- University Engineering
2017 - Grenade 2 - Modified Dual Cavity Design
Driver Design Process
As told by University of Vermont Engineering students. (2012-2013 Academic Year)
We began by creating a problem statement to give our team a focused goal of what a successful design consisted of for this project and to provide guidance. The problem statement: BombTech Golf wants a radically new golf driver head to be sold to the public. The driver head must adhere to USGA standards and must not infringe on any existing patents. It should have a loft of 10.5 degrees, be compatible with common shaft sizes and should be designed with the average golfers’ ability in mind. Wind-tunnel testing and CFD modeling should prove that this new head is aerodynamic while offering a large sweet spot. The driver head design will be manufactured out of a Ti-1188 titanium. Samples will be tested to provide physical data as well as user tested and graded to insure that a high quality club has been created.
To gain some general ideas and a starting point we researched patents and prior art for “aerodynamic” woods that had already been designed. This led us to club heads with dimples, channels, and grooves. We realized that a club head with a feature that reduced drag such as a cavity, such as these patents, would be more innovative and visually appealing than simply creating the most sleek club head possible.
We researched cars, boats, and trucks to see how they tried be more aerodynamic. We found our answer with trucks. A truck, like a golf club, has a large front surface that increases drag and cannot be streamlined like a small sports car. Everyone has heard the myth that you get better gas mileage with your tailgate up. This has been proven by different entities, most popularly Mythbusters. The tailgate creates a pocket of air to form in the bed of the truck which lets the oncoming air to travel over it instead of diving into the bed of the truck creating drag. We believed we could do something similar with a golf club head by making cavities in the sole of the club.
It was decided that two cavities was best to keep the center of mass directly behind the center of the club face. We created a 3-D model of a club head in SolidWorks, a Computer Aided Drafting (CAD) program. In this program we were able to use a Computational Fluid Dynamics (CFD) simulation to test different shaped cavities. We performed some simplified calculations to get a rough number for what our drag force should equal to prove the CFD models were accurate. We then began running dozens of tests to find which shape, depth, and angles of the triangles created the least amount of drag.
In order to make certain that our CDF simulations were accurate we analyzed the drag force on the club using the following equation:
The density of air is known. The drag coefficient is based on a geometrical assumption and therefore also a known constant of 1.17. Since the density of air and the drag coefficient are intrinsically predetermined, we wanted to be very precise with the projected area. Using the maximum allowable face dimensions, we arrived at an area of 0.0070939047m2. It is important to have this many decimal places, as it is a multiplier of the entire equation. We also decided on a club velocity of an average amateur golfer (85mph). This is an arbitrary number as long as we use this value for all testing, both physical and computational.
This value served two purposes. It gave us a reference number allowing us to be certain that our simulations were accurate. 7.21 Newtons also served as a target maximum. Since the projected area was exaggerated our drag values at 85mph should fall below this mark. We were pleased when our simulations of our most aerodynamic design (now the GRENADE) was returning drag values of just above 5 N, well below our calculated maximum of 7.21 N
The basic shape of the club head was created to be a streamlined shape that was similar to current drivers on the market. The innovative feature is the Dual Cavity Design. Using CFD modeling on dozens of different designs, the optimum shape and depth of the cavities was found. The current triangular shape of the cavities with an angle of 55.8 degrees and a depth of 1 inch is shown in figure E1.
Figure E1: Dimensioned Drawing of the Grenade Dual Cavity Design.
As shown by the CFD modeling the cavities create a vortex behind the club-head to decrease drag. This vortex allows air to flow over it instead of the club head, decreasing friction and therefore drag. The decreased drag allows the player to achieve higher club-head speed with the same amount of energy put into the swing. A higher club swing correlates to a greater driving distance.
Drag Reduction was measured in a wind tunnel at 84 mph and showed a 48% reduction in drag versus a traditional shaped golf driver. Further tweaking of the design such as perfectly rounding the crown and slightly altering the depth and orientation of the cavities resulted in better and better aerodynamics according to our simulations. We knew we had the right design, it was original, sleek, and high performing.
Why Design a Putter?
As told by University of Vermont Engineering students. (2013-2014 Academic Year)
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 Stable Putting Stroke
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.
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.
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.
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 club 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.
Dual Cavity Design - Fairway Woods And Hybrids
The dual cavity design has been so beneficial for our driver design, that I applied the same concepts to our new fairway woods and hybrids. As you can imagine, the design had to be modified to accommodate for hitting off the fairway. The rear edge of the dual cavities was flattened, this was done to prevent any digging when hitting of the deck. In addition to flattening out one side, the cavities were designed to be less shallow relative to the fairway woods and hybrids face depth.