Battery Performance Meter for Electric Propulsion Systems
Semester Report
Fall 2007
Team Watt's Up
Ryan Bickham, Dennis Blosser, Cody Dinkins, Todd Dutton, Rachel Shively
Project Sponsor: Patrick Taylor, Ph. D., AMRDEC
Project Adviser: Andy Dozier, Ph. D., Vanderbilt University
12-17-08
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Table of Contents
Abstract/Operational Concept Opening ……………………………………………3
System Overview/Description ……………………………………………………..4
System Diagrams …………………………………………………………………..5
System Requirements ………………………………………………………...……6
Major Component Definition ……………………………………………………...8
Interface Definition ……………………………………………………………….13
Project Plan/Schedule …………………………………………………………….16
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Abstract / Operational Concept Beginning
The purpose of this project is to develop a method of determining the real-time electrical
loading and power dissipation status of battery systems housed within unmanned aerial vehicles
(UAVs). In particular, the goal of this project is to characterize a UAV electrical propulsion
system in order to design and construct a prototype device capable of monitoring the electrical
power conditions of a lithium-polymer based battery system. This type of battery system is
found in numerous UAV systems as well as commercial electronics such as laptop computers
and digital cameras.
The device shall be capable of providing output to the user with real-time details about
the following parameters: operating voltage, current, and power. It shall also provide output in
the form of remaining battery capacity and elapsed mission time. The device will be
programmed using an electrical motor similar in size and class to those that are currently under
evaluation for use in future electric propulsion systems. The data for loading and cycling
behavior of a motor and battery system will be gathered by the group using an eddy current
dynamometer, which shall be used to simulate the loading conditions that would normally be
experience by the motor during flight.
If time permits, the group will perform a series of wind tunnel tests to determine the
amount of power required to perform various mission movements such as banking, climbing, and
diving. The acquired data will then be used to further characterize the battery monitoring system
so that it may report additional parameters including remaining mission duration and remaining
mission range. The end goal of performing the wind tunnel testing shall be to enable the user to
plan a trajectory and mission onboard a UAV based on the amount of battery power required to
complete that mission.
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1. System Overview
Within the initial stages of the project, we have defined three major parts to our system.
The first of these parts is called the "device under test" (DUT). This part of the system is
comprised of the battery pack and the motor. Its name derives from the fact that these
components will be the ones that the testing will be concentrated on. This does not imply that
these are the only components that will be worked on during the project. Also, a motor mount
will have to be designed and built that will effectively secure the motor during testing.
Moving on, the second part of the system is the dynamometer. This part of the system
includes anything that either inputs to the dynamometer or receives an output from the
dynamometer. The components included in this system are the dynamometer, the coupler, the
water cooling system, the TSC 401 torque and speed conditioner, and the DES 310 power
supply. The conditioner and power supply will be responsible for delivering the torque, speed,
and excitation output from the dynamometer to the system instrumentation. The coupler will
connect the motor to the dynamometer and the cooling system will pass water through the
dynamometer. All parts of the dynamometer system will be interfaced to the system
instrumentation.
The third part of the system is the instrumentation. The instrumentation related to the
dynamometer will include the DSP6001 controller, thermocouples, and a personal computer.
The DSP6001 controller was designed specifically for our dynamometer and will monitor the
torque, speed, and excitation output from the dynamometer. The thermocouples will be used to
monitor the water temperature entering and leaving the dynamometer. Finally, the PC will be
responsible for compiling all information taken from the dynamometer.
In addition to all of the instrumentation devices that are related to the dynamometer, there
is the battery monitor. This is going to occupy most if not all of the electrical engineering effort.
The monitor will be designed to measure the voltage and current of the battery and based on
modeling data, it will calculate the remaining battery life.
The above systems are diagrammed and outlined in the following section System
Diagrams.
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2. System Diagrams
Fig. 1. System Diagram, 3-Part
This simple three-part diagram in Fig. 1 displays the operational breakup of the three individual
systems required to perform the desired tasks as defined in the System Overview.
Fig. 2. System Diagram, Expanded
Fig. 2 diagrams the individual systems of the project with emphasis given to inputs and outputs
of components. The individual systems are color-coded according to the key at the upper-left
corner and are contained within dotted lines to emphasize boundary definitions.
