Nick Frazey, Trace McGrady, Gregory Parker,Vincent Colson, Andy Ivy

Team INSTAR

Table of ContentsIntroduction.................................................................................................................................................3

Executive Summary.................................................................................................................................3

Background..............................................................................................................................................3

Problem Definition..................................................................................................................................4

Concepts Considered...................................................................................................................................5

Stator Split...............................................................................................................................................5

Cooling Structure/Rotor Lifting Mechanism............................................................................................5

HTS Geometry.........................................................................................................................................6

Microcontroller.......................................................................................................................................6

Active Magnetic Bearing (AMB) Control..................................................................................................6

Component Design and Manufacturing.......................................................................................................7

Stator Assembly.......................................................................................................................................7

Rotor Assembly........................................................................................................................................9

Lifting Assembly (Cooling Structure)......................................................................................................12

HTS Assembly........................................................................................................................................13

Sensor Mounting Assembly...................................................................................................................14

Miscellaneous........................................................................................................................................17

Team Member Roles & Contact.................................................................................................................17

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Introduction

Executive Summary

The University of Idaho senior design team, Team INSTAR, is prototyping a Flywheel Energy Storage system for the purpose of lunar colonization. This team is building on research and designs completed by Phase I of the project. Solar power is the primary energy source available on the moon, and periods of darkness can continue for up to 336 hours consecutively. Therefore, it is vital to implement energy storage systems during periods when solar energy is not available. NASA requires a reliable, efficient and economically viable design. Funding for the NASA flywheel project is provided by the Ralph C. Steckler Grant. The design consists of many subsystems; Vacuum systems, field reluctance regulation machine, liquid nitrogen cooling, microcontroller correction, and magnetic levitation systems are examples of a few of

The goal of phase II is to provide a levitating and spinning version of the prototype that is operable at relatively low operational speeds (less than 2000 rpm). Proof of concept and energy density of Flywheel Energy Storage is key in this project design. Upon receiving funding for the third and final project phase, the flywheel design would need to be revisited in order to operate at speeds of nearly 40000 rpm.

Background

The National Aeronautics and Space Agency (NASA) would like energy generation as well as storage methods for future colonization on the moon. Lunar daylight cycles between 336 hours of light and darkness, and because power generation would come mainly from solar sources energy storage is of paramount importance during periods of darkness. Flywheel Energy Storage (FES) is an option the University of Idaho has been chosen to explore. The flywheel provides several design advantages, including operability in low temperature

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environments, high efficiency, relatively low maintenance requirements, high energy density, and long-term storage capability. Thus, it is a highly viable option for NASA’s future designs. A comparison between common energy storage devices can be seen in Figure 1 below.

Figure 1 Energy Density Comparison

Flywheel Energy Storage operates on the principle of kinetic energy storage – that is, energy stored in a rapidly rotating disk. This design will use magnetic-levitation bearings while operating in a vacuum chamber to both minimize friction and air drag losses while mimicking a lunar environment. This design would allow NASA to increase mission time on the moon and the technology can potentially be applied to many other applications in the future.

Problem Definition

Design Team Goals:

Develop & test a working prototype of the Flywheel Energy Storage system Provide a stable and reliable design Implement microcontrollers to control flywheel positioning Run hub-less flywheel prototype at rotational speeds near 2000 rpm

Deliverables:

Updated CATIA modeling of final prototype, with drawing package Manufactured and tested flywheel subsystems Microcontroller algorithm programming for future designs Final Design Report for the University of Idaho and NASA Final design presentation for Engineering EXPO in May 2013

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Stakeholders:

Individuals with interest in the completion of the flywheel design:

NASA Sponsors Professors Law, Riley, and Berven – University Mentoring Faculty Mechanical, Electrical and Physics Graduate Students Senior Design Team Members

Concepts Considered

Stator Split

It was decided early on by the graduate team members that the stator was to be redesigned to a split orientation. Having the stator divided and separated allows for the control system to generate forces that cause a transaxial torque on the rotor, and will give control over the angle of the rotor rotation axis. Inertial moments of the rotor were to be analyzed for any design change to check for rotor dynamic instability. The rotational velocities at which instabilities occur coincide when the ratio of the moments of inertia (MOI) of the rotor, I x , I Y /I z=1. These coincidences are likely to cause catastrophic failure, and are to be avoided at all costs.

