Wireless Test Instrumentation System for Rotating Parts

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Nov 2, 2013 (3 years and 9 months ago)

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1

Wireless Test Instrumentation
System for Rotating Parts

December 5, 2012




Team 29 (ME)

Sean Handahl

Caleb Browning

Kenneth Thompson

Faculty Advisor
-

Dr. Robert Gao

Team 167 (ECE)

Michael Golob

Lawrence Bogan

Jeremy Neaton

Adam Bienkowski

Faculty
Advisor
-

Dr. Rajeev Bansal



Sponsoring Organization:
Sikorsky Aircraft

Paul Inguanti (Company Advisor)

Chris Winslow (Senior Test Engineer)


Table of Contents


2

1

Executive Summary ________________________________________________

3

2

Introduction _______
_______________________________________________

4

a

Problem ___________________________________________________

4

b

Detailed Background _________________________________________

5

c

Brief Overview ______________________________________________

7

d

System
Specifications ________________________________________

8

3

Preliminary Component Assessment ___________________________________

8

a

Electrical Components ________________________________________

8

b

Mechanical Components ___________________________________
___

12

c

Alternate Designs ___________________________________________

16

4

Proposed Design Analysis ___________________________________________

16

a

Analysis ___________________________________________________

16

b

Testing Methods ___________________________
_________________

17

c

Budget ____________________________________________________

17

5

References _______________________________________________________

17

6

Appendices _______________________________________________________

18


























3

1.
Executive Summary

Sikorsky, a United Technologies aircraft manufacturer, would like to solve a problem with
monitoring pitch change bearings in the tail rotor of their helicopters. These bearings are
located inside a shaft that rotates at up to 1200 revolu
tions per minute, and are crucial for
keeping control of the aircraft during flight. However, their location makes it expensive and
inconvenient to access for regular maintenance, and so pilots have relied on manufacturer data
to attempt to predict when th
ese bearings fail. The current system used for monitoring consists
of a wired sensor with a slip ring, causing liabilities with wires failing due to breakage or from
being shot off in a hostile environment. The slip rings also have brushes that add weight
and
eventually wear down. A team consisting of seven University of Connecticut engineers were
given a 4000$ budget to find a wireless solution that would allow for the monitoring of these
bearings over a minimum timespan of a year, without having to perfor
m additional
maintenance. More specifically, the team was asked to show that a wireless solution is feasible,
and to test this information was given on the Sikorsky S
-
92 helicopter. The solution the team
found for proof of concept was a Wireless Test Senso
r System (WSN) that can monitor variables
such as vibration or temperature of the bearing to indicate when the helicopter needs to be
repaired. This WSN consists of a microcontroller, transceiver, and accelerometer that can
record data to be transmitted to

a stationary system, once a day, in the helicopter cabin up to
40 feet away. It will be capable of recording and storing data to memory, until the data is
requested for evaluation, at which point the system will remove any onboard data. The WSN
will be tu
rned on by a wakeup signal in order to save power by only recording data while the
helicopter is operational. It will all be powered by a battery, which will suffice to power the
network for the one year minimum, and allow the system to power on after 30 d
ays of
inactivity, as requested by Sikorsky. However, the system may also include vibrational energy
harvesting technology, which would boost the lifespan of the system past the minimum
requirement for convenience. Furthermore, Sikorsky provided requiremen
ts on temperature,
packaging, and size in order for the system to work inside the 1.5” by 5.1” lubricated electronics
cavity of the shaft. The team’s final design meets all of these requirements except for
temperature, because commercially available compon
ents do not meet the high end of the
-
20
to 250 degrees Fahrenheit range. However, it has been confirmed that there are military grade
components that can be used, but that the team would not have access to them, and so the
team will provide proof of conce
pt and the company can further improve the design. It is
predicted that the suggested WSN will accurately give readings on the vibration of the tail shaft,
and will have no issues with the power supply over the entire time frame. In order to test this,
the

engineers also designed a test rig using a variable speed motor, an imitation shaft, and
cartridge bearings to simulate the actual rotating conditions in the helicopter, and to allow for
the collection of data of broken bearings and healthy bearings for c
omparison. If implemented
into Sikorsky helicopters the WSN will provide a more accurate readout on the condition of this
4

bearing, improving the safety of all pilots and crews, and allowing for savings in maintenance
for the company.



