Abstract:
The present invention is a derailleur for moving a chain to a different sized sprocket in a drive sprocket nest comprising: a feed arm for directing onto one of multiple sprockets within the drive sprocket nest when the feed arm is rotatably mounted at a pivot end onto a frame of a vehicle; a take up roller attached to the feed arm supporting the chain so that when the take-up roller moves laterally the chain moves from one sprocket to another sprocket in the drive sprocket nets; a roller feel sprocket supporting the chain so that the chain contacts over ½ the perimeter of the sprocket contacting the chain in the drive sprocket nest; an opposite chain guide end attached to the feed arm so that the chain guide end traces a path substantially parallel to a tangent to the outer periphery of the drive sprocket nests.

Description:
CLAIM OF PRIORITY 
     This application is a continuation in part of co-pending U.S. application Ser. No. 12/898,817 filed on Oct. 6, 2012 entitled DERAILLEUR. 
    
    
     TECHNICAL FIELD 
     This application relates to a speed changing device for rider propelled vehicles using a chain drive and a sprocket nest with a plurality of different sized sprockets. The sprocket changing device is a pivoting derailleur system with a derailleur and a chain slack take-up mechanism. 
     BACKGROUND OF THE INVENTION 
     The derailleur system currently used in bicycles has been adequately engineered to allow the chain to smoothly move to an adjacent sprocket at selected locations around each sprocket. Each sprocket is modified to provide clearance for chain shifting with a small plurality of reduced size chain pickup teeth with modified shape at selected locations on the sprocket, but with adjacent normally sized teeth providing adequate chain grip and strength around the rest of the sprocket&#39;s outer periphery or circumference. 
     The chain travel is directed by a movement of the derailleur guiding the chain from the sprocket it is on and feeding the chain onto an adjacent larger sprocket when decreasing the speed or a smaller sprocket when increasing the speed. 
     The bicycle derailleur devices are physically mounted on the frame of the bicycle and its movement is generally operated by a guide wire or cable extending from a shifting lever attached on the handle bar to the derailleur. When the rider selects a new sprocket, he moves the lever moving the wire or cable which in turn repositions the derailleur to effect a sprocket change. The derailleur is a sophisticated device that has a fixed structure attached to the frame or rear axle and a movable structure that is held in position by at least one double pivot with multiple heavy duty springs that allow the movable elements to rotate or move in the path of a parallelogram created by two opposing plates hinged to move parallel relative to the other. This movement enables the chain guide portion of the derailleur to move relative to the sprocket nest in a relatively uniform path in relation to the guide and the sprockets while minimizing twisting the chain. 
     In order to function properly, the chain slack that exists when the chain is on the sprocket must be taken up. The amount of chain slack is reduced as the chain moves to larger sprockets. In bicycles, the derailleur chain guide system is positioned to extend well below the axle and frame. This enables the chain to serpentine through the low hanging derailleur guide system by having the chain extend well below the largest of the sprockets. 
     These prior art derailleur devices allow the chain to be moved along the various sized sprockets with relative ease. In U.S. Pat. No. 7,780,558 entitled “Bicycle Rear Derailleur” assigned to Shimano Inc.; a rather detailed description is provided of these rather sophisticated devices for changing sprockets on a bicycle. Shimano is a world leader in the manufacture of derailleurs and is known for providing some of the best devices for changing sprockets on chain driven bicycles. Their rear derailleurs are engineering marvels exhibiting good reliability and durability. 
     These excellent products, however, because they are so well made with much sophistication are costly. A need exists to provide a simpler, less complex derailleur design that is reliable and durable. 
     Recently, a new generation of scooters and bicycles has been developed with reciprocating foot pedals. These vehicles, particularly the scooters, have frames that have a very low center of gravity to make the vehicles more stable. The frames are so low to the ground that the prior art derailleurs conventionally positioned below the rear sprocket nest are virtually useless. Nevertheless, these vehicles need a shifting device to allow the rider to selectively change speeds. 
     It is therefore an objective of the present invention to provide a derailleur type device and chain slack take-up assembly that does not extend into the ground clearance of the vehicle. It was a further objective of the present invention to provide a reliable and less complex device that can be manufactured at an affordable cost. 
     It was still another objective of the present invention to provide a derailleur device with a large range of motion to facilitate the range of rear sprocket sizes in a single rear sprocket nest equivalent to present bicycle derailleurs. 
