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Smart Golf Clubs for Player Enhancement
Spring 2020 MAE 156B Sponsored Project
University of California, San Diego
Sponsored by:
Ken Loh, Ph.D.
Ms. Morgan L. Funderburk
Background
Although today's game of golf maintains most of its original characteristics from when it was first created, it has been revolutionized through technologies which seek to optimize and enhance player performance. Golfers have turned to technology to improve their training regime, enhance their techniques and skill sets, and ultimately heighten their chances of winning.
The Active, Responsive, Multifunctional, and Ordered-materials Research (ARMOR) Laboratory at UC San Diego, led by Dr. Ken Loh, aims to safeguard and enhance the capabilities of structural and human assets by designing stimuli-responsive materials coupled with novel interrogation, modeling, and analytical methods. Their studies center around conducting fundamental research, advancing innovative ideas and technologies, and prototyping new sensing and actuation systems. By partnering with TaylorMade Golf, this project makes use of the sensing technologies already being developed in the ARMOR Lab but applies them in a way they have never been used before.
The objective of this project was to design a sensing strategy and data acquisition system to accurately depict and quantify the strike location of a golf ball on a club face at high resolution in order to enhance player performance. Unlike other training aids used in golf today, this project sought to develop a device that could be attached to any driver at a profile that is non-disruptive to the golfer’s movement.
Objectives
Primary:
Develop and implement a data acquisition system (DAQ)
Demonstrate that acquired data can indicate the strike location of a golf ball on a club face
Secondary:
Demonstrate that acquired data can quantify the magnitude of impact force
Tertiary:
Incorporate angle detection for future product development
Statement of Requirements
Locate the strike of a golf ball on a driver face with a tolerance of +/- 5 mm
Accurately quantify the magnitude of force, ranging up to 13 kN, that the golf ball strikes the driver face with
Sensing strategy must be durable enough to withstand impact of 8 kN to 13 kN
Does not affect player performance when implemented
The final product is comparable in shape, size, and weight considerations of golf drivers in the market
Description of Final Design
The final design solution included a complete mockup of a driver club with the driver handle, driver shaft, and driver head shown in Figure 1 to the right. This design incorporated a multi-layer sensing strategy composed of Polyvinylidene fluoride (PVDF) piezoelectric sensor strips for impact location detection and a larger PVDF sensor for impact force quantification as shown in Figures 2-3.
Figure 1: Driver Club Final Design
Figure 2: Sensor Layout Isometric View Final Design
Figure 3: Sensor Layout Top View Final Design
The sensor layout design was encased in and adhered to the back side of the acrylic driver face with insulative epoxy adhesive, shown in Figures 4-5, which was then secured to the driver head as seen in Figures 6-7.
Figure 4: Sensor Layout Adhered to Acrylic with Epoxy Front View
Figure 5: Sensor Layout Adhered to Acrylic with Epoxy Back View
Figure 6: Driver Head Final Design
Figure 7: Driver Head Final Design
The main components of the data acquisition system (DAQ) are shown in Figures 8-10. The DAQ featured a 16 to 1 multiplexer that enables a single analog to digital converter to be used, significantly cutting down on space. Additionally, the DAQ featured a Teensy 4.0 microcontroller capable of clock speeds up to 600 MHz. There are two levels of printed circuit boards (PCB), one for analog inputs and one for digital. The dual PCB helped save space and helped to reduce the system noise between analog and digital components. The analog PCB featured the signal conditioning components all for the purpose of cleaning the analog signal before converting to a digital signal. The digital PCB served to connect and communicate with the digital components such as the accelerometer, memory, and wireless transceiver. The block diagram detailing the DAQ components is shown in Figure 11.
Figure 8: Analog Components PCB Final Design
Figure 9: Digital Components PCB Final Design
Figure 10: DAQ Components Stack Up
Figure 11: DAQ Block Diagram
The main DAQ components were encapsulated inside the driver head using a bilayer potting method, illustrated in Figure 12, which consisted of a hard epoxy interior layer to provide rigidity to the printed circuit board (PCB) for deflection prevention and a soft silicone exterior layer to absorb shock.
Figure 12: Bilayer Encapsulation Method
The potting mold pictured in Figure 13 featured a tiered design that brought a majority of the mass closer to the bottom rear of the driver head as depicted in Figures 14-15 which ensured that the moment of inertia was moved as low and towards the back of the driver head as possible and that the center of gravity remained in a location in line with standard driver heads.
Figure 13: Electronic Component Encapsulation Layers
Figure 14: Electronic Component Encasement Embedded Mold Final Design
Figure 15: Electronic Component Encasement Embedded Mold Final Design
Additional electronic components such as the wireless transceiver and battery were encased inside the driver handle, as detailed in Figures 16-17, to address safety concerns regarding impact to the battery if it had been placed in the driver head and to address the risk of signal loss if the wireless transceiver had been placed in the driver head. Wires connecting components in the driver head and driver handle ran inside along the purchased TaylorMade Fujikura Speeder 65 Regular Flex shaft.
