GB2481140A

GB2481140A - A cricket bowling machine with a guide member arranged to assist with spin

Info

Publication number: GB2481140A
Application number: GB1109770.6A
Authority: GB
Inventors: Henry Charles Pryor; David James Cross
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-06-10
Filing date: 2011-06-10
Publication date: 2011-12-14
Anticipated expiration: 2031-06-10
Also published as: GB201109770D0; GB2481140B

Abstract

A ball projecting machine comprising a pair of counter rotating wheels 1A and 1B and a rotary guide member 4, the driving wheels 1 having spaced ball engaging surfaces which cooperate with the guide member 4 to grip and project a ball wherein the axes of rotation of the drive wheels can be changed to impart spin on a ball and the guide member 4 can be rotated by the spin. The guide member 4 may be a ball mounted on a ball bearing track 4A so that it can freely rotate about a range of axes depending on the spin on the ball. Alternatively rollers mounted on a central axis may be employed. The device may be used to mimic a cricket bowler and by varying the speed and angle of the drive wheels can produce Yorkers, bouncers, swinging deliveries, breaks and cutters. The frame of the device may also be pivotally mounted.

Description

BALL-PROJECTING MACHINE

The present invention concerns a ball-projecting machine, and is particularly but not exclusively concerned with a two-wheel bowling machine for use in cricket coaching. By a two-wheel ball-projecting machine is meant a ball-projecting machine in which the ball is impelled by two powered wheels, Bowling machines are commercially available, one of the best known being the Merlyn (RTM) bowling machine as disclosed in GB 2,293,979B (in the name of the present applicant). This machine has four counter-rotating wheels which are spaced apart and disposed at 900 intervals with their axes lying in a common plane transverse to the axis of projection of the ball. One pair of opposed counter-rotating wheels can be used to impart a spin about one axis orthogonal to the axis of projection and the other pair of diametrically opposed counter-rotating wheels can be used to apply spin about the other axis orthogonal to the axis of projection, in each case by varying the relative speeds of the opposed wheels.

However since each of the four wheels requires its own electric motor, the weight of the individual motors, control mechanism, frame and lifting gear needed to raise the head of the machine to bowling height is quite considerable and the machine is somewhat heavy and cumbersome.

An improvement of the above bowling machine is disclosed in GB 2,430,892A (also in the name of the present applicant). This bowling machine is a two-wheel bowling machine in which the opposed drive wheels are mounted on a sub-frame which is rotatable about the axis of projection of the ball in order to vary the orientation of the axis of the spin applied to the ball and hence achieve a range of standard cricket deliveries.

GB 2,451,904B (also in the name of the present applicant) discloses an improvement of the above two-wheel ball projecting machine in which the rotatable sub-frame is dispensed with. This machine comprises upper and lower counter-rotating drive wheels which are mounted such that the axes of rotation of the drive wheels are mutually angularly offset about an upright common axis which is substantially orthogonal to the axis of projection of the ball. The upright orientation of the common axis is maintained by a supporting frame. By varying the angular offset of the axes of rotation of the drive wheels, and varying a speed differential of the drive wheels, different deliveries (in particular, the deliveries used in cricket) can be achieved.

In particular, spin about the axis of projection of the ball (approximately a horizontal axis) can be achieved by the angular offset between the axes of rotation of the drive wheels.

Further, in order to guide the ball trajectory in the azimuth direction, two unpowered jockey wheels are disposed on either side of the gap between the upper and lower drive wheels and engage the sides of the ball as it passes through the nip of the upper and lower drive wheels.

However, although the jockey wheels improve the accuracy of bowling, because their axes of rotation are fixed (ie maintained vertical) any spin applied about the axis of projection of the ball (ie about an approximately horizontal axis) will be resisted by friction between the ball and the jockey wheels in the common plane of the jockey wheel axes.

