SeaPerch Remotely Operated Vehicle, Construction Manual, Page: 102 / 110

SeaPerch ROV Construction Manual
– Version 2010-04NW
T-4
Ballast items can be attached to the ROV in various ways, such as using tape, tie
wraps, or fasteners such as screws or clamps. The weights can be attached to
the frame or to the payload net; however
, it is best to keep the front center area of
the net clear to enable the ROV to pick up items without interference.
Students should also consider how the tether cable affects ballasting and trim, for
different operating depths. At deep depths, or if a camera cable is paired with the
standard ROV tether cable, added floatation may be needed on the cable to
enable the ROV to surface.
Initial In-Water Testing in the Classroom, Lab, or Pool
Buoyancy Check:
A quick check for positive buoyancy can be made by pushing the ROV to the
bottom of a tank or even a large bucket (making sure to get all of the air out of
the pipes) and letting go. A properly ballasted ROV should very slowly rise to
the surface. Most initially pop up like a cork
. If it just sits on the bottom, it’s
time to re-evaluate ballast already installed and/or check the floats to make
sure that they have not leaked. Students should iteratively adjust ballast and
recheck their ROVs until near-neutral buoyancy is achieved.
Trim Check:
After attaining neutral buoyancy, it is helpful to quickly check that the ROV
sits level in the water. Simply hold it at a depth somewhere between the
surface and the bottom, let go, and observe it for a moment, before it floats to
the surface. If the trim needs adjustment, this is the time to do it, usually by
redistributing the ballast weight. If movable floats are used, they can also be
adjusted slightly, moved toward the front or back of the ROV to adjust its trim.
Thruster and Control Test:
Beyond getting the SeaPerch ROV properly ballasted and trimmed, the in-
water test provides an opportunity to make sure that its thrusters can drive it
straight and predictably, that it can dive and surface, and that the controls
work reliably. This can be accomplished in a swimming pool, a small water
tank, such as a water trough, or even in a bathtub. By placing the ROV on
the surface at one end of the tank or tub, there should be enough running
distance to observe whether it will run in a generally straight line when both
horizontal thrusters are switched on in the forward direction at the same time.
Similarly, a foot or two of depth is sufficient to determine whether the ROV
can pull itself from the surface to the bottom and back. The goal of the initial
test is to identify any thruster speed or mounting angle problems before
testing in open water. Plus, the test gives the builder a great feeling of
accomplishment (
the ROV really works! ).