My "MINIRAY" Rov.

[bigbadbob]

A rather wet day today but I took the ROV for a swim to stretch it's legs....

On the pier.


Off the pier. (camera fogged up)


One or two problems I need to sort-
Camera fogged up- This shouldn't happen as the hull is filled with dry nitrogen but I'll stick a desicant pack in there.
Weed in the props- I need to think about prop guards.
Not holding heading- I'll try increasing the prop drive power during Auto Heading mode.

[Oddmar]

I used 1/4" hardware cloth (Metal screen with 1/4" or 1/2" holes) over my ducted props to keep weeds and debris out.

Also keeps fingers out of the props while on the dock or the operating table.

[bigbadbob]

cheers Oddmar. I'll check it out.
I can't say I've ever stuck my fingers in there but weed and debris are definately an issue.

It looks like the desicant pack in my camera dome might be saturated but I have to do a lateral flow covid test tomorrow so I'll keep the desicant pack out of the test kit and use that.

I've also updated my arduino code to increase thruster power when autohead is active but I've misplaced my programming magnet so that will have to wait.

[Oddmar]

FYI, desiccant packs can be dried in an oven on low heat, and if you want to build your own cheaply, crystal kitty litter is the same material.

[bigbadbob]

Thanks for your suggestions Oddmar.
I've replaced the desicant pack, uploaded new firmware and found a stainless mesh bird feeder blowing around in the garden.



next time out I'll see how the guards effect thrust and think about covering the sharp wire ends so they don't catch on weed and do more harm than good. a drop of epoxy might do the job or maybe some slit tubing over the leading edges.

I also had an amazon voucher left over from xmas so ordered a pair of these to play with-





Specification:
- Item name: JRUIAN propeller 12V 24V underwater thruster
- No-load speed：6105±10%rpm
- No-load current: ≤1000mA
- The load speed: 2500±8%rpm
- Load current: ≤16.0A
- Resistance: 50±10% mΩ
- Insulation class：A
- Insulation resistance：100MΩ Min
- Insulation strength：AC500V/1s≤5mA
- Item name: 3-blades propeller
- Type: CW/CCW
- Material: carbon fiber

no mention of depth rating but I'll let yous know if they're any good.

[bigbadbob]

I had an e-mail from the thruster supplier to say it might be 50-60 days before they arrived as it was a special order item.
48 days later they arrived.

(pic to follow here)

Nice timing as last time out my stbd thruster motor flooded with seawater and rotted the brushed motor.

(pic to follow here)

I thought i'd ordered 2 of them but it turns out I ordered 4. haha. that's cool, good to have spares.
They also came with potted hull penetrators on the wiring which I wasn't expecting so that's a bonus too although only one came with an o ring and none came with the required m10x1 backing nuts.
They seem to be designed for boats as they have a through-hull prop shaft tube with bearings and gland so presumably they will flood if taken to any decent rov depth but the windings are potted in epoxy so no problem if they flood. as long as the bearings cope with seawater. they look like stainless bearings so should be ok.
not bad for $15 each, i'm quite impressed.
They come with 44mm props fitted and my ducts are 50mm so I put a spare 60mm prop in the lathe and turned it down to 50mm which squared off the prop tips which should be more efficient in a ducted prop setup.
watch this space....

[Oddmar]

Could you somehow flood them with mineral oil to fill the interior void, so water can't get in to do nasty things, as there is no empty space for it to fill?

I have Toyota 4x4's so i have bins full of M10x1.0tp bolts and nuts.

[bigbadbob]

Yeah, i'm tempted by mineral oil. I'll have to experiment and make sure the oil doesn't attack the insulation.
I have found some m10x1 nuts at work but might not use the penetrators, i'll probably re-use my existing pneumatic push-fit fittings and back pot them.
I might use the penetrators for lamp wires at some point.

edit- 6 wires won't fit through my existing penetrator so i will use the ones that came with it and just seal all the wiring and let the motor flood with water.

[bigbadbob]

I had a busy weekend but found the time to program a couple of ESC's (emax blheli 20A) to make them bi-directional, wired them in and set about tweaking my ROV code to centre the
motor stop position with my joystick centre position.
all was going well but the motor bearings sounded very noisy and then both ESC's burned out two of their FETs.
these are the same ESC as I use for the vertical thruster (which works fine) and have been flashed with the same blheli firmware so I suspect either the motors are producing excessive back EMF
when I stop them or the 48v-12v dc-dc converter supplying them doesn't respond quickly enough to load changes and produces over voltage spikes.
either way I'm hoping some capacitors will solve the problem.
Today I replaced the FETs on my ESC's with known good quality ones, the ESC's came fitted with a variety of different FETs, chinese floor sweepings maybe.
I'll see if they survive any better.

update-
having replaced the ESC fets all seems to be well, No more burned out ESC's and motors running well.
I have turned down another 60mm prop to 50mm so now just need to cram all the new wiring into my hull and seal it back up.
Looking forward to sea trials soon.