Abstract:
Foot operated control linkages overlie the conventional control lever operating system on a spin turn mower to operate the mower in either forward or reverse directions. Each control linkage uses a foot pedal to control the speed of the mower while the control levers remain operable, even while the mower is moving, to change the forward or reverse direction of travel of the mower. The forward control linkage includes a first set of springs that pull the control levers against a stop while a second control spring prevents the first springs from moving the mower until the foot pedal is depressed. Thus, when the foot pedal is allowed to return to a non-depressed position, the mower will revert to a neutral detent position in which the mower is not powered in any direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims domestic priority on U.S. Provisional Patent Application Ser. No. 61/910,659, filed on Dec. 2, 2013, the content of which is incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to spin-turn lawn mowers that are driven by hydrostatic motors and operated through pivoted control levers, and more particularly, to a control linkage that controls the speed of operation of the lawn mower while allowing the pivoted control levers to be utilized for steering control and reverse operation. 
     BACKGROUND OF THE INVENTION 
     Spin turn lawn mowers are becoming popular for use in mowing lawns by both commercial lawn care operations and residential owners, displacing the conventional tractor-like mowers which are controlled via a steering wheel and a separate speed control. Spin turn lawn mowers are typically operated from the operator seat by moving one or both of a pair of pivoted control levers that are position in front of the operator seat for easy access by the operator. Forward movement of the lawn mower is accomplished by pushing forward on both pivoted control levers, while steering is accomplished by an unequal displacement of the control levers. For example, a forward moving left turn would be accomplished by pushing the right control lever forwardly more than the left control lever. The term “spin turn” is derived by the ability of these hydrostatically driven lawn mowers to be turned in place by pulling one control lever rearwardly while pushing the other control lever forwardly. 
     The structural configuration of many spin turn lawn mowers is that the engine is mounted on the frame of the mower over the rear wheels and behind the operator seat. The frame is supported by four wheels with the two rear wheels being driven by hydrostatic motors and pumps and the two front wheels being caster wheels that have very little weight on them. This weight distribution produces an inherent stability problem, particularly when the spin turn lawn mower is operated on wet slopes. The apparent problem with the conventional spin turn mower configuration is that the front wheels are not controlled. Thus, if either of the rear wheels loses traction, e.g. while traveling over a wet sloped lawn surface, the mower goes into a flat spin and often results in a loss of control of the lawn mower. 
     Manufacturers of spin turn lawn mowers have been addressing this control problem with hydrostatic control systems that are spring-biased to a neutral position so that releasing the control levers allows the control system to cease driving the mower; however, under many conditions, once the mower has started into a flat spin the mower will continue the motion until the surface conditions change. Walker Manufacturing of Fort Collins, Colo., manufactures a spin turn mower that has a single lever on the console for controlling the speed of operation of the mower and then a pair of levers centrally in front of the operator to vary the speed of each wheel individually to accomplish turns of the mower. The Walker Manufacturing control mechanism would limit the ability of an operator to make radical movements of the pivoted control levers which can cause traction loss for the mower. 
     In U.S. Pat. No. 5,725,068, granted on Mar. 10, 1998, to Theodore Smith, Jr., a mechanical linkage is disclosed to limit the forward speed of the hydrostatic drive to provide a more effective operation of the vehicle to rake sand traps on golf courses. An integrated steering wheel that controls the movement of the rear steering wheels is disclosed in U.S. Pat. No. 7,234,301, granted to Raymond Hauser on Jun. 26, 2007. Another version of a steering wheel control can also control the front wheels in addition to the rear steering wheels; however, such a steering mechanism is complicated in construction, although the steering mechanism does improve stability on sloped surfaces since the front wheels are placed under control by the steering mechanism. 
     The spring-biased neutral position for hydrostatic, spin-turn lawn mowers is disclosed in U.S. Pat. No. 7,634,953, granted to Brad Hoffman, et al on Dec. 22, 2009, and assigned to Deere &amp; Company. An electronic system for monitoring a hydrostatic drive, and for bringing the hydrostatic drive into a safe state when a control fault occurs, is disclosed in U.S. Pat. No. 8,386,135, issued to Michael Brand, et al, on Feb. 26, 2013. A steering mechanism and ground speed control for a windrower, a hay harvesting machine that is hydrostatically driven, is taught in U.S. Pat. No. 6,523,635, Issued on Feb. 25, 2003, to Robert Johnston, et al. 