Cooling Structure/Rotor Lifting Mechanism

The HTS passive magnetic bearing allows a self-regulated elevation height of the rotor during machine operation. To accomplish this, the elevation of the rotor must be controlled during the cooling of the HTS, after a vacuum is pulled. The vacuum chamber was purchased in the previous year of the project, and added a spatial constraint parameter to the design. The lifting height capability of the mechanism needed to include an elevation range of at least 50 mm above the surface of the HTS. Mechanism needs to be clear of rotor during operation, and not obstruct magnetic field.

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HTS Geometry

The HTS array is a very large expenditure for this phase of the project. Geometry of the array is to be decided to allow for full operation of the passive magnetic bearing, while minimizing cost. Individual superconductors were available for machining in three puck diameters, 28 mm, 35 mm, and 44 mm. Since cylindrical pucks in a circular array are to be used, they must be trimmed to be adjacent for full coverage of the permanent magnets in the rotor, disallowing any incongruous patterns of magnetic field repulsion. Geometry must be calculated to give an integer number of pucks while also calculating coverage.

Microcontroller

For the 1st semester of this project, we worked with an Atmel board. However, for the 2nd semester of this project, we decided to switch from the Atmel board to the Microchip PIC32MX7. There were a few reasons behind this. To start with, the Atmel IDE was a very difficult and frustrating tool that we found out to be more of a struggle than we anticipated. This wasn’t really a huge deal, but when we were trying to learn how to use the IDE and get the adapted form of C to work on this board, it became a hassle. When we finally got the ADC code working on the Atmel board, we found out that it took a long time for the ADC to read and store a value. This board had only 2 ADC channels that could be read simultaneously, and switching between the channels took way too long (approximately 120 us each read). This may have been able to work for our simple demo, but adapting this to a large scale high-speed flywheel would have been impossible. From this point, we knew that we had ADC code that worked for the PIC board that we used in the microcontroller classes and labs that we had previously taken. The timing we characterized for this board was an impressive 20 us sample time for 4 channels reading and storing values. The ease that we were able to set up this ADC and timing characteristics led us to think that we had been wasting our time trying to get the Atmel board to work, and rather that we could do the same things with the PIC and have familiarity with the IDE and code for the board. The PIC board has a 16 channel ADC, so if we want to eventually use more than 4 channels then we will have to adapt the development board so that we can get all of the pins needed to correlate to the correct ADC pin. In the end, it took us all of first semester to get the ADC and LCD screen working on the Atmel board, when it took us about two days to characterize and get everything we had done on the Atmel board on the PIC development board.

The features we use on the PICMX7 are the 80 MHz core, a 16 channel Analog to Digital converter each running at 10 bit resolution and its built-in Pulse Width Modulation functions.

Active Magnetic Bearing (AMB) Control

The active magnetic bearing (AMB) control is responsible for maintaining the one millimeter air gap between the rotor and the stator. The rotor is levitated by the high temperature superconductors (HTS) and permanent magnets, but a method is needed to control the horizontal position of the rotor. The stator includes 24 coils, which will be individually controlled. For rotation, each coil will be powered to behave as a field winding or

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an armature winding, depending on rotor position. When the rotor begins to drift, the AMB control can temporarily adjust the power in a coil to push or pull the rotor.

In the first semester of the project, we initially tried to implement the calculation of the air gap using a sensorless method. However, we determined that this would not be possible with our setup and tools at hand, so we bought air gap distance sensors that are read on the microcontroller to determine what the air gap is.

Based off of the air gap, the AMB can then take corrective action to adjust the power to certain coils to properly push and pull the rotor back into the proper position. The AMB will provide a desired current value to the current controller. This current value will correlate with the desired air gap. The current controller will then properly pulse width modulated signals to an H bridge to ensure the proper current gets passed through the coil. This adjusted current flowing through the coil will adjust the rotor position. A block diagram description is shown below.

