Update on ROV Mercury

Published: March 07, 2011
Tags: rov mercury rov

It's been a while since I posted about anything at all, but about my ROV project in particular. Progress has been ongoing, though. I'll try to get fully up to date with this entry.

First of all, I've finally decided on a name for the ROV: Mercury, after the US's first manned spaceflight program. I've decided to name my first three ROVs Mercury, Gemini and Apollo, after America's pre-shuttle era spacecraft.

Now, time for some photos:

This photo shows the lower half of the ROV, now with all four of the bilge pump thrusters installed. The thrust from the pumps is directed using a combination of flexible plastic tubing and PVC pipe fittings. As luck would have it, the size of plastic tubing that fits snuggly over the outputs of the bilge pumps is also just the right size for 15mm PVC pipe to fit inside it very snuggly. At the back of the ROV is a small black plastic box which all the wires feed into, which is where the relays are housed. Once absolutely all the wiring is done (which isn't yet), I'll completely flood this box with melted candle wax, so that when it sets the entire things is totally waterproof. You can see a short "tail" coming out the end of the ROV. The plastic PVC end cap you can see at the end of this is the beginning of a screw-shut coupling I'm making from a PVC barrel union. This way I don't end up with the full 30m tether permanently attached to the ROV. You can also see some orange nylon rope running between the very beginning of the tail and the black box: this length of rope is slightly shorter than the lengths of cable which run from the box to the same point on the tail, so that if tether gets snagged on anything and the ROV runs right out to its full length, the nylon rope will absorb the shock of the sudden stop, rather than the cables. The two sets of thin red and black cable from the box to the front of the ROV will carry power to the lights. Also visible in this photo are two new lengths of PVC pipe underneath the mounting grid, which weren't included during the initial round of frame construction. These are where ballast will eventually go to keep the ROV neutrally bouyant.

Above is a (rather blury) photo of the camera I'm planning to use (on the left). It's designed to be installed in a car as a reversing camera, and I got it off eBay for $30. I had thought that a reversing camera would be ideal for use on a ROV for a number or reasons: they're small, cheap, designed to work in low light conditions, and they run off 12V DC. However, since getting one I learned of a few details that make them less than ideal: for one thing, they actually mirror the image, so that the picture on the screen can be interpreted in the same way as the image in a rear-view mirror. For another, many of them seem to super-impose a set of converging lines with distance gradations on them, rather than just giving you a pure image. So, not exactly an ideal solution, but I'm going to use it nevertheless. On the right of the image is a "balun", which converts the unbalanced signal from the camera into a balanced signal, suitable for transmission over long distances via cat5 or cat6 cable. The balun takes a BNC input and gives an RJ45 output, but the output on the camera is RCA, so I need to use a BNC-RCA converter.

This is a quick mock-up to give an impression of the camera housing. It's just going to be a shorth length of 90mm PVC pipe with endcaps, one endcap having a hole cut into it with a clear acrylic window over it. This will eventually be painted orange like the rest of the ROV.

This picture shows off some of the components of the lighting system, which I've not really started working on yet. At the far left is an Australian 10 cent coin (23mm diameter) to provide scale. To the right of this is a single 3W LED "star", which puts out 180 lumens. I don't really have any intuitive appreciation for the unit lumen, but apparently this is quite bright. To the right of this is a special constant-current power supply, or "driver", for the LED. The driver can power up to 3 LEDs in series, and carefully regulates the current delivered to the LEDs to maximise their lifespan. I eventually plan to have two drivers on the ROV, on to the left of the camera housing and one to the right, each powering a cluster of 3 LEDs for a total output of 1080 lumens. Hopefully this is enough to provide a clear camera image when deep underwater.

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