Homebuilt Rov Forum

Exploring the Hobby of Building your own ROV - Imagine, Create, Inspire.
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 Post subject: Re: My "MINIRAY" Rov.
PostPosted: Jul 11th, 2017, 3:19 pm 
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Joined: Nov 28th, 2011, 11:24 am
Posts: 103
It's been a while but I'm back at it...
Took Miniray for a swim in a hydro electric reservoir at the weekend, the glen was flooded in the 1960's to create the reservoir and the water levels are really low at the moment so all the old bridges, roads and just the chimneys of a house are exposed so we threw the ROV in for a look.

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here's a couple of snapshots from the video footage of a submerged bridge.
Visibility was pretty poor as the water is full of peat and stirred up vegitation
so the video was 28 mins of bad vis with the occasional something worth seeing.

spot the fish.
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Under the bridge with daylight showing on the far side.
Image

keystones of the bridge.
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 Post subject: Re: My "MINIRAY" Rov.
PostPosted: Jul 18th, 2017, 7:13 am 
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Joined: Nov 28th, 2011, 11:24 am
Posts: 103
Is there anyone still out there???? Forum seems very quiet!!!!
After my last outing I decided to do something about my interferance on my video signal.
I previously had two thruster power lines, one electronics power line and a common ground wire in my umbilical.
BUT due to volt drop on the ground wire when running 3 thrusters (6A+) I was getting a lot of motor noise on my video.
So I've re-wired my system to use one thruster power wire, one thruster ground wire, one electronics power wire and one electronics ground wire, grounds are not common at the ROV end, only at the top side.
This sorted 99% of my interferance but increased my volt drop over the thruster power wires as the current for all three thrusters is now on one pair of wires, I'm thinking of increasing thruster supply voltage to 18v to overcome that.
We'll see how that affects the current though. more volts= more current= more volt drop = more heat in the cable warming up the water.
The diagonal lines on my video (see stills above) turned out to be generated by the SD card recorder putting shit on the electronics power line, rewiring it's supply so it's closer to the battery terminals has got rid of most of it.
I have a lighter tether design in the pipeline too as I have tether drag issues...
oh well.. onwards and downwards.
I'm planning on doing a dive on a submerged house this weekend.
Fingers crossed for good vis.
Anyone else doing anything?


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 Post subject: Re: My "MINIRAY" Rov.
PostPosted: Jul 20th, 2017, 4:13 pm 
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Joined: Nov 28th, 2011, 11:24 am
Posts: 103
I've been looking for a suitable sized parspex dome since I started this build about 5 years ago and one finally came up on e-bay from a company called "project plastics".
70mm dome diameter, 3mm thick and has a 10mm flange, sounded perfect and at only £7.50 it had to be worth a try.
It arrived today so I've been having a play with it.

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It's not optically perfect but at that price I'm not surprised and it doesn't show up much once you're under water.
I had to add 250g of ballast to overcome the dome's bouyancy (8 M12 stainless nuts) so the extra drag of the ballast might over-rule the reduced drag from using the dome, we'll see on sunday. also see below.
Of course, with the flat face plate I could mask the ring of led lights from reflecting off the perspex and back into the camera, I can't do this with the dome so the lights are useless but the camera has excellent low light specs and at the depths i go to i don't need them anyway.

Depth rating wise, a similar camera dome port 3.5" diameter and 3.8mm thick is rated to 750m with a 2:1 safety factor so I think I'm totally safe down to a couple of hundred metres or more and I don't go anywhere near that.

I also found someone selling 3.5" pump gaskets so I got a couple to try, they're quite thick at 4mm but I kept having to replace my old ones every time I opened the pressure hull as they were soft neoprene. These are much stronger and seem good.

Thinking about drag....
drag coeficient of flat plate = 1.17
drag coeficient of solid hemisphere = 0.42
Ok so there's more to it than that because of the shape of the hull, bouyancy, thrusters etc but you get the idea.


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