EMPS ME191 FINAL REPORT

Spring 2015 ME 191: Senior Project Design II
Electromagnetic Propulsion Systems
Final Report
Robby Beard, Josh Prather, Brett Spruitenburg, William Winston
21 May 2015

EMPS ME191 Spring 2015
2 | P a g e
Executive Summary
ME 191 EMPS is a senior project to validate the use of an induced magnetic field to accelerate
a 6061 aluminum armature weighing 4 grams (0.009 lb) up to a target velocity of 60 mph and then
decelerate to a stop using eddy currents from another magnetic field produced across the object's
path. Electromagnetic forces are used in cutting edge technology for a variety of applications, and
can make applications more efficient. Electromagnetic forces have the potential to decrease design
footprints and increase maximum system potential in systems such as electromagnetic aircraft and
spacecraft launching, and advanced material testing.
A system was created that was used to validate electromagnetic principles and demonstrate
how acceleration and deceleration could be achieved with conventional means. The rail system
creates acceleration in a conductive armature by applying both current and a magnetic field, while the
magnet system causes deceleration in that same armature by creating opposing eddy currents. The
armature is made of 6061-T6 aluminum and was manufactured by using a Bridgeport milling machine.
The electromagnet H-type shell is created from 1018 steel, which was CNC’d in the Sacramento
State CNC lab. The coils were made of 14 gauge AWG magnet wire. The wire was hand wound to
create the two sets of coils.The solid enclosure front, top, back, and bottom, were machined out of ½
inch thick 1018 steel to provide an extra measure of safety. The clear enclosure walls as well as the
photogates and photogate flanges were machined out of polycarbonate. Analysis of the rails system
was accomplished by _________________. The photogates were used to measure the velocity of the
armature at two separate locations, first at the entrance of the magnet, and finally at the exit of the
magnet. These measurements were to measure the efficiency of the electromagnets ability to act as
a brake in opposition to a high speed conductive armature.
This project accomplished____________. This is an important finding due to_____________.

3 | P a g e
TABLE OF CONTENTS, INCLUDING LIST OF FIGURES AND TABLES
PROBLEM STATEMNT & INTRODUCTION
FUNCTION AND CONSTRAINTS
FINAL DESIGN AND CHANGES
MANUFACTURING SUMMARY
TESTING
DISCUSSION, CONCLUSION AND RECOMMENDATIONS
References
Tables
Figures
Appendixes
Problem Statement:
Validate the use of an induced magnetic field to accelerate a 6061 aluminum armature
weighing 4 grams (0.009 lb) up to a target velocity of 60 mph and then decelerate to a stop using
eddy currents from another magnetic field produced across the armature's path.
Introduction:
The problem statement can be broken down into two distinct sections, acceleration, and
deceleration. The following overview will discuss how this project contributes to fulfilling the problem
statement. Theories, formulas, analysis, and design are all discussed below.
Acceleration

4 | P a g e
Figure 1. A Basic Example of a Rail System.
A relationship called the Lorentz Force Law exists between a current carrying object and a
magnetic field. According to the Lorentz Force Law, when a current carrying object, such as a wire, is
placed in a magnetic field, there will be a force exerted on that object at a right angle to the plane
formed by the direction of both the current and the magnetic field.
F=il×B
Since all our vectors are at exactly right angles, the magnitude of our force can be re-written
as:
F=ilB
Here i is the current flowing through the system, l is the height of the armature, and B is the magnetic
flux density produced by the current.
As detailed in [1], A preliminary assumption is made for the purpose of calculation that the two
rails are two parallel round wires. Shown in the figure below:
Figure 2. Two infinite parallel wires used in the calculation for the force exerted on the armature
The magnetic field of a round wire is given by the Biot-Savart Law is:
B=μ0I2πr
Computing the force between two wires:
dF=Bidx

5 | P a g e
F=μ0i22π RR+l 1x+12R+l-x dx = μ0i22πln [(R+l)2R2]
Thus μ0πln [(R+l)2R2] =Inductanceunit length=L' (Henrysmeter)
Thus the governing equation describing the Lorentz force on an armature for for an ideal rail
system is:
F=12L'i2
Further analysis of the rail system is detailed in the analysis done by Robby Beard.
Deceleration
Other relationships exists between a conductive object and a magnetic field called Faraday’s
law of induction and Lenz’s Law.
Faraday’s Law of induction states that a changing magnetic field produces a curling, or rotating
electric field:
∇ ×E= -∂B∂t
Using the definition of Ohm’s law:
J= σE ; σ= 1ρ
Where J is the current density, σ is the electrical conductivity of a material, which is the
reciprocal of electrical resistivity ρ. Faraday’s law can now be re-written as:
∇ ×ρJ= -∂B∂t
Both of these equations are related to Lenz’s law, which states that a changing magnetic flux
induces an electromotive force, or voltage, across an object:
E=-dΦBdt ⇒ I=-1RdΦBdt
This law states that as a conductive object experiences a changing magnetic field, small
currents are induced within that object called eddy currents. These currents produce their own
separate magnetic field which opposes the direction of the initial magnetic field. This new induced
magnetic field will produce a deceleration that acts against the initial relative velocity between the
object and the magnetic field.
A system consisting of an H-type dipole magnet was designed to create an intense magnetic
field concentrated along the path of the armature. The initial magnetic field is produced by the
magnet’s two coils. Using Ampere’s law, the magnetic field produced by a solenoid can be estimated
using the number of turns of the coil and the current flowing through the coil. The magnetic flux
density produced by the current is greatly increased due to the presence of the steel core since the
permeability of a the steel is about 1000 times greater than that of air.
B=μrμ0H=μH, H=nI (6)
H = magnetic field produced by coil windings
B = magnetic flux density, can be thought of the total magnetic field of a particular region
μr=μ/μ0 = Relative permeability of a material. For steels this number is initially around 1000.
μ0 = permeability of free space = 4π×10-7 H/m. For most non ferromagnetic materials: μ≅μ0
μ = material permeability. In ferromagnetic materials, μ is a function of H.
n = number of turns per unit length
I = current
Magnetic fields will follow the path of highest permeability. The electromagnet was also
designed to fully saturate the material. When a ferromagnetic material is placed inside of the magnet
coil, the magnetic flux density inside the coil grows exponentially due to both the field produced by the