     Another objective of the invention is to have the chain feed to the derailleur chain take-up directed so as to be fed close to the centerline of the drive sprocket. 
     These and other features of the derailleur system of the present invention are described as follows. 
     SUMMARY OF THE INVENTION 
     A derailleur, for moving a chain to different sized sprockets arranged small to large in a sprocket nest is disclosed. The derailleur has a feed arm for directing the chain onto one of multiple sprockets within the sprocket nest. The feed arm is rotatably mounted at a pivot end on an angular pivot and when the feed arm rotates on the pivot an opposite chain guide end of the feed arm traces a path substantially parallel to a tangent to the outer periphery of the sprocket nest. The movement of the feed arm is mechanically driven by a user command and is preferably moved by a connected rod, wire or cable. The guide end of the derailleur has a chain guide, wherein the chain guide can be a smooth surface or a roller or toothed roller. The derailleur further has a chain slack take-up assembly having a pivotal take-up idler arm for chain slack take-up, which is pivotably connected to the chain guide end of the feed arm. Preferably, the feed arm and the pivotal take-up idler arm share a chain guide wherein the feed arm and idler arm are both spring loaded, preferably sharing the same spring wherein one spring biases both the feed arm and idler arm, the spring being connected to the idler arm and onto the angular pivoting feed arm. 
     One end of the spring is connected to the feed arm at or near the frame pivot, the opposite end of the spring is connected to the idler arm on a pin eccentric to the pivot biasing the idler arm providing the chain slack take-up, wherein the chain feed arm and take-up idler arm assemblies lie within a space between the driver sprocket and driven sprocket nest, the space defined as the area between the major diameter sprocket of the driver sprocket and driven sprockets. 
     A chain take-up assembly has a pivotal idler arm for taking up chain slack, the idler arm having a pair of chain guides, one being a feed guide, the other a take-up guide, at opposite ends to serpentine the chain through the guides; and a spring, pulling the idler arm to maintain chain tension; and wherein the excess chain slack is stored in the space between the driver and driven sprockets. 
     The assembly allows the chain to straighten when positioned on the largest sprocket pairs. The chain take up assembly lies within a space between the driver sprocket and driven sprocket nest, the space defined as the area between the major diameter sprocket of the driver sprocket and driven sprockets. The chain guides are smooth surfaces or rollers with or without teeth. 
     The present invention can include a derailleur for moving a chain to a different sized sprocket in a drive sprocket nest comprising: a feed arm for directing onto one of multiple sprockets within the drive sprocket nest when the feed arm is rotatably mounted at a pivot end onto a frame of a vehicle; a take up roller attached to the feed arm supporting the chain so that when the take-up roller moves laterally the chain moves from one sprocket to another sprocket in the drive sprocket nets; a roller feel sprocket supporting the chain so that the chain contacts over ½ the perimeter of the sprocket contacting the chain in the drive sprocket nest; an opposite chain guide end attached to the feed arm so that the chain guide end traces a path substantially parallel to a tangent to the outer periphery of the drive sprocket nests. 
     The take up roller can support the chain so that the chain contacts over ½ the perimeter of a pedal sprocket. The feed arm can cause the chain to move from a first pedal sprocket to second pedal sprocket once the chain is at the smallest sprocket of the drive sprocket nest so that the chain can be moved about the drive sprocket nest and the pedal sprocket with one derailleur. The feed arm causes the chain to move from a first pedal sprocket to second pedal sprocket once the chain is at the largest sprocket of the drive sprocket nest so that the chain can be moved about the drive sprocket nest and the pedal sprocket with one derailleur. 
     The movement of the feed arm can be moved by tensioning a first cable connected to the feed arm causing the take up roller to move in a lateral direction relative to a long axis of the frame of the vehicle causing the chain to move from one sprocket to another in the drive sprocket nest. The movement of the roller feed sprocket can be actuated by tensioning a second cable connected to the feed arm causing the roller feed sprocket to move in a lateral direction relative to a long axis of the frame of the vehicle causing the chain to move from one sprocket to another in a pedal sprocket nest. 
     The excess slack in the chain can be is taken up in a slack area defined by a horizontal tangent of the top perimeter of a pedal sprocket and a largest sprocket in the drive sprocket nest and a horizontal tangent of the bottom perimeter of a pedal sprocket and a largest sprocket in the drive sprocket nest. The slack area can be further defined by a horizontal tangent of the top perimeter of a largest sprocket of a pedal sprocket nest and a largest sprocket in the drive sprocket nest. The slack area can be further defined by a vertical tangent on a forward point of the largest sprocket of the sprocket nest and a vertical tangent on a rearward point of a pedal sprocket. The pivot end can be carried by the frame forward an axis defined through the drive sprocket nest. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side view of a bicycle with a prior art rear derailleur for a bicycle shown. 
