A new device for evaluating distance and directional performance JOHNNY NILSSON

Journal of Sports Sciences, February 2006; 24(2): 143 – 147
A new device for evaluating distance and directional performance
of golf putters
JOHNNY NILSSON1,2 & JON KARLSEN1
1
Norwegian School of Sport Sciences, Oslo, Norway, and 2University College of Physical Education and Sports, Stockholm,
Sweden
(Accepted 21 March 2005)
Abstract
The purpose of this study was to construct and evaluate the reliability of an apparatus for testing golf putters with respect to
distance and direction deviation at different impact points on the clubface. An apparatus was constructed based on the
pendulum principle that allowed putter golf clubs to swing at different speeds. The mean speed of the club head before ball
impact, and of the ball after impact, was calculated from time measurements with photocells. A pin profile rig was used to
determine the directional deviation of the golf ball. Three different putters were used in the study, two that are commercially
available (toe-heel weighted and mallet types) and one specially made (wing-type) putter. The points of impact were the
sweet spot (as indicated by the manufacturer’s aim line), and 1, 2 and 3 cm to the left and right of the sweet spot. Calculation
of club head speed before impact, and of ball speed after impact (proportional to distance), showed errors 0.5% of interval
duration. The variability in ball impacts was tested by measuring time and direction deviations during 50 impacts on the
same ball. The mean duration (+ s) after ball impact in the test interval (1.16 m long) was 206 (0.8) ms and the standard
deviation in the perpendicular spreading of the balls in relation to the direction of the test interval was 0.005 m. A test – retest
of one putter on two consecutive days after remounting of the putter on the test apparatus showed less than 1% difference in
distance deviation. We conclude that the test apparatus enables a precise recording of distance and direction deviation in golf
putters as well as comparisons between different putters. The apparatus and set-up can be used in the laboratory as well as
outdoors on the putting green.
Keywords: Golf putting, methodology, sweet spot, direction deviation, distance deviation
Introduction
In golf, play on the green has a large impact on the
final score (Pelz, 2000) and a great amount of time is
spent on practice greens to perfect the putting
technique. This focus on putting in golf is also seen
in the equipment industry, with the sale of approximately US$1 billion worth of putters each year. As an
example, the Callaway Company sold putters worth
US$142.8 million in 2003 (www.callawaygolf.com,
20040320). There are numerous club brands and
club specialities on the market today.
Many aspects of the putting technique have been
described in scientific reports, including the basic
swing technique (Brooks, 2002; Gwyn & Patch, 1993),
temporal aspects of the back and down swing of the
putter, strike variability patterns on the clubface in
relation to the sweet spot, direction sense, and body
alignments and kinematics (Coello, Delay, Nougier, &
Correspondence: Johnny Nilsson,
E-mail: Johnny.nilsson@ihs.se
University
College
of
Orliaguet, 2000; Craig, Delay, Grealy, & Lee, 2000;
Delay, Nougier, Orliaguet, & Coello, 1997). Farrally
et al. (2003), who examined the proceedings from
major golf science conferences, reported that 85
scientific papers across academic disciplines had been
published on golf equipment since 1994.
To our knowledge, however, no scientific study
has focused on the performance of the putter (and
the ball), including distance and direction deviation
related to impacts inline or offline with the club head
centre. And, no study has evaluated the reliability of
a test apparatus for testing golf putters. The aims of
the present study were to construct a putt tester to
resemble an optimal putting technique, which Pelz
(2000) describes as a perfect inline stroke, and to
evaluate the reliability and implementation of the
apparatus for testing golf putters with respect to
distance and directional deviation at different impact
points on the clubface.
Physical Education
ISSN 0264-0414 print/ISSN 1466-447X online Ó 2006 Taylor & Francis
DOI: 10.1080/02640410500131225
and
Sports,
Box
56 26,
SE-114
86 Stockholm,
Sweden.
144
J. Nilsson & J. Karlsen
Methods
Putt tester construction and test procedures
The apparatus (putt tester) works as a simple
pendulum in a single plane, thereby allowing
repeatable club downswings at predefined speeds.
Figure 1 depicts the apparatus with a putter mounted.
The putter is attached to the axis of rotation, which
rests on two low friction bearings. A specially
designed clamp allows the golf putter to be attached
to the axis of rotation and the putt tester frame.
The clamping of the putter shaft followed a
standardized procedure. The fixation of the shaft
grip in the cuff was secured by means of stiff high
friction rubber bars between the shaft grip and the
cuff. The shaft was always tightly clamped to the cuff
and the friction between them was tested by
manually applying a twisting torque to the shaft.