6 | P a g e
windings as well as from the large field produced by the alignment of all the ferromagnetic domains
within the material. However, this effect has a limit. The ferromagnetic material’s permeability begins
to decrease in value for large values of H, up to the point where all the domains are completely
aligned and material’s permeability equals that of air. At this point the material is considered saturated
and from this point onward, any more increase H will no longer produce a large exponential increase
in B, but the same small linear increase that the coil would produce as if it were an air core coil.
Different materials have different saturations, air for example has no saturation limit, and can have
infinite magnetic field through it. However other materials such as steels have a saturation limit, that
is there is maximum amount of magnetic field than can flow through the material.
The magnet design used will exploit the fact that high magnetic fields can be produced in a
ferromagnetic materials for low amounts of magnetizing current. This will create the maximum
magnetic field that can be practically produced across the path of the armature in effort to maximize
the eddy current braking force. Since the armature is made out of 6061 series aluminum, which is a
good conductor, it will experience eddy currents when passed through the poles of the
electromagnet. The greater the magnetic field is and the faster the armature is moving, then the
greater the eddy currents and their induced magnetic fields. Since these fields are acting against the
change in magnetic flux, they will attempt to slow down the armature.
Usage
Currently, linear electromagnetic acceleration devices are being developed and applied in
many fields including but not limited to military weapon and missile defense systems, aircraft and
spacecraft launch, industrial linear motors and motion controllers, and academic
research. Electromagnetic rail guns and aircraft launch systems are being designed and
implemented onto US Navy ships (2). NASA is also interested in using similar technology to launch
payloads into space, and someday even people. Electromagnetic acceleration is also being used to
power objects such as trains and roller coasters (3).
Electromagnetic deceleration is also used in a variety of fields. These fields include frictionless
braking systems, industrial brakes on machinery, roller coaster brakes, high speed train brakes. Both
completely dissipative ones as well as regenerative braking systems are a high demand new
technology.
Larger versions of the dipole magnet described above are used in synchrotron particle
accelerators as bending magnets to force the beams of charged particles to travel in a circle. Many of
the design ideas of particle accelerator bending magnets were used in the design of the magnet used
brake the aluminum armatures.
Function:
The electromagnetic rail and braking system will accelerate and decelerate a conductive
armature. The acceleration will occur while a rectangular armature made from 6061 series aluminum
is constrained between two 110 series copper rails. First, a capacitor bank will be charged to a
desired voltage, which will later be activated with a thyristor switch. The armature will be given an
initial velocity into the rails with a spring/plunger system. As the armature enters the rails, the
capacitor bank will release current into the rails via the switch. As the current flows through the rails
and armature, the Lorentz force will propel the armature down the rails. The capacitor bank will only
release current until the armature reaches the end of the rails. As the armature leaves contact with
the copper rails, it will enter a track with an integrated photogate, magnet, second photogate, and
ballistic gel safety stop.
A photogate will be positioned after the end of the rails and will measure the armature’s
entrance velocity into the electromagnet. The magnet was designed so that the area between the
poles creates a track for the armature to travel through. As the armature travels through the magnet

7 | P a g e
between its poles, eddy currents will be created and the armature will experience a deceleration. A
second photogate is positioned after the magnet, and will measure the armature’s exit velocity, which
will be considerably lower than the entrance velocity. An enclosure filled with ballistic gel is
positioned after the second photogate which is the final stop along the track. This gel will dissipate
any energy not dissipated by the electromagnet. The system is designed also with the final safety
check, that if for whatever reason, the magnet didn’t pulse, and the operator took the ballistic gel out
of the system, that if the rail system was fired, there would be no way that the armature could break
through the back of the gel enclosure, since it is made out of 0.5in thick steel, nor would any glancing
blow or the nearly impossible scenario of a head on collision between the armature and the
polycarbonate, due to impact energy equations that will be detailed later in the analysis
section.
Constraints:
 Powered by 120VAC from a standard wall socket
 Each component will be able to be transported by hand
 No single component weighing more than 100 lbs weight
 The rails and armature will be made of a highly conductive material
 Rails are fully enclosed in a non-conductive high strength material
 During any part of its movement, the armature contained on rails or in containment unit
 No exposed high voltage wiring
 Rails and armature machined to close tolerances such as 0.005in or greater to ensure rail
longevity
Design constraints were determined by the basic physics of the system, the convenience of
portability, as well as the safety regulations given by the university. The rails and armature both need
to be highly conductive since current only passes through conductive material. The device must be
powered by a standard wall socket since that is what is available to the team. It must be light enough
to carry since equipment for carrying heavier objects is inaccessible. In order for the rail system to
operate, the rails must be enclosed in a reasonably high-strength non-conductive material, to rigidly
constrain the rails in place. All high-voltage components will be secured and unable to be
accidentally touched. Also, the armature must be constrained within the system at all times so that it
will not accidentally exit the system.

