My "MINIRAY" Rov.

[bigbadbob]

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 1950'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.



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.


Under the bridge with daylight showing on the far side.


keystones of the bridge.

[bigbadbob]

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?

[bigbadbob]

I've been looking for a suitable sized perspex 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.



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.

[bigbadbob]

We went back to the drowned house on sunday and paddled out to the chimneys.



and threw the ROV in for a look see.



this should be a video on flikr, if you click on it it might play. lol.

https://flic.kr/p/VSnYLn

I had a bit of bother with my video recorder so actually only got 3 mins out of an hours dive.
New recorder on order.
Saw a lot though and was well pleased.

[bigbadbob]

Today I added a thruster speed control.
It's a 20A brushed ESC driven from a servo tester.
As it's mounted top-side and controls the thruster power pair in the umbilical, it controls the speed of all thrusters at the same time. This shouldn't be a problem as when i use it to hover with the vertical thruster, I also want to reduce manouvering thruster speed as well.
The servo tester has a half speed switch position which might come in handy.
I'd like to change the servo tester firmware so i can have half power/full power/variable power. we'll see if that's possible.
I have to reduce speed control to zero at power up, otherwise the ESC will not run, however once the system is up I can set the speed and switch in different thrusters.

[bigbadbob]

I added my gripper today, it's pneumatic and operated by co2 from a bicycle tyre inflater.
I've threaded a 4mm polyurethane tube down my umbilical which helps float the cable as well as supplying the gripper.
The gripper is sprung to the open position and closes when pressurised.
I'll add a pressure guage to the top side unit so i can control the strength of the grip.





The gripper weighs almost 400g so I had to remove as much weight and ballast as possible from the hull and add the two red floats to get it back to slightly positively bouyant.

Will test it out in the pool soon.

[bigbadbob]

I decided to upgrade my bouyancy as I'd been using kingspan insulation skinned with gellcoat and it doesn't survive decent depths so I scrounged around and scored an old broken ROV umbilical float rated for 3000m.
I originally thought it was going to be too dense as it's 0.48g/cm3 (about the same as wood) but most of my existing bouyancy was hollow so i had room to play with.
The new stuff is very easy to machine and shape so I carved this out and sprayed it with floor line marking paint to give it a tough coating. Looks pretty neat if I say so myself.







The bouyancy turned out to be pretty much spot on and I only had to add 60g of ballast for fresh water, I guess i could drill out 60g worth of bouyancy so i dont need ballast but I'll need some for seawater use anyway.

[bigbadbob]

I've upgraded my controller too.
This one's a bit more splashproof and I can shut the lid if it rains.

[bigbadbob]

After a vertical thruster failure due to seawater ingress, and life having higher priorities, MiniRay sat on the shelf for a while gathering dust but I'm re-visiting it and giving it a major upgrade.

List of things I plan to do:
replace tether to ROV connector with 8 pin mini impulse connector. (as used in videoray) this will be lighter and have 2 extra pins.
replace tether video coax and comms lines with 2x 24AWG twisted pairs stripped out of CAT5. these will be lighter and less noisy.
fit video baluns both ends to enable video over twisted pair.
replace velleman control system with arduino nano's top and bottom and add rs485 converters to each.
replace switched joystick with PS2 controller.
replace relay board with 3 ESC's for thrusters.
replace vertical thruster.
Add 12v to 48v dc-dc converter to top side and 48v to 12v dc-dc converter to ROV to reduce current in tether to 1/4 of what it was with 12v supply and therefore reduce volt drop to 1/4 of what it was too.
bottom end converter will be mounted external to the ROV as it's potted and waterproof so will be watercooled.
Spend a fortune on e-bay.

[Ianth3impler]

What are you going to use for ESC's?