Component Design and Manufacturing

Stator Assembly

The stator is the powerhouse of the flywheel energy storage system. It is responsible for converting electrical energy into rotational kinetic energy. The stator is a combination of mechanical and electrical systems that work together to convert energy efficiently. The stator is housed on a central shaft made of stainless steel that holds ferromagnetic laminations design to induce strong magnetic fields. These laminations are wound with coil wrappings in specific patterns to create an optimum magnetic field for the rotor’s given polarity.

There are two sets of coils in the stator assembly; the drive bearing (bottom) and the active magnetic bearing coils (top). Each set of coils are designated to directly change specific degrees of freedom in the rotor. The drive bearing coils are given most of the power to charge

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and discharge the rotational inertia of rotor. These coils are oriented vertically and force the laminations on the rotor rotationally around the center axis. The active magnetic bearing coils are wrapped cylindrically away from the center axis of rotation. These coils force the rotor laminations laterally. The combination of these two magnetic bearings allows for controlled rotation of the rotor. The active magnetic bearing is designed to correct any imbalance in the rotor by creating repelling moments about the center of gravity. This allows for accurate and stable control of the rotor during operation.

The AMB and DB coils are insulated electrically by a wrapping. This wrapping has an upper temperature range of 200 degrees C, and thus cannot reach or exceed that temperature. The center shaft is designed with an inner coolant channel that provides forced internal convection cooling using a water supply. The lower end of the shaft has the wider diameter and holds the two fitted connection for routing the water in and out of the shaft. The shaft was drilled out to the deepest length that was possible using a 3/4” drill bit. The hole depth reached 11.5in which reaches the active magnetic bearing laminations. This should be suitable for removing heat produced in the coils. The water system will be separated by a baffle that runs up through the middle of the hollow shaft. The baffle should allow space water can flow up one side then over and down the other side. This design was chosen for ease in machinability and assembly. It is understood that an annulus channel is ideal for heat transfer but nearly impossible to create in house.

This system is bolted to a steel base plate. It serves several purposes; mainframe that all subsystems are bolted to, acts as the bottom layer of the vacuum chamber, and stabilizes the entire flywheel system in rigidity. Currently the base plate sits on a movable cart for accessibility. The subsystems that are bolted to the base plate are the stator, copper plate assembly, lifting mechanism, and sensor mounting bracket. The vacuum collar is also sealed outside of these subsystems onto the base plate completing the seal. The base plate was made to be the foundation to the flywheel system. Therefore it is inch thick steel and allows for large bolts to secure the stator. The machining of the base plate was specific to subsystem placement. Since the flywheel system has specific geometric constraints, each subsystem must be oriented in a specific way that optimizes this issue. Using different views in CATIA, it was possible to find the best radial orientation for each subsystem. This explains the somewhat randomness of the base plate holes and placement. The holes were tolerance within a thousandth of an inch.

Originally this flywheel design had no split involved, and consisted of the DB lamination stack alone. Due to the redesign, it became necessary to disassemble the previous design team’s central shaft (remove coils, laminations, etc) in order to reuse the drive bearing laminations. To do this, Strom electric had to reheat and cut the original shaft assembly so that the laminations could be removed from the wires. Due to the excess amounts of oil and dirt from these processes, each lamination had to be cleaned in an oil solvent so as to not damage the vacuum pump.

The new center shaft was machined in the meantime from 2” diameter stainless stock; machining for the shaft occurred on the CNC Haas Lathe. As mentioned previously, a ¾” center hole was drilled, reaching nearly 12” in depth, for the purpose of removing heat from the coils. The coolant channel is sealed with a 303s stainless plug on the bottom, featuring ½ - 14 NPT threads. Threads at the

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base of the shaft, designed to fit with the pipe flange for mounting to the baseplate, are 1 ½” NPT and had to be cut using mastercam code. Finally 1” stepped diameter had to be turned to provide a press fit for both the original drive bearing laminations, as well as the AMB laminations. Note: Press fit was completed using a liquid nitrogen shrink fit, as well as mechanical press fit to ensure the strongest fit; the ME shop’s arbor press was too small for the new shaft, thus facilities’ hydraulic press was used to complete each press fit. AMB laminations were water jet cut with too small of an inner diameter so that a precision bore could be made afterwards. This bore was completed by Russ Porter in the ME shop.