8 | P a g e
Data Acquisition
Photogates will be used as the main data acquisition device for velocity. The photogates
operate as follows:
There are a total of four laser and receiver pairs. These pairs are grouped into two sections of
two pairs. The first section is located before the entrance of the electromagnet, and the second group
is located at the exit of the electromagnet. In each of these groups, the laser-receiver pairs are
spaced 1.5 inches apart, with the laser's path being perpendicular to the path of the traveling
armature. The laser shines into the receiver and the receiver takes this as a “HIGH” signal and
reports this to the Arduino. As the armature passes through the laser’s path, the laser's connection to
the receiver broken, and this sends a signal of “LOW” to the Arduino. A “LOW” signal, means that
there is no voltage being received. The Arduino then records the time of the LOW signal, in
microseconds, relative to the start of the test (time A). As the armature passes through the second
laser-receiver pair of the group, a second “LOW” signal is reported and the Arduino records this time
(time B) as well. The arduino then does a calculation of distance divided by the change in time, D/(tB-
tA) and this is the velocity of the armature entering the electromagnet. This same process is
duplicated for the second photogate located at the exit of the electromagnet. The second photogate
has labels of C and D for its first and second laser positions respectively. The velocities of the
armature from A to B will be compared to the velocity of the armature from C to D. If the
electromagnet has worked appropriately as an eddy current braking system, then there should be a
noticeable decrease in velocity shown by the exit photogate. In other words, the velocity from C to D
should be much less than the velocity of A to B.
Electromagnet
In order for the electromagnetic braking system to function, the solenoid needed to be
successfully wound without damaging the wires. In order to test for damage, each solenoid was
attached to a multimeter and measured using a 4 wire resistance test. The resistance of each coil
was measured with the test. This test was accurate because it subtracted the resistance in the lead
wires from the total giving the exact resistance of the coil. One coil had a resistance of .740 ohms and
the other had a resistance of .630 ohms. This means that each coil was successfully wound. If the
resistance was unable to be measured, the coils would contain shorts that would make them
unusable.
A drop test was performed with the electromagnet to verify that the magnetic field produced
inside the magnet had an appreciable effect on the velocity of the armature passing through it. The
magnet was attached to a 15 volt power supply. The magnet was situated so that the path of the
armature was vertical. The power supply was activated and an armature dropped through the
magnet poles. The time for the armature to reach the other side of the magnet was recorded. This
test was also done with the power supply turned off.
The results of this test did not show any effect of the magnet on the armature. This is most
likely because the power supply was not large enough. The power supply that the magnet was
designed for would have been able to create a much larger current in the solenoids and therefore a
much larger magnetic field. Ongoing testing is planned using a much larger power source.
Rails-ROBBY