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3. System Requirements
3.1 Electrical System and Instrumentation Requirements
The battery and battery monitor shall meet the following requirements based on the battery and
electrical specifications:
3.1.1 Physical dimensions: minimum size allowable to retain ease of adjustment.
3.1.2 Electrical:
3.1.2.1 Operating voltage: 11.1V
3.1.2.2 Operating current: less than 1.5A
3.1.3 Battery source:
3.1.3.1 Battery type: Li-polymer
3.1.3.2 Battery capacity: 2200 mAh
3.1.4 Output / Feedback Parameters
3.1.4.1 Voltage level report: to precision of 0.01V
3.1.4.2 Current level report: to precision of 0.01A
3.1.4.3 Remaining battery capacity: to precision of 0.01 Ah or 0.1 Ah
3.1.4.4 Elapsed mission time: to precision of 0.1s
3.1.5 User Interface
3.1.5.1 Display: parameters reported by LCD or PC Monitor
3.1.5.2 Control: manual keypad if stand-alone LCD is installed
3.2 Dynamometer and Mechanical Instrumentation Requirements
The dynamometer and mechanical instrumentation shall meet the following requirements as
defined by operational standards and safety specifications:
3.2.1 Coupler parameters:
3.2.1.1 Physical limitations: Ф<1.5”, L<3”
3.2.1.2 Slippage allowance: .003” tolerance
3.2.1.3 Structurally sound and withstand operation at: 20,000 RPM
minimum
3.2.2 Motor mount parameters
3.2.2.1 Physical limitations: fit within the physical constraints of the table and
mounting holes (not yet defined)
3.2.2.2 Adjustability: adjustable in 6 directions—3 rotational, 3 translational
3.2.2.3 Capacity: hold the motor stationary and in alignment without slippage at
a rating of approx 2 ft. labs of torque
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3.2.3 Coupler shield
3.2.3.1 Dimensions: to be determined in order to enclose entire coupler prevent
shards of shattering coupler from harming people. Must enclose tired
coupler.
3.2.3.2 Energy absorption: able to absorb ≥50 J of energy
3.2.4 Dynamometer cooling system
3.2.4.1 Maintain dynamometer temperature of: 0 - 50°C
3.2.4.2 Meet the physical requirement of the dynamometer heat exchanger
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4. Major Component Definitions
The following lists and defines the major components of the system while providing
incite to the current status of the project with regards to each component.
4.1 Electrical instrumentation component: battery monitor
One of the main goals of this project is to develop a battery monitor that will project the
remaining battery life in the UAV. In a general description of its operation, the monitor will read
the current running through the battery and based on battery characteristics and testing data, the
monitor will calculate how much longer the battery will be operational. While the idea seems
simple in theory, it will require the design of a FPGA circuit to implement it.
As previously mentioned, the monitor will rely on battery characteristics and test data.
Because we will be using a lithium polymer battery, Peuckart's Law does not apply. This
requires us to determine the battery characteristics through our own investigation. Through
battery tests, we will develop a model that we can apply to our case and begin our design from
there. As of now we are aware of five components needed for the battery monitor: FPGA,
scaling circuitry, converter, shunt resistors, and display.
4.1.1 Battery monitor component breakdown
4.1.1.1 Field programmable gate array (FPGA)
For the creation of the battery monitor, we have decided to use a field programmable
gate array (FPGA) and not a microcontroller. This decision was rooted by the fact that our
sponsor would want to build on what we develop. If we only use a microcontroller, the
project will be limited to what we develop and no further progress can be made without
completely redoing the design. With this said, the FPGA provides the flexibility to change
and progress on what we create. Once we decided to use and FPGA, we began to look for
the one that would suit our needs.
While there are many brands and makes of FPGA's, we limited ourselves to the Altera
brand. Projects in previous years have successfully used this brand. Also, Professor
Robinson uses Altera in his FPGA course. Knowing that we would have a bank of
knowledge to feed off of, we decided that an Altera FPGA would be the best choice. With
the brand chosen, we had to pick out a model.
The Nios II development kit became our top choice for one simple reason. It had what
we needed to fulfill the scope of the project and any future needs and did not have anything
that was superfluous. This kit includes the Nios II integrated development environment,
Quartus II design software, and Cyclone II FPGA. The Cyclone II is deemed as being one
of the top contenders in simple performance as well as being cost efficient. Now that the
FPGA has been decided on, we needed to start identifying what needed to be done.
