US3658343A

US3658343A - Contourable green with randomly operable contour selection

Info

Publication number: US3658343A
Application number: US782528A
Authority: US
Inventors: Albert P Rogers; Robert M Conklin; Bradford J Baldwin
Original assignee: Brunswick Corp
Current assignee: Brunswick Corp
Priority date: 1968-12-10
Filing date: 1968-12-10
Publication date: 1972-04-25
Anticipated expiration: 1989-04-25

Abstract

A contourable putting green ideally suited for use in indoor golf games including a contourable platform having an upper putting surface thereon and secured by tensioned springs to a parallel series of spaced, pivotally interconnected movable beams pivotally connected intermediate their ends to stationary beam support members. Motor driven self-reversing hydraulic jacks move the beams differentially to distort the platform and thereby vary the contour of the green. An electronic control circuit is provided for each jack, including an RC timer circuit having a discrete time constant, and is arranged so that operation of all of the jacks is simultaneously initiated by a master control switch, yet the operation of each jack continues to operate independently over its discrete period of time; resulting in unsynchronized movement of the various portions of the platform and a putting surface of substantially random contour.

Description

Rogers et a1.

[ 1 Apr. 2, 197

[s41 CONTOURABLE GREEN WITH RANDOMLY OPERABLE CONTOUR SELECTION Dolce ..273/l76 H X Primary Examiner-George J. Marlo Attorney-Hofgren, Wegner, Allen, Stellman and McCord [5 7] ABSTRACT A contourable putting green ideally suited for use in indoor golf games including a contourable platform having an upper putting surface thereon and secured by tensioned springs to a parallel series of spaced, pivotally interconnected movable beams pivotally connected intermediate their ends to stationary beam support members. Motor driven self-reversing hydraulic jacks move the beams differentially to distort the platform and thereby vary the contour of the green. An electronic control circuit is provided for each jack, including an RC timer circuit having a discrete time constant, and is arranged so that operation of all of the jacks is simultaneously initiated by a master control switch, yet the operation of each jack continues to operate independently over its discrete period of time; resulting in unsynchronized movement of the various portions of the platform and a putting surface of substantially random contour.

8 Claims, 3 Drawing Figures PATENTEB APR 2 5. I972 SHEEI 1 EF 2 CONTOURABLE GREEN WITH RANDOMLY OPERABLE CONTOUR SELECTION BACKGROUND OF THE INVENTION Because of the ever-increasing popularity of. the game of golf, there have been a number of proposals for indoor golf games as of late to relieve the congestion on natural, outdoor courses. Such indoor games are also intended to permit golfers to play golf year around in some of the less temperate zones and in both respects, such indoor golf games have been suc cessful to a greater or lesser degree.

The primary factor affecting the degree of success of an indoor golf game resides in the degree of sophistication of the equipment with respect to realistically simulating conditions experienced by a golfer on an outdoor course. In one commercialized game, realism has been substantially enhanced by providing a so-called contourable green to provide the indoor golfer with realism in around the green and on the green play.

Such a contourable green generally comprises a relatively rigid but distortable platform having an upper putting surface on which the golfer may walk and putt a golf ball towards a cup. Additionally, various fringe areas and sand traps around the putting surface may be provided for enhancing the realism of on the green play and in order to insure realism, such contourable greens are relatively large in size. However, due to the fact that such greens must be housed in a building, it is somewhat impractical to make a contourable green of a size that completely proximates the size of a natural outdoor green. As a result, such greens have typically been long and narrow with the result that for anything other than short length putts, the golfer may be putting from virtually the same position on the green for each shot.

In order to preclude the golfer from having substantially the same putt for each hole for 18 different holes in an indoor game, heretofore such greens have utilized programming devices for controlling the contour thereof to provide a distinct green contour for each of the 18 holes. However, when a golfer plays an indoor game with a great deal of frequency, each time he plays the same hole, he may have substantially the same putt round after round.

It will be recognized that such will not normally occur on an outdoor course. Specifically, while the contour of an outdoor green is never changed, the cup location is frequently changed so that each time the golfer plays the particular hole, he will be faced with a different putt due to, at the very least, a change in cup location.

While cup locations on an indoor green could be changed, but not without difficulty, any substantial change in cup location would have a tendency to diminish the amount of putting surface available for extremely long putts and would cause untold confusion with respect to the use of grid-like markings for fringe areas or green areas at which the golfer places the ball in accordance with infonnation provided to him by the remainder of the indoor golf game system.

