US2933681A - Golf practice device - Google Patents

Description

April 19, 1960 H. M. CRAIN 2,933,631

GOLF PRACTICE DEVICE Filed April 28. 1955 3 Sheets-She et 1 /z 4/ l l v C ,Q/

Z INVENTOR.

BY a, dug. wa MW X/IS 47'7'0fi/Y5VS p i 19, 1960 H. M. CRMN 2,933,681

GOLF PRACTICE DEVICE Filed April 28, 1955 3 Sheets-Sheet 2 Ii'7///////////A uvmvron 4 M404) 4/. cAu/zv BY April 19, 1960 H. M. GRAIN 2,933;681

GOLF PRACTICE DEVICE Filed April 28, 1955 3 Sheets-Sheet 3 INVENTOR. MAW M 624W 1am 4-144, vw-

United States Patent OfiFice 2,933,681 Patented Apr. 19,1960

GOLF PRACTICE DEVICE Harry M. Crain, Philipsbnrg, Pa. Application April 28, 1955, Serial No. 504,462 '5 Claims. (Cl. 324-68) This invention relates to a golf practice device, and more particularly to a device for analyzing the swing of the golf club with respect to the velocity of the club head during a portion of the swing.

In some phases of the game of golf it is important to obtain maximum distance in the flight of the ball. Other things being equal, that distance is proportional to the velocity of the club head at the time of impact; and it is frequently desirable to determine how much that velocity is affected by varying ones stance, grip or backswing. While there are many practice devices involving the actual hitting of a real or simulated ball to get an indication of the distance it would travel, such devices do not permit the velocity of the club head to be measured independ ntly of other factors aifecting the flight of the ball, such as the material of which the ball is constructed, the angle of attack of the club at the moment of impact, etc. Other devices that do measure the velocity of the club head alone require the use of high speed sequential photographs, which are costly and time consuming.

it is accordingly among the objects of this invention to provide a golf practice device'that will permit the velocity of the swinging club head to be measured between any two predetermined points in the arc of its swing without the necessity of actually hitting a ball, that can be cheaply made, and that will be inexpensive and simple to operate. Other objects will appear from the following description of the invention, a preferred embodiment of which is shown in the attached drawings, in which Fig. 1 is an isometric drawing of one form of the physical device;

Fig. 2 is a schematic circuit diagram showing theelectrical elements involved in its operation;

Fig. 3 is a modified schematic circuit diagram incorporating an automatic resetting circuit;

Fig. 4 is an isometric drawing of a modified form of the physical device, shown in Fig. 1;

' Fig. 5 is a vertical section along the line V--V of 'ig. 4;

Fig. 6 is a schematic circuit diagram of the device of Fig. 4;

Fig. 7 is a supplemental wiring diagram of a portion of the same device;

Fig. 8 is a wiring diagram of an automatic resetting circuit that can be incorporated in the circuit of 6;

Fig. 9 is a wiring diagram on anotherform of .automatic resetting circuit that can be substituted for that shown in Fig. 8..

Broadly, the present invention comprises an electrical circuit, including a pair of circuit actuating means and a condenser, in which the circuit actuating means are mounted to be operated in sequence by a swinging golf club head during successive stages of its swing. The time interval between their operation, which is inversely porportional to the velocity of the club head, is measured by timing circuit means for .varying the potential on the condenser at a predetermined rate during that interval, and

2 by indicating circuit means for measuring change inthat potential.

