In recent months, interest has grown considerably in the new foam core (Gen-4) paddles, such as the Selkirk Labs Project Boomstik. This has generated numerous claims from the manufacturer, retailers, reviewers and players, some of which appear to be counter-intuitive or contradictory. For example, it is often claimed that foam core paddles develop more power than polycarbonate honeycomb core (polycore) paddles; however, others claim that the foam core absorbs or dissipates more energy than the polycore paddles, resulting in a softer touch or increased dwell time. How can that be? If a foam paddle absorbs more energy from the ball, how can it return this energy back to the ball and thus produce more power or velocity on rebound? In this article, we will test and analyze the Boomstik paddle to help prove or disprove some of these claims.
Vibration Modes
The first thing you will notice about the Boomstik (as well as other foam core paddles) is that they have a distinctive low frequency or hollow “thud” when striking a ball verses the higher frequency “plink” of polycore paddles. This is typical, which implies that foam core paddles vibrate at lower frequencies than polycore paddles. How does this affect their performance?
As we discussed in our article “Paddle Dynamics”, when you strike a ball, two paddle vibration modes are excited – a diving board mode and a trampoline mode. The paddle diving board mode (Figure 1a) is characterized by bending about the paddle throat, where the point of maximum deflection is along the upper edge of the paddle face. The trampoline mode (Figure 1b) is characterized by bending of the paddle face, where the point of maximum deflection is at the ball contact location (assumed to be at the center of the paddle face). As we discussed in “Paddle Trampoline Modes”, the trampoline mode can take on several different shapes, some of which are more effective than others in returning energy back to the ball on rebound. Figure 1b shows the classic “basket” mode, which is the most effective trampoline mode. Other less effective trampoline modes include the “taco” bending and “potato chip” bending modes.
a. Diving Board Mode
b. Trampoline Basket Mode
Figure 1. Paddle Bending Modes
Frequency Response Functions
The frequency response function (FRF) is a complex-valued measurement of the acceleration (in g’s) at a point on a body caused by the application of a force (in pounds or lbf) at an arbitrary location on the body. The paddle FRFs are generated by striking the paddle at the geometric center of the paddle face and measuring the acceleration response at various points on the paddle. One important FRF is the so-called “driving point transfer function” which is essentially an indication of the dynamic loads applied to the ball by the paddle at impact. Figure 2 shows the driving point transfer function at the center of the face of a Selkirk Labs Project Boomstik 16mm elongated paddle (Gen-4). Here, we see that the paddle has three peaks in the transfer function, occurring at 463 Hz, 646 Hz, and 893 Hz.
Figures 3a-c show an animation of the three Boomstik vibration modes, including the diving board mode at 463 Hz and two trampoline modes at 646 Hz, and 893 Hz. The 646 Hz mode is characterized by “taco bending”, whereas the 893 Hz mode is characterized by “potato chip bending”. We discuss these vibration modes in detail in our article, “Paddle Trampoline Modes”.
a. Diving Board Mode
b. Taco Mode
c. Potato Chip Mode
Figures 3. Boomstik Vibration Modes
Paddle Power & Control
It is well known in the field of baseball that hollow aluminum bats are “hotter” than wooden bats and must therefore be regulated at the high school and college levels and are not allowed in the pros. According to the technical literature, hollow aluminum bats exhibit “hoop” (or trampoline) vibration modes that occur at sufficiently high frequencies that they add energy back to the ball on rebound. On the other hand, wooden bats exhibit only lower frequency bending (or diving board) modes about the handle, which tend to dissipate energy. This is due in part to the fact that the bat is still bent backwards when the ball rebounds off the bat. We explained this phenomenon in “Why Paddles Are Like Baseball Bats”.
In our article, “Are Paddles Like Tennis Racquets?”, we observed that during contact with the ball, the paddle face vibrates at the trampoline frequency, however after contact, the paddle face vibrates at the diving board frequency. From this, we surmised that the vibration energy in the trampoline modes is recovered by the ball, but the vibration energy in the diving board modes is dissipated by the paddle. In general, we found that paddles with lower frequency trampoline modes had greater power, and paddles with higher frequency diving board modes had more control.
Figure 4 shows a comparison of the driving point transfer functions for a Gen-2, Gen-3, and Gen-4 paddle. As you may know, Gen-2 paddles are comprised of polycores, Gen-3 paddles have polycores surrounded by foam edges, and Gen-4 paddles have cores that are comprised only of foam. While the dynamics of individual paddles vary, this chart illustrates that in going from Gen-2 to Gen-3 to Gen-4, the frequencies of the diving board modes tend to increase, and the frequencies of the trampoline modes tend to decrease.
Boomstik Control vs Power
In “The 2-D Power vs Control Spectrum”, we postulated that paddles with higher frequency diving board modes create more control, and paddles with lower frequency trampoline modes produce more power. Numerically, the Control / Power Frequency Criterion is shown in Table 1.
Table 1. Control / Power Frequency Criterion
Conventional wisdom suggests that paddles are classified as “control”, “hybrid”, or “power” paddles. However, according to our dynamic testing criteria, it is possible for a paddle to exhibit both high control and high power. The Boomstik is one such paddle, with a diving board mode that exceeds 400 Hz and a trampoline mode of less than 650 Hz.
Overall, our tests show that the Boomstik exhibits a high degree of control with a moderately high amount of power. The power is not overly high, as the first trampoline mode at 646 Hz is barely below the 650 Hz power threshold, and the 2nd trampoline mode at 893 Hz puts it into the low power category. Furthermore, the shapes of these trampoline modes (taco and potato chip) are not the most efficient in returning power back to the ball on rebound.
The Selkirk Labs Project Boomstik* might be ideal for players desiring a paddle with greater power together with a higher degree of control. One common problem among players transitioning from conventional Gen-2/3 polycore paddles to foam core Gen-4 paddles is that they tend to over-hit the ball since the paddles have too much power. The Boomstik’s higher control capability together with moderately high power may enable players to accurately place their shots with greater velocity.
Future Work
As illustrated by our tests of the Selkirk Labs Project Boomstik paddle, the foam core enables (some but not all) Gen-4 paddles to achieve a high degree of control together with a high amount of power. By virtue of their design, this may not be an easy task for conventional Gen-2 polycore or Gen-3 foam edge paddles. It is possible for manufacturers of Gen-4 foam core paddles to adjust the amount of power or control in their paddles by changing the foam material properties and/or by modifying the design of the foam core. We may discuss how this can be accomplished in a future article.
We will also provide dynamic test data for other foam core paddles, such as the Bread & Butter Loco, the CRBN 3 TruFoam, and the Selkirk Project 008 paddles. Other Gen-4 paddle manufacturers are welcome to contact us if they would like their foam core paddles dynamically tested and included in this evaluation. Since foam core paddles are not for everyone, we will also compare the dynamics of these foam core paddles with more conventional polycore Gen-2 and foam edge Gen-3 paddles which may provide similar power and control characteristics.
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