2. Introduction

a. P
roblem

The goal of this project is to design a Wireless Test Sensor System to monitor the condition of
the pitch change bearing in the tail rotor of a Sikorsky S
-
92 helicopter. Doing so will allow the
helicopter crew, or whomever is performing maintenance
on the helicopter to reasonably
assess the condition of the bearing inside the tail rotor without having to take apart the entire
tail rotor transmission. As it is, the bearings have life expectancies provided by the
manufacturer to predict when failure mi
ght occur, giving the crew an estimate of when it needs
to be replaced, thus eliminating the chance for loss of control during flight. Having a sensor of
this nature will allow the bearings to be easily monitored throughout their life, allowing
Sikorsky to

improve safety of the crew, and save on maintenance costs due to the difficult
process of physically accessing this bearing.


If the pitch change bearing fails, there will be no way to control the aircraft, as this component
changes the pitch of the blade
s in the tail rotor, and is sealed away inside the tail rotor gearbox.
It is desirable to monitor the temperature and vibration on these bearings. One of the biggest
issues with the previous attempts at monitoring the system are the use of wires, a brush,

and a
slip
-
ring to transmit an electric signal from a rotating shaft to a stationary receiver. This kind of
system has many components, which can fail and wear down. Although maintenance is simple
and the technology is well established, wired sensors are
heavy, the wires break, the
connections fail, and can be shot away due to the operating environment. Using a wireless
system would cut down on the number of components, thus saving weight and minimizing the
need for part replacement. This switch eliminates

these undesirable features but creates
problems of its own [1].



A wireless test instrumentation system consists of an accelerometer placed on the rotating
components. The data from the accelerometer would be processed using a Fast Fourier
Transform, com
pressed for storage, temporarily stored, then transmitted upon request to a
stationary system for long
-
term storage and analysis. The measurement system
(sensor/transmitter package) would be lightweight, self
-
powered, reliable, and would be
hardware/softwa
re configurable to accommodate multiple sensor configurations. The receiver
package would distinguish signals in an electrically noisy environment, would have embedded
fault detection and notification capability, and would interface with existing fixed da
ta
collection systems [2].



Team 29’s project goals as defined by Sikorsky are:

5

-

to survey commercially available low
-
cost wireless test instrumentation systems which meet
Sikorsky
-
defined measurement and weight requirements, and which potentially could
be
configured to operate in a an electrically noisy environment

-

procure equipment

-

install on a representative rotating system

-

configure/program to demonstrate signal transfer capability in rotating system tests


b. Detailed Background


Fig. 1
-

Tail Rotor Gearbox Cutaway


Requirements Overview
-


The sensor system will be placed inside an electronics cavity, which is 1.5” in diameter and 5.1”
long, operating within a temperature range of
-
20 to 250 degrees Fahrenheit, and will have to
transmit 40

feet to the cabin. In order to accomplish this, the group must choose proper
temperature and vibration sensors, a receiver and flash memory to temporarily store data, and
a transceiver to transmit data. Each of these components must operate within the des
ign
constrictions, and be housed in a packaging to seal out moisture. Each of these components
must also be powered for a minimum of 1 year, transmitting only once a day, and be able to
power back on after 30 days of inactivity [2]. A major component of th
e project is finding a
battery capable of sustaining this workload, and exploring whether or not the group can take
advantage of any energy harvesting possibilities to make the desired lifespan more attainable.