         FIG. 2  is a side view of a bicycle with reciprocating pedals with the derailleur of the present invention shown in the large sprocket position. 
         FIG. 3  is perspective view of the derailleur assembly with a chain slack take-up assembly oriented in the large sprocket feed position. 
         FIGS. 3A and 3B  are a top view and a side view taken from  FIG. 3 . 
         FIG. 4  is an exploded view of the derailleur assembly of  FIG. 3 . 
         FIG. 5A  is a partial plan view of the chain and derailleur wherein the small rear sprocket is engaged with the chain shown in dashed lines. 
         FIG. 5B  is the schematic view of  FIG. 5A , but with the large sprocket engaged with the chain shown in dashed lines. 
         FIG. 6  is an alternative embodiment derailleur assembly with a hub projection to allow pivot rotation in excess of 180 degrees. 
         FIG. 7  is another alternative embodiment for over 180 degrees rotation of the derailleur with a lanced spring support. 
         FIG. 8  is a view of a top swivel connector for the spring. 
         FIGS. 9A ,  9 B and  9 C are diagrammatic bottom views of the derailleur assembly showing the position of the feed chain path and the idler sprocket when the small, medium and large nest sprockets are engaged. The top portion of the chain is not shown for clarity. 
         FIGS. 10A ,  10 B and  10 C are schematic views of the rear sprocket nest and front drive sprocket and the space between the sprockets in which the derailleur moves; 
         FIG. 11  is a schematic view of a rear sprocket and front drive sprocket and the space between the sprockets in which the derailleur can be disposed; and, 
         FIGS. 12 and 13  are schematic views of aspects of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a side view of a prior art single derailleur assembly  202  moved by a shift mechanism  206  and guide cable  209  at the handle bar  208  used on a bicycle  200 . As can be seen the device is attached to the rear wheel hub and therefore positioned well below the rear wheel sprocket nest  201 . This enables the chain  204  to extend from the forward drive sprockets  203  rearwardly with the chain  204  forming two almost parallel straight lines to the rear wheel  205  sprocket nest  201  and derailleur assembly  202 . The derailleur assembly  202  is shown directly under the combination of the rear sprocket nest  201  and the rear axle  207  which means the lower part of chain  204  is positioned close to the ground as shown, but well above the lowest point on the pedal  210 . 
     The revolution of the pedals  210  is a continuous 360 degree movement with the lowest point of the pedal stroke clearing the ground by several inches, thus providing adequate ground clearance during a severe leaning turn. 
     With reference to  FIG. 2 , a reciprocating pedal bicycle  100  is illustrated. The bicycle has a low slung frame  110  with a pair of reciprocating foot pedals  102  that move up and down to provide forward propulsion. The ground clearance on both the frame and the bottom stroke of the foot pedals  102  is a mere few inches in some models. The reason for the low center of gravity is a desire to maintain superior ride stability with reduced rider&#39;s ability requirements. Those bicycles and in some versions, scooters can achieve excellent speeds which are best accomplished with the use of a gear shifting mechanism. As is readily apparent, conventional low hanging derailleur assemblies simply would drag on the ground unless the ground clearance was raised, sacrificing ride stability and the ability to design a low frame with a frame bottom adapted to ride down railings similar to techniques used in skateboarding. 
     To overcome this problem, an improved concept in gear shifting design was required that still utilized an existing gear shift mechanism  106  mounted on the handle bar  108  and a single shift cable  109 . 
     As shown in  FIG. 2 , and in greater detail in  FIG. 3 , a derailleur assembly  10  with a chain slack take-up assembly  20  is illustrated. A low-hung system such as scooters can not use a guide system that requires major clearance between the driven wheel center and ground, however, a system that utilizes the space beneath the top driving links of chain and above a line between the bottom of the largest nest sprocket  101  L and the bottom of the largest forward drive sprocket  103 . As illustrated, the entire derailleur assembly  10  is located between the space of the largest or major diameter rear sprocket  101 L of the sprocket nest  101  and the major diameter of the forward drive sprocket  103 . Accordingly, an upper line and a lower line drawn between these major diameter forward and rear sprockets is all the space needed for the chain take-up and derailleur assemblies. As shown, the derailleur assembly  10  does not occupy the ground clearance space as required in the prior art devices, but rather is packaged between the pair of major diameter sprockets. This is a significant breakthrough in gear shift mechanisms because it dramatically reduces the vertical space required for the chain. The design is useful not only in low hung vehicles, but in any bicycle. Consider how many derailleurs have been bent or broken when they hit a rock or downed tree when mountain biking This more protected position of the derailleur assembly  10  of the present invention dramatically reduces this type of risk. 