This is shown in Figure 2, wherein the jockey wheels J have fixed vertical axes Aj and hence frictionally impede the spin (shown by the curved arrow on cricket ball 3) about the axis of projection imparted by the drive wheels 1 A and 1 B. The spin is controlled by the angular offset of the drive wheels about a common vertical axis Al.

Because the above frictional resistance to spin will depend on the exact size of the ball and the surface properties of the ball and the jockey wheels at the regions of engagement, all of which are variable, the degree of spin actually applied to the ball is not perfectly reproducible. Hence there is some variability in the ball trajectory which is undesirable in a training context.

An object of the present invention is to provide a ball-projecting machine in which the above disadvantage is overcome or alleviated.

Accordingly the invention provides a ball-projecting machine comprising counter-rotating drive wheels and at least one rotary guide member, said drive wheels having spaced-apart peripheral ball-engaging surfaces which cooperate with a ball-engaging surface of said rotary guide member to grip and project the ball, the axes of rotation of the drive wheels being mutually angularly offsettable about a common axis so as to impart a spin about the axis of projection of the ball during their engagement with the ball, said ball-engaging surface of said rotary guide member being rotatable by said spin.

Because the ball-engaging surface is rotatable by the spin of the projected ball, the spin is largely unaffected by the (or each) rotary guide member, or at least any braking effect on spin is less variable than the braking effect of jockey wheels which cannot rotate about the axis of projection.

Preferably said ball-engaging surface of said at least one rotary guide member is freely rotatable about an axis whose orientation is variable according to the spin and projection velocity of the ball. This feature minimises any frictional braking effect and further enhances the reproducibility of deliveries.

Preferably the ball projecting machine comprises two rotary guide members with opposed ball-engaging surfaces spaced apart in a direction transverse to the direction in which opposed ball-engaging surfaces of said drive wheels are spaced apart, the spacing between the ball-engaging surfaces of the rotary guide members being greater than the spacing between the ball-engaging surfaces of the drive wheels. This feature accommodates the distortion of the ball caused by the gripping action of the drive wheels and avoids or alleviates any squeezing of the ball between the rotary guide members which would otherwise affect its trajectory, possibly in a variable manner.

Preferably the or each said rotary guide member comprises a ball mounted for rotation on a ball bearing track. This feature provides a robust construction with low friction. Such arrangements are commercially available in the form of ball transfer units, as used in horizontal planar arrays for conveying applications, for example.

In another embodiment, the or each said rotary guide member comprises a roller mounted for rotation about a roller axis which is transverse to the plane orthogonal to said axis of projection, said roller being mounted on a wheel which is rotatable about an axis transverse to said roller axis. One such arrangement is known as the Mecanum wheel, and is disclosed in US 3,876.255, which is hereby incorporated by reference. Mecanum wheels are typically used as road wheels for vehicles such as fork-lift trucks which need to move sideways in confined spaces.

The use of ball transfer units and Mecanum wheels (or a variant therof in which the roller axes lie in a common radial plane) as guides for projectiles is novel.

Preferably the ball-projecting machine is suitable for projecting cricket balls, said machine having first means for varying the mutual angular offset of said axes of rotation of the drive wheels and second means for varying a speed differential between the drive wheels, said first and second means having settings which in combination correspond to standard cricket deliveries. The variable speed differential enables spin to be applied about an axis transverse to the axis of projection. The rotational freedom of the novel rotary guide members minimises frictional interference with spin about the above transverse axis as well.

Preferably respective setting combinations correspond to at least two of the following cricket deliveries: i) straight ii) bouncer iii) yorker iv) in swing v) away swing vi) off break vii) leg break viii) off cutter ix) leg cutter.

Preferably the planes of rotation of said upper and lower drive wheels are settable to at least three orientations on each side of a central orientation corresponding to a straight delivery.

More preferably the planes of rotation of said upper and lower drive wheels are seftable to four orientations on either side of said central orientation.

Preferably the angle between adjacent settable orientations of said planes of rotation is in the range 3 to 7 degrees.