To Do:

Insert internal convection flow baffle separating inlet and outlet flowo A taper should be milled into material to ensure proper fit

Repair thermocouple wire that was cut during assembly Create and validate heat transfer model predicting required flow rate of water

Rotor Assembly

The rotor assembly (rotor or flywheel) is the flywheel portion of the flywheel system. This is the portion that will store kinetic energy converted from electrical energy by the stator. The energy held in the rotor is proportional to the rotational inertia of the rotor and the square of the

rotational velocity by KErot=12I ω2. The rotor assembly is

the only part in the flywheel system that is able to move during operation. The inside-out design with magnetic bearings means that the rotor will not have physical contact with any other part during operation. All degrees of freedom except for the rotor's levitation height will be governed by the control system through the AMB and position sensors. Levitating the nearly 40 lb rotor is done by repelling the magnetic field created by neodymium magnet arrays in the bottom of the rotor (mag plate) with HTS in the copper plate (see PMB). Levitation height target is achieved by near-field cooling the HTS in the PMB system. Magnetic field strength is optimized by arranging magnets in a Halbach array.

In a high-speed FESS, hoop stress is the limiting factor on energy density. For phase II of the project, however, only low speeds are considered and material strengths are less of a concern. Materials used in the rotor's construction are also limited by the ratio of moment of inertia. Due to potential magnetic issues, the components (other than the laminations) are constructed from nonmagnetic materials.

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The two stacks of laminations (dark grey in the picture above) are two different AMB's. The top stack (stabilizing bearing, or SB) was added to the design in early 2013, and exerts only horizontal forces intended to help control changes in the rotation axis of the rotor. The bottom stack (drive bearing, or DB) provides similar forces as the SB, with the addition of the torque control that charges/discharges the rotor.

The 2011-2012 senior design team designed a shorter rotor with only the drive bearing. At the time it was thought that the rotor would stay on axis due to the force couple generated by the DB and the PMB's pinning effect. After the change to the split stator design (see Stator Split in Concepts Considered section) it became necessary to calculate geometry driven properties like the MOI ratio and CG of the rotor. The rotor was idealized and a calculator was written in EES, but may be copied to any equation solver. The EES calculator and literature on it may be found in the CG+MOI calc folder on the shared drive. The calculator was also handed off to Bridget Wimer and Brent Kisling, who adapted the equations for Mathcad.

The calculator helped us with design decisions regarding the shape of the rotor, such as the inner and outer diameters and density of the fill material between the lam stacks. Senior design decided on a nylon fill material based on low cost and a density that matched with a favorable rotor MOI ratio. The decision to manufacture a top plate with a 1" height for sensor target was confirmed similarly, along with the EE grads' decision to use 41 laminations in the SB.

The stacked rotor components are held on axis by 4 stainless steel standoffs run through with a nylon threaded rod. Absence of these standoffs could result in shifts of the rotor's components, particularly the drive bearing laminations, during operation. The nylon rods thread into the mag plate and are capped with stainless acorn nuts at the top of the top plate. Nylon was chosen to tie the rotor vertically due to very few forces acting in the vertical direction. Also, nylon is inexpensive and nonmagnetic.

Components in close proximity to the AMBs have generally been constructed of nonmagnetic materials. The top plate, mag plate, standoffs, and acorn nuts of the rotor assembly are all from an easier machining austenitic stainless steel (303 or 304 stainless). Decisions in design should consider manufacturing difficulty with stainless steels. In the event that decisions are made to machine parts from stainless, measures should be taken to reduce shop downtime due to tool wear or breakage. Additional drill bits, taps, or end mills could be acquired before the machining task is started to insure completion. Russ Porter will be a valuable asset in advising under what circumstances and to what degree preventative measures should be taken for a smooth manufacturing experience.

