ECE193/ME32
November 25, 2013
Sikorsky Wireless Test
Instrumentation for Rotating
Parts
ECE 193:
Olivia Bonner
David Vold
Brendon Rusch
Michael Grogan
ME 32:
Andrew Potrepka
Kyle Lindell
UCONN Faculty Advisors:
Rajeev Bansal
Robert Gao
Sikorksy Contacts:
Paul Inguanti
Chris Winslow
Dan Messner
University of Connecticut Storrs, CT 06269
Website: http://ecesd.engr.uconn.edu/ecesd193/ E-Mail: first.last@uconn.edu
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Table of Contents
1 Abstract………………………………………………………………………………………………………………...3
2 Introduction………………………………………………………………………………..………..………………3
3 Problem Statement.………………………………………………………………………………………………4
3.1 Statement of Need………………………………………………………………………………….4
3.2 Preliminary Requirements……………………………………………………………………….5
3.3 Basic Limitations……………………………………………………………………………………..6
3.4 Other Data………………………………………………………………………………………………6
4 Proposed Solution Overview………………………………………………………………..……………….7
5 Power Circuitry……………………………………………………………………………………………………..8
5.1 Voltage Regulator…………………………………………………………………………………..9
5.2 Charging Circuit…………………………………………………………………………………….10
6 Electronics…………………..………………….......…………………………………………………………….13
6.1 Microcontroller………………………………………………………………………………….…13
6.2 Sensors………………………………………………………………………………………………….14
6.3 Wireless Transceiver..…………………………………………………………………………...16
7 Data Analysis……………………………………………………………………………………………………….16
7.1 Data Transmission…………………………………………………………………………………17
8 Battery…………………………………………………………………………………………………………………17
9 Energy Harvesting……………………………………………………………………………………………..…19
10 Test Rig……………………....…………………………………………………….……………………….……..23
11 Budget……………………………………………………………………………………………………………….24
11.1 Estimated Costs…………………………………………………………………………………..25
12 Timeline…………………………………………………………………………………………………………….26
13 References…………………………………………………………………………………………………………27
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1 Abstract
Sikorsky has requested of this team a wireless sensor system for use within rotating
parts to replace wired slip rings. The system must be able to transmit a clean signal
from at least two sensors a distance of at least 40 feet in a range of environmental
operating conditions. The system must also be able to function for a minimum of 12
hours per day for a full year and continue functioning after a 30 day period of
inactivity. The team has proposed a solution utilizing an Arduino Nano v3.0, a WiFly
module attachment and several sensors. The unit will be powered by a 2-cell lithium
polymer battery coupled with an energy harvesting unit that will recharge the
battery while the unit is rotating. All parts have been ordered save for a rectifier and
power switching circuit. The unit will be tested using the same test rig as last year’s
team.
2 Introduction
Sikorsky helicopters rely on numerous rotating systems. These systems are crucial to
the operation of the aircraft and must be monitored in order to detect system faults.
Sikorsky currently utilizes a monitoring system that consists of wired sensors and
slip rings. These slip rings, however, are extensively utilized at high rotational speeds
and often fail due to erosion. Additionally, the wires from the sensors and slip rings
add unnecessary weight to the aircraft.
Consequently, Sikorsky has proposed the concept of a wireless electronic monitoring
system; this system would more quickly and more efficiently monitor parameters
such as temperature, noise, stress, strain and vibrations. United Technologies,
Sikorsky Aircraft, has asked UCONN team EE193/ME32 to come up with a wireless
solution to monitor the pitch change bearings of their S92 Helicopter. The team was
allocated a budget of $2,000 to update and redesign the system created by the
previous senior design team (2012-2013)[1].
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The 2012-2013 UCONN student team created a wireless system in which one sensor
was used. The system was powered by a battery that could handle 12 hours of
operation per day and a lifetime of at least a year. In order to successfully
demonstrate their system the team created a test rig to represent the tail rotor of
the S-92 helicopter. The test rig included an accurate representation of the
electronics cavity. An accelerometer was used to measure the acceleration near the
tail rotor bearings. The 2012-2013 UCONN student team successfully created a test
rig for the tail rotor of an S-92 helicopter and a wireless sensor system that utilized
one sensor and was powered by a battery.
Sikorsky has asked the current team to further the project with the addition of at
least one other sensor and the utilization of energy harvesting. The team will be
using a new Arduino nano microcontroller due to lack of documentation of the
previous PCB and microcontroller. The team will test the following sensors as viable
options for the second sensor: microphone, infrared temperature and thermometer.