In order to spearhead our design for the battery monitor, we met with Professor
Robinson, who lectures on the use of FPGAs. Through the course of our discussion, we
discovered that the FPGA kit he teaches with is very similar to the one we chose to use. As
he described what our initial plans should be, we found that there were essentially two
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options. We could either go the microcontroller design route, using the FPGA, or create a
software heavy design. Seeing that none of the electrical engineering students in our group
have microcontroller experience or heavy programming experience, we felt a little pressure.
In order to gain comfort with the FPGA and related hardware, all of the electrical
engineering students have decided to audit Professor Robinson's FPGA course. Our hope is
that along with normal coursework and lectures and self-education, we will be able to have
a sound enough understanding to build a competent battery monitor.
Fig. 3. Altera Nios II / Cyclone II FPGA Development Board
4.1.1.2 Scaling circuitry
For the battery monitor to operate, we plan on feeding off of the battery. In order to
accomplish this, we will need to scale the voltage coming off of the battery monitor. This
will be achieved through the use of scaling circuitry, which will reduce the voltage coming
from the battery. Using electrical calculations, we will determine what size of resistors will
be necessary. In addition to these components, we utilize operational amplifiers and
capacitors. Before any connection between the battery and the monitor, we will test the
output to ensure that the proper voltage level is being attained.
4.1.1.3 Analog/digital converter
The battery will put out an analog signal that must be converted a digital signal. In
order to accomplish this, we plan on finding a prefabricated converter that will work with
our design. Within the circuit design, this will follow the scaling circuitry and come before
the FPGA.
4.1.1.4 Shunt resistors
To drain the battery and enable us to perform tests on it, we will require shunt
resistors. These resistors have minimal resistance and allow a large current to pass through.
In addition, they can act as test points within the circuitry. By having test points, we will be
able to optimize and troubleshoot any problems or inefficiencies we may have.
4.1.1.5 Display
Seeing that our sponsor has permitted us the use of a pc as our output display, we feel
it will be the best option. This prevents the need for additional circuit development and
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interface. Although we may not utilize an external display, this does not prevent any future
groups from integrating this into the system. The display technology will be more of a back
end development that will not require the alteration of the main circuitry of the battery
monitor.
4.2 Mechanical instrumentation components
4.2.1 Eddy current dynamometer
Our dynamometer is a Magtrol WB 43 (model 2) series eddy-current dynamometer.
It offers a maximum braking power of 3.0 kW and a maximum speed of 50,000 rpm. It is
an ideal model for high speed applications and as the speed increases, torque also increases.
In addition, it has a small rotor diameter which results in a small moment of inertia. The
dynamometer is secured onto a testing table as shown below.
Fig. 4. Model 2 WB 43 Dynamometer
Fig. 5. Dynamometer Mounting Table
4.2.2 Dynamometer controller
Magtrol manufactures a programmable dynamometer controller that provides
effective control for any Magtrol eddy-current dynamometer. The Magtrol DSP6001
controller generates data that can be stored, displayed, and printed in either a table or graph
format. It runs test sequences that with good accuracy and efficiency. The controller has a
built in alarm system and torque/speed analog outputs that can be sent to a data acquisition
system. It collects data at 120 torque and speed points per second.
Fig. 6. DSP6001 Dynamometer Controller
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4.2.3 Motor / dynamometer coupler
In order to connect the motor under test to the dynamometer, a coupler will have to be
designed and machined. The coupler will need to be able to manage rotational speeds of
approximately 20,000 rpm. A preliminary sketch is shown below.
Fig. 7. Team-designed ProE Coupler Model
4.2.4 Torque speed condition
Magtrol’s TSC 402 torque speed conditioner connects the dynamometer to the
DSP6001 controller. The conditioner filters and amplifies the torque signal and is based on
a precision instrumentation amplifier. The speed pickup sensor is located in the
dynamometer but the signal conditioner provides the power and connections. The entire
signal conditioner is powered by the DSP6001 controller.
Fig. 8. TSC 401 Signal Conditioner
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4.2.5 DES 310 Power Supply
Magtrol’s DES series power supply controls the excitation current output from the
dynamometer. The nominal value of the excitation current can be adjusted by internal
resistance or by remote control. The DSP6001 controller uses its analog and digital setpoints to manage the power supply. The power supply has two digital outputs that generate
an alarm in case of electrical fault or overheating. The supply voltage can be selected for
operation at either 50 or 60 Hz.
Fig. 9. DES 310 Power Supply
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5. Interface Definitions
The following describes the interconnects between system components for both the
electrical and mechanical subsystems.
