Rotationally balanced smart ball

Abstract

An inflatable ball comprises a bladder having a bladder wall defining an inflatable interior of the ball. At least one electronic device is mounted on or over the bladder wall 11 such that a centre of

Description

FIELD OF THE INVENTION The invention relates to inflatable balls, particularly sports balls, containing electronic devices and to techniques for balancing the additional mass introduced by the electronic devices. BACKGROUND Data collection and usage has become a vital part of modern-day sports and are only likely to increase in importance. Data collection in sports is beneficial for many reasons. Firstly, data collection is valuable for training, as it allows the athletes to gain a better knowledge of their performance and key statistics. For example, the total distance covered in a match by a certain player may be a useful indicator of their fitness and level of participation. Secondly, statistics and data figures have become an increasingly important aspect of the viewer experience during sporting events. Increasingly, sensors and trackers are being incorporated into sports balls. Such ball devices allow spectators to see statistics such as speed, distance, number of passes, or the force exerted by an athlete during kicking, for example. There are two main ways of introducing electronics into the ball. A first involves mounting the electronics near the centre of the ball, which keeps the ball rotationally balanced. This technique has the problem that it can be difficult to manufacture an inflatable sports ball in which an electronic device is suspended in the centre of the ball. It also makes it practically impossible to access the electronic device after manufacture. A second option is to mount the electronics on the periphery of the ball. The electronics can either be mounted to the inside surface of the bladder or dropped into a recess in the bladder from the outside of the sports ball, for example. Balls constructed in line with this technique are generally easier to manufacture and may allow more convenient access to the electronic device for maintenance and charging. However, this option has the downside that it tends to unbalance the ball. It is known to offset the mass of an electronic device mounted on the periphery of the sports ball by placing a balancing mass opposite to the electronic device. However, this solution has the problem that it introduces a preferred rotation axis of the ball or otherwise changes the way the ball rotates about other axes. It is desirable to devise a means of rotationally balancing a sports ball that does not suffer from this problem. SUMMARY OF INVENTION In accordance with a first aspect of the invention, there is provided an inflatable ball comprising: a bladder having a bladder wall defining an inflatable interior of the ball; at least one device mounted on or over the bladder wall such that a centre of mass of the at least one device is located away from a centre of the inflatable interior of the ball, the at least one device including at least one electronic device, the centre of mass of the at least one device defining a first point on the bladder wall coincident with or closest to the centre of mass of the at least one device and a second point on the bladder wall opposite the first point; and a distributed balancing mass for at least partially rotationally balancing the mass of the at least one device, the distributed balancing mass comprising one or more balancing mass elements on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality of locations spaced around the second point on the bladder wall and closer to the second point than the first point. The inventor has recognised that in order to balance the mass of an electronic device mounted at or near the periphery of the sports ball, it is advantageous not to simply provide a balancing mass opposite the device (the second point), but to space the balancing mass at a series of locations around this opposite point. Since the balancing mass is closer to the second point than it is to the first point, it will still achieve the effect of moving the centre of mass closer to the centre of the ball, but does this while reducing the effect the balancing mass will have on different rotation axes of the ball. A bladder may be used to describe any component which provides an inflatable ball with its general shape and rigidity once inflated. A bladder may be elastic and may be made of rubber or any other elastic polymer, or non-elastic and made of a stiff polymer, for example. The bladder defines an inflatable interior of the ball allowing for inflation of the inflatable ball to a substantially rigid form. The bladder wall is considered to be any part of the bladder that defines the perimeter between the inside and the outside of the bladder. This will generally be a thin membranelike structure, but may also include integrally moulded wall features, such as a mounting point for the electronic device, or feature regions adhered over an opening through the bladder to make the bladder airtight. For example, some embodiments may feature a pocket-like recess into which the electronics are inserted that is moulded into the bladder wall or arranged in an opening through the bladder. A bladder is usually encased in a layer of material which forms an outer surface of an inflatable ball, which is often the case for traditional soccer balls. However, the bladder itself may form the outermost layer of the inflatable ball. The bladder may also have additional layers between itself and an outer layer. Any outermost layer may be used with the present arrangement. The devices will generally be arranged on or over an inside surface of the bladder wall. That is, they will generally be located inside the inflatable interior defined by the bladder wall. In this position, the devices are less likely to interfere with the external appearance or feel of the ball. However, in some embodiments the devices could be arranged on the outer surface of the bladder wall, particularly in a recessed pocket in the bladder wall. The term “distributed balancing mass” will be understood to encompass several discrete balancing mass elements, that can be individually positioned on or over the bladder wall around the second point, or a single balancing mass element whose shape and / or dimensions allow it to extend at least partially around the second point, preferably at least 50% of the way around the second point, most preferably substantially entirely around the second point. As will be discussed in more detail below, an example of a suitable singular balancing mass element may be a continuous strip that may, for example, extend in a closed loop around the second point. It should be noted that a balancing mass element may also be provided substantially at the second point in addition to those spaced around the second point. Preferably all balancing mass elements that are provided in the ball are provided closer to the second point than the first point and preferably no balancing mass element is arranged at the second point; however, this is not essential. Preferably, all balancing mass elements are provided in a range more than 50% and less than 95% of the distance along the bladder wall from the first point to the second point, more preferably in a range more than 55% and less than 90% of the distance along the bladder wall from the first point to the second point. Preferably, the one or more balancing mass elements comprises one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of at least two balancing points equally spaced around the second point, preferably at least three balancing points equally spaced around the second point. While preferred, it would also be possible for balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of t at least six balancing points equally spaced around the second point, or at least nine balancing points equally spaced around the second point. As will be described below, preferably the number of balancing mass elements is a multiple of three. Here, each balancing mass element may be located substantially at a respective balancing mass point. Alternatively, a plurality of balancing mass elements may be divided into a plurality of sets of balancing mass elements, wherein each set of balancing mass elements is substantially evenly distributed by mass with respect to a respective balancing point. Aset of balancing mass elements may be considered evenly distributed by mass with respect to a balancing point when the centre of mass of the set of balancing mass elements substantially coincides with the balancing point or wherein the balancing point is the point on the surface of the bladder closest to the centre of mass of the set of balancing mass