Download Sikorsky Aircraft - ECE Senior Design

December 8, 2013
Wireless Test Instrumentation for Rotating Parts
ECE 193:
Olivia Bonner
David Vold
Brendon Rusch
Michael Grogan
ME 32:
Andrew Potrepka
Kyle Lindell
Faculty Advisor:
Rajeev Bansal
Office: ITE 463
Phone: (860) 486-3410
E-Mail: [email protected]
Robert Gao
Office: UTEB 456
E-Mail: [email protected]
Sikorsky Aircraft:
Paul Inguanti
[email protected]
Chris Winslow
[email protected]
Dan Messner
[email protected]
Table of Contents
1 Abstract ………………………………………………………………………………...3
2 Introduction…………………………………..………………..………..………………3
3 Problem Statement.……………………….….…………………………………………5
3.1 Statement of Need…………………………………………………………….5
3.2 Preliminary Requirements…………………………………………………….6
3.3 Basic Limitations……………………………………………………………...6
3.4 Other Data……………………….……………………………………………7
4 Proposed Solution………….…………………………………………..……………….8
4.1 System Block Diagram……………………………………………………….8
4.2 Power Circuitry……………………………………………………………….9
4.3 Voltage Regulator……………………………………………………………10
4.4 Rectifying Circuitry……...…………………………………………….…….11
4.5 Charging Circuit……………………………………………………….…….12
5 Electronics…………………..………………………………………………………….15
5.1 Microcontroller…………………………………………...……………….…16
5.2 Accelerometer….…………………………………………………………….17
5.3 Ambient Temperature Thermometer……………………………………...…17
5.4 Infrared Body Temperature Sensor…………………………………...……...18
5.5 Microphone…………………………………………………………………..18
5.6 Wireless Transceiver………………………………………………………....19
6 Data Analysis………………………………………….……………………………….20
6.1 Data Transmission……………………...……………………………………20
7 Battery…………………………………………………………………………………21
8 Energy Harvesting…………………………………………………………………..…23
8.1 Thermoelectric Energy Harvesting…………………………………………..23
8.2 Piezoelectric Energy Harvesting……………………………………………..24
8.3 Magnetic Energy Harvesting……………………………………………...…24
9 Test Rig…………………….....………………..……….……………………….……..26
9.1 Potential Modifications to the Test Rig……………………………………...27
10 Budget……………………...……………………………...………………………….27
11.1 Costs to Date and Estimated Costs……..…………………………………..28
11 Timeline………………………………………………………………...…………….29
12 References……………………………….……………………………………………30
2
Abstract
1
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.
Introduction
2
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 (20122013)[1].
3
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
4
Problem Statement
3
The proposed problem statement, Sikorsky’s statement of need, is discussed below
including preliminary requirements, basic limitations and other data.
Statement of Need
3.1
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 selfcontained with an independent power source, it can be easily replaced.
5
Preliminary Requirements
3.2
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 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.
Basic Limitations
3.3
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
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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)
Other Data
3.4
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 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.
7
Proposed Solution
4
The team came up with a general system block diagram in order to illustrate our proposed
solution. The proposed power circuitry, voltage regulator, and charging circuit will also
be discussed.
System Block Diagram
4.1
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 communication with the wireless transceiver via
another SPI Bus and a sleep/wake, input/output signal. The transceiver will communicate
8
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.
Power Circuitry
4.2
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.
9
DC Generator
Battery Charge
Manager
Voltage Regulator
Wireless Sensor System
Charging
Source Switch
Battery
FIGURE 4. Power system block diagram
Voltage Regulator
4.3
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
~67%
No Noise
Switching Regulator
PTH08080W
93.5% [2]
Noise induced by
switching frequency
TABLE 1. Regulator Comparison
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
10
smaller implementation. A diagram of the implementation of the PTH08080W from [2] is
shown in Figure 5.
FIGURE 5. PTH08080W Switching Voltage Regulator, RSET =348 Ω for 5V output [2].
Rectifying Circuitry
4.4
An AC brushless generator and a DC brushless generator were purchased for testing in
our power circuitry. If the team decides to utilize the AC brushless generator, a rectifying
circuit will be necessary in order to generate the required DC output.