5.1 Electrical interfaces
5.1.1 Scaling circuitry between battery and monitor
The battery shall interface the A/D converter by means of scaling circuitry. This
circuitry shall be able to sense voltage, current, and temperature from the battery and scale
the measured signals to appropriate levels that the ADC can accept. This circuitry shall
consist of proper combinations of resistors, capacitors, and op-amps as to be later
determined. Each of the three sensory circuits are described below.
5.1.2.1 Voltage sensory circuitry
The voltage circuitry shall interface the ADC via connections straight to the battery
bank. The circuitry shall first consist of a simple resistor-based voltage divider to scale the
battery output to between 0 and 5V. This signal shall then be passed through a simple lowpass filter consisting of capacitors and resistors to remove any excess noise created from the
battery.
5.1.2.2 Current sensory circuitry
The current circuitry shall consist of three stages: A current shunt, a low-pass filter
stage, and an amplification stage. The shunt shall be connected to the battery’s terminals by
standard electrical wire. The signals measured at the shunt shall then be fed into the simple
low-pass RC filter very similar to that found in the voltage circuitry. From there, the signal
shall propagate to gain stages consisting of op-amps and resistors to produce an output
usable by the ADC.
5.1.2.3 Temperature sensory circuitry
Like the current sensing circuitry, the temperature sensing circuitry shall consist of
three stages: A thermocouple, a low-pass filter stage, and an amplification stage. The
thermocouple shall be connected to the battery and create a readable voltage drop based on
the temperature reading. The poles of the thermocouple shall then be connected to a lowpass RC filter for noise removal. Finally, the signal shall pass from the low-pass filter and
into an amplification stage consisting of op-amps and resistors to bring the signal to a
readable level for the ADC.
The ADC shall then convert the data from the signals described above into digital form
suitable to the needs of the FPGA for processing. After processing the given information, the
FPGA shall deliver the desired output via the user interface as defined below.
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5.1.2 User interface
The user interface for the system shall be created for simplistic use while delivering
all of the desired outputs as defined in the system requirements. Ideally, the user interface
will be stand-alone functional and able to be placed anywhere alongside the battery monitor.
If this is possible, then the interface shall consist of an LCD screen and a user keypad. The
user shall be able to use the keypad to scroll through options and view the battery’s current
operating voltage, current, and power along with the elapsed mission time and remaining
battery capacity on the LCD screen. If a stand-alone user interface is unable to be created,
the readable output levels shall be presented simply through a PC to which the FPGA shall
be attached.
5.1.3 FPGA interface
During programming, the user shall interface with the FPGA through the use of a
high level C++ code written to designate the required SOPC (System On Programmable
Chip) to perform the necessary calculations for the battery monitor.
The FPGA shall be interfaced with the programming PC via a standard USB
connection. Once the user interface is decided upon, the FPGA shall read inputs from the
user via either a keypad or keyboard and return the desired output via either an LCD screen
or computer monitor.
5.2 Mechanical interfaces
5.2.1 Thermocouples
The thermocouples provide useful temperature data in a number of ways. The
preferred method is to have them read directly into the M-test software via a thermocouple
controller. This would provide real-time data of the cooling system, but may require a
DAQ card in addition to the controller. If these cannot be feasibly attained, then data may
be taken periodically by means of a handheld multimeter that can read off of probe type K
thermocouples. The automatic safety temperature monitoring built into the dyno would still
be in effect, and periodic sample measurements, built into the standard operating
procedures, would provide auxiliary data by which the system could be monitored.
5.2.2 Dynamometer / Instrumentation
Input to the dynamometer system will come from the motor. The motor will be
connected to the dynamometer by means of a mechanical coupler. This coupler will be
designed by us and fabricated by a machine shop. The tolerances will be within .003" for
shaft alignment. It will attach to the motor via compression, and to the dynamometer via
dog tip set screws tightened into keyways.
The dynamometer itself will have several outputs to the instrumentation part of the
system.
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5.2.2.1 Cooling system
The dynamometer will be cooled with water that will be taken from a wall faucet. It
will be an open system that uses water that has passed through a pressure regulator in an
internal heat exchanger, then exits to a drain. The pressure must remain below 2 bar, and
the temperature of the cooling water must be greater than 0°C at the entrance and less than
50° C at the exit. The temperatures of the input and output water will be monitored with
thermocouples. The thermocouples will be connected to the instrumentation by means of a
LabVIEW data acquisition card. A personal computer will be running LabVIEW, which
will display the measured water temperatures.