     Furthermore, the operation of hydraulically driven mowers is difficult to control for novice operators. The sensitivity of the lever controls results in a turn in direction of movement when one of the control levers is moved without a corresponding movement of the other control lever. Novice operators are known to have difficulty in keeping the position of the two control levers at corresponding positions, resulting is further instability of the operation of spin turn lawn mowers. Accordingly, a cruise control linkage could be desirable to enable the spin turn lawn mower to be operated in a straight line while mowing. 
     It would be further desirable to provide a control mechanism for a spin turn lawn mower that improves stability of the mower without changing the overall configuration of the mower. It would also be desirable to provide a control mechanism that overlies the conventional pivoted control lever system for a spin turn lawn mower to separate the forward speed control from the steering control for the mower. Providing a foot control for operating the spin turn lawn mower in either a forward or a rearward direction would be of further desirability, particularly if the control levers could be operated to override the foot controls to provide directional control. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to overcome the disadvantages of the prior art by providing a control linkage that is cooperable with the conventional lever control mechanism on a spin turn mower to provide forward speed control through a foot pedal. 
     It is a feature of this invention that the forward speed control of the spin turn mower would be manipulated by operation of a user-friendly foot pedal instead of requiring the use of the conventional lever controls. 
     It is an advantage of this invention that the stability of the mower operation would be enhanced. 
     It is another feature of this invention that the control linkage overlays on the conventional lever controls of a spin turn mower. 
     It is another advantage of this invention that the changes in direction of the spin turn mower are accomplished through utilization of the conventional lever controls. 
     It is still another feature of this invention that the changes in direction for the spin turn mower are accomplished by slowing the operative speed on one side of the mower, rather than increasing the operative speed on one side of the mower. 
     It is another feature of this invention that the control linkage prevents the operator of a spin turn mower to change direction of travel by increasing the operative speed on one side of the mower. 
     It is still another advantage of this invention that controllability of the spin turn mower is enhanced by requiring changes in direction of travel to be accomplished by slowing operative speed on one side of the mower. 
     It is another advantage of this invention that the overall speed of operation of the spin turn mower does not increase as the mower is manipulated to change direction when the control linkage is utilized. 
     It is another object of this invention to provide a control linkage for the operation of a spin turn mower that utilizes a foot pedal to control forward speed of the mower while relying on the conventional operation of the lever controls to change direction and to move into a reverse direction. 
     It is still another feature of this invention that the lever controls can be used while the foot pedal is engaged to move the spin turn mower in a forward direction to change the direction of travel of the mower, or to override the foot pedal control linkage. 
     It is still another advantage of this invention that the operation of a spin turn mower can be intuitive and, therefore, more easily operated and controlled. 
     It is yet another object of this invention to provide an overlying control linkage that can operate to take command of the forward speed function of the conventional control levers on a spin turn mower, while permitting the control levers to be manipulated in a normal, conventional movement to affect turning of the mower in either direction, and to also retain the reverse movement operation of the control levers. 
     It is yet another feature of this invention that the control linkage includes a first spring configuration that urges the conventional control levers toward a maximum forward position and an offsetting second spring that maintains the hydraulic pumps operated by the conventional control levers in a neutral detent position until the foot pedal is depressed. 
     It is yet another advantage of this invention that the second control spring allows the foot pedal control to manipulate the conventional control levers into a forward moving direction, while maintaining the integrity of the internal bias of the hydraulic pumps to urge the system into the neutral position as intended by the design of the hydraulic system. 
     It is a further advantage of this invention that when the spin turn mower encounters an unstable situation and starts into a flat spin, the operator need only to raise his/her foot to allow the foot pedal to retract to its rearwardmost position and stop the driving of the mower, which will help the mower to cease spinning and return the mower to proper operational control by reason of the foot pedal tension spring pushing the sleeves against the stops to push the control levers rearwardly into the neutral position. 
     It is still another advantage of this invention that the natural instinct to raise one&#39;s foot to cease forward speed, which is greater than the instinct to manipulate one&#39;s hands to change forward speed, can be utilized in a panic situation to stabilize the operation of a spin turn mower. 
     It is a further feature of this invention that the overlying control linkage can be installed as an after-market kit on existing spin turn mowers, as well as incorporated into the factory control linkage therefor. 
