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

 

 

Table of Contents

1. Abstract…………………………………………………………………………………2

2. Introduction…………………………………………………………………………..2-3

3. Problem Statement…………………………………………………………………...…4

3.1 Design Requirements………………………………………………………………….4

3.2 Technical Limitations…………………………………………………………………5

4. Proposed Solution………………………………………………………………………6

5. Electronics…………………...…………………………………………………………7

5.1 Microcontroller……………………...………………………….…………………..8-9

5.2 Accelerometer………………………………………………………………………..10

5.3 Ambient Temperature Sensor…………………………………………………….10-11

5.4 Infrared Body Temperature Sensor………………………………...………………..11

5.5 Microphone…………………………………………………………………………..11

5.6 Wireless Transceiver…………………………………………………………………12

5.7 Power Cell...…………………………………………………………………………12

6. Power Circuitry…...…………………………………………………………………..13

6.1 Battery……………………………………………………………………………14-15

6.2 Battery Testing…………………………………………………………………....15-16

6.3 Energy Harvesting……………………………………………………………….......17

6.3.1 Thermoelectric Energy Harvesting………...…………………………………..17-18

6.3.2 Piezoelectric Energy Harvesting…………………...………………………….…..18

6.3.3 Magnetic Energy Harvesting……………………..…………………………….19-21

7. Signal Transmission & Signal Processing…………………..………………………...22

7.1 Signal Display………………………………………………………………………..22

8. Signal Analysis…………………………………………………………………….23-25

8.1 Sensor Testing & Analysis…………………………………………………………...26

9. Test Rig………………………………………………………………………………..27

9.1 Capsule Design………………………………………………………………………28

10. Budget & Timeline……………………………………………………………….…..29

11. Brief Summary of Results………………………………………………………….…30

12. Appendix………………………………………………………………………….31-32

13. References……………………………………………………………………………33

 

     

  2

1. Abstract  

Sikorsky has requested a wireless sensor system to monitor the rotating parts located in

the tail rotor of the S92 helicopter; this proposed proof of concept will advance the

current 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 Pro Mini 3.3V model, a WiFly module

attachment and several sensors. The unit will be powered by a single-cell lithium polymer

battery coupled with an energy-harvesting unit that will recharge the battery while the

unit is rotating. 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.

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.    

 

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. Sikorsky Aircraft has asked the team 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 [1].

The previous team created a wireless system in which one sensor was used. The system

     

  3

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.  

 

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 the Arduino

Pro Mini 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 sensors and ambient temperature sensor. 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

3. Problem Statement  

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.  

 

3.1 Design Requirements  

Sikorsky has asked the team to expand upon last year’s project proposal. The company

requested that the team 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

team was to propose a sensor design in which the signals are able to pass through

barriers, such as doors, without interference.

     

  5

3.2 Technical 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)  

 

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.  

     

  6

4. Proposed Solution

The team began the design stage with a general system block diagram in order to

illustrate communication between individual components. As displayed in the figure

below, the microcontroller will be in communication with the sensors, data storage, and

wireless transceiver, while the power assembly will harvest and provide the system with

necessary power.

 Figure 2. Wireless electronic monitoring system block diagram  

 

As depicted in Figure 2, the sensors will be in communication with the microcontroller

through an SPI Bus and an interrupt signal. The interrupt signal will temporarily pause the

program from collecting data, as it is only necessary to collect and store data upon user

command. The system will remain in an idle state when not collecting data in order to extend

battery life. Furthermore, the microcontroller will be in communication with the Static

Random Access Memory (SRAM) via data lines and an address, in addition to the wireless

transceiver, which will communicate information via another SPI Bus and a sleep/wake,

input/output signal. The wireless transceiver will communicate data via the antenna receiver.

Lastly, the microcontroller is to be powered by rechargeable cells and an energy harvesting

system in order to restore and maintain battery life. Each component of the system described

above will be discussed in detail in later sections.

