ECE 4901 Fall 2012
Written Proposal
Wireless Test Instrumentation
System for Rotating Parts
Team 167/29:
ECE
Michael Golob
Lawrence Bogan
Jeremy Neaton
Adam Bienkowski
ME
Sean Handahl
Caleb Browning
Kenneth Thompson
Faculty Advisor:
Rajeev Bansal
Office: ITE 463
Phone: (860) 486-3410
E-Mail: rajeev@engr.uconn.edu
Robert Gao
Office: UTEB 456
E-Mail: rgao@engr.uconn.edu
Sponsoring Organization: Sikorsky Aircraft
Paul Inguanti
PInguanti@sikorsky.com
Chris Winslow
CWinslow@sikorsky.com
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Table of Contents
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2
3
4
5
6
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Executive Summary ________________________________________________ 3
Introduction ______________________________________________________ 4
Background
__________________________________ 4
Specifications
___________________________________________ 4
Solution
___________________________________________________ 5
Budget
_______________________________________________________ 10
Timeline
_______________________________________________________ 10
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1. Executive Summary
Sikorsky, a United Technologies aircraft manufacturer, would like to solve a problem with
monitoring pitch change bearings in the tail rotor of their helicopters. These bearings are
located inside a shaft that rotates at up to 1200 revolutions per minute, and are crucial for
keeping control of the aircraft during flight. However, their location makes it expensive and
inconvenient to access for regular maintenance, and so pilots have relied on manufacturer data
to attempt to predict when these bearings fail. The current system used for monitoring consists
of a wired sensor with a slip ring, causing liabilities with wires failing due to breakage or from
being shot off in a hostile environment. The slip rings also have brushes that add weight and
eventually wear down. A team consisting of seven University of Connecticut engineers were
given a 4000$ budget to find a wireless solution that would allow for the monitoring of these
bearings over a minimum timespan of a year, without having to perform additional
maintenance. More specifically, the team was asked to show that a wireless solution is feasible,
and to test this information was given on the Sikorsky S-92 helicopter. The solution the team
found for proof of concept was a Wireless Test Sensor System (WSN) that can monitor variables
such as vibration or temperature of the bearing to indicate when the helicopter needs to be
repaired. This WSN consists of a microcontroller, transceiver, and accelerometer that can
record data to be transmitted to a stationary system, once a day, in the helicopter cabin up to
40 feet away. It will be capable of recording and storing data to memory, until the data is
requested for evaluation, at which point the system will remove any onboard data. The WSN
will be turned on by a wakeup signal in order to save power by only recording data while the
helicopter is operational. It will all be powered by a battery, which will suffice to power the
network for the one year minimum, and allow the system to power on after 30 days of
inactivity, as requested by Sikorsky. However, the system may also include vibrational energy
harvesting technology, which would boost the lifespan of the system past the minimum
requirement for convenience. Furthermore, Sikorsky provided requirements on temperature,
packaging, and size in order for the system to work inside the 1.5” by 5.1” lubricated electronics
cavity of the shaft. The team’s final design meets all of these requirements except for
temperature, because commercially available components do not meet the high end of the -20
to 250 degrees Fahrenheit range. However, it has been confirmed that there are military grade
components that can be used, but that the team would not have access to them, and so the
team will provide proof of concept and the company can further improve the design. It is
predicted that the suggested WSN will accurately give readings on the vibration of the tail shaft,
and will have no issues with the power supply over the entire time frame. In order to test this,
the engineers also designed a test rig using a variable speed motor, an imitation shaft, and
cartridge bearings to simulate the actual rotating conditions in the helicopter, and to allow for
the collection of data of broken bearings and healthy bearings for comparison. If implemented
into Sikorsky helicopters the WSN will provide a more accurate readout on the condition of this
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bearing, improving the safety of all pilots and crews, and allowing for savings in maintenance
for the company.