A scholarly article, distributed by Advances in Radio Science, analyzes the power
circuitry that is necessary in energy harvesting applications in order to minimize losses
[19]. From this analysis, a number of rectifying components were researched for
applicability. The team decided that a diode bridge rectifier would be the most applicable
type of converter for our circuitry; bridge rectifiers allow for full wave rectification from
a two-wire AC input. The manufacturer, Future Electronics, provides a number of
rectifying devices based on required circuit characteristics such as maximum average
rectified current, maximum peak current, and forward voltage [20].
11
Due to the team’s uncertainty of whether we will need a rectifying component, the part
order is currently pending. We plan to solidify our final plans with the rectifying
component over winter intercession.
FIGURE 6. The team plans to utilize a single stage power conversion circuit as such, including an AC
generator, rectifier, buffer, DC/DC conversion, and load application [19].
Charging Circuit
4.5
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.
12
FIGURE 7. Lithium-Ion Battery Charger [17].
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:

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
13
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 Auto Comp
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 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 [18].
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Electronics
5
The electronic components necessary to accomplish our proposed solution will be
discussed. The microcontroller, sensors, and battery selections will also be discussed in
detail. The initial prototype can be seen in the picture below. This picture includes the
Nano evaluation board (left, blue board) and the wifi module (right, red board) connected
via the add-on board. A quarter is included for size reference.
FIGURE 8. Nano
evaluation board (left, blue board) and the wifi module (right, red
board).
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Microcontroller
5.1
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. It has a wide range of compatible sensors from third party sources.
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 a mild 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 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.
16
Operating Voltage
5V
Input Voltage Range
7-20V
Digital I/O Pins
14 (6 PWM Outputs)
Analog Input Pins
8
Flash Memory
32 KB
SRAM
2 KB
Dimensions
0.70” x 1.70”
TABLE 2. Arduino Nano v3.0 Specifications
Accelerometer
5.2
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.
Input Voltage Range
1.6V - 3.5V
Active Power
2uA at 100Hz
Standby Power
10nA
Resolution
1mg/LSB
TABLE 3. ADXL362 Component Specifications
Ambient Temperature Thermometer
5.3
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 of accuracy. The
ambient temperature of the cavity is an important metric that measures whether the
electronics are within safe operating temperatures.
Input Voltage Range
2.7V – 5.5 V
Linearity
0.5°C
Accuracy
±1°C (typical), ±2°C
Temperature Range
-40°C - +125°C
TABLE 4. TMP36 Thermometer Component Specifications
17
Utilizing the component data sheet and a simple circuit, the ambient thermometer was
tested to have a voltage output of about 0.78V. The expected output voltage at room
temperature is 0.75V; therefore, our results prove valid. The following equation was
utilized in order to calculate the temperature of the room
Temperature in Celsius = [(Vout (mV) – 500]/10 =[787-500]/10=28.7
Infrared Body Temperature Sensor
5.4
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.
Input Voltage
3V
Accuracy
±0.5°C
Resolution
0.02°C - 0.14°C
Temperature Range
-70°C - +380°C
TABLE 5. MLX90614 Temperature Sensor Component Specifications
Microphone
5.5
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.
Input Voltage Range
2.7V – 5.5V
Frequency Range
100-10,000Hz
Sensitivity
-46 ± 2dB
TABLE 6. Electret Microphone Component Specifications
18
Component Testing
FIGURE 9. Oscilloscope illustrating microphone sensor operating at varying frequencies
The EE members examined and tested the accuracy of the microphone sensor to
determine any detrimental issues. Constructing a simple circuit with VIN = 3.01V, the
component was examined and no present issues were found; the device operated as
expected under a large range of frequencies.
Wireless Transceiver
5.6
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.
On-board Regulator
3.3V, 250mA
Dimensions
3.7”x1.1”
TABLE 7. XBee Add-on Component Specifications
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
19
features configurable transmit power for power savings when we don’t need the extra
range and a low power sleep mode.
Average Active Current
38mA
Sleep Current
4uA
Input Voltage
3.3V
Serial Data Rate
464 kbps
Encryption Support
Yes
Transmit Power
0-12 dB
TABLE 8. RN-XV WiFly Module Component Specifications
Data Analysis
6
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.
