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Old Mar 30, 2011, 12:52 AM
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Joined Mar 2011
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First ROV - Questions

Hi Everyone,

I've decided to build a ROV for the final project of a class and wanted to just voice my ideas and a few questions so I could get some advice from people that actually have a good idea of what they are doing. First of all, all the ROV really needs to be ale to do is operate in the pool on campus to show my professor that it functions, however I would eventually like to be able to use it in the ocean, down to 200 ft (deeper would be great though) when I am out fishing.

So here go my ideas: The system would be run from laptop, hopefully using a joystick. The ROV would be connected to the surface by Cat5 cable and some sort of cable that would provide power to the ROV (what gauge would be appropriate here?). The ROV itself would be propelled by 4 brushless motors positioned to provide forward/reverse, swing left, swing right, and tilt up/down. I am also concerned with using the brushless motors openly in the ocean, however I've found no cost effective solution (I thought about magnetic couplers but couldn't find a reasonable price) with a sealed motor that would function at a depth of 200 ft+. I would feel much more comfortable if the motors were sealed. I know each motor needs to be controlled by an ESC and I was thinking of using a reversible one, which would allow me to work with less motors. Can 4 ESC's (the one I list below for example) be powered from a 12V surface source? Also, just to make sure that I understand, you provide power to the ESC and hook it to the motor and also hook the ESC up to something else which then tells the ESC how to control the motor? This is what I really need to understand because the main idea of the project, at least for the class, is designing the circuit that will interface with the computer and control the ROV. Beyond the motors I would like 2 lights and a camera. I was thinking of these lights (http://www.ledssuperbright.com/3w-le...e-module-p-218), which would also need to be wired into the circuit controlled by the computer. I was thinking of this camera (http://www.overstock.com/Electronics...id=123620#none) which I would just feed the signal up over the Cat5 to the laptop. However, if anyone has suggestions for a camera that could pan and tilt and how to interface and control that I would be interested.

These are the motors I picked (http://www.hobbyking.com/hobbyking/s...dProduct=16229) paired with this ESC (http://www.hobbyking.com/hobbyking/s...dProduct=11742) tipped with this propeller (http://www.hobby-lobby.com/55mm_prop..._2943_prd1.htm). Any advice on these selections would be great.

Also, any recommendation in terms of the frame that I should put this all on? At this point I'm thinking of just building an aluminium frame and mounting everything on that.

All help is much appreciated!

Thanks in advance,
Nick
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Old Mar 30, 2011, 02:08 AM
NeverAgainVolunteerYourse lf
nick_75au's Avatar
Australia, QLD, Regents Park
Joined Mar 2007
3,725 Posts
Hi,

Build one for the pool first, look for the book "how to build your own underwater robot" and use the designs in that, you can then design the deep water one.
http://www4.rgu.ac.uk/eng/robotics/page.cfm?pge=19897

I have got 2 of the ESC's they are fine and the motor is a good match, but the prop is too big for 12 volts go for around a 40-45 mm 3 blade prop that has rounded blades, Like this

http://www.hobby-lobby.com/40mm_l_100_prd1.htm

If you run on 6 volts the larger 55 mm prop will be ok.

ESC's require a PPM signal, usually provided by a receiver and transmitter from RC equipment, for shallow operation you can even control wirelessly provided its NOT 2.4 Ghz equipment.

200 ft needs 2 AWG wire at 12 volts to get away with reasonable voltage drop, most ROV's use 250 volt and higher over long distance wiring.

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

Better to put power in the ROV and leave control at the surface.
For the pool version you can get away with surface power on light gauge wire

Brush-less ESCs do not tolerate voltage drop well so on-board power is better for this reason as well.

Hope this gives you a start,

Cheers
Nick
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Old Mar 30, 2011, 12:17 PM
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Joined Mar 2011
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So what exactly would I have to do to control the ESC's via the computer? Also, what if I were to send 120V AC down to the ROV and then use a transformer to provide 12V or 6V DC power? Or is it better to start with DC and use a boost converter on the surface and send higher voltage DC down to a buck converter on the ROV to give me 12V or 6V DC. I'm just kind of hesitant to put power on the ROV, what type of run time would I get from that with a reasonable number of batteries onboard? Maybe the battery route would be more cost effective and simple.

Thanks for the help Nick, I really appreciate it.
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