Power Supply
-

To supplement the battery and

possibly make achieving the one
-
year lifespan feasible, this
project will attempt to incorporate energy harvesting into the design plans. Energy harvesting is
6

a relatively new technology that allows one to gather the otherwise wasted energy of the
environ
ment and convert it into power, normally in small amounts, for the system. However,
since it is a secondary power source, its implementation is completely dependent on the size of
the other components in the system, and whether or not there will be room in

the electronics
cavity. This combined with the fact that most energy harvesters require some kind of converter
to regulate their output voltage, adding to size, hinders these systems applicability [4]. While
these will in no way sustain the entire system
by itself, it will supplement the power coming
from the battery to assist in powering the network. The battery that will be implemented in this
system will have to be able to power all of the components in the electronics cavity with the
assistance of the
energy harvesting systems. Due to the extreme temperatures that this system
will be reaching, the battery will need to include some sort of insulator, which may also have to
be applied to the entire system as some electronic components may not be able to
attain these
temperatures either.

For this project’s purposes, the possible energy harvesting venues are in magnetic
energy harvesting, vibrational energy harvesting, and thermoelectric energy harvesting (TE).
The magnetic option uses a magnet and coils, o
ne stationary and one in motion, to create a sort
of alternator, generating power whenever the moving portion passes the stationary portion.
Thermoelectric energy harvesters use a temperature gradient to generate a voltage between
two conductors. While the

helicopter shaft will almost certainly create a gradient with the
outside air due to the increase in internal temperature while running (up to 250 degrees) the TE
will require access to a colder air source to maintain that gradient. Otherwise, the TE will

simply
rise to equilibrium with the internal temperature of the helicopter shaft, eliminating the
temperature gradient and the power output. Therefore, the unit will need to be mounted
outside of our electronics package, and rewired into the system, which

may or may not be
possible due to the necessity of having a lasting seal around the rest of the electronics.
Vibrational takes advantage of the piezoelectric effect, which states that certain solids
accumulate a charge when they undergo mechanical stress
[5]. In the helicopter shaft, there is
a constant vibration, which will become the needed mechanical stress, allowing us to
accumulate a charge and use that energy as power. This makes vibrational energy harvesting
the most viable option because of its pot
ential for placement inside the system, and ability to
generate a rather constant power supply.


Test Rig
-

The main focus of the project lies with the electronic component selection and making sure
that they work. In order to do this, a representation of
a tail rotor shaft with the electronics
cavity at the tip will have to be produced. This cavity is the only space currently available in the
helicopter’s design for emplacing all the required components. The final test rig model will be
created in Siemens
NX8 computer aided design modeling software. The rotating shaft will be
7

powered by an electric motor, which will also be the source for the natural vibrations induced
to the system. The level of vibrations is motor dependent and can be adjusted by adding o
ffset
mass to the rotating system in order to get the amplitude of the vibrations to an acceptable
level for measuring. This motor will have an adjustable speed controller to allow for the testing
of sensor readings at various speeds.

The vibrations of the

test rig would ideally try to match those of the S
-
92 in terms of g
-
force, magnitude and frequencies, but this data cannot be obtained from Sikorsky. These are
the natural vibrations of the system due to the engine, rotors, and transmission operating
duri
ng flight. A spherical roller cartridge bearing and an angled roller cartridge bearing will
support the rotating shaft. These two bearing types mimic those in which the actual tail rotor
shaft rotates in, with the pitch change bearing being the spherical r
oller type and the shaft
support closer to the blades being the angled roller type. The cartridge type allows for them to
be removed and switched out with a purposely
-
damaged set. These will allows us to see how
the vibrations of the system are altered whe
n the bearings do go bad. The requirement of this
project is to be able to analyze and transmit the data, not necessarily to distinguish between
the readings obtained from a good bearing and that of a bad bearing. However, this will allow
for a meaningful
demonstration of the effects the bearing’s condition has on the system and
readings.

