directional terms such as “ left ”, “ right ”, “ horizontal ”, “ vertical ”, “ transverse ” and “ longitudinal ” are used in this description merely to assist the reader to understand the described embodiments and are not to be construed to limit the orientation of any described method , product , apparatus or parts thereof , in operation with or in connection to another object . referring to fig1 , an example wheelchair 1 is depicted having a wheelchair frame 2 with attached rear wheels 3 . the rear wheels 3 are attached to the wheelchair frame 2 by axles inserted into camber bodies 6 . the camber bodies 6 are coupled to horizontal tubes 4 which are members of the frame 2 and which extend longitudinally ; that is , the tubes 4 extend from the front to the rear of the frame 2 . the camber bodies 6 and horizontal tubes 4 are also coupled to a transverse tube 5 that transversely spans across the frame 2 . the front of the wheelchair 1 also has caster wheel assemblies 14 attached to the frame 2 . the geometry of this example wheelchair 1 is such that the horizontal tubes 4 lie in a horizontal plane , parallel to the ground , and the housing tubes 18 of the caster wheel assemblies 14 lie in a vertical plane , perpendicular to the horizontal plane . in this configuration , a wheel mount assembly can provide an adjustable camber angle of the rear wheels 3 , while also maintaining negligible toe - in and toe - out effects of the rear wheels . such a configuration would provide low rolling resistance and an efficient wheeling mechanism . referring now to fig2 ( a )-( c ), which depict three views of the exemplary embodiment of the wheel mount assembly in detail , the transverse tube 5 consists of a tubular structure with alloy plugs 17 inserted into either end to a depth of approximately 2 . 5 inches . the ends of the transverse tube 5 are shaped to concentrically couple to the horizontal tubes 4 of the wheelchair frame 2 . oval or elongated through - holes 12 are formed in the transverse tube 5 through the tube 5 and alloy plugs 17 such that a bolt 8 may pass through the tube 5 at various angles to the vertical . the end of the elongated holes 12 are further shaped to be an elliptical counterbore 11 , such as may be obtained through the use of a ball nose end mill . this counterbore 11 is shaped to receive a spherical washer 9 through which the bolt 8 passes such that regardless of the angle of the bolt 8 to the vertical , the bolt may fasten firmly to the transverse tube 5 . the counterbore 11 is shaped with a sufficient depth to enable the spherical washers 9 to snugly couple to the transverse tube 5 . the bolt 8 can be a socket button head cap screw , for instance , with a head with a flat surface to coincidentally mate with the flat side of the spherical washer 9 . in an alternative embodiment ( not shown ), instead of using the counterbore 11 to receive the spherical washer 9 , a female spherical washer can be used to receive the spherical washer 9 , with the female spherical washer sitting flat on a machined flat shoulder . the bolt 8 is screwed into the bottom of a camber body 6 . the camber bodies 6 are shaped to concentrically couple to the horizontal tubes 4 of the wheelchair frame 2 . another bolt 10 is screwed into the camber body medial to the bolt 8 . this bolt 10 is a socket button head cap screw , for instance , which has a head with a radius . the distal surface of the head of the bolt 10 is coincidentally and approximately concentrically coupled to an elliptical counterbore hole 13 shaped in top of the transverse tube 5 and alloy plugs 17 . this elliptical hole 13 is sufficiently deep to provide a surface with a radius closely matched to the head of the button head screw 10 , again optionally by using a ball nose end mill . when the bolt 8 is firmly screwed into the camber body 6 , the camber body 6 and the transverse tube 5 mate to the horizontal tube 4 on opposing sides of the tube 4 , the spherical washer 9 mates to the elongated counterbore 11 , and the bolt 10 mates to the elongated counterbore hole 13 . thus the force of the bolt 8 provides sufficient clamping force to rigidly secure the wheel mount assembly to the wheelchair 1 . an axle receiver insert 7 is inserted into the camber body 6 . one example of an axle receiver insert 7 is a threaded rod approximately 2 inches long with a bored hole through it to accept a wheel axle . the axle receiver insert 7 can be screwed to various depths into the camber body 6 , thus effectively spacing the wheels 3 laterally with respect to the wheelchair frame 2 . the distance that the bolt 10 is screwed into the camber body 6 determines the angle α of the camber body 6 to the horizontal . the more the bolt 10 is screwed into the camber body 6 ( the shorter the bolt 10 has an exposed length ), the greater the angle α becomes . the angle α determines the angle of the wheels in the following relationship . the angle α between the camber body 6 and a horizontal plane is equal to the camber angle of the wheelchair 1 rear wheels 3 with respect to a vertical sagittal plane . the embodiment depicted in fig2 ( a )-( c ) provide for the angle α to be adjusted from 0 degrees to approximately 12 degrees . it is appreciated that the angle α can be made even greater by changing the coupling shapes of the camber bodies 6 and transverse tube 5 , as well as the diameters and sizes of the camber bodies 6 , the transverse tube 5 , and the horizontal tubes 4 , and the length of the bolt 10 . an alternative embodiment is shown in fig3 . essentially , the wheel mount assembly described above and shown in fig2 ( a )-( c ) is flipped upside down . to similarly achieve adjustable wheel camber angles , the bolt 10 is screwed into the camber body 6 to various depths . in contrast to the embodiment depicted in fig2 ( a )-( c ), a longer exposed length of the bolt 10 equates to a greater wheel camber angle . one benefit of the embodiment illustrated in fig3 is that the head of the bolts 8 , 10 face upwards , which can make their adjustment easier than that of the bolts 8 , 10 of the embodiment illustrated in fig2 ( a )-( c ). in both embodiments described above , and referring to the example wheelchair 