As a result, a golfer playing an indoor golf game has heretofore been faced with some monotony in putting each time the same hole is played with the net result being a lesser degree of realism in simulating outdoor play.

SUMMARY OF THE INVENTION It is the principal object of the invention to provide a new and improved contourable green for use in golf games.

More specifically, it is an object of the invention to provide a new and improved contourable green wherein the contour of the green during its use as a golf game is randomly selected.

Another object is the provision of a contourable green including a supporting structure, a platform having an upper playing surface mounted on the supporting structure, motor means for moving the supporting structure to distort the platform and thereby the playing surface and control means for the motor means for randomly operating the motor means so that the contour of the playing surface is randomly selected.

III

A further object is the provision of a contourable green such as that set forth in the preceding paragraph wherein the motor means comprise at least two powered means secured to the supporting structure at spaced locations and the control means comprise two circuits, one for each of the powered means, for energizing the associated power means, with one of the control circuits being operative to energize its associated power means for a longer period of time than the other circuit.

Another object is the provision of a contourable green such as that set forth above wherein the power means include hydraulic cylinders and the control circuits include a RC network that determines the period of energization of the hydraulic cylinders.

Other objects and advantages will become apparent from the following specification taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a room housing a contourable green made according to the invention;

FIG. 2 is a side elevation of the contourable green structure; and

FIG. 3 is a schematic of the random control circuitry utilized in the green.

DESCRIPTION OF THE PREFERRED EMBODIMENT An exemplary embodiment of a contourable green made according to the invention is shown in the environment of a room, generally designated 10, housing indoor golf game equipment. The room 10 includes side walls 12 and 14 and

end walls

16 and 18 and an access opening (not shown) into the room is also provided.

The side walls 12 and 14 have a significantly greater length than the

end walls

16 and 18 and may be on the order of as much as feet long. The

end walls

16 and 18 may have a length in the neighborhood of 25 to 30 feet. The purpose of the elongated configuration of the room 10 is such that a green may be housed therein which may provide putts of up to as long as 60 feet as may be typically found on outdoor greens and yet minimize overall space requirements.

Within the room 10 is a contourable green which, in the exemplary embodiment, consists of a fixed portion 20 and a contourable portion 22. The fixed portion 20 is elevated above the floor 24 of the room and will generally have its playing surface 26 in a horizontal plane. However, for the sake of realism, there may be provided a depressed playing surface 28 in the fixed portion 20 and separated from the playing surface 26 by means of a randomly contoured wall 30. In such a case, the depressed playing surface 28 may consist of finely divided sand particles and the randomly contoured wall 30 will be arranged to slope upwardly and toward the contourable portion 22 to define a bunker from which sand shots may be played.

The actual putting surface 36 may be formed of a short pile carpet or the like and is defined by a closed line 34. The putting surface 36 is located primarily on the contourable portion 22 although a small portion thereof is located on the fixed portion 20, the latter serving as a starting point for extremely long putts. A conventional golf cup 38 including a flag stick 40 bearing a pennant 42 is located in the putting surface 36 relatively remotely from the fixed portion 20 and relatively close to the end wall 16. Preferably, a spacing on the order of about 15 feet from the cup 38 to the end wall 16 is preferable in order to allow balls played from a point adjacent the end wall 18 to roll significantly past the cup 38 if the golfer strikes them with too much force.

A fringe area 44 which may be formed of a carpeting having a somewhat longer pile than the putting surface 36 completely surrounds the putting surface 36 on both the fixed portion 20 and on the contourable portion 22. At various locations on the fringe 44, specialized lie mats for chipping purposes may be located. One such lie mat is illustrated at 46 and interposed between the same and the putting surface 36 is a small corrugated surface 48 which will force the golfer to actually chip the shot from the lie mat 46 as opposed to putting it across the fringe 44 to the green. The use of such a corrugated surface 48 enhances the realism of the game in that it compells an actual chip shot as opposed to a mere putt from certain locations off of the putting surface 36.

