Acrylic vs. Aluminum?

Blue Robotics Products Watertight Enclosures
1

If cost was of no concern, which would you prefer? (endcaps, main tube, accessory tube, etc).

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If money were no object, custom Titanium (6AL4V alloy, 120ksi yield) housings/plates or maybe 17-4 PH 900 stainless (passivated in nitric acid), and Sapphire domes. But, hard anodized Aluminum tubes, end plates, and acrylic dome from the Blue Robotics store will be more than enough for 300m and will last a long time. I do recommend the Aluminum housings over the Acrylic, and certainly aluminum for the end plates.

3

I realize we could go for some very exotic alloys. That wasnt really where I was inquiring. I have to imagine acrylic comes with the BR2 because its the more affordable option, and more affordable is better for the consumer. But if aluminum were just as affordable, how many would switch? Or is acrylic “good enough” for most?

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I would definitely go for aluminium over acrylic if I could afford it as I think it trebles the depth range (100 vs 300m).

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Practically speaking, upgrading from our acrylic enclosures to our aluminium ones may increase the vehicle’s effective depth rating to 300m, but that’s largely dependent on the other components on the vehicle.

It’s also worth noting that material selection is one of several design variables which influence the component attributes (and resulting vehicle attributes), and depth is not the only relevant factor. To clarify, it’s true that mass for mass, and volume for volume, aluminium is stronger than acrylic, but it’s also the case that thicker tubes are stronger than thin ones, and acrylic can be optically clear, but also traps more heat inside the enclosure, may fail when submerged for long durations, and is harder to manufacture to tight tolerances.

Our technical reference is a good place for comparing general properties of our components, although for the BlueROV2 specifically there’s also a table of component depth ratings on the product page. Considering the enclosures as the initial depth-related limitation:

  1. our 300mm 4" electronics enclosure tubes are rated to 100m / 1000m for acrylic / aluminium (and 150m / 1000m for the battery enclosure), but
  2. the dome and our Lumen lights are only rated to 500m,
  3. our standard buoyancy foam is only tested to 300m,
  4. our Bar30 depth/pressure sensor is only rated to 300m, and
  5. our tethers typically only communicate well up to ~200m / ~300m of length (for the slim / standard options)

so upgrading only the enclosure tubes just means they’re no longer the determining factor for the practical depth rating / range of the vehicle.

We design our products to fit what we consider to be reasonable compromises between the properties and costs (including expected demand, and economies of scale), but as with most designs there are other trade-offs that are technically possible, and sometimes alternatives may be preferable or even necessary to meet specific design requirements :slight_smile:

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Many Thanks for clarifying Eliot as lots of great information and reference link. Wasn’t aware of the heat loss issue of aluminium vs acrylic which is another reason to upgrade to these.

So guess i can be confident saying 300m is the maximum depth for the BlueROV with aluminium enclosures/standard tether with tether length being the limiting factor?

I did see a post recently where someone had used a 1km tether for a pipe inspection - guess this wasnt a blue robotics tehter and probably fibre optic?

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7

Indeed, although going deeper would also require a different pressure sensor (e.g. a Bar100), and either coating the buoyancy foam or using a different type.

There are some range gains to be had with newer / higher end HomePlug modules (like the LX200V50, instead of the LX200V20 on our Fathom-X boards), but 1km is indeed most likely fibre optic.

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8

Some other thoughts regarding upgrading from Acrylic to Aluminum housing to get more depth and robustness.

For those how know. Let’s say I want to upgrade my ROV and only change the 3" & 4" housing and upgrade to cylindrical locking flanges.

Would there are any known problems regarding the sensors like compass, IMU and such… That they would need more, often calibrating, more errors?

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Hi @diveexplorer -
There are a few impacts the aluminum enclosures have, besides depth and durability.
The compass and IMU will likely need to be recalibrated, but should continue to work normally after the swap and calibration process.

The aluminum enclosures are also rated for continuous usage - acrylic can have issues with creep if used at depths greater than 25-30m for more than 2-4 weeks - whereas a BlueROV2 with aluminum tubes has worked for a full year at depth!

The other major benefit is cooling - the aluminum walls are thinner, considerably more conductive to heat, and opaque. It’s still good to keep the ROV from exposure to direct sunlight at the surface, at least for long periods, but if this were to happen things would at least cool off significantly quicker once in the water and underway. I once developed some shallow water (10-15m) cameras for aquaculture using 3" housings, and had real issues with clear water and keeping the internal electronics cool - the greenhouse effect is killer even at depth! Aluminum tubes solved it.

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Hi Tony, great explanation and good information… I guess there is more beneficial to have AL housing over the acrylic one. I was just concerning that the sensors inside, like the compass and IMU on the Pixhawk which can be sensitive, would “degrade” or could be interfered by the aluminum enclosing… But doing recalibrations and such is no big deal.
Thanks again for your answers.

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I went aluminium due to recommendation of heat dissipation. A friend has a BR1 which is affected by overheating in its acrylic housing. I appreciate that things have moved on since BR1, however when buying new the cost upgrade was negligible and he basically told me I would be an idiot to not spend the little extra for aluminium.