According to Senior Test Engineer at Sikorsky Chris Winslow, the most commonly seen
method of failure is spalling and melting. Spalling is a type of macropitting generally

caused by
unbalanced loads and is common when the load is unidirectional, as is the case with the tail
rotor. This contact fatigue can also occur when flakes of the bearing surfaces break off (spall)
and get lodged, and from when axial loads reverse quick
ly [6]. Melted bearings causes seizure,
occurring when the bearings heat up and become discolored due to excessive loads, insufficient
lubrication, or a drop in the hardness due to irregular temperature rise (metal on metal
contact).


c. Brief Overview

Thi
s project will consist of creating a Wireless Sensor Network (WSN) in order to monitor both
the temperature and the vibrations of the system. This will be accomplished by using one
sensor mounted on the bearings to measure the temperatures, while an accel
erometer will also
be mounted on the bearings to determine if the system is rotating freely and if the bearing
assembly is damaged. These sensors will be connected to the microcontroller, which will
record and store the data, until it receives the signal
to transmit the data. The power for the
system will be controlled and distributed by the microcontroller. Currently a single battery will
be used in addition to the energy harvesting system, which will draw energy from the
vibrational energy of the rotat
ing system. When the microcontroller receives the signal, it will
send the data using the ZigBee transmitter and once the data has been verified as sent, will
8

remove the onboard data. This entire system will require a packaging system, which will keep
a
ll of the components in place when rotating and will protect all of these parts from dislodging
and damaging the other components, as well as protect the components from liquid damage
due to the oil lubrication in the shaft. This packaging system may also

require an insulator to
surround all of the components to prevent damage to them caused by the temperatures its
surroundings will be reaching.


Generic Block Diagram


d. System Specifications

Electronics Compartment:

• Size: 1.5” diameter x 5.1” long


Temperature:
-
20 to 250 degrees F

Rotating Speed of Tail Rotor Shaft

• 1200 RPM

Battery Life

• 1
-
year min (3 years recommended)

• Runs for 12 hours a day, needs to survive 30 days of inactivity

Data Processing

• Measure vibration

• Store data temporarily



Transmit to stationary system and available at request of user

• Data must travel wirelessly upwards of 40 ft.

Environmental Parameters

• Can’t be visible from outside (hostile environment)

• Cavity is oil lubricated

• Moisture Possibility

9

• High vibratio
n level


3. Preliminary Assessment

a. Electrical Components

Wireless transceiver:

The ZigBee chip will be used as our wireless transceiver to transmit data from the
measuring system, which is located within the tail rotor to the stationary receiver that wi
ll be
located in the cabin. We chose to use this as our wireless interface for two main reasons. The
first main reason is that it consumes only 14 milli amperes, which is very low power
consumption in our design. In sleep mode, it only consumes .02 microam
peres, which in return,
only saves us more power. The second main reason is the fact that it can transmit data over a
very far range and at even a far more range than what is required in our parameters. However,
these two reasons were ideal in selecting th
e ZigBee chip as our transceiver.

Part No.

Operating
Temperature

Transmission
Current

Idle
Current

Voltage

Max. Data
Rate

AT86RF231

-
40°C to 125°C

14 mA

0.02 µA

1.8
-
3.6
V

2Mbp/s

AT86RF233

-
40°C to 85°C

13.8 mA

0.02 µA

1.8
-
3.6
V

2Mbp/s




These were two
transceivers that we considered and looked into. We selected the
AT86RF231 primarily because of the operating temperature. The specifications for these parts
were nearly identical, but we also needed to satisfy the temperature parameter so this part was
se
lected.

For the stationary side receiver, we will use an ATmega128RFA1, which combines a
microcontroller and ZigBee transceiver on one chip. We selected this chip because the
combination of microcontroller and transceiver simplifies the receiver system,
and power
consumption is not critical for the stationary side system.


Sensor:

The sensor will be used to measure the vibration of the bearing. The defect frequencies
we calculated occurred between 156Hz and 274Hz, meaning we needed a sensor with a
bandwid
th above 274Hz. The sensor needed to have an interrupt in order to tell the
microcontroller to start recording data. By keeping the microcontroller in idle, we are able to
save more power. We needed the sensor to have a very low power consumption, to prese
rve
the battery.

