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ECE 792 Final Project Report
Electric Snowmobile
Team Members
Lindsey Chiron
Roger Gauthier
Patrick Hingston
Parker McDonnell
Michael Swanson
ECE Faculty Advisor
Dr. Gordon Kraft
Project Completion Date
May 9, 2011
Courses Involved
ECE 541,548, 617, 618, 651, 649
Abstract
The objective of this project was to enhance the design of a zero-emission, low-noise snowmobile
in order to provide the user with a safer and more reliable vehicle. A charging system was designed to
improve the practicality of charging the snowmobile batteries. A user interface was implemented through
the use of a touch panel and programmable automation controller (CompactRIO). The touch panel
displayed battery voltages, speed, instantaneous current consumption, and temperature. In order to obtain
this information, sensors were installed in the snowmobile and outputted data to the controller. A
gasoline generator was also mounted on the back of the snowmobile, serving as an emergency backup
power supply.
Introduction
The wilderness of New England can be a harsh and dangerous place especially during the
winter months. Snowmobiles are used for recreational activity and also have uses in search and
rescue. While snowmobiling can be enjoyable, it can also be dangerous at times. Making
improvements to modern day snowmobiles can minimize some of the risks and inherent side
effects. Becoming stranded in the wilderness is a very real possibility when long trips are taken
or insufficient amounts of fuel are brought. Gasoline powered snowmobiles produce a lot of
noise pollution which can make search and rescue missions harder to accomplish. By designing
an electric snowmobile, noise and fuel pollution concerns can be diminished.
Building off of last year’s electric snowmobile we made a number of improvements to
help reduce risk and increase usability. A main concern was for a user to be able to view what
was going on with the snowmobile while driving it. In order to warn the user of any potential
problems with the vehicle, a heads-up display system was added, allowing the user to monitor
system status. A programmable automation controller (NI CompactRIO) was used to take data
from various sensors and display them on touch panel. The controller used Labview to analyze
and present the information to the user. In order to gather the vital diagnostic information, a Hall
Effect current sensor and RPM sensor were added, along with a battery voltage monitoring
circuit. To further increase the safety of the vehicle, functioning headlights were installed, as
well as a redesigned PWM throttle linkage.
Another main objective of the project was the charging of the snowmobiles batteries. A
charging unit was designed to allow an easier method for the user to charge the batteries. This
charging system allows the user to avoid removing each individual battery and charging them all
separately. In addition to the charging unit, a gasoline generator was mounted on the back of the
vehicle. This safety feature allows the user to charge the batteries even when a wall outlet is not
available. The charging system plugs directly into the generator, allowing the generator to
substitute for a wall outlet. A 12V auxiliary port was implemented to allow for the user to plug in
a GPS system.
Design
Three major systems were designed, fabricated and tested during the past two semesters. These consisted
of a charging circuit, monitoring/GUI system and an emergency generator. The following diagram details
the completed systems.
figure 1
Monitoring and GUI

NI CompactRIO 9074
The heart of the monitoring system consists of the national instruments compactRIO embedded
control and acquisition system. The cRIO was used to acquire analog and digital values in addition to
exporting analog signals through its hot swappable modules. For our project purposes three NI
modules were selected including the NI 9411 digital input module, NI 9263 Analog output module
and the NI 9205. Signals which stored there information in terms of frequency or pulse width were
applied to the 6 channels of the NI 9411. All standard DC voltages were read in using the 32 channel
analog input NI 9205 module. The three modules perform the task of converting analog and digital
values, conditioning the signals and writing them to the cRIO’s volatile memory.
figure 2