9 | P a g e
Analysis: Josh Prather
General Properties of the Coil
The coil was made from Essex 14 AWG copper wire purchased online. It was hand wrapped and
each layer coated with a high temperature epoxy resin called EPOTECH 360.
EMPS Bill Of Materials
Item Number
Number
purchased Description
Date of
purchased Purchaser Price ($) Total ($) Use
Section Total
($)
RAIL SYSTEM
1 1 X 1/4 Bar Stock 110 Copper 1/10/2015 Robby Beard 130 130 Rails
1 48 X 48 X 1.050 1/10/2015 Robby Beard Donated 0 Rail Insulation
22 1/4-20 X 3 1/4 Grade 5 Bolts 1/10/2015 Robby Beard 0.14 3.08 Rails
22 1/4-20 Grade 8 Nuts 1/10/2015 Robby Beard 0.14 3.08 Rails
22 1/4 Grade 8 Washers 1/10/2015 Robby Beard 0.14 3.08 Rails
1 6061 Aluminum 5/8 x 1.5 x 12 4/9/2015 Brett Spruitenburg 9.96 9.96 Rail Bracing
1 6061 Aluminum 1/4 x 1 x 6 4/9/2015 Brett Spruitenburg 15.53 15.53 Rail Bracing
12 1/4-20 X 1 Machine Screw 3/15/2015 William Winston 0.12 1.44 Rail Attachment
6 1/40-20 X 4 Bolt 3/16/2015 William Winston 0.12 0.72 Rail Attachment
6 1/4 - 20 X 2 1/2 Bolt 3/17/2015 William Winston 0.12 0.72 Rail Attachment
1 1/4 X 1 X 12 Acrylic 4/13/2015 Robby Beard Donated 0 Rail Spacers 167.61
EXPANSION CHAMBER
1 4 x 6 x 12 Extrusion 1/2 Thickness 4/8/2015 Brett Spruitenburg 95.46 95.46 Expansion Chamber and Magnet Extensions 95.46
PHOTOGATES
4 1/4-20X5" Hex Bolt 3/2/2015 William Winston 1.6 1.6 Photogate
8 1/4-20X2" Hex Bolt 3/2/2015 William Winston 1.44 1.44 Photogate
12 1/4 Cut Washers 3/2/2015 William Winston 1.32 1.32 Photogate
12 1/4 Hex Nut 3/2/2015 William Winston 0.72 0.72 Photogate
1 Polycarbonate .5 x 12 x 12 1/14/2015 William Winston 16.28 16.28 Photogate top and Flange
1 Polycarbonate 1 x 6 x 6 1/14/2015 William Winston 64.75 64.75 Photogate top and Flange
10 Laser Diodes Robby Beard 0.48 4.86 Laser Diodes
10 Phototransistors Robby Beard Donated 0 Phototransistors
1 Arduino Uno R3 William Winston Donated 0 Arduino 90.97
MAGNET
1 4 X 6 X 24 1018 Steel 1/10/2015 Robby Beard 170 170 Magnet Bodies
1 11lbs 14 AWG Magnet Wire 1/29/2015 William Winston 155.2 155.2 Magnet Coils
1 EPO-TEK 360 Epoxy Resin 3/20/2015 William Winston 50 50 Magnet Coils
4 1/4-20 X 2.5 Bolts 5/10/2015 Josh Prather 0.1 0.4 Magnet Coils
1 12 1/4 X 5/8 X 3 1/4 Aluminum Bar 5/1/2015 Robby Beard 10 10 Magnet Mold
1 31 X1 X 1/4 Aluminum Plate 5/1/2015 Robby Beard 20 20 Magnet Mold
2 1/4-20 X 1.5 Machine Screw 5/1/2015 Robby Beard 0.1 0.2 Magnet Mold
1/4X1 machine screw 3/30/2015 William Winston 5.24 5.24
1/4 zinc washers 3/30/2015 William Winston 8.98 8.98
1/4-20 hex nut 3/30/2015 William Winston 3.54 3.54
1/4-20-1/2 machine screw 3/30/2015 William Winston 2.36 2.36
1/4-20-1 machine screw 3/31/2015 William Winston 2.36 2.36 428.28
ENCLOSURE
2 ClearBallistics Ballistics Gel 11/26/2014 William Winston 31.5 71 Ballistic Gel
1 1018 Steel .5 x 4 x 8 2/23/2015 William Winston 16 16 Enclosure
1 1018 Steel .5 x 6 x 5 2/23/2015 William Winston 24 24 Enclosure
1 1018 Steel .5 x 5 x 10 2/23/2015 William Winston 20 20 Enclosure Top
1 1018 Steel .5 x 4 x 9 2/27/2015 William Winston 16.28 16.28 Enclosure Bottom
1 Polycarbonate .5 x 12 x 12 1/14/2015 William Winston 16.28 16.28 Enclosure Walls 163.56
POWER SUPPLY 1 20" x 12" x 1/8" polycarbonate sheet William Winston 10.66 10.66 Power Supply top Cover
1 Rail system Capacitor bank Robby Beard Donated 0 Rail system Capacitor bank
1 Magnet System Capacitor bank Robby Beard 34 34 Magnet System Capacitor bank
1 Capacitor Bank Enclosure Box Robby Beard 15 15 Capacitor Bank Enclosure Box
2 1200V 200Amp recovery diode 5/12/2015 Robby Beard 16.81 33.62 Diodes
Miscellaneous Wire Robby Beard Donated 0 Cables
1 1000V 50Amp Bridge rectifier 5/12/2015 Robby Beard 6.03 6.03 Bridge rectifier 99.31
unused 1045.19
4 extension spring 81008 4/8/2015 brett spruitenburg $16.96 $76 Original spring initiator

10 | P a g e
The grade of the wire is important because as more current is used on the wire, its temperature will
increase, due to the fact that the wire acts like a resistor and dissipates current passing through it as
heat. The Grade 200 MW-35C means that this wire with its insulation is rated up to 200 degrees
Celsius, which is one of the better wire ratings in the market.
Another important wire property noted above is its resistivity. As the resistance increases, the amount
of voltage required to produce the desired current through the wire increases. This means that the
power source will need to be tailored to fit this specific voltage requirement. The resistance of the
designed wire coil is calculated below.
Magnetic Properties of the Coil
The magnetic field produced by an air core solenoid depends on the current, wraps of coil, and
permeability of free space. The magnetic field, H, increases as the current increases, and as the
number of wraps increases. Also, as the distance from the magnet pole increases, the magnetic field
decreases. A solenoid that uses the same number or wraps that the coil used in the electromagnet
uses will create a field of approximately 1.568 T, according to FEMM. When the iron core is added,
the magnetic field is increased by the effects of the magnetic core material. The specific relative
permeability is a material property and has yet to be determined for the steel being used for the
magnet. However, Finite Element Method Magnetics (FEMM) software was used to analyze a model
of the electromagnet. The software required a 2-D drawing of the geometry of the magnet, values for
the type of wire, number of turns, and current through the wire, and the type of core material. Using
these values, the software was able to analyze the magnet and output the profile and magnitude of
the magnetic field produced by the magnet. Specific FEMM results can be seen in analysis by Will
Winston.
Calculating the resistance of coil:
In order to determine how the coil will respond to a certain voltage difference between the ends of the
wire, the resistance of the wire will need to be calculated. This will allow a power source to be
designed that will create enough voltage to create the current necessary to fulfill the optimum FEMM
designed magnetic field. Here is the equation for resistivity of a wire:
R=ρLA