     It is still another object of this invention to provide a foot control for operating a spin turn lawn mower in a reverse direction during which the control levers can still be manipulated to change the direction of movement of the mower. 
     It is another feature of this invention that the foot control overlying the conventional hydraulic lever control system for a spin turn mower will provide a cruise control operation. 
     It is yet another object of this invention that the cruise control operation associated with a foot operated control linkage can be applied to other configurations of spin turn mowers, including one where the operator stands during operation of the mower. 
     It is another advantage of this invention that the operation of the foot control mechanism results in a straight line operation of the spin turn mower. 
     It is still another advantage of this invention that the foot control mechanism enables a novice operator to maintain a more stable straight line control over a spin turn mower. 
     It is still another feature of this invention that the foot controls can be configured to selectively move the spin turn mower in both forward and rearward directions while allowing the hydraulic control levers to be utilized to change direction of movement in either the forward or rearward direction. 
     It is a further object of this invention to provide a control linkage for a spin turn mower having a pair of control levers operatively connected to a hydraulic drive mechanism to power the movement of the spin turn mower, each control lever being pivotally mounted about a hinge point such that a forward movement of said control levers from a central neutral position results in a forward powered movement of the spin turn mower in which a foot pedal is pivotally supported for movement in a fore-and-aft direction, the foot pedal being operatively connected to said control levers to control speed of forward movement of the spin turn mower, and in which a connecting linkage permits movement of each said control lever in a forward or rearward direction to effect a change of direction of travel of the spin turn mower. 
     These and other objects, features and advantages are accomplished according to the instant invention by providing control linkages that overlie a conventional control lever operating system on a spin turn mower to operate the mower in either forward or reverse directions. Each control linkage uses a foot pedal to control the speed of the mower while the control levers are operable, even while the mower is moving, to change the direction of travel of the mower. The forward control linkage includes a first set of springs that pull the control levers against a stop while a second control spring prevents the first springs from moving the mower until the foot pedal is depressed. Thus, when the foot pedal is allowed to return to a non-depressed position, the mower will revert to a neutral detent position in which the mower is now powered in any direction. The reverse control linkage also permits the conventional control levers to be used to change direction of the mower in a reverse direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a left, front perspective view of the frame of a spin turn lawn mower with the conventional pivoted control levers shown and the overlying forward and rearward speed control linkages incorporating the principles of the instant invention, the conventional power transmission components, operator seat, mower deck and other components of the spin turn lawn mower being removed for purposes of clarity; 
         FIG. 2  is a left side elevational view of the frame and controls as shown in  FIG. 1 ; 
         FIG. 3  is a front elevational view of the frame and controls as shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a top plan view of the frame and controls as shown in  FIGS. 1-3  representative rear drive wheels and associated hydraulic motors being shown in phantom; 
         FIG. 5  is a right side perspective view of the frame and controls as depicted in  FIG. 1 ; 
         FIG. 6  is a left side perspective view of the frame and controls as depicted in  FIG. 5 ; and 
         FIG. 7  is a right, rear perspective view of the frame and controls as depicted in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, the structural components of the frame of a spin turn lawn mower can best be seen. Any left and right references are used as a matter of convenience and are determined by standing at the rear of the frame F and facing the forward direction, the normal direction of travel, with the foot control and foot rest being mounted at the forward end of the frame F. The conventional configuration of the spin turn lawn mower on which the overlying control mechanism  20 , incorporating the principles of the instant invention, is based can be seen in U.S. Pat. No. 7,634,953, granted to Brad Hoffman, et al on Dec. 22, 2009, the content of which is hereby incorporated by reference in its entirety. 
     With reference to the drawings and, specifically, with reference to  FIG. 1 , the frame components of a spin turn lawn mower as depicted in the aforementioned U.S. Pat. No. 7,634,953, the content of which is incorporated herein by reference, is shown. Such components of the frame  10  would include a pair of longitudinally extending frame rails  12  interconnected at the forward ends thereof by a foot rest  14 . The forward ends of the frame rails  12  are formed with caster mounts  13  to allow the mounting of the front caster wheels (not shown). The rear drive wheels  11  are supported on the rear ends of the frame rails, along with the engine (not shown), hydraulic pumps (not shown) and hydraulic motors  19 . Additional frame members (not shown) have been removed from the drawings for purposes of clarity with respect to the instant invention; however, one skilled in the art will recognize that certain components of the instant invention described in greater detail below require anchoring on such additional frame components. 