2. Introduction
Sikorsky aircraft have typically used wired sensors to take measurements of critical
systems. There are some problems associated with this method of monitoring, particularly when
the measurements take place on a rotating part, in which case sliprings are used to connect
between rotating and stationary parts. Mechanical failure of wires and connectors can lead to
open or short circuits. Long wires add to the weight of the aircraft, and any weight added to the
aircraft reduces the weight it can carry. If a suitable wireless system to collect and transmit
sensor data could be developed, it would eliminate or reduce many of these issues.
3. Background
This project will focus specifically on a wireless interface for sensors to monitor the tail
rotor pitch change shaft bearing for signs of failure. Vibration has been shown to be a good
measure that are good indicators of bearing status, with high vibration being indicative of
bearing failure. This sensor will be on a rotating part, which means that in order to eliminate the
need for sliprings and wires, the entire system to collect and transmit the sensor data, including
a power source, must be contained within the rotating part.
Sikorsky would like us to be able to measure the bearing, whether it is the temperature,
vibration, or strain. We need to then process the measurement data by using a filter, and then
digitize that data. The measurement data must also be able to be stored temporarily. This data
needs to be transmitted to a stationary system where it can be accessed for analysis. The
measurement system and the receiver must be powered, either by a battery or energy
harvesting. The battery need to last a minimum of one year, but should be three years. The
battery needs to be able to still give power after thirty days of inactivity, and be able to collect
data for up to twelve hours per day.
4. Specifications
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)
• Runs for 12 hours a day, needs to survive 30 days of inactivity
Data Processing
• Measure vibration
• Store data temporarily
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• Transmit to stationary system and available at request of user
• Data must travel wirelessly upwards of 40 ft.
Environmental Parameters
• Can’t be visible from outside (hostile environment)
• Cavity is oil lubricated
• Moisture Possibility
• High vibration level
5. Solution
Generic Block Diagram
Technical Specifications:
Wireless transceiver:
The ZigBee chip will be used as our wireless transceiver to transmit data from the
measuring system, which is located within the tail rotor to the stationary receiver that will be
located in the cabin. We chose to use this as our wireless interface for two main reasons. The
first main reason is that it consumes only 14 milli amperes, which is very low power
consumption in our design. In sleep mode, it only consumes .02 microamperes, which in return,
only saves us more power. The second main reason is the fact that it can transmit data over a
very far range and at even a far more range than what is required in our parameters. However,
these two reasons were ideal in selecting the ZigBee chip as our transceiver.
Part No.
Operating
Temperature
Transmission
Current
Idle Current
Voltage
Max. Data
Rate
AT86RF231
-40°C to 125°C
14 mA
0.02 µA
1.8-3.6 V
2Mbp/s
AT86RF233
-40°C to 85°C
13.8 mA
0.02 µA
1.8-3.6 V
2Mbp/s
These were two transceivers that we considered and looked into. We selected the
AT86RF231 primarily because of the operating temperature. The specifications for these parts
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were nearly identical, but we also needed to satisfy the temperature parameter so this part was
selected.
Sensor:
The sensor will be used to measure the vibration of the bearing. The defect frequencies
we calculated occurred between 156Hz and 274Hz, meaning we needed a sensor with a
bandwidth above 274Hz. The sensor needed to have an interrupt in order to tell the
microcontroller to start recording data. By keeping the microcontroller in idle, we are able to
save more power. We needed the sensor to have a very low power consumption, to preserve
the battery.
