EMPS ME191 FINAL REPORT

Spring 2015 ME 191: Senior Project Design II

Electromagnetic Propulsion SystemsFinal Report

Robby Beard, Josh Prather, Brett Spruitenburg, William Winston

21 May 2015

EMPS ME191 Spring 2015

Executive SummaryME 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_____________.

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TABLE OF CONTENTS, INCLUDING LIST OF FIGURES AND TABLES

PROBLEM STATEMNT & INTRODUCTIONFUNCTION AND CONSTRAINTSFINAL DESIGN AND CHANGESMANUFACTURING SUMMARYTESTINGDISCUSSION, CONCLUSION AND RECOMMENDATIONSReferencesTablesFiguresAppendixes

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

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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×BSince 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=μ0I2πrComputing the force between two wires:

dF=Bidx

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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'i2Further analysis of the rail system is detailed in the analysis done by Robby Beard.

DecelerationOther 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∂tUsing the definition of Ohm’s law:

J= σE ; σ= 1ρWhere 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∂tBoth 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=-1RdΦBdtThis 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 windingsB = magnetic flux density, can be thought of the total magnetic field of a particular regionμr=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≅μ0μ = material permeability. In ferromagnetic materials, μ is a function of H.n = number of turns per unit lengthI = 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

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coil, the magnetic flux density inside the coil grows exponentially due to both the field produced by the 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.

UsageCurrently, 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

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poles creates a track for the armature to travel through. As the armature travels through the magnet 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.

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Data AcquisitionPhotogates 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.

ElectromagnetIn 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

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EMPS Bill Of Materials

Item NumberNumber

purchased DescriptionDate of

purchased Purchaser Price ($) Total ($) UseSection Total

($)RAIL SYSTEM

1 1 X 1/4 Bar Stock 110 Copper 1/10/2015 Robby Beard 130 130 Rails1 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 Rails22 1/4-20 Grade 8 Nuts 1/10/2015 Robby Beard 0.14 3.08 Rails22 1/4 Grade 8 Washers 1/10/2015 Robby Beard 0.14 3.08 Rails1 6061 Aluminum 5/8 x 1.5 x 12 4/9/2015 Brett Spruitenburg 9.96 9.96 Rail Bracing1 6061 Aluminum 1/4 x 1 x 6 4/9/2015 Brett Spruitenburg 15.53 15.53 Rail Bracing12 1/4-20 X 1 Machine Screw 3/15/2015 William Winston 0.12 1.44 Rail Attachment6 1/40-20 X 4 Bolt 3/16/2015 William Winston 0.12 0.72 Rail Attachment6 1/4 - 20 X 2 1/2 Bolt 3/17/2015 William Winston 0.12 0.72 Rail Attachment1 1/4 X 1 X 12 Acrylic 4/13/2015 Robby Beard Donated 0 Rail Spacers 167.61

EXPANSION CHAMBER1 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

PHOTOGATES4 1/4-20X5" Hex Bolt 3/2/2015 William Winston 1.6 1.6 Photogate8 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 Photogate12 1/4 Hex Nut 3/2/2015 William Winston 0.72 0.72 Photogate1 Polycarbonate .5 x 12 x 12 1/14/2015 William Winston 16.28 16.28 Photogate top and Flange1 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 Diodes10 Phototransistors Robby Beard Donated 0 Phototransistors1 Arduino Uno R3 William Winston Donated 0 Arduino 90.97

MAGNET1 4 X 6 X 24 1018 Steel 1/10/2015 Robby Beard 170 170 Magnet Bodies1 11lbs 14 AWG Magnet Wire 1/29/2015 William Winston 155.2 155.2 Magnet Coils1 EPO-TEK 360 Epoxy Resin 3/20/2015 William Winston 50 50 Magnet Coils4 1/4-20 X 2.5 Bolts 5/10/2015 Josh Prather 0.1 0.4 Magnet Coils1 12 1/4 X 5/8 X 3 1/4 Aluminum Bar 5/1/2015 Robby Beard 10 10 Magnet Mold1 31 X1 X 1/4 Aluminum Plate 5/1/2015 Robby Beard 20 20 Magnet Mold2 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 5.241/4 zinc washers 3/30/2015 William Winston 8.98 8.981/4-20 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 2.361/4-20-1 machine screw 3/31/2015 William Winston 2.36 2.36 428.28