The geometry of the rotor and stator laminations was designed by the EE grads and Dr. Law. The laminations were water jet cut by Northwest Wire EDM out of 26 gauge M-15 silicon electrical steel. 108 laminations are used in the DB and 41 in the SB. Repeatability error of the water jet cut was brought up by senior design after measurement of lamination stacks, and it has been suggested that dies be manufactured for cutting laminations in the event of redesign or remanufacture. Wire EDM may be a good alternative for greater precision barring any possible material degradation.

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The nylon spacer between the lam stacks was machined in house from a 7 1/2" OD 1" thick nylon tube. The major dimensions were machined on a manual lathe and the 4 standoff holes were machined on manual mill by Russ Porter at the request of senior design. The stainless steel standoffs were drilled and cut to length from 1/2" rod stock on manual lathe. The drilling of the 1/4" hole through the length of the standoffs needed to be drilled from both ends due to the depth (over 6") of the cut. The process took much longer than expected partially due to a broken cobalt drill bit.

The mag plate was designed and manufactured by the 2011-2012 senior design team and Russ Porter. The critical feature of the mag plate is the 60 pockets in the bottom of the part that are intended to hold the 3-cube (1/4" cubes) Halbach arrays of nickel plated neodymium magnets. Each pocket is meant to hold 2 stacked Halbach arrays, for 6 magnets per pocket, and a total of 360 magnets held by the part. Assuming that the magnets were 0.250" on a side, the pockets were machined at 0.249 width for a 0.001 interference fit. During the spring 2013 semester Dan Schneider created a mock-up of the magnet pockets. He found that as magnets were pressed into the pockets, the walls of the pocket would deflect into the next adjacent pocket, causing a progressively tighter fit until the interference was so great that pressing became impossible. It was determined that 0.001" in every pocket is far too much interference for the fit of the magnets. It was also discovered that variance in the width of the magnets was too great to make a predictable press fit. The issue has been brought to the attention of all involved parties, and many possible solutions have been discussed, but none decided upon. Surface grinding the magnets has been frequently suggested, but appears to introduce far too many new unknowns to be a viable solution (and may actually be dangerous). Alternating the press order and hand-selecting measured magnets from a larger pool seems to have potential as a solution. By increasing the quantity of magnets available it may be possible (statistically, it is possible) to fix this problem without having to re-machine the mag plate. Russ Porter is likely the greatest available asset in solving this problem.

To do:

Find a way to fit the 120 3-cube Halbach arrays into the bottom of the mag plate - This task should be a collaborative effort between the reader, Dr. Berven, Dr. Law, Dr. Riley, Chris Mirabzadeh, Daniel Schneider, Russ Porter, and any IEW mentors available with knowledge of the issue.

Measure physical rotor properties (weight, density, etc.) to remove assumptions from CG+MOI calc, and attempt to remove idealizations.

Outsource balancing of the rotor assembly after all geometry is finalized.

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Lifting Assembly (Cooling Structure)

The lifting mechanism serves as a tool to allow proper levitation and six degree of freedom operability of the flywheel system. The parts which actually allow the levitation to occur reside in the Passive Magnetic Bearing (PMB), which consists of the high temperature superconductors (HTS) as well as the permanent magnet array embedded in the bottom of the rotor assembly. In order to understand the function of the lifting assembly, it is first necessary to know basic functionality of superconductors.

Superconductors operate with virtually no electrical resistance and expel all magnetic fields perfectly from their internal structure. However, it is important to note that the superconducting material only operates in such a manner when it is cooled below its critical temperature. This design uses the aforementioned “high temperature” superconductors, which essentially means that the material operates at a relatively high temperature as compared to other superconducting material. The HTS purchased for this project operate at or below a critical temperature of 77 K (-329 ⁰F), which is also the boiling temperature of liquid nitrogen.

To achieve proper levitation height against the superconductors, the lifting mechanism must achieve what is called “near-field cooling,” a process by which the permanent magnets intended to achieve levitation are held at a certain height while the superconductors transition to their operating temperature. Superconductors are manipulable as their magnetic field expulsion depends on the existing magnetic field as they are cooled to their critical temperature (see Meissner Effect – Wikipedia). In this design, once the HTS array is cooled effectively, the rotor (containing the permanent magnet array) must be lowered perfectly straight down onto the superconductors. Once it is close enough to the HTS array to achieve levitation, the lifting mechanism must then vacate the operating space of the rotor.