1 in fig1 , it is appreciated that changing the camber angle α of the rear wheels 3 would also change the relative height of the rear of the wheelchair frame 2 . such a change may tilt the plane in which the horizontal tubes 4 lie such that it is no longer parallel with the horizontal plane , and may also tilt the plane in which the housing tubes 18 of the caster wheel assemblies 14 lie such that it is no longer parallel with the vertical plane . such changes may increase the toe - in or toe - out of the rear wheels 3 and impact rolling resistance and pushing efficiency . this could be mitigated in the example wheelchair 1 by changing the relative height of the housing tubes 18 of the caster wheel assemblies 14 for a given wheel camber angle in order to adjust the tilt of the planes in which the horizontal tubes 4 and vertical housing tubes 18 of the caster wheel assemblies 14 lie . the relative height of the housing tubes 18 may be changed with washers or spacers . given the embodiments of the wheel mount assemblies described above , the toe - in and toe - out would then be negligible . referring to fig4 , an axle receiver insert 7 with an eccentrically placed hole 15 is shown . this alternative embodiment may be needed if by changing the camber angle of the wheels 3 , the rear height of the wheelchair 1 is raised or lowered , and that this changed height could not be compensated for by changing the height of the caster wheel housings 18 . such a change in rear height may alter the toe - in toe - out of the rear wheels 3 , thus impacting rolling resistance and pushing efficiency . to alter the toe - in and toe - out to a negligible amount , the axle receiver insert 7 with an eccentric hole 15 can be rotated in the camber body 6 . the eccentric hole 15 would then provide a means to subtly alter the toe - in and toe - out of the rear wheels 3 . once the optimum rotational placement of the axle receiver insert 7 with an eccentric hole 15 is achieved , the position can be fixed in place by tightening the jam nut 16 firmly against the camber body 6 . referring now to fig5 ( a )-( c ) and 6 ( a )-( c ), embodiments of the present invention wherein the transverse tube 5 is absent are depicted . in fig5 ( a )-( c ) and 6 ( a )-( c ), in lieu of the transverse tube 5 , a lower camber body 19 is present . the bolt 10 abuts against the lower camber body 19 instead of the transverse tube 5 when the camber body 6 is at the desired camber angle α . referring specifically to fig5 ( a )-( c ), the lower camber body 19 is welded to the horizontal tube 4 , as evidenced by the presence of a weld bead 20 . referring specifically to fig6 ( a )-( c ), the lower camber body 19 is secured to the horizontal tube 4 with a pin 19 , which extends through the lower camber body 19 , the horizontal tube 4 , and the camber body 6 . the combination of the pin 19 and the clamping force resulting from the bolt 8 result to prevent movement of the camber bodies 6 , 19 about the tube 4 . while the camber bodies 6 , 19 depicted in fig5 ( a )-( c ) are necessarily fixed to the horizontal tube 4 at the location of the weld bead 20 , the camber bodies 6 , 19 depicted in fig6 ( a )-( c ) are movable to different positions along the horizontal tube 4 so long as at each position to which the camber bodies 6 , 19 are to be moved , a channel for receiving the pin 19 exists within the tube 4 . all embodiments described above , and others not shown here , also provide another feature : the wheel mount assembly can be slid rearwards and forwards along the horizontal tubes 4 and clamped in position . by changing the clamping position along the horizontal tubes 4 , the center of gravity of the wheelchair 1 can be changed . the components of the wheel mount assembly can be manufactured from a light alloy material to reduce the weight of the wheelchair 1 . suitable such materials include steel alloys , aluminum alloys , titanium alloys , magnesium alloys , plastics such as polycarbonate , carbon fibre composites , and other materials suitable for such an application . by selecting such materials and by utilizing the design of the wheel mount assembly described here , it is expected that the weight of the wheelchair 1 can minimized . the embodiments described herein can offer several advantages . for instance , the lateral distance between the rear wheels 3 may be adjusted by varying the insertion depth of the axle receiver insert 7 within the camber body 6 . in the embodiments of the invention wherein the camber bodies may be coupled at different positions along the horizontal tubes 4 , the center of gravity of the wheelchair may be adjusted . the camber angle of the wheels 3 may be adjusted by removing bolts 8 and un - clamping the wheel mount assemblies . the depths of the bolts 10 can then be adjusted and the wheel mount assemblies re - clamped . the toe - in and toe - out of the wheels 3 may be adjusted by changing the heights of the caster wheel housings 18 or by rotating the axle receiver inserts 7 with eccentrically placed holes 15 . while the present invention has been described herein by the preferred embodiments , it will be understood to those skilled in the art that various changes may be made and added to the invention . the changes and alternatives are considered within the spirit and scope of the present invention .
a wheel mount assembly for mounting a drive wheel to a frame of a wheelchair is provided . the assembly includes a camber body attachable to an axle of one of the drive wheels and operable to pivotably couple about the frame through a range of camber angles ; a spacer operable to set a desired camber angle , the spacer contacting the camber body at the desired camber angle ; and a clamp operable to secure the camber body and the spacer to the frame at the camber angle . optionally , a transverse member , extending between the drive wheels , may engage a portion of the frame such that the clamp is prevented from pivoting through the camber angles of each respective camber body . again , optionally , the wheel mount assembly may be clamped to the frame at a multitude of positions , thus providing a means to adjust the center of gravity of the wheelchair .