elements. It should be noted here that each balancing point will typically be a point on the bladder wall; however, the balancing points could also be points over the bladder wall. For example, if the at least one device is inset towards the centre of the ball from the bladder wall, then it may be desirable to balance the at least one device with respect to balancing points that are likewise inset. This could be done by mounting the balancing masses so that they are spaced away from the inside surface of the bladder wall. It is particularly preferred to have three balancing points, so that the balancing masses and the first point and / or the centre of mass of the at least one device define the vertices of a tetrahedron. However, when few balancing points are used, as is the case here, this may require these balancing mass elements to be individually quite large. Therefore, a plurality of balancing mass elements may be evenly distributed by mass with respect to each balancing point. For example, a respective set of balancing mass elements may be distributed around each balancing point, so that the centre of mass of that set substantially coincides with the respective balancing point. Alternatively, more than three balancing points may be used, as will be described in more detail below. The present inventor has identified that a particularly preferred arrangement of the mass of the device and the distributed balancing mass is one in which the device and the balancing mass elements are arranged at the four vertices of a substantially regular tetrahedron. Therefore, preferably, the one or more balancing mass elements comprises one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of three balancing points (preferably evenly) spaced around the second point, the three balancing points together with the first point and / or the centre of mass of the of the at least one device preferably defining four vertices of a tetrahedron, most preferably a substantially regular tetrahedron. In some embodiments, the mass distribution of the at least one device may be such that a substantially regular tetrahedron shape is not ideal for balancing; however, it may be preferred that the three balancing points are nonetheless evenly spaced around the second point, e.g. so that the three balancing points define three vertices of an equilateral triangle. This (regular) tetrahedron shape is particularly suited to moving the centre of mass towards the centre of the ball while also preventing the appearance of preferred rotation axes of the ball. Since three balancing mass elements that, together with the first point / centre of mass of the at least one device, define a regular tetrahedron results in a substantially perfectly balanced ball where all have the same mass, consider the case in which the balancing masses each have half the mass of the at least one device. This will balance half of the mass of the at least one device. Next, consider rotating the tetrahedron around the axis passing through the first point / centre of mass of the of the at least one device and through the centre of the three balancing points. If three more balancing points are defined by this new tetrahedron, and three more balancing masses placed at these new balancing points, each having half the mass of the at least one device, then these will again balance half the mass of the at least one device. The combined effect of the six balancing masses, each with half the mass of the at least one device, will be essentially identical to the effect of three balancing masses each having the same mass as the at least one device. In accordance with this principle, the ball may comprise at least six balancing mass elements arranged substantially in a single plane, wherein each balancing mass element has two corresponding balancing mass elements which, together with the first point and / or the centre of mass of the at least one device, define four vertices of a substantially regular tetrahedron. It will be appreciated that these balancing masses can be divided into smaller and smaller mass elements defining more and more substantially regular tetrahedra together with the first point and / or the centre of mass of the at least one device, tending towards the balancing mass elements defining a circular track along the bladder wall defining a cone together with the first point. In line with the above, it will be preferred that the number of balancing masses is a multiple of three, i.e. such that each set of three may define a tetrahedron with the first point. However, once the balancing mass elements are sufficiently small and sufficiently many, this multiple of three requirement for good balancing becomes less important, i.e. the effect of omitting one or two balancing mass elements becomes negligible. As indicated above, a preferred arrangement is one in which the first point and the distributed balancing mass define a cone shape, with the first point being the tip of the cone and the distributed balancing mass extending around the base of the cone. Much like the tetrahedron shape described above, this shape is particularly suited to moving the centre of mass towards the centre of the ball while also preventing the appearance of preferred rotation axes of the ball. Therefore, preferably, the one or more balancing mass elements comprises one or more mass balancing elements arranged along one or more tracks along the bladder wall defining all or part(s) of the circumference of a circle or an ellipse, wherein preferably the first point lies perpendicular to the plane of the circle or the ellipse from the centre of the circle or the ellipse. A cone with a circular base is particularly suited to spherical balls. A cone with an elliptical base is suited to balls whose shape is a prolate spheroid, such as rugby balls or American footballs. It will be noted that these latter ball shapes already have a preferred rotation axis; however, the present balancing arrangement preserves this balance so that a ball with an electronic device, balanced in this way, behaves substantially the same as a standard ball without any electronic devices. It will be appreciated that the “tracks” described here could be formed by continuous balancing mass elements, such as a strip, or could be formed by a series of balancing mass elements arranged in a line, as will be described in more detail below. Another embodiment foreseen is one in which the at least one device comprises a first device and a second device, wherein the one or more tracks along the bladder wall pass through first and second balancing points spaced around the second point and define part(s) of the circumference of a circle or an ellipse passing between the first and second devices. In one variant of this embodiment, the first device is positioned at or over a first vertex of a regular tetrahedron whose vertices are located in the bladder wall of the ball, and the second device is positioned at or over a second vertex. In this case, the first and second balancing points may be the third and fourth vertices of this tetrahedron. The balancing masses then define one or more tracks passing through the first and second balancing points and preferably also the second point. In a conventional arrangement in which the mass of the device is offset by a balancing mass on the opposite side of the ball, the balancing mass generally has substantially the same mass as the mass of the device. However, in the present embodiment, balancing masses are provided between the first and second points. Therefore, typically, the balancing masses will have a total mass of at least 1.5 times the mass of the at least one device, preferably at least 2 times the mass of the at least one device, more preferably at least 2.5 times the mass of the at least one device, most preferably at least 3 times the mass of the at least one device. Preferably, the balancing masses will have a total mass of less than 8 times the mass of the at least one device, preferably less than 6 times the mass of the at least one device, most preferably less than 4 times the mass of the at least one device. In particular, preferably the balancing masses have a total mass of between 2 times and 4 times the mass of the at least one device. The precise mass required will depend on the arrangement of the at least one device and the distance of the balancing mass elements between the first and second points. Indeed, in the above described arrangement in which a substantially regular tetrahedron shape or a cone shape is defined, it may be ideal for the balancing masses to have a total mass of approximately 3 times the mass of the at least one device. As alluded to above, one preferable way that the balancing mass element(s) may be formed is by providing one or more continuous