Wi-Fi will be used instead of Zig-Bee to transmit the signals. In order to power the
system the team will use a small electric generator coupled with a battery. The
generator will use gravitational torque to keep the shaft stationary via an off-center
weight.
Figure 1. An interior sketch of the tail rotor gearbox on the S92 helicopter
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3 Problem Statement
3.1 Statement of Need
Sikorsky helicopters rely on numerous rotating systems. These systems are crucial to
the operation of the aircraft and must be monitored in order to detect system faults.
Technicians and mechanics have been responsible for monitoring these rotating
parts via manufacturer specifications; such maintenance testing occurs after a
designated number of flight hours. This type of system monitoring, however, has
proven to be very inefficient. These rotating parts are deeply embedded in the
aircraft and, consequently, are very difficult to get to when maintenance is required.
Additionally, the time and labor essential for this type of guess-and-check
maintenance has proven to be costly.
Sikorsky currently utilizes a monitoring system that consists of wired sensors and slip
rings. These slip rings, however, are extensively utilized at high rotational speeds
and often fail due to erosion. Additionally, the wires from the sensors and slip rings
add unnecessary weight to the aircraft.
Consequently, Sikorsky has proposed the concept of a wireless electronic monitoring
system; this system would more quickly and more efficiently monitor parameters
such as temperature, noise, stress, strain and vibrations. This advancement would,
thereby, allow system faults to be detected at an earlier stage, and essentially create
a safer environment onboard the aircraft. Wireless electronic monitoring also
presents an overall weight reduction by eliminating unnecessary leads and wires
that run from sensors to on-board computers. Assembling the monitoring system in
a more readily accessible area can also reduce labor and repair costs. Additionally, if
the monitoring system can be self-contained with an independent power source, it
can be easily replaced.
3.2 Preliminary Requirements
Sikorsky has asked the 2013-2014 UCONN team to expand upon last year’s project
proposal. The company requested the UCONN team to design a self-contained,
wireless monitoring system with an independent power source, all within an
enclosure of a specified size. Sikorsky requires the system to have at least two
sensors (i.e. a thermocouple, strain gage, microphone, etc.) with each sensor
measuring a different parameter. The primary objective is to transmit and receive a
clear signal over a minimum distance of 20 feet. In order to assure the quality of the
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generated signals, they will be compared to a calibrated signal during prototype
testing. The company proposed a second objective of increasing the battery life
possibly via energy harvesting within the enclosure. The final objective presented to
the UCONN team was to propose a sensor design in which the signals are able to
pass through barriers, such as doors, without interference. Sikorsky is currently
planning a date for the spring semester for the UCONN team to test /demonstrate
this design at company facilities.
3.3 Basic Limitations
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)
• Run for 12 hours a day
• Must 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 feet
Environmental Parameters
• Oil lubricated cavity
• Moisture
• High vibration level
• Must not be visible on the exterior (hostile elements present)
3.4 Other Data
The UCONN team will be expanding upon last year’s system model, incorporating
the updated requirements proposed by Sikorsky. The company has given the team a
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budget of $2,000 to further advance the 2012-2013 wireless, self-powered
transmitter package.
Sikorsky is interested in this project on a conceptual basis; therefore, the team’s
design will behave as research to see if a wireless monitoring system is feasible and
acceptable for their helicopters.
4 Proposed Solution Overview
Figure 2. General system block diagram
Figure 2 illustrates the general system block diagram that the team will be utilizing. The
two sensors, the accelerometer and the thermometer, are illustrated to the far left and
will be communicating with the Arduino via a Serial Peripheral Interface Bus (SPI Bus)
and an interrupt. The interrupt signal temporarily stops the program from collecting
data, as it is only necessary to collect this information upon user command. When the
device is not collecting data, it shall remain in standby mode in order to save battery
life. The Arduino will be in communication with the Static Random Access Memory
(SRAM) via data lines and an address. Additionally, the Arduino will be in
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communication with the wireless transceiver via another SPI Bus and a sleep/wake,
input/output signal. The transceiver will communicate with the antenna receiver.
Lastly, the Arduino will be powered via an applicable battery and an energy-harvesting
source (to save/maintain battery life).
Figure 3. Circuit schematic utilized from the previous team (2012-2013)[1]
The team has the above circuitry from the previous team; we plan to further analyze
the system they created in order make necessary improvements.
