interesting robot design idea

Idea 1 seems somewhat impractical. High power strobe lights and digital cameras could easily zap a battery in just a few minutes of use. That coupled with the low efficiency of present solar technology and your bot might have to bob around for days recharging.

Idea 2 sounds a little more practical, especially if the tether can transfer power. I'm not sure how well IR travels underwater, but presumably the deeper you get the worse the signal will become. Ideally, if your going to have a tether, it might as well carry data and power lines.

Both ideas in general make me a little nervous. As far as I know, there are no truely autonomous deep sea submersibles, and for a good reason. If the thing gets hit by a boat or eaten by a whale or suffers a simply malfunction, there'd be no one around to help it or even know what happened. There's a reason why many scientists consider the ocean a far more hostile environment than space.

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Hi Chris,

I think you misunderstood me on idea 2...I was still planning the camera/strobe module to be sealed and self contained and lowered with just fishing line, not a data or power carrying tether. Fishing line is cheap, strong and lightweight, and a deep see fishing reel makes a nice high quality winch mechanism. The IR transmission I was refering to was the method of transfering the data from the camera/microcontroller inside the sealed module to the floating mothership above, once it has been winched back up. At most this would be a few inches away from the mothership transmitter/reciever. Also, I don't think strobe circuits or digital camera modules would draw so much power that a suitable small high energy density battery would be out of the question. Maybe I am wrong about that though. Actually, I have no idea what type of picture you would get at great depths with a small strobe and camera...maybe all you would see is a few feet.

After reading about the rafos project

I am considering a borosilicate (pyrex) tube to house the strobe, microcontroller, camera, and battery. You can buy these tubes in something like 34mm diameter,

3mm wall thickness, 1 meter length for under $10 each. Pretty cheap housing for the components, and if the ends can be sealed very well, it should be capable of extreme depths. Perhaps if the strobe is placed at one end and the camera at the other end, with the circuit board and battery inbetween, the camera will not be as affected by the reflections from the glass. This would take some experimentation.

Dropping something off in the ocean makes me nervous too, and I also would not want to create a navigation hazard. I think keeping the whole unit very small and very cheap addresses both problems to some extent...the whole thing can be considered a gamble and not financially detrimental if it is completely lost, and the small size should not present a significant hazard to ocean craft.

There is at least one autonomous craft that travels many km over and under the ocean:

I would really like to know how they control bouyancy to 1000 meters! It is also fascinating that they can move at such speeds without any thrusters.

Rick

I understood you perfectly. I just don't see the point in *not* using the tether for power and data. It would allow greater range than IR and you wouldn't have to worry about your pod running out of power.

Unless you have an extremely bright light, you'd see almost nothing since water attenuates light quite rapidly. Naturally, sonar would be a more useful "long range" sensor. You could use it to activate your cameras once it gets close enough to an object.

It looks like they use a number of tricks to accomplish this. They're all summed up in their publications. First is the compressible hull, which helps match the surrounding density. Second is the pendulum-like shape. By regulating its displacement through compressible gas or ballast, and balancing this discrepancy between both ends of the craft, you could control descent speed and angle. The fins utilize this vertical movement and orientation to help produce directional thrust. The craft could turn by spinning a large weight internally.

The pressure at 3000 ft below sea level is about 1300 psi. Your lexan sphere may not implode, but anything inside it will be crushed if it isn't properly housed.

Every component needs to be pressure tested. You are very likely to find that anything with the least bit of air inside it will crush. Any intrusion through the hull is a likely point for catastrophic failure.

In outer space, you have the internal air pressure forcing it's way out. At

3000' below the surface, you have 3000' of water trying to get in.

If you build it, you should fill it with oil, then purge it in a vacuum to remove any entrapped air. Then repeat, and seal.

Hmmm, these seem to do ok, and have been for years it seems:

Obviously you have to make sure there is no intrusion into the vessel. This borosilicate glass (pyrex) is very cheap. I found a source of 34mm dia, 3mm wall, 1 meter lengths for $10 each. Not sure how to seal up the ends to withstand 1300 psi though....jbweld? :-)

Rick

I think it is very likely you will get problems with the fishing line solution. The oceans aren't empty and you will get old kelp and what not tangled in the lines. I guess there is also a risk your sphere might be eaten ;-) If you make the contraption really huge with high strength wire...and some device that can clear the vire when it reaches your floating device maybe....but then we are talking about a very different type of project.

/Peter A

rick wrote:

Yes, but those are floats. Not meant to be submerged at great depths.

From the Rafos site:

The glass pipe deserves special discussion. Borosilicate glass has a number of very attractive properties: it is transparent to radio waves, it is completely resistant to saltwater corrosion, as an industrial material it is widely available at low cost, it is strong, and it has a very small coefficient of thermal expansion. Its transparency means that the satellite radio antenna can sit inside the pipe, simplifying construction and increasing reliability; its extraordinary strength means that it can operate at great depth (as deep as

4,000 meters). The glass pipe is also very pleasing to the eye!

Rick

[...]

How do the Rafos folks do it?

I would look into building up my glassblowing skills if I were you.

none the less, polycarb is not borosilicate. One way or another, something cannot be compressable. If your housing is compressable , then the guts can't be.

I am sorry, but you are not making sense to me. Who said anything about making the housing out of polycarb?

"The same solar powered robot released into a good ocean current, but this time the main robot does not submerge, but rather a small sealed spherical pod made of lexan containing a small microcontroller, battery, light source and digital camera. "

Polycarbonate is generic for Lexan.

Anyhow, my friend at work did a lot of the design of Jake and elwood, the submersible craft that Jim Cameron of Titanic and Terminator fame used to photograph the titanic. Believe me when I say that the materials you choose and the methods of construction are critical. Generally, the smallest possible volume will be air filled. This will be a stainless steel pressure vessle, with a higly engineered hemispherical glass or acrylic portal, or a conical flat glass. This is generally reserved for the camera and recording instrumentation. The remainder will be hydrophobic plastics like UHMW polyethelene, and filled with oil.

Everything will be pressure tested, IC's, batteries, fiberoptic umbillicals, you name it. Anything with air in it will crush, and that change in internal volume can cause catastrophic results unless these factors are engineered in. Batteries may well be the most critical to test, especially Lithium primary or rechargable cells, since internal damage can result in overheating and possibly further damage. Even the optical deformation of the viewing ports is accounted for.

Leaks can be deadly to humans in close proximity during a run, and if you have a leak at 3000 feet, then bring it up to sea level, you have the potential of bringing up a vessle with an internal pressure of 1300PSI.

Granted he is building to go way past 1000m( closer to 4000m), but the safety issues are still pertainent.