Greetings from a newbie in Michigan

[jescholz]

Greetings from a newbie in Southwest Michigan. I hope to build a video ROV for shipwreck documentation and searching here in Southwest Michigan. I have been looking at the "Open ROV" but thought I would see what other ideas are out there before I bought the kit. I want to document some wrecks that have been recently located in the 250-300 foot range, and would like to use surface supplied power in a compact unit. Lighting will be my greatest power draw as natural light at that depth is an issue. I also think I want to be able to move side to side so I can swim up to the wreck and keep the camera at the same angle and move the ROV around the wreck.

I notice that most ROVs do not have tilt, but seem to remain level when floating and only some have lateral thrusters.. What are the pros and cons of adding the extra thrusters to do this? I am thinking I can control the standard Forward/Back - Left turn/Right turn on one joystick and the tilt up/tilt down - Left Lateral/Right Lateral on another joy stick. Thoughts and comments?

[scubersteve]

Welcome to the forum!

I am a big fan of lateral thrusters (or at least of the ability to move laterally) for the same reason you mentioned.
keeping an object in view while moving along it or along with it if it is moving seems like an imperative.

I'll be interested to see what your power arrangement looks like as pushing power down 350' of tether is going to be quite a task.
I would doubt that lighting would constitute your biggest draw as LED lighting consumes far less power than thrusters.(unless you've got lots of LEDs)
Good luck and keep us posted.

[berossm]

Nice to see another member in Michigan.


I think the reason you do see tilt is its not really something you can do easily with thrusts. Your ROV would have to be very well balanced and very fine control of the power output. One think I was thinking about was actually having piston style ballast so I could, while keeping over all natural buoyancy, adjust the angle of the bow.

[Lomax]

Greetings from a newbie in Southwest Michigan. I hope to build a video ROV for shipwreck documentation and searching here in Southwest Michigan.

Welcome aboard! Shipwreck hunting sounds really exciting, I hope you'll share some footage when you're finally there!

I have been looking at the "Open ROV" but thought I would see what other ideas are out there before I bought the kit. I want to document some wrecks that have been recently located in the 250-300 foot range, and would like to use surface supplied power in a compact unit. Lighting will be my greatest power draw as natural light at that depth is an issue.

I don't think the OpenROV has enough power for your needs, both in terms of dive time and current supply. Another drawback is the webcam based video, which isn't as good as some other options.

Like you I also intend to power my ROV with surface power, but I plan to have a small LiPo battery on-board to buffer the starting current for the thrusters and to have some spare capacity for extra lights. Unless you're going to send high-voltage down the tether (which could be very dangerous!) I think you'll find that the losses over a long tether severely limits the amount of power you can deliver.

There's a depressing trade-off between tether cable area (and hence weight/drag), amperage and the incurred voltage drop. On the one hand you want as thin/light a tether as possible - on the other you want to deliver as much power as possible. I've thought about this for some time and it seems clear to me that a mix between on-board and surface power is the way to go. If the tether can supply the average power needed then you can use the spare capacity while the ROV is drawing less to top up an on-board battery, and the tether can be made much thinner.

Luckily there are power management ICs around that have been developed for use with photovoltaic panels, which will perform exactly this job. Having looked around I've found an ideal candidate in the Linear Technology LTC4000-1, see attached datasheet. I plan to feed 48V over the tether, which will have fallen to ~37V (@ 2.5A) over 100m of 1.5mm2 (18AWG) cable. This goes into a 48V to 12V DC/DC converter, which in turn feeds the LTC4000-1. This magic chip then balances power usage between the tether and a LiPo battery pack, charging it back up when possible. If you're running low you just have to turn off a few lights and go easy on the thrusters for a while, giving you practically indefinite dive time and plenty of current when needed. Pretty neat eh?

The only problem I'm having is designing the complete circuitry for the LTC4000-1, it needs a couple of power MOSFETs to perform the actual balancing act, and a few other bits - and I'm not that good at electronics design so it's pretty difficult for me!

[MNDeepROV]

Lomax: This is an interesting idea! I'm a newbie too and it seems a few others also use hybrid arrangements which I am now looking into, but this is the first time I've come across your concept.

Generally, I don't think we can really charge a battery while it's in use (unless some fast switching is in use maybe), but like you said one could limit, or power down for a while while it catches back up. I don't have experience yet with Lipos, nor the circuitry to know how this might affect their performance, etc., so testing needs to be done, but it's definitely an interesting concept if we can't use high voltage systems to get a longer bottom time.

Any luck with your design?

I know an electrician that installs and configure solar arrays so I'll run the concept by him and pass anything along if learned.