Referring now to FIGS. 1 and 2, the details of construction of the green will be described. The interface between the fixed portion 20 and the contourable portion 22 is defined by a suitable framework 50 which mounts a spaced pair of pivots 52 and 52' having their pivot axes in a horizontal plane and extending generally transverse to the direction of elongation of the room 10. A pair of pivot arms 54 and 54' are mounted for rotation about the pivots 52 and 52' and in turn mount a pair of spaced, conventional l-

beams

56 and 56 for pivotal movement about the pivot points 52 and 52'. As the l-beam structures are identical only one will be described. At the end of each l-beam 56 opposite the pivot arm 54, there is located a second pivot arm 58, each of which mounts a pivot 60. The pivot 60 pivotally interconnects each l-beam 56 to a respective link 62 which in turn mounts a second pivot point 64. The pivot point 64 of each link 62 is, in turn, engaged with a pivot arm 66 on respective ones of a pair of similar, conventional, spaced l-beams 68.

Each of the l-beams 68 is suspended above the floor 24 by means of a pivotal connection 70 at the approximate midpoint of each l-beam 68. The pivotal connection 70 has a horizontal axis running transverse to the direction of elongation of the room 10 and is maintained in an elevated position with respect to the floor 24 by a suitable framework 72.

As a result of the just-described construction, it will be apparent that there are two green supporting beam structures each in turn comprised of two I-

beams

56 and 68 which are pivoted together at their point of adjacency with each l-beam 56 further pivoted to a fixed structure by pivot point 52. Mounted on the two beam structures comprised of the

lbeams

56 and 68 is a rigid but distonable platform. In the exemplary embodiment, the rigid but distortable platform is formed of% inch plywood sheets 74 mounted on two-by-fours 76 which extend across the spaced beam sections defined by the l-

beams

56 and 68. By means of relatively heavy springs 78 secured by any suitable means to either the plywood sheets 74 or the two-by-fours 76, the platform is resiliently secured to the l-

beams

56 and 68. Specifically, the springs 78 are interposed between the platform and the l-

beams

56 and 68 and secured to the latter by means of cleats 80. As a result of the just-described construction, it will be apparent that movement of the I-

beams

56 and 68 will yieldably draw the platform including the plywood sheets 74 and the two-by-fours 76 with the l-

beams

56 and 68 to distort the platform thereby providing something other than a planar contour for putting and chipping purposes.

Such movement of the l-

beams

56 and 68 and their counterparts 56 and 58' is provided by means of double acting

hydraulic jacks

82 and 82 which are pivotally attached such as at 84 to a bracket 86 secured to the floor 24. As the operation of the

jacks

52 and 82 are identical, the operation of jack 82 alone will be described. The double acting hydraulic jack 82 has its piston rod 88 secured to either one of the pivots 60 or 64 at the interface between the I-

beams

56 and 68.

As a result of the just-described construction, it will be appreciated that application of fluid under pressure to the hydraulic jack 82 will either cause the adjoining ends of the

lbeams

56 and 68 to be raised or lowered thereby elevating or depressing that portion of the platform immediately above the cylinders 82. Because of the presence of the pivot 70, that portion of the platform over the right-most end of the I-beam 68 as viewed in FIG. 2 will be depressed or raised then the portion of the platform over the cylinders 82 is raised or depressed, respectively. During such movement, by virtue of the resilient connection of the platform to the beams, the platform will tend to separate from the beams so that there is not an abrupt discontinuity at the joint between the

beams

56 and 68 resulting in the platform, with the fringe 44 and the putting surface 36 on the upper surface thereof, having an upper, rolling surface closely akin to that found on a natural, outdoor green.

it should also be noted that in the course of such movement, the tendency of the adjacent ends of the

beams

56 and 68 to separate due to the fact that they are pivoted respectively at the fixed pivots 52 and 70 is accommodated by the presence of the link 62 which is pivoted to the beam 56 at pivot 60 and to the beam 68 at the pivot 64.

Before describing the control circuit for the hydraulic jacks 82 and 82', some mention should be made of the details of construction of the conventional double acting jacks Each conventionally includes a reversing valve which, when the cylinder piston reaches its full extent of travel in either direction, will be actuated to reverse the application of fluid under pressure to the piston so that the direction of piston travel is reversed. This feature permits a simplified control without any requirement for servo mechanisms or bidirectional motors. Additionally, conventional check valve systems are employed so that when fluid under pressure is not being applied to the cylinders, the pistons thereof will not be permitted to change position.

The exemplary embodiment of the control circuit is illustrated in FIG. 3 and inasmuch as the control circuit for each of the

jacks

82 and 82 is similar but not identical, reference will be made primarily to but one of the circuits with the difference in the second circuit being explained.

