Soccer Ball Impact Measuring System
Travis Colosi, Michael Muse, Matthew Salame,
Ryan Wexler, Chris Woodsum
Design Advisor
Sinan Müftü
Abstract
The objective of this project was to design, analyze, produce, and test a soccer ball launcher which could
replicate the actions of a soccer player. A prototype was designed, subjected to structural analysis and
manufactured. A force plate was also designed and built to measure the impact force of a launched soccer
ball. This force can be related to the impact which soccer players experience while heading soccer balls
during practice or matches. Research was conducted on existing products, patents, force plate
configurations, and soccer ball flight mechanics to effectively accomplish the goals of this project.
Component selection, analysis and construction have been completed. An effective frame and control
system has been constructed in conjunction with a force plate; however, safety concerns discovered through
testing have delayed progress in delivering a working prototype.
For more information, please contact [email protected].
The Need for Project
The construction of a soccer
Injuries sustained from a career involving frequent impacts to the
ball impact measurement head can have lifelong implications. Trauma specifically relating to the
system aims to quantify the heading of soccer balls has proved concerning for both professional
injuries sustained from heading athletes and youth players. The first steps to quantifying the effects of
a soccer ball. soccer ball impacts can be accomplished by creating a soccer ball
impact measuring system.
The Design Project Objectives and Requirements
To achieve the desired testing Design Objectives
results, the launcher needs to
The main design goal is to produce a launcher that can replicate
replicate a professional soccer any kick produced by a professional soccer player and measure the
player’s kick by producing impact via a force plate. Each simulated kick must be highly repeatable
repeatable and accurate while maintaining control over direction, accuracy, velocity, and spin.
launches with varied speed and It is critical to deliver a launcher that supersedes the abilities of current
curvature. launchers on the market (Ref 7.4) while maintaining a reasonable
budget. By providing a launcher that meets these requirements, it
enables the university to conduct testing and produce results
quantifying the impact of a soccer ball.
Design Requirements
In order to achieve the level of performance necessary, each aspect
of the launching mechanism underwent research, influencing design
decisions. Propulsion, rotation, and aiming methods, as well as overall
packaging were considered. The best methods to achieve the 65 MPH
top speed kick of a professional player while being able to curve the
ball were determined. Launching a ball and hitting a target repeatedly
from a distance of 18 yards would qualify as a successful result. A
successful frame would be able to support the propulsion device, pivot
in all three axes, and impart spin on the ball, all while maintaining a
portable form factor. (Ref 4.1) The force plate used to measure the
impact is based upon common designs with modifications to fit the
calculated range for impact forces from the soccer ball.
Design Concepts Considered
The requirements drove the
Propulsion Method
development of independent
Most existing ball launchers consist of two counter-rotating wheels
modules of the launcher which
driven by electric motors. The group investigated this method along
include the propulsion method,
with a potential energy striking systems (gravity and springs),
ball launch control, and overall
compressed air, linear actuators, and chemical reactions. Compressed
frame packaging.
air and chemical reactions were ruled out due to safety and portability
concerns.
Linear actuators were expensive and could not deliver
required speeds. Potential energy systems offered low cost options that
could achieve our desired speed. The only means of imparting spin on
the ball with these methods involved applying a friction load to the ball
which works against the balls forward motion. These also require the
user to supply energy to the system manually between launches. The
remaining feasible solution is counter-rotating wheels powered by
electric motors.
Counter-Rotating Wheel Design and Manufacturing
Different propulsion wheel contours were considered.
These
included convex (inflated), flat, concave, or “V” shaped contours.
Fiberglassing, molding, and outsourcing were considered to produce
these wheels, but it would be difficult to achieve a uniform contour.
Molding a rubber tire around a metal hub provides contour uniformity
and a high friction interface. The custom outsourcing option is
expensive due to low desired quantity. (Ref 10.4)
Ball Launch Control
Spin could be imparted to the ball either by rotating the wheels
about the launch path or by applying unbalanced friction to the ball.
Rotating the wheels creates a complicated frame but offers the most
control. Imparting friction is simpler but works against the balls
forward motion and is not as versatile or predictable. (Ref 9.1)
Force Plate
To keep the focus of the project on the launcher, an inexpensive
force plate was needed. Many force sensors were considered (Ref
13.1), but strain gauges were chosen for their low cost and wide use.
