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 s.muftu@neu.edu.

The Need for Project Injuries sustained from a career involving frequent impacts to the

head can have lifelong implications. Trauma specifically relating to the

heading of soccer balls has proved concerning for both professional

athletes and youth players. The first steps to quantifying the effects of

soccer ball impacts can be accomplished by creating a soccer ball

impact measuring system.

The Design Project Objectives and Requirements Design Objectives

The main design goal is to produce a launcher that can replicate

any kick produced by a professional soccer player and measure the

impact via a force plate. Each simulated kick must be highly repeatable

while maintaining control over direction, accuracy, velocity, and spin.

It is critical to deliver a launcher that supersedes the abilities of current

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 Propulsion Method

Most existing ball launchers consist of two counter-rotating wheels

driven by electric motors. The group investigated this method along

with a potential energy striking systems (gravity and springs),

compressed air, linear actuators, and chemical reactions. Compressed

air and chemical reactions were ruled out due to safety and portability

The construction of a soccer

ball impact measurement

system aims to quantify the

injuries sustained from heading

a soccer ball.

To achieve the desired testing

results, the launcher needs to

replicate a professional soccer

player’s kick by producing

repeatable and accurate

launches with varied speed and

curvature.

The requirements drove the

development of independent

modules of the launcher which

include the propulsion method,

ball launch control, and overall

frame packaging.

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 Design Description

The finalized design for the prototype launcher, as seen in Figure

1, represents the best attempt to satisfy all design constraints while

maintaining ease of construction. The design centers about the

propulsion system, as it is the most critical aspect of the launcher. A

support frame built around the motor and wheel assembly allows for

aiming in the Y and X axes, and rotation about the Z. The entire chassis

is easily portable, sitting on casters for steering in the front and large,

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

The final design consists of a

central rotating assembly with

two independently powered

motors spinning custom made

concave wheels. The

supporting frame allows three

degrees of freedom, pitch, roll

and yaw for varied, repeatable,

and accurate launches.

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

direction for the entire launcher. The main aspects that needed to be

finalized before moving forward were wheel height, diameter, and

shape. An increase in the surface contact interaction between the ball

and propulsion wheels would decrease the stress and increase the

energy transfer. A concave contour was chosen to increase the surface

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.

(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

1. Scissor Jack

2. DC Motor

3. Custom Wheel

4. Ring running on

Bearings

Figure 1

1. Force Plate

2. Stand

Figure 2

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 High volume manufacturing processes and price points have not

been evaluated for this project. Rapid prototyping procedures are more

costly, but provide the lead time needed to conduct an iterative design.

The motor and powered wheel assemblies were the high cost

drivers in this prototype. To save money, the design included

repurposed treadmill motors and polyurethane molded steel wheels.

The treadmill motors and associated controllers cost $160; the wheel

assemblies totaled $80. Although these choices satisfied the design

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 To achieve a stable and more consistent system, professionally

balanced wheels are required due to the speed requirements. Any

imbalance can be reduced with vibration damping attachments to the

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.

The frame design capable of

meeting all design goals

totaled $660 with the motor

and wheel assemblies totaling

$240. To preserve launch

integrity and safety, cost cuts

should not be considered

acceptable for the motors and

propulsion wheels..

A new motor and controller

package, as well as properly

balanced wheels need to be

implemented.