     The hydraulic pumps (not shown) are controlled through manipulation of the control levers  15   a ,  15   b  in a forward or rearward direction from the neutral position depicted in the drawings. As noted in the aforementioned U.S. Pat. No. 7,634,953, this neutral position is spring-biased so that a release of the control levers  15   a ,  15   b  will result in the hydraulic pumps being placed in the neutral position so that the pumps do not power the associated hydraulic motors  19  to propel the frame  10  of the spin turn mower. The control levers  15   a ,  15   b  are pivotally mounted on the frame  12  at respective pivots  16 . Thus, as each control lever  15   a ,  15   b  is pushed forwardly, the lower ends thereof move rearwardly. As a result, the connecting rods  17 , extending from the lower ends of the control levers  15   a ,  15   b  stroke the hydraulic pumps (not shown) appropriately to drive hydraulically the hydraulic motors  19  to propel the spin turn mower forwardly. 
     In the conventional configuration, the further forwardly the control levers  15   a ,  15   b  are pushed the faster the spin turn mower moves in the forward direction. The same applies to the rearward movement of the mower. The further rearwardly the control levers  15   a ,  15   b  are pulled toward the operator, which is seated immediately behind the control levers  15   a ,  15   b , so as to have convenient access thereto, the faster the mower moves rearwardly. One skilled in the art will recognize that the conventional controls of the spin turn mower are configured that the mower will have a maximum forward speed that is significantly greater than the maximum rearward speed. Turning the mower is accomplished by moving the respective control levers  15   a ,  15   b  at different relative positions with respect to the operator. 
     For example, pushing the left control lever  15   a  further forwardly than the right control lever  15   b  will result in the mower moving forwardly and simultaneously turning to the right. By pulling the left control lever  15   a  rearwardly and pushing the right control lever  15   b  forwardly, or vice-versa, the left rear wheel will rotate in reverse while the right rear wheel will rotate forwardly, resulting in the mower doing a spin turn in place. The dampening cylinders  18  are provided to smooth out the movement of the control levers  15   a ,  15   b  so that radical movement of the control levers  15   a ,  15   b  is restricted. 
     A primary object of the instant invention is to provide an overlying control linkage  20  that can operate to take command of the forward speed function of the control levers  15   a ,  15   b , while permitting the control levers  15   a ,  15   b  to be manipulated in a normal, conventional movement to affect turning of the mower in either direction, and to also retain the reverse movement operation of the control levers  15   a ,  15   b . A secondary object of the instant invention is to provide a cruise control function that will enable a novice operator to operate the spin turn mower easily in a forward straight line of operation. Another object of this invention is to provide a foot control that will operate the mower in a rearward direction while allowing the operator to manipulate the control levers  15   a ,  15   b  in a rearward direction to control changes in direction of travel. 
     The forward control linkage  20  includes an extension  22  to each of the control levers  15   a ,  15   b  to extend the downward length of the control levers  15   a ,  15   b  in order to balance the movement of the other components of the control linkage  20 , as will be described in greater detail below. The forward control linkage  20  also includes a transverse rock shaft  25  that has a pair of downwardly extending mounting tabs  26  corresponding to the opposing extensions  22 . Each mounting tab  26  is formed with a sleeve  27  that slidingly receives a connecting rod  23 . Each connecting rod  23  a positionably adjustable stop, such as a nut  24  threaded onto the end of the rod  23 . The rearward end of each the connecting rod  23  is pivotally connected to the corresponding extension  22  such that the movement of the control levers  15   a ,  15   b  results in a corresponding movement of the connecting rods  23 . 
     The forward control linkage  20  further includes an upwardly extending mounting tab  28  that is fixed to the rock shaft  25  and rotates therewith, as will be described in greater detail below. Extending forwardly from the upwardly extending mounting tab  28  is a longitudinally extending control rod  29  that is pivotally connected to a foot control pedal  30  pivotally supported on the foot rest  14 . A tension spring  32  interconnects the foot pedal  30  and the mower frame  10  to bias the foot pedal into a rearward position, corresponding to a zero speed position. In other words, the foot pedal  30  is biased to the neutral position by the tension spring  32 . 