strips or patches, preferably adhesive strips or patches, attached on or over the bladder wall. Such strips or patches may be weighted with a relatively dense material, such as a rubber. The use of strips or patches allows relatively heavy balancing mass elements to be provided with thin, easy to apply elements. The primary advantage of using these strips or patches is that they may be applied to a conventional ball bladder, meaning that balls with and without electronic devices can be manufactured using the same bladder design. They may also be thin enough that they can be applied to or over an outer surface of the bladder, allowing the balancing to be performed after the ball has been assembled and inflated, which prevents the balancing masses from interfering with inflated shape of the ball. Indeed, it will generally be preferred for the strip or patch to be as thin as possible, and so preferably each strip or patch has a thickness of no more than 5 mm, preferably no more than 4 mm, more preferably no more than 3 mm, even more preferably no more than 2 mm, most preferably no more than 1 mm, to facilitate application to an outer surface of the bladder. Alternatively, these types of balancing mass elements, as well as others, could be applied on or over an inner surface of the bladder wall. However, applying on or over the outer surface of the bladder allows for application after inflation of the bladder and also allows the bladder to be tested for balancing and rebalanced if necessary. An alternative balancing mass type (although it is also envisaged that a mixture of types may be used) is to provide one or more balancing mass elements formed integrally with the bladder wall. This allows the bladder to be produced with the balancing mass elements already provided in the bladder wall fora predetermined device arrangement, which removes the requirement for application or insertion of separate balancing mass elements. For example, if the bladder is injection moulded, then the balancing mass elements may be defined by the injection mould. Preferably, a plurality of balancing mass elements formed integrally with the bladder wall are formed by increased wall-thickness portions of the bladder wall. It will be appreciated that the increased wall-thickness portions have a greater wall thickness than the wall thickness of the majority of the bladder wall, or a greater wall thickness than the median wall thickness of the bladder wall. Typically, the majority area of the bladder wall, i.e. more than 50% will be of substantially constant thickness, with the increased wall thickness portions having a greater thickness than this substantially constant thickness across the majority area of the bladder wall. A minority area of the bladder wall, i.e. less than 50%, preferably less than 25%, more preferably less than 10%, most preferably less than 5%, will have an increased wall thickness compared to the remaining bladder wall area. A problem with providing the balancing mass elements by increased wall thickness portions of the bladder wall is that the thickness of the bladder wall can affect how the bladder wall stretches when it inflates. Large contiguous regions of increased bladder wall thickness may therefore distort the inflated shape of the ball. Therefore, preferably, each increased wall-thickness portion has at least one lateral dimension of no more than 2 cm, preferably no more than 1 cm, more preferably no more than 0.5 cm. More preferably, each increased wall-thickness portion has a largest lateral dimension of no more than 2 cm, preferably no more than 1 cm, more preferably no more than 0.5 cm. Here, a lateral dimension refers to a dimension along the bladder wall surface, i.e. generally perpendicular to the bladder wall thickness direction (accounting for the fact the bladder wall defines a curved surface). By providing that the increased wall thickness portions are small in at least one, preferably each lateral direction, the affect on the inflated shape of the bladder may be minimised. Indeed, preferably, each increased wallthickness portion of the bladder wall is surrounded by a portion not having the increased wall thickness. In particularly preferred embodiments, each increased wall-thickness portion projects from an inner surface of the bladder wall towards the centre of the inflatable interior of the ball. This prevents the increased wall-thickness portions from affecting the external shape or appearance of the inflated ball. While preferred, the increased wall-thickness portions could project outwards, or could project both inwards and outwards, in which case a suitable cover may need to be provided to cover or disguise the projections. Preferably, the wall thickness of the increased wall-thickness portions is no more than five times the wall thickness of the thinnest part of the bladderwall, preferably no more than four times the thickness, even more preferably no more than three times the thickness, most preferably no more than twice the thickness of the thinnest part of the bladder wall. Alternatively, there may be localised regions of decreased thickness, in which case the wall thickness of the increased wallthickness portions may be no more than five times the median wall thickness or the substantially constant wall thickness of the majority area of the bladder wall, preferably no more than four times the thickness, even more preferably no more than three times the thickness, most preferably no more than twice the median wall thickness or the substantially constant wall thickness of the majority area of the bladder wall. Particularly (but not exclusively) where the balancing mass elements are formed integrally with the bladder wall, preferably there are at least 10 balancing mass elements, more preferably at least 15 balancing mass elements, most preferably at least 20 balancing mass elements. It will be appreciated that, in cases where the balancing mass elements are formed integrally with the bladder wall, they are nonetheless considered discrete balancing mass elements where they are separate projections separated from one another by bladder wall having the standard bladder wall thickness. It will generally be preferred for any devices, including all electronic devices, to be applied at one location in the ball. Therefore, preferably, the at least one device balanced by the distributed balancing mass is mounted at a substantially single point on or over the bladder wall. This simplifies the balancing arrangement and simplifies manufacture. While preferred, the present technique can be extended to balance devices located in multiple positions on or over the bladder wall. Indeed, as indicated above, this can be done by balancing with respect to the centre of mass of several devices at different positions. In some embodiments, it may be preferable to provide multiple devices at different positions in the ball. One approach is for the first device to be provided at a first vertex of a substantially regular tetrahedron, a second device (preferably having substantially the same mass as the first device) to be provided at a second vertex of a substantially regular tetrahedron, and for the one or more balancing mass elements to be arranged substantially at or substantially evenly distributed by mass with respect to two other vertices of the substantially regular tetrahedron. Another approach may be to balance multiple devices, or multiple sets of devices, separately. In particular, the at least one device may be a first device or first set of devices, and the ball may further comprise a second device or second set of devices mounted on or over the bladder wall such that a centre of mass of the second device or second set of devices is located away from a centre of the inflatable interior of the ball, the centre of mass of the second device or second set of devices defining a third point on the bladder wall coincident with or closest to the centre of mass of the second device or second set of devices and a fourth point on the bladder wall opposite the third point; and a second distributed balancing mass for at least partially rotationally balancing the mass of the second device or second set of devices, the distributed balancing mass comprising one or more balancing mass elements on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality of locations spaced around the fourth point on the bladder wall and closer to the fourth point than the third point. Indeed, if one considers that one or more devices (the first device or first set) may be balanced by the techniques described above, the result may be a ball that is balanced essentially identically to a ball without the devices or balancing masses. Therefore, the second device or second set of devices, may be assessed and balanced