Why Design a HIGH MOI Golf Putter?
After the success of the Grenade driver, BombTech Golf’s founder Tyler “Sully” Sullivan returned to UVM looking for a group of engineering seniors to lead a new project – the design and production of BombTech’s first putter. This is when the “Dream Team” was born.
The primary objective of the project was to design, engineer, and oversee production of a putter that could improve the average golfer’s short game. Similarly to driving, putting is heavily influenced by the golfer’s mentality and confidence so there was only a small window in which we could focus our efforts. This limited the extent to which we could explore and produce innovations but it also helped to produce a putter that was exclusively designed for excellent performance and to live up to the aesthetic standards set forth by the Grenade driver.
A big issue with golfers is a stable putting stroke. When the putter head wanders, the likelihood of a mishit is increased. We learned that by increasing the weight of the clubhead, it would promote a pendulum style swing path. We believed that increasing the clubhead mass will keep golfers from mishitting putts and subsequently raising their score.
But what happens if you have a perfectly stable stroke and still hit the ball a distance off the sweet spot? If the putter mass is large and strategically placed, the putter’s moment of inertia can be optimized to be highly efficient. The term “moment of inertia” gets thrown around often, but not many golfers may know what it truly signifies. When a putter has a high moment of inertia, it will resist the urge to rotate when a force is applied to its heel or toe. This resistance theoretically lowers the distance that a putt will miss the desired target. So on a shot of the toe with a high MOI putter, the golfer could be 3 feet from the hole rather than 7 feet, which could be make a huge difference.
Finally, the putter material selection was a major factor in our design considerations. Current top market companies utilize a single piece of carbon steel and a computer numerical controlled (CNC) milling process to create products that lead the competition in terms of qualitative feel, sound, and performance. BombTech Golf’s mission is to release premium products that can compete with the big names. For this reason, we decided that the putter would be milled out of a single piece of low carbon steel. On top of this, the entire milling and finishing process takes place here in Vermont!
Design Process
The first phase of the design after determining the desired metrics, was the prototyping phase where we designed nearly thirty clubs and prototyped about ten that would achieve all the goals we had for performance. We utilized a 3D-printer to rapid prototype clubs straight from computer modeling software. In the software we were able analyze properties of each club head and compare them side by side.
From the prototyping phase arose one club that hit every design goal and that had a great look to it. That club was nearly what you see today as the BombTech Golf Grenade Putter. We worked with Stephen’s Precision Milling in Bradford, VT who helped to develop the final product that the club is today.
3D printed prototype of the final design
With freshly cut putter in hand, we began testing it with a standardized putter testing rig. We proceeded to test nearly one thousand ball impacts to gather the data on the performance. We then used statistical analysis software to provide hard hitting evidence that the Grenade was the real deal.
Design Details
The putter was developed mainly to be a forgiving club and to prevent human error while putting. This was achieved by pursuing a high moment of inertia about the z-axis. Moment of inertia is the clubs resistance to being torqued by an off-center impact. The grenade putter clocks in at a stomping 5850 grams per centimeter squared. This as will be shown in the consistency test makes the sweet spot on the club head huge compared to other putters. This allows for slight errors in swing path to influence the end result less.
Many of the geometry features in the club are designed to maximize this moment of inertia (MOI). The center cut hole is there for weight management to ensure the best feel and allow for weight to be moved into other areas. This is also why we chose a mallet putter over a blade putter design. It allows for more movement of mass and contributes to a much higher moment of inertia. Our efforts to increase the moment of inertia paid off as in our testing our club performed significantly better at minimizing ball dispersion on off-center hits.
The club is heavy. At 445 grams it is one of the heaviest putters on the market. This was intended as well. The increased weight prevents psychological factors like nerves from overcoming your swing and influencing the swing path. We encourage the user to not fight the weight but let it guide the hands through the motion. Research has shown that putter head velocity shakes around as the swing is executed. The heavier head stabilizes the jittery velocity and forces the transitions to be more fluid.
We also chose a loft angle of 2.5 degrees to promote “pure roll”. Slow motion analysis of the high MOI golf putter impacts shows that the ball pops off the ground and does not begin rolling for quite some distance. The grenade putter minimizes this distance and gets the ball rolling almost twice as fast as comparable putters.
We also chose our material very carefully. Since this putter is completely milled from one piece of solid steel the material properties were crucial. 12l14 steel is a modern composite that has recently begun being used in many applications but was rather exotic just a few years ago. While 12l14 is still a steel alloy that can withstand pulling forces upwards of 60,000 psi, it is as soft as aluminum. This tough as nails and humble material is what gives the putter that solid pleasant feel and sound that makes the Grenade putter feel like a thousand bucks.
Engineered Results
So how does the Grenade high MOI golf putter perform compared to other putters? To determine this, we subjected the putter to three different sets of tests. The first test looked at the Grenade’s consistency and accuracy, the second test analyzed its initial roll characteristics, and the third test was a qualitative assessment, where the Grenade was given to local golfers who gave their feedback and opinion on the putter.
Since the primary objective of putting is to put the ball in the cup, the first test we conducted was a consistency and accuracy test. We hit numerous balls off different face locations, ranging from the heel to the toe, and measured the radial distance the resultant putt was from the determined distance of a putt of the center. The radial distance was compared to the optimal center distance to produce a metric that could be used to compare the three putters we tested. Below are the results of the experiment.
What this graph shows is the relationship between off-center shots and a dispersion ratio. The dispersion ratio is essentially a percentage that a shot is away from the hole. For example, a 30’ putt with a dispersion ratio of 0.2 means you are 20% of the 30’ away from the hole – leaving you with a 6’ putt to the hole. The above graph shows that the Grenade putter has a dispersion ratio ranging from 0.034 to 0.166 (1’-5’ dispersion on a 30’ putt).
The second test was an analysis of the Grenade’s initial roll characteristics compared to the other two clubs tested. Using a high-speed camera, we were able to record how each club imparted spin on the ball in high definition. As evident in the video (linked below), the Grenade produces topspin almost immediately,.
In addition to these quantitative tests, we displayed the finished Grenade putter and allowed local golfers to try it out. The initial feedback was very positive, with emphasis put on the Grenade’s soft and responsive feel, stable stroke, and highly satisfying impact sound. We now invite you to pull the pin and give the Grenade putter a shot! Make more putts, guaranteed!