     

  7

5. Electronics  

The team conducted thorough research of commercial electronic components in order to

meet Sikorsky’s desired system specifications. After rigorous research, the team selected

a microcontroller, an accelerometer, an ambient temperature sensor, an infrared body

temperature sensor, a microphone, and a wireless transceiver. The final electronics

package is depicted below. The individual components are discussed in detail in the

following sections.

Figure 3. Electronics package design (left), electronics package within capsule (right)

Figure 4. Schematic of electronics package designed in Cadence CIS

The lithium polymer cell is referenced in the center of the system design with the Wi-Fly

module on one side and the microcontroller and sensor components on the other. As

depicted in the figure, there is a great amount of space that remains to include additional

sensor components if desired. Each component will be discussed in detail below.

     

  8

5.1 Microcontroller  

After careful consideration, the team selected the open-source Arduino environment as

the micro-controlling element. The Arduino platform allows great flexibility in terms of

system design and has been utilized in many low-power application projects.

Additionally, the platform is compatible with a great number of sensing devices from

third party sources, such as Spark Fun electronics. Due to the commercial nature of

Arduino electronics, the components are readily available for the team and within our

delegated budget. The Arduino platform also offers a vast amount of project

documentation; this gives the team a great advantage in terms of delegating solutions to

problems we may encounter down the road.

The team took last year’s PCB system design into consideration; however, after much

research and component analysis we collectively decided that the benefits of utilizing the

Arduino platform outweighed the benefits of last years PCB design. The previous team

left very minimal documentation on the PCB system design; therefore, it would be

increasingly difficult and time consuming to learn the full capabilities of their design.

Consequently, the team decided that a new system design was in order. The Arduino

environment will allow the construction of our proposed system at highest efficiency and

lowest commercial cost.

Specifications Arduino Custom PCB

Cost $9.95 $1300

Documentation/References Arduino Forums Limited

Power Consumption (ON) 10mA 312uA

Energy Harvesting Magnetic Energy Harvester N/A

Table 1. Comparison of system design

The Arduino Nano and Arduino Pro Mini (3.3V) were selected as proposed

microcontroller elements. The team constructed the table below as a reference to select

the most applicable component. Conclusively, the 3.3V model Arduino Pro Mini was

selected, as this component offers greater compatibility and is applicable with all sensing

     

  9

components. The reduction in memory is not a foreseen issue with our system design.

Table 2. Comparison of Arduino microcontroller options

Conclusively, the 3.3V model Arduino Pro Mini was selected, as this component offers

greater compatibility and is applicable with all sensing components. The reduction in

memory is not a foreseen issue with our system design.

Part Number Voltage Active

Current

Power down

Current

Power save

Current

Idle

Current

Operating

Temperature

Arduino Pro

Mini 328

1.8V-

5.5V

1.2-

2.5mA

0.1-2uA 0.9uA 0.21-

0.7mA

-55 to 125°C

Table 3. Arduino pro mini component specifications

Specifications Arduino Nano Arduino Pro Mini Pros/Cons Pro Mini

Processor ATmega328 ATmega168 N/A

Operating Voltage +/- 5V +/- 3.3V Compatible with all sensors

Input Voltage 7V-9V 3.35V-12V Lower power device

CPU Speed 16MHz 8MHz Slower clock speed

Analog I/O 8/0 6/0 Reduction analog I/O pins

Digital IO/PWM 14/6 14/6 No change

EEPROM (KB) 1 0.512 Reduction in memory

SRAM (KB) 2 1 Reduction in memory

Flash (KB) 32 16 Reduction in memory

USB Mini-B External External USB port

Dimensions 0.73” x 1.70” 0.70” x 1.30” Reduction in size

     

  10

5.2 Accelerometer  The team selected two options for the accelerometer sensor; therefore, a table comparison

was constructed in order to select the most applicable component.

Table 4. Accelerometer component specifications

The team selected the ADXL362 accelerometer; this component is an ultra low power 3-

axis MEMS accelerometer. The component 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.

