The buoyancy foam I’m using in my AUV is a polyurethane based closed cell foam. while it is rated for 100m of depth, it will still absorb water over time. to fix this I’m looking at the similar Blue Robotics foam, and while they do have a depth rating, has there been any testing done to study water ingress over time?
The foam i have here currently was at 1m for 48 hours and gained 7% of its mass in water. not ideal for an AUV.
One of the options I came across is an epoxy with microbalons or micro spheres, don’t really know the exact name, that seems to be the most resistant and water tight. The downside is was denser than other solutions like the polyurethane foam.
I’ve played around with these before. I think they would be great for 1000m and deeper, but they were really dense for anything above that. i think the best I was able to get after mixing them with epoxy was maybe .8g/cm^3. So I’d need a lot of volume to displace the needed amount of weight. they were also relatively expensive compared to the polyurethane foam that most places sell.
With that said, I bet they don’t suffer from the water ingress problems that I’ve been having.
Hi @brad_smith,
I’ve asked internally whether we have any data on this, and will get back to you if there are more details we can share 
Another potential option is some kind of larger air-filled enclosure (or set of them), though there is still the inherent tradeoff between density and depth rating, and costs may be prohibitive depending on your requirements and scale. We’re working on a product in that space, but it’s still in the concept stage so there’s no timeline for when it will be available (and we’d likely be targeting our standard ROV depth rating, which may not match what you’re after).
Hi Eliot,
Thanks so much for looking into this! I’ve been talking to your supplier at General plastics as well but I was told they didn’t have any data they could share. I bought a sample kit from them to do some testing myself. I’ll share the results if you guys don’t have anything on this already.
I explored something like this as well with waterproofing 3D printed parts. I was able to get it to survive 300m without taking on water, but the risk of using some homemade system like this is uncomfortably high compared to off the shelf foams. The foam is slightly lighter too. The 3M glass spheres are a good option for going deep, but the stuff i was able to make was still quite heavy at .8g/ml. Most of the industrial vehicles I’ve worked with just use a huge dry bay as buoyancy, but they aren’t limited by size, weight, or cost.
If it’s not proprietary, or outsorced, are you able to share the process you guys use for coating your ROV foam? Or would it be posable to chat with the people at BR looking into the air filled buoyancy? I’m neck deep in this problem right now and would like to find a solution too this soon.
Thanks!
Hi @brad_smith
We don’t really do any foam coating at Blue Robotics- I’ve seen typical two part marine epoxy used with good results on the foam (West Maine 105?)
The cylindrical injection molded buoyancy tubes Eliot mentioned are going to be rated to about 500m, is that enough for your application? While they may not be available soon, perhaps if you shared how much buoyancy you needed we could get you a few prototype samples…
I’ve used west 105 on my printed parts as well. I’ve found it a bit finicky as any small pinhole leak can sink a part, but I think that’s more of a process problem. at the moment this is looking like the path forward though.
I’m building a system that would be 300m rated tops, so the injection molded cylinders sound ideal. I’d love to give one a try along side my other tests to compare if you’re able to send one to me. Do you have samples made already, or is this still in the concept phase?
Hi @brad_smith -
When it comes to coating printed parts, I agree - a silly pursuit. Easier to use gyroid infill and drill holes, and encourage such parts to flood - this doesn’t impact mechanical strength, I’ve seen parts used this way at 6k m +!
We’ve got some initial prototypes - the design engineer isn’t available this week but we’ll follow up!
In my case I was using the printed parts to provide the buoyancy. It was almost the same density as foam and I could make some weird shapes with it, but the advantages are moot compared to not getting your hardware back.
Do you know what the size and weight is of the floats? Are they less dense than coated foam?
Following up:
This is a huge help!!! thanks so much for finding this.