entirely separately from the first device or first set. This approach may be preferred when the multiple devices are spaced relatively far apart, but be used for any spacing of the device sets. It will be noted that preferably the second device or second set of devices comprises at least one electronic device. Any of the balancing approaches used above for the one or more devices (referred to in the present context as the first device or the first set of devices) may be used for the second device or second set of devices. In particular, the second distributed balancing mass may comprise one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of at least two balancing points equally spaced around the fourth point, preferably at least three balancing points equally spaced around the fourth point. The second distributed balancing mass could also comprise one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of at least three balancing points spaced around the fourth point, the three balancing points together with the third point and / or the centre of mass of the of the second device or second set of devices defining four vertices of a substantially regular tetrahedron. The second distributed balancing mass could also comprise at least six balancing mass elements arranged substantially in a single plane, wherein each balancing mass element has two corresponding balancing mass elements which, together with the third point and / or the centre of mass of the of the second device or second set of devices, define four vertices of a substantially regular tetrahedron. Alternatively, the second distributed balancing mass may comprise one or more mass balancing elements arranged along one or more tracks along the bladder wall defining all or part(s) of the circumference of a circle or an ellipse,wherein preferably the third point lies perpendicular to the plane of the circle or the ellipse from the centre of the circle or the ellipse. In all embodiments, preferably each device being balanced comprises an electronic device, although other devices that contribute to the mass of the ball could also be balanced in this way. Preferably, the or each electronic device comprises one or more of: a battery, a wireless charging module, an accelerometer, a gyroscope, a pressure sensor, a magnetometer, a pressure transducer and a location tracking device, such as an ultra-wideband transmitter and / or receiver. Generally, it is preferred that the present technique is not used to balance the mass of the bladder valve. This is because this mass is generally not balanced in regular sports balls, and so athletes are generally accustomed to and indeed expect the effect of the bladder valve. An advantage of the present balancing technique, applied to balance only devices, such as electronic devices, other than the valve, is that the resulting ball may behave substantially identically to a conventional ball, including any effect from the valve. Therefore, preferably the bladder further comprises a valve for inflating the inflatable interior of the ball, wherein the valve is not one the devices balanced by the distributed balancing mass. The present technique is most advantageous in application to spherical balls, which generally do not have much if any of a preferred rotation axis. Therefore, preferably, the bladder defines a substantially spherical inflatable interior of the ball. While this is preferable, the present technique can also be applied to other ball shapes, such as prolate spheroid shapes. Preferably, the inflatable ball is an inflatable sports ball, preferably a soccer ball, basketball, netball, volleyball, or handball. However, other ball types may also be used. In accordance with a second aspect of the invention, there is provided a method of manufacturing an inflatable ball, the method comprising: providing a bladder having a bladder wall defining an inflatable interior of the ball; providing at least one device mounted on or over the bladder wall such that a centre of mass of the at least one device is located away from a centre of the inflatable interior of the ball, the at least one device including at least one electronic device, the centre of mass of the at least one device defining a first point on the bladder wall coincident with or closest to the centre of mass of the at least one device and a second point on the bladder wall opposite the first point; and providing a distributed balancing mass for at least partially rotationally balancing the mass of the at least one device, the distributed balancing mass comprising one or more balancing mass elements provided on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality of locations spaced around the second point on the bladder wall and closer to the second point than the first point. The method according to this aspect corresponds to a method of manufacturing an inflatable ball according to the first aspect, and so each of the preferred features and advantages discussed above applies equally to the method of this aspect of the invention. In some embodiments, providing the distributed balancing mass comprises attaching one or more continuous strips or patches, preferably adhesive strips or patches, on or over the bladder wall. As mentioned above, this may take place in a step after inflation of the bladder. In other embodiments, providing the bladder comprises moulding the bladder, and providing the distributed balancing mass comprises moulding one or more balancing mass elements integrally with the bladder wall when moulding the bladder. Moulding one or more balancing mass elements integrally with the bladder wall when moulding the bladder may comprise moulding a plurality of increased wall-thickness portions of the bladder wall. These increased wallthickness portions are the same as described above. BRIEF DESCRIPTION OF DRAWINGS The invention will now be discussed with reference to the accompanying drawings, of which: Figure 1 is a schematic cross-section of a first example of an inflatable ball; Figure 2A schematically illustrates a balancing arrangement for the inflatable ball of Figure 1 and Figure 2B is an enlarged view of the distributed balancing mass in region A; Figure 3A schematically illustrates another balancing arrangement for the inflatable ball of Figure 1, and Figures 3B and 3C are an enlarged views of the distributed balancing mass in region B; Figure 4 schematically illustrates another balancing arrangement for the inflatable ball of Figure 1; Figure 5A schematically illustrates another balancing arrangement for the inflatable ball of Figure 1 and Figure 5B is an enlarged view of the distributed balancing mass in region C; Figure 6A schematically illustrates another balancing arrangement for the inflatable ball of Figure 1 and Figure 6B is an enlarged view of the distributed balancing mass in region D; Figure 7A schematically illustrates another balancing arrangement for the inflatable ball of Figure 1 and Figure 7B is an enlarged view of the distributed balancing mass in region E; Figure 8A schematically illustrates another balancing arrangement for the inflatable ball of Figure 1 and Figure 8B is an enlarged view of the distributed balancing mass in region F; Figure 9 is a schematic cross-section of a second example of an inflatable ball; Figure 10 schematically illustrates a balancing arrangement for the inflatable ball of Figure 9; Figure 11 is a schematic cross-section of a third example of an inflatable ball; Figure 12 schematically illustrates a balancing arrangement for the inflatable of Figure 11; Figure 13 schematically illustrates a balancing arrangement for another inflatable ball; Figure 14 schematically illustrates a balancing arrangement for another inflatable ball; and Figure 15 schematically illustrates a balancing arrangement for another inflatable ball. DETAILED DESCRIPTION Figure 1 shows a first example of a ball 1 in need of balancing in accordance with the present invention. The ball comprises a bladder 10 comprising a bladder wall 11, which defines a spherical inflatable interior of the ball. The bladder wall 11 is continuous except for a circular opening, at which a valve 4 is bonded to the bladder wall 11 to make the interior of the bladder airtight and to allow for the bladder to be inflated via the valve 4. Inside the ball is an electronic device 2. The electronic device 2 is contained in a housing 3 (which may also be considered a device within the meaning of this disclosure), which is adhered to an inner surface of the bladder wall 11. The electronic device may comprise one or more of a battery, a wireless charging module, an accelerometer, a gyroscope, a pressure sensor, a magnetometer, a force transducer and a location tracking device, such as an ultra-wideband transmitter and / or receiver. The