Figure 16: Driver Handle Assembled View
Figure 17: Driver Handle and Inner Components Exploded View
The wireless transceiver in the driver handle transmitted the data to another wireless transceiver located inside the receiver enclosure illustrated in Figures 18-20. The Arduino Mega, also housed in the receiver enclosure, was directly connected to a laptop, where MATLAB analyzed the data and presented the impact force and impact location on the liquid crystal display of the enclosure display. A more detailed view of the strike location was shown on the laptop as in Figure 21. The receiver enclosure was designed to be small, lightweight, and portable, making it convenient for the user to carry with them along with their laptop.
Figure 18: Receiver Enclosure and LCD Screen
Figure 19: Receiver Enclosure Inner Components
Figure 20: Receiver Enclosure
Figure 21: Display Setup
Summary of Performance Results
Full Sensor Layout Validation:
The full sensor layout was validated through the testing with a National Instruments NI PXIe-1082 data acquisition system capable of collecting data from all 16 sensors, given that at the time of testing, the DAQ system for the Smart Golf Clubs was not yet complete. The detection of impact location was achieved through normalization of the data collected and data training analysis.
Theoretical Predictions:
Sensors' output voltages are not proportional to location of golf strike based on a Solidworks simulation where largest deflection of sensor is not correlated to where the golf ball strikes
Normalizing voltage readings from a given impact location will enable a distinction between different impact locations
Sensors' output voltages normalized by its center location output maximum voltage could be compared to all other sensors and can each have a unique ratio of all sensors' outputted voltages for each specific location
A unique identification tag of sensor output voltages for each specific location can be found through data machine learning (data training through hitting multiple trials at each major sensor intersection)
Test Conditions:
Driver face secured to driver head
Force applied using impulse hammer (PCB® Modally Tuned® Impulse Hammer, Model: 086C03)
Variable force applied to driver face at 25 locations specified in Figure 22
10 consecutive impacts at each location
Figure 22: Full Sensor Layout Impact Locations (Major Intersection Spots)
Figure 23: Full Sensor Layout Test Setup
Results:
Some sensors outputted negative voltages, inconsistent data, or no voltage
86.8% test accuracy based out of code correctly calculating simulated data 868 trials out of 1,000 trials although inaccurate calculations determine locations fairly close to the correct location still
Figure 24 shows the average ratio for each sensor at each spot which was calculated with the data training results
Figure 24: Unique Identification Sensor Voltage Ratios for Each Major Intersection Spot
Comparison of Results to Initial Performance Requirements:
Could not perfectly replicate golf strike during experiment because force output voltage would rail
Accuracy of location calibration could be improved by performing more trials per location, adding in more working sensors, and incorporating a method of considering the variable force involved in the location calibration
Figure 24 and the accuracy test result support the notion that data training was effective in characterizing the location of a golf strike
Isolated DAQ Validation:
The isolated DAQ validation was conducted to test if the DAQ could truly sample 16 separate sensor channels at any one time and successfully output that data to individual arrays. To prove that each channel could separately sample individual signals, each channel was set to sample the same signal, and the differences between each channel's output signal to the analog to digital converter were noted. The test was conclusive that each channel could distinctly sample when the same signal was resolved on each channel output, but on a zoomed in scale, small differences could be seen due to delays in sampling time and individual noise on each channel.