The eventual rotation of the shaft was checked after
every impact by inspection of the clubface angle. The
height of the frame was adjusted to fit clubs with
different lengths and the putter was aligned to fit the
lie. The alignment of the club was standardized by
adjusting the aiming line of the club right over the
predefined roll line. The vertical and horizontal
position of the club head was governed by a
millimetre scale. By applying different drop heights
for the downswing of the club, the speed of the club
head was varied. In the start position before dropping
down, the club was held by an electro-magnet, which
was then released by the experimenter. Two photocells (SICK, Type WL25-714, Hego Systems AB,
Sweden), placed 0.24 m apart, recorded the time
when the club head passed them. The photocells
were triggered by reflective tape attached to the club
head. The putt tester was placed on an evenly
painted wooden sheet (2.1 6 0.9 m) that was fixed to
the top of the table.
We were interested in studying the implementation of the device on different typical putters.
Therefore, we used three types of putters in the
study (toe-heel weighted, mallet and wing-type
putters). After impact, the golf ball rolled over the
sheet through a 0.7 m long interval. Two photocells
(SICK, Type WL25-714, Hego Systems AB, Sweden) recorded the time spent in the interval and,
based on these, the ball speed and roll distance were
calculated. The detection windows of the photocells
were reduced to a width of 3.5 mm. The duration
between the photocells was registered and printed by
a timing unit (Hego Systems AB, Sweden). The
duration after ball impact is proportional to ball
speed and roll distance. Wilson True Tour golf balls
were used with all putters.
After impact, the rolling ball was stopped by a pin
profile rig. When hit by a ball, the pins were pushed
into the rig and an indent or spherical pattern
occurred. This was used to determine medio-lateral
deviation. The spatial resolution of the pin markers
was 13 pins per centimetre. The distance from
the impact point to the profile rig was 1.16 m
(Figure 1D).
In this study, the apparatus was placed on a table
for a normal laboratory setting, but the putt tester has
also been tested outdoors on a putting green. In the
outdoor setting, all parts of the putt tester, apart from
the pin profile rig, were used.
The test for distance and medio-lateral deviation
after impact with golf putters was performed using a
series of ten golf ball hits. Impacts on the sweet spot
and 1, 2 and 3 cm to the toe and heel side of the
sweet spot were performed. Here, the sweet spot was
Figure 1. Test apparatus for measuring golf putter performance.
(A) Sagittal view of the test apparatus: (1) pendulum frame, (2)
adjustable metal arm to hold the putter in a drop down ready
position (3a), (4) clamp to hold the club shaft, (5) photocells for
recording time duration of the club head in the downswing, (6) golf
ball in position for putter impact, (7) power supply for the
photocells, (8) time unit to the downswing photocells. (B) Rear
frontal plane view of the test apparatus: (1) pendulum frame, (2)
adjustable metal arm to hold the putter in a drop down ready
position (3b). The Putter in an impact position, (4) clamp to hold
the club shaft, (9) position adjustable club holder cuff that connects
the shaft clamp to the axis of rotation (10) of the pendulum, (11)
ball bearings for the axis of rotation, (12) electro-magnet that holds
the club in a drop down ready position, (13) photocells to measure
time of the ball in an interval after impact, (14) horizontal levelling
device. (C) Sagittal view of the time measuring interval after ball
impact: (13) photocells, (15) pin profile rig to measure lateral
deviation of the ball, (16) power supply for the (17) timing unit. (D)
Schematic overhead view showing the distances (units ¼ metres)
between different components of the test apparatus set-up.
Photocells to measure interval time for speed calculation of the
club head before impact (1 – 2) and golf ball after impact (3 – 4).
The whole apparatus was placed on a table.
A new device to evaluate performance of golf putters
defined as a point on the clubface that is vertically in
the middle and directly under the manufacturer’s
defined aim line. The same vertical position was used
for all impact points. The ball was placed on the line
of impact (Figure 1D) and centred in front of the
point of impact. During both the laboratory tests and
the outdoor test on a green, two conventional
commercially available and commonly used putters
were employed. In addition, a specially made wingtype putter was used. Comparison of data obtained
in the laboratory with data obtained on an outside
putting green was done. By using the same drop
height of the club on the putting green (110 ms in the
interval before ball impact), the roll distance and
medio-lateral deviation could be determined. The
roll friction on the golf green was measured with a
stimpmeter.
Statistics
Descriptive statistical methods, including means and
standard deviations (s), were employed in the data
analysis.
Results and discussion
Methodological considerations of the reliability
of the apparatus
An important factor for the precision of the time
measurements is the triggering of the photocells. The
temporal resolution of the photocells was 1 ms,
following the technical specifications of the manufacturer. Accordingly, time was measured to the
nearest millisecond. The photocells were supported
with a plastic plate on the photocell window so that
only a 3.5 mm wide detector window was used on
each photocell. To test the variability in photocell
triggering, a sliding ruler with a nano-scale was used.
A sharp piece of plastic was attached to the ruler.
This was moved by the sliding ruler until triggering
of the photocell. The procedure was repeated 20
times. The results show that the standard deviation
was only 0.04 mm, which corresponds to 0.006% of
the distance between photocell 1 and photocell 2
(Figure 1D) and therefore this error can be
neglected.