Further preferred features are defined in the dependent claims.

Reference is directed to GB 2,430,892A (noted above) which discloses certain electronic control features and feed mechanisms which can optionally be utilized in the ball-projecting machine of the present invention. The disclosures of the above electronic control features and feed mechanisms in the above patent application are hereby incorporated by reference.

However the preferred embodiment is hand operated (i.e. the angles of the drive wheels are selected manually), only the drive wheel speeds being determined electronically. This preferred apparatus can preferably be tilted and turned manually and is not programmable, although the angles of the drive wheels as well as the amount of tilt and turn are recorded by counters on the winding mechanism and in consequence can be collected for future use.

Preferred embodiments of the present invention are shown in Figures 1 to 7 of the accompanying drawings, wherein; Figure 1 is a front elevation of a two-wheel cricket bowling machine in accordance with the present invention; Figure 1A is a detail taken on Figure 1 with the ball 3 omitted and showing the relative spacing between the ball-engaging surfaces of the rotary guides and the drive wheels; Figure 2 is a diagrammatic front elevation showing the engagement of the jockey wheels and drive wheels in the ball-projecting machine of 2,4519O4B; Figure 3 is a corresponding diagrammatic front elevation showing the engagement of the rotary guides and drive wheels of the ball-projecting machine of Figure 1; Figure 3A is a corresponding diagrammatic side elevation showing the motion of a ball-engaging surface of one rotary guide member in response to the spin and linear motion of a projected ball; Figure 4 is a corresponding diagrammatic front elevation showing a variant of Figure 1 in which the rotary guides are Mecanum wheels; Figure 5 is a schematic side elevation of the cricket-bowling machine shown in Figure 1, with the delivery arrangement shown schematically in cross section; Figure 6 is a top plan view showing the range of angular orientations of the drive wheels in the embodiments of Figures 1 and 4, and Figure 7 is a diagrammatic representation of the cricket ball trajectory in plan view (or in elevation in Figures 7d) and e)) for various standard cricket deliveries achievable by the above bowling machine.

Referring to Figure 1, the machine comprises a turntable 6 carrying a yoke Y and rotatable about a vertical axis. A generally rectangular frame F is mounted at the mid- point of its long sides for rotation about a horizontal axis A2 on yoke Y and in the mid-points of its short sides carries upper and lower pivots 7A and 7B on which are mounted generally L-shaped mounting brackets B which are rotatable about a common axis Al.

Axis Al lies in the mid plane of frame F and is orthogonal to the axis of projection of the ball 3 and to tilt axis A2.

Upper bracket B carries a variable speed electric drive motor 2A and an upper drive wheel 1A is mounted on the drive shaft of this drive motor. Similarly lower bracket B carries a lower variable speed electric drive motor 2B and a lower drive wheel 1 B is mounted on the drive shaft of this drive motor.

The upper and lower drive wheels 1A and lB are spaced 54 mm apart which is less than the diameter of a cricket ball, namely 70 mm. A cricket ball 3 is shown engaged by and compressed between their peripheral regions which are driven to counter rotate in the sense indicated by the arrows to project a ball along an axis of projection extending out of the plane of the drawing. The cricket ball is maintained between the opposed peripheral regions of the drive wheels by opposed rotary guides 4 which in this embodiment are in the form of commercially available ball transfer units. These comprise steel balls 4B mounted on a ball bearing track (as shown in the right-hand guide which is shown in cross-section). Track is preferably in the form of a closed loop which allows its steel balls 4A to roll around the loop in response to rolling of ball 4B in any direction. Various designs of ball transfer units are available with different track configurations; a preferred ball transfer unit is model 2019-23-16-NO, available from Aiwayse Engineering Ltd of Miller Street, Birmingham B6 4NF.