Referring to Fig. 1, one embodiment of the golf practice device includes a platform 1, provided with two switches generally designated as S1 and S2. Each switch includes a conducting post 2, which is mounted at one, end of the platform and extends vertically above it, and a horizontally extending spring wire 3, adapted to make electrical contact with the adjacent post. The inner end of each spring wire is turned downward and formed into a coil spring 4, the lower end of which is mounted on the platform, the function of those coil springs being to urge the spring wires 3 into electrical contact with their adjacent posts 2. The outer ends of both of the spring wires are preferably turned upward to present two vertically extending wire portions 6, spaced apart a predetermined distance and positioned in the normal arc of a swinging golf club head. In other words, if an operator (not shown), standing to the left of and facing the platform in Fig. 1, swings a golf club in the normal fashion, the head of that club will first engage portion 6 of switch S1 and a moment later will engage the corresponding portion of switch S2. In each case, the switch is opened by its engagement with the club head and closed a moment later by the action of its coil spring 4. It will be readily apparent that the interval of time between the openings of switch S1 and switch S2 will be inversely proportional to the velocity of the club head between portions 6 of those two switches.

That velocity is measured by means of the electrical circuit shown in Fig. 2. Switches S1 and S2 are there shown diagrammatically as part of a circuit, including a source of direct current E, voltage-dividing resistances R1 and R2, a delayed action relay X, a condenser C, a triode vacuum tube V, a meter M, fixed resistances R3 and R5, and a variable resistance R4. The various elements just mentioned are interconnected as shown in Fig. 2, and operate as follows.

With switches S1 and S2 both in their normally closed positions, the operator closes a battery switch S and then momentarily closes a foot-operated switch S5. The circuit through the coil 12 of relay X is now closed; and that relay is energized, locking itself in energized position through the closing of its armature switch S4, so that relay remains energized after foot switch S5 is released. Resistance R1 (and the coil of relay X) and resistance R2 now act as a voltage divider in establishing through closed armature switch S3 a reference potential or charge on condenser C, which is also connected to the grid 11 of vacuum tube V. That tube, together with resistance R5,

the resulting forms one branch of a bridge circuit; the other branch includes resistance R3 and variable resistance R4. Connected across this bridge is meter M. Variable resistance R4 is initially adjusted to cause meter M to register a predetermined value, corresponding to the reference potential on condenser C. c j

The operator then swings the golf club in the usual manner. As the club head descends and comes in contact with portion 6 of switch S1, that switch is opened. Thereupon, the charging circuit to the condenser C, through the. coil of relay X and through resistance R1 is opened; and condenser C will begin to discharge through resistance R2 at a definite rate determined by the time constant of the R2-C circuit. That circuit includes switch S3 (which, for the reasons given below, remains closed during the interval between the sequential openings of switches S1 and S2) and closed switch S2. A moment later, when the club head contacts the portion 6 of switchS2 and opens that switch, resistance R2 is removed from across condenser C, which thereafter dis- 7 charges very slowly through high impedance leakage paths, so that for practical purposes its potential does any set of operating conditions. normal swing of a golf club, the usual range of velocity 7 released.

not substantially change for a short period. This permits sufficient time for the operator to complete his swing, including the normal follow through, and read the meter M. That meter will indicate the change in potential of condenser C during the interval when the condenser was discharging through resistance It will be obvious that the longer that interval, which is initiatedby the opening of switch S1 and terminated by the opening of switch S2, the greater will be'the discharge of condenser C, and lower will be its potential at the end of that interval. in other words, the change in that potential will be inversely proportional to the velocity of the club head.