electronic device and housing may have a mass of, for example, 15 grams. By its position adjacent to the inner surface of the bladder wall 11, the electronic device causes the ball to have a different centre of gravity than a ball without the electronic device. In order that balls without electronic devices feel substantially the same to a user, the mass of the electronic device and housing need to be balanced. As will now be described with respect to Figures 2Ato 8B, the present invention uses a distributed balancing mass 12 comprising one or more mass elements 13 to balance the mass of the electronic device 2 and housing 3. To maintain the rotational balance of the ball, as it was before the introduction of electronics 2, the electronics and the distributed balancing mass 12 should not contribute any unbalanced forces or moments when the ball is spinning about any axis. To achieve this, it is preferable that two criteria are substantially met. Assume there is a ball with initial centre of mass centred at the origin. Then let there be A / masses introduced. Let the i’th mass have position vector and mass m,. The ball will be statically balanced, and the dynamic centrifugal forces will sum to zero if the centre of gravity of the electronics and the added masses coincide with the ball’s original centre of mass. By the earlier statement this must be the origin, therefore: The second criterion relates to ensuring there are no unbalanced moments when the ball is rotated about any axis. The definition of the inertia tensor for rigid body 5 rotation with point masses is: N [—>-> Ti i=l (2) It can be shown there will be no unbalanced moments if the second term in Equation (2) satisfies the following condition: > mtz? 1 0 0' a 0 1 0 = a / (3) .0 0 1. (3) The above condition says, firstly, that the added masses and their positions must 10 be such that the products of inertia are all zero, and secondly, that the principal moments of inertia are all equal. Several embodiments of balancing a sports ball will now be described, which either fulfil the above criteria, i.e. the centre of gravity of the electronics and the added masses coincide with the centre of mass of the ball and the principal 15 moments of inertia are all equal, or which are closer to these criteria than many other conventional balancing methods. When one considers dynamically balancing a sports ball, the fewest masses is often the most desirable solution and the above criteria can be fulfilled with the fewest masses by using a tetrahedral balancing method, which is demonstrated in Figures 2Aand 2B. Figure 2A shows a tetrahedral balancing arrangement of the spherical ball shown in Figure 1. In this embodiment, the centre of mass of the electronic device 2 and the housing 3 is substantially coincident with the first point 101 on the bladder, which in the Figure is the uppermost point of the bladder wall 11. Opposite the first point 101 is a second point 102. The first point 101 is treated as the first vertex in a regular tetrahedron whose other three vertices 111, 112, 113 also coincide with the bladder wall 11. In other words, the regular tetrahedron that is circumscribed by the sphere of the bladder wall. The other three vertices of this regular tetrahedron, which are referred to herein as balancing points, define the preferred locations of three balancing masses for offsetting the balance of the electronic device 2 and its housing 3. As shown in Figure 2A, a straight line along the bladder wall passing through these three balancing points 111, 112, 113 defines a circle. The first and second points 101, 102 are both perpendicularly offset from the plane of this circle from the centre point of this circle. This plane, and all three balancing points 111,112,113 are closer to the second point 102 that the first point 101. The balancing masses located at the three balancing points 111, 112, 113 are collectively referred to as a distributed balancing mass 12. Figure 2B shows an enlarged region A of Figure 2Ain cross-section and illustrates one balancing mass element 13 of the distributed balancing mass 12. Figure 2B shows the bladder wall 11 as flat for simplicity, but it will be appreciated that the inner surface of the bladder wall is concave in practice. In this embodiment, the balancing mass element 13 is a block of rubber that has been moulded to have the correct size and shape, i.e. suitable for adhering to the concave inner surface of the bladder wall 11, and is adhered to the inside of the bladder wall 11 by and adhesive 13a. To prepare the inner surface of the bladder and the balancing mass elements for adhesion, the bonding surfaces should be sanded and cleaned with a suitable solvent. The adhesive 13a, which should be a contact adhesive, should be applied to the clean surfaces and left for ten minutes. A second application of the contact adhesive should be performed, left for ten minutes, and then the bonding surfaces pressed together and allowed to cure for 24 hours. Each balancing point 111, 112, 113 is provided with a corresponding balancing mass element 13 in the manner illustrated in Figure 2B and as described above. If the electronic device 2 and the housing 3 have a combined mass of, for example, 15 grams, then each balancing mass element 13 at each balancing point 111, 112, 113 should have a mass of approximately 15 grams, such that the total mass of the distributed balancing mass is three times that of the electronic device 2 and the housing 3. It will be noted that the mass of the valve is not taken into account here. This choice is made since it is generally desired for a ball with electronic devices to behave as similarly as possible to one without the electronic devices. It would, however, be possible to factor in the mass of the valve to achieve a ball whose total centre of mass is substantially at the centre. While the above tetrahedral arrangement can satisfy the criteria of the two equations set out above and may be considered the mathematically most efficient arrangement, applying the balancing mass elements is a time-consuming and labour-intensive process. Therefore, several alternative solutions for achieving substantial balancing of the ball, in line with the above equations, that are more procedurally straightforward are also suggested and described with reference to Figures 3A to 8B. Figure 3A illustrates an alternative balancing arrangement for balancing the ball of Figure 1. Instead of using three essentially point-masses on the vertices of the tetrahedron’s base at the balancing points 111, 112, 113, the masses can be split into a much larger number of smaller point masses around the base of an inscribed cone. Figure 2A showed a straight line along the bladder wall 11 passing through the three balancing points 111, 112, 113, defining a circle. Instead of providing a single mass element at each balancing point, the mass is distributed evenly along this line, as shown in Figure 3A. The distributed mass element 12 is thus defined by a track of small mass elements 13 that defines the circumference of a circle. Now, each mass element 13 is much smaller than the three point masses provided at the balancing points 111, 112, 113 in the embodiment of Figure 2. These masses may now be of a size that they can produced by directly moulding the mass elements into the bladder wall 11, particularly by providing localised regions of increased bladder wall thickness. Figures 3B and 3C shows an enlarged region B of Figure 3A in cross-section to illustrate these integrally moulded balancing mass elements 13. When the bladder mould is designed, a series of recesses are provided on the surface of the mould that will define the inner surface of the bladder. In the present arrangement a series of circular recesses are provided so that the inner surface of the bladder features a row of circular protrusions 13 as the integrally moulded balancing mass elements. These circular protrusions 13 are thus provided by regions of the bladder wall 11 having increased wall thickness as a result of the recesses in the moulding tool used to mould the bladder wall. Each circular protrusion may have a thickness of approximately twice that of the surrounding bladder wall thickness. Each circular protrusion may have a diameter of no more than 0.5 cm and may be separated from one another by an intervening bladder wall portion 11a that does not have the increased wall thickness. As a result, when the bladder is inflated, the bladder is still able to expand without any significant restriction that would be caused by large areas of increased wall thickness. As with the above embodiment, the circular protrusions, which act as the balancing mass elements 13, may have a mass of three times that of the electronic device 2 and the housing 3. In some