Download Technical Justification for the CompactRIO

AUTONOMOUS UNDERWATER VEHICLE
ADAM HEWITT
EDWARD MCHENRY
JAIME ENGLAND
COREY VAILLANCOURT
TECHNICAL JUSTIFICATION FOR THE COMPACTRIO
OBJECTIVE
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.
POSSIBLE OPTIONS
BASIC Stamp12
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
expanded.
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 in order to
control the vehicle on a rudimentary level; however, it while we would be able to use either
language for effective feedback control it would be much more diffcult to maintain in future
1
http://www.parallax.com/dl/cat/05Cat.pdf
2
http://www.wd5gnr.com/stampfaq.htm
years. In addition, the speed of the processor in the Stamp 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.
PROS
CONS

Inexpensive



Small form factor/ low weight
Up to 16 I/Os


BASIC or assembly programming
languages
Slow processor speed
Limited program size
Table 1 – BASIC Stamp Pro/Con
PLC
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.
PROS4
CONS

Good at turning outputs on or off based on
the state of inputs.

Not designed for reading and writing
databases.

Good at bringing together and
concentrating a lot of data and status that
is uploaded into a computer in a compact
form
More rugged than computers and typically
last five, seven, ten years without needing
replacement

Requires external hardware to handle
large amounts of data, complex data, or
advanced math functions.

Difficult to adapt for displaying data and
information to the operator

Best when used with external systems
for generating report data.
Larger form factor and inconvenient to
transport
Often require separate power cabinet
Not adaptable to changing situations




Table 2 – PLC Pro/Con
PC/1045
3
4
http://developers.cogentrts.com/cogent/cogentdocs/gl-defs.html
http://www.htservices.com/Tools/PLC/index.htm
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 may not be effective use of the team’s resources.
PROS6
CONS

Small form factor, 3.6x3.8”

Lacks storage space and processor speed


Relatively inexpensive
Stackable modules


Programs execute very slowly
Lacks data analysis capabilities

System is PC compatible


Aging and slow technology
Extensive research required to determine
necessary hardware and software.
Table 3 – PC/104 Pro/Con
CompactRIO7
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
5
http://www.pc104.org
http://www.htservices.com/Tools/PLC/index.htm
7
http://www.nationalinstruments.com
6
programmed on a hardware level with relative ease. Please see Table 4 for a list of pros and
cons.
PROS








CONS
Sample speed is at least 100kS/s
Size/Weight: Controller is only
7x3.5x3.5” and 3.5lb
Industrial Grade with international safety
certifications
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

Expensive
Table 4 – CompactRIO Pro/Con
RECOMMENDED CHOICE
The AUV Team recommends the purchase of a 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. 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. The expected cost of the PC/104, including software and all hardware is approximately
$1500. At this price point the AUV Team will have a fully functioning PC with data acquisition
capabilities.
Another important reason for the recommendation of the PC/104 is that it won’t only be an asset
to the AUV Team but possibly the Clean Snowmobile Team and other future projects. Since the
PC/104 is easily configurable both teams could be working on development of applications for
respective projects and the device could be changed as needed with the ability to use other PCs
to develop the respective applications in another Windows based environment. 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 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 a 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.
Regards,
The AUV Team