A source of line power is provided and is connected through a conventional circuit breaker 102 for protective purposes to the primary winding of a transformer 104. The secondary winding of the transformer 104 is connected as an input to a conventional full wave rectifier 106 and the output of the rectifier 106 is applied across a Zener diode 108 to limit the maximum voltage applied to the remainder of the control circuit.

A manually operable switch 110 is located on one side of the output of the full wave rectifier 106 and, as will be seen hereinafter, may be manually actuated by a golfer to randomly change the contour of the green. From the switch 110, the line passes through a diode 112 to a relay coil 114 which is connected in series with a transistor 116 and in parallel with a diode 118.

Contacts 120 are adapted to be closed when the coil 114 is energized and have one side thereof connected to the anode of the diode 112 and a resistor 122. The resistor in turn is connected to a control terminal of an electronic switch 124 of conventional construction interposed between a lead 126, which is connected in common to the output of the rectifier 106 as well as the power source 100, and a load in the form of a hydraulic pump 128. The circuit is completed by connecting the hydraulic pump 128 through a conventional circuit breaker 130 used for protective purposes to the other side of the power source 100. As a result, it will be apparent that when the electronic switch 124 is caused to conduct, the hydraulic pump 128 will be energized.

Returning to the transistor 116, it will be seen that its base is connected to the common junction of a resistor 132 and the anode of a silicon controlled rectifier 134. The cathode of the silicon controlled rectifier 134 is connected to the anode of the diode 112 while the resistor 132 is connected to the common line 126.

The gate of the silicon controlled rectifier is connected to the common junction of a resistor 136 and a unijunction transistor 138. The unijunction transistor is connected through a resistor 140 to the common line 126 and through the resistor 136 to the anode of the diode 112.

The trigger of the unijunction transistor 138 is connected to an RC circuit comprised of a relatively large capacitor 141 and a resistor comprised of a fixed resistor 142 and a variable resistor 144. More specifically, the connection of the trigger of the unijunction transistor is to the junction of the capacitor 141 and the variable resistor 144.

The operation of the system is as follows. Initially, the entire circuit is deactivated except that power is available from the rectifier 106. When a golfer, in readiness to putt on the contourable green, desires a change in the contour of the same, he will momentarily close the switch 110 by manually depressing the same and the momentary closing of the switch 110 together with the bias applied to the base of the transistor 116 through the resistor 132 will cause a circuit from the common line 126 through the transistor 116 and the coil 114 to be completed. This will result in the contacts 120 being closed and the same serve as a holding circuit to bypass the switch 110 which opens after its initial depression. At the same time, power is applied through the resistor 122 to the electronic switch 124 thereby causing energization of the hydraulic pump 128. Energization of the hydraulic pump 128 will then cause operation of the corresponding hydraulic cylinders 82. Of course, due to the construction of the hydraulic cylinders, it cannot be predicted at this time whether the associated cylinder piston will extend or retract.

The application of power to the above circuit either through the closing of the switch 110 or the closing of the contacts 120 also results in power being applied across the RC circuit comprised of the capacitor 141 and the resistors 142 and 144. As a result, the capacitor 141 will begin to charge and after a predetermined time period determined by the resistance values of the resistors 142 and 144 as well as the capacitance of the capacitor 141 and the characteristics of the unijunction transistor 138, the unijunction transistor 138 will be fired. When the unijunction transistor 138 is fired, there will be a change in the potential level at the junction thereof and the resistor 136 which, it will be recalled, is connected to the gate of the silicon controlled rectifier 134. This change will cause the silicon controlled rectifier 134 to fire and as a result, a path of conduction will be established through the resistor 132 and the silicon controlled rectifier 134. This conduction will then cause a voltage drop across the resistor 132 thereby changing the bias applied to the base of the transistor 116 to cause the same to revert to a non-conducting state. Of course, when the transistor 116 is not conducting, the coil 114 cannot be energized and the contacts 120-will open. As a result, the electronic switch 124 will be turned off thereby de-energizing the hydraulic pump 128 and stopping movement of the associated hydraulic cylinder 82.

At the termination of movement of the associated hydraulic cylinder 82, the control circuit therefor described above automatically resets itself to be in readiness for a subsequent operation. Specifically, the charge on the capacitor 141 is reduced to zero by means of a path including the resistors 142 and 144, the line 126, the resistor 132 and the silicon controlled rectifier 134. As soon as the charge on the capacitor 141 has been reduced to zero, the silicon controlled rectifier 134 and the unijunction transistor 138 will revert to a nonconducting state and will be rendered conducting again only when the unijunction transistor 138 has again been fired.