Another factor potentially affecting reliability was
the relative time error in the recording by photocells
1 and 2 (Figure 1D), as the time spent in the interval
was short (80 – 200 ms, typically 112 ms was needed
to collect the present data). Using 112 ms as an
example of interval time, a duration of 111.5 –
112.4 ms was possible with the clock unit still
indicating 112 ms. The relative time error in the
interval before ball impact can therefore, in the worst
case, be +0.4% with the present duration setting. To
145
reduce the relative error, the interval before impact
can be lengthened. The error in the interval after ball
impact is, in the worst case, +0.2% based on the
longer interval duration (200 – 220 ms).
To test the variability in time measurements
related to photocell time resolution or other
possible factors as well as direction variability, a
series of 50 repeated impacts was performed on the
same ball with the same pre-impact interval time
(110 ms). The results showed a very small time
variation in relation to the mean post-impact
interval time (206 + 0.8 ms) and perpendicular
deviation from the line of interval direction
(s ¼ 0.005 m).
To assess the reliability of the putt-tester when the
golf club had been tested, demounted and remounted on the shaft clamp as well as repositioned
and realigned, a test – retest was performed. This was
done with a toe-heel weighted putter on two
consecutive days with the same golf balls in the same
order. The results are presented in Figure 2 and the
deviation between the two tests was small. The
average difference between the seven pairs of mean
values, representing the different impact points, was
less than 1%. The largest difference in deviation
between test and retest for the mean value of one
impact point was 1.5% (Figure 2). These results
indicate that repeated mounting and alignment can
be done without adversely affecting reliability (i.e.
the calculation of ball speed and roll distance). The
results indicate that the reliability of the putt-tester is
sufficient to perform the type of measurement
described above.
Figure 2. Test – retest of the same putter on two consecutive days.
On the abscissa the impact point 0 represents the sweet spot of the
club head and 1, 2 and 3 represent deviation (in cm) of impact
points to the toe (þ) and heel side (7) of the sweet spot. On the
ordinate 100% represents roll distance at impact point 0. Each
data point in the figure represents the mean + s of 10 repeated ball
impacts.
146
J. Nilsson & J. Karlsen
Comparison of distance and direction
deviation – implementation of the putt-tester
In Figures 3A and B, the differences in roll distance
after ball impact on the sweet spot and three
positions (1, 2 and 3 cm) on the toe and heel side
of the sweet spot, using two conventional and
commercially available golf putters as well as a
specially made putter, are presented. The results in
Figure 3A clearly reflect the curvo-linear relationship
between medio-lateral clubface impact point deviation and roll distance, as well as differences in
performance between the three golf putters at certain
deviations from the sweet spot. The decrease in roll
distance due to deviation in impact point was, for the
putters in the present example, about 13% in the
worst case. In Figure 3B, differences in direction
Figure 3. (A) The relationship between relative roll distance
(ordinate) and horizontal impact point deviation (abscissa) for
three different putters. On the ordinate 100% represents roll
distance at impact point 0. (B) The relationship between relative
medio-lateral deviation as a percentage of roll distance after ball
impact (ordinate) and horizontal impact point deviation (abscissa)
for three different putters. In both plots on the abscissa the impact
point 0 represents the sweet spot of the club head and 1, 2 and 3
represent deviation (in cm) of impact points to the toe (þ) and heel
side (7) of the sweet spot. Each data point in the figure represents
the mean + s of 10 repeated ball impacts.
(medio-lateral) deviation, in relation to impact point,
are shown. The largest relative deviation was about
3.5% of the roll length after ball impact. All putts
made with the putt-tester in this study equal
approximately a 9 m putt on a flat green with an
average roll friction. The latter was checked with a
device (stimpmeter) for measuring roll friction on
golf greens, which showed a value of 8 feet. (For
further information about the stimpmeter, see www.
usga.org/turf/articles/management/greens/stimpmeter.
html.)
The putt-tester was also tested on a golf green and
the results obtained (Figure 4) were in line with the
results from the laboratory tests (Figures 3A and B).
The results above indicate that the test apparatus can
be used with different types of putters, and is able to
show differences in distance and direction performance.
In conclusion, the results presented here show that
the putt-tester can detect differences in distance and
medio-lateral deviation related to different points of
Figure 4. Distance and directional deviation in 10 m long putts
with the putt-tester on a golf green with two different putters where
putts were made at the sweet spot and 1 – 3 cm to the toe or heel
side of the sweet spot. In all putts the same club head speed at
impact was given by the putt-tester. X marks the point of ball
impact. Black dots represent ball positions after impact with a
commercially available mallet putter. White dots represent ball
positions after impact with a specially made wing-type putter.
A new device to evaluate performance of golf putters
impact on the putter club face with high reliability.
Although the present data are from horizontal offcentre hits, the putt-tester can also be used to test
deviation from vertical off-centre hits, or a combination of vertical and horizontal miss-hits. The
apparatus and set-up can be used in the laboratory
as well as on an outdoor putting green to evaluate the
distance and directional performance of putters
already on the market and to monitor the process
to perfect putters in the future.
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