5 Power Circuitry
The battery and energy harvester will need to have special circuitry to facilitate their
interaction with the rest of the system. The energy harvester will need conditioning
circuitry to ensure its output voltage and current are within limits that are useful for the
demands of the system. The conditioning circuitry may include an AC to DC rectifier
circuit if a vibrational energy harvesting method is utilized. Two options are possible for
the interaction of the energy harvester with the battery. The system may switch
between energy sources, depending on whether the energy harvester is providing the
necessary power for the system, or the energy harvester may be dedicated to charging a
rechargeable battery. A block diagram of the power system is shown in Figure 4.
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DC Generator
Battery Charge
Manager
Voltage Regulator
Wireless Sensor System
Charging
Source Switch
Battery
Figure 4. Power system block diagram
5.1Voltage Regulator
A voltage regulator is required to keep the voltage supplied to the wireless sensor
package constant. Two options were considered for voltage regulation; linear
regulators and switching regulators.
Regulator type
Part number
Efficiency
Noise
Linear Regulator
L7805
Approximately 67%
No noise
Table 5.1
Switching Regulator
PTH08080W
93.5% [2]
Noise induced by
switching
frequency.
The efficiency for the linear regulator can be approximated by the ratio of output
voltage to input voltage: VO/VI x 100% [3]. Using a 7.4 V battery the efficiency would
be 5/7.4 x 100% = 67%. Due to low efficiency, linear regulators dissipate power as
heat and sometimes require heat sinks which take up extra space. A drawback of the
switching regulator is that the switching frequency can add undesirable noise to the
system [4]. The switching regulator option was chosen due to its superior efficiency
which allows for a smaller implementation. A diagram of the implementation of the
PTH08080W from [2] is shown in Figure 5.
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Figure 5. PTH08080W Switching Voltage Regulator, RSET=348 Ω for 5V output [2].
5.2 Charging Circuit
We have analyzed several methods to charge two lithium polymer cells. The first
method we looked into was to completely create our own circuit. The first circuit we
discovered through research is seen below.
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Figure 6. Lithium-Ion Battery Charger
The circuit could provide an output voltage that we desire. The circuit is also fairly
simple and is focused around the use of a transistor. However, the problem with
creating our own charging circuit is the size and PCB. We would need to have a PCB
made for the circuit. Also, due to the transistor a heat sink might be needed. This
would also take up space in the small compartment.
The second method the team investigated was the use of power management IC
chips. Linear Technology offers a few chips specifically made for energy harvesting.
The chip that caught the team’s attention was the LTC4071. This chip specializes in
low current applications. The applications listed on the datasheet for it are:
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





Low Capacity, Li-Ion/Polymer Battery Back-Up
Thin Film Batteries
Energy Scavenging/Harvesting
Solar Power Systems with Back-Up
Memory Back-Up
Embedded Automotive
The first problem with this chip is that it can only output 3.7 V to 4.2 V. Also, we
would need to create a PCB with the chip or order a premade evaluation board from
Linear Technology. The evaluation board from Linear Technology was far too large
for our dimensions. A second chip the team studied was a Texas Instrument
DVT2057. TI states this chip can combine high-accuracy current and voltage
regulation, battery conditioning, temperature monitoring, charge termination,
charge-status indication, and AutoComp charge-rate compensation in a single 8-pin
IC.This chip is made specifically for two cell lithium polymer. We ran into the same
problem with size constraints. The evaluation board offered by TI is also too large.
The final method the team has chosen to implement is to use PRT-1123 lithium
polymer chargers. These chargers feature:

MCP73831 Single Cell LiPo charger at 500mA

TPS61200 Boost Converter

Selectable output voltage 3.3 or 5V

5V @ 600mA max

3.3V @ 200mA max

Undervoltage lock out at 2.6V (with disable jumper)

Quiescent current, less than 55uA

JST connector for LiPo battery

micro-USB connector for charge power source

Inductor: 4.7uH, 1.2A Sumida CDRH2D18
The chargers contain a charging IC chip with accompanying PCB. The two charger
will be wired to the two batteries in parallel. The Arduino will then be wired in series
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which balances the charge between the batteries. The reason the team chose this
product is due to the small size. We will not have a problem implementing the
chargers in the electronics compartment.