National Instruments Labview
Labview served as the programming language used to control the CompactRIO’s functionality. Labview
is known as a graphical programming language where wires, blocks and figures are used instead of lines
of code. This serves the user the ability to rapidly deploy code and easily transition from flow diagrams
to functioning programs. The NI 9205, 9263 and 9411 served as the gateways between physical hardware
(sensors, circuits, signals) and our Labview code. All incoming signals were converted to digital values
and stored in memory allowing for our code to be updated. The module update timing or scan engine was
set to update volatile memory every 10ms allowing for real time monitoring of all vital systems. For this
particular project two .Vi files were created similar to .c or .java source code in other programming
languages. One .Vi was downloaded to the cRIO to read in values, crunch data and make decisions based
on these values. The other .Vi was sent to the touch panel to control the graphical user interface. The two
.Vi’s communicated through shared variables with the cRIO publishing values to the network and the
touch panel fetching these values from the network

Touch Panel
The TPC-2206 touch panel runs Windows XP and sports a dual core 1.33 GHz atom processor. The
NI cRIO is known as a headless system as it has no way of displaying calculated data. Connecting a
touch panel to the cRIO we were able to displayed vital system information including, throttle, MPH,
Armature current, RPM and Battery voltages. As mentioned earlier the code running on the touch
panel fetched updated variables from the network and displayed the values on dials, graphs and
indicators. Through some tweaking of startup programs and the .Vi options we were able load our
.Vi at the boot of windows.
Network Shared Variable (figure 3)
Touch panel Instrument Cluster (figure 4)

Sensors and Signals
o Ferromagnetic Hall effect Sensor: To measure the revolutions per minute of the motor
a ferromagnetic Hall Effect sensor was mounted 2mm from the edge of one of the motors
gears. The sensor outputs a voltage equal to Vsource at the lack of a gear tooth and drops to
zero when a tooth is present. This function is performed through the use of an open
collector output connected to a pull up resistor hooked to Vsource. Therefore a square
wave is generated with a frequency proportional to that of the motor RPM. To interpret
the incoming signal the high pulse time was measured using the NI 9411. To calculate
the revolutions per minute we divided 60 by the number of gear teeth (PPR) times the
pulse high time (PHT) 𝑅𝑃𝑀 = (60)/(𝑃𝑃𝑅 × 𝑃𝐻𝑇). This equation was realized in
Labview and the output values were sent to the touch panel to display.
RPM Sensor Configuration (Figure 5)
o
Pulse Width Modulation Signal: the snowmobile motor is controlled by a PWM signal
which is effectively equivalent to throttle for a gasoline engine. The output of the PWM
circuit was wired back to the NI 9411 for high pulse and period measurement. To find
the duty cycle from the signal the high pulse width was divided by the period and
multiplied by 100.
PWM Measurement (Figure 6)
o
Current Sensor: This Hall Effect sensor is used to measure the amount of current being
drawn by the DC motor. The 2AWG wire which carries the motors armature is passed
through the sensor closed core structure. As current increases a stronger magnetic field is
generated causing the Vout of the sensor to drop by about 5mv per amp. The voltage is
passed to the NI 9205 for signal condition and calculation of current in Labview using the
simple linear relation between the sensors voltage and the armature current.
Current Sensor Configuration (Figure 7)
o
o
NTC Thermistor: A negative temperature coefficient thermistor was used to measure
the temperature of the motor driver IBGT transistor. The thermistor was connected in
series with a 5KΩ and the voltage was measured over the thermistor. As the temperature
increases the resistance of the thermistor decreases along with the voltage across the
device. This voltage is read into the NI 9205 analog input module and temperature is
calculated in Labview using the B parameter equation.
Voltage Monitor Sensor: in order to measure the voltages of the 10 snowmobile
batteries an electro isolator voltage step reduction circuit was developed. Originally each
battery was to be measured differentially across the terminals. Concerns were raised
since the NI 9205 has a max input voltage of 10v while the Open circuit voltage of each
lead acid battery is 13.2v. Therefore the voltage will need to be stepped down linearly in
order to be within the range of the modules input channels. Additionally noise was
another consideration as the DC motor generated large amounts of back EMF and high
frequency noise. To perform the task of electrical isolation and voltage reduction
optoisolators were used. The following circuit diagram shows the left battery side of the
circuit is isolated from the right side by a dielectric medium. With large battery voltages
the output voltage a V is relatively small as the transistor is driven on. When the battery
voltage drops lower and the transistor effectively off and Vout is pulled to Vsupply. The
voltage at the output of the transistor is linearly related to the battery voltage at the input.
The transfer function of each optoisolator was found and an equation was derived for the
battery voltage as a function of the output. Measuring the voltage at the transistors
collector we could solve for the batteries voltages.
Opticoupler Circuit and Voltage Output (figure 8)