 5.3 Ambient Temperature Sensor  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.

 

Part

Number

Voltage Supply Current Idle Current Scale Factor Temperature

TMP36 2.7 – 5.5 <50uA 0.5uA 10mV/°C -40 to 125

°C

Table 5. Temperature sensor data specifications

The ambient thermometer was tested in order to ensure accuracy; with an experimental

output voltage of 0.78V and an expected output voltage of 0.75V, the sensor results

proved efficient. The following equation was utilized to calculate the temperature of the

Part Number Voltage Supply

Current

Wake Up

Current

Standby

Current

Bandwidth Temperature

ADXL362 1.6V-

3.5V

1.8uA 0.27uA 0.01uA 50Hz

(100Hz ODR)

-40 to 85°C

ADXL335 1.8V-

3.6V

350uA 40uA 0.1uA @

2.5V

0.5-1600Hz (x,y)

0.5-550Hz (z)

-40 to 85°C

     

  11

room:

℃ =  𝑉!"# 𝑚𝑉 − 500

10 =  787− 500

10 = 28.7℃

5.4 Infrared Body Temperature Sensor  The MLX90614 was selected as the infrared body temperature sensor. This component

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.

Part Number Voltage Supply

Current

Power down

supply current

Output drive

current

Object

Temperature

MLX90614 2.6-3.6V 1-2mA 1-6uA 4.5mA -70 to 380° C

Table 6. MLX90614 component specifications    5.5 Microphone  The CEM-C9745JAD462P2.54R was selected as the electret microphone. Although it

does not have a direct helicopter application, it will allow us to determine the wireless

signal quality.

Part Number Voltage Maximum Active

Current

Frequency Range Sensor

Temperature

CEM-

C9745JAD462P2.54R

1-10

VDC

0.5mA 100-10,000Hz -20 to 60 °C

Table 7. Electret Microphone component specifications

Ultimately, the electret microphone was not utilized in the final system design, as the

component was drawing too much current for the remaining system to operate as

designed.

     

  12

5.6 Wireless Transceiver  The RN-XV Wi-Fly module was selected for the wireless transceiver. This low power

module operates on the 802.11b/g standard and supports a serial data rate of 464kps. The

component also features configurable transmit power, which may be utilized to save and

maintain power when the additional range is not required.

Part

Number

Voltage Active

Current

Standby

Current

Sleep

Current

Transmission

Rate

Temperature

RN-XV 3-3.3V 38mA 15mA

40mA RX,

180mA TX

4uA

1-11Mbps for

802.11b

-40 to 85 °C

Table 8. RN-XV Wi-Fly module component specifications

5.7 Power Cell

A power cell was selected for the dual purpose of charging the lithium polymer cells and

regulating the 3.3V output. The selection of lithium polymer cells will be discussed in

detail in the next section.

Part Number Minimum

Input

Voltage

Quiescent

Current

Supply

Current,

Charging

Discharge

Current

Temperature

MCP73831/2

(charger)

3.75V

(3.3V @

200mA max)

50-70uA 510-

1500uA

0.15-2uA -65 to 150°C

TPS61200

(regulator)

0.3V-5.5V <55uA

- -40 to 125°C

Table 9. Power cell component specifications

The power cell and lithium polymer batteries were tested for performance; results

published in the next section.

     

  13

6. Power Circuitry

The system will be powered by a combination of battery power and harvested energy;

therefore, special circuitry was designed in order to facilitate the interaction of these

components with the rest of the system.

Figure 5. Power circuitry within rotating compartment

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. 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 the lipo cell. Due to

unforeseen complications with the selected generator, the system will cycle between ON and

idle in order to charge the battery cell. Although these conditions are not ideal, the group is

confident that with a greater budget, a more capable generator could be custom-ordered to

meet the needed specifications.

     

  14

6.1 Battery

In order to select the appropriate battery to efficiently power the system, the total power

consumption from each component was analyzed and recorded.

Component Active Current Transmission Current Idle Current

Accelerometer 2uA - 0.010uA

Microphone 0.5mA - 0.5mA

Thermometer 50uA - 50uA

Infrared Thermometer 2.5uA - 2.5uA

Arduino Pro Mini 10mA - 1mA

Wi-Fly Module 38mA - 4uA

Power Cell ~5mA - 72uA*

Calculated Totals 53.055mA - 1.0565mA

Measured Totals 65mA ~1mA

Table 10. Current consumption from each component

Applying the calculations of required power, the team analyzed multiple battery types to

achieve the most optimal system design.