6 Electronics
6.1 Microcontroller
We’ve decided to move the project to the open source Arduino platform. The switch
has several advantages compared to the PCB used by last year’s team. Arduino will
give us more flexibility in our design, as the platform offers more connectivity with a
greater number of inputs, and has a wide range of compatible sensors, which are
readily available. Arduino is also available at a much lower price point than similar
custom designs. For comparison, the custom built PCB from last year cost the team
around $1300, while a stock Arduino nano evaluation board costs around $30 and
offers additional functionality. Lastly, Arduino is a mature platform with plenty of
documentation. This is arguably the greatest advantage in the platform switch, as
any problems or questions that arise during development can likely be solved using
the ample sources available online. Last year’s team did not leave much information
about the specifics of their design, and it would be a significant hurdle just to learn
the full capabilities of their design, which may or may not meet our needs for this
year. The one drawback of switching to Arduino would be an increase in power
consumption. However, the additional power requirements will be mitigated by the
new energy harvesting solution, which will be discussed in detail in section 9.
The particular evaluation board we will use is the Arduino Nano v3.0. We believe this
board offers the best combination of features while still fitting inside our size
specifications. Measuring just 1.70” by 0.73”, the nano is a compact package that
actually reduces the space needed from the custom PCB of last year. It however
does not compromise on speed by offering the same 16Mhz Atmel ATmega328
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microcontroller that is used on full sized Arduino packages. It also provides 8 analog
input pins and 14 digital I/O pins, which should satisfy our connectivity needs.
Arduino Nano v3.0 Specifications
Table 6.1
Operating Voltage
5V
Input Voltage Range
7-12V
Digital I/O Pins
14
(6 PWM Outputs)
Analog Input Pins
Flash Memory
8
32 KB
SRAM
2 KB
Dimensions
0.70” x 1.70”
6.2 Sensors
Accelerometer:
The accelerometer we are utilizing is the ADXL362; this component is an ultra low
power 3 axis MEMS accelerometer. It consumes less than 2uA at 100Hz output data
rate. This device samples the full bandwidth of the sensor at all data rates. It also
features ultra-low power sleep states with “wake on shake” capability.
ADXL362
Table 6.2
Input Voltage Range
1.6 – 3.5V
Active Power
2uA at 100Hz
Standby Power
10 nA
Resolution
1mg/LSB
Ambient Temperature Thermometer:
The thermometer we are utilizing is the TMP36 Temperature Sensor. The
thermometer can read ambient temperatures from -40°C to 125°C to a high degree
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of accuracy. The ambient temperature of the cavity is an important metric that
measures whether the electronics are within safe operating temperatures.
TMP36 Temperature Sensor
Table 6.3
Input Voltage Range
2.7 – 5.5V
Linearity
0.5°C
Accuracy
±1°C (typical), ±2°C
Temperature Range
-40°C - +125°C
Infrared Body Temperature Sensor:
The infrared sensor we are utilizing is the MLX90614. This sensor allows us to take
measurements of the temperature of an external body. The sensor has a wide range
of measurable temperatures and could theoretically be used to measure the heat
given off by a bearing.
MLX90614 Infrared Thermometer
Input Voltage
Accuracy
Resolution
Temperature Range
Table 6.4
3V
±0.5°C
0.02°C - 0.14°C
-70°C - +380°C
Microphone:
The microphone we will be utilizing is a CEM-C9745JAD462P2.54R Electret
microphone. Although it does not have a direct helicopter application, it will allow us
to determine the wireless signal quality.
Electret Microphone
Table 6.5
Input Voltage Range
2.7V to 5.5V
Freq. Range
100-10,000Hz
Sensitivity
-46 ± 2dB
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6.3 Wireless Transceiver
We are purchasing an add-on board for the Wi-Fi module to make initial prototyping
easier. It is not yet known whether it will be used in the final prototype design as it
adds considerable bulk.
XBee Add-on
Table 6.6
On-board Regulator
3.3V, 250mA
Dimensions
3.7”x1.1”
The wireless transceiver is an RN-XV WiFly module. It is a low power wifi module
that operates on the 802.11b/g standard, and supports a serial data rate of 464kps.
It also features configurable transmit power for power savings when we don’t need
the extra range and a low power sleep mode.
RN-XV WiFly Module
Table 6.7
Average Active Current
38mA
Sleep Current
4uA
Input Voltage
3.3V
Serial Data Rate
464 kbps
Encryption Support
yes
Transmit Power
0 -12 dB
7 Data Analysis
Once the circuit has been assembled and the wireless system set up to interface
with the computer, the data from the sensors will need to be analyzed to confirm
the validity of this project. If a wired set of sensors have data similar to data
transmitted from the wireless sensor network, this wireless data will be considered a
"clean" signal.