Isolated Grounds
A major concern with an electrically noisy device such as a DC motor is the possibility of damaging
or inducing error in a sensitive embedded system. To prevent noise coupling to the cRIO’s sensitive
modules, measures were taken to retrain accuracy and safety of our devices. The motor and battery
bank of the snowmobile is electrically isolated from that of the PWM driver circuit, cRIO embedded
computer, touch panel module and various sensors. The battery bank and motor are floating as they
are not grounded to the vehicle chassis. The sensors, data acquisitions and displays are grounded to
the chassis using metal grounding strips. All signals that flow between the two systems are optically
coupled preventing noise from propagating from the motor.



Voltage Regulator:
Two 12V batteries were added to the front of the snowmobile to power the electronics.
These batteries powered a voltage regulator, which outputted a constant 12V and a constant 19V.
The CompactRIO and touch panel ran off of the 19V signal, while the sensors ran off of the 12V
signal. The sensors’ output was dependent on the input voltage, so if the input voltage varied, the
output from the sensor would not be consistent. The voltage regulator provided constant
reference voltage, ensuring accuracy in the data.
Warning LEDs:
The CompactRIO contains an analogue output module. This module was used to power
warning LEDs that notified the user of potential hazards. The motor batteries, PWM battery, and
IGBT temperature each had their own warning LED. When the voltages of the batteries got too
low, the CompactRIO sent out a signal that caused green LEDs to start blinking. When the
temperature of the IGBT became too high, the controller powered a red LED. The LEDs are
located right next to the touch panel display, making it easy for a user to see when they are lit.
These LED are an important safety feature that prevents potentially hazardous situations.
Generator
The generator provides the user with an emergency backup charging system. It is able to provide
3KW of power for 2.5 hours under full load and will allow the user to charge the batteries enough
to return to safety and avoid being stranded in the woods. The charging system plugs directly into
the generator as a substitute for the wall outlet as the generator provides the same AC input
signal.