Table 11. Battery comparison

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  

     

  15

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 following calculations prove that only

one lipo cell will be required to power the system, as this cell will be coupled with the

voltage regulator/charging circuit and energy harvester in order to maintain sufficient

power for the one-year minimum period. The team purchased 1000mAh and 850mAh

lipo cells for testing.

850𝑚𝐴ℎ  ×1  𝑑𝑎𝑦

12  ℎ𝑜𝑢𝑟𝑠 = 70.833𝑚𝐴

1000𝑚𝐴ℎ×1  𝑑𝑎𝑦

12  ℎ𝑜𝑢𝑟𝑠 = 83.333𝑚𝐴

The unit draws about 65mA when the system is ON and running; therefore, one 850mAh

or1000mAh lipo cell alone will provide sufficient power over the duration of 12 hours.

Ideally, the lipo cell would be coupled with charging circuit/energy harvester in order to

achieve the 365-day requirement. However, due to unforeseen complications with the

generator providing sufficient power to the system, the team cycled the system from ON

to idle to allow the cell to charge and maintain battery life.

6.2 Battery Testing

The following test was conducted in order to verify the unit was able to maintain

operability after 30 days of inactivity.

For the 1000mAh lithium polymer cell, the maximum current consumption:

1000𝑚𝐴×ℎ𝑜𝑢𝑟𝑠  ×1

720  ℎ𝑜𝑢𝑟𝑠 = 1.38𝑚𝐴

For the 850mAh lithium polymer cell, the maximum current consumption:

850𝑚𝐴×ℎ𝑜𝑢𝑟𝑠  ×1

720  ℎ𝑜𝑢𝑟𝑠 = 1.18𝑚𝐴

Due to the given current consumption constraint between 1.18mA-1.38mA, the electret

microphone was eliminated as a sensor component. The microphone alone consumed

     

  16

0.5mA, which proved to be far too great for the overall system power consumption.

Consequently, the remaining components were set up in a dummy load circuit in order to

test the idle system conditions over a 30-day period. The approximate 0.65mA load

current was calculated utilizing the experimental regulated 3.24V output:

𝐼 =𝑉𝑅 =  

3.24𝑉4.7𝑘Ω = 0.69𝑚𝐴

This over-calculation of the load provided by the system will accurately test the lipo cells

over the 30-day test. Both lipo cells proved to provide the system with sufficient power

over the required duration, as depicted in figure 5. A complete battery discharge is shown

in figure 6; the 30-day inactivity test stayed well within the linear region and well above

the 3.35V minimum input to the Arduino.

Figure 6. The lithium polymer cells operated as

expected over the 30-day trial period; both cells

began the test fully charged ~4.2V and

discharged to ~3.7V. The 1000mAh cells were

selected in the final system design.

 

   

Figure 7. Complete battery discharge test

conducted with a dummy load to discharge the

cells.

 

     

  17

6.3 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. Each energy

harvesting method will be discussed in detail.  

 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 12. Comparison of energy harvesting methods    6.3.1 Thermoelectric Energy Harvesting  

Thermoelectric energy harvesting requires a thermal gradient 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). Due to

undisclosed information about temperature conditions, general approximations were

assumed. The maximum temperature expected within the electronics cavity is

approximately 250°F, while the temperature at the outboard end of the cavity will likely

be between 0°F and 150°F. This leaves a temperature difference of between 100° -

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 [13]:

𝑉 =  −𝑆Δ𝑇

The necessary Seebeck coefficient can thus be calculated from temperature conditions

     

  18

and the required voltage for the best and worst case scenario, respectively:

𝑆 =  𝑉Δ𝑇 =

5𝑉250℉ =

0.02𝑉℉

𝑆 =  𝑉Δ𝑇 =

7𝑉100℉ =

0.07𝑉℉

These values are unrealistically high for a thermoelectric generator; therefore,

thermoelectric energy harvesting was eliminated from the proposed system.  