Part Number

Voltage

Activ e
Current

Idle
Current

Size

Bandwidt
h

Measurement
Range

Temperature

LIS3DH

1.71V
-
3.6V

11μA

0.5μA

3 x 3 mm

2.5kHz

±2g, ±4g, ±8g, ±16g

-
40°C to
125°C

10

SCA3060
-
D01

3.0V
-
3.6V

150μA

5μA

7.6 x 8.6
mm

100Hz

±2g

-
40°C t o
105°C

KXTI A
-
1006

1.8V
-
3.6V

325μA

10μA

3 x 3 mm

1.59kHz

±2g, ±4g, ±8g

-
40°C to 85°C


Trying to find a sensor with an interrupt limited our options for accelerometers. The sensor we
choose was the LIS3DH. The three sensors above all have interrupts and are

among the three
best options we could find. The LIS3DH accelerometer had an extremely low current
consumption, which help us have lower power consumption. This was the main factor we looked
into when deciding upon the sensor. We had a tight constraint on
the power we have available,
so we needed to save power where we could. The sensor we choose also is very small and
allows us to operate at the 3.6V the battery provides. As discussed in the background we
needed a bandwidth that was above 400Hz. The sensor

we choose allows us to choose a wide
range of bandwidths below 2.5kHz. Compared with the other two sensors, our sensor was the
only one that satisfied the temperature constraints given to us.


Memory:

Memory will be needed in addition to the memory in the

microcontroller to store data
from the sensor. The size of the memory is limited by the power restriction, as higher capacity
memories use more power. The amount of raw sensor data collected between data accesses is
much more than the maximum memory siz
e possible with the power restrictions. There are
several methods to reduce the amount of memory needed. The first is to use a technique called
time synchronous averaging, which involves averaging consecutive sets of samples together.
In this case, only

the average of a series of samples needs to be stored, which will greatly
reduce the memory need. Another method is to sample for short periods of time with time in
between samples when no data will be collected. A third method will be to transmit the d
ata
whenever the memory is full. With this solution, the full data will be stored on the receiver
system, on a non
-
rotating part of the aircraft, which will have less strict power restrictions,
allowing for a larger capacity memory.

Part Number

Voltage

Active
Current

Idl e
Current

Capacity

CY62167DV30

2.2
-
3.6 V

2 mA

10 µA

16 Mbit

CY62177EV30

2.2
-
3.7 V

4.5 mA

17 µA

32 Mbit




These are two options for low power SRAM. The 16 Mbit option was selected because
4.5 mA is too high to meet the battery life
specifications with the chosen battery. None of the
memories researched met the given temperature specification, because military temperature
rated parts are not commercially available.





11

Microcontroller:

Part Number

Supply
Voltage

Acti ve
Current

Idle

Current

Size

Operating Temp

Program
Memory

IO
pins

MSP430G2332
-
EP

1.8
-
3.6

220 μA

.5 μA

6.6x6.6mm

-
40 to 125 deg C

4kB

16

MSP430F5438IPZR

2.2
-
3.6

312 μA

2.6 μA

14x1.4mm

-
40 to 85 deg C

256kB

83


The lower power consumption option out of these two does
not have sufficient program
memory or input/output pins to meet our needs. The microcontroller we chose has slightly
higher power use, but has enough program memory and input/output pins. Both of these
support Serial Peripheral Interface (SPI), which is
needed to interface with the sensor and the
ZigBee transceiver.


Battery:

Our calculations for current use using the parts discussed above are as follows:

Part

Data Acquisition
Current

Transmission
Current

Idle
Current

Sensor

11 µA

0.5µA

0.5 µA

Memory

2mA

2mA

22µA

Microcontroller

312µA

312µA

2.6µA

Transceiver

0.02µA

14mA

0.02µA

Totals

2.32mA

16.31mA

25µA


Assuming time synchronous averaging or periodic sampling, 16Mb transmitted at 2 Mbps once
daily = 8 sec of transmission time per day.


