SeaPerch Remotely Operated Vehicle, Construction Manual, Page: 100 / 110

SeaPerch ROV Construction Manual
– Version 2010-04NW
T-2
Closed-Switch Tests:
With the continuity tester or meter connected, close each switch, one at a time,
to check for continuity through the thrusters. A typical thruster has some
electrical resistance, but little enough to allow a continuity tester to indicate
continuity. An ohmmeter should show a relatively low resistance, typically from
about 10 to 50 ohms. Conduct this test for each pushbutton switch (if used) and
for the two
“on” throw positions of each toggle switch. If the resistance reads
near zero on an ohmmeter, that indicates either a shorted thruster or another
short-circuit wiring problem in the control box or tether cable. Solve the problem
before connecting power to the ROV.
Testing for Proper Thruster Operation:
After passing the tests above, it is time to connect the ROV to its battery.
Connect the two power leads (the alligator clips or the quick-disconnect
terminals) to the appropriate positive and negative terminals of the battery.
Then, close each switch, one at a time, for each pushbutton switch (if used) and
for each throw direction of the toggle switches. The propellers should spin
counter-clockwise (looking into the end of the shaft) when the controls are
switched to the “forward” position for the horizontal thrusters and for the “down”
position of the vertical thruster. If any thruster spins in the wrong direction or
does not spin properly, see Appendix A
, “Troubleshooting Your SeaPerch ROV”
for some common solutions. Students should try to solve the problems on their
own before using that aid, at least until running out of ideas!
Ballasting and Trimming the ROV
Understanding Neutral Buoyancy:
ROVs work best when they are nearly neutrally buoyant, with a slight positive
buoyancy to enable them to slowly return to the surface should they fail. An
ROV is neutrally buoyant in water when the force exerted by its total buoyancy
(due to the vehicle’s own buoyancy plus any added flotation materials) pulling it
toward the surface is the same as its total weight (due to the vehicle’s own
materials plus any added ballast materials) pulling it down by gravity. By being
neutrally buoyant, not tending to sink or rise, the ROV can move through the
water based only upon the power applied from its thrusters. However, the total
mass of the vehicle compared to the power of its thrusters is also an important
consideration. Even a massive ROV that has lots of flotation matched with lots
of ballast can still be neutrally buoyant, but that large mass may also be difficult
to move using the relatively small thrusters employed for SeaPerch ROVs.
The general goal for adding flotation and ballasting is to keep the ROV
reasonably nimble and responsive to its thrusters, whether moving about
horizontally or lifting a payload vertically.
Minimizing the ROV’s
total mass as
well as its in-water drag , which is addressed in the next section, will help in
meeting this goal.