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
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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.
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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
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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
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(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.
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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
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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.
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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.
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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
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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
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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
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Figure 27. System design with smaller generator, satisfying all special requirements
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<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.
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[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>