The control circuit for the second one of the hydraulic jacks 82' is substantially identical to that just described with the exception that the position of adjustment of the wiper of the variable resistor 144 is changed from that used in the circuit described above thereby altering the time period determined by the RC characteristics of the resistors 142 and 144 and the capacitor 141. As a result, the closing of the switch 110 and the second jack 82 will be operated for a period of time differing from the period of time of operation from the first jack 82 as determined by the difference in the position of the wiper of the variable resistor 144 in their respective control circuits.

Because both cylinders are operated for different periods of time any may be operated prior to the putt for each group of golfers playing a hole, it will be appreciated that the contour of the putting surface will be relatively randomly selected so that a golfer will not be faced with substantially the same putt each time he plays a given hole on an indoor golf game. A further contributing factor to the random selection of the green contour is the use of hydraulic cylinders as jacks.

Specifically, because of the load continually placed on the jacks, it will be appreciated that a given period of operation of the hydraulic pump for each jack will cause less upward movement of the platform than downward movement due to the gravity assist provided by the weight of the contourable green. When this factor is coupled with the differences in times of operation of each jack, a virtually truly random contour selection is obtainable, thereby eliminating virtually all possibility of the golfer being faced with substantially identical putts from time to time and significantly enhancing the realism of an indoor golf game.

While the preferred embodiment as described employs electronic timers to achieve a random contour, the invention is not to be so limited except as stated in the appended claims. The electronic timers described herein are the preferred form of timer because of the high reliability obtainable with solid state devices. However, in some instances, a degree of reliability may be sacrificed for a more economical construction and in such cases, any suitable switch operating mechanical or electromechanic timing movement may be used in lieu of the elec tronic timer specifically described. Of course, two such devices must be employed and each should have a different time period of operation.

Having described the preferred embodiment of the invention, we do not wish to be limited to the details set forth, but rather to have our invention construed according to the true spirit thereof as set forth in the following claims.

We claim:

1. In a contourable green for a golf game including a supporting structure, a platform having an upper playing surface mounted on the supporting structure, and means for moving the supporting structure to distort the platform and thereby the. playing surface, an improvement wherein said moving means comprises a plurality of independently operated selfreversing power operating means for reciprocally moving portions of the platform up and down over a preselected vertical range and means to control said moving means comprising an electronic timer circuit for each of said power operating means said timer circuit being operative upon initiation to activate its associated power operating means for a preselected period of time, said operative time periods being so related to the operating speed and vertical range of said self-reversing power operating means as to result in each stopping sequentially at a multitude of unique vertical positions upon successive periods of operation, and manually operated means for simultaneously initiating each of said timer circuits; whereby said upper playing surface is caused to sequentially assume a great multitude of unique three dimensional contours upon successive actuations of said manual operating means.

2. A contourable green according to claim 1 wherein each of said power operated means comprises a motor driven hydraulic pump and a double acting hydraulic cylinder, and wherein each of said timer circuits is operative to energize one of said motor driven hydraulic pumps.

3. A contourable green according to claim 2 wherein each of said timer circuits includes an RC circuit operative to deenergize said motor driven hydraulic pump after a predetermined time period dependent upon the electrical characteristics of said RC circuit.

4. A contourable green according to claim 3 wherein the RC circuit of the timer circuit for one of said motor driven hydraulic pumps is set to have a different time constant than the RC circuit for the other of said pumps.

5. A contourable green for use in a golf game comprising: a rigid but distortable platform having an upper playing surface; a plurality of laterally spaced beam structures supporting said platform, each said beam structure .being comprised of a plurality of pivotally interconnected beams; means mounting each said beam for pivotal movement in the vertical plane; means yieldably securing said platform to said beams; at least two double acting hydraulic cylinders, each interposed between a stationary structure and one of said beam structures and connected to the latter at a point remote from said pivotal mounting means for each beam; at least two energizable hydraulic pumps for providing fluid under pressure to an associated one of said hydraulic cylinders; and means for energizing each of said energizable pumps, said energizing means comprising a plurality of electrical circuits, one for each pump, and having a common master actuating switch adapted to be momentarily closed by a golfer for applying power simultaneously to said control circuits, each said circuit further comprising means to energize an associated pump upon the actuating of said master switch and means to de-energize said pump at the expiration of a predetermined time interval including an RC circuit energizable upon the closing of said master switch and responsive to a predetermined charge thereon, the RC circuit of one of said control circuits having a different time constant than the RC circuit for another of said control circuits.

