I make something for use in swimming pools out of plastic plumbing pipe, but
a fellow I was talking to last night had a more demanding use; design
suggestions, and perhaps pointers/offers to manufacture would be
This fellow needs to have video camera underwater, salt water, on device
that is moored to the bottom on cables. The device is mobile, and the
maximum depth is around 30 metres, with a video cable run of about 100
metres. Currents range up to about 10 knots. There could be a bit of
turbulence, rocks, and general knocking about.
Off the top of my head I was thinking that a small surveillance-type camera
with a flood light and some sort of video amplifier, all mouted in a small a
stainless steel tube as possible, caps and an end window for the camera &
30 metres depth is about 100 psi, so sealing will be an issue, but this
should just be proper design and workmanship, not innovation.
100 metres of a video run seems like a long way, and as well I do not know
if the video cable will be exposed to salt water; probably not, but the
possibility should not be ignored.
Mounting the device: would welded ears on the tube be likely to fail given
the environment, materials, and forces? Or would it be better to have some
sort of clamp to grab the tube?
There seems to be a need for more than one of these, and although I guessed
a figure of $1000 for a cheap proof-of-concept unit, the fellow didn't
seemed worried about sums in that range.
Back in the 70's and 80's when I was big into scuba diving, they had
housing already made to fit the most popular cameras, as well as
generic housings. It takes a heap of light at most any depth, lots
more than what is needed above surface........All the housings I have
seen were always a one piece body that was molded, with access cover.
I would think that any solvent welded joints no matter how well made
are going to be the weak issue. I owuld check on the web for already
made housings. They have come down in price considerably over the
Put some color in your cheeks...garden naked!
"The original frugal ponder"
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30 meters of depth is only about 50 PSI of pressure. Surveillance
cameras only need a small window. This should not be difficult at
all. You'll want to purge the housing with dry nitrogen (or argon
from the TIG welder) before sealing, to avoid condensation at cold
depth. I'd put a dessicant pack in there as well.
Attenuation of RG59 cable is only about 1 dB/100 ft at video
frequencies. You shouldn't need a video amp.
I would not house the light with the camera because of thermal
considerations. Use a dive light that is already packaged for depth.
The light is probably the more difficult problem, and many models are
How many do you need? I can supply them by the car load.
"Pax Americana is a philosophy. Hardly an empire.
Making sure other people play nice and dont kill each other (and us)
off in job lots is hardly empire building, particularly when you give
them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you
for torturing the cat." Gunner
I just saw a piece on our local news last night about a couple of guys
who build homemade underwater ROVs. Most of the parts are PVC plumbing
fittings, available at the local hardware store.
I have some 1.25" Schedule 40 that is rated for 370 PSI. That's internal
pressure. It might be good for even more externally.
--If it's going to get bumped or dragged along the bottom
you'll want something tougher than PVC pipe. Under pressure with a
pointy side load it might collapse. Also there's the matter of the end
caps. They'll need to be thick and at least one will have to be
removable. The traditional method is to have it screwed onto a housing
that has sufficient surface area on the sealing edge to accomodate an
O-ring in a groove and a dozen threaded fasteners. Best way to do this
would be to lay up your own housing using fiberglas.
I've got a buddy who used to make camera housings and that's
the way he did it. IIRC he used threadserts in predrilled holes to hold
the faceplate bolts. A light bar could be attached in a similar way
with threadserts in other parts of the housing. The O-ring groove was
molded in as a half-round groove by using half-round dowel glued around
the base of a male plug mold.
One great advantage of a fiberglas housing is that you can make
it conform tightly to a specific camera shape, so that ballasting is
not as big an issue.
I would be cautious about using stainless steel. Might be okay, but
without disolved oxygen in the salt water, stainless corrodes.
Powder coated aluminum would be better.
Recommend using both piston and face seal orings on the end caps. You
don't need much to keep it together.