     As shown in  FIGS. 3 ,  3 A, 3 B and  4 , the basic element of the derailleur assembly is a pivot arm  11  located on a pin  12  fixed to the frame  110  or otherwise affixed to a bracket for mounting onto the frame  110  at an angle relative to the change sprocket assembly or rear sprocket nest  101 . The upper end of the pivot arm supports a guide roller  30  as well as the upper end of the take-up idler arm  20  with a take-up roller  40  at the bottom opposite end of the take-up idler arm  20 . The pivot pin  12  being at an angle tends to promote chain twist, but the sprockets themselves limit that motion to allow smooth change of position. Each of the roller sprockets  30  and  40  as shown has a small amount of gap between the take-up frame sides  21 ,  22  holding them which allow the rollers to  30  and  40  to shift slightly to reduce the amount of chain twist. 
     As shown in  FIG. 4  the rollers  30  and  40  are held between the frame sides  21 , 22  through openings  24 , 25  by threaded fasteners  19 A, 19 B with a small tubular bearing  18  that acts as the bearing in the openings  31 , 41  of the sprockets  30 , 40 , respectively. Fastener  19 A has a longer threaded end for securing the take-up idler arm  20  at the tapped opening  14 . The shift cable  109  is to be attached in the hole or opening  15 . As further shown the guide feed arm  11  has a bent over portion  16  with a pivot hole  17  into which fits a tubular bearing sleeve  12 A mounted on the pivot pin  12 . A single spring  50  is shown that is connected at one end  51  to a bent over tab  19  at the bottom end of the guide feed arm  11  and is further connected at an opposite end  52  onto a stop pin  26  on the take-up idler arm  20 . 
     In  FIG. 5A  and as is schematically shown in  FIG. 10A  (reversed looking from the opposite side), when a small sprocket  101 S is selected, a long section of chain  60  must be stored in a back-and forth configuration adjacent to or beside the derailleur sprocket nest  101 . In  FIG. 5B  and schematically in  FIG. 10B  but similarly reversed, when a large sprocket  101 L is selected, the pivot arm angle allows the guide roller to drop and receive the chain in almost straight line from the drive sprocket  103 . 
     A single spring  50  connected to the guide arm  11  and the angled pivot idler arm  20  supplies all the motion and take-up requirements for the system. When a chain  60  shift between small diameter sprockets in the sprocket nest is initiated, the chain  60  and the guide arm  11  are moved sideways out of line with the top driving section of chain to avoid interfering between chain sections moving in opposite directions. 
     Referring back to  FIGS. 3B and 4 , the pin  12  is shown attached to a mounting bracket  13  which is to be attached by welding or otherwise fixed to the frame  110 . The mounting bracket can be attached to the bottom of the frame, the side of the frame or the top of the frame. The base of the bracket  13  aligns with the frame  110 , and the pin  12  is projecting at an angle to the inclined surface of the bracket  13 . The inclined surface is oriented at an angle θ relative to the frame  110  as illustrated in FIGS.  9 A, 9 B, and  9 C. The angle θ should be equal to the tangent slope of the sprocket nest  101 , as shown in  FIGS. 9A ,  9 B and  9 C, the angle θ was 30 degrees. The angled guide arm  11  fits over the pin  12  and is rotatable about the pin  12  while it translates back and forth to line up with the sprockets in the nest  101 , and thus the guide arm  11  rotates forward and translates sideways. As shown in  FIG. 11 , one embodiment includes the mounting plate disposed along a plane generally orthogonal to the axis of the roller sprockets. 
     The angled guide arm  11  as shown has a projecting tab  9  with a hole  15  for securing the gear shifting rod or wire  109 . The tab  9  is located in close proximity to the pivot pin  12  to exactly duplicate the control wire motion of a conventional derailleur on bicycles. The guide arm  11  is twisted about 30 degrees so that the orientation of the chain  60  passing through the guide rollers  30  and  40 , shown as shallow toothed sprocket rollers, is substantially parallel to the drive sprockets and the rear sprockets of the nest  101 . 