Assuming
periodic transmission, transmit when memory is full:

12


The 11.011Ah we calculated is the absolute maximum needed. We calculated based on the
parts running continuously over the 12 hours. For periodic sampling, the memory will not be
running for the amount
of time used in these calculations, reducing the power used.

Battery model

Dimensions

Capacity

Output
Voltage

Operating
Temps

Eaglepicher LC 3155

Diameter 30.7 mm (1.21”)
height 54.6 mm (2.15”)

12.7Ah

2V

-
30C to 50C

Eaglepicher LC 3355

Diameter 33.3 mm
(1.31”)
height 54.6 mm (2.15”)

15.5Ah

2V

-
30C to 50C



Tadiran 15
-
5930
-
yy505

Diameter 32.9mm

Height 61.5mm

17Ah

3.6V

-
55C to 125C


From the batteries above, we choose the Tadiran 5930. Although most of the batteries we found
were the correct dimensions,
we found one that met the capacity we needed. The output
voltage of 3.6V satisfies the voltage requirements of our components, while the 2V from the
other batteries does not.


b. Mechanical Components

Energy Harvester:

Without energy harvesting, our design

meets the minimum requirements for how long
the system needs to last, powered purely by the battery. However, we will continue to research
ways to add energy harvesting to our design to further extend the life of the battery.
Vibrational energy harvesting

is the most feasible solution with our system due to relatively
constant vibration in the tail shaft, and the systems ability to be implemented inside of the
electronics package.


Temperature based energy harvesting (TE) was researched and is not viable b
ecause
the TE needs a temperature gradient in order to provide power. While there is a reliable
gradient in the tail shaft, the components would need access to additional cooling to keep the
13

components from reaching equilibrium and ending the TE power outp
ut. To achieve this, the
team coul d attach the TE to the outside of the package to provide air
-
cooling, but this would
reduce the gradient available because of the material between the heat source and the energy
harvest. This method would also require rewi
ring the harvester back into the package, which
would not be possible due to the requirement of having a sealed electronic system, to keep all
other components dry and operational.

Piezoelectric vibrational energy harvesting would turn strain into energy,
and allow this
energy to be collected by the system to provide a small amount of additional power. The
output of the vibrational energy harvester is sinusoidal or alternating current and the rectifier
board is used with the system to take this alternating
current and convert it into direct current
that can be used for all of the electronics. Commercially available rectifier boards are too large
to fit inside the small cavity available, and so a custom rectifier board must be made to allow
our system to imp
lement energy harvesting. This size constraint is also a controlling factor on
the amount of power the harvester can output. Depending on how small we can make the
rectifier board, we will be allowing more or less vertical tip
-
to
-
tip vibration in the harve
ster,
creating more or less strain, which can be converted to energy. This vertical tip
-
to
-
tip
displacement will also control which energy harvester we would use, as different models have
different maximum allowable displacements. Shown below are different

sample raw energy
harvesters that the group will use with a custom rectifier board. These raw harvesters are
provided by Mide Technologies under the Volture
TM
product line. They will collect raw strain
energy and send that through the rectifier board so i
t may be used with the system. The custom
board will contain a rectifier and a charge pump, to output a DC voltage at the same level as the
battery. If a custom rectifier board cannot be created to accompany the energy
-
harvesting
device, then the system w
ill be powered solely by the battery and will reduce the total
operating time.


Electronics Package:

The electronics package will be made out of aluminum. The end cap will be either screw on or
press fit and made of plastic, based on the material’s stre
ngth. The battery sits on the bottom
and will have O
-
rings around it to secure it in place. The electronics board will be placed
14

vertically and housed within a plastic encasement whose size and dimensions will be
determined later based off of the dimension
s of the board and wires running to it. The plastic
encasement will be made using a 3D printer due to the intricacies and fine details that milling
cannot provide. For CAD drawings of the electronics package, please refer to Appendix A.


