Embed Size (px)
Citation preview
Assessment of DST® Impact Line Technology
A comparison between a lag-style swing and flip-style swing using a forward dynamics model
Dr. Sasho MacKenzie September 20, 2019
Influence of Muscle Timing Variability on Impact
Kinematics
Dr. Sasho MacKenzie
Background•The premise of DST® Impact Line Technology is that a reference line etched onto the hosel of a club can improve a golfer’s shaft orientation at impact with the golf ball. •The club handle will be located in such a position where the club shaft will trail behind an extension of the player’s lead forearm, creating a positive lag angle.
9/23/19 2
Dr. Sasho MacKenzie
An iron engraved with the DST® Impact Line Technology
9/23/19 3
Dr. Sasho MacKenzie
Purpose of Study• The purpose of the consultation work was to determine if the swing mechanics associated with a relative angle between an extension of the player’s lead forearm and club shaft (lag angle) at impact are inherently more repeatable than the swing mechanics associated with a ‘flip’ style swing in which the club shaft has already overtaken an extension of the lead forearm at impact.
9/23/19 4
Dr. Sasho MacKenzie
Lag vs Flip
9/23/19 5
Dr. Sasho MacKenzie
Methods: Rationale• It is challenging to determine a cause and effect relationship between lag angle at impact and the repeatability of club head and ball impact conditions. • For example, perhaps it is a speed generating mechanism, or perhaps better golfers are simply trying to achieve a more favourable dynamic loft. • An alternative approach to live golfer testing involves employing a forward dynamics model of golfer.
9/23/19 6
Dr. Sasho MacKenzie
Methods: Baseline Swings• For this project, a model was ‘optimized’ to generate two swing styles with impact conditions (e.g., speed, path, face angle) that would generate a straight ball flight. • A 7 iron swing with 12 deg of relative lag angle between lead
forearm and club shaft at impact. • A 7 iron swing with 6 deg of relative flipped angle between
the lead forearm and club shaft at impact.
9/23/19 7
Dr. Sasho MacKenzie
Impact Parameters for Optimized Swings
9/23/19 8
Swing Style Loft (°) Face Angle (°)
Path (°) Attack Angle (°)
Club Speed (mph)
Flip 34.9 0.0 0.51 1.3 90.9
Lag 25.5 0.0 0.62 -6.0 89.9
• The 7-iron used in this study had a design loft of 33°
Dr. Sasho MacKenzie
Methods: Approach• The two swing styles were evaluated by making a thousand
swings with slight modifications to the predetermined ‘optimal’ muscle activation patterns. • Muscle activation timing errors between ± 0.01 s were
introduced for the start and duration times of the model’s muscles. • Timing errors were introduced into all muscles that powered
the model. E.g., muscles that generated pelvis rotation, torso rotation, flexion and extension of the shoulders, supination at the elbow, wrist flexion, wrist extension, and wrist ulnar deviation.
9/23/19 9
Dr. Sasho MacKenzie
Results Description• Results are presented in terms of Average Absolute Error • Each of the 1000 “miss-timed” swings will have different impact
conditions compared to the optimized. For example, the face angle may be 5° more closed or 5° more open. The absolute value of the difference is taken for each swing and an average error was calculated for all 1000 swings.
9/23/19 10
Dr. Sasho MacKenzie
Aver
age
ABS
Loft
Err
or
(�)
0
1.3
2.5
3.8
5
2.5
4.6
Average Absolute Loft Angle Error
9/23/19 11
• Flip swing had a greater mean loft error
Lag Impact 46% more consistent
Dr. Sasho MacKenzie
Aver
age
ABS
face
Err
or (�
)0
1.5
3
4.5
6
2.9
5.4
Average Absolute Face Angle Error
9/23/19 12
• Flip swing had a greater mean face angle error
Lag Impact 46% more consistent
Dr. Sasho MacKenzie
Aver
age
ABS
Path
Err
or (�
)0
0.28
0.55
0.83
1.1
0.93
1.04
Average Absolute Path Error
9/23/19 13
• Flip swing had a greater mean path error
Lag Impact 10% more consistent
Dr. Sasho MacKenzie
Aver
age
ABS
AA E
rror
(�
)0
0.25
0.51
0.76
1.01
0.971.01
Average Absolute Attack Angle Error
9/23/19 14
• Flip swing had a greater mean attack angle error
Lag Impact 4% more consistent
Dr. Sasho MacKenzie
Aver
age
ABS
CHS
Erro
r (m
ph)
0
0.35
0.7
1.05
1.4
1.261.37
Average Absolute Clubhead Speed Error
9/23/19 15
• Flip swing had a greater mean clubhead speed error
Lag Impact 8% more consistent
Dr. Sasho MacKenzie
Discussion: Optimized Swings
9/23/19 16
• Both optimized swings would generate straight ball flights with less than 1 yard of lateral deviation. The club head speed for the lag swing (90 mph) is equivalent to the PGA Tour average, while the club head speed for the flip swing (91 mph) is just above. • The optimized swings differed meaningfully in the amount of loft
delivered (flip = 34.9° vs lag = 25.5°) and attack angle (flip = 1.3° vs lag = -6.0°). These lag numbers are representative of a PGA Tour player, while the flip numbers could be associated with a high handicapper. • The lag swing would launch the ball at 128 mph at 18° with 6200 rpm of
backspin resulting in a carry of 181 yards, while the flip swing would launch the ball at 129 mph at 25° with 6700 rpm of backspin resulting in a carry of 175 yards.
Dr. Sasho MacKenzie
Discussion: Average Absolute Errors
9/23/19 17
• The face and path errors for the lag swing would generate an average lateral miss of about 23 yards, while the face and path errors for the flip swing would almost double the average lateral miss to approximately 40 yards. Remember that identical timing errors were introduced into both swings. • The delivered loft and attack angle errors for the lag swing would
introduce carry distance errors ± 3 yards, while the loft and attack angle errors for the flip swing would introduce carry distance errors of ± 6 yards. • Club head speed errors would not likely generate meaningful
differences in ball flight.
Dr. Sasho MacKenzie
Summary• The findings from this project suggest that both a ‘lag style’ swing and a ‘flip
style’ swing can produce a straight ball flight with sufficient distance. However, it is important to note that the flip swing was about a half club short of the lag swing.
• However, this research provides evidence to suggest that changes in key club head delivery parameters are meaningfully larger when muscle timing errors are introduced into a ‘flip style’ swing compared to a ‘lag style’ swing.
• Human golfers are not perfectly repeatable and will inadvertently introduce errors in the timing of their muscular contraction.
• Having a swing with an outcome that is less effected by these muscle timing errors would be beneficial.
• As such, since the DST® Impact Line Technology encourages a ‘lag style’ swing, then it is promoting a club delivery pattern, which is less susceptible to typical human error.
9/23/19 18