ENCLOSURE2 ClearBallistics Ballistics Gel 11/26/2014 William Winston 31.5 71 Ballistic Gel1 1018 Steel .5 x 4 x 8 2/23/2015 William Winston 16 16 Enclosure1 1018 Steel .5 x 6 x 5 2/23/2015 William Winston 24 24 Enclosure1 1018 Steel .5 x 5 x 10 2/23/2015 William Winston 20 20 Enclosure Top1 1018 Steel .5 x 4 x 9 2/27/2015 William Winston 16.28 16.28 Enclosure Bottom1 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 Cover1 Rail system Capacitor bank Robby Beard Donated 0 Rail system Capacitor bank1 Magnet System Capacitor bank Robby Beard 34 34 Magnet System Capacitor bank1 Capacitor Bank Enclosure Box Robby Beard 15 15 Capacitor Bank Enclosure Box2 1200V 200Amp recovery diode 5/12/2015 Robby Beard 16.81 33.62 Diodes

Miscellaneous Wire Robby Beard Donated 0 Cables1 1000V 50Amp Bridge rectifier 5/12/2015 Robby Beard 6.03 6.03 Bridge rectifier 99.31

unused 1045.194 extension spring 81008 4/8/2015 brett spruitenburg $16.96 $76 Original spring initiator

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.

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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

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A: Cross sectional area of wireD: Diameter of wireρ: Resistivity, Ω-mL: 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.

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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.

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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

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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){valA = digitalRead(photogateA);}

while (valA == LOW){timeA = micros();valA = digitalRead(photogateA);}

while (valB == HIGH){valB = digitalRead(photogateB);}

while (valB == LOW){timeB = micros();

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valB = digitalRead(photogateB);}

while (valC == HIGH){valC = digitalRead(photogateC);}

while (valC == LOW){timeC = micros();valC = digitalRead(photogateC);}

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 photogatemphAB = 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 photogatemphCD = 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 }}

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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.

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Attachment PointsAttachment 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 PropertiesFrom 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 CubicA 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

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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 modelsThe 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.

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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.

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DISCUSSION, CONCLUSION AND RECOMMENDATIONS

Problems ExperiencedThroughout 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 atPhotogates: 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

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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. Print4. “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#c49. “Multi-tasking the Arduino - Part 1”. Bill Earl. Web. https://learn.adafruit.com/multi-tasking-the-

arduino-part-110. “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

SpringsTo 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

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https://learn.adafruit.com/multi-tasking-the-arduino-part-2


https://learn.adafruit.com/multi-tasking-the-arduino-part-1/overview



https://learn.adafruit.com/multi-tasking-the-arduino-part-1/overview

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html#c4

http://www.hephy.at/en/physics/techniques/particle-accelerators/

http://www.hephy.at/en/physics/techniques/particle-accelerators/

http://machinedesign.com/archive/basics-electromagnetic-clutches-and-brakes

http://www.unc.edu/~bhuang/limcoasters.htm

http://www.ga.com/emals


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/inxeq 3.9 inF 48.36 lb-ft

# of springs 4

m(plunger assembly)

0.00435 slugs

m(armature) 0.00028 slugsm(spring) 0.01242 slugsm(total) 0.01705 slugs

a 2836.4 ft/s2d 0.325 ftVf 42.93 ft/sVf 29.27 mph

Table A1. 4 Springs in Parallel

Spring Manufacturerhttp://www.centuryspring.com/Store/item_detail.php?StockNumber=12372

FrictionTo 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.

μk0.23

marmature

0.00028 slugs

g 32.2 ft/s2

N 0.009 lb

Ff0.00207 lb

Ff (Total) 0.00828 lbTable A2. Friction Calculations

Bolt Spacing

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http://www.centuryspring.com/Store/item_detail.php?StockNumber=12372


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,

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

Lmax8.5in 2in

Dmin.08in .25in

Table A3 Rail analysis Results

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Documents

EMPS ME191 FINAL REPORT