In the configuration shown in Figure 1, in which the axes of drive wheels 1A and lB are parallel (both horizontal in the plane of the drawing), no spin about the axis of projection is applied and the balls 4B rotate in opposite directions about vertical axes in the plane of the drawing eg as shown by arrow Referring to Figure 1A, the spacing S between the ball-engaging surfaces of balls 4B is suitably 75 mm, about 21 mm greater than the spacing between the ball-engaging surfaces of the drive wheels 1A and 1 B. assuming a standard cricket ball diameter of 70 mm. Thus S is greater than the ball diameter whereas s is less than the ball diameter. As noted above, this ensures a gentler engagement between the rotary guides 4 and the ball 3 (Figure 1).

Referring to Figure 5, it will be seen that the yoke Y is in the form of a frame which is coupled to frame F by an adjustable linkage 5 to enable the angle of elevation of the axis of projection Ap to be varied. Figure 5 also shows a guide tube G carried by frame F extending between the drive wheels 1A and lB and carrying a ball 3 which is fed into the nip of the drive wheels by gravity either manually or, when a remote control is used, mechanically from a magazine. The rotary guides 4 (Figure 1 -omitted from Figure 5 for the sake of clarity) are suitably mounted onbrackets supported from frame F. Frame F is suitably mounted on a base for rotation about a vertical axis.

The drive wheels 1A and lB are provided with solid polyurethane tyres T in order to ensure that the cricket ball 3 is resiliently gripped as it passes through their nip. The overall diameter of each drive wheel is suitably 286 mm (111⁄4") and the maximum speed of rotation achievable by the drive motors 2 is suitably about 4,000 rpm, corresponding to a peripheral velocity of approximately 60 ms'. The thickness of the drive wheels is suitably 57 mm (21/4'). The upper drive wheel 1A rotates clockwise and the lower drive wheel 1 B rotates anticlockwise. Hence the peripheral ball-engaging surfaces engage, grip and project cricket balls 3 in the left-hand direction as indicated by the broad arrow in Figure 5.

Referring to Figure 3, in which the axis of projection of the ball 3 is orthogonal to the plane of the drawing, the spin about the projection axis is shown by the curved arrow on the ball 3. The balls 4B can rotate freely about all three perpendicular axes and the combined effect of the forward motion of the cricket ball 3 and its spin results in a rotation of the balls 413 defined by outwardly inclined axes Av. For ease of illustration, these axes are shown inclined downwardly in the drawing, but in practice axes Av will be horizontal.

Figure 3A is a view from the left of Figure 3, with only the ball 4B behind cricket ball 3 shown. The line joining the centres of balls 4B intersects axis Al about which the drive wheels can be angularly offset.

As cricket ball 3 is impelled (towards the right as shown by the broad arrow) along axis of projection Ap and spun about this axis it engages the surface of ball 413 (ie the ball-engaging surface). The resulting motion vector X of the region of ball 4B engaging cricket ball 3 will be the vector sum of a) the motion of the contacting cricket ball surface attributable to the spin about axis Ap and b) the rectilinear motion of the cricket ball along this axis. The resulting axis of rotation Ar of ball 4B is orthogonal to vector X and (assuming purely for the sake of simplicity the rotational speeds of the drive wheels are identical, so that no top spin is applied) will lie in the plane of Figure 3A.

Thus vector X and the corresponding axis of rotation Ar of ball 4B have a variable orientation in the plane of Figure 3A according to the degree of spin about projection axis Ap applied to the ball 3 by the drive wheels 1A and lB. This in turn is dependent upon the angular offset of the drive wheels about axis Al.

It is not essential for the ball-engaging surfaces of the rotary guides 4 to be spherical (as defined by balls 4B). Thus in the variant shown in Figure 4, the rotary guides 4 are replaced by rotary guides 40 in the form of Mecanum wheels, as disclosed in US 3.876,255. In this variant, the Mecanum wheels are in the form of wheels 42 mounted for rotation about vertical axes A3 which are coplanar with axis Al. Each wheel 42 has a peripheral array of barrel-shaped rollers 41 mounted thereon (by means not shown) for rotation about their respective longitudinal axes A4. Axes A4 are inclined with respect to the radial mid-plane of each wheel 42.

