AUTONOMOUS UNDERWATER VEHICLE. overview. Control. Thrust Experiment. The ultimate purpose of the AUV is to participate in the annual International Autonomous Underwater Vehicle Competition sponsored by ONR and AUVSI. It takes
The ultimate purpose of the AUV is to participate in the
annual International Autonomous Underwater Vehicle
Competition sponsored by ONR and AUVSI. It takes
place at the US Navy SPAWAR Systems Center in San Diego (pictured). The competition
involves such tasks as locating bins on the pool bottom, dropping markers, locating sonar
pingers, and surfacing in an specified space. Participants in past competitions have included
schools such as MIT, Cornell, Virginia Tech, Duke, and many others. With continued
Success for UMaine’s AUV team, the possibility of participating in the next one or two years
is very good.
The bilge pump thrust experiment was performed to find the nozzle
size that would give the AUV the maximum thrust downward. A
digital scale was connected to the bilge pump, and a variety of
signals were sent to the servo control board from the Lab PC. This
caused the bilge pump to thrust downward over the range that would potentially operate at. The range
of signals was tested for each nozzle (ranging in diameters from ¼” to ¾”). The results gave a clear
indication that the ½” nozzle was the right one to use.
The control system for the AUV has beenthe
most important part of the work this year.
The concept is essentially this: the motors are
driven by motor controllers that run off a servo
signal. This signal comes from a servo control
board. The servo control board communicates
with a computer (which can be on-board or not)
via serial port. There are multiple programs
which can easily send servo signals to the
board, and it is also easy to do by programming.
This gives the sub excellent proportional
control, because the servo board gives 255
signals which would ideally give the motors 255
different possible speeds.
The computer used on board to control the
AUV is the Prometheus LC PC/104. A PC/104
is essentially a PC with a different form factor.
Due to the small size, PC/104s are widely used
in applications where there is a need for an
embedded programmable controller. The
Prometheus LC is has a 486 MHz processor, 16
MB of RAM, and 1 MB of Flash memory. Because the AUV must be
completely autonomous and powered by on-board batteries, a feature which
makes a PC/104 very desirable is the low power consumption. The
Prometheus uses only 2 Watts total power consumption.
The solution to the problem of propulsion proved to be
two small Sevylor SBM 12 Volt trolling motors. The
motors are light, and each provide about 15 pounds of
thrust at full speed. The motors were modified to fit the AUV’s needs and mounted to the
wings. Along with the control systems, these motors do a fantastic job propelling and
turning the sub.
The submersion problem was solved with two Attwood
12 Volt, 2.9 Amp, V750 bilge pumps. To get the
maximum thrust out of the bilge pumps, an experiment was performed to find the optimal
nozzle size. The idea is to get the AUV as close to neutrally buoyant as allowed by the
competition rules. Once that has been achieved, the bilge pumps have the thrust it takes
to submerge the AUV. The bilge pumps are located inside the hull, and have a
combination of rubber tubing and PVC piping to connect them to the nozzles at the front
and back of the sub.
The final work done with the AUV was the pool tests. On the very
first time, the sub functioned marvelously, exceeding any expectations
we may have had for it. The thrust of both the motors and the bilge pumps
were more than enough for what the sub needed to move around quickly.
It proved to have the capability to move forward quickly and turn sharply.
This gives the teams who will take this project on in future years a great
starting point. While the tests were not done with the computer on board,
it was the PC/104 running them. This means that with a little more
programming, the AUV will be able to run without a serial tether attached.
The AUV Team