The design chosen and built is a vertical lifting plate supported by three lead screw pillars, with three nuts located in an equilateral position to provide vertical support for the plate. The design can be actuated through the vacuum by way of vacuum capable rotary shaft feedthroughs. The vacuum encapsulated shaft is attached to a 1.75” pitch diameter gear, which meshes with a 2” pitch diameter gear secured to a lead screw (this provides a small gear reduction). When rotated, the shaft feed through will rotate the smaller gear, and in turn the larger gear, causing rotation of the lead screw. Each of the three lead screw nuts is machined into the lifting plate to prevent rotation; this provides vertical translation of each nut.

The material used to construct the lifting plate is G-10 FR4 glass epoxy, chosen for its non-magnetic properties, high yield strength, machinability, and cryogenic temperature rating. These features are important as it was necessary to create a low profile (i.e. thin) lifting plate to be clear of the operating space of the flywheel while deflecting minimally as it held the rotor (approximately 40 lbs of weight). Material for lead screws, nuts and gears were chosen as ferrous steels as they didn’t conflict with any magnetic field and for cost effectiveness.

Ultimately, this design was chosen for repeatability, cost effectiveness, simplicity and strength. The design also provides a guard for the HTS array during operation, should the rotor fail to maintain

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levitation.

IMPORTANT: It is ESSENTIAL that each lead screw turns simultaneously. If one is turned even slightly while the rotor is around the stator, the rotor will collide with the stator assembly due to the small air gap.

To do:

Design and manufacture a system of simultaneous lowering for each nut Chamfer lead screws to allow set screw in gear to lock. Set screw can be damaged if

operated without the chamfer

Suggestions: Sprocket and chain assembly capturing each shaft below baseplate to allow for uniform lowering. An optional crank arm could be added above the plate next to the vacuum chamber for ease of operation.

HTS Assembly

Since one of the main functions of this flywheel system is efficiency, levitating the rotor played a large role in specific design. The HTS assembly is the structure on which the rotor levitates. The rotor will never touch the HTS assembly since the lifting plate is in between. This assembly is to house these superconductors and provide structural support for the weight of the rotor.

The main part of this assembly is the copper plate. The purpose on choosing copper for this structure is because it has high thermal conductivity and a relatively low coefficient of thermal expansion, making it a better candidate at cryogenic temperatures. Since the superconductors operate at 77K, the biggest challenge is to cool these superconductors and maintain this strict temperature throughout operation. Therefore the copper plate has a liquid nitrogen channel underneath the superconductor array to transfer the heat out of the system. The superconductors are recessed into the copper plate to allow for three surfaces of direct contact with the copper, allowing greater heat transfer.

Another major goal of this design is avoiding any magnetic flux gaps from HTS to HTS. This becomes an issue of geometry, the challenge being to allow the magnet array in the base of the rotor to “see” the HTS array with absolutely no gap. This design achieves that with two angled cuts at 17.14o

with a chord length of 0.953in on each superconducting circular puck. This allows for 21 superconductors at a radius of 3.392in on center. The reason there are 21 superconductors is due to any possible magnetic oscillation effect. Since there are 60 magnet slots in the bottom of the rotor, there can’t be any factor of 60 in the superconductor array. If there was this would mean that factor of the magnets would rotate over the ends of each superconductor. In this case if we chose 20

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Figure 2. Liquid Nitrogen Cooling Channel

superconductors, 20 magnets every third slot would rotate over the chord of each adjoining superconductor. Since there is a possible lack in magnetic flux, it would decrease repelling force on the rotor initiating unwanted vertical oscillation. At high speeds this could cause drastic system failures. The chord length on these superconductors was over predicted to exceed minimum requirements for the magnet length of .75in. Therefore it is over predicted by.203in which is large enough to hopefully never cause any gap in magnetic gap.