11 | P a g e
A: Cross sectional area of wire
D: Diameter of wire
ρ: Resistivity, Ω-m
L: length of wire
Calculating Voltage Current Relationship
Using Ohm’s Law of V=iR. A power source is needed that will give enough current to provide a large
enough magnetic field. It needs to be taken into account that an increase of resistance with an
increase in temperature. At 75% max operating temperature, the wire will increase in resistance, and
require a higher voltage to give the required current.
The resistance of the coil of wire was calculated to be around .74 ohm. This means that for every voltage
potential difference, the system will produce approximately 1 amp of current through the wires. This
means that in order to provide 100 amps, approximately 74 volts are needed. At a temperature 75
percent of maximum temperature for the wire, the resistance increases to almost 1.15. This means that
instead of 100 volts needed, 114 would be needed to produce the same current. This problem will be
avoided by not letting the coil be turned on for very long. The wires will not have enough time to heat up,
and the resistance increase will be insignificant.
Initiator mechanism analysis relied upon three primary dimensions; velocity, ease of use, and cost
benefit analysis. The initial design called for a spring mechanism that would impart a fair amount of
velocity to the armature(SEE APPENDIX). However, once the springs arrived we determined the pullback
force required to engage the springs would be too high to reliably control. There was also the issue of
locking and unlocking the mechanism, as the bar would need to be in the rear position before loading.

12 | P a g e
Gas 2 System, with expansion chamber
After determining that the springs were not a viable option we decided to look into gas injection.
Gas injection is the standard for most EM guns but we had estimated that it would be too costly to
implement. after doing some additional research a simple design utilizing a paintball cylinder was found
that would hopefully be able to achieve acceptable velocities. This design revolved around a valve which
was bought at a paintball store which could quickly release the gas. this was crucial because solenoid
valves are incredibly expensive. Several prototypes were built to attempt to achieve the greatest velocity.
It was found that these designs were increasingly expensive as they used brass fittings. Brass fittings
from Home Depot were the only fittings that we could purchase on short notice that can handle 1200psi,
but they are also very expensive. The first prototype cost $55, while the second cost $120. The second,
much more complicated design utilized an expansion chamber after the co2 needle valve which allowed
more gas to build up before the valve was opened. The needle valve internal to the paintball tank was
found to be the limiting factor for flow rate. While both of the designs functioned adequately, they were
ultimately not what we needed. Both designs required the user to be nearby the railgun to trigger the
initiation. This was undesirable due to the unknown outcome of the first test.

13 | P a g e
Marker 2 system, with modified barrel, adapter, and upgraded spring rod
After much consideration it was determined that retrofitting an old paintball marker would be safer,
cheaper, and more reliable than the fitting designs. The paintball marker (Spyder E99) had a built in
solenoid and expansion chamber which would give us the velocity that we required. It would also only cost
$30, the price of a replacement barrel. the barrel was cut and threaded and an adapter plate was created
for the breach. the device would be triggered by a string that could extend to a safe location. the marker
velocity was also easily adjusted by a knob on the rear of the marker, and interchangeable spring rods.
The final design was, simple, inexpensive, and reliable. Unfortunately we were unable to test the
velocity because of our faulty photogates. the only analysis we could perform was a visual observation of
the marker firing a test armature. one observer stated that “the gun shoots really fast.”
Analysis: William Winston
Photogate speedometer controls
The photogate data acquisition was handled by Arduino. The coding process took much longer than
expected. Arduino has a large selection of libraries and example code, and the group intended to find
a suitable code in those libraries, since each member of the group were inexperienced in coding.
However, the original code that the team thought would work for the application did not fit the desired

14 | P a g e
requirements. A new code was created based from code found in a YouTube video. This new
modified code worked perfectly with the prototype photogates that were built, however, it has so far
only worked for the first of the two photogates in the actual photogate system.
Arduino code:
int photogateA = 4;
int photogateB = 5;
int photogateC = 6;
int photogateD = 7;
unsigned long timeA, timeB, timeC, timeD;
float fpsAB, fpsCD, mphAB, mphCD, deltatAB, deltatCD;
int valA;
int valB;
int valC;
int valD;
int trial = 0;
void setup()
{
Serial.begin(9600);
pinMode (photogateA, INPUT);
pinMode (photogateB, INPUT);
pinMode (photogateC, INPUT);
pinMode (photogateD, INPUT);
}
void loop()
{
Serial.println("...TRIAL...");
Serial.println(trial);
Serial.println("Photogate 1 Ready ...");
valA = digitalRead(photogateA);
valB = digitalRead(photogateB);
Serial.println("Photogate 2 Ready ...");
valC = digitalRead(photogateC);
valD = digitalRead(photogateD);
while (valA == HIGH)
{
}
while (valA == LOW)
{
timeA = micros();
}
while (valB == HIGH)
{
}
while (valB == LOW)
{
timeB = micros();