The inclination of axes A4 in combination with the barrel-shape of each roller 41 provides a substantially arcuate roller profile in the radial plane at the periphery of each Mecanum wheel and these arcuate profiles in combination form a substantially cylindrical envelope which engages cricket ball 3 when the latter is compressed between the drive wheels 1A and 113. Each roller 41 defines a ball-engaging surface which can perform a compound rotation made up of rotation about its longitudinal axis A4 (as shown by the curved arrows indicated on two of these axes in Figure 4) and rotation of its associated wheel 42 about its axis A3. As a result, each ball-engaging roller surface can move freely in the vertical direction in the plane of Figure 4 to follow the spin (as indicated by the curved arrow thereon) of cricket ball 3 about the axis of projection, as well as in the horizontal direction orthogonal to the plane of Figure 4 to follow the projection of the cricket ball 3. In a variant, the axes A3 could be coplanar but tilted out of the vertical plane; the required compound rotation could still be achieved.

In a further variant, the rollers 41 could be oriented with their axes of rotation A4 in the radial mid-plane of and tangential to wheel 42.

In a further, simpler, variant the guides could be in the form of rollers with their axes of rotation parallel with and disposed either side of the axis of projection of the cricket ball 3 so that their axes and the axis of projection are coplanar. Spin of the ball about the axis of projection would then be accommodated by rotation of the rollers.

As shown in Figure 6, the angular offset of each drive wheel 1 A, 1 B can be varied from the centre direction C (corresponding to a straight delivery) by ± 200, this range including four settings at +7°, + 13°, + 170 and +20° respectively in the off break direction and similarly including four settings at 70, -13°, -17° and -20° respectively in the leg break direction. Thus leg and off breaks of varying intensity can be delivered by varying the mutual angular offset of the drive wheels between 14° and 40°, These settings can be provided mechanically or electromechanically (by means not shown) and optionally can be programmable.

The range of deliveries and corresponding angular and speed settings for the wheels are set out below in the Table:

TABLE

Wheel Speeds Speed Delivery Wheel Angles (% of 4,000 rpm) Differential Ball Speed Top -Bottom Type (mis) Bottom Top Bottom Top mis(% of __________ _______ ________ __________ _________ 4,000rpm) _______________ Straight _______ _______ variable Tariable 0 7ariable In Swing 70 55 58 2 mIs (3%) 36-37 __________ _______ _______ _________ _________ ____________ (80-82 mph) 70 0 way Swing F1 -55 58 2 m/s (3) 36-37 __________ _______ _______ _________ _________ ____________ (80-82 mph) eg Break -20° F20° 28 42 8.4 m/s(14%) 20-21.5 __________ _______ ________ __________ _________ _____________ (45-48 mph) )ff Break F20° 20° 28 42 8.4 m/s(14%) 20-21.5 __________ _______ _______ _________ _________ ____________ (45-48 mph) eg Cutter-13° F13° 55 60 3 m/s (5%) 36-37 __________ _______ _______ _________ _________ ____________ (80-82 mph) )ff CutterFl3° -13° 55 60 3 mis (5%) 36-37 __________ _______ _______ _________ _________ ____________ (80-82 mph) The wheel angles can be reduced to give off and leg breaks of lower intensity. The larger the angle the greater will be the break provided also that the speed of the top wheel is about 14 percentage points higher than the bottom wheel. Increasing the speed of the bottom wheel, and thereby reducing the speed differential between the wheels, will result in a lower bounce to replicate the conditions found at different cricket grounds.

A bouncer delivery can be obtained by a modification of the Straight delivery shown in the Table in which the top wheel has a greater speed than the bottom wheel. A yorker delivery can be achieved by a modification of the Straight delivery shown in the Table in which the bottom wheel has a greater speed than the top wheel.