     Referring to  FIGS. 10A ,  10 B and  10 C, the single spring  50  connected near or at the pivot  12  provides torque through the chain take-up idler arm  20 . When the chain  60  is on the major diameter rear sprocket  101 L, the spring provided torque is modest but when the guide arm  11  arm rotates to the smaller sprocket  101 S, the single spring  50  is stretched but acts over a shorter distance to provide torque. This means as the derailleur  10  is shifted upward through the gears, the spring  50  assist in the movement of the derailleur assembly  10  and insures the slack in the chain  60  is fully taken out by the chain take-up idler arm  20 . 
     Particular attention in  FIG. 10C  is called to the chain  60  when moved onto the smallest rear sprocket  101 S. In this position, the derailleur  10  is orientated such that the chain  60  can encircle substantially more than 180 degrees around the sprocket  101 S. As shown, almost 240 degrees of the smallest sprocket  101 S is engaged by the chain  60 . This feature is very beneficial in that the wrapping of the chain enables more sprocket teeth to be engaged. In a conventional low hung derailleur, 180 degrees of engagement is the best to be hoped for; and typically less than 180 degrees is experienced. The device according to this present invention enables far more teeth to be engaged. This means that even a smaller sprocket diameter can be used increasing the range of gear ratios available in a single nest. 
     As further illustrated in  FIG. 9B , the idler arm  20  is modified such that its orientation is centered or aligned with the middle sprocket  101 M, but as shown in  FIGS. 9A and 9C , is slightly canted at either extreme major or minor diameter sprockets at the roller feed end F sprocket  30  and the idler I sprocket  40  of the chain  60 . This creates a slight twist in the chain  60 , but because the guide rollers  30  and  40  have a gap or clearance when mounted in their respective frame sides  21 ,  22  in which they are held, they move laterally allowing the twist to straighten out relative to the sprocket to which it is attached. This along with the fact the single spring  50  provides less torque at both the top and the bottom of its range permits the chain  60  to straighten out. In one embodiments, the take up roller remains centered while the sprocket selector roller is slightly canted either at the extreme major diameter or minor diameter of the roller feed end. 
     Conventional derailleurs use massive spring force and therefore require precise parallel alignment. The derailleur  10  according to the present invention is greatly simplified in its design and thus can easily accommodate this small amount of chain twist. This assumes of course the adequate distance is provided between centers of the forward drive sprocket  103  and the rear stacked sprocket nest  101 , for example at least 10 inches, preferably 11 inches for a 0.5 inch bicycle chain and a six sprocket nest. This for a six speed derailleur allows a sufficient length of chain  60  to allow the twist angle to be small enough to straighten out due to the flexibility of standard bicycle chain. 
     A unique feature of this new derailleur design is that it can be used with a nested and stacked rear sprocket nest combined with a multiple forward drive sprocket nest and is capable of chaining not only the rear gears, but the forward gears as well. Presently, two conventional derailleurs are required to develop adequate speed change on bicycles. The single spring tension of the present derailleur  10  of the present invention allows it to move the chain at both locations. While this has obvious cost benefits, it is believed the present inventions use of multiple forward sprockets is not providing the benefit for the cost required. This is true because of the duplication of gear ratios available means little or no real advantage is achieved. 
     A 27 speed derailleur system on a bicycle with rotating pedals actually provides about 8 distinct speeds with multiple redundant combinations requiring two sets of derailleur devices providing the intermediate speeds. The present invention derailleur  10  can provide a single location with a wider gear tooth range to equal the total gear ratio of a two derailleur bicycle system without the redundancy, reduced stress and wear of the multiple rear sprocket set and safer chain safety near the pedals. 
     The prior art has a 27 speed with a three sprocket nest at the pedal driving one of 9 rear wheel sprockets at the rear wheel derailleur positions providing duplicate intermediate speeds. The derailleur  10  of this invention offers a compact single control derailleur system without redundancy with equal step up ratios between speeds. This provides reduced stress and wear on the sprockets due to greater wrap around for small sprockets and greater safety near the pedals when a single chain location must be guarded instead of a 3 chain wide protected area. 
