Mods for 1,500' depth rating?

What would I need to do to upgrade my BlueROV2 to explore 1,500’ depths?

Here’s the things that I have thought about so far. Am I missing anything?

  • upgrade enclosure tubes to the new version
  • remove sonars and maybe Newton gripper
  • coat buoyancy foam
  • upgrade tether to fiber optic
  • maybe upgrade penetrators to wetlink?

Also, Is it worth upgrading to the Navigator controller? I have looked through several posts, but I haven’t seen anyone mentioned if it’s a direct upgrade right now or if it’s just aimed at new customers.

In my opinion the most important consideration when sending a small ROV over 1000’ is how to get it down there on the location your aiming for, and keep it there with some level of mobility. Small ROVs can not drag that much tether around (the tether will be dragging the ROV around). You should plan on using some type of clump weight to decouple the long tether from the vehicle. Also, with 1500’+ of tether you will probably want a good spool for winding in the tether and weight. I use an electric winch because my weight is very heavy. In the ocean I use from 5 to 30 lbs of weight and the current can still be an issue. If your in a lake the clump weight can probably be much less than what I use.

A fiber tether is not a requirement for 1500’. I use over 1500’ of good CAT6 cable down to my clump weight, and then through another 60’ of BR tether to the ROV. I am transmitting more data that a standard configuration as well. Results on that may vary, but it does work for me and switching to fiber is a large investment.

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@nperry Thanks. That is the kind of information that I am looking for since I don’t know what I don’t know.

My mission is to explore the deepest part of Lake Chelan in Washington State, so the target location is a reasonably sized area and not a single point. Everyone on the internet seems to agree that no one has ever seen the bottom, so I though that it might be fun to try to be the first (or one of the first).

Do/can you use the clump weight to drag the ROV down to the target depth without using battery power? One of my considerations is my single battery. I don’t want to waste most of it just driving down to the bottom. I thought about tying a rock with string and grabbing the knot with my Newton Gripper to make the ROV negative to get it down there, but a clump weight would have the same effect while also taking up some of the tether tension.

Do you just use regular direct burial grade CAT6 cable? Do you have any kind of jacket to protect it? What about if the jacket gets cut and water runs down the inside of the cable?

I was looking at the 1Km ROV fiber tether from DeltaROV, which is a little over $5,000.

Looks like direct burial grade CAT6 is 10X cheaper and I assume that it’s more durable than the in-wall installation stuff, but I don’t want to risk my ROV flooding if the cable gets kinked or sliced.

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Hi @btrue :

I think your list of changes will work fine. We modified a ROV to dive to the bottom of Lake Tahoe, which is a little bit deeper than Lake Chelan. In this forum post, I talked a bit about coating floats, and linked to a YouTube video that showed the modifications we made.

One change we made that is not on your list is to go to a thicker back plate. I see that Blue currently rates their 14-hole 4" endcap to 500m, so maybe its not an issue. We were worried about it bowing at depth, so we custom-machined a similar 14-hole endcap out of 10mm aluminum stock. The 18-hole endcap is already made from this thicker stock, but Blue had not released this at the time we were doing our modifications.

To amplify what @nperry said, a fiber tether is not a requirement for doing basic work at 500m. You can use a VDSL modem for this purpose, and I’m guessing that even the RAK V30 board would work fine if you want to stay with homeplug. That being said, if you feel that you’re going to graduate to multiple cameras, or very high definition cameras, then you will probably need fiber at some point. Fiber tethers can be pretty fussy, and have handling restrictions related to minimum bend radius. For most general-purpose diving we don’t consider them to be worth the bother.

Walt Holm
Mission Robotics

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Hi @nperry

If you’re using Cat6 cable for a downline, do you have a separate strength member attached to that, or have you found Cat6 cable with an embedded strength member?

-W

I us a fairly cheap CAT6 cable with stranded wires. I pair it with 7/64" Amsteel Blue Dyneema to handle the load (7/64" can lift 1400 lbs with very little stretch). I attach the dyneema to the CAT6 with tape every couple feet. This is the only way I have found to get the lifting capacity I need without spending a ton on a cable. I use a Seacon connector to link the CAT6 lifting cable to the ROV tether, so if I had damage to the cable it will not cause a leak into the ROV, it will just ruin the cable, which is fairly cheap. I do wrap the bottom 30 feet of cable for protection. I have about 100 dives with my current cable and no issues, but I will replace it soon since it is prone to some stretch and wear over time. Most wear is from spooling on/off the winch.

Looks like the Delta fiber optic tether has a breaking strength of about 300lbs? I dont know what the working strength is, but in your case it is probably good enough for a smaller clump weight.

Yes, I would plan to drag the ROV down to save battery power, or if you have a gripper, you can hold onto a line attached to the weight.

Years ago I invited the BR guys for a trip out on my boat to test all this out with an ROV to see if it will work. They were happy to try it and it worked really well. In that case I was using a camera sled as the weight, but I also use a lead ball when the sled is not needed. Here is a pic of the winch/cable, and one of the camera sleds, and some videos from the tests with Rusty and Adam from BR.

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Hi Walt,

Yea, I use Amsteel Blue for the strength member. Its a lot of work attaching it to the CAT6, but works really well.

Are there any downsides of fiber other than the cost and watching the bend radius?

How are they fussy? Does the communications drop out or something?

2 posts were merged into an existing topic: New Product: The Navigator Flight Controller and BlueOS!

Hi @btrue

The fussiness I refer to is mainly related to observing the bend radius. If one has a winch and everything nicely goes over sheaves then fiber works fine. But for small ROVs where you’re typically hand-holding the tether, there’s always that chance where in a moment of inattention you snap the fiber.

The lake environment you’re in is probably not that harsh, so fiber might work out fine for you. If you do go down the fiber-optic tether route, please post to the forum occasionally regarding your setup and how its working.

-W

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