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In order to compare signals there are two properties that should be considered:
amplitude and frequency. In order to compare amplitude, the data can be sent to an
Excel file or to Matlab and plotted. Depending on how the amplitude changes,
relative maximum and minimum values can be found at different periods. To
compare the frequencies, a fast Fourier transform (FFT) can be calculated using
LabView software.[5] Comparisons between the frequencies and amplitudes can
also be done in Excel and/or Matlab.
7.1 Data Transmission
One option to save energy and battery life is to choose that data be sent only when
a certain threshold or change triggers the sensor network to output a stream of
continuous raw data until the sensor network resets to a sleep state after a set
number of signaling cycles. [6] The use of WiFi with the Arduino limits the protocols
available for use. TCP and UDP have been considered. TCP is a protocol which
confirms that each packet of data has been received once it has been transmitted.
This would draw too much power and slow down transmission of data while
processing confirmation of received packets. UDP does not check that every packet
is received, so it is favorable to TCP for streaming continuous raw data where speed
is favored over absolute accuracy.
8 Battery
The Arduino Nano and add-ons can be run through the Arduino’s on-board linear
regulator with an input voltage of 7V to 12V or powered directly from a regulated 5V
source, preferably using an efficient switching regulator.
Item
Arduino Nano [7]
Current Draw
Table 8.1
17mA (direct 5V power with LED removed)
to 25mA (on-board regulator used, LED
intact)
Wi-Fi Module [8]
38mA
Sensors
<10mA (depending on sensors chosen)
Total
65mA-73mA
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If power is regulated with the on-board linear regulator, total power draw will be
7V * 73mA = 511mW
If power is regulated with an external switching regulator with minimal loss, total
power draw will be 5V * 65mA = 325mW
Using the on-board regulator, minimum input voltage (7V) necessitates a 2-cell
lithium battery pack (7.4V) or a 6-cell NiCd or NiMH pack (7.2V). Being a linear
regulator, all energy from voltage over 5V is dissipated as heat.
Sikorsky’s minimum requirement is that the unit must operate 12 hours per day for
one year.
(12 hours/day)*(365 days/year)*(73mA) = 319740mAh
Thus, in order to meet Sikorsky’s requirements with a battery alone, the unit would
need a 320Ah battery, either as a two-cell lithium pack or a six-cell NiCd/NiMH pack.
Using an external regulator, minimum input voltage could be lower, close to 5V, and
potentially slightly lower with a step-up regulator.
(12 hours/day)*(365 days/year)*(325mW) = 1423500Wh
For a two cell lithium pack,
(1432500Wh) / (7.4V) = 384730mAh = 193Ah
For a four-cell NiCd/NiMH pack,
(1432500Wh) / (4.8V) = 296563mAh = 297Ah
In all cases, the battery requirements cannot be achieved within the unit’s space
constraints. Thus, our design will have only a small battery coupled with an energy
harvesting unit. The main functions of this battery will be to power the unit during
startup and shutdown and to ensure a constant power source, as power received
from an energy harvester will vary through time.
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Several types of battery were considered:
NiCd
Poor
NiMH
Average
Li-Ion
Good
Li-Poly
Good
Voltage Output Per
Cell [9]
Poor (1.2V)
Poor (1.2V)
Good (3.6V-4.2V)
Good (3.6V-4.2V)
Memory [10]
Significant
Minimal
None
None
Charging Method
[11]
Simple
Simple
More Complex
More Complex
Operating
Temperature Range
[9]
Suitable for low or
average
temperatures
Average, no
specialty
Suitable for
average or high
temperatures
Suitable for
average or high
temperatures
Impact/Shock
Resistance [9]
Good
Good
Poor
Poor
Energy Density [9]
Table 8.2
For this application, lithium polymer cells are the most suitable option due to high
energy density, high voltage output per cell, lack of memory issues, and a higher
maximum operating temperature than nickel-based cells.
The unit must be able to turn on after 30 days of inactivity. In standby mode, the
Arduino draws much less than 1mA of current. Assuming that it draws a full
milliampere, we can calculate a battery size that will definitely meet this
requirement:
1mA * (30 days) * (24 hours / day) = 720mAh
Thus, a 720mAh or larger 2-cell pack would be more than sufficient for our purposes.