Recommended Design Concept
The final design consists of a
Design Description
central rotating assembly with
The finalized design for the prototype launcher, as seen in Figure
two independently powered
1, represents the best attempt to satisfy all design constraints while
motors spinning custom made
maintaining ease of construction. The design centers about the
concave wheels. The
propulsion system, as it is the most critical aspect of the launcher. A
supporting frame allows three
support frame built around the motor and wheel assembly allows for
degrees of freedom, pitch, roll
aiming in the Y and X axes, and rotation about the Z. The entire chassis
and yaw for varied, repeatable,
is easily portable, sitting on casters for steering in the front and large,
and accurate launches.
easy rolling wheels in the rear. The final force plate design uses four
strain gauges, connected in a full Wheatstone bridge, applied to flexible
members supporting a rigid honey comb face plate. As the members
flex from impact to the plate, data is dynamically recorded through an
arduino and adjusted by a calibration curve to output force. The design
was optimized through several iterations to minimize torsion on the
strain gauges while producing enough strain to be recordable.
Counter Rotating Wheels
In order to propel the ball in a way that fulfilled the design
constraints, counter rotating wheels were determined to be the most
viable option. Following research into the maximum ball velocity and
ball flight mechanics (Ref 5), it was clear that independently spinning
wheels would produce the best results. This design constraint set the
1.
Scissor Jack
direction for the entire launcher. The main aspects that needed to be
2.
DC Motor
finalized before moving forward were wheel height, diameter, and
3.
Custom Wheel
shape. An increase in the surface contact interaction between the ball
4.
Ring running on
and propulsion wheels would decrease the stress and increase the
Bearings
energy transfer. A concave contour was chosen to increase the surface
Figure 1
contact area, with the most economical and effective production
method of molding polyurethane over a steel hub. (Ref 10)
Motor Selection
Properly powered motors to spin the chosen wheels were the
second aspect of the launcher to be finalized. In order to design a
suitable support system, the dimensions and power ratings had to be
known. Initial research into determining the requirements for speed and
control resulted in the acquisition of 100VDC motors. Accompanied
with properly rated controller boards and a potentiometer for variable
speed, they spun the 6” diameter steel wheels at the required top speed.
1.
Force Plate
2.
Stand
Figure 2
(Ref 12.1)
Ball Control
Once the launching method was finalized, the ability to aim in all
directions and impart spin on the ball had to be determined. Pitch, yaw,
and roll were all necessary degrees of freedom in order to replicate a
variety of soccer kicks. A hydraulic jack was chosen to control the
pitch, with an angle indicator mounted on the base frame to indicate the
incline. This provides a smooth, continuous method of controlling the
pitch with minimal effort on the user’s part. The yaw is controlled by
moving the launcher side to side on the casters, which include a dual
direction locking mechanism for repeatability. The roll is constrained
by two rotating rings that support the motor assembly. The rings roll on
transfer bearings and are held in place by low friction guide rails. The
wheels rotate around the center of the ball, allowing the ball to always
Figure 3
be launched from the same location. A handle has been affixed to the
top of the launcher to assist with rotating the assembly and a pin with
location holes that locks the position. (Ref 9.1)
Experimental Investigations
A large influence on the final design was the testing completed
with the JUGS soccer ball launching machine, and testing performed by
the group with the motor and wheel assembly. The JUGS launcher
provided insight into aspects that were previously low priority. Wheel
spacing and shape provided subpar performance that led to inconsistent
launches. (Ref 8.1) This shifted the focus to the contoured wheels.
Unfortunately, the testing of the molded contoured wheels proved that
balancing and vibration with imperfect wheels is problematic. Proper
wheel spacing testing was not conducted due to wheel failure, but did
call for an adjustable design in the prototype.
Financial Issues
The frame design capable of
High volume manufacturing processes and price points have not
meeting all design goals been evaluated for this project. Rapid prototyping procedures are more
totaled $660 with the motor costly, but provide the lead time needed to conduct an iterative design.
and wheel assemblies totaling
The motor and powered wheel assemblies were the high cost
$240. To preserve launch drivers in this prototype. To save money, the design included
integrity and safety, cost cuts repurposed treadmill motors and polyurethane molded steel wheels.
should not be considered The treadmill motors and associated controllers cost $160; the wheel
acceptable for the motors and assemblies totaled $80. Although these choices satisfied the design
propulsion wheels.. specifications, the motors had low speed control sensitivity and the
wheels were not held to high of enough tolerances to rotate safely at
high speeds. For this project to be successful, higher quality motors,
motor controllers, and powered wheel s must be purchased at a higher
cost. The frame cost $660, the highest expense for the project.
Recommended Improvements
A new motor and controller
To achieve a stable and more consistent system, professionally
package, as well as properly balanced wheels are required due to the speed requirements. Any
balanced wheels need to be imbalance can be reduced with vibration damping attachments to the
implemented. frame depending on how severe the imbalance is. A standard motor
and control system with speed feedback will make the launcher more
user-friendly and be easier to mount. Additional testing to optimize
ball compression and wheel contours can increase system consistency.