The function of relay X is to allow electrical resetting of the circuit; another function is to provide for adequate continuation of the open circuit conditions initiated by the opening of switches S1 and S2. For proper circuit operation, this relay must possess certain ime lag characteristics, such that the minimum time for the opening of its armature switches S3 and 54 after the current is interrupted to the energizing coil by the opening of switch S1 will be longer than the time interval to be measured. Further, this timelag must not be greater than the time it takes for either switch S1 or switch S2 to reclose after being opened. in other words, coil spring 4 forming part of switch S1 should not return that switch to its closed position against conducting post 2 until after switch S2 has been opened, and relay X should not release its armature switches S3 and S4 until after switch S2 is opened, but should do so before either switches S1 or S2 are reclosed. The foregoing limits in the operation of relay X and switches Slpand S2 can be calculated for of the club head at the bottom of the swing is from 60 to.l80 miles per hour, or from 88 to 264- feet per secend. If the portions 6 of switches S1 and S2 are assumed to be four inches apart, the time reuired for the club head to traverse that distance at the extreme velocities given above would be from .0038 second down to .0013. second. It will usually take atleast milliseconds (.01 second) for either switches S1 or S2 to return to their normal closed positions. Preferably, the moment of inertia of the wires 3 of each of those switches is such that up to one second or more will elapse between the For example, in the order of several seconds, sufiicient to permit the operator to read the meter M after completing his swing, as described in connection with Fig. 2. In place of the resetting foot switch S5 of Fig. 2, there is substituted in Fig. 3 an automatic resetting circuit that includes additional resistances R6 and R7, a second condenser C1 and a gas triode tube V1. Those elements are connected as shown in Fig. 3, with resistance R7 acting as a current limiting resistor for the grid of the triode V1. In addition, the delayed action relay (the characteristics of which are otherwise unchanged) is'proyided with an extra contact so, which is closed when that relay is deenergized and open when that relay is energized; and resistance'Ri is opening of either switch and its subsequent reclosing. 7

Under the foregoing conditions, if the reclosing time of switches S1 and S2 is made to be greater than 0.5 second, then the relay can be selected that will release anywhere in'therange from .0038 to 0.5 second after current to the-relay coil is interrupted. I

When relay X is used as above described, it will, release its armature switches S3 and S4 after S2 has been opened but before either S1 or 82- has reclosed. Upon such release, and after the reclosing of switches S1 and S2, the-circuit is in thesame condition as it was initially.

and may again be reset fora second swing of the golf' club by momentarily closing foot switch S5. If, on the other hand, it is not desired to reset the device electricah 1y, but to do so mechanically or manually, it is possible with slight modifications in the structure of switches. 51

' and S2 to entirely eliminate the delayed action relay X,

in which case switch S2 would be connected to the up-. per terminal of condenser C directly, rather than through switch S3 as shown in Fig. 2; and the upperterminal of resistance R1 wouldbe connected to conductor 15 directly, rather than throughrelay X. The only modification in switches S1 and S2. would then be to provide,

mechanical means, such as a latch, that would act to re tain those switches in their open position, after they had once been opened by the club head, until mechanically The modified circuit shown in Fig. 3 will be preferred inmany instances because it provides for automatic resetting of the device after an interval of time, on the now connected in seriesbetween switch S4 and the coil 12 of relay X, instead of (as in Fig. 2) between the coil of that relay and switch S1. However, resistance R1 (and the relay coil) and relay R2 still act as a voltage divider forchargingcondenser C. The. other elements in Pig. 3 correspond to those in Fig. 2 and'are similarly designated.

The operation of the automatictresetting circuit of Pig. 3 is as follows. When battery switch 5 is closed, the circuit path to condenser C1 is also closed. On one side of the condenser, that path follows conductor 15', closed switch S6, resistance R6 and conductor 16; on the other side of condenser C1, the path follows conductor 17. As a result, condenser C1 is charged at a definite rate determined by the time constant of the R- -Cl circuit. A constant is chosen for that circuit that will charge condenserCl to the desired potential only after an interval of several seconds following the opening or release of delayed action relay X on the completion of a swing of the'golf club head and the sequential opening of switches Si and S2. This delay in the charging of condenser Cl allows sufficient time for the observer to read meter M after completing his swing. Whenthe potential on condenser C1 has increased to the desired point, which is the voltage necessary to ignite or fire the gas triode V1, the condenser will discharge through that triode and through the series connected elements 32, closed switch S1 and coil relay X. While this discharge current has a hi h valueffor only a short period of time, condenser C1 is chosen with sufiicient capacity to assure that its discharge current will momentarily energize relay X, thereby closing its armature switches including the switch S4 that locks the relay in its energized position. Thereafter,

the operation of the circuit in measuring the velocity of described in connection with the circuit of Fig. 2 after the relay in the latter circuit was locked in its energized position by the momentary closing of foot switch With the opening of switch S6 on the energizing of relay X, condenser C1 and the gas triode V1 are disconn'ected from the source of current, the potential of C1 has decayed and the gas'triode is extinguished until the resetting circuit is again put intooperation after the release of relay X and the closing ot'switch S6 following the completion of the next swing of the golf club head. At the beginning of the next resetting cycle, condenser C1 will again require a definite time interval to build up sufiicient potential to again fire the gas triode V1.

