AUTONOMOUS UNDERWATER VEHICLE
TECHNICAL JUSTIFICATION FOR THE COMPACTRIO
The Autonomous Underwater Vehicle (AUV) Team intends to procure an embedded controller.
The vehicle is required to control the motors, bilge pumps, and all of the sensory activity without
human intervention. The team’s aim is to introduce a controller for the AUV that will be easy to
program and have the flexibility to be expanded and/or reconfigured. The physical constraints of
the new control system include small size, low weight, a variable temperature and pressure
environment and the ability to operate on 12VDC power.
A BASIC Stamp is a microcontroller made by Parallax. This microcontroller has onboard
memory, a clock, and a voltage regulator on an integrated circuit. An external PC is required for
programming of the controller. Program size is limited by storage capacity that cannot be
Although the Basic Stamp is very inexpensive to purchase, we would be limited to using BASIC
or assembly as the programming language. It is possible to use BASIC or assembler y in order
to control the vehicle on a rudimentary level; however, it would be highly unlikely that while we
would be able to use either language for effective feedback control it would be much more
diffcult to maintain in future years. In addition, the speed of the processor in the Stamp is may
not be fast enough to adequately process the sensor data and convert that data into a motor
control signal depending on the sensors that are required for the 2006 mission. Please see Table
1 for a list of pros and cons.
Inexpensive BASIC or assembly programming
Small form factor/ low weight Slow processor speed
Up to 16 I/Os Limited program size
Table 1 – BASIC Stamp Pro/Con
A Programmable Logic Controller (PLC) is “A specialized device used to provide high-speed,
low-level control of a process. It is programmed using LD or some form of structured language,
so that engineers can program it. PLC hardware typically costs a lot of money, and often has
very good redundancy and fail-over capabilities.”3
In addition to the list above PLC’s do not have the capability to control or receive digital signals
as well as no camera functionality. Please see Table 2 for a list of pros and cons.
Good at turning outputs on or off based on Not the best at designed for reading and
the state of inputs. writing databases.
Good at bringing together and Not the best at Requires externamanl
concentrating a lot of data and status that hardware to handleing large amounts of
is uploaded into a computer in a compact data, complex data, or advanced math
More rugged than computers and typically Not the best at Difficult to adapt for
last five, seven, ten years without needing displaying data and information to the
Formatted: Indent: Left: 0.25"
Not the best Best when used with Formatted: Bullets and Numbering
external systems at for generating
Larger form factor and inconvenient to
Often require separate power cabinet
Not adaptable to changing situations
Table 2 – PLC Pro/Con
PC/104 is in many ways a small form factor PC which has been around since 1987. It measures
3.6x3.8” and can be configured in stackable modules, to conserve space. The current PC/104
unit contains a 486 class processor and 1 MB of onboard flash storage. Many different modules
exist on the market that can plug into the PC/104 for data acquisition and control. The PC/104 is
not an all in one package. One has to determine which extra modules are needed as well as come
up with a power solution within the voltage tolerances as well as storage for an operating system.
Please see Table 3 for a list of pros and cons.
A new PC/104 unit with a faster processor and more onboard storage would be required if the
team were to pursue this option. The current unit lacks capacity to install LabView software (350
MB required). In addition, a Pentium 4 processor is recommended to run LabView on either a
Windows or Linux platform. The cost required to procure the new PC/104 unit and other
associated hardware and software would may not be effective use of the team’s resources.
Small form factor, 3.6x3.8” Lacks storage space and processor speed
Relatively inexpensive Programs execute vaery slowly
Stackable modules Lacks data analysis capabilities
System is PC compatible Aging and slow technology Formatted: Bullets and Numbering
Extensive research required to determine
necessary hardware and software.
Table 3 – PC/104 Pro/Con
The CompactRIO is a reconfigurable controller manufactured by National Instruments. The
controller consists of one real-time processor and a chassis that can contain either 4 or 8 I/O
modules. The modules are hot pluggable and can be digital I/O, analog I/O or even Pulse Width
Modulation (PWM). LabView software is required to program the CompactRIO. The software
takes the programming process to a higher level by dragging and dropping objects and
connecting them with a series of lines to create the necessary loops. Also the controller can be
programmed on a hardware level with relative ease. Please see Table 4 for a list of pros and
Sample speed is at least 100kS/s Expensive
Size/Weight: Controller is only
7x3.5x3.5” and 3.5lb
Industrial Grade with international safety
Hot pluggable I/O modules
Regional consultant that travels to campus
Runs LabView as its operating system.
Reprogrammable at the hardware level
Data analysis and logging
Table 4 – CompactRIO Pro/Con
The AUV tTeam recommends the purchase of the CompactRIOa PC/104 controller. The vehicle
needs a feedback control system and the alternatives above cannot complete this task either
economically or due to hardware limitations. The alternatives lack data logging capabilities as
well as analysis. It is also important to note that the alternatives are based on aging technology
and are inherently slow. Also, the CompactRIO has an extremely intuitive program interface.
This will allow the AUV team to quickly develop the applications required with minimal time
loss due to the learning of another programming language. With today’s technology an easy
operating system such as Windows 2000 can be put on the PC/104. This allows for easy
adaptation to this new unit because all of the team members are familiar with the series of
Windows operating systems. Another advantage is that this allows the AUV Team to choose
what software package to interface with the sensor array. Because of these reasons, the PC/104
allows for more functionality than any of the controllers above. This allows the team to
accomplish more than if time had to be spent learning another language. The LabView software
that is accompanied with the CompactRIO has hundreds of complex math functions which will
allow us to use a variety of sensors with the AUV. The expected cost of the
CompactRIOPC/104, including software and all hardware is betweenapproximately $1500
$5,000 and $6,000. At this price point the AUV Team will have a fully functioning PC with data
acquisition capabilities. This includes a 75% discount on all software and a 10% discount on
hardware. There is also the possibility of receiving a grant from a company interested in the
automation of underwater robotics, and we are looking into the prospect of an increased discount
and possible donation from National Instruments.
Another important reason for the recommendation of the CompactRIO PC/104 is that it won’t
only be an asset to the AUV Team but possibly the Clean Snowmobile team Team and other
future projects. Since the CompactRIO PC/104 is easily configurable both teams could be
working on development of applications for respective projects and then the device could be
changed as needed with the ability of hot pluggable modulesto use other PCs to develop the
respective applications in another Windows based environment. and by executing the respective
applications with the onboard storage space. Also, due to the inexpensive purchase costs of the
unit, the Clean Snowmobile Team could purchase an additional unit and use the research the
AUV Team has done to speed up the development of their controller. It is also important to note
that the CompactRIO PC/104 is the most versatile out of the alternatives due to its industrial
construction and the ability to work with almost any sensor on the market today. With the
purchase of the CompactRIOa PC/104 it will allow Mechanical Engineering students at the
University of Maine to have access to controller technology of today which will make them even
more lucrative in industry.
The AUV Team