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.
Data Transmission
6.1
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
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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.
Battery
7
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]
Wi-Fi Module [8]
Sensors
Total
Current Draw
17mA (direct 5V power with LED removed) to
25mA (on-board regulator used, LED intact)
38mA
<10mA (depending on sensors chosen)
65mA-73mA
TABLE 9. Arduino Nano and related component specifications
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. Incorporating the requirements, (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.
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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.
Battery
Material
Energy
Density [9]
Voltage Output
per Cell [9]
Memory
[10]
Charging
Method [11]
NiCd
Poor
Poor (1.2V)
Significant
Simple
NiMH
Average
Poor (1.2V)
Minimal
Simple
Li-Ion
Good
Good (3.6V-4.2V)
None
More
Complex
Li-Poly
Good
Good (3.6V-4.2V)
None
More
Complex
Operating
Temperature
Range [9]
Suitable for low
or average
temperatures
Impact/Shock
Resistance
[9]
Good
Average, no
specialty
Suitable for
average or high
temperatures
Suitable for
average or high
temperatures
Good
Acceptable
Acceptable
TABLE 10. Battery Comparison/Selection Criterion
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 milli-ampere, 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.
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Component Testing
EE members plan to test the charging capabilities of the purchased batteries as soon as
the necessary components arrive via mail; we believe this will occur over intersession.
For the sake of component necessary testing for this report, a voltmeter was utilized to
measure the voltage when the devices were in their idle state; all components
demonstrated appropriate output values. More information will be added as the remaining
components arrive.
Energy Harvesting
8
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.
Energy Harvesting
Method
Thermoelectric
Piezoelectric
Power
Output
Insufficient
Insufficient
Size
Optimal Operating Conditions
Small
Workable
Magnetic
Sufficient
Workable
Large Temperature Gradient
Consistent vibration frequency
within narrow band
Fairly high rotation rate
Additional Operating
Conditions
-----
Gravitational torque
or attachment to
stationary
component necessary
TABLE 11. Energy Harvesting Method Comparison/Selection Criterion
Thermoelectric Energy Harvesting
8.1
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
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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 difference across it by the Seebeck
coefficient, S, utilized in the following equation: V = -SΔT [13]. 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) and (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; thermoelectric energy harvesting is
unlikely to work for this application.
Piezoelectric Energy Harvesting
8.2
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 mill watts. 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, 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.
Magnetic Energy Harvesting
8.3
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
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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
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 and the 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
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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.
Test Rig
9
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
26
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.
Potential Modifications to the Test Rig
9.1
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 10. Test rig created by the previous team (2012-2013)
Budget
10
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.
27
Costs to Date and Estimated Costs
10.1
The cost of components ordered are shown below, as well as cost estimates for planned
components, which have not yet been finalized.
Items
Cost
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 Thermometer
$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)
$10.00
Total
$625.20
TABLE 12. Shopping list of purchased components and components on order
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Timeline
11
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 11. Overall team goals/timeline.
29
References
12
[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-lithiumbattery-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/Cat
8.20&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-cmPermanent-Magnetic/dp/B00858RX36/ref=sr_1_19?ie=UTF8&qid=1384970142&sr=819&keywords=dc+motor>.
[17] Henion, Scott. "Lithium Ion Charger." SHDesigns. SHDesigns, 2 Mar. 2003. Web. 07 Dec. 2013.
[18] Earl, Bill. "Multi-Cell LiPo Charging." Adafruit Learning System. Adafruit, 28 Feb. 2013. Web.
[19] Maurath, Peters, Hehn and Manoli, “Highly Efficient Integrated Rectifier and Voltage Boosting
Circuits for Energy Harvesting Applications” 2008. Nov2013 Web.
<http://www.adv-radio-sci.net/6/219/2008/ars-6-219-2008.pdf>
[20] “What is a Bridge Rectifier, Half Wave Rectifiers, Semiconductor Diodes, Diode” Future Electronics.
Nov2013 Web. <http://www.futureelectronics.com/en/diodes/bridge-rectifiers.aspx>
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