15 | P a g e
}
while (valC == HIGH)
{
}
while (valC == LOW)
{
timeC = micros();
}
while (valD == HIGH)
{
valD = digitalRead(photogateD);
}
while (valD == LOW)
{
timeD = micros();
valD =digitalRead(photogateD);
}
{
deltatAB = timeB - timeA;
fpsAB = 125000/deltatAB; //distance in feet, converted from inches. 1.5inches/12inches. measured in
microsec divided by delta time for entrance photogate
mphAB = fpsAB*0.68181818;
Serial.println("Time A...");
Serial.println(timeA );
Serial.println("Time B...");
Serial.println(timeB );
Serial.println("Velocity from A to B (fps)...");
Serial.println(fpsAB );
Serial.println("Velocity from A to B (mph)...");
Serial.println(mphAB );
deltatCD = timeD - timeC;
fpsCD = 125000/deltatCD; //distance in feet, converted from inches. divided by delta time for exit photogate
mphCD = fpsCD*0.68181818;
Serial.println("Time C...");
Serial.println(timeC );
Serial.println("Time D...");
Serial.println(timeD );
Serial.println("Velocity from C to D (fps)...");
Serial.println(fpsCD );
Serial.println("Velocity from C to D (mph)...");
Serial.println(mphCD );
trial++; // add 1 to the trial count
}
}

16 | P a g e
This arduino photogate code was modified from code found on a youtube video named “How to
Measure Speed With Arduino (Of a Projectile)” by BreadboardBasics located at
https://www.youtube.com/watch?v=V_2JUTnXn6I&index=58&list=WL
Material analysis of Polycarbonate Photogate
Polycarbonate Properties
As a safety check, an analysis was performed to determine a worst case scenario of the
maximum impact of the accelerated armature into the polycarbonate. The polycarbonate is rated to
have notched Izod impact strength of 14 Ft*lbs/inch. The target velocity of the armature entering the
polycarbonate photogate is 60mph, but for a worse case scenario calculations were made at 150 mph.
The armature has a weight of 0.009 lb.
Using these values
1ft*lbsin=1.355 J
14*1.355 J= 18.97 J
Therefore the polycarbonate can withstand an impact energy of 18.97 J.
150 mph=67.056 m/s
0.009 lb=0.00408 kg
Kinetic energy can be calculated:
12mv2 = 12(0.00408 kg)(67.056)2=9.1728 J
Therefore the maximum energy of the armature impacting the polycarbonate photogate in a
worst case scenario is 9.1728 J. This means that the polycarbonate is capable of withstanding twice
the maximum impact force if the armature strays from its course. The armature will stay safely
contained.
These calculations were used in determining the material choice for the photogates. These same
calculations were carried out for acrylic, and it was found that acrylic would withstand 1.2195 J. This
solidified the decision to use polycarbonate instead of acrylic.

17 | P a g e
Attachment Points
Attachment points from the rail system to the photogates and from the photogates to the
magnet will experience no forces in the horizontal direction, and will only experience a vertical force
due to gravity. The connections from the exit of the magnet, to the photogate to the enclosure will
experience a force in the horizontal direction once the armature enters the ballistics gel, however the
ballistics gel will dissipate all of the remaining energy of the armature. The enclosure with the
ballistics gel added weighs __________ and is heavy enough to stop the in the ballistics gel and the
heavy weight of the enclosure.
Ballistics Gel Properties
From the clearballistics.com website description of the 10% ballistics gel:
• Size: 9 inches in length, 4 inches in
• width, and 4 inches in height (9L X 4W x 4H) Weight: 4.2 lbs Volume: 144 Cubic
A greater understanding of the product was gained through correspondence with a representative
from ClearBallistics,
“Since you will be launching 1100 aluminum rather than a bullet, your armature will be traveling at a
much slower rate. When we fire a .177 caliber steel BB at 590fps (402mph) into our 10% gel block it
penetrates anywhere from 2.95-3.74 inches. Now this calculation is based on us standing 10ft away
from the block. You mentioned that your armature would be traveling at approximately 150-200mpg
which is about 50% slower than a steel BB and you will also be standing closer to the block. It’s hard
to calculate how far your armature would penetrate into our gel block since we have not tested this.
But I would recommend using our 10% gel for this experiment mainly because I would have concern
that our 20% gel would be too stiff for your specific application.”
From this discussion, the group decided to switch from the 20% gel to the 10% gel.
Enclosure Material Properties
The Enclosure is made of 1018 Steel on 4 of 6 sides. The sides are made of High impact
resistant Polycarbonate. The walls will be see through in order to allow for better visualization of the
armature’s behavior into the ballistics gel. A block of clear 10% ballistic gel will be stored inside of the
enclosure and will occupy a 4 x 4 x 9 inch volume, which will spread wall to wall of the enclosure. The
Armature will enter the Enclosure from the photogate, pass into the enclosure from the 3/4 inch radius
hole in the front panel of the Enclosure and then enter immediately into the Ballistics gel. Based on
the results of the ClearBallistics tests using the .177 caliber steel BB at 590fps, It is estimated that the
ballistics gel will penetrate approximately 3.3 inches into the ballistics gel block. This value was
estimated that the average penetration depth of the armature into the gel would be based from the
ClearBallistics BB test average stopping distance of 3.345 inches.
2.95+3.742=3.345 in
The enclosure weighs approximately 20 lbs while empty, and will weigh 24.5 lbs when loaded
with the ballistics gel.
The ballistics gel and the enclosure worked as planned from the testing performed on them.
The ballistics gel was set up in the enclosure and team members threw metal bolts and nuts at the
gel with great velocities. Although these were not at velocities as high as the armature would
potentially be travelling, these tests were performed to gauge the effective penetration resistance at
velocities at which it was hoped that the armature would be travelling after having been through the
electromagnetic brake. After all of the “object throw” tests, it was determined that the ballistics gel
would not be penetrated at low velocities and that if the electromagnetic brake worked as planned,
and slowed the armature to very low velocities, the armature would collide with the front of the
ballistics gel, and could potentially rebound to the steel front of the enclosure, or potentially enter into