6.3.2 Piezoelectric Energy Harvesting  Piezoelectric energy harvesting takes advantage of the mechanical strain, and converts

this source of strain into electric current or voltage. Maximum output for a piezoelectric

unit that could fit within the electronics cavity is on the order of tens of milli-watts. One

unit in particular [12] was investigated, having the following properties:

Operating

Frequency

Open Circuit

Voltage

Closed Circuit

Current

Dimensions

52Hz 20.9V 2.964mA 3” x 1.25” x 0.07”

Table 13. Piezoelectric energy harvesting unit parameters examined [12]

Closed Circuit Current:

𝐼!! =  5.7×10!!𝐴𝐻𝑧×52  𝐻𝑧 = 2.964𝑚𝐴

Consequently, even if this unit could provide this voltage and current simultaneously, the

power output would be well below that required of it:

𝑃 = 𝐼×𝑉 = 20.9𝑉×2.964𝑚𝐴 = 61.9𝑚𝑊 < 330𝑚𝑊

This output power is well below the 330mW minimum power requirement; therefore,

piezoelectric energy harvesting was eliminated from the proposed system design.

 

     

  19

6.3.3 Magnetic Energy Harvesting

Magnetic energy harvesting is by far the most promising method of harvesting power;

however, significant difficulties exist with installing such a unit within the electronics

cavity, due to lack of access to stationary parts. The only 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. The

weight is kept stationary by gravitational force while the rest of the unit rotates, as

illustrated in the figure 7. Gravitational force (red, downward) multiplied by distance

from axis of rotation (blue) produces a moment (red). Gravitational force is counteracted

by normal force in the bearing (yellow, upward) and torque produced by the generator as

power is drawn from it (yellow).

Figure 8. Diagram of counterweight

The amount of torque needed to keep the shaft stationary can be calculated from the

power draw and the operating RPM:

𝜏 =  𝑃𝑓 =  

0.325𝑊20𝐻𝑧 = 0.01625𝑁𝑚

The maximum available torque from a weight within the compartment can be calculated

from its dimensions and density. The following parameters were measured in order to

calculate the length of counter weight required.

Table 14. Calculated parameters to determine minimum length required

Radius of

compartment

Centroid of half

circle

Area of half

circle

Torque Lead Density

0.09905m 0.008085m 0.0005700m2 0.01625Nm 11340kg/m3

     

  20

𝐶𝑒𝑛𝑡𝑟𝑜𝑖𝑑  𝑜𝑓  ℎ𝑎𝑙𝑓  𝑐𝑖𝑟𝑐𝑙𝑒 =4𝑟3𝜋

𝐴𝑟𝑒𝑎  𝑜𝑓  ℎ𝑎𝑙𝑓  𝑐𝑖𝑟𝑐𝑙𝑒 =  𝜋𝑟!

2

𝑇𝑜𝑟𝑞𝑢𝑒  (𝜏) = 𝐿×𝐴×𝑑×𝑟!"#$%&'(  ×𝑔

Table 15. Calculated parameters for magnetic energy harvester

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 = 𝐿×0.0005700𝑚!×11340𝑘𝑔𝑚!×0.008085𝑚×9.8

𝑚𝑠!

The length, L, is therefore calculated to be approximately 0.0317m or 1.25 inches. This

length was sufficiently small to fit the counterweight inside the casing with the other

components.

There are limitations to the gravitational torque design that would likely create problems

when used in a helicopter. For example, when at extreme angles, the weight would no

longer be kept stationary and could potentially begin rotating, thus producing significant

vibrations. Consequently, alternatives to the concept of gravitational torque will continue

to be explored.