Part Number
Voltage
Idle Current
1.71V-3.6V
Active
Current
11μA
LIS3DH
SCA3060-D01
KXTIA-1006
Size
Bandwidth
Measurement Range
Temperature
3.0V-3.6V
1.8V-3.6V
150μA
325μA
0.5μA
3 x 3 mm
2.5kHz
±2g, ±4g, ±8g, ±16g
-40°C to 125°C
5μA
10μA
7.6 x 8.6 mm
3 x 3 mm
100Hz
1.59kHz
±2g
±2g, ±4g, ±8g
-40°C to 105°C
-40°C to 85°C
Trying to find a sensor with an interrupt limited our options for accelerometers. The sensor we
choose was the LIS3DH. The three sensors above all have interrupts and are among the three
best options we could find. The LIS3DH accelerometer had an extremely low current
consumption, which help us have lower power consumption. This was the main factor we looked
into when deciding upon the sensor. We had a tight constraint on the power we have available,
so we needed to save power where we could. The sensor we choose also is very small and
allows us to operate at the 3.6V the battery provides. As discussed in the background we
needed a bandwidth that was above 400Hz. The sensor we choose allows us to choose a wide
range of bandwidths below 2.5kHz. Compared with the other two sensors, our sensor was the
only one that satisfied the temperature constraints given to us.
Memory:
Memory will be needed in addition to the memory in the microcontroller to store data
from the sensor. The size of the memory is limited by the power restriction, as higher capacity
memories use more power. The amount of raw sensor data collected between data accesses is
much more than the maximum memory size possible with the power restrictions. There are
several methods to reduce the amount of memory needed. The first is to use a technique called
time synchronous averaging, which involves averaging consecutive sets of samples together.
In this case, only the average of a series of samples needs to be stored, which will greatly
reduce the memory need. Another method is to sample for short periods of time with time in
between samples when no data will be collected. A third method will be to transmit the data
whenever the memory is full. With this solution, the full data will be stored on the receiver
system, on a non-rotating part of the aircraft, which will have less strict power restrictions,
allowing for a larger capacity memory.
Part Number
CY62167DV30
CY62177EV30
Voltage
2.2-3.6 V
2.2-3.7 V
Active Current
2 mA
4.5 mA
Idle Current
10 µA
17 µA
Capacity
16 Mbit
32 Mbit
These are two options for low power SRAM. The 16 Mbit option was selected because
4.5 mA is too high to meet the battery life specifications with the chosen battery. None of the
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memories researched met the given temperature specification, because military temperature
rated parts are not commercially available.
Microcontroller:
Part Number
MSP430G2332-EP
MSP430F5438IPZR
Supply
Voltage
1.8-3.6
2.2-3.6
Active
Current
220 μA
312 μA
Idle Current
Size
Operating Temp
Program
Memory
IO pins
.5 μA
2.6 μA
6.6x6.6mm
14x1.4mm
-40 to 125 deg C
-40 to 85 deg C
4kB
256kB
16
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The lower power consumption option out of these two does not have sufficient program
memory or input/output pins to meet our needs. The microcontroller we chose has slightly
higher power use, but has enough program memory and input/output pins. Both of these
support Serial Peripheral Interface (SPI), which is needed to interface with the sensor and the
ZigBee transceiver.
Battery:
Our calculations for current use using the parts discussed above are as follows:
Part
Data Acquisition Current
Transmission Current
Idle Current
Sensor
11 µA
0.5µA
0.5 µA
Memory
2mA
2mA
22µA
Microcontroller
312µA
312µA
2.6µA
Transceiver
0.02µA
14mA
0.02µA
Totals
2.32mA
16.31mA
25µA
Assuming time synchronous averaging or periodic sampling, 16Mb transmitted at 2 Mbps once
daily = 8 sec of transmission time per day.
2.32mA*12 hours/day*365 days/year = 10161.6 mAh
16.31mA*8sec/day * hours/3600 sec*365 days/year = 13.23mAh
25µA*12 hours/day*365 days/year = 109.5mAh
Total = 10284.33 mAh
Assuming periodic transmission, transmit when memory is full: 16 bits/sample*1.25kHz
sampling frequency*3600sec/hour*12 hours/day =864Mbit/day
864Mbit/day2Mbps transmission rate =432sec/day transmission time
16.31mA*432sec/day * hours/3600 sec*365 days/year = 714mAh
New total capacity needed = 10284.33+714+13 = 11011 mAh
The 11.011Ah we calculated is the absolute maximum needed. We calculated based on the
parts running continuously over the 12 hours. For periodic sampling, the memory will not be
running for the amount of time used in these calculations, reducing the power used.