18 | P a g e
the polycarbonate photogate channel again where the energy would be dissipated. This gave greater
validation to the selection of polycarbonate over acrylic as the photogate material.
FEMM models
The original design of the electromagnet called for two, 162 turn coils of 14 gage AWG wire
with 60 amps through them. These coils would encircle a 1018 steel core. With the FEMM software,
(Finite Element Method Magnetics) analysis of the potential magnetic field from the electromagnetic
brake was determined and a magnetic field of approximately 1.66T in the center of the magnet was
calculated. While these amperages may seem high, they will only be active for durations of
approximately two seconds.

19 | P a g e
The magnet experienced several redesigns during the course of the semester, and even
underwent an adjustment in the final day before testing. Several unfortunate situations changed the
plans for the magnet.
The magnet was originally planned to produce a 1.685Tesla Magnetic Flux field. This was due
to the magnets having 2 magnet wire coils of 162 turns each, running 60 amps through them.
However in the reality of the process, there were issues with the magnet wire winding, and one coil
has 100 turns, while the second coil had 115 turns. This brought our expected magnetic flux density
down to 1.236 Tesla. This corresponds to a 26.6 percent loss of magnetic field density from the
original magnet design.
With the magnet turns set at 100 and 115 turns, the decision was made to increase the
amperage to 80 amps in order to try to recover some of the lost magnetic field density. According to
the FEMM analysis of the magnet with 100 and 115 turns, and 80 Amps produces a total magnetic
flux density of 1.568T. This corresponds to a 6.9 percent loss of magnetic field density from the
original design.

20 | P a g e
DISCUSSION, CONCLUSION AND RECOMMENDATIONS
Problems Experienced
Throughout senior project, many challenges were experienced. These problems took the form
of manufacturing challenges, availability of materials, scheduling of shop time, along with many
others.
One of the major problems was scheduling of shop time. Although 6 hours per week was
allotted for ME 191 students, The number of students needing to use the mills often exceeded the
number of mills available. Machining often was reduced to only one mill available and therefore only
one part being worked on at a time. This increased the amount of machining time that was required
to fully manufacture all components.
Another problem experienced was adhesive availability. Although high temperature epoxy
resin is not necessarily uncommon, it is extremely difficult to find an appropriate supplier to fit the
requirements of this project. In addition to this, once suppliers of appropriate epoxy were found, it is
not often available in small quantities. The epoxy resin that was needed for the magnet coils needed
to be specially ordered. This took extra time and pushed the magnet manufacturing time back
muchfarther than expected.
In order to finish:
Rail System: The rail system will have to be connected to the rail system power supply, and
activated for testing. The testing will include running the rail system at
Photogates: The photogates will be tested again to determine if the problems that they are
experiencing are from hardware or software. If the problems are determined to be from the hardware,
the hardware will be replaced with more reliable components, if the problem is found to be the
software, then the code will be debugged, or completely remade.
Magnet: Now that the there is a power supply that has been tested and works correctly to provide
enough power to the magnet system, the power supply will need to be connected to the magnets and
the completed magnet system will have to be tested. This testing will originally involve several drop
tests at different applied voltages, these drop tests velocities will be compared to gravity drop tests
velocities to establish a base relation of supplied voltage to braking forces. These supplied voltages

