Complete Specification Innovation Patent A Cantilevered Arm Suspension System (CASS) for use with Mid Wheel Drive powered wheelchairs using a system of flexible bearings, sliding links and pivot points BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the suspension system for an electrically powered wheelchair, more particularly a power wheelchair that has six wheels in contact with level ground when stationary. This invention has been specifically designed to provide a smoother, more comfortable ride for the wheelchair client, at the same time with good stability both the frontwards/rearwards and the side to side directions when travelling over uneven surfaces. Description of the Prior Art Some electrically powered wheelchairs have suspension systems that will allow them to offset the displacement when driven over uneven surfaces. The most common styles are: - rear wheel drive and front wheel drive power wheelchairs. These wheelchairs have four wheels on the ground and usually have a pair of anti tip bars or wheels as well to prevent the wheelchair from tipping over should the wheelchair be highly displaced. - "mid wheel drive" or "centre wheel drive" power wheelchairs with four wheels on the ground. This style of power wheelchair is also usually equipped with a pair of anti tip bars or wheels to prevent the wheelchair from tipping over. As this style of wheelchair usually has a shorter wheelbase, the wheelchair can often be less stable in both the frontwards/rearwards and the side to side directions. - "six wheel, mid wheel drive" or "six wheel, centre wheel drive" power wheelchairs which have six wheels on the ground. This type of chair requires a more complex arrangement in its suspension system to allow the wheels to move so as to offset displacement from uneven ground. Several different styles are now used by different manufacturers. Depending upon the design, this type of wheelchair can offer a smoother ride and better stability for the wheelchair user than the above types. SUMMARY OF THE INVENTION The Cantilevered Arm Suspension System (CASS) is designed to improve the ride comfort and the safety of the wheelchair user by allowing misalignment between the arms supporting the wheelchair's six wheels in a manner that assists to keep all six wheels in contact with the ground surface at all times. The Cantilevered Arm Suspension System (CASS) consists of: a) two cantilevered arm assemblies (5 and 6 in figure 1) that support the two leading swivelling castors (25 and 26 in figure 1) and drive wheels (49 and 50 in figure 1) b) a pivoting cross bar (2 in figure 1) that connects the two cantilevered arm assemblies (5 and 6). This pivoting cross bar (2) also attaches to and pivots on the wheelchair base frame (1 in figure 1) c) flexible bearings (9, 10, 11,and 12 in figure 1) at each end of the pivoting cross bar (2) that connects the pivoting cross bar to the cantilevered arm assembly (S and 6) d) a spacing collar (20 and 21 in figure 1) on each cantilevered arm assembly (5 and 6) that connects the cantilevered arm assembly (5 and 6) to the wheelchair base frame (1) and allows the cantilevered arm assembly (5 and 6) to pivot e) a rear arm assembly (35 and 36 in figure 1) that pivots on a shaft (3 and 4 in figure 1) of the base frame (1) and is attached to the cantilevered arm assembly (5 and 6) by either * a spring (16 in figure 1)or other means, or * with a link to the front rigging assembly (23 and 24 in figure 1), or Page 2 of 7 * fixed to the cantilevered arm assembly as required. f) an arrangement of sliding links (31 in figure 1), spacers (32 in figure 1) and locating members (33 and 34 in figure 1) that connects the front rigging assembly (23 and 24) to the cantilevered arm assembly (5 and 6) The cantilevered arm assembly (5 and 6) preferably consist of plate or tubing of mild steel, bright steel or stainless steel that may be chrome plated or powder coated. The flexible bearings (9, 10, 11 and 12) preferably will be of rubber, polyurethane or materials of similar properties to achieve different levels of resistance to flexing. It is the primary object of the present invention to allow any of the six wheels to be displaced by uneven ground in the vertical direction yet allow the other wheels to maintain contact with the support surface. It is another object of the present invention to keep the seat level when the wheelchair is being operated over uneven surfaces. It is a further object of the present invention to provide good stability