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Battery model
Dimensions
Capacity
Output
Voltage
Operating Temps
Eaglepicher LC 3155
Diameter 30.7 mm (1.21”) height
54.6 mm (2.15”)
12.7Ah
2V
-30C to 50C
Eaglepicher LC 3355
Diameter 33.3 mm (1.31”) height
54.6 mm (2.15”)
15.5Ah
2V
-30C to 50C
3.6V
-55C to 125C
Tadiran 15-5930-yy505
Diameter 32.9mm
Height 61.5mm
17Ah
From the batteries above, we choose the Tadiran 5930. Although most of the batteries we found
were the correct dimensions, we found one that met the capacity we needed. The output
voltage of 3.6V satisfies the voltage requirements of our components, while the 2V from the
other batteries does not.
Energy Harvester:
Without energy harvesting, our design meets the minimum requirements for how long
the battery will last. We will continue to research ways to add energy harvesting to our design
to further extend the life of the battery. Vibrational energy harvesting is the most feasible
solution with our system.
Piezoelectric vibrational energy harvesting is the best option for energy harvesting for
our system. Temperature based energy harvesting is not viable because the system lacks a
reliable temperature gradient. The output of the vibrational energy harvester is sinusoidal or
alternating current. A rectifier board is used with this system to take this alternating current and
convert it into direct current that can be used throughout the system. Commercially available
rectifier boards are too large to fit inside the small cavity available, so in order to use energy
harvesting a custom board must be made. This custom board will need to contain a rectifier
and a charge pump, to output a DC voltage at the same level as the battery. If a custom
rectifier board cannot be created to accompany the energy-harvesting device, then the system
will be powered solely by the battery and will reduce the total operating time.
Test Rig:
The main focus of the project lies with the electronic component selection and making
sure that they work. In order to do this, a representation of a tail rotor shaft with the electronics
cavity at the tip will have to be produced. This cavity is the only space currently available in the
helicopter’s design for emplacing all the required components. The final test rig model will be
created in Siemens NX8 computer aided design modeling software. The rotating shaft will be
powered by an electric motor, which will also be the source for the natural vibrations induced to
the system. The level of vibrations is motor dependent and can be adjusted by adding offset
mass to the rotating system in order to get the amplitude of the vibrations to an acceptable level
for measuring. This motor will have an adjustable speed controller to allow for the testing of
sensor readings at various speeds.
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The vibrations of the test rig would ideally try to match those of the S-92 in terms of gforce, magnitude and frequencies, but this data cannot be obtained from Sikorsky. These are
the natural vibrations of the system due to the engine, rotors, and transmission operating during
flight. A spherical roller cartridge bearing and an angled roller cartridge bearing will support the
rotating shaft. These two bearing types mimic those in which the actual tail rotor shaft rotates in,
with the pitch change bearing being the spherical roller type and the shaft support closer to the
blades being the angled roller type. The cartridge type allows for them to be removed and
switched out with a purposely-damaged set. These will allows us to see how the vibrations of
the system are altered when the bearings do go bad. The requirement of this project is to be
able to analyze and transmit the data, not necessarily to distinguish between the readings
obtained from a good bearing and that of a bad bearing. However, this will allow for a
meaningful demonstration of the effects the bearing’s condition has on the system and readings.
Current Block Diagram
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6. Budget:
● Battery (x4):
$100.80
● Sensor:
$2.27
● Transceiver:
$5.16
● Microcontroller: $9.86
● Memory:
$15.75
● Antenna:
$5.19
● Balun:
$2.58
● Programmer: $70.54
Total: $212.15
7. Timeline
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