     The forward control linkage  20  further includes a pair of control lever tension springs  35  that bias the control levers  15   a ,  15   b  toward a full speed forward position, i.e. urging the control levers fully forwardly relative to the operator. In this configuration, the springs  35  pull the control lever extensions  22  rearwardly, thus pushing the control levers  15   a ,  15   b  forwardly, until the stop  24  engages the sleeve  27  carried on the mounting tabs  26  and biases a rotation of the rock shaft  25  in a manner to urge the upwardly extending mounting tabs  28  forwardly, which serves to urge the foot pedal  30  forwardly toward the foot rest  14 . However, because the foot pedal tension spring  32  exerts a greater biasing force on the foot pedal  30  to pull the foot pedal rearwardly than the two control lever tension springs  35  exert to push the foot pedal forwardly, the foot pedal  30  does not move forwardly as a result of the bias force exerted by the tension springs  35 . The tension springs  35 , however, do have the effect of keeping the stops  24  engaged with the sleeves  27 , until steering the mower is desired, as will be described in greater detail below. 
     One key to the operation of this particular control linkage configuration is that the hydraulic pumps are configured with a neutral detent and an internal biasing force that urges the control levers  15   a ,  15   b  into the neutral position. The control springs  35  exert a substantial biasing force that is capable of overcoming the internal bias of the hydraulic pumps that keep the system centered in neutral, but the more powerful foot pedal tension spring  32  offsets the force exerted by the control springs  35  to keep the system centered in the neutral position as intended by the design of the hydraulic system. 
     When the operator desires to move the mower forwardly, the operator depresses the foot pedal  30  toward the foot rest  14 , overpowering the bias force exerted by the foot pedal tension spring  32  such that the force exerted by the operator combined with the bias force exerted by the control lever tension springs  35  is greater than the bias force from the foot pedal spring  32 . The depressing of the foot pedal  30  pulls the upwardly extending mounting tab  28  and interconnecting control rod  29  forwardly and results in a rotation of the rock shaft  25  to move the downwardly extending mounting tab  26  rearwardly. Because of the force exerted on the extensions  22  by the control lever tension springs  35 , the stop  24  stays engaged with the sleeve  27  and allows the control levers  15   a ,  15   b  to move forwardly, and stroke the hydraulic pumps to move the mower forwardly at a speed corresponding to the extent of depression of the foot pedal  30 . According, the further the foot pedal  30  is depressed, the faster the mower is powered forwardly. 
     One skilled in the art will recognize that the action of depressing the foot pedal  30  causes an equal displacement of the two control levers  15   a ,  15   b  so that the mower is moved forwardly ahead along a straight line. Accordingly, the use of the foot pedal  30  results in a cruise control operation that helps a novice operator in controlling the operation of the spin turn lawn mower. When a change in forward direction is desired, the operator need only pull rearwardly the control lever on the same side of the mower as the desired turn direction. For example, if the operator wants to turn to the left as the mower is moving forwardly as a result of the operator depressing the foot pedal  30 , the operator would pull the left control lever  15   a  slightly rearwardly to slow slightly the left hydraulic motor and cause the mower to turn to the left. 
     Using the example of a left turn as described above, the movement of only the left hand control lever  15   a  rearwardly causes the connecting rod  23  to push forwardly through the corresponding sleeve  27  and push the stop  24  at the end of the connecting rod  23  forwardly of the sleeve  27 , while the opposing connecting rod  23  stays in the selected position with the stop  24  thereof engaged with the corresponding sleeve  27 . Accordingly, the receipt of the connecting rods  23  through the sleeve  27  carried at the end of the downwardly extending mounting tab  22  allows the control levers  15   a ,  15   b  to continue in use to change direction of forward travel of the mower in substantially the same manner as is conventional for known spin turn lawn mowers. However, one skilled in the art will recognize that changes in direction of travel in a conventional spin turn mower can be accomplished also by pushing forwardly the control lever opposite the desired direction of turn to speed up the opposite hydraulic pump. Accordingly, the forward directional turns can only be accomplished through the control linkage  20  by slowing the same hydraulic pump as the desired turn. 
     In addition to the forward control linkage  20 , a reverse control linkage  40  is provided to move the spin turn mower in reverse. One skilled in the art will recognize that the reverse control linkage  40 , as will be described in greater detail below, utilizes a separate foot pedal  41  from the forward direction foot pedal  30 ; however, the pedals  30 ,  41  could be combined or re-positioned from that shown in the drawings to provide the same function as described below. The operation of the reverse control linkage  40  operates on the same general principle as the forward control linkage  20 , a foot pedal is manually operated to control the movement of the hydraulic control levers  15   a ,  15   b  through connecting rods having stops mounted thereon that allow the operation of the hydraulic control levers  15   a ,  15   b  to be utilized to affect changes in direction. 