 

An electric motor was selected as the generator component in the system design. The

most important property of the motor for our purposes is the KV rating – 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 utilized as a generator. An estimate of

the necessary KV rating can be calculated from the RPM of the tail rotor and the input

voltage needed to charge the batteries: 1200  𝑅𝑃𝑀4.0𝑉 =

300𝑅𝑃𝑀𝑉

Power Consumption Operating RPM Torque

325mW 1200RPM @20Hz 0.01625Nm

     

  21

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

rating for our application. A smaller generator [16] was also purchased with the intention

of building a gearbox for it. After some consideration, the smaller generator was selected

for the final unit due to size constraints. Rather than creating a gearbox for it, the voltage

output of the generator was increased by adding 100 additional windings to the stators;

these additional windings raised the voltage output from 3V @ 1200RPM to 4.1V @

1200RPM - achieving sufficient voltage to communicate with the input pins on the power

cell.

Unforeseen issues with the energy harvesting system surfaced during the testing phase.

While the generator was able to provide sufficient voltage to charge the battery under low

current draw conditions, powering the charging circuit and Arduino alone, the addition of

the WiFly module resulted in a great decrease in output voltage due to a surplus of

current draw from the system.

The group suspected that the use of very fine wire in the stators of the generator resulted

in high internal resistance, causing the voltage to drop off significantly as the current

draw increased. As a result, the group was instructed to cycle the system between ON and

idle in order to allow the battery cell to charge. This cycling will demonstrate all aspects

of system design had the chosen generator provided sufficient power requirements, but

will result in the system transmitting data at set intervals rather than continuously

transmitting. The group proposed that a more capable generator could be custom-ordered

to meet the needed specifications.

             

     

  22

7. Signal Transmission & Signal Processing  The wireless signal was thoroughly tested for range of operation. When the electronics

package was outside of the metal enclosure, the Wi-Fi unit was able transmit data 143

feet in direct line of sight. When the electronics package was in the metal enclosure, the

Wi-Fi unit was able to transmit data a maximum of 60 feet in direct line of sight and a

maximum of 30 feet through a concrete barrier.

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 Wi-Fi 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.

7.1 Signal Display

In order to present sensor data in the most meaningful form, a real-time graphical display

was researched and implemented for demonstration day using Processing.

Figure 9. Real-time graphical display of accelerometer data, as displayed on demonstration day

     

  23

8. Signal Analysis  

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.

Accelerometer data was collected from the test rig then analyzed in Excel/MATLAB with

Fast Fourier Transforms. In both the Z and X axes, using different sets of 32 consecutive

points from the same bundle of 48 consecutive points from the raw data, the first local

maximum in both directions seems to be around 20 Hz (1200 RPM). This means that

these accelerometers are both measuring different perpendicular components of the

centripetal acceleration. It makes sense that they are different magnitudes because the

sensor is not centered along all three axes in the tube and it may not lie perfectly parallel

to the axes at all.

Figure 10-11. Fourier Analysis of x and z data directly from the test rig

The following graphs illustrate the FFT results of the shaker tests, from sets of 64 data

points, which were performed at frequencies of 10, 20, 50, 75, 100, 200, and 300Hz. It

should be noted that the 300 Hz graph does not clearly show a response because our

sampling frequency is ~470Hz, so the greatest frequency we can show is ~235Hz

     

  24

(Nyquist Criterion). What should be noted from these plots is that the main spike in each

plot is very near the calibrated frequency at which the capsule was shaking, thus

confirming that the accelerometer responds well to frequency and that none of the

components were resonating due to the lack of other spikes in frequency.

     

  25

Figure 12-18. Fourier Analysis of the z-axis accelerometer data from the shaker test

Shown below is a graph of our temperature data taken while the sensor unit was spinning

in the test rig. The top left graph displays the raw ADC values read directly from the

sensor; the time stamps were reset to zero, therefore, the x-axis is in microseconds and

the y-axis data is the raw data directly from the temperature sensor (no conversions). The

top right graph is the raw temperature sensor data with appropriate conversions made; the

time axis is in seconds, and the temperature axis is in degrees Fahrenheit. The bottom left

graph shows the data through a simple filter – averaging every 10 data points and the

bottom right graph averages every 50 data points.

 Figure 19. Filtered temperature sensor data

     

  26

8.1 Sensor Testing & Analysis

The accelerometer was tested by varying the rotational speed of the test rig; the speed

was varied from 1200RPM to lower settings then returned again to 1200RPM.

