Fall 2013 Final Semester Report

Electrical & Computer Engineering Team 193: Olivia Bonner, David Vold, Brendon Rusch, Michael Grogan

Faculty Advisor: Dr. Rajeev Bansal

Mechanical Engineering Team 32: Kyle Lindell, Andrew Potrepka

Faculty Advisor: Dr. Robert Gao

Sponsoring Organization: Sikorsky Aircraft Company Advisor: Paul Inguanti

Senior Test Engineer: Chris Winslow

Sikorsky Wireless Data System for Aircraft Component Monitoring

 

 

   

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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

   

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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 (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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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 self-

contained with an independent power source, it can be easily replaced.

   

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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.

   

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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

   

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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.

   

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DC  Generator

Battery

Battery  Charge  Manager

Charging

Source  Switch Voltage  Regulator Wireless  Sensor  System

 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.

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

Regulator Type Part Number Efficiency Noise

Linear Regulator L7805 ~67% No Noise

Switching Regulator PTH08080W 93.5% [2] Noise induced by

switching frequency

   

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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].

   

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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.

   

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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

   

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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.

   

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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

   

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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

   

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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

   

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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.

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.

Item Current Draw Arduino Nano [7] 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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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.

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.

Battery Material

Energy Density [9]

Voltage Output per Cell [9]

Memory [10]

Charging Method [11]

Operating Temperature Range [9]

Impact/Shock Resistance [9]

NiCd Poor Poor (1.2V) Significant Simple Suitable for low or average temperatures

Good

NiMH Average Poor (1.2V) Minimal Simple Average, no specialty

Good

Li-Ion Good Good (3.6V-4.2V) None More Complex

Suitable for average or high temperatures

Acceptable

Li-Poly Good Good (3.6V-4.2V) None More Complex

Suitable for average or high temperatures

Acceptable

   

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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

Power Output

Size Optimal Operating Conditions Additional Operating Conditions

Thermoelectric Insufficient Small Large Temperature Gradient --- Piezoelectric Insufficient Workable Consistent vibration frequency

within narrow band ---

Magnetic Sufficient Workable Fairly high rotation rate 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

   

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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.

   

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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.

TABLE 12. Shopping list of purchased components and components on order

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

   

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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.

                   

   

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 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-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/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-cm- Permanent-Magnetic/dp/B00858RX36/ref=sr_1_19?ie=UTF8&qid=1384970142&sr=8- 19&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>