While the time interval between the sequential openings of switches S1 and S2 may be measured, as described above, by measuring the decay of the potential on condenserC in the R2C circuit, it will be obvious that the interval could likewise be measured by measuring the increase of potential on the condenser through a similar R-C-timingcircuit. In other words, it isthe measurement of the change in potential that is important and not the direction, of that change.

Manygolfers, when addressing the ball and just before making a full'sw'ing, indulge in a preliminary movement of the club head (commonly called a waggl) adjacent the ball, presumably for the purpose of relieving muscular practice swings. Such a golfer maypremature'l-y open switches S1 and S2 and would not be able to'measure the velocity of his club head during a full swing until the circuit had been reset.

The foregoing difiiculty may be overcome, without changing the habits of the golfer, by replacing the switches S1 and S2 with a sensing means that need not be physically contacted by the club head and that will provide a rate signal proportional to the velocity of the club head, rather than the abrupt on-ofl signal of a contact switch. Such a sensing means will accordingly discriminate between diirerent instantaneous velocities of the club head, and when associated with a high-pass filter circuit and the grid of a thyratron tube, will initiate the operation of a timing circuit in connection with the high club head velocities incident to a full swing, but not in connection with the relatively low club head velocities incident to.a waggle. A sensing means of this type can have a variety of forms, such as a coilassociated with an oscillator circuit, whose output would be afiected by the proximity of the metal in the club head; a radiation detector, used in conjunction with a small amount of radioactive material applied to the club head as a signal source; or a light sensitive cell, whose output is afiected by'the light interruption, or shadow, of the club head. The latter means, as illustrative of various forms of sensing means, is described below in connection with Figs. 4 to 9.

Figs. 4 and 5 show a modified form of the physical device that is illustrated in Fig. 1. Instead of the mechanically operated switches S1 and-S2 adapted to be sequentially engaged by the moving club head, there are substituted photocells L1 and L2 positioned below the surface of a mat 20 in holes 21 and 22 therein. These photo cells are separated a convenient distance, about four inches has been found satisfactory, in the line of swing of the club head approaching a tee 23 on the mat. A source of light (not shown) above the mat is adapted to shine on the photocells, so that the light fluxthereto will be interrupted as the club head moves successively over the two photocells in the course of its swing. The rate of change in the light flux due to such interruption will obviously be proportional to the velocity of the club head passing over the photocells.

To discriminate between different club head velocities, the photocells are connected in the circuit shown in Fig. 6. Photocell L1 is connected in series with a battery "E and a resistance R8, and across L1 is, a high-pass filter circuit that includes a condenser C10, a potentiometer P1 and a battery E12 having its polarity reversed with respect to battery E10. Photoce1l L2 is connected in similar circuits comprising battery E11, resistance R9,

condenser C11, potentiometer P2, and battery E13. The

operation of each photocell circuit as a discriminating means is the same, and will be explained in connection with photocell L1 only. I