cases, particularly where the electronic device 2 and the housing 3 is especially heavy, it may not be possible to balance the mass with a single row of integrally moulded balancing mass elements 13 while still having them small enough and spacing them far apart enough to allow acceptable inflation of the bladder. Figure 4 shows an alternative embodiment in which three parallel tracks of integrally moulded balancing mass elements 13 are provided, each one defining the circumference of a circle to which the first point 101 is perpendicularly offset from a centre point of that circle. Each integrally moulded balancing mass element is nonetheless closer to the second point 102 (opposite the first point) than the first point 101. The balancing mass elements 13 are nonetheless formed in the same manner as those described with reference to Figure 3. Again, the total mass of all balancing mass elements 13 may be substantially three times the mass of the electronic device 2 and the housing 3. Figures 5A and 5B illustrate another variant using integrally moulded balancing masses arranged along tracks along the inner surface of the bladder wall 11. In this embodiment, rather than extending along the entire circumference of a circle, the integrally moulded balancing masses 13 arranged along three tracks that define an arc corresponding to part of the circumference of that circle. Each arc is of the same length and has the same number of integrally moulded balancing masses 13. The three tracks are evenly spaced apart. Accordingly, each track is effectively centred on one of the three balancing points 111, 112, 113 described with respect to Figure 2A. A downside to integrally moulded balancing elements 13 is that they need to have specialised moulding tools produced. Any changes to the design of the electronics module that changed the weight would require its own specially designed bladder. Also, the effect of integrally moulded balancing elements 13 on ball inflation can be minimised but not removed entirely. Figures 5A and 5B illustrate an embodiment that addresses these issues, while also removing the requirement in the context of the Figure 2 arrangement to attach the masses inside the bladder during assembly of the bladder. In the embodiment of Figure 6A and 6B, instead of being formed by integrally moulded balancing elements, the distributed balancing mass 12 is formed by a continuous strip 13 as the balancing mass element, which is applied to the bladder wall 11. The strip may be a rubber strip whose mass is approximately three times that of the electronics device 2 and housing 3. In this embodiment, the rubber strip is applied to the outside of the bladder using an adhesive 13a after inflation of the bladder. The rubber strip is applied along the same track defining the circumference of a circle that the integrally formed balancing mass elements of Figure 3A were arranged on. Specifically, an equilateral triangle formed by three points along the circular track should form the vertices of a regular tetrahedron with the first point 101, which is substantially where the electronic device 2 is positioned. While the embodiments of Figures 3A to 6B have all distributed the mass of the balancing mass elements 13 along tracks around the bladder wall, instead of having the essentially point masses of Figure 2, two other examples for distributing the balancing mass are shown in Figures 7A to 8B. Figures 7Aand 7B show an embodiment in which each balancing mass element 13 is formed by a relatively large patch. Like the strip of the previous embodiment, each patch 13 is applied to the outside of the bladder using an adhesive 13a after inflation of the bladder. Each patch may again be a patch of rubber or another thin flexible mass. Referring again to Figure 2A, one patch is applied centred on each of the three balancing points 111, 112, 113. Each patch may have the same mass as the electronic device 2 and housing 3, but can be conveniently applied to the outer surface of the bladder after the bladder has been inflated due to their large area and hence low thickness. Figures 8A and 8B show an embodiment which once again use balancing mass elements 13 that are integrally formed in an inner surface of the bladder wall 11. This embodiment differs the embodiments of Figures 3Ato 5B in that the balancing mass elements 13 cover three circular regions of the bladder wall, each circular region being centred on one of the three balancing points 111, 112, 113 that were described with reference to Figure 2A. Within each circular region, the integrally formed balancing mass elements 13 are arranged in a two-dimensional array across the inner surface of the bladder. Again, each integrally formed balancing mass element 13 may be a circular region of increased wall thickness compared to the rest of the bladder wall 11. The integrally formed balancing mass elements 13 may once again be spaced from one another by intervening wall portions 11a that do not have the increased thickness, to minimise the effect these elements have on the inflation of the bladder. The above embodiments have all dealt with a ball with additional mass introduced by an electronic device in one location around the periphery of the bladder. Techniques will now be described for embodiments in which additional mass is introduced by multiple electronic devices at different locations around the periphery of the bladder. Figure 9 shows a ball 1 with a bladder 10 having bladder wall 11 and valve 4, as described above with respect to Figure 1. A first electronic device 2a is provided in a first housing 3a, which is constructed and arranged identically to that described above with respect to Figure 1. Additionally, this ball 1 comprises a second electronic device 2b. The second electronic device 2b is secured in a second housing 3b, which is adhered to an inner surface of the bladder wall. As shown in Figure 10, the position of these two electronic devices has been selected so that they are at two of the four vertices of a regular tetrahedron circumscribed by the sphere of the bladder wall 11. It is assumed here that the electronic devices 2a and 2b have the same mass or that the housings 3a, 3b can be weighted so that the first electronic device 2a and first housing 3a have the same mass as the second electronic device 2b and second housing 3b. According to this positioning of the electronic devices 2a, 2b, there are two options for balancing the mass of the electronic devices. A first option is to provide two balancing masses at first and second balancing points 111,112 corresponding to the other two vertices of this regular tetrahedron. This could be a point like balancing mass as described with reference to Figure 2, a patch centred on each balancing point, as described with reference to Figure 7, or a region of integrally formed balancing masses centred on each balancing point, as described with reference to Figure 8. As a second option, consider a first point 101, which is the point of the bladder wall 11 that is closest to the combined centre of mass of the two electronic devices 2a, and a second point 102 opposite the first point. The distributed balancing mass may be provided by any mass distributed around this second point 102 and closer to the second point than the first point. In Figure 10, a circular track 114 is shown extending around the second point and which also passes through the two balancing points 111, 112 mentioned in connection with the first option of the preceding paragraph, although this is not essential. This circular track 114 defines a plane, such that the first point 101 is perpendicularly offset from the plane from a centre point of the circle, as illustrated by the arrow R Distributing mass evenly along this circular track 114, and particularly, evenly with respect to the balancing points 111, 112, will substantially allow for both of the criteria set out in equations (1) to (3) above to be met. The mass may be distributed along this track using any of the techniques described above with respect to Figures 3A to 6B, including tracks of integrally formed balancing mass elements or a continuous strip attached on or over the bladder wall 11. Finally, Figure 10 shows a ball 1 with a bladder 10 having bladder wall 11 and valve 4, as described above with respect to Figure 1. A first electronic device 2 is provided in a first housing 3, which is constructed and arranged identically to that described above with respect to Figure 1. Additionally, this ball 1 comprises a second electronic device 2’ secured in a second housing 3’, which is adhered to an inner surface of the bladder wall. It is possible to address and balance the masses of these electronic devices separately from one another, essentially ignoring any effect of the other. If we