9 Energy Harvesting
The wireless test sensor system will require an energy harvesting unit in order to
recharge its battery. This unit will be expected to provide power at least equal to
power consumed so that no external charging of the battery is required. Energy
harvesting methods investigated include piezoelectric, thermoelectric, and
magnetic.
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Power Output
Thermoelectric
Insufficient
Piezoelectric
Insufficient
Magnetic
Sufficient
Table 9.1
Size
Small
Workable
Workable
Optimal Operating
Conditions
Large temperature
gradient
Consistent vibration
frequency within narrow
band
Fairly high rotation rate
Additional Operating
Conditions
--------
--------
Gravitational torque or
attachment to
stationary component
necessary
Piezoelectric energy harvesting will not be able to supply the necessary power for
the wireless system. Maximum output for a piezoelectric unit that could fit within
the electronics cavity is on the order of tens of milliwatts. One unit in particular [12]
was investigated, having the following properties:
Operating frequency: 52Hz
Open circuit voltage: 20.9V
Closed circuit current: (5.7*10-5A/Hz )*(52Hz) = 2.964mA
Even if this unit could provide this voltage and current simultaneously (impossible to
achieve), the power output would be well below that required of it.
(20.9V)*(2.964mA) = 61.9mW < 325mW (minimum power requirement)
The space occupied by the unit (3” by 1.25” by 0.07”) also precludes the possibility
of fitting more than one within the electronics cavity, and it may even be too large
on its own.
Thermoelectric energy harvesting requires a thermal gradient from which to draw
energy. Within the electronics cavity, it is expected there will be some temperature
difference between the inboard end (closer to the bearing) and outboard end (near
ambient air). Sikorsky has not yet provided very specific temperature conditions, so
only general approximations can be made at present. The maximum temperature
expected within the electronics cavity is approximately 250°F and the temperature
at the outboard end of the cavity will likely be somewhat above ambient, between
0°F and 150°F. This leaves a temperature difference of between 100°F and 250°F.
The voltage output of a thermoelectric generator is related to the temperature
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difference across it by the Seebeck coefficient, S [13].
V = -SΔT
The necessary Seebeck coefficient can thus be calculated from temperature
conditions and the required voltage.
S = V/ΔT
(5V) / (250°F) = 0.02V/°F (best case scenario with external regulator and maximum
temperature difference)
(7V) / (100°F) = 0.07V/°F (worst case scenario with on-board regulation and
minimum temperature difference)
These values are unrealistically high for a thermoelectric generator, so
thermoelectric energy harvesting is unlikely to work for this application.
Magnetic energy harvesting is by far the most promising, but there are significant
difficulties with installing such a unit in the rotating electronics cavity due to lack of
access to any stationary parts. The only immediately apparent way to overcome this
is with a unit that utilizes gravitational torque [14]. Such a unit would consist of a
generator mounted to the rotating unit and an off-center weight attached to its
shaft. Gravity would keep the weight stationary while the rest of the unit rotates.
The amount of torque needed to keep the shaft stationary can be calculated from
the power draw and the operating RPM:
Power draw = 325mW, operating at 1200RPM = 20Hz
Torque = Power / Frequency of rotation
0.325W / 20Hz = Torque = 0.01625N*m
The maximum available torque from a weight within the compartment can be
calculated from its dimensions and density. The weight is assumed to be a half
cylinder:
Radius of electronics compartment = 0.75in = 0.01905m
Centroid of half circle is located at 4r/3π from circle center = 0.008085m
Area of half circle = πr2/2 = 0.0005700m2
Torque = length*area*density*centroid radius*gravitational acceleration
Assume lead weight, density = 11340kg/m3
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Setting the torque provided by the weight equal to the torque needed for the power
draw allows calculation of the minimum length of weight needed:
0.01625N*m = length*0.0005700m2*11340kg/m3*0.008085m*9.8m/s2
minimum length = 0.0317m = 1.25in
This length is a little larger than ideal, but should still be possible to fit with the other
components. Using a more dense material, such as tungsten, a smaller weight could
be used, reducing the space concerns.
There are limitations to the gravitational torque design that would likely create
problems when used in a helicopter- when at extreme angles, the weight would no
longer be kept stationary and could potentially begin rotating, producing significant
vibrations. Thus, alternatives to gravitational torque will continue to be explored.
