ROV Tether Voltage Considerations

[pcolaboy]

I'm currently experimenting with building a small ROV to check out several sites as deep as 100 feet. I have the overall platform built and I'm now working on the electrical and control systems. I'm using three 600gph bilge pump motors with the housings removed and a ducted fan installed for each. I will have an array of 4 smallish LED lights on the front as well as a small ccd video camera. I haven't calculated my amp requirements yet but my main concern will be voltage loss on the ambilical.

Can anyone suggest a good way to calculate how much voltage loss to expect on a given conductor size at a given distance? There may be other questions I have overlooked so please fire away with the advice.

Thanks,

Pcola

 

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[ScubaDude]

http://www.powerstream.com/Wire_Size.htm

Look past the tables and there is a calculator below that may help.

 

[rgecy]

Scott,

Depending on the wire size and voltage requirements, what I would suggest is bumping up the voltage and reducing it at the rov. I had a 100' umbilical and used 12/2 stranded for the power, cat5 for controls and was sending 18 volts down for power. You could even go smaller on the wire size and bump it up to 24 or 48 volts. Just remember, you will need some way to cool the heat sinks. They will get hot when you start drawing a lot of amps through them.

Have you been reading at the Yahoo ROV Groups http://groups.yahoo.com/group/robotrov/?yguid=195345130

I have some ideas for you. What bilge pumps ae you going to use? Just remember, they are only good to around 30-40'. I flooded mine at 60'. The water came in through the bilge pump wires and flooded the housing. I have since taken it mostly apart, but have some left over components. It really didn't do good in any current, and pretty much every where I dive there is a fairly strong current.

Robert

This picture doesn't have the floats installed, but you can see the basic design.

 

[pcolaboy]

Hey Guys,

Thanks for the great link and information!

Robert, I totally forgot you had built an ROV :-). My thruster motors are simple 500 gph replacement bilge cartridges (essentially the pump motor and impeller without the housing). I had worried about the wire entry becoming flooded so I have epoxied where they enter the housing - I'm not sure if this will give me better depth or not but the bulk of my work will be less than 30' anyway.

I'm probably going to use heavy duty trailer wire (6 conductor) for power coming down the tether - unless you can think of a more economical method. The two horizontal thrusters will have their own conductor set drawing less than 4 amps each. I'm hoping to be able to share the vertical thruster's conductor set with the lights and camera depending upon the combined amp draw. The camera I'm going to use initially is a ccd board cam - ive got a spare Hi8 camcorder that I plan to build a housing for and mount once I get a good ROV working. I would imagine that the camcorder's field of view and resolution should be much better.

I will keep you posted as things develop. Feel free to forward me any other suggestions or do's and don'ts.

Thanks again,

Pcola (Scott)

 

[rgecy]

Here is the wiring diagram I used. The joystick is an 8 way controler turned so that when you push forward/backward/left/right it will actually push two buttons to activate the relays.

In the diagram, it shows a twelve volt battery, but 18or24v would be better stepped down to 12v in the rov. Power consumption will be an issue if you put lights on it like I did. By the way, the light design is pretty solid. They went to 60' no problem. The bilge pumps are the only thing that failed.

 

[rgecy]

Older pictures of first version using just the 6 bilge pumps. Last one is newer version with modified bilge pumps. From the first to the last is two years. Look at how much my son changed!

 

[Dinkydick]

Tether cable losses can be calculated using ohms law.

Hook your ROV (only the robot with short wires) and run it with all the electrical
devices attached and activated. Measure the total (maximum) current you require
at the operating voltage (ie 12 volt). Measure the resistance of the tether and apply
ohms law E=IXR. The voltage loss over the tethers' length can be calculated. Use
this figure in your overall power equation. Then select the best power source to
employ.

Dinkydick

 

[pcolaboy]

WHOA...Robert!!!! Thnx bro. That is exactly what I was looking for!!!! Yeah it's amazing how quickly kids change in just months, let alone a couple of years. My son is 5 1/2 and looking back at photos from his 5 year old birthday compared with now are just crazy.

Dinky....thanks very much for the suggestions. I will put them to work as soon as I get all my motors in.

Pcola