Test Rig:



Ball Bea
rings: The original plan was to try and match the bearing sizes of the test rig
exactly with those on the S
-
92’s tail rotor shaft. The specifications for the pitch change
bearing (which is a double row spherical design), and the outboard and inboard shaft
support bearings (which are a tapered roller design) are provided in the table below.
These were used to calculate the defect frequencies for each bearing. These frequencies
were instrumental in determining the sampling frequency of the sensor, which in tu
rn
affects the memory needed and rate at which the data is transmitted. Below, two
methods were used to determine the defect frequencies, one found online and one
developed by Sikorsky.

Double row spherical:
tapered roller:


Defect Frequencies


Pitch Chan
ge
-

Double Row
Spherical

Outboard
-

Tapered Roller
(Timken)

Inboard
-

Tapered Roller
(Timken)

PD
-

Pitch Diameter (in)

1.915

5.040

5.860

BD
-

Ball Diameter (in)

0.460

0.510

0.680

# Of Rollers

9 (18)

25

22

Contact Angle (deg)

~23

~30

~30

Approximations of Defect
Frequencies

http://www.update
-
intl.com/VibrationBook8g.htm




Outer Race Defect (Hz)

156

2
26

196

15

Inner Race Defect (Hz)

204

274

244

Ball Defect (Hz)

178.6

249

219

Cage Fault (Hz)

8.6

9.04

8.9

Sikorsky’s Defect Frequencies




Outer Race Defect (Hz)

140.2

228.1

197.9

Inner Race Defect (Hz)

219.8

271.9

242.1

Ball Defect (Hz)

79.2

196.1

170.6

Cage Fault (Hz)

7.83

9.12

9.00

Bearing Defect Frequency Equations developed by Sikorsky:

Outer race defect in Hz = (# of balls / 2) * rev/sec* (1


((BD/PD)* cos
B
))

Inner race defect in Hz = (# of balls / 2) * rev/sec* (1 + ((BD/PD)* cos
B
))



Ball Defect in Hz = (PD/BD) * rev/sec * [1
-

((BD/PD)*cos
B
))2]



Cage Fault in Hz = 0.5 * Rev/sec * [1
-

(BD/PD) * cos
B
]




Where BD is ball diameter, PD is Pitch Diameter (usually OD + ID / 2)


Matching the provided d
imensions to cartridge bearings from manufacturer catalogs
yielded a match to bearing 22205C; a double row spherical bearing with a cylindrical
bore. This has a rated rpm of 6500 rpm, which is the only other requirement necessary
for the bearing to meet. T
he outboard tapered roller bearing was matched to 30313U,
which is rated at 2800 rpm. Many manufacturers produce these bearings, so selection
will come down to availability and cost from a supplier. Differing brands means that
these bearings vary in cost f
rom $25 to $60.



Motor: The search for a motor began using rough estimations for what power would be
needed to spin the test rotor shaft at the necessary speed. Alternating current motors
were initially looked at due to the ability to use wall power outlets
. The output speed
would also need to be varied as most pump motors ran at a fixed speed of 1750 rpm.
This meant that a speed controller would be necessary. Everything from ceiling fans
adjustment speed controllers to custom AC motors with built
-
in speed c
ontrollers were
looked at. However, due to cost, Tom Mealy of the Mechanical Engineering Department
lab staff was contacted to aid in the search for a motor. A ¼ HP DC motor with speed
controller was found and is currently being repaired for use. This was
a significant
acquisition as the motor was the most expensive component of the test rig and
purchasing a brand new motor for a single short
-
term use is not advisable.



Shaft: The shaft will be made of aluminum. The diameter changes to match the inner
diamet
ers of the bearings. At one end is a keyhole, which matches the key of the
16

motor’s output shaft. The test shaft will slide onto the motor’s shaft, and a grub screw
will be tightened down to prevent it from sliding off. At the other end of the test tail
rot
or shaft is the electronics cavity. It will have either a screw
-
on or press fit cap made
of plastic to secure the electronics package inside.