Permutations of the angles and offsets shown in the Table are permissible to obtain variants of the above deliveries. For example the speed differential in column six of the Table could be 1 to 3 rn/s for the In Swing and Away Swing deliveries, 5 to 10 mIs for the Leg Break and Off Break deliveries and 2 to 4 mis for the Leg Cutter and Off Cutter deliveries.

Off and leg cutters are achieved with the same wheel angles as for a middling break, but with the difference that, to achieve the opposite swing before the ball straightens up on impact with the ground, the speed of the bottom wheel is about 3 mIs (5 percentage points) lower than that of the top wheel.

The wheel speeds are shown as a percentage of the maximum wheel speed (4,000 rpm, corresponding to a peripheral speed of 60 ms1) and the speed differentials are similarly given in percentage terms. It will be understood that although some variation in the speeds is contemplated, a speed differential having the same sense as that in column six and having a similar order of magnitude is required in order to achieve the delivery type shown in column one. Referring to Figure 6, the angle of each successive setting is suitably as shown. Some latitudein the angles is permissible in practice. Preferably the settings are within ± 5°, more preferably ± 3° and most preferably ± 1° of those shown.

In a variant the frame F could be mounted on a universal joint which allows tilting about an axis orthogonal to the axis of projection and turning (about a vertical axis) from a fixed mounting. The universal joint in this variant would be constrained to prevent significant tilting about the axis of projection. The yoke Y could then be dispensed with.

The types of delivery are shown in Figure 7, wherein 4a) shows a straight delivery towards wicket w (in which the angular velocities of the wheels 1A and 1 B are equal and opposite).

Figure 7b) shows an in swing resulting from a spin about the vertical axis of the ball and Figure 7c) shows an out swing as a result of a similar spin but in the reverse sense.

The back spin delivery shown in Figure 7d) is achieved by rotating the lower drive wheel 1 B faster than the upper drive wheel 1 A, with both drive wheels in a centered orientation C, (as used for a yorker delivery).

Figure 7e) shows the reverse arrangement in which the upper drive wheel rotates faster than the lower drive wheel, resulting in a top spin (as used for a bouncer delivery).

Figure 7f) shows an off break delivery (in which the upper drive wheel rotates faster than the lower drive wheel).

Figure 7g) shows a leg break delivery involving back spin.

Figure 7h) shows an off cutter, and Figure 7i) shows a leg cutter.

Additionally, variants of the above deliveries can be obtained as shown, using similar differentials in wheel speeds and angles.

In a further variant, means are provided for sequentially feeding stored balls into engagement with the drive wheels for projection in sequence. The sequence can be controlled by a timer or remote controller. Warning lights are suitably provided to signal the sequence of deliveries.

Alternatively, balls can be fed singly by hand.

