Abstract
Imparting topspin on a golf ball from putter impact can be achieved either by oblique impact from negative-lofted putter faces or by vertical eccentric impact (commonly referred to as ‘vertical gear-effect’). Negative loft gives a small amount of topspin but should preferably be combined with positive putter-head trajectory to give the ball lift at impact. Vertical gear-effect can provide high spin rates for impacts above the sweet spot and desirably gives the ball a small upward lift at impact. This paper outlines the theory of spin generation in putter impact, discusses how high vertical gear-effect can be implemented and considers the effect that such designs have on putt length control, directional accuracy and impact vibration. Ballistic measurement techniques to validate putter designs are described and an unexpected experimental result dependent on shaft coupling is analysed.
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Abbreviations
- αi :
-
putter face loft angle at impact
- δ:
-
impact point lateral offset towards heel or toe
- D:
-
distance between shaft axis and putter-head rotation axis
- dr :
-
ball roll distance on green
- ds :
-
ball slide distance on green
- Φ:
-
putter-head rotation angle due to offset impact
- g:
-
acceleration due to Earth’s gravity (9.81 m s−2)
- h:
-
distance between line of impact and putter-head centre of mass
- hc :
-
height of centre of mass above extreme bottom surface of putter head
- hi :
-
impact height above extreme bottom surface of putter head
- hs :
-
height of sweet spot
- Ix :
-
putter-head moment of inertia about heel-toe axis through centre of mass
- Iz :
-
putter-head moment of inertia about vertical axis through centre of mass
- Kx :
-
putter-head radius of gyration about heel-toe axis through centre of mass
- Kz :
-
putter-head radius of gyration about vertical axis through centre of mass
- L:
-
effective length of shaft during impact
- M:
-
putter-head mass
- μr :
-
coefficient of rolling friction of golf ball on green
- μs :
-
coefficient of sliding friction of golf ball on green
- p:
-
distance of centre of mass behind putter impactface
- r:
-
radius of shaft
- R:
-
ball peripheral velocity due to vertical spin as a ratio of its linear velocity (roll ratio)
- t:
-
wall thickness of shaft
- ts :
-
duration of skidding phase
- v:
-
ball launch velocity at eccentric impact
- vc :
-
ball launch velocity at central impact
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