     The reverse control linkage  40  includes a transverse bar  42  to which the reverse foot pedal is rigidly affixed. The transverse bar  42  is supported for pivotal movement by support brackets  43  located on the opposing frame rails  12  such that when the reverse foot pedal  41  is depressed the reverse foot pedal  41  and transverse bar  42  pivot with the support brackets  43  to move in a forward direction. A pair of laterally spaced connecting rods  45  is connected to the transverse bar  42  by sleeves  44  that slidably receive the connecting rods  45 . Each of the connecting rods  45  have a stop member  46  mounted at the forward end thereof such that the forward movement of the transverse bar  42  moves the sleeves  44  forwardly with the transverse bar  42  and the stop members  46  pull the connecting rods  45  forwardly. 
     The rearward ends of the connecting rods  45  are connected to the extensions  22  on the hydraulic control levers  15   a ,  15   b  adjacent to the connections of the connecting rods  23 . Thus, the forward movement of the connecting rods  45 , as described above, results in a rearward movement of the hydraulic control levers  15   a ,  15   b  that is associated with the rearward movement of the spin turn lawn mower. The positioning of the stop members  46  at the forward ends of the connecting rods  45  enables either of the hydraulic control levers  15   a ,  15   b  to be pulled rearwardly beyond the movement induced by the movement of the reverse foot pedal  41 . One skilled in the art will recognize that the movement of the hydraulic control levers  15   a ,  15   b  induced by the reverse foot pedal  41  is not intended to force the mower to move rearwardly at the maximum possible reverse speed permitted by the hydraulic motors. Most operators infrequently move a spin turn mower in reverse and when reverse is utilized the speed and duration of the reverse movement is typically minimal. 
     Rearward movement of the spin turn lawn mower can also be accomplished in the same manner as is conventional for such mowers, i.e. the operator pulls rearwardly on the control levers  15   a ,  15   b  until the control levers  15   a ,  15   b  are rearward of the central neutral position, irrespective of whether the reverse foot pedal  41  is depressed. Even if the operator would forget to release the forward foot pedal  30 , the manual movement of the control levers  15   a ,  15   b  rearwardly of the position corresponding to the depression of the forward foot pedal  30  will slow the mower&#39;s forward speed and allow the mower to be operated in reverse in a conventional manner known for spin turn lawn mowers. Preferably, with the foot pedal  30  released, the foot pedal spring  32  will return the foot pedal  30  to its rearwardmost position, corresponding to a central neutral position for the hydraulic control levers  15   a ,  15   b  and allow any additional rearward movement of the control levers  15   a ,  15   b  to operate the mower in a conventional manner known for spin turn mowers. The further rearward movement of the control levers  15   a ,  15   b  results in a movement of the connecting rods  23  through the sleeve  27  carried at the distal end of the downwardly extending mounting tabs  26  with the stops  24  pushing forwardly of the corresponding sleeves  27 . The further rearward movement of the control levers  15   a ,  15   b  also results in a forward movement of the connecting rods  45  through the sleeves  44  carried by the transverse bar  42 . 
     Once the controlled rearward movement of the mower is completed, the operator need only release the reverse foot pedal  41 , and any grip the operator might have on the control levers  15   a ,  15   b , to allow the control lever tension springs  35  and the internal biasing of the hydraulic pumps to return the hydraulic drive mechanism into the central neutral position. Once the foot pedal  30  has been released to allow the foot pedal  30  to be raised to the maximum rearward position, the aforementioned relationships between the tension springs  32 ,  35  are such that the mower drive mechanism is returned to the neutral position. 
     In the event the spin turn mower encounters an unstable situation and starts into a flat spin, a panicked operator need only raise his/her foot to allow the foot pedal to retract automatically to its rearwardmost position to stop the driving of the mower, which will help the mower to cease spinning and to return the mower to proper operational control by reason of the foot pedal tension spring  30  pushing the sleeves  27  against the stops  24  to push the control levers  15   a ,  15   b  rearwardly into the neutral position. One skilled in the art will recognize that the instinct to raise one&#39;s foot to cease forward speed is greater than the instinct to manipulate one&#39;s hands to change forward speed in a panic situation. 
