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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

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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

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.

Vertical Thrust

Pool Testing

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

Derrick Brown

Dominique Corriveau