Changes to tether


#1

I updated my OpenROV to the homeplug adapter and changed the tether from the CAT5E cable to 200 ft. of 22 AWG one twisted pair. It was getting stuck on weeds in the pond because it sunk to the bottom. I then added wooden dowels every 24 inches to make it float. This didn't work either as it still gets stuck on the weeds that are near the top of the water. I have added a connector on my tether so it will be easy to try different wires for the tether. I used an eight pin microphone connector because I have a box of them and don't plan on being in salt water. I also figure the design will keep changing, so if this shorts out, I will just change it. I am passing 12 volts from a car battery down the cable to the ROV. My biggest problem is the tether getting stuck on stuff.

We need to find a good wire for the tether.

1402-tethermikeconn.jpg (141 KB) 1403-elechomelinkmounting.jpg (150 KB) 1404-elechousingconnectors.jpg (166 KB)

#2

John,

Thanks for showing us those mods. We're working on perfecting the tether setup here at OpenROV HQ as well. I plan to do some more extensive research and documentation on this stuff later, but to get your thoughts flowing, there are two things you may be interested in:

1. We (accidentally) discovered that a tether from an ROV can inductively couple with the tether from a different ROV if the two tethers are run next to each other, so that you can establish communication with the first without being physically wired to it. This may mean that slip-rings will not be necessary for a spooling tether management system.

2. I've been working on an idea to use silly putty to cover electrical connections that are submerged in water. While moving slowly, silly putty acts as a fluid and will flow into any volumes that are at lower then ambient pressure (much like something that is oil-filled to be liquid compensated). This way, there is no incentive for water to flow into those places, so connectors can be kept waterproof. Because silly putty is non-Newtonian, it will act more like a solid of moved rapidly, so this means you can access the connector easily without the mess of an oil-filled chamber. I had this idea several months ago and have built a few prototypes, but I still have to do more testing before really pushing the idea.

Keep us in the loop with your developments- this is really great to see!

Eric


#3

I think silly putty is an interesting approach and hope it works.

The only question that came to mind was temperature, ie you place the silly putty into the electrical connections at 24C, but water water temperature is 5C. Wouldn't the putty contract in the colder temperatures and thus allow water seepage?


#4

That's a valid question, and honestly I haven't experimented around that particular issue. I suppose my naive assumption was that since thermal expansion happens slowly, the silly putty would adjust for it at a speed that would not cause departure from the surfaces it's pushed against. More testing on the matter certainly is needed though. I'll let you know what we find!

E