Multibeam T500 rov build for wreck and reef surveys

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Hi there.

We are trying to put together a T500 rov. We just threw ourselves in and ordered the parts we thought we’d have use of together with a complete BlueROV2 to make acquaintance with the architecture and to use on inspection jobs.

We are a company supporting the foundation VOTO, Voice of the ocean who wants to:

  1. Support science.
  2. Visualize the past.
  3. Create engagement.

It is all about the sea, have a look at: https://voiceoftheocean.org/. VOTO shares a lot of high-resolution oceanographic data for all scientists to take part of and might support your research in other areas. Recently involved with an unmanned sail drone project in Hudson Bay.

Back to the vehicle, it is to be custom made to carry a relatively big echosounder our R2 Sonic 2024 (+16kg) and a SprintNAV mini. Positioning will be from HiPap.

The frame machined out of PP plastic is in the making and should arrive shortly.

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It is also planned for a fibre mux to be able to handle the data and run on a thin tether.

We intend to go for two battery pods containing two batteries each like the Mega battery. Pods will still be light in water and are stacked in the top.

Its not a vehicle made for pipeline survey but smaller grids of work like shipwrecks or reefs. Possibly it could be refitted/ rebuilt for photo, photogrammetry or film later.

The best would be if the batteries could be connected into one big battery, thinking of making a power hub where batteries join and the ESC:s are housed and then thrusters connect to. Possibly moving the Pie in together with the mux.

The first idea was to use a 400mm 4" bottle and just change out the 200-ESCs, but even if we removed the dome and added another flange for connectors, yea I’m not sure. Maybe better to move the Pie and just run a cable with signals to the ESCs.

Another idea is to put (four and four) ESCs with the batteries. Its not as straight forward of how to (evenly) supply the rest of the vehicle with power then.

Its not going to be a perfectly executed plan, but the intension is to get a prototype up and running. A home made ROV built on T200s (top side powered though) managed to pull of a survey with this MBES last year.

I have a lot of questions. I am trying not to spend too much time on issues like heat dissipation or tether entanglement around the trusters just yet. No, it can’t even sit on deck like that, but staying slick would not create unnecessary drag, it can sit in a crib. Plenty of space to manufacture buoyancy in the top.

It is hard to dimensioning things out. Cabling can’t be dimensioned for running all thrusters at full speed simultaneously (43x8 Amps). The initial idea was to use 500s for their efficiency. Verts just running on idle while on site just to maintain depth. Probably could have gone with just two 500s or four T200, still can. Thrusters should be able to limit in the software, add fuses to that.

It would be preferable to seize up in dimension battery cables going to a power hub, I haven’t found any good connectors for more than 50 Amps. To hardwire one cable with two conductors through a gland would save some end cap space. I am all ears for solutions and parts.

Robin Claesson - Midocean

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Is there a reason that your using a 2024 vs a lighter MB like a Norbit IWbms or Winghead depending on your resolution requirements. Just a thought. Looks like a cool project.

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We hope that we could interpret the multispectral backscatter if I’ve understood things right. So we could possibly look at other things in the returns than just seabed or not. If the data could be interpreted so one could find a certain coral in the signature for example. I am no expert in this MBES.

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We built it.

Sensors are up and running. I think we managed to get the SprintNav to be navigational sensor for the vehicle as well. The top frame is getting new and more pieces to make it stronger. But it is fine as it is for lifting in calm conditions.

Battery pods got heavier than planned with additional components. So yes it feels top heavy. More lead, more bouancy or a complete frame re-design, we will see.

It seem to fly reasonable in the tank, but we need more water. Waiting for some boat time.

Yea it can’t sit by its own on the floor, it needs a cradle. I wanted a slim construction with as little drag as possible. You wouldn’t really put this vehicle on the seabed with down trim anyways.

Tether is 3,5 or 4,6mm fiber optic from Linden. The idea is still a “patch tether” of like 40-60 metres to a poor mans TMS, the bullit of our survey winch which has got an fiberoptic interface…

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Hi @IntoTheBlue -
Chiming in here rather than the dual batteries thread on your power approach.

If you’ve co-located the ESCs with the batteries in your two side enclosures, then the high current has a nice short, “dry” path from the batteries to the ESCs, and you only need 1 ground and signal wires for each ESC connected to the flight controller in your center housing. You could have a single set of power wires making your two pods batteries be in parallel - only small currents would flow down this cable, if any at all, caused by thrusters on one half working harder than the opposite - as those batteries voltage went lower, a bit of current from the other side would be sourced. Does that make sense?
The center enclosure, if only the flight controller, INS and communications won’t pull much power - you could connect it to either battery pod, and “balance” current would come to that sides batteries via the paralleling cable.

A very cool ROV! Best of luck

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Thanks for showing interest!

Yes the co-location off batteries, ESCs and thruster outputs gathered saved me from finding high current cables out in the water. Now I can stick to original cables.

We did have it like that during one early test dive. I paralleled them through a big resistor for leveling out differencies before connecting them. I was of course easy on the stick.

But what if some cells on one side fails? Wouldn’t the draw want to travel “the longer way” then?

No the center enclosure should have like a maximum of 100W with echosounder, gyro, Pi, lights, camera etc. There are some losses of DC/DC regulators and such.

Now we are trying to tweak parameters making it fly as its best. All ears for similar set up threads.

Thanks.

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Hi @IntoTheBlue
I’m a bit confused on the resistor- it’s better to charge the batteries to full to equalize.
It’s highly unusual for cells to fail, and would likely only occur if over-discharged or dead-shorted?