3, S4, S5, S6, S7, S8) that is centrally disposed on the second shaft (A2) allows for exerting a higher thrust on the second shaft (A2), avoiding the generation of a bending moment on the second shaft (A2) because the feelers (T1 , T2, T3, T4, T5, T6, T7, T8) simultaneously exert their thrust in three different directions on the same propeller (S1 , S2, S3, S4, S5, S6, S7, S8).

Likewise in the solution shown in Figs. 26 and 27, also in this solution the feelers (T1 , T2, T3, T4, T5, T6, T7, T8) connected to the same shaft (A1 , A3, A4) are staggered by 45°, whereas the propellers (S1 , S2, S3, S4, S5, S6, S7, S8) mounted on the second shaft (A2) are staggered by 15°, in such a way that, during the rotation of the shafts (A1 , A2, A3, A4), at least one of the feelers that are respectively connected to the first, to the third and to the fourth shaft (A1 , A3, A4) is in contact with a propeller of the second shaft (A2).

With reference to Fig. 35, the drive assembly according to the invention can comprise four propellers (S1 , S2, S3, S4) mounted in series on the second shaft (A2), on the third shaft (A5) and on the fourth shaft (A6), and four feelers (T1 , T2, T3, T4) connected in series to the first shaft (A1 ).

In such an embodiment, in order for at least one feeler (T1 , T2, T3, T4) to be in contact with at least one propeller (S1 , S2, S3, S4) of the second shaft and/or of the other two shafts (A5, A6), at least four feelers staggered by 30° are necessary.

More precisely, the first and the second feeler (T1 , T2) are staggered by 30°, the first and the third feeler (T1 , T3) are staggered by 60°, and the first and the fourth feeler (T1 , T4) are staggered by 90°.

Considering that three propellers (S1 , S2, S3, S4) are provided for each feeler (T1 , T2, T3, T4) and disposed around the same feeler (T1 , T2, T3, T4), in such a case the number of feelers (T1 , T2, T3, T4) and the mutual staggering must be calculated in such a way that at least one feeler (T1 , T2, T3, T4) is in contact with a propeller (S1 , S2, S3, S4) on 120°, instead of 360°.

Otherwise said, the number of feelers (T1 , T2, T3, T4) and the mutual staggering must be calculated in such a way that said feelers (T1 , T2, T3, T4) cover an angle of 120°, instead of 360°. The coverage of an angle of 120°, instead of 360°, is due to the fact that, at every complete rotation of the feeler (T1 , T2, T3, T4), said feeler (T1 , T2, T3, T4) comes in contact with all the propellers mounted on the second shaft (A2) and on the other two shafts (A5, A6).

More precisely, if in a first time instant the feeler (T1 , T2, T3, T4) is in contact with the initial portion (211 ) of the concave curved edge (21 ) of one of the curved blades (20) of a propeller (S1 , S2, S3, S4), in a second time instant, wherein the first shaft (A1 ) is rotated by 120° relative to the first time instant, the feeler (T1 , T2, T3, T4) will be again in contact with the initial portion (211 ) of the concave curved edge (21 ) of one of the curved blades (20) of a propeller (S1 , S2, S3, S4) in successive position (according to the direction of rotation of the first shaft (A1 )) relative to the propeller (S1 , S2, S3, S4) that has cooperated with the feeler (T1 , T2, T3, T4) in the first time instant.

Every 120°, the cyclic contact of the feeler (T1 ) coupled to the first shaft (A1 ) disposed between the second shaft (A2) and the other two shafts (A5, A6) is shown in Figs. 28, 29 and 30.

With reference to Fig. 35, the fourth feeler (T4) and the third feeler (T3) are in contact with the fourth propeller (S4) and the third propeller (S3) of the third shaft (A5).

During the travel of the fourth feeler (T4) along the concave curved edge (21 ) of the fourth propeller (S4), the first feeler (T1 ) comes in contact with the first propeller (S1 ) of the second shaft (A2), as shown in Fig. 3.

Therefore, in each time instant, at least one feeler (T1 , T2, T3,

T4) is in contact with one propeller (S1 , S2, S3, S4)

The advantages of the drive assembly according to the invention are evident.

The presence of feelers that are pushed by a linear actuator (1 ) allows for converting a linear motion in a rotational motion, reducing the stress and the load suffered by the gear reduction means. Moreover, the staggered position of the feelers allows the feelers to exert a continuous thrust on the propellers, thus providing a continuous contribution to the rotation of the second shaft.

Numerous variations and modifications can be made to the present embodiment of the invention, which are within the reach of an expert of the field, falling in any case within the scope of the invention as disclosed by the appended claims.