5.2.2.2 Power supply
The Magtrol DES series 310 power supply will be connected via integrated cables to
the excitation output of the dynamometer. The power supply must be electrically and
thermally mounted on the testing table near the dynamometer in order to allow heat
dissipation. The excitation current will be controlled by a set-point in the range of 0 to 10
VDC. The nominal current will be adjustable via a remote or by internal resistors. Also,
the power supply includes a galvanic separation between the dynamometer power and the
supply circuit. The supply voltage can be selected as either 230 or 115 VAC (50 or 60 Hz).
The excitation current will pass from the dynamometer through the DES power supply to
the dynamometer controller, which will provide the analog and digital set-points.
5.2.2.3 Signal conditioner
The Magtrol TSC 401 signal conditioner will be connected to the torque and speed
outputs of the dynamometer via a 1.5 meter integrated cable. The signal will pass from the
dynamometer through the conditioner to the dynamometer controller. Using a precision
instrumentation amplifier, the conditioner will amplify and filter the torque signal to the
dynamometer controller. In addition, the signal conditioner will provide power and
connections to the controller for the dynamometer’s speed pickup sensor.
5.2.2.4 Dynamometer controller
The Magtrol DSP6001 dynamometer controller will be connected to the dynamometer
via the DES 310 power supply and the TSC 401 signal conditioner. The controller will
provide power to the signal conditioner. The torque, speed, and excitation signals will be
analyzed and transmitted to the instrumentation via a RS-232 connection. The controller
itself will be able to display the torque, speed, and power at all times but will also be used to
input analog torque and speed signals at a rate of 120 points per second to a PC system that
will be running LabVIEW software.
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6. Project Schedule
The following is a brief introduction to the team’s preliminary schedule. It is, of course,
subject to change at any given time. It will be updated throughout the year and reposted to the
group’s website as changes are made.
*Note: The schedule begins on this page and is continued into the next. A printed version of the
Gantt chart appears after the schedule description.
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Fig. 10. Preliminary Schedule of Tasks
6.1 Brief schedule description
The project began with selecting good members for our team. After fall break, members
of the team met with our project sponsor. Dr. Patrick Taylor of AMRDEC traveled from
Huntsville to Nashville to deliver certain parts for the project. Dr. Taylor met with Todd Dutton
(ME) and Cody Dinkins (EE) explaining the project in greater detail. Todd and Cody then
relayed the necessary project fundamentals to the remaining members.
None of our project parts had arrived by the time of our first presentation. However, Dr.
Taylor assured us we would receive the dynamometer within a week. Initially, our mechanical
engineering team members designed a preliminary coupler and our electrical team members
researched possible ways of designing a battery monitor. The electrical members read a previous
group’s report involving a battery monitor (Remotec’s Battery Power Management System).
While reading this report, we discovered our need for a field programmable gate array (FPGA).
Our electrical team members did not have previous experience concerning FPGA’s or similar
components such as microprocessors. However, the mechanical team members were previously
familiar with dynamometer usage.
On the mechanical side of the project, the team members designed rough depictions of a
motor coupler, motor mount, and cooling system. Shortly after on November 30, 2007, the team
received the eddy current dynamometer complete with mounting table. Dr. Taylor included
excitation, torque, and speed connectors to the dynamometer in the dynamometer crate. All
machining for this project will be provided by AMRDEC or outside machinists. Dr. Taylor
proposed a completion of the coupler would take a couple of weeks after submission to
AMRDEC’s machine shop. The team will also build a cooling system for the dynamometer.
On the electrical side of the project, team members met with Dr. William Robinson
concerning his FPGA course. He agreed to allow the auditing the course for the 2008 spring
semester. Then he gave details regarding his course’s specific FPGA. So starting in the spring,
the electrical engineers can begin developing coding for the FPGA and input circuitry. Also in
the spring, the team will order the FPGA, Altera’s Nios®II Development Kit, Cyclone® II,
analog/digital converter, and battery bank. As of now, we are still unsure of an output display.
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Consequently, we will wait to order an LCD screen if deemed feasible to implement. We are
planning to receive the majority of the parts during the time frame of middle to late January. We
will begin assembling FPFA parts during February and began testing during March.
The mechanical and electrical engineers will integrate the battery monitor with the motor
in March. At this point in the project, there may possibly be wind tunnel testing spearheaded by
the mechanical members, but this may fall out of the final scope of the project if time does not
permit. The team will finish writing the final report and updating the website after testing,
examining results, and addressing sponsor concerns.
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