Base: The base will be made of aluminum and consists of a platform for the motor to be
affixed to, along with 2 ve
rtical supports to house the bearings. Each bearing will be
pressed into a recess in the support. Each recess has a small ramp and each support has
a hole behind the bearing, which will allow for easy removal of the bearing cartridge.

For CAD drawings of t
he test rig, please refer to Appendix B.


c. Alternate Designs

One of the biggest issues during the design process was finding an energy harvesting system
that would be able to fit inside the small cavity available. The output of the vibrational energy
ha
rvester is sinusoidal or alternating current. A rectifier board is used with this system to take
this alternating current and convert it into direct current that can be used throughout the
system. The problem with size does not pertain to the energy harv
esting device, but the
rectifier board accompanying it. Commercially available rectifier boards are too large to fit
inside the small cavity available, so in order to use energy harvesting a custom board must be
made. This custom board will need to conta
in a rectifier and a charge pump, which will be used
to increase the voltage. If a custom rectifier board cannot be created to accompany the
energy
-
harvesting device, then the system will be powered solely by the battery and will reduce
the total operatin
g time.


4. Proposed Design Analysis

a. Analysis


17

Proposed Block Diagram


First, the sensor will collect the data. The microcontroller will acquire this data, process
it (FFT and Time Synchronous Averaging), and send it to the memory chip. When it is
time to
transmit, the microcontroller will read the data from the memory chip and send it to the ZigBee
transceiver chip to be transmitted to the stationary side receiver.


b. Testing Methods


To test the electrical components, we will first try to
transmit data using the
microcontroller and ZigBee interface. We will then try to transmit sensor data directly through
the microcontroller and ZigBee chip. Finally, we will add the memory and try storing sensor
data and later retrieving the data and tra
nsmitting it using ZigBee. We will also test the
response of the voltage level of the battery to extended use. Once these components are
tested, we will assemble them in the packaging to be used in the test rig.


c. Budget



Battery (x4):
$100.80



Sensor (x1): $2.27



Transceiver (x1): $5.16



Microcontroller (x1): $9.86



Memory (x1): $15.75



Antenna (x1): $5.19



Balun (x1): $2.58



Programmer (x1): $70.54



Motor (x1): Provided



Total: $212.15


5. References

[1] Adamnson, Alan., Berdugo,Albert., 2010, “Helicopter Slip Ring Replacement System,”
Research Paper, www.ttcdas.com/products/daus.../tp_2010_helicopter_slip_ring.pdf


[2] Winslow, C., “Wireles
s Data System for Aircraft Component Monitoring,” Sikorsky, Stratford,
CT


[3] Bai, H., Atiquzzaman, M., Lilja, D., 2005, “Wireless Sensor Network for Aircraft Monitoring,”
Research Paper, http://cs.ou.edu/~atiq/papers/05
-
China
-
Comm
-
Sensors.pdf


[4] Weddel
l, Alex S., Merrett, Geoff V., Harris, Nick R., Al
-
Hashimi, Bashir M., “Energy Harvesting
and Management for Wireless Autonomous Sensors,” University of Southampton, UK.


18

[5] Inman, Daniel J., Sodano, Henry A., Park, Gyuhae , 2005, “Comparison of Piezoelec
tric
Energy Harvesting Devices for Recharging Batteries,” Research Paper,
institute.lanl.gov/ei/pdf_files/JIMSS2005.pdf


[6] Errichello, Rich, 2005, “Spalled Bearings,” Practicing Oil Analysis, Machinery Lubrication
Publication, http://www.machineryl ubrica
tion.com/Read/718/spalled
-
bearings


6. Appendices


A.
Electronics Package

developed in NX8



19

B.
Test Rig

developed in NX8
-

The base has been made parametrically so that any change in
bearing size or height of the supports can be made easily.

The motor is not included because
it has not been acquired yet.



Side View

20




End View (from motor side)