Claims

CLAIMS: 1. A ball-projecting machine comprising counter-rotating drive wheels and at least one rotary guide member, said drive wheels having spaced-apart peripheral ball-engaging surfaces which cooperate with a ball-engaging surface of said rotary guide member to grip and project a ball, the axes of rotation of the drive wheels being mutually angularly offsettable about a common axis so as to impart a spin about the axis of projection of the ball during their engagement with the ball, said ball-engaging surface of said rotary guide member being rotatable by said spin.
2. A ball-projecting machine according to claim 1 wherein said ball-engaging surface of said rotary guide member is freely rotatable about an axis whose orientation is variable according to the spin and projection velocity of the ball.
3. A ball-projecting machine according to claim 1 or claim 2 comprising two rotary guide members with opposed ball-engaging surfaces spaced apart in a direction transverse to the direction in which opposed ball-engaging surfaces of said drive wheels are spaced apart, the spacing between the ball-engaging surfaces of the rotary guide members being greater than the spacing between the ball-engaging surfaces of the drive wheels.
4. A ball-projecting machine according to any preceding claim wherein the or each said rotary guide member comprises a ball mounted for rotation on a ball bearing track.
5. A ball-projecting machine according to any of claims 1 to 3 wherein the or each said rotary guide member comprises a roller mounted for rotation about a roller axis which is transverse to the plane orthogonal to said axis of projection, said roller being mounted on a wheel which is rotatable about an axis transverse to said roller axis.
6. A ball-projecting machine according to any preceding claim, for projecting cricket balls, said machine having first means for varying the mutual angular offset of said axes of rotation of the drive wheels and second means for varying a speed differential between the drive wheels, said first and second means having settings which in combination correspond to standard cricket deliveries.
7. A cricket bowling machine according to claim 6 wherein respective setting combinations correspond to at least two of the following cricket deliveries: i) straight ii) bouncer iii) yorker iv) in swing v) away swing vi) off break vii) leg break iix) off cutter ix) leg cutter
8. A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer or yorker delivery, at least one in swing or away swing delivery, and at least one off break or leg break delivery.
9, A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer delivery, at least one in swing or away swing delivery, and at least one off cutter or leg cutter delivery.
10. A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer or yorker delivery, at least one off break or leg break delivery, and at least one off cutter or leg cutter delivery.
11. A cricket bowling machine according to claim 6 wherein the planes of rotation of said upper and lower drive wheels are settable to at least three orientations on each side of a central orientation corresponding to a straight delivery.
12. A cricket bowling machine according to claim 6 wherein the planes of rotation of said upper and lower drive wheels are settable to four orientations on either side of said central orientation.
13. A cricket bowling machine according to claim 11 or claim 12 wherein the angle between adjacent settable orientations of said planes of rotation is in the range 3 to 7 degrees.
14. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower drive wheels for the following deliveries (if available) are as follows: straight 0 ms-' in swing 1 to 3 ms-1 away swing 1 to 3 ms-1 off break 5 to 10 ms-1 leg break 5 to 10 ms'
15. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower drive wheels for the following deliveries (if available) are as follows: straight 0 ms' in swing 0.25 ms to 0.75 ms-1 away swing 0.25 ms-1 to 0.75 ms-1 off cutter 2 to 4 ms' leg cutter 2 to 4 ms'
16. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower wheels for the following deliveries (if available) are as follows: straight 0 ms-1 off break 5 to 10 ms' leg break 5 to 10 ms' off cutter 2 to 4 ms' leg cutter 2 to 4 ms-1
17. A two-wheel cricket bowling machine according to any of claims 6 to 16 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the plane of rotation of each driving wheel is variable in orientation.
18. A two-wheel cricket bowling machine according to any of claim 6 to 17 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein said upper drive wheel and an associated drive means and said lower drive wheel and an associated drive means are independently pivotally mounted on said supporting frame for rotation about said common axis.
19. A two-wheel cricket bowling machine according to claim 18 wherein said supporting frame is pivotally mounted for tilting about a substantially horizontal lateral axis.
20. A two-wheel cricket bowling machine substantially as described hereinabove with reference to Figures 1 to 3A and 5 to 7, optionally as modified in accordance with Figure 4 of the accompanying drawings.