The liquid nitrogen system works as an open system from outside of the vacuum chamber. The idea is that when the liquid nitrogen boils off it vaporize in the copper plate channel. The vapor will rise to the top and follow a grove cut out along this channel. This will lead the vaporized nitrogen to the port outlet, allowing liquid nitrogen to enter due to a simple density gradient. The ports will be attached to piping that exits the vacuum chamber in a gravity fed system. In designing this system, steps should be taken to ensure ease of escape for vaporized nitrogen.

Attached to the copper plate are three standoffs or supports that are secured to the base plate. These standoffs determine the specific height of the copper plate which in turn determines the rotor’s elevation with respect to the stator. This is highly critical in knowing the elevation of the rotor since it needs to be within a small vertical range of just a few millimeters. This results in the levitation height given by the superconductors and the standoff height. Since both of these parameters are defined in this assembly it is important to understand the high tolerance in making the standoff the proper height.

To do:

Machine pockets for HTS arrayNote: be cautious of differing thermal expansion coefficients between

HTS material and copper material. If pockets are too small, breakage of HTS pucks may occur.

Machine G-10 standoffs to exactly the same length, at given standoff height corresponding to rotor levitation height.

Note: G-10 was designed as a press fit to disallow any possible vibration between steel nuts and G-10 due to lateral reaction forces caused by the rotor.

Design and test vacuum capable liquid nitrogen feed system

Sensor Mounting Assembly

The sensor mount assembly is designed to accomplish a few different tasks. First, the assembly gives a stable location to clamp the sensors that are to be used to detect the location of the rotor assembly with respect to the stator. A control algorithm is used to apply forces between the rotor and stator based on the readings of the sensors mounted in this assembly. This is to correct horizontal and axial shifting of the rotor.

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Second, the assembly is strong enough to provide structural support to the stator shaft. It was estimated by Dr. Riley that deflection of the stator shaft could be significant under operation with heavy forces. With the addition of the thick steel mounting bracket, the stator shaft is changed from a cantilevered beam to a simply supported beam, and will be much more rigid under heavy forces.

The assembly is also used as a wire routing guide. Due to the split-stator design there are wires that must be routed from the top of the stator. These must be out of the way of the rotor, and so are routed up and around the arms of the mounting bracket. The arms are bolt-jointed between the upper and lower arms to allow the top portion to come off for disassembly without disrupting the sensors.

Sensor mounting concept was initialized when microcontroller shortcomings prevented sensorless design. Sensors to locate the rotor's axis tilt and horizontal position demanded a mounting scheme. Early design consisted of two small brackets mounted to the baseplate at 90° from each other, each to hold two sensors at different elevations. This design failed to measure the location of the rotor with respect to the stator under conditions where the stator shaft is deflected due to forces between rotor and stator. A next design iteration suggested the upper sensors be mounted from the top of the stator shaft to compensate for stator deflection, and lower sensors mounted to the baseplate using reasoning that deflection of the stator shaft at that elevation will be minimal. That design may have been adequate for sensing the location of the rotor with respect to the stator, but concerns over wire routing led to a different design. The current design (shown below) allows for the four sensors to be mounted in the correct locations, provides structure for wire routing, and greatly stabilizes the top of

the stator shaft. Known problems with this design include a potential vibration issue in the sensor mount ring that may be solved with the addition of damping pads at the rings' mounting locations and a spatial issue with the elevation of the lower ring conflicting with the liquid nitrogen fittings in the copper plate. The lower ring can be raised up and out of conflict by redesigning the sensor mounts to orient the sensors on the underside of the ring.

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The upper and lower arms of the mounting bracket were plasma cut from 1/2" plain steel sheet by Pacific Steel in Coeur d' Alene (formerly Forest Steel) with material left for finish machining in the ME shop. The top disk of the bracket was machined by manual mill to fit the thicknesses of the upper arms. The top disk and upper arms were machined as an assembly (by Russ Porter, at the request of senior design) to fit to the top of the stator shaft. The

height of the lower arms made it necessary to use the CNC mill to create the hardware holes. The arms and disk of the mounting bracket are shown assembled to the baseplate in the photo below.