The generator in this design will be an electric motor. The most important property
of the motor for our purposes is the KV rating. This is the RPM output of the motor
per volt input. The inverse of this will provide the approximate voltage output for a
given RPM input when the motor is used as a generator. An estimate of the KV
rating needed can be calculated from the RPM of the tail rotor and the input voltage
needed to charge the batteries:
(1200RPM) / (7.4V) = 162RPM/V
This is a fairly low KV rating, and most available motors of this rating are too large to
fit within the electronics compartment. Gearing allows us to run a higher KV motor
at a higher RPM in order to get a high enough voltage output. One motor with a
built-in gearbox [15] was selected, as it has a low enough effective KV for our
purposes. A smaller generator [16] was also purchased with the intention of building
a gearbox for it. From the voltage/RPM data given, it provides 1.5V at 500RPM =
333KV. In order to provide at least 7.4V, the following gear ratio is needed:
7.4 = 1200*r / 333
r = 2.05
A gear ratio of 2.5 to 1 would provide more than sufficient voltage to charge the
cells at 1200RPM.
Sikorsky Wireless Test Instrumentation
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10 Test Rig
The previous team (from 2012-2013), created a rig in order to test the wireless
sensing system[1]. This team’s main goal was to test and analyze specific parameters
of a rotating system through the use of sensors. What was produced was a mock-up
of the tail rotor without the propellers. The rig has an open compartment on the end
to insert the electronics capsule into and holes bored for screws which mount the
capsule onto the rig once it is in the compartment. Since the size of our electronics
cavity is the same dimensions as the previous year, we will be reusing the same
motor and attached rig. We have ideas to modify the rig to work better with our
design this year outlined below in this section.
A variable-speed electric motor was mounted to a plate. The driveshaft of the motor
was then connected to a shaft of the same diameter via a clutching mechanism. The
shaft then tapers to the diameter of the helicopter’s rotor shaft and its length at this
diameter is just longer than the electronics capsule, which fits into a center-bored
cylindrical cavity, opening to the end. There are two sets of bearings: the smaller is a
spherical cartridge bearing, along the taper and the larger is a roller cartridge
bearing, around the midsection of the wider portion of the shaft (the portion with
the same diameter as the rotor shaft). The bearings are mounted to the same plate
as the motor. The use of cartridge bearings last year allowed for the team to switch
out a working bearing with an intentionally damaged bearing to see if they could
test the difference with their sensing system. The previous team did research into
the bearings and found the larger bearing to fit the design specifications designated
by Sikorsky. It was originally thought that these bearings would need replacement
because they created a loud scraping sound, which would interfere with sensing via
a microphone, but upon inspection of their physical condition, it was found that they
only needed lubrication from a Teflon spray to reduce the noise.
Sikorsky Wireless Test Instrumentation
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Potential Modifications to the Test Rig:
The main purpose of this design project is to be able to transmit, receive and then
analyze data from the sensor network, but if time is available, the plate may be
mounted so the pitch of the motor and shaft can change. The data from an
accelerometer in the cavity could be used to derive the pitch angle of the mount and
confirm the validity of the project. Since we will be using different circuitry and
electronics from last year, the electronics capsule may need to be redesigned as well
to better hold everything in place.
Figure 7. Test rig created by the previous team (2012-2013)
11 Budget
Sikorksy has granted team EE193/ME32 a budget of $2,000 to update and redesign
the 2012-2013 Wireless Network System[1]. The team has planned to utilize the
mechanical components from the previous year, which should reduce the total cost
to prototype and test the design.
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11.1 Costs to Date and Estimated Costs
The cost of components ordered are shown below, as well as cost estimates for
planned components, which have not yet been finalized.
Shopping List
Table 11.1
Arduino Nano
$70.00
Mini B USB Cable
$4.50
XBee Add-On Board
$25.00
Wifi Module
$35.00
Nano Protoshield
$15.00
Triple Axis Accelerometer
$15.00
Infrared Thermometer
$20.00
Thermometer
$1.50
Electret Microphone
$8.00
Motor/Generator
$59.10
Power Management Circuitry (Estimated)
$30.00
Battery
$83.60
Battery Charging Circuit
$40.00
Wires
$8.50
Printed Circuit Boards (Estimated)
$200.00
3D Printed Electronics Capsule (Estimated)
Total Price
$10.00
$625.2
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12 Timeline
The team has come up with an orderly timeline in order to track our progress.
The timeline illustrated below displays our project goals over the course of the year.