21. A two-wheel cricket bowling machine substantially as described hereinabove with reference to the accompanying Table.Amendments to the claims have been filed as follows:S1. A ball-projecting machine comprising counter-rotating drive wheels and at least one rotary guide member, said drive wheels having spaced-apart peripheral ball-engaging surfaces which cooperate with a ball-engaging surface of said rotary guide member to grip and project a ball, the axes of rotation of the drive wheels being mutually angularly offsettable about a common axis so as to impart a spin about the axis of projection of the ball during their engagement with the ball, said ball-engaging surface of said rotary guide member being rotatable by said spin.2. A ball-projecting machine according to claim 1 wherein said ball-engaging surface of said rotary guide member is freely rotatable about an axis whose orientation is variable according to the spin and projection velocity of the ball.3. A ball-projecting machine according to claim I or claim 2 comprising two rotary guide members with opposed ball-engaging surfaces spaced apart in a direction transverse to the direction in which opposed ball-engaging surfaces of said drive wheels are spaced apart, the spacing between the ball-engaging surfaces of the rotary guide members being greater than the spacing between the ball-engaging surfaces of the drive wheels.4. A ball-projecting machine according to any preceding claim wherein the or each said rotary guide member comprises a ball mounted for rotation on a ball bearing track.* * 5. A ball-projecting machine according to any of claims I to 3 wherein the or each said * : *.: rotary guide member comprises a roller mounted for rotation about a roller axis which intersects a plane orthogonal to said axis of projection, said roller being mounted on a wheel which is rotatable about an axis transverse to said roller axis. j.. ******* * 6. A ball-projecting machine according to any preceding claim, for projecting cricket * : * balls, said machine having first means for varying the mutual angular offset of said * : * 35 axes of rotation of the drive wheels and second means for varying a speed differential between the drive wheels, said first and second means having settings which in combination correspond to standard cricket deliveries.7. A cricket bowling machine according to claim 6 wherein respective setting combinations correspond to at least two of the following cricket deliveries: i) straight ii) bouncer iii) yorker iv) in swing v) away swing vi) off break vii) leg break iix) off cutter ix) leg cutter 8. A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer or yorker delivery, at least one in swing or away swing delivery, and at least one off break or leg break delivery.9, A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer delivery, at least one in swing or away swing delivery, and at least one off cutter or leg cutter delivery.10. A cricket bowling machine according to claim 7 wherein respective setting combinations correspond to at least one straight or bouncer or yorker delivery, at least one off break or leg break delivery, and at least one off cutter or leg cutter delivery.11. A cricket bowling machine according to claim 6 wherein the planes of rotation of said upper and lower drive wheels are settable to at least three orientations on each side of a central orientation corresponding to a straight delivery.12. A cricket bowling machine according to claim 6 wherein the planes of rotation of said upper and lower drive wheels are settable to four orientations on either side of said central orientation.13. A cricket bowling machine according to claim 11 or claim 12 wherein the angle between adjacent settable orientations of said planes of rotation is in the range 3 to 7 degrees.14. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower drive wheels for the following deliveries (if available) are as follows: straight 0 ms-' in swing 1 to 3 ms-1 away swing 1 to 3 ms-1 off break 5 to 10 ms-1 leg break 5 to 10 ms' 15. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower drive wheels for the following deliveries (if available) are as follows: straight 0 ms' in swing 0.25 ms to 0.75 ms-1 away swing 0.25 ms-1 to 0.75 ms-1 off cutter 2 to 4 ms' leg cutter 2 to 4 ms' 16. A two-wheel cricket bowling machine according to claim 7 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the speed differentials between the periphery of the upper and lower wheels for the following deliveries (if available) are as follows: straight 0 ms-1 off break 5 to 10 ms' leg break 5 to 10 ms' off cutter 2 to 4 ms' leg cutter 2 to 4 ms-1 17. A two-wheel cricket bowling machine according to any of claims 6 to 16 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein the plane of rotation of each driving wheel is variable in orientation.18. A two-wheel cricket bowling machine according to any of claim 6 to 17 having an upper drive wheel and a lower drive wheel disposed below the upper drive wheel and wherein said upper drive wheel and an associated drive means and said lower drive wheel and an associated drive means are independently pivotally mounted on said supporting frame for rotation about said common axis.19. A two-wheel cricket bowling machine according to claim 18 wherein said supporting frame is pivotally mounted for tilting about a substantially horizontal lateral axis.20. A two-wheel cricket bowling machine substantially as described hereinabove with reference to Figures 1 to 3A and 5 to 7, optionally as modified in accordance with Figure 4 of the accompanying drawings.21. A two-wheel cricket bowling machine substantially as described hereinabove with reference to the accompanying Table.