Charging Circuit/System
Two important factors come in to play when designing a battery charging circuit. For the system
designed for this particular snowmobile, both voltage regulation and current limitation proved to
be staples of the design specifications.
o
Voltage Regulation: A regulated voltage was necessary since under certain
circumstances the batteries would have different voltages in addition to different internal
impedances. One of the significant benefits in terms of application for using the optima
Yellowtop batteries is their extremely low internal impedance. This was an important
trait to strive for since the “series” internal resistance of the batteries would essentially be
negligible when driving the motor. It does however cause an issue when charging since
the batteries act almost like a short circuit. The regulated voltage was achieved using a
fairly simple configuration which employs a high power Darlington transistor with a base
voltage biased using a zener diode. The zener diode was selected to hold the base of the
transistor at thirty volts which regulates the emitter voltage to be thirty volts minus the
characteristic base-to-emitter voltage. This left the approximate regulated output voltage
at 27.8 volts. Another important part to account for is the turn-on current for the base of
the transistor. The datasheet for the particular transistors used showed that the base
required eight milliamps in order to function. This base current was generated by
connecting the collector to the base with a 2K ohm power resistor. This allowed for an
adequate current to enter the base and operate the transistor properly. With the desired
output voltage achieved, the final aspect to account for was the current limiting.
o
Current Limiter: Not only was it necessary to limit the current for safety purposes and
to prevent the circuitry from overheating, it was important to think of the real life
application of the charger as well. A standard wall outlet operates off a 30 amp breaker
which, if exceeded, trips and shuts off that network of outlets. Ideally, the current for
each charging circuit would not exceed 6 amps in order to accommodate the circuit
breaker issue in addition to matching the power specifications for the emergency
generator. Again, a Darlington NPN transistor is the focal point of the circuitry used to
achieve the desired current. A 2K ohm resistor connected to the base and collector
provides enough current to turn on the transistor. Unlike the voltage regulator, the current
limiter employs standard diodes to connect the emitter to the base. A .3 ohm sense
resistor was selected at the output of the emitter which provides a reference voltage for
the diodes. As the current through the transistor increases(which also flows through the
sense resistor) the voltage drop over the sense resistor also increases. Once the
combination of the voltage loss over the sense resistor and the base-to-emitter voltage
matches the forward voltage of the two diodes that connect the emitter to the base, the
diodes then begin to conduct. With the diodes conducting, there is essentially a short
between the base and the emitter which draws current away from the base of the
transistor. Since the transistor operates by generating a current gain from the base current,
the output current is limited due to the current into the base being reduced by the
conducting diodes. See attached schematic diagram:
Q1
ZT X605
Q2
ZT X605
R9
.3Ω
R8
2k Ω
V2
120 V
D1
D2
1N 4938
1N 4938
R2
R6
2k Ω
5Ω
95%
Ke y =A
D4
B ZV 90-C30
D3
1N 4938
V1
24 V
Charging Circuit (Figure 9)
Conclusion
Through the completion of the snowmobile project mistakes were made and lessons were
learned. As a team we struggled in the beginning to find a way to work effectively together but
by the second semester progress had become very efficient. The biggest problem at the start was
finding individual task to assign to everyone so we could work independently without tripping
over each other. By working in parallel as much as possible tasks were accomplished
exponentially faster. Working independently is not without its faults as many times team
members needed components from there project to be compatible with that of another. Through
the practice of good communication many of these compatibility issues were reduced or avoided
outright. Scheduling was another issue as there were times when parts hadn’t arrived which
were necessary for the continuation of the project. These issues were ironed out by transitioning
our resources to other tasks which could be completed while these parts were shipping. Staying
flexible throughout the project was a critical skill that we learned early on. Often time simple
tasks or shipping of parts would take much longer than we ever expected. Staying flexible
allowed us to focus our energy elsewhere in order to maximize our working time. Compatibility
of components was also a serious issue as many sensors and circuits required conditioning before
there functions could be performed. For example the open circuit voltages of the snowmobile
batteries were greater than the max input voltage to the analog input module. The biggest issues
we ran into in terms of system functionality was getting the touch panel to talk to the
CompactRIO. After spending a good amount of time writing code and debugging the problem a
simple call the National Instruments solved all of our problems. Critical software which was
supposed to ship with the touch panel never made it on the system which was necessary for
communication between the CompactRIO and touch panel module. Other issues on the project
were heating issues with the charging and voltage regulator circuits. These problems were
solved with heat sinks and proper airflow allowing for longer operation of the systems. As our
team continued a project built the year previous, lots of debugging needed to be completed to
determine the functionality of the included systems. Overall this project has taught us to work
well independently or as a team effectively and efficiently.
Contributors
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University of New Hampshire
UNH Parents Association
UNH ECE Department
UNH Energy Club
Dr. Gordon Kraft
Dr. Barbara Kraft
Vincent Pelliccia
Kevin White
Tom Reis (Substructure)
Stephen Doran
Luke Vartuli
Doug McMillan
Lesley Yu (National Instruments)
Generator Connections
Daniel Mooney
Adam Perkins
Joyce Perkins
Kathy Reynolds
Future Project
 Automatic charging of the batteries using the generator when the voltage levels drop too low
 Charging with alternative systems such as regenerative breaking or solar panels
 Emergency communication systems
 Increase operating frequency of PWM to reduce noise