Let's Make Robots!

myROV version 2.0

Home made ROV for shallow waters

Update 11/9-2011

So I finally got a chance to take the ROV out for a test. I knew that there was a buoyancy issue as it floats to high in the water. So I took along a bag of small pebbles and some zip lock bags.
It turned out that I need an extra 700g of weight to get the ROV almost neutrally buoyant in the water. So I’m adding a bracket to hold some square plates that gives me 100g a plate.

The video isn’t all that great but it shows that the system works. Notice the bags on top with blue tape on.

 - end of update -

 

Update 13/9-2011

I have reprinted the brackets for the battery to accommodate two M8 bolts to hold my ballast weights. The ROV has now an extra 800g of ballast and now I only need some good weather to do a second test.

- end of update -

 

Some of you might remember my ROV project http://letsmakerobots.com/node/19254 that I made for my kids and me. It failed miserably as I never got the USB webcam to work over the 15m CAT5 cable and the whole project went on a shelf (it was destined for the bin, but I couldn’t bring my self to throwing it away).

As this is a complete rebuild I’m starting a new page instead of updating the old project. I hope that’s ok.

I felt that my initial design of having 40mm PP plastic tubing to hold the electronics and motors, and the battery below as power source and ballast where sound so I kept this design.
The webcam where replaced by a CMOS/CCD car rear view camera. That had the added effect that I no longer had to bring my PC along to view the video stream. So I bought a cheap 7” LCD TFT monitor and found myself a great case to mount it in.

There are plenty of room inside for my Arduino, power regulator and LiPo battery

And on the lid I have a spool for the cable


The drive system is still the same and uses my custom made stuffing-box / motor mount. They are still driven by the serial motor driver from Pololu http://www.pololu.com/catalog/product/1110 The motor drivers work great and I had no problem stacking two of them together inside the 40mm pipe.
I’ve also gotten a 3D printer sins my first attempt and could print out all sorts of stuff for this project.


One of my biggest problems with the ROV was how to get at waterproof connection to the CAT5 cable. I dident want to permanently mount the cable to the ROV so I got myself some waterproof connector and packed Sugru http://sugru.com/ around the cable and penetration. It made a solid but yet slightly flexible bond.

The pipe fittings them self are not glued together but there is a rubber gasket inside the fitting that makes it waterproof. On top of that I added some self vulcanizing tape on the joints to aid the waterproofing. On that several layers of paint.

Some more pictures of the ROV

I got it reassembled after painting today, but it has been raining all weekend so I’ll put up a video sometime next week (hopefully).

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Do you have the code?

Where did you get the water proof conectors?

It was somewhere on eBay but they were not that waterproof after all.

That is a lot of buoyancy to counteract!

However, great progress, Geir! Do you consider the first test as highly successful? It certainly looks that way in the video.

You should try to implement some sort of video recording inside the case. I bet that you get some cool images from below the water.

Andrés

It’s easier to add weight than flotation so that is no big issue. I’m reprinting the brackets that holds the battery so I get two M8 bolts on each side of to add weights. I have 10x 50x50x5mm steel plates that weigh 80g each so I can probably balance it pretty good.
So yes I’m happy with my first test run.
When it comes to video. I could probably split the signal that’s going to the monitor and record that. But that’s a bit in the future.
Thank you for your comments!

It looks cool indeed. It really surprise me the battery go underwater still working!

Filming underwater is not really clear with low-end camera. I tried to record underwater with GoPro but either the lake was too dirty that I can't see anything further than 20CM or the camera wasn't good enough.

Hi Geir,

Patrick linked me to this post and I had to leave a comment about your design. The exposed battery terminals is going to cause you major problems. In salt water, the battery will cook itself to death as if it was shorted. You can test this if you like. Mix table salt into water at about 1/2 cup to gallon ratio until dissolved. Strip some wires to at least .5" to replicate the same exposed surface area as your battery and put them in the water 1-2" apart and apply 12V from a bench power supply or something else that monitors current. You will get 1-2 amps current draw. I have observed this using water from my salt water fish tanks in a similar experiment.

In fresh water, the immediate danger of cooking battery isn't so bad, but there will be some current flow between the terminals. You might not notice it right away, but it will corrode your terminals on both the battery and your connectors over time, making you have to replace a working battery and redoing the connectors every so often.

I work for the Navy building robots, and one of the past designs of my base was a crawler or robot that crawled along the bottom of surf zones looking for things. One of it's power sources was just banks SLA batteries like this, but we had to seal the connections to avoid all the problems. We did it by erecting a box around the terminals with the battery already connected and sealing it all up with epoxy. This effectively gave them permanent pigtails and we used waterproof connectors to be able to swap them in and out.

Hi Madsci1016
So I did your experiment and my findings are not so bad.
In fresh water the current drawn was 2mA and in my saltwater solution it was just above 200mA. Nowhere near cocking the battery as far as I can see.
The exposed wire and distance matches my battery.

Fresh water

Salt water

Just out of curiosity I added a motor that draws 200mA to the power source. When the contacts were out of the saltwater it pulled 200mA. When I submerged the contacts the current only got to 300mA and not the 400mA that I expected. The motor where connected parallel to the contacts and not on the contacts them self.

Anyone care to explain this as ohm’s law is a vague concept to me :-)

Hmm, I may have given you a bad salt to water ratio, or there's more needed to simulate ocean water; here's what I measure when I do it:

About 700mA, using certified Florida Gulf salt water. I remember more the first time I personally ran this test for someone, but I think the exposed wires were closer, which makes a difference.

More importantly, look at the wires after only 30 seconds of exposure:

And a few minutes back in the air:

 

That's only 30 seconds of corrosion. Imagine the 30+ minutes I'm sure you would like to be down there. You will be replacing your battery and crimp connectors after every dive, if they even last that long. That 8.5 Watts of energy wasted is doing nothing but eating away at the exposed terminals till there is nothing left.

You can see (and hear) the reaction in this video: http://www.youtube.com/watch?v=1sAjw7vfNJ4

The reaction is almost violent, eletricity and salt water just don't mix.

Not to mention and enviromental concern for what the reaction is putting in the water. Look at my cup of salt water now:

I'm not going to put that back in my fish tank, would you?

Here's after a few hours of sitting, you can see all the junk left over from the reaction in the bottom of the glass.

Again, that was just 30 seconds. I don't think that will be healthy for the fish and life where you want to operate your ROV.

I have taken your advice Madsci1016 and sealed up my contacts and added a waterproof plug. The Sugru that I have used will set in 24 hours and should make a waterproof seal around the contacts. I also added some Sugru where the cable goes into the plug.