for the wheelchair in both the frontwards/rearwards and the side to side directions when the wheelchair is being operated over uneven surfaces. It is a still further object of the present invention for the suspension to flex sufficiently to allow the wheelchair to climb over small obstacles. It is a still further object of the present invention for the suspension to flex sufficiently to allow the wheelchair to cross over ground depressions without losing contact by the drive wheel, and thereby the ability to drive in any direction. It is a still further object of the present invention to provide a suspension that is safe for the client when being used in a normal manner as intended. The objects are achieved through the flexible bearings (9, 10, 11 and 12) allowing the cantilevered arm assembly (5 and 6) to move out of alignment with each other as the wheels travel over rough and/or uneven ground. This misalignment or movement of the components of the suspension system in relation to each other allows the wheels to individually keep in contact with the ground up to the maximum amount of distortion capable in the flexible bearings (9, 10, 11 and 12). Should a front wheel and drive wheel on either side of the wheelchair be lifted or to drop in relation to the other side, - the cantilevered arm assembly (5 and 6) will pivot around the shaft (3 and 4) connecting it to the wheelchair base frame (1) - the flexible bearings (9, 10, 11 and 12) at each end of the pivoting cross bar (2) will distort proportionally to the amount of movement of the cantilevered arm assembly (5 and 6), up to the limit of distortion of the bearing (9, 10, 11 and 12) - the pivoting cross bar (2) will pivot around the pivot point (48) attaching it to the wheelchair base frame (1) Page 3 of 7 This ability for the movement of the components of the suspension system in relation to each other thereby helps keep all individual wheels on the ground, thus maximizing the stability of the wheelchair for different ground conditions and slopes. This improvement in stability thus lessens the chances of the wheelchair being overturned and the user thereby being possibly injured. Because the flexible bearings (9, 10, 11 and 12) allow smooth movement of the components of the suspension system in relation to each other, the wheelchair user is less likely to be displaced in the wheelchair as the chair travels over rough and/or uneven ground. The smoother ride of the Cantilevered Arm Suspension System (CASS) thus lessens the chances of the wheelchair user losing control over the Mid Wheel Drive power wheelchair. BRIEF DESCRIPTION OF THE DRAWINGS The invention may be better understood with reference to the drawings of the embodiments of the invention as follows: Figure 1 shows an exploded view of the present invention; Figure 2 shows an isometric, front and side view of the present invention; Figure 3 shows a cross-sectional view of inactive flexible bearings in the present invention; Figure 4 shows a cross-sectional view of activated flexible bearings in the present invention; Figure 5a and 5b are views showing the movement of the embodiment when a front wheel is displaced vertically upwards Figure 6a and 6b are views showing the movement of the embodiment when a mid wheel is displaced vertically downwards Figure 7a and 7b are views showing the movement of the embodiment when both front wheels and mid-wheel on one side only are displaced vertically upwards Figure 8a and 8b are views showing the movement of the embodiment when a mid wheel is displaced vertically upwards DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in figures 1 through 8, a preferred embodiment of the present invention comprises of a base frame (1), in which a pivoting cross bar (2) and two shafts (3 and 4) of aforementioned base frame (1) are supporting and connecting two cantilevered arm assemblies (5 and 6) on either side of the base frame (1). Shouldered bushes (7 and 8) which are suspended in the flexible bearings (9, 10, 11 and 12) and locating members (13) are used to secure the cantilevered arm assembly (5 and 6) to the pivoting cross bar (2). Each cantilevered arm assembly (5 and 6) has a collar (14 and 15), two spring support lugs (17a and 17b) at the top, a leading shaft (18 and 19) and a spacing collar (20 and 21) at the rear of the assembly. The collar (14 and 15) is housing the aforementioned flexible bearings (9, 10, 11 and 12). At the top of the cantilevered arm assembly (5 and 6), a compression spring (16) is