take a ball that has been balanced in accordance with the technique of Figure 2A, for example. This ball now has essentially the same centre of mass and moment of inertia about any axis as a ball without an electronic device and distributed balancing mass. Therefore a second device may be balanced in just the same way as the first. Figure 11 illustrates this. In Figure 11, the first electronic device 2 of the ball of Figure 10 defines a first point 101, which is the point on the bladder wall 11 that substantially coincides with the centre of mass of that electronic device. A second point 102 is defined opposite the first point. The mass of the first electronic device 2 is balanced by a track of integrally formed balancing elements 13 extending along the circumference of a circle defining a cone together with the first point, as described above with respect to Figure 3A. Additionally, the second electronic device 2’ defines a third point on the bladder wall 11 that substantially coincides with the centre of mass of that second electronic device. A fourth point 104 is defined opposite to the third point. Again, that third point may be taken as the first vertex of a regular tetrahedron defined by four points lying in the bladder wall, and then the other three points of that tetrahedron used to describe a circular track around the bladder wall so that another cone is defined, wherein the third point is offset perpendicularly from the plane of this circle from the centre of the circle. This described circular track may be provided with a series of integrally formed balancing mass elements 13’, which collectively form a second distributed balancing mass 12’ in the same way as the first track of balancing mass elements 13 that was defined with respect to the first point. Figure 13 illustrates another balancing arrangement that is a variant of the arrangement of Figures 11 and 12. In Figure 13, a first electronic device is located at a first point 101 on the bladder wall 11. It is assumed that the electronic device essentially coincides with this first point. The position also defines a second point 102 opposite the first point and the first electronic device. A second electronic device is located at a third point 103 on the bladder wall. If the first point is considered the first vertex of a regular tetrahedron that is circumscribed by the sphere defined by the bladder wall 11, then the third point corresponds to another one of the four vertices. The position of the second electronic device also defines a fourth point 104 opposite the third point. The first electronic device located at the first point 101 is balanced by a first distributed balancing mass 12. The first distributed balancing mass is formed of a track of balancing mass elements 13 along the bladder wall 11. The track of balancing mass elements 13 define the circumference of a circle, which together with the first point define an inscribed cone. The position of the balancing mass elements is defined using the same method as Figure 3A. In particular, the regular tetrahedron circumscribed by the sphere of the bladder wall is found where a first vertex is the first point 101. The circular track of balancing mass elements is thus defined by the plane defined by the other three vertices. Because of this arrangement, the second electronic device at point 103 lies along the track defined by the distributed balancing mass 12. The second electronic device located at the third point 103 is balanced by a second distributed balancing mass 12’. The second distributed balancing mass is formed of a track of balancing mass elements 13’ along the bladder wall 11. The track of balancing mass elements 13’ define the circumference of a circle, which together with the third point define an inscribed cone. The position of the balancing mass elements is defined in the same way as for the first electronic device. In particular, the regular tetrahedron circumscribed by the sphere of the bladder wall is found where a first vertex is the third point 103. The circular track of balancing mass elements is thus defined by the plane defined by the other three vertices. Because of this arrangement, the first electronic device at point 101 lies along the track defined by the second distributed balancing mass 12’. Figure 14 shows another embodiment for balancing first and second electronic devices 2a, 2b. These two electronic devices are located at two of the four vertices of a regular tetrahedron circumscribed by the sphere of the bladder wall. The other two vertices define first and second balancing points 111, 112. A first point on the bladder wall 101 is the point on the bladder wall 11 closest to the centre of mass of the two electronic devices. If the two electronic devices have the same mass, this point will be equidistant between the two electronic devices 2a, 2b. A second point 102 is defined opposite this first point. The first and second balancing points 111, 112 are positioned around the second point 102, separated by 180° measured about the second point, and the first and second balancing points are closer to the second point 102 than the first point 101. In this embodiment, the distributed balancing mass 12 is formed by a track of small balancing mass elements, the track extending along a line of a great circle that passes through the first and second balancing points 111, 112 and through the second point 102. The track defines only part of this great circle, in particular the track extends two thirds of the way around the bladder wall, that two thirds being centred on the second point 102, such that the track may be considered as having two halves, each centred on the first and second balancing points 111, 112. In this case, some balancing mass elements may be provided that are closer to the first point than the second point; however, the ball still comprises some (indeed most) balancing mass elements positioned around the second point and closer to the first point than the second. A longer or shorter track could be used, or two separate shorter tracks could be used, each respectively centred on one of the firstand second balancing points, 111, 112. While the embodiments of Figures 12 to 14 tracks of small, spaced balancing mass elements, it should be appreciated that these tracks could also be formed by continuous strips, in the same way as Figure 6A. Alternatively, fewer more more massive balancing mass elements could be used, in the case of Figure 12 and 13, down to singular balancing mass elements on the vertices of the or each regular tetrahedron defined with respect to the first point, and third point, if provided. Finally, Figure 15 illustrates the extension of the above principles to prolate spheroid-shaped balls. The ball 1 again comprises a bladder wall 11 defining the inflated shape of the ball. An electronic device 2 is provided. The device is positioned on the inner surface of the bladder wall at a position half way along the length of the ball. The valve 4 is positioned opposite to the electronic device, although because of the present balancing arrangement, this is not essential. The position of the electronic device 2 defines a first point 101 that substantially coincides with the position of the electronic device 2 on the bladder wall 11, and defines a second point 102 opposite the first point, i.e. coincident with the valve 4. First, second and third balancing points 111, 112, 113 are defined by vertices of a tetrahedron whose four vertices coincide with the bladder wall and which has a first vertex at the first point 101. The first, second and third balancing points 111, 112, 113 define an ellipse, wherein the first point 101 is perpendicularly offset from a centre point of the ellipse. The first balancing point 111 is located at the vertex of this ellipse. The second balancing point 112 is located between the second vertex of the ellipse and a first co-vertex of the ellipse. The third balancing point 112 is located between the second vertex and a second co-vertex of the ellipse opposite to the first co-vertex. The first, second and third balancing points are positioned such that a centre of mass of three identical masses positioned on those balancing points will lie on the axis extending between the first and second points 101, 102. With the above balancing points defined, the mass of the electronic device 2 may be balanced in the prolate spheroid ball 1 by arranging balancing mass elements with respect to these three balancing points. The balancing mass elements could take the form of three essentially point mass elements, analogous to Figure 2A, 5 or could be arranged along tracks along the ellipse analogous to Figures 3A, 4, 5A, or 6. They could also be distributed around the three balancing points analogously to Figures 7A or 8A.