The rings were rolled by facilities out of strip steel to a 12" outer diameter. The size should allow for a damping pad to be placed between the rings and arms for mounting the rings to the assembly. Some shop creativity may be needed in order to accurately place holes in the ring to allow for set screws to solidify the assembly. It is also possible to have facilities re-roll the steel rings with pre-drilled holes as it is a simple, fast and inexpensive process. Resonance may be an issue with the sensor mount ring, and the damping pad will have to be revisited if it should fail to damp the ring. Dr. Riley can be contacted for assistance with this issue.

The sensor mounts should be designed to relocate the sensors to the underside of the rings. Assistant Dan Schneider suggested a design with an aluminum body and a single set screw. The body is shaped such that one side of the mount will deflect when the set screw on the other side is tightened.

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This design will allow for a much cleaner installation and alignment of the distance sensors. Contact or Dan Schneider through Dr. Berven for details on this sensor mount design.

Wires from the top of the stator can be routed along the arms unused by sensors. The wires can be fixed to the lower arm, but should be easily detachable from the upper arm to facilitate quick disassembly. A connector could be mounted near the top of the lower arm with wires leading to vacuum feedthroughs, and the top stator wires could be plugged into it and tied to upper arms if necessary.

The sensors themselves are very expensive components, and extreme care should be used in handling them. They were purchased from Kaman Precision Products and are the 9U sensors. Further details on the sensors can be obtained from Kevin Ramus's Distance Sensor Specs power point located on the shared drive or from Kevin himself. A 3/8"-32 tap set was purchased for mounting the sensors, and is located in EP 305 with the entire assembly and miscellaneous components.

To do:

Redesign the sensor mounts to relocate sensors to underside of rings. Mount sensor mount rings at proper elevation with proper damping between

rings and arms. Collaborate with Kevin Ramus and others for wire routing solutions. Bead blast rings to match the rest of the assembly.

Miscellaneous

Vacuum Assembly: Dr. Berven should be contacted and met with regarding any vacuum assembly or use prior to any attempt to pull a vacuum. She is very experienced with experimental vacuum components and since the assembly purchased from Kurt J. Lesker is of high value, extreme care and consideration should be taken before using it.

Parts Location/Organization: All of the finalized parts for the NASA Flywheel project are located in EP 305 under Dr. Berven’s supervision for the summer. These parts are organized in a 3 Tupperware drawer set, large grey tote, various cardboard boxes, and of course the portable assembly cart itself. They should include all of the various sub-assemblies discussed above, as well as the vacuum components (electrical feedthroughs, liquid feedthroughs, etc.), various tooling, parts from previous design teams, extra stock from machining, and other various material used for the project. Dr. Berven should be sought if there is any confusion on what belongs to the NASA Flywheel project.

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Team Member Roles & ContactAndy Ivy (ME) – Team Lead & Treasurer:

Tasks: -organized team meetings, and usher interdisciplinary communication

-completed all orders and inventoried parts in excel documentation

-main design on lifting mechanism, and helped design & machine most physical parts

-arranged any and all outsourced work (i.e. plasma cut parts, facilities work, etc.)

Contact Info:

Phone: (907) 903-1557 email: andyivy52@gmail.com

Nick Frazey (ME):

Tasks: -CATIA model updating

-main design on HTS cooling channel, Sensor Mounting Assembly

-oversaw most machined components

-created EES Rotor MOI code, as well as optimization code for HTS array

Contact Info:

Phone: (208)-874-4202 email: fraz1229@vandals.uidaho.edu

Vince Colson (ME):

Tasks: -CATIA model updating

-oversaw most machined components

-drawing package for machined components

-assembly of rotor w/ split

Contact Info:

Phone: (775)-741-8482 email: cols7422@vandals.uidaho.edu

Greg Parker (CompE):

Contact Info:

Phone: (907)-398-1100 email: park7229@vandals.uidaho.edu

Trace McGrady:

Contact Info:

Phone: (208)-283-9552 email: mcgr5514@vandals.uidaho.edu

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