Design Report Brief (CEAC)
Team 15: Coach Jav
Kwesi Asare, David Dadzie, Ofiliojo Ichaba, Landon Potts
Introduction
Competitive athletes have a constant objective of improving their performance. In order to do
this, the athletes and their coaches adopt a wide spectrum of methods to get the necessary
feedback of athlete performance. For instance, Zepp Tennis is a program that monitors the speed
of the serve and other important performance parameters of tennis players. Other sports such as
golf, sprints, and baseball have similar feedback systems in place.
One sport that does not have such a system is the javelin throw in the sport of track and field.
Javelin throwers and their coaches have difficulty getting performance feedback, because the few
systems that currently exist are both bulky and expensive, and/or require a controlled
environment with an indoor facility, 8-10 high speed cameras, and force sensors; as can be seen
in the image on the title page above.
Team #15 Coach Jav, made up of four electrical engineering students, designed a device to fill
this need for javelin athletes and coaches. The device was designed to record data from a javelin
throw and send it to the athlete or coach.
Team Organization and Management
The project design team consists of four senior electrical and computer engineering students.
They are Landon Potts, Ofiliojo Ichaba, Kwesi Asare, and David Dadzie. The team is setup to be
very transparent, meaning we all have equal tasks and roles and distributed the assignment
among team members. In addition, to avoid replicative work which would be redundant, each
member of the team has been assigned a significant portion of the project for which they are
responsible. The breakdown of assigned roles are as follows:
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David Dadzie - Microcontroller Unit and hardware design (for PCB). Basic requirements
will be to design and program the microcontroller unit to control what happens between the
initial run, release and landing of the javelin and how it triggers the sensors to record the
required data.
Landon Potts - Communication between the system of the javelin and the user interface on
the device. Also, filtering data and coding the microprocessor.
Kwesi Asare - Sensors to be employed in the device. As of now the list of sensors includes a
gyroscope, magnetometer, an accelerometer, GPS module, and a touch sensor.
Ofiliojo Ichaba - User interface for the athlete or the coach.
It is also worth noting that the team is in close collaboration with the head Track & Field coach
at Calvin College, Bret Otte, as well as senior design advisor Professor Michmerhuizen and
industrial engineering consultant Mr. Eric Walstra.
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Design
CoachJav was designed as a device to record data throughout a javelin throw and send it to a
mobile device. Specifically, the coaching tool combines multiple sensors (gyroscope,
accelerometer, magnetometer, and GPS module) to collect data, crunch the numbers with a
microprocessor, and transmit the useful information through Bluetooth communication to an
Android mobile device application. Then the coach or athlete can see the velocity of the throw,
the angle of release of the javelin, and the distance thrown, all in real time. The coaches or
athletes can use the quantitative data to effectively assess the athlete’s performance, monitor
their progress, and help the athlete see what they are doing well and what they can improve
upon. A brief overview of the system design can be seen below in Figure 1.
Figure 1: CoachJav System Overview
Most of the work done on the project so far has been about getting the necessary data from the
sensors employed. Looking back, choosing the hardware was the easy part, and the hard part is
capturing and making sense of the data acquired by the hardware. At first, the team decided to
try just an accelerometer and gyroscope IMU to obtain the data from the throw.
The velocity could be found for small straight movements, but compounding error in integration
of acceleration to get to position (over 8 m/s off) led the team to scrap the idea of getting the
velocity from just the accelerometer and gyroscope. Recently the team ordered a GPS module
with which new testing can be done and the velocity can be found. The addition of a GPS does
make the device slightly bigger, but will be useful to obtain accurate data. Thus, the team is
considering making a specific PCB complete with sensors and microcontroller for a smaller size.
For the angle calculations, the team relied on mathematical theory of Euclidean Space to obtain
the position the javelin in space, as well as the fact that the force of gravity is a constant
acceleration down. The angle can be found quite easily with the accelerometer if the device is
simply rotating about slowly. With translating motion and quicker rotation, this calculation also
becomes inaccurate. The team is currently working on error correction using the gyroscope data,
and now also the GPS module. The data from these sensors will be filtered using a Kalman filter;
however, this filter, though very accurate, is not the simplest to implement. The team will
consider implementing a complementary filter for the same purpose, given less noise from the
sensors.
The android app development is in its early stages. The team is designing a very simple app that
displays the stats (angle, velocity, and distance) received from Bluetooth communication, as well
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as a reset button to clear current stats and receive new stats. Simple Bluetooth communication
has been tested and works up to 30~35 yds away in engineering building. If a better module is
needed, one can be obtained that is specified up to 100m (world record javelin throw is ~94m).
Throughout the year, the team kept to the design norms chosen at the beginning of the year to
govern the design process. These norms included trust, caring, and cultural appropriateness. The
user needs to trust that the device will work reliably and give accurate data. The design is also
caring. For engineers, make sure that the design does not infringe on any current patents, but also
make sure Team 15 and Calvin College protect their own intellectual property. For the athlete,
the device helps them achieve their best, as Colossians 3:23 tells us that “Whatever your task
may be, put forth your very best effort, as for the Lord and not for men”. Finally, the device must
be culturally appropriate to the sport, not altering the javelin or its trajectory in any way.
Prototype and Testing
A preliminary model has been designed and wired up on a breadboard to start the preliminary
testing, as shown in Figure 2 below. This is mostly to make sure that the data collected gives
Figure 2: CoachJav Preliminary Model
Figure 3: Preliminary Design for Testing Apparatus
accurate. To make sure the data is accurate, a method to test the device has been created. First
the team will set up a repeatable throw (as shown in Figure 3 above). Then, the data desired will
be measured both with the device and with other known devices (velocity from radar gun like
baseball; angle from filming the throw and measure from the horizon, and distance with a tape
measure). The angle and throw can be changed or repeated, so the team will perform both to
make sure data is accurate over a range of throws and to provide standard deviations and errors
in measurement of the device.
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