Claims

1. An inflatable ball comprising:a bladder having a bladder wall defining an inflatable interior of the ball;at least one device mounted on or over the bladder wall such that a centre of mass of the at least one device is located away from a centre of the inflatable interior of the ball, the at least one device including at least one electronic device, the centre of mass of the at least one device defining a first point on the bladder wall coincident with or closest to the centre of mass of the at least one device and a second point on the bladder wall opposite the first point; anda distributed balancing mass for at least partially rotationally balancing the mass of the at least one device, the distributed balancing mass comprising one or more balancing mass elements on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality of locations spaced around the second point on the bladder wall and closer to the second point than the first point.

2. An inflatable ball according to claim 1, wherein the one or more balancing mass elements comprises one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of at least two balancing points equally spaced around the second point, preferably at least three balancing points equally spaced around the second point.

3. An inflatable ball according to claim 1 or claim 2, wherein the one or more balancing mass elements comprises one or more balancing mass elements arranged substantially at or substantially evenly distributed by mass with respect to each of at least three balancing points spaced around the second point, the three balancing points together with the first point and / or the centre of mass of the of the at least one device defining four vertices of a substantially regular tetrahedron.

4. An inflatable ball according to any of the preceding claims, comprising at least six balancing mass elements arranged substantially in a single plane, wherein each balancing mass element has two corresponding balancing masselements which, together with the first point and / or the centre of mass of the at least one device, define four vertices of a substantially regular tetrahedron.

5. An inflatable ball according to any of the preceding claims, wherein the one or more balancing mass elements comprises one or more mass balancing elements arranged along one or more tracks along the bladder wall defining all or part(s) of the circumference of a circle or an ellipse.

6. An inflatable ball according to claim 5, wherein the first point lies perpendicular to the plane of the circle or the ellipse from the centre of the circle or the ellipse.

7. An inflatable ball according to claim 5, wherein the at least one device comprises a first device and a second device, wherein the one or more tracks along the bladder wall pass through first and second balancing points spaced around the second point and define part(s) of the circumference of a circle or an ellipse passing between the first and second devices.

8. An inflatable ball according to any of the preceding claims, wherein the one or more balancing mass elements comprises one or more continuous strips or patches, preferably adhesive strips or patches, attached on or over the bladder wall.

9. An inflatable ball according to any of the preceding claims, wherein the one or more balancing mass elements comprises one or more balancing mass elements formed integrally with the bladder wall.

10. An inflatable ball according to claim 9, comprising a plurality of balancing mass elements formed integrally with the bladder wall by increased wall-thickness portions of the bladder wall.

11. An inflatable ball according to claim 10, wherein each increased wallthickness portion has at least one lateral dimension of no more than 2 cm, preferably no more than 1 cm, more preferably no more than 0.5 cm.

12. An inflatable ball according to claim 11, wherein each increased wallthickness portion has a largest lateral dimension of no more than 2 cm, preferably no more than 1 cm, more preferably no more than 0.5 cm.

13. An inflatable ball according to any of claims 10 to 12, wherein each increased wall-thickness portion of the bladder wall is surrounded by a portion not having the increased wall thickness.

14. An inflatable ball according to any of claims 10 to 13, wherein each increased wall-thickness portion projects from an inner surface of the bladder wall towards the centre of the inflatable interior of the ball.

15. An inflatable ball according to any of claims 10 to 14, wherein the wall thickness of the increased wall-thickness portions is no more than five times the wall thickness of the thinnest part of the bladder wall, preferably no more than four times the thickness, even more preferably no more than three times the thickness, most preferably no more than twice the thickness of the thinnest part of the bladder wall.

16. An inflatable ball according to any of the preceding claims, wherein the at least one device balanced by the distributed balancing mass is mounted at a substantially single point on or over the bladder wall.

17. An inflatable ball according to any of the preceding claims, wherein the atleast one device is a first device or first set of devices, and further comprising a second device or second set of devices mounted on or over the bladder wall such that a centre of mass of the second device or second set of devices is located away from a centre of the inflatable interior of the ball, the centre of mass of the second device or second set of devices defining a third point on the bladder wall coincident with or closest to the centre of mass of the second device or second set of devices and a fourth point on the bladder wall opposite the third point; and a second distributed balancing mass for at least partially rotationally balancing the mass of the second device or second set of devices, the distributed balancing mass comprising one or more balancing mass elements on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality oflocations spaced around the fourth point on the bladder wall and closer to the fourth point than the third point.

18. An inflatable ball according to any of the preceding claims, wherein the or each electronic device comprises one or more of: a battery, a wireless charging module, an accelerometer, a gyroscope, a pressure sensor, a magnetometer, a force transducer and a location tracking device, such as an ultra-wideband transmitter and / or receiver.

19. An inflatable ball according to any of the preceding claims, wherein the bladder further comprises a valve for inflating the inflatable interior of the ball, wherein the valve is not one the devices balanced by the distributed balancing mass.

20. An inflatable ball according to any of the preceding claims, wherein the bladder defines a substantially spherical inflatable interior of the ball.

21. An inflatable ball according to any of the preceding claims, wherein the inflatable ball is an inflatable sports ball, preferably a soccer ball, basketball, netball, volleyball, or handball.

22. A method of manufacturing an inflatable ball, the method comprising:providing a bladder having a bladder wall defining an inflatable interior of the ball;providing at least one device mounted on or over the bladder wall such that a centre of mass of the at least one device is located away from a centre of the inflatable interior of the ball, the at least one device including at least one electronic device, the centre of mass of the at least one device defining a first point on the bladder wall coincident with or closest to the centre of mass of the at least one device and a second point on the bladder wall opposite the first point; andproviding a distributed balancing mass for at least partially rotationally balancing the mass of the at least one device, the distributed balancing mass comprising one or more balancing mass elements provided on or over the bladder wall, the one or more balancing mass elements being arranged at a plurality oflocations spaced around the second point on the bladder wall and closer to the second point than the first point.

23. A method according to claim 22, wherein providing the distributed balancing mass comprises attaching one or more continuous strips or patches, 5 preferably adhesive strips or patches, on or over the bladder wall.

24. A method according to claim 22 or claim 23, wherein providing the bladder comprises moulding the bladder, and wherein providing the distributed balancing mass comprises moulding one or more balancing mass elements integrally with the bladder wall when moulding the bladder.10 25. A method according to claim 24, wherein moulding one or more balancingmass elements integrally with the bladder wall when moulding the bladder comprises moulding a plurality of increased wall-thickness portions of the bladder wall.

26. A method according to any of claims 22 to 25, adapted to manufacture an 15 inflatable ball according to any of claims 1 to 21.34

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