Figure 8. EE193/ME32 Timeline for 2013-2014
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13 References
[1] Bienkowski, Bogan, Browning, Golob, Handahl, Neaton and Thompson, “Wireless Test Instrumentation
System for Rotating Parts” 2013. Nov2013 Web.
<http://ecesd.engr.uconn.edu/ecesd167/files/2012/09/team29_report.docx>
[2] “2.25-A, Wide-Input Adjustable Switching Regulator” 2013.Texas Instruments Inc. Nov2013 Web.
<http://www.ti.com/lit/ds/slts235d/slts235d.pdf>
[3] Hunter and Rowland, “Digital Designer’s Guide to Linear Voltage Regulators and Thermal
Management” 2003. Nov2013 Web. <http://www.ti.com/lit/an/slva118/slva118.pdf>
[4] “Understanding How a Voltage Regulator Works” 2009. Analog Devices Inc. Nov2013 Web.
<http://www.analog.com/static/imported-files/pwr_mgmt/PM_vr_design_ 08451a.pdf>
[5] "Discrete Fourier transform" princeton.edu. Princeton University [US]. Nov2013 Web.
<http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Discrete_Fourier_transform.html>.
[6] Paradis and Han, "A data collection protocol for real-time sensor applications." Pervasive and Mobile
Computing Vol.5-2009: p.369-384. Microsoft Corporation [US], Department of Math and Computer
Sciences, Colorado School of Mines [US] Nov2013 Web.<http://inside.mines.edu/fs_home/qhan/
research/publication/pmc09.pdf>
[7] "Arduino Board Nano" arduino.cc. Nov 2013. Arduino SA. Nov2013 Web.
<http://www.arduino.cc/en/Main/ArduinoBoardNano>.
[8] "RN-XV WiFly Module - Wire Antenna" sparkfun.com. 2011. Spark Fun Electronics Inc [US]. Nov2013 Web.
<https://www.sparkfun.com/products/10822>.
[9] Linden and Reddy, "Engineering Processes Battery Primer" Handbook of batteries. Massachusetts Institute of
Technology. Nov2013 Web.<http://web.mit.edu/2.009/www/resources/mediaAndArticles/
batteriesPrimer.pdf>.
[10] Buchmann, Isidor. "Memory: Myth or Fact" batteryuniversity.com. Mar2011. Cadex Electronics Inc. [CA].
Nov2013 Web. <http://batteryuniversity.com/learn/article/memory_myth_or_fact>.
[11] Keeping, Steven. "A Designer's Guide to Lithium Battery Charging" digikey.com. Sep2012. Digi-Key
Corporation [US]. Nov2013 Web.<http://www.digikey.com/us/en/techzone/power/resources/articles/
a-designer-guide-lithium-battery-charging.html>.
[12] "Piezoelectric Energy Harvesting Kit." Piezo Systems CATALOG . Vol8-2011: p.20-21. Piezo Systems, Inc. [US].
Nov2013 Web. <http://www.piezo.com/prodproto4EHkit.html><http://www.piezo.com/
catalog8.pdf%20files/Cat8.20&21.pdf>
[13] Molki, Arman. "Simple Demonstration of the Seebeck Effect " scienceeducationreview.com Science
Education Review Vol. 9(3)-2010. The Petroleum Institute, Abu Dhabi [UAE]. Nov2013 Web.
<http://www.scienceeducationreview.com/open_access/molki-seebeck.pdf>.
[14] Toh, Bansal, Hong, Mitcheson, Holmes and Yeatman, "Energy Harvesting from Rotating Structures"
imperial.ac.uk. 2007. Department of Electrical & Electronic Engineering, Imperial College London [UK].
Nov2013 Web. <http://www3.imperial.ac.uk/pls/portallive/docs/1/34453718.PDF>.
[15] "Wind Turbine Generator W/ Wires" kidwind.org. Kid Wind Project. Nov2013 Web.
<http://store.kidwind.org/wind-energy-kits/parts-materials/parts-to-build-a-turbine/
wind-turbine-generator>.
[16] "Amico DC 12V 50mA 500RPM 0.3Kg-cm High Torque Permanent Magnetic DC Gear Motor" amazon.com.
Amico. Nov2013 Web. <http://www.amazon.com/Amico-500RPM-0-3Kg-cm-Permanent-Magnetic/
dp/B00858RX36/ref=sr_1_19?ie=UTF8&qid=1384970142&sr=8-19&keywords=dc+motor>.