Putter-Golf Ball Impact
November 15, 2004
Advisor: Prof. Zable
University of Colorado at Boulder
Department of Mechanical Engineering
Intro: Currently there are many golf swing analysis programs on the market, but none
of them use a device that is portable and attached to a golf club. Two companies, Dulles
and MotionCoach, perform swing analysis by video taping the swing from multiple
angles, digitalizing the images, and displaying them on a computer that tracks the path
and speed of the club head. This method is efficient in picking out obvious swing flaws,
but it does not provide specific information about the impact location of the ball and club
head. Titelist has a more advanced system that is able to analyze swing speed, launch
angles, and shaft flex, but like the other systems it is not portable.
The goal of this project is to design a portable device that measures the location of impact
between a golf ball and putter. This project is not so much a research project as it is a
design challenge. Documented work done on this project or similar projects to this is
very limited. Therefore, the focus of my literature review was on various sensing devices
that I may use to collect data in determining the impact location. I also reviewed the
work done here at the University of Colorado by previous students. Though the students
did not meet all of the design requirements, their methods and findings will influence the
approach I take.
Previous Work on “Ping” Project: A group of students did a significant amount of
work on this project. Using an array of photodiodes located along the top face of the
club, they were able to triangulate the impact location. This was done by examining the
voltage outputs from the various individual photodiodes, specifically the intensity of the
readings. The voltage output corresponded to the distance the ball was from the sensor.
Photodiodes with higher readings were closer to the impact location, while a low voltage
output occurred with photodiodes located a larger distance away from impact.
The group designed and constructed a device using an array of 11 Panasonic CNB2001
photodiodes mounted on top of the club head. They then took many readings, moving a
golf ball in 1/10” increments along the face of the club. They used these readings to
determine impact location in test runs.
This system seemed to work fairly well but it had many flaws. The size and mass of the
device exceeded the allowable limit. Also the measurements were not taken in a
controlled lighting environment, which would greatly affect the readings taken by the
sensors. Even if the lighting was controlled in the testing laboratory, it would be difficult
to control it on a golf course, where this device is intended to be used. From these
conclusions I decided to look into other types of sensors, and further into the use of
Many different types of sensors could potentially be used in collecting data for this
project. The sensors I am currently reviewing and will be testing are accelerometers,
electrostatic proximity detectors, as well as photodiodes. The following information
obtained has helped me determine appropriate selection criteria for each sensor, as well
as whether or not a particular method will be viable.
Accelerometers: Accelerometers are sensors used for measuring, displaying, and
analyzing acceleration and vibration. They can be used individually, or in conjunction
with a data acquisition system. Accelerometers are available in many different forms.
Size, sensitivity, accuracy, a sampling rates vary from one accelerometer to another.
Accelerometers can have from one axis to three axes of measurement, the multiple axes
typically being orthogonal to each other. These devices work on many operating
principles. Below is simple schematic of a typical accelerometer. The common types of
accelerometers are piezoelectric, capacitance, null-balance, strain gage, resonance,
piezoresistive and magnetic induction.
Raymond R. Bouche, Endevco Tech Paper 243
There are many important features to consider when selecting a particular accelerometer.
The three main features that must be considered are: amplitude range, frequency range,
and ambient conditions. The acceleration amplitude range is measured in G’s, and
frequency is measured in Hz. For the ambient conditions, temperature should be
considered, as well as the maximum shock and vibration the accelerometers will be able
to handle. For my project, the temperature and maximum shock are not factors, therefore
ordering parts that operate at extreme temperatures, and in extreme conditions is not
necessary. Electrical output options depend on the various systems being used with the
accelerometers. Common analog options are voltage, current, or frequency. For making
higher frequency measurements, such as typical vibration measurements, accelerometers
with a good AC response should be selected. The majority of AC accelerometers use
piezoelectric ceramic or quartz sensing elements which create a charge output (Bouche).
After selecting the proper accelerometer to be used, the mounting method must be
determined. If the motion of the device being measured is not accurately transmitted to
the sensor, it cannot be accurately measured. The most secure method is stud mounting.