     The earlier described derailleur of  FIGS. 1 through 5B  has the normal tension spring action and stops on the guide arm  11  to stop the pin  26  set to produce rotation of the pivot arm about a pivot limited less than 180 degrees rotation. When additional rotation is required, a hub projection  80  about or near the pivot can be located to rest against the spring coils and prevent or limit the tension spring coils from reaching the center of rotation of the pivot arm, as shown in  FIG. 6 . In this case one of the limit stops on the guide arm  11  can be moved or eliminated. This effect was demonstrated on a scooter derailleur system. Wherein the correct selection of pivot projection in the shape of a cylindrical hub  80  with an appropriately sized cylinder diameter allowed the rotation to go well past the 180 degree rotation to well over 240 degrees represented as angle .alpha. This increased rotation can be designed to fit the need. 
     This rotation over 180 degree for an arm with a single tension spring drive provides several alternate configurations. The equivalence of the cylindrical hub to develop over 180 degrees rotation of a spring return tension spring arm as shown in  FIG. 6  can be achieved by lancing a segment  90  of sheet metal adjacent to the hub or pivot and form it to project outwardly and act as a guide supporting the spring smoothly against the side coils of the tension spring, as shown in  FIG. 7  represented by the angle .beta. 
     As shown in  FIG. 8A , tension spring top swivel connector  86  may be built as a tube  86  with the ID swivel on a shaft or the pin  26  and the OD modified with a groove  88  to prevent the end twist loop of tension spring from falling off on a spring groove at the spring contact area. 
     As shown, the entire derailleur assembly  10  can occupy and function between the space defined as a pair of tangent lines between major driven and major diameter nest sprockets. However, it is important to note the ground clearance needed simply requires the derailleur and take-up assembly to occupy a space between the horizontal tangent lines of the largest sprocket diameters. 
     Furthermore, as shown in  FIGS. 9A ,  9 B and  9 C the rear sprocket nest has a conical linear tangency shown as straight but preferably, can be made having a non-linear tangency or a curved peripheral profile. In such a case, the straight line angle formed between the largest sprocket and the smallest sprocket can be used to set the pivot pin angle. This means the distance between the derailleur feed sprocket  30  and the different sized sprockets will vary. This variation can be accommodated without detriment due to the sole requirement of feeding the chain  60  onto a specific sprocket. 
     It is understood that because the system moves along a fixed angle set by the pivot, the sweep angle of the derailleur lies in a curved plane, accordingly the invention relies on a movement that uses this fact to set the appropriate variable distances between the derailleur guide feed roller sprocket  30  and the individual sprockets of the sprocket nest  101 . Adjustment of these different aspects of the invention can be varied. 
     Referring for  FIG. 12 , in one embodiment, mounting plate  13  is disposed along a plane generally parallel to the axis of the roller sprockets  20  and  30  and parallel to frame  110 . As shown, the mounting plate is attached to the bottom of the frame. In one embodiment, the mounting bracket can be attached to the top or side of the frame. The spring is a coil spring  300  with one end attached generally in the center of the take up idler arm and the other end attached to a connecting plate  302 . The connecting plate is rotatably attached to the idler arm  20  and attachment idler arm spring attachment point  304 . The connecting plate can include an angled portion  308  so that when the idler arm is moved, the roller sprockets move in a lateral direction in relation to a long axis of the frame causing the chain to move from sprocket to sprocket. The connector plate can also include angled portion  316  to properly position the guide arm. Referring to  FIG. 13 , in one embodiment, the chain guides  320   a  and  320   b  can be smooth. 
     An idler arm guard  310  can in attached to the connecting plate to assist in in preventing the connecting plate from interfering with movement by guiding the connecting plate along the mounting plate and frame. Cable  312   a  can be connected at cable connection point  314   a  so that when tension in applied to the cable the idler arm moves effecting the chain. In one embodiment, cable  312   b  can be attached a cable attachment point  314 b. 
     When the mounting plate is attached to the top of the frame, the upper roller sprocket can be disposed above the axis of the drive axle or rear wheel axle so that the derailleur is disposed in the shifting area. The lower roller can be disposed below the axis of the drive sprocket or rear wheel. Further, the cable can cause the upper roller to move orthogonal to the long axis of the frame by either pulling the guide arm forward or in one embodiment, rearward. 
     Variations in the present invention are possible in light of the description of it provided herein. While certain representative embodiments and details have been shown for the purpose of illustrating the subject invention, it will be apparent to those skilled in this art that various changes and modifications can be made therein without departing from the scope of the subject invention. It is, therefore, to be understood that changes can be made in the particular embodiments described which will be within the full intended scope of the invention as defined by the following appended claims.