21 | P a g e
will eventually be increased to levels at which it can be determined to supply enough retarding force
to slow down the accelerated armature. At this point, the magnet system will be connected to the
photogates, rail system and the enclosure, and complete tests cof the entire system can be
completed.
Recommendations:
If this project is to be duplicated, it is recommended to not buy cheap lasers from China. Buy
high quality lasers, and this will make the manufacturing and testing of photogates much easier and
more efficient.
If possible, have someone proficient in coding do the Arduino photogate programing. Even
though the Arduino is a tool used to teach people with little to no programing experience about coding,
there is still a relatively high learning curve for the type of program needed to make photogates of this
kind.
References
1. “Design and Construction of a one meter Electromagnetic Railgun” by Fred Charles Beach, NPS,
July 1996
2. “Design and Construction of a Expandable Series Trans-Augmented Electromagnetic Railgun” by
Michael R. Lockwood, NPS, June 1999
3. Halliday & Resnik. Fundamentals of Physics 9th
Edition. John Wiley & Sons 2011. Print
4. “EMALS” General Atomics and affiliated company. Web. http://www.ga.com/emals
5. “Linear Induction Motors” unc.edu. Web. http://www.unc.edu/~bhuang/limcoasters.htm
6. Flemming, Frank “The Basics of Electromagnetic Clutches and Brakes” Machine Design. Web.
http://machinedesign.com/archive/basics-electromagnetic-clutches-and-brakes
7. “What is a particle accelerator” HYPHY. Web. http://www.hephy.at/en/physics/techniques/particle-
accelerators/
8. Hyperphysics. Web. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html#c4
9. “Multi-tasking the Arduino - Part 1”. Bill Earl. Web. https://learn.adafruit.com/multi-tasking-the-
arduino-part-1
10. “Multi-tasking the Arduino - Part 2”. Bill Earl. Web. https://learn.adafruit.com/multi-tasking-the-
arduino-part-2
11. “How to Measure Speed With Arduino (Of a Projectile)”. BreadboardBasics. Web.
https://www.youtube.com/watch?v=V_2JUTnXn6I&index=58&list=WL
Appendixes
Fall 2014 Analysis: Brett Spruitenburg
Springs
To calculate the velocity of the armature as it enters the rails, kinematic equations are used. First, the
force imparted on the armature by the springs is calculated via
F=k∆x; ∆x=x-x0=xeq
Where k is the spring constant and x is the distance that the springs are stretched. For multiple
springs keq and xeq are used in place of k and x. That force is then used to calculate the acceleration

22 | P a g e
of the armature. Here m is the sum of the masses of the armature, the springs, and the plunger
assembly.
F=ma
Finally the acceleration is used to calculate the velocity of the armature as it enters the rails via,
Vf2=Vi2+2a∆x
Vi is equal to zero, therefor the equation reduces to:
Vf=2a∆x
keq 12.4 lbs/in
xeq 3.9 in
F 48.36 lb-ft
# of springs 4
m(plunger assembly) 0.00435 slugs
m(armature) 0.00028 slugs
m(spring) 0.01242 slugs
m(total) 0.01705 slugs
a 2836.4 ft/s2
d 0.325 ft
Vf 42.93 ft/s
Vf 29.27 mph
Table A1. 4 Springs in Parallel
Spring Manufacturer
http://www.centuryspring.com/Store/item_detail.php?StockNumber=12372
Friction
To calculate the friction caused by the armature on the rails basic kinematics are again used.
Ff=μkN
N=mg
Here it is assumed that the maximum possible friction is equal to the friction on the bottom rail times 4.
μk
0.23
marmature
0.00028 slugs
g 32.2 ft/s2
N 0.009 lb
Ff
0.00207 lb
Ff (Total) 0.00828 lb
Table A2. Friction Calculations
Bolt Spacing
To calculate the spacing between the bolts along the insulation the force acting on them must be
determined. The primary force within the rail assembly is the magnetic force created by the moving
armature. This force acts outward effectively trying to push the rails apart vertically. This force is
governed by the equation,

23 | P a g e
F= μ°i2l2πr, (1)
Where i is the current through the rails, l is the length of the rails and r is the separation distance
between the rails. Since the force is not equally distributed along the rails (it is concentrated around
the armature as it travels) we can treat the insulators as simply supported beams whose ends are any
two adjacent bolts. Then, by rearranging (1),
Fl= μ°i22πr=W, (2)
we can calculate the applied load. Here we assume that the force is equally distributed. Now we can
use,
ymax= WL3384EI, (3)
to solve for maximum length of the beam, i.e. the bolt spacing. Rearranging (3) gives,
L=(ymax384EIW)13. (4)
The maximum deflection must be very small so we set ymax=.0002in. I, the moment of inertia is
calculated by determining an equivalent cross section using the ratio between the modulus of
elasticity for the two materials. Ephenollic is 900ksi and Ecopper is 15600ksi which makes Eeq 17.3333. After
calculating the new dimensions of the equivalent cross section equation (5) is used to calculate the
moment of inertia.
I=i=1n(112bh3+ad2), (5)
Finally we can use (4) to solve for the maximum bolt spacing which was found to be 8.494in. This
result seems reasonable because our current is considerably lower than similarly sized devices (due
to safety concerns). We can then use (6) and (7) to solve for the minimum bolt diameter.
a=Wl4YS, (6)
D=(4aπ)12, (7)
Using 130ksi for the yield strength of stainless steel for find that Dmin = .0798in
Calculated Values Chosen Values
Lmax
8.5in 2in
Dmin
.08in .25in
Table A3 Rail analysis Results

EMPS ME191 FINAL REPORT

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to EMPS ME191 FINAL REPORT

Similar to EMPS ME191 FINAL REPORT (20)

EMPS ME191 FINAL REPORT