Replies to This Discussion

Permalink Reply by Alasdair Allan on April 5, 2008 at 4:39am

You might want to look at these guys (http://www.dailyack.com/2005/08/autonomous-underwater-vehicles.html), and this homebrew ROV (http://techreport.com/forums/viewtopic.php?t=31609) for ideas.

The deployable surface pod idea, pretty reasonable, that's one of the ways submarines handle the problem, although it mostly for radio communication. But, the water wheel idea... that's a sub-class of perpetual motion machine, you can't build anything like that. It doesn't work...

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Permalink Reply by Neal Clark on April 5, 2008 at 1:42pm

There is a project at the University of Victoria you might be interested in (http://www.auvic.uvic.ca/).

Thanks,

Neal

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Permalink Reply by Alasdair Allan on April 5, 2008 at 5:21pm

There are various reasons to use a "retractable pod", aka a communication buoy. For instance what if the (autonomous) ROV can't surface? Then it can at least release the buoy to (hopefully) surface and broadcast its current position. Depending on the buoyancy systems used by the ROV releasing, and then reeling back in, a small buoy is going to take considerably less power than surfacing. From a military perspective a small buoy on the surface won't leave much wake, and that reduces the chance of detection. It also generally means that the Submarine (or ROV) can maintain full speed underwater while the buoy is deployed. Surfacing is time consuming, and the speed of a vehicle designed to operate underwater (like a sub) is usually severely reduced on the surface. So, basically, lots of reasons but they all sort of depend on what the (autonomous) ROV is designed to actually do... for a hobbyist point of view, because it's quite a cool way to do things?

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Permalink Reply by Neal Clark on April 5, 2008 at 5:28pm

There is no need to get nasty. I'm sure we can all agree that there were many concepts we didn't have quite right when we were 16.

You might want to look at this project for ideas.

http://www.cormp.org/glider/index.php

I would imagine you could do some really interesting things with a winged design and an air tank to refill the ballast tanks. A small tank could go a long way if the sub was carefully designed.

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Permalink Reply by James Ross on April 5, 2008 at 6:23pm

Simon, look into underwater gliders. They use very little power so you could run for days or weeks without having to recharge. They are rather slow moving, however, and don't do so well in currents.

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Permalink Reply by Nullified on April 5, 2008 at 6:38pm

Sounds like an interesting project. As far as the idea of using a water wheel to regain energy, if you give the energy to move the vehicle, then harvest the energy back you are only wasting energy. In an ideal situation (assuming everything is 100% efficient) you could regain just as much energy as you exerted to overcome the extra drag of the water wheel, but in practice you would be losing quite a bit of energy. But assuming you are not exerting energy to move the vehicle, then it could be useful, but to get any decent amount of energy out of it you would need it to be rather big. Which then causes problems when you try to move it the AUV yourself (with your own power) because of the extra drag of having a big water wheel. Overall it doesn't seem like a very practical idea.

As far as using cell phones for communication, those would only work within the range of a cell tower, unless you use a satellite phone. So if you're not using a satellite phone then your range would be limited to staying within cell tower's range.

For energy a combination of Lithium Polymer batteries with solar cells and a bouy seems like a good combination, or you may be able to harvest thermal energy from the ocean (I don't know much about it, but I know its been done).

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Permalink Reply by Alasdair Allan on April 5, 2008 at 6:52pm

I supposed you could have the 'deployable' wheel. It sits inside the AUV body shell until you deploy it into the current. If you have the AUV stationary (and somehow anchored) on the bottom in a heavy current with the wheel deployed you could (theoretically at least) recharge the battery, and if it sits (hides?) inside the AUV when its moving, then you don't have any drag problems. I think its going to be really borderline whether you could juggle volume vs mass vs power consumption to get anything from it though.

The easiest way to recharge a long range AUV at sea is probably going to be covering the top of the body shell with solar cells and then surfacing for a (potentially quite long) recharge. Of course, having vulnerable solar cells covering the external shell of a AUV produces a whole new set of problems.

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Permalink Reply by Simon Pan on April 5, 2008 at 8:24pm

Thanks guys,

Looks like cell phones and 'water wheels' are out of the picture

I will focus on this retractable buoy idea and possibly underwater gliding.I'll take a look at the links

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Permalink Reply by James Ross on April 5, 2008 at 10:33pm

Don't toss out the cell phone modem idea just yet. I've talked on a cell phone 5-8 miles from shore and I imagine they could work beyond that.

Satellite phone modems can get expensive. If you stay close enough to land, you might be able to use a cell phone modem.

Check out SparkFun for cellular modems. Some even have integrated GPS. http://www.sparkfun.com/commerce/categories.php?cPath=66_68

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Permalink Reply by Alasdair Allan on April 6, 2008 at 2:23am

Yup, depending on where you are in the world there is cell phone coverage a fairly long way out to sea. After all there isn't much to get in the way of your line of sight to the tower except a stray oil tanker. It's not a totally mad idea. After all you're not weight or size limited like an aerial vehicle. Adding yet another way for it to communicate isn't a bad thing, and the SparkFun modules are pretty cheap...

...Iridium kit, and air time, on the other hand really isn't.

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ModeratorPermalink Reply by Sgt Ric on April 6, 2008 at 8:18am

We have had disappointing results with Sat phones for real time video because of the packet transmitting method the carriers' use.

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Permalink Reply by Charles Peterson on August 13, 2009 at 11:58am

Has there been any movement on this topic in the past year?

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