     The overlying control linkages  20 ,  40  serve to control the overall forward and rearward speeds of the spin turn mower, removing that function from the exclusive operation of the control levers  15   a ,  15   b . Changing direction of travel in either the forward or rearward direction is simply accomplished through manipulation of a single control lever  15   a ,  15   b . In the operation of a prototype control linkage  20 , changing the forward direction of travel was accomplished through the use of a single hand of the operator resting on the two control levers  15   a ,  15   b  with a simple turn of the wrist to nudge the selected control lever  15   a ,  15   b  to cause a turning of the spin turn mower. 
     While the above-described control linkages  20 ,  40  can be provided as a kit or kits to retrofit existing spin turn mowers having a central neutral detent, one skilled in the art will recognize that such control linkages could be incorporated into the original manufacture of spin turn mowers. Still further, the function of the aforementioned control linkages  20 ,  40  can be incorporated into the hydraulic drive mechanism for a spin turn mower without requiring all of the component parts of the control linkage, as are described above. For example, a foot pedal  30  can be incorporated into a spin turn mower that either mechanically or electronically controls the forward speed of the spin turn mower, allowing the control levers  15   a ,  15   b , or other steering devices, such as a T-bar control or a conventional steering wheel control, to be manipulated to change direction of travel, and/or to effect a reverse direction of travel. 
     The basic premise is that the forward speed control is separated from the steering control such that the forward speed control is attained by manipulation of the foot pedal  30 , while the control levers  15   a ,  15   b  are utilized to control the changes in direction of travel by trimming the speed of one of the hydraulic drive motors over the other hydraulic drive motor. Similarly, the rearward movement of the mower is separated from the steering control as well. As a result, a more precise steering control can be obtained while reducing the risk of overcontrolling the control levers in a panic situation. Accordingly, the principles of the instant invention can be adapted for use as original equipment on a spin turn lawn mower, either as a mechanical linkage or built into the hydraulic control mechanism, and can be utilized with lever controls, T-bar controls or conventional steering wheel controls for spin turn lawn mowers. 
     One skilled in the art will recognize upon a reading of this disclosure that the drawings exaggerate the orientation of the connecting rods  23 ,  45  relative to sleeves  27 ,  44  so that the stops  24 ,  46  can be seen. In the drawings, the respective positions of the stops  24 ,  46  relative to the corresponding sleeves  27 ,  44  are the equivalent of the foot pedals  30 ,  41 , respectively, being released to return to its home position while the control levers  15   a ,  15   b  are manipulated to move the spin turn mower for changes in forward or reverse directions, since both stops  24 ,  46  are shown pushed forwardly of the corresponding sleeves  27 ,  44  with the control levers  15   a ,  15   b  being equally displaced relative to the frame  10  of the spin turn mower. 
     In summary, the forward and rearward control linkages  20 ,  40  provide an alternative mechanism for operating the forward and rearward movements of a spin turn lawn mower in a manner that does not prevent the normal, conventional utilization of the hydraulic control levers  15   a ,  15   b  to move the mower in either the forward or rearward directions. With both the forward and rearward control linkages  20 ,  40  installed, the operator can ignore the control linkages  20 ,  40  and completely control the lawn mower using the hydraulic control levers  15   a ,  15   b . When the control levers  15   a ,  15   b  are pushed forwardly to move the mower forwardly, the stops  24  on the connecting rods  23  engage the sleeves  27  and pull the control rod  29  forwardly to cause the foot pedal  30  to depress. Simultaneously, the reverse connecting rods  45  also pull rearwardly to engage the stops  46  with the sleeves  44  and cause the transverse bar  42  to pivot rearwardly, which in turn forces the reverse foot pedal  41  to push upwardly. The rearward movement of the control levers  15   a ,  15   b  to cause the mower to move rearwardly simply pushes the connecting rods  23 ,  45  forwardly, due to the connection thereof below the hinge point, whereupon the connecting rods  23 ,  45  simply slide through the respective sleeves  27 ,  44  separating the stops  24 ,  46  from the sleeves  27 ,  44 . 
     It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention. 
     For example, farm machinery often utilizes hydraulic drives with lever controls, including hay mowing machines commonly referred to as windrowers. Such windrowers are often controlled through the manipulation of hydraulic controls levers as described above with respect to spin turn mowers. Such windrowers would also benefit from cruise control operations that are provided by the foot-operated control linkages described above.