6. A variably contourable playing surface comprising: a supporting structure a rigid but distortable platform the top surface of which comprises a playing surface and means for movably supporting said platform upon said supporting structure, means to vary the contour of said playing surface comprising a plurality of power driven units each varying the elevation of an associated portion of said platform over a predetermined vertical range as a function of time in operation, said power driven units being self-reversing at the upper and lower extremities of the predetermined vertical range, and

means to control the operation of said plurality of power driven units including means to commonly initiate operation of said units and means including an electronic time constant circuit to independently terminate the operation of each of said power driven means upon the expiration of discrete time intervals selected to cause each of said power driven means to move to a substantially unique position upon each such common initiation.

7. The device of claim 6 wherein said means to control said plurality of power units comprises a manually operable switch adapted to be momentarily closed by a golfer, a control circuit for each of said power units energized upon closing of said manually operable switch, means in each of said control circuits operable upon the momentary closing of said manually operable switch for maintaining said circuit energized for a preselected time period, including an RC network in each said circuit having a different time constant than the RC network in any other of said circuits.

8. The device of claim 6 further including means attaching said platform to said contour varying means, said attaching means comprising tensioned elements urging said rigid platform into contact with said contour varying means.

Claims

1. In a contourable green for a golf game including a supporting structure, a platform having an upper playing surface mounted on the supporting structure, and means for moving the supporting structure to distort the platform and thereby the playing surface, an improvement wherein said moving means comprises a plurality of independently operated self-reversing power operating means for reciprocally moving portions of the platform up and down over a preselected vertical range and means to control said moving means comprising an electronic timer circuit for each of said power operating means said timer circuit being operative upon initiation to activate its associated power operating means for a preselected period of time, said operative time periods being so related to the operating speed and vertical range of said self-reversing power operating means as to result in each stopping sequentially at a multitude of unique vertical positions upon successive periods of operation, and manually operated means for simultaneously initiating each of said timer circuits; whereby said upper playing surface is caused to sequentially assume a great multitude of unique three dimensional contours upon successive actuations of said manual operating means.

3. A contourable green according to claim 2 wherein each of said timer circuits includes an RC circuit operative to de-energize said motor driven hydraulic pump after a predetermined time period dependent upon the electrical characteristics of said RC circuit.

5. A contourable green for use in a golf game comprising: a rigid but distortable platform having an upper playing surface; a plurality of laterally spaced beam structures supporting said platform, each said beam structure being comprised of a plurality of pivotally interconnected beams; means mounting each said beam for pivotal movement in the vertical plane; means yieldably securing said platform to said beams; at least two double acting hydraulic cylinders, each interposed between a stationary structure and one of said beam structures and connected to the latter at a point remote from said pivotal mounting means for each beam; at least two energizable hydraulic pumps for providing fluid under pressure to an associated one of said hydraulic cylinders; and means for energizing each of said energizable pumps, said energizing means comprising a plurality of electrical circuits, one for each pump, and having a common master actuating switch adapted to be momentarily closed by a golfer for applying power simultaneously to said control circuits, each said circuit further comprising means to energize an associated pump upon the actuating of said master switch and means to de-energize said pump at the expiration of a predetermined time interval including an RC circuit energizable upon the closing of said master switch and responsive to a predetermined charge thereon, the RC circuit of one of said control circuits having a different time constant than the RC circuit for another of said control circuits.

6. A variably contourable playing surface comprising: a supporting structure a rigid but distortable platform the top surface of which comprises a playing surface and Means for movably supporting said platform upon said supporting structure, means to vary the contour of said playing surface comprising a plurality of power driven units each varying the elevation of an associated portion of said platform over a predetermined vertical range as a function of time in operation, said power driven units being self-reversing at the upper and lower extremities of the predetermined vertical range, and means to control the operation of said plurality of power driven units including means to commonly initiate operation of said units and means including an electronic time constant circuit to independently terminate the operation of each of said power driven means upon the expiration of discrete time intervals selected to cause each of said power driven means to move to a substantially unique position upon each such common initiation.