· Wi-Fly Settings: Baud rate 115200, WLAN TX 12

· Sampling Rate (ADXL362): 465Hz

Figure 20. Time domain analysis of the accelerometer data

A performance test was conducted, specific to the temperature sensor. The accuracy test

was conducted with the application of an ice cube to analyze the sensor response and

temperature range.

Figure 21. Time domain analysis of calibrated temperature sensor data; as the ice cube was

applied to the sensor, the temperature decreased at an appropriate rate and increased once

again, when the ice cube was removed.

     

  27

9. Test Rig  The previous team, created a rig in order to test the wireless sensing system [1]. Their

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

allowed for the previous 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.  

               

     

  28

9.1 Capsule Design  

The main purpose of this updated design is to be able to transmit, receive, and analyze

data from the sensor network. Since different circuitry and electronics are being used

from the previous year, the electronics capsule was redesigned to better enclose the

system. The enclosure dimensions are the same, however, rather than a 3D-printed

model, the team concluded to utilize PVC. The 3D-printed HDPE containers displayed

signs of cracking due to micro-fractures introduced from the imperfect layering of the

3D-printing process. Therefore, Polyvinyl Chloride was selected as it is very durable and

much more resistant to fatigue. The 1.25 inch inner-diameter-rated piece of PVC was

turned down on a lathe to the proper inner diameter. The same mounting holes were

machined so that the same test rig could be used.  

 

Figure 22. PVC Capsule Design, with one end cap on display

                             

     

  29

10. Budget & Timeline  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.

• Arduino Nano (x2)

• Arduino Pro Mini (x2)

• Sensors (x2)

• Lithium Polymer Cells (x8)

• Wi-Fly Module (x2)

• DC Generator, large/small (x6)

• Total finances spent: $759.87

The team utilized less than half of the provided budget granted by Sikorsky.

 

 Figure 23. Outlined tasks over the course of the second semester

 

     

  30

11. Brief Summary of Results

Range testing was done with the unit rotating at 1200rpm in the team’s test stand. Signals

from the accelerometer and temperature sensor were transmitted and received, reliably, at

a line-of-sight distance of 40ft, meeting the sponsor’s requirement. This test was

performed several times to ensure accuracy.

Output from the temperature sensor was calibrated using known temperatures, ensuring

accurate data. The accelerometer was calibrated using a shaker from UConn’s sensors

lab. Data is sampled at 400Hz and displayed graphically with a web application written

by the team. Without the web application, the unit outputs data in the following format:

XDATA = 198 YDATA = -1252 ZDATA = 111 Temperature = 444

This line is repeated for each data point taken.

The unit’s battery was shown to be capable of lasting through a 30 day period of

inactivity as required by the sponsor. The energy harvester was capable of providing

enough power to charge the batteries at a slow rate while the Arduino and WiFly module

are in sleep mode. Charging data is shown in table 16 below.

Time (Minutes) Battery Voltage (Volts)

0 3.241 5 3.243 10 3.244 15 3.245 20 3.246 25 3.247

Table 16. Data from charging batteries with power from energy harvester The team programmed the Arduino to cycle into and out of sleep mode in order to

maintain battery voltage by recharging while in sleep mode and discharging to transmit

data. For future continuation of this project, a more suitable generator could likely be

custom ordered to provide sufficient power without sleep mode cycling. A generator of

slightly larger diameter and length and two stators rather than three should have sufficient

space to allow larger diameter wire to be used in the stators. This would significantly

reduce the resistance of the stators, reducing the voltage drop of the generator as current

     

  31

is drawn from it.

12. Appendix

A. CAD Models of Proposed System Designs  

 Figure 24. Arduino Nano with Wi-Fly breakout board, illustrating special issue; the break out board was eliminated.    

     

 Figures 25-26. System design with larger generator, illustrating special issue; the larger generator was eliminated  

     

  32

 Figure 27. System design with smaller generator, satisfying all special requirements

                                                                 

     

  33

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/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>