My attempt

[manhattan]

Getting the final quirks sorted out and could use some advice.

In short, main body getting ready, I’m happy how it turned out and would like to stick to this path. Resemblance to Steve’s Stinger and the more commercial Observer type. Many, many, many mistakes along the way, some of which I would be happy to share and some that I will keep for myself . Right now I am figuring out a better buoyancy setup since body is too heavy. My ROV will be used mostly in salt-water but from time to time in a lake as well, so I am thinking to use some kind of tank on top that can be water filled as needed. I will check the posts again to see if I find any text on that. Overall balance is fine however, just a bit back-heavy thanks to the connectors, think I can compensate that fairly easy.

Will post pictures of the control system as soon as I manage to squeeze all on a board. I had to change a lot because of some power issues (some of which I got help on here). Was thinking of cutting the tether to 60 m but decided to stick to the original plan of 150m. Control seems to work fine (on reel and on land) I am sending 24v topside to a 12V 20A converter for power. The brushless motors I have tested as deep as 20m (lake) without issues and I changed to a small HD camera that’s ballooned topside instead of the Axis 221 beast (could not fit it in). Tether management I will worry about later, right now depth and seals are priority followed by motors.

Will post updates regularly I hope.

Best

[sthone]

It's looking great... what did you use for brushless motors? I've been looking to try some but don't know where to start yet.

-Steve

[manhattan]

Thanks Steve,
You could start by doing it right from the start, not like myself… I tried 7-8 motors + esc combos, burned a few until I found a good pair. My conclusions would be:

1. Even though In-runners are far more practical to attach, slimmer etc. their downside is too high rpm (kv) = less torque and cooling. They either rely on pass-through water or air cooling. I really wanted them to work but for me it was impossible. Out-runners are the way to go.

2. Goal for me was to get as small motor with as low KV rating as possible which is not the easiest since kv is related to size, unless you wind your own motors. As example this

http://www.hobbyking.com/hobbyking/stor ... 0_55_.html

has loads of trust but as you can see impractical. (It’s Uber-cool however )

I settled with a 600Kv version of this. Loads of trust in a tiny package. Think mine are under-propped (50mm robbe) and that I should change to 60mm.

http://www.hobbyking.com/hobbyking/stor ... 750kv.html

Paired with this esc,

http://www.hobbyking.com/hobbyking/stor ... R_ESC.html

Which is total overkill since current will never come close to 35A/motor + that the controller fuse is 10A. Also the fan on top is only rated 7V and makes a funny sound before it blows when connected to 13V . I also have a few of this:

http://www.hobbyking.com/hobbyking/stor ... ramm_.html

Think they are better suited for the above motor. I will give them a try.

3. One useful thing frequently unnoticed with ESCs is that most of them have a BEC (battery elimination circuit) which diverts some power from the motor to other devices on lower voltage (5v) With this you can have 4 X 5v outputs which are always on. In RC they are used to lower landing gears on planes when motors are shut down due to voltage drop. For us maybe it can be used to power servos and/or solenoids in case of drained battery.

4. Power: Tried to measure current in a tub but it was difficult. Without load my setup draws 1.5A/motor. I tried to stall one motor (by holding the prop shaft) and got the current to 9A. I think it draws 13A if fully stalled. In tub I climb up to 3-4A/motor when running with load.

5. Magnetic Couplers: Was really considering this. I even pre-order some from a milling facility but cancelled due to the cost of motors. They wanted 280$ per coupler and after reading on the German ROV forums on how they use their brushless in saltwater open with great success I decided to go that way. I can buy 28 motors for the price of one coupler. ESCs cost more but they are fuse protected anyway.

Hope this helps, anything I forgot?

[derelicte]

Nice job!

There is a type of rc escs commonly called "opto" escs which don't have becs.


http://www.hobbyking.com/hobbyking/stor ... Opto_.html

you may have a hard time finding an opto esc that has reverse, though.

you could always take the esc apart and remove the bec. it would be pretty easy to do.

[manhattan]

Hi Derelicte,

I was actually referring to the BECs as a positive add-on to ESCs. Somewhere that one can connect the lower voltage accessories without needing a step-down converter or resistors while keeping 12v or higher as main for motors. (I have soldered my 5 v fans directly on to BECs, seems to work fine)

Did I miss something negative? Why would I remove BECs or buy ESCs without?

[derelicte]

I misunderstood. I thought you didn't want the bec.

sorry!

[manhattan]

Ah, scared me there for a sec...

[derelicte]

how are you controlling the escs?

[manhattan]

A final test before the lake. Did not include lights yet (still working on them).
Changes include new skids, tether cut down to 80m, floats added (temporary and ugly), video feed, control box.

[shaneb24]

how are you sending your PWM commands