DIY underwater detector advice?

[bigkahuna]

Hi,

First post here. I have no previous metal detecting experience but am thinking about building a detector to be operated underwater by my mini remotely operated vehicle (ROV). Working depth will be less than 50 feet SW and the wire tether from my control station to the vehicle will be 100 feet long. This is an experimental project so I'd like to keep it low budget and simple. We have a lot of submerged wrecks in the area and the idea is to explore these visually and with the aid of a metal detector with the ROV. One thought was to buy an el cheapo detector, keep the electronics topside (out of the water) and mount the coil on the ROV, and then connect the two with a small, shielded cable. Of course I have no idea whether that will work so I thought I'd ask here.

I also see that there are a wealth of schematics and plans for DIY detectors on this website, would any of these be suitable for what I'd like to do?

Another consideration is the ROV itself, which has an aluminum frame as well as parts made from brass or stainless steel. How far away from the ROV would the coil have to be in order to minimize its influence? I studied the system offered by JW Fisher and it looks to be about 12 inches ahead of the ROV, does that sound about right?

Many thanks in advance!

[Carl-NC]

You probably want a pulse induction detector, so you will want the electronics at the ROV. The easiest solution is to buy a used PI; for example, a used White's Surfmaster PI can be found for ~$250 and is waterproof to 100'. Otherwise, you will have to build a circuit (~$50), get a loop (~$50-100), and then find a waterproof box.

Yes, 12" should work. The key is to have no moving metal nearby. Static metal is tolerable.

- Carl

[grungymike]

now that' a wild idea!!!

Hey is your ROV a Schilling Robotics system?

A coupla considerations...

1) All decent detectors I've seen have at least a coupla adjustments (threshold, gain, VSAT, etc.). Unless the detector is integrated with the rover, You'll have to adjust it as best you can on the surface, then submerge.

2) you'll need some kind of signal system, most detectors use an audio signal, some use lights, a meter, or a vibrator. This will have to be accomodated.

3) The cable length from coil to control box can effect performance on PI detectors, I don't know about VLF type. I would recommend focusing on the PI units, they're a better choice for that enviroment.

4) In order to do this right, I think you're gonna have to integrate a detector system into the the ROV system. Possibly repackage a Surmaster or similar, with audio or other ouput and possibly adustments piggybacked on your ROV control cable up to the control station on surface (on board a research vessel I assume). I suspect the Surfmaster case could handle the enviroment, but the board and case would have to be modified to accomodate the wiring harness going topside. I think the biggest challenge is going to be the control station interface.

5) The Surmaster is a simple rugged unit designed originally for beachcombing. Another possibility is the Minelab Excaliber (they say good to 200 ft, I haven't tried it...).

6) If you're up to building from scratch with an eye toward an integrated system, take a look at Carl Moreland's Hammerhead circuit (available on this site, look in projects). I'm building a land based version myself.


I'm looking forward to seeing how this project develops. it's a serious engineering challenge.

gm

[bigkahuna]

Thanks Carl and Mike. No, the ROV is not a Schilling Robotics, far from it. It's a custom mini-ROV of my design that I'm building. Size-wise about halfway between a VideoRay and a Seabotix, but more powerful than either of those. Our "research vessel" is an inflatable boat with outboard. I plan on operating in less than 50', most of the time probably less than 25'. We've got several hundred miles of protected sounds and estuaries to explore. This project is completely out of pocket so pretty low budget.

If I am able to extend the sensor's cable then I would run an extended cable to the surface and keep the controls topside, otherwise I'll package them in a watertight container and send the audio signal up the video feed from the ROV. I found a couple kit detectors I may give a try before moving up to a full scale detector.