The electrical system consists of everything inside the main tube. Although we use mostly pre-manufactured products, this year we added custom PCBs for our PID and hydrophone PICs.
Here
are the main components that makes up the electrical system:
Compass
We have been using a Precision Navigation compass for
three years. Our compass is the TCM2-50 and has proved to be very
resilient and accurate, correcting quite well for both tilt and
the strong magnetic fields present within the submarine. When operating
in fast mode, it provides more than enough data to keep the heading and pitch
control of the submarine quite responsive.
Speed Controller
Novak Super Roosters. Rated for 150 amps of current and
are reversible. The roosters are based on a reliable H-Bridge and are
controlled using RC pulses. Their original purpose is for RC Car
Electric engines, however these are more than adequate for our trolling
motors and have worked flawlessly as long as they are kept dry.
As a result of the huge currents that are being switched, the
controllers generate considerable heat. To accommodate this we mounted
them to the rear aluminum cap in a fan formation. This allows the
controllers to dissipate as much heat as possible through the aluminum
to the cooler water, though in the past we have found that the
controllers continue to function normally in extreme heat (150+ F).
Pressure Transducer
The pressure sensor is embedded in the back end cap to expose the pressure transducer to the water. It transforms the mechanical pressure of the water into voltage readings, which can then be used to calculate the depth of the submarine. This year we perfected our calculation by setting the sub at various depths underwater, getting 16 data points, plotting these and using linear regression to come up with an equation that correlates the output to the actual depth in meters. The regression line came surprisingly accurate, with an r-square (a statistical term for "goodness of fit") of 0.998--the value of a perfect fit being 1.
Serial to Servo Board
Mounted
to the connector plate is an off-the-shelf serial-to-servo board made
by Scott Edwards Electronics. This board takes serial commands from the
control board and converts them into appropriate PWM servo signals that drive
the Novak speed controllers. In addition, it drives the relay that
controls the marker-dropper.
Battery Pack
The battery pack is stored under the rack board in the tube. We use two 14.8V Tenergy batteries with 3150 mAh capacities wired in parallel for extended battery life. These batteries allow the sub to continue with its mission for at least 1 hour at full power, longer during normal mission conditions. These batteries were selected for their high discharge rate, which allows for the motors to draw the considerable amounts of current for normal operation and the current spikes during start up.