With maximum light flux reaching photocell L1, the circuit is static, and there will be a given potential drop across the photocell. When the light flux is interrupted by the club head passing over the photocell, the resistance of the photocell increases at a rate proportional to the velocity of the club head, so that the potential of junction 24, which is positive with respect to conductor 33, will increase at the same rate. The rate of change of that potential will determine the magnitude of the voltage across the potentiometer P1 in the R-C filter circuit. In other words, the magnitude of the voltage developed across the otentiometers P1 and P2 will be proportional to the speed of the club head as it passes successively above the photocells L1 and L2. Since the speed of the club head during a waggle is much less than the speed encountered at the bottom of even a slow full swing, that voltage will be correspondingly small for a waggle as compared with that resulting from a full swing. The potentiometer P1 has a sliding contact 25 connected to control grid.26 of a 'gas thyratron tube T1. Similarly,

potentiometer P2 has its sliding contact 27 connected to control grid -28 of a second gas thyratron tube T2. By adjusting these contacts, a threshold can be established which will provide insufiicient voltage to the control grids of the thyratrons to cause them to fire during a waggle, but which will be exceeded during a full swing. Once the thyratron fires, the grid loses control and the tube continues to fire until its anode circuit is interrupted. The circuit so far described constitutes a circuit-actuating means that possesses rate discrimination between low speeds of the club head, which it is not desired to measure, and high club head speeds, which are to be measured.

Assume that the club head passes first over L1 above the threshold speed necessary to fire the thyratron T1, current will then flow from the positive terminal of battery E10 through normally closed contact 29 of a push button switch PS and conductor 30 to anode 31 of thyratron T1, then to the? cathode 32 of that tube, and through resistances R12 and R13 to a ground bus 33 connected'both to ground and to the negative terminal of battery E10. Accordingly, the cathode of thyratron T1 will be positive with respect to ground; and junction 45 will also become positive, but at a reduced potential because of the voltage divider action of resistances R12 and R13. A portion of the current fiowing through resistance R12 will flow through the branch circuit comprised of resistance R14 and conductor 34 to anode 35 of a diode D, and then to cathode 36 of that diode and through a conductor 37 to a condenser C26, which is also connected to the ground bus 33 by a conductor 38. Condenser C20 will now accumulate a charge in proportion to the interval of time a conductive path is maintained from the battery E10 through T1, R12, R14 and diode D. This conductive path will be interrupted a short interval later as the club head passes over photocell L2, causing thyratron T2 to fire, bringing about a reversal of polarity, from positive to negative, of both the junction and the anode 35 of diode D directly connected thereto. Such operation is obvious under the circuit conditions that resistances R12, R13, R14, R15 and R19 are of the same value and the voltage of battery B10 is" equal to that of battery E11, since under these conditions the IR drop across resistance R19 will exceed that across resistance R13. However, other combinations of resistance values and battery potentials could be used to obtain equivalent results as would be obvious to anyone versed in the electronic or electrical fields. When anode 35 of diode D becomes negative with respect to its cathode 36, no more current will thereafter flow through that diode to further charge condenser C20, nor can that condenser discharge except through high resistance leakage paths made up of the circuit components. Therefore, the charge that has accumulated on condenser C20 will be a function of the time interval between the successive firings of thyratrons T1 and T2, which in turn will be a function of the velocity 'of the club head in passing successively over the sensing elements L1 and L2. The duration of this interval is indicated by a meter reading on the meter M, which is connected in a Wheatstone bridge circuit, along with the triode V and resistances R3, R4 and R5, across the condenser in the same manner as the similarly designated elements in Figs. "'2 and 3, and already described.

However, this metering orindicating circuit has a further feature in association with the circuit of Fig. 6 that is not found in its association with the circuit of Pig. 2. Referring toFig. 7, there is shown a supplemental wiring diagram that includes cathode heaters 50, 51, 52 and 53 associated, respectively, with the thyratron T1, diode D,

triode V and thyratron T2 of Fig. 6. These heaters are connected in parallel by conductors and 61 to a source of current E14. Heater 51 of diode D is connected in series with a variable resistance R18. it has been experimentally verified that, by adjusting the heater current of diode .D by means of this variable resistance,

' switch PS.