In this project though, the accelerometers will be arrange on the putter and drilling on the
club head is not an option. Other possibilities include using a cyanoacrylate adhesive,
such as a super glue, or double-sided tape (Romanchik, 2003). If a glue is used the
stiffness of the cured adhesive is critical to the accuracy of the measurements obtained.
The adhesive should not dampen out the vibrations that are being measured. Though no
adhesive is as stiff as a normal mounting stud, using the proper glue will still yield fairly
accurate results. Whether using glue or tape, the surface must be cleaned thoroughly to
ensure good bonding.
Powering the accelerometer is also a critical issue. In most cases the data acquisition
system will serve as the power source, and supply the necessary current. These cables
attached to the accelerometer must also be carefully dealt with. Flexing of the cables can
create distortions in the data being measure. In order to prevent these errors the cables
should simply be mounted securely, so that they themselves do not vibrate. Lastly,
accelerometers being used should not be overloaded, and need to be calibrated regularly
to ensure accuracy.
Photodiodes: Photodiodes are used to create an electronic signal proportional to the
incident light intensity perceived. These were used by the previous group to determine
the impact location of the ball hitting the flat face of the putter. Advantages to using
photodiodes include the low cost, the small size, and the versatility.
Photodiodes are most often fabricated from silicon semiconductors. The silicon absorbs
light photons, which creates a reaction that can be measured in terms of current
variations. Photodiodes are available in a wide range of shapes and sizes for different
applications. When selecting a photodiode the most important performance
characteristics are response speed, sensitivity, and the size of the active area. For this
particular application the response speed is not significant and the active area is relatively
small, on the order of 1-2 square inches. The sensitivity is the parameter that becomes
important in selecting a proper photodiode. Though the light level will not be
dramatically low, the sensor must be able to adequately pick up small variations as the
golf ball impacts the putter. One advantage in using photodiodes is that many companies
sell prepackaged arrays. This would eliminate the difficult task of creating an array from
individual diodes and integrating them for data acquisition.
Electrostatic Proximity Detectors: Electrostatic or capacitive proximity sensors
produce an electrostatic field that is able to sense metallic objects as well as nonmetallic
materials. The sensing surface of a capacitive sensor is formed by two metallic
electrodes of an unwound capacitor. As an object nears the surface of the sensor it enters
the electrostatic field of the electrodes which changes the capacitance in the circuit. This
causes oscillation in the component which is measured and ultimately used to determine
the objects location. This oscillation is proportional to the targets distance from the
sensor. Below is a simple diagram of an electrostatic proximity sensor.
(Diagram from siemens.com)
Proximity detectors such as this are manufactured for many applications. When
selecting a sensor of this type the most important characteristic is the targets that are
specified for the capacitive sensor. This is defined by the dielectric constant of objects
that the sensor can identify. For this project the object is a hardened plastic, so finding an
electrostatic proximity detector that can measure such a material is key. Care must also
be taken to ensure that the sensor is kept dry. Liquid on the sensing surface could prevent
the sensor from operating properly.
Conclusion: From these various reviews I have been able to move forward efficiently.
The work already done on this project has given me a good starting point, from which I
hope to be able to create a working prototype. Understanding better the functionality of
the various sensors has enabled me to select appropriate products to order. Testing these
sensors will ultimately enable me to construct an efficient and accurate working system.
Bouche, Raymond R. “Accelerometers For Shock And Vibration Measurements”
Endevco Technical Paper 243
Koren, Brock. “Photodiodes” OE Magazine, August 2001, pp 34-36
Hultgren, Charlie. “Innovative photoreceivers simplify measurements” Laser Focus
World, September 1998, pp 123-129
Paisely, Kegan with Alan Prucha, Tim Tetrault, Linda Wikstrom, Adam Zarlengo “Ping
Project, Design Review” University of Colorado at Boulder, March 3, 2003
Romanchik, Dan. “Seven tips for making better accelerometer measurements,” Test &
Measurement World, 9/1/2003
Siemens, “Capacitive Proximity Sensors Theory of Operation” siemens.com