Theoretical Predictions:
Each channel outputs an almost identical waveform replicating the 20 Hz sine wave signal
The sine wave signal was attenuated by 1/2 by the voltage divider
Test Conditions:
Sine wave signal output from the National Instruments myDAQ at 20 Hz with a 1 V peak to peak amplitude and a 1 V offset
Signal was outputted to 15 channels on the DAQ, channels 2 through 16
Channel 1 was not fed the 20 Hz signal, leaving it as a control
Analog board was set to sample at the same rate it would measure the PVDF signals, at 5 microseconds per sample, 200 kSa/s aggregate or 12.5 kSa/S per channel
Analog board had its voltage divider enabled, and the programmable gain amplifier was set to 1, so the observed output signal was predicted to be half of the input signal into each of the 16 analog inputs of the analog board
Test setup shown in Figure 25
Input sine wave signal to each of the 15 channels, 2 through 16, is shown in Figure 26 with a 1 V peak to peak amplitude and a 1 V offset
Figure 25: Isolated DAQ Test with Connections to NI myDAQ
Figure 26: Isolated DAQ Test NI myDAQ Output Signal
Results:
Output signal of each channel was sent from the analog PCB and then sampled by the Teensy onboard ADC at 250 kSa/s
Each channel's output is pictured in Figures 27 and 18
Figure 27 shows the full signals, as sampled by the 15 channels and the control at the bottom which was sampling noise
Figure 28 is zoomed in to show the distinction between the different channels as they sample the same signal, due to small switching time delay and individual noise in each channel
Output signal of analog PCB successfully showed a 1/2 gain of the signal
Each sensor input successfully sampled the same signal
The differences in each output signal implied that each channel was truly sampled independently through a different channel on the PCB and through the multiplexer
Figure 27: 20 Hz Sine Wave into 15 Channel Inputs Sampled by Teensy 4.0 ADC
Figure 28: Zoomed in 20 Hz Sine Wave into 15 Channel Inputs Sampled by Teensy 4.0 ADC
Comparison of Results to Initial Performance Requirements:
The DAQ developed for the Smart Clubs project can in fact resolve 16 different signals while maintaining an acceptable sampling rate of above 10 kSa/s
Multiplexer switching time was adequate
The code to separate successive data acquired was successfully implemented to delineate between the stream of data output from the analog PCB into the individual channel arrays
Complete System Validation:
The complete system validation was conducted to verify the sampling capability of the DAQ when connected to the PVDF sensor layout. At the beginning of this test, the primary acrylic driver face failed along a fatigue point very close to the connection points. The fatiguing of the brittle acrylic driver face was not considered as an issue that would significantly affect the plate during testing. Testing was done with the emulation of a 1% strain as the final goal. As such, the sensors were tuned through a resistor network in the DAQ to output in a higher range than the acrylic could ultimately withstand for repeated impacts. The acrylic was impacted many times before final testing of the DAQ was completed, and the useable life of the face expended before the full DAQ could acquire location and force data.
Tests were continued on the fractured acrylic test plate, with full understanding the the percentage strains felt by the PVDF sensors was significantly different than the percentage strains felt under a typical driver face scenario. The PVDF sensors experienced significantly more strain closer to where the fracture occurred no matter where the face was impacted. While any location of force data acquired with the fractured acrylic was not meaningful to data analysis, what could be shown from testing on the fractured acrylic face was the DAQ's ability to read different values from all 16 sensors for different impacts. The tests could also verify that the DAQ could observe variation in the signals, confirming that it could in fact resolve changing voltage outputs from the PVDF sensors.
In continued testing on the fractured acrylic plate, another fracture occurred on the left side of the plate, but substantial data was acquired before the second fracture allowing the PVDF sensor readings on the DAQ to be displayed.
Theoretical Predictions:
The DAQ is capable of sampling the full sensor layout (16 sensors) shown in Figure 29
Validation of DAQ with variations between the values of each sensor for different impacts demonstrates DAQ functionality and can be applied to a newly fabricated PVDF array on an acrylic or titanium driver face
Figure 29: Acrylic Driver Face Fracture
Test Conditions:
Driver face secured to the driver head
Force applied using impulse hammer (PCB® Modally Tuned® Impulse Hammer, Model: 086C03)
Variable force applied to driver face
Results:
Table 1 shows the variations in the sensor output values and control test where no impact was imparted on the face
The values listed are in units of bins of the analog to digital converter
Table 1: Data from Impacts Imparted on Fractured Acrylic Driver Face
Comparison of Results to Initial Performance Requirements:
The varying impact bin values compared to the non-impact maximums clearly indicated that the DAQ could read different voltages presented by the separate sensors
Each sensor responded differently to difference impact forces, impact locations, and amount of sensor flex due to the cracked driver face
Sensor 4 gave very high readings consistently for every location and force value, indicating that it most likely needed a different resistor value for the differential amplifier to match its impedance and bring its overall level lower
Conclusion
The objective of this project was to develop a data acquisition system and sensing strategy capable of capturing the location, force, and attack angle of a golf ball strike on a driver face. The individual components of this project, the DAQ and sensing strategy, succeeded in proving their feasibility of their respective objectives. The Smart Golf Clubs DAQ successfully proved the feasibility of sampling 16 PVDF sensors at a rate of 10 kSa/s. Additionally, the sensing strategy was capable of both localizing and quantifying the force imparted on the driver face via method of calibration and normalization of sensor outputs. Unfortunately, due to the failure of the primary acrylic driver face used for testing, the DAQ and full sensing strategy could not be coupled to form a unified product. Despite this challenge, the success of the individual components of this prototype successfully demonstrated the feasibility of the concept to develop a smart golf club. If this project were to continue, future iterations of the prototype would seek to incorporate a gyroscope and accelerometer combination capable of detecting both the high angular velocities and accelerations typical of a driver swing to enable angle of attack detection. Additionally, future improvements to the DAQ to broaden the detectable range of forces and to decrease its overall size profile would be considered. Apart from the topics involved in producing this prototype, the team learned invaluable lessons on communication and problem solving that were magnified due to the worldly circumstances during which the project was undertaken.
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