, of thyratron T2.

answe *7 the efiects of component leakage on theehargc .accumu: lated by the condenser C can be compensated for, to

the extent that a charge accumulated by that condenser in one millisecond can be held for over six seconds with less than five percent loss. A six second period is quite adequate to:read the meter after having completed a swing. The compensatory efiect mentioned above, appears to result from the cancelation of two circuit characteristics. If the grid 44 of triode V were left floating across condenser C26 without being connected, as it is, to the cathode 36 of diode D, a negative charge woald tend to build up on the condenser. as a result of minute grid current flow. On the other hand, if the cathode of diode D wereileft floating across condeuserCZt) without being connected, as it is, to the grid 44 of triode Vs a positive charge would tend to develop across the condenser. By adjusting the heater current of diode B through the variable resistance R18, and thereby varyingthe cathode emission in that tube, the tendency to accumulate a negative charge through the grid action of triode V can be compensated for. To obtain a six'second holding period for the meter indicator without appreciable change of reading means that the efiective shunting resistance across condenser C20 must be in excess of 100 megohms.

The high shunting resistance thus efiected allows the use of a relatively small value for condenser C29 and results in a high circuit sensitivity. A value of 0.1 microfarad has been used to successfully operate a single tube metering circuit. 7

After a swing has been completed and the meter read ing observed, it is necessary to reset the circuit. This can be done manually, by pushing the momentary switch PS to open its contacts 29 and 43. Contact 29 is con nected by conductor 62 in series with battery B10; and, when that contact is opened, the anode circuit through conductor 36 to thyratron T1 is broken. Similarly, the opening of contact'43 breaks the anode circuit through conductorsoii and 42 of thyratron T2. Consequently, when switch PS is operated, those tubes will cease to fire, and the control grid of each tube will again assume control of the further operation of the tube. In addition, the removal of the anode potential from triode V, with the opening of contact 29, allows the grid and cathode elements of this tube to function temporarily as a diode and effectively discharge condenser C20. This condenser could also be discharged by a shunting circuit that would be closed by a separate set of contacts associated with However, such a circuit would provide addi tional component leakage paths that might be trouble- 8', in which the elements common to Fig. 6 are similarly numbered, shows one method for automatically resetting the circuit, as contrasted with the manual resetting previously described in connection with Fig. 6 Here a thermal delay switch TD has its heater coil 65 connected in series with resistance R19 and the anode 4% previously described in connection with Fig. 6.

Another circuit modificationfor automatically resetting the circuit is shown in Fig. 9, where again the ele-' ments common to .Fig. 6 aresirnilarly numbered. Here a resistance R29 and a condenser C4 in series therewith are connected across resistances R14 and R15. Between the resistance R20 and condenser C4 is connected one terminal of a neon lamp N, the other terminal of which is connected-in series'with a coil of a rel'ayjZ: to the anode 40 of thyratronx'l'l After this thyratronghas .fired,

When hat tube fires, coil d'begins' 'to heat up and after a-predetermined period, determined the potential developed across resistances R14 and R15 charges up condenser C4 through resistance R20 until the breakdown-voltage of neonlamp N is reached. The condenser Cd then discharges through that lamp to energize the coil cry-relay Z. The normally closed contacts 29 and 43 of that relay are thereby opened to reset the circuit as previously described.