positioned and secured between the two spring support lugs (17a and 17b) using locating members. The spacing collar (20 and 21) is positioned at the rear of the cantilevered arm assembly (5 and 6). After inserting Page 4 of 7 the spacing collar (20 and 21) of the cantilevered arm assembly (5 and 6) in the rear arm assembly (35 and 36), the assembly is positioned over the shaft (3 and 4) of the base frame (1). The front rigging assembly (23 and 24) of the suspension system is suspended from the leading shaft (18 and 19) of each cantilevered arm assembly (5 and 6). The front rigging assembly (23 and 24) is secured at the front to the aforementioned cantilevered arm assembly (5 and 6) with locating member (22). The aforementioned front rigging assembly (23 and 24) is made up of the leading swivelling castor (25 and 26) and the motor and gearbox drive unit (27 and 28) which propels the wheelchair. A collar (29) is positioned in between the leading swivelling castor (25 and 26) and the motor and gearbox drive unit (27 and 28). This collar (29) slides over the aforementioned leading shaft (18 and 19) of the cantilevered arm assembly (5 and 6). The front rigging assembly (23 and 24) is also secured at the rear to the aforementioned cantilevered arm assembly (5 and 6) by a second collar (30) by means of an arrangement of sliding links (31), spacers (32) and locating members (33 and 34). In one embodiment the sliding links (31), are replaced by a bar, connecting the front rigging assembly (23 and 24) directly to the rear arm assembly (35 and 36). In this embodiment the compression spring (16) is optional. The range of the front rigging assembly (23 and 24) clockwise rotation can be controlled by adjusting an adjuster bolt (37). The primary components of the rear arm assembly (35 and 36) are the two concentrically positioned and spaced collars (38 and 39), a support plate (40 and 41) and the two trailing castors (42 and 43). The support plate (40 and 41) is inclusive of tapped holes. It positions and secures the rear spring support lug (44), using locating members (45). The concentrically positioned and spaced collars (38 and 39) of the rear arm assembly (35 and 36) are positioned over the spacing collar (20 and 21) of the cantilevered arm assembly (5 and 6), and aligned and simultaneously positioned over shaft (3 and 4) of the base frame (1). It is secured with shaft cap (46) and locating member (47). The movement of the rear arm assembly (35 and 36) is dampened by a compression spring (16) positioned between the aforementioned rear spring support lug (44) and the spring support lugs (17a and 17b) of the cantilevered arm assembly (5 and 6). Degree of movement The pivoting cross bar (2) is limited in its movement to rotation around the axis of its pivot point (48). Further restraints are governed by the linear distance between the collar (14 and 15) and the spacing collar (20 and 21) of the cantilevered arm assembly (5 and 6). Lateral movements are constrained. The cantilevered arm assembly (5 and 6) is limited in its movement to rotation around the shaft (3 and 4) of the base frame (1). Further restraints are defined by the aforementioned pivoting cross bar (2). Lateral movements are constrained. Rotational movements of aforementioned pivoting cross bar (2) and cantilevered arm assembly (5 and 6) are limited by the maximum amount of distortion capable in the flexible bearings (9, 10, 11 and 12). The front rigging assembly (23 and 24) is limited in its movement to rotation around the axis of the leading shaft (18 and 19) of the cantilevered arm assembly (5 and 6). When viewed from the right hand side of the wheelchair, the clockwise, rotational movement of the front rigging assembly (23 and 24) is controlled and limited by adjusting the adjuster bolt (37). When viewed from the right Page 5 of 7 hand side of the wheelchair, the counter clockwise rotational movement is limited by the physical proportion of the design. Lateral movement is constrained. The rear arm assembly (35 and 36) is limited in its movement to rotation around shaft (3 and 4) of the base frame (1). When viewed from the right hand side of the wheelchair, the clockwise rotational movement is limited by the physical proportions of the compression spring (16). When viewed from the right hand side of the wheelchair, the counter clockwise rotational movement is dampened and ultimately limited to the physical proportions of the compression spring (16). Lateral movement is constrained. Page 6 of 7