It is among the advantages of this invention that no relays are employed in the timing circuit itself, since relays are'prone to introduce significant and inconsistent errors measuring intervals in the millisecond range. Rather, time intervals are measured by the change, at a predetermined rate, of the potential on a condenser connected into a resistance-capacitance circuit having a predetermined time constant. It is a further advantage that, while the velocity of the club head is immediately indicated, that indication persists without change for a sufiicient interval to permit the operator to complete his swing and examine the indicating meter at his leisure. Since there is no perfect electrical insulator, it is impossible to-maintain 'a potential on condenser C after switch S2 has been opened, but the circuit arrangements shown in Figs. 2 and 3 provide leakage paths of such high. resistance that the charge on condenser C at the moment switch S2 is open will be substantially unchanged for a sufiicient period to permit the operator to read the meter. Particularly high resistance leakage paths are provided for the circuit shown in Fig. 6 and its supplemental circuit shown in Fig. 7. A still further advantage of this invention is that the resettingmems are simple and positive in their operation, being eitherifully automatic when using the circnitsof Figs; 3 and 6 .(the latter as modified by the circuits of Figs. 8 ,01 9) or being controlled by a foot switch, or other manually operated means, when using the circuit of Fig. 2 or Fig. 6 above. in addition, the embodiment illustrated in'Figs. 4 6 provides switch means that will actuate'the tirning circuit-only when the club head velocity exceeds a predetermined minimum, thereby ignoring waggles of the club head preliminary to a' full swing. 7

According to. the provisions of the patent statutes, 1 have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. ,However, I desire to have it understood that, 'withinthe scope of the appended claims, the invention may be practiced otherwise than as specifically. illustrated and described.

I claim:

1. A device for measuring the velocity of a swinging golf club head, comprising an electrical circuit including a source of direct current and a fixed resistance and a first contact switch and a second contact switch and a condenser, said elements being connected in series in the order recited, a second fixed resistance connected across the second switch and the condenser, and high impedance potential measuring means for measuring the potential on the condenser, thepair' of contact switches being normally closed and adapted to be opened in sequence by direct physical contact with the clubhead during suece'ssive stages of its swing, whereby the decay of the potential on the condenser during the time interval between the sequential opening of those contactswitches will be a function oflthe velocity of the club head during that interval. i

2. A device for measuring'thevelocity of a swinging golf club headcornprising a pair of normally closed contact switches that are adapted to be opened in sequence by direct physical contact with the club head during successive stages of its swing, spring means for reclosing each of the contact switches after both switches have been opened by contact with the moving club head, a delayed action .relay having an energizing coil and a plurality oral-mature switches controlled by the coil,an electrical circuit that includes .a source of direct current and a firstarmature switch that isuclosed when the relay is energized and a first fixed resistance and the coil of the relay and the first and second contact switches and a second armature switch that is closed when the relay is energized and a condenser connected in series, a second fixed resistance connected across the second contact switch and the condenser, means for initially energizing the relay coil, and high impedance potential measuring means for measuring the potential on the condenser, whereby when the first contact switch is opened by impact of the moving club head there will be a predetermined delay before the relay is deenergized to disconnect the condenser from across the second fixed resistance and the second contact switch.

3 A device in accordance with claim 2, in which the means for initially energizing the relay coil includes a resistor and a second condenser and a gas triode tube and a third armature switch of the relay that is closed when the relay is deenergized, the resistor and the second condenser being connected in series with the source of current through the third armature switch in its closed position to charge the second condenser at a predetermined rate to a predetermined potential, the gas triode tube and the relay coil being connected in series across the second condenser, and the tube being adapted to discharge when the potential on the second condenser has increased to said predetermined point, thereby sending a momentary pulse of current through the relay coil to initially energize the relay.

4. A device in accordance with claim 2, in which the delay in the deenergization of the delayed action relay mounted at one end with the other end positioned in the path of the swinging club head, a conducting post rigidly mounted adjacent to the conductor, and spring means urging the conductor into electrical contact with the post.

References (Iited in the file of this patent UNITED STATES PATENTS 1,526,337 Hartley Feb. 17, 1925 1,946,290 Lord Feb. 6, 1934 2,058,211 Brown Oct. 20, 1936 2,101,076 Laboureur Dec. 7, 1937 2,102,166 Roberts 'Dec. 14, 1937 2,235,188 Womer Mar. 18, 1941 2,284,850 Smith June 2, 1942 2,571,974 Walker Oct. 16, 1951 2,587,775 Sheldon Mar. 4, 1952 2,651,022 Shelley Sept. 1, 1953 2,795,273 Putnam June 11, 1957

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