Homebuilt ROVs Forum

Can an outrunner type motor be run underwater? Saltwater?? Maybe replace bearings with graphite filled nylon or something and coat components with marine epoxy? Chrome plated shaft? I think this has been done. Bluerobotics does it somehow.

Randy

@rehoward,
Take a look at this Blue Robotic outrunner (https://www.bluerobotics.com/store/thru ... -motor-r1/) brushless motor for use in salt/fresh water.
The motor is not cheap, but you will not be replacing it as often in relation to a normal brushless outrunner motor.
Regards,
SSN626B/TCIII

Yes, I was looking at the Bluewater motors yesterday and that got me thinking about how they might have done that. From what I have found so far brushless motors can run submerged but the bearings succumb to failure from corrosion. And the shaft and armature gets rusty. I was wondering if anyone modified a cheaper motor as from HobbyKing to operate wet in salt water?

Randy

It's been done, but as mentioned before, will have a fairly limited lifespan. OpenROV's use stock outrunners and recommend you flush with fresh water and lube with spray silicon after every dive. Blue Robotics motors are completely redesigned and purpose made for underwater use. You can re-invent the wheel or just buy a wheel. Your choice.

Another issue might be the price of the wheel . I was originally planning to buy bluerobotic thrusters but for the six thrusters with shipping to Sweden and import taxes I felt it became to expensive at least for my first ROV. So I am going with a homemade brushless setup with a bluerobotics design, I post more on that when I start working on it.

As a side note I saw that they started using resellers, so now it's cheaper for Europeans to buy them, Doh!

I have some Igus composite bushings I want to test some day. I believe they are the same type as is used in the Bluerobotics thrusters.
Designed to work in submerged environments. Only problem was that the exact size I needed for my motors didn't exist so I have to file them down from 5 to 3mm if I want to use them. Both inner and outer diameter fits perfect.
If anyone wants to try them I would suggest looking at the Igus websites and sending them an email.
I got 5 of each size for free as a test I was quoted a price of $5 pr piece if I were to buy more.

Also. I am currently testing a "why the hell not" idea I had.
I have printed bushings using Taulman 910 nylon 3d printer filament. I just wanted to see if they would hold up at all.
So far they have only been running in water for 5 hours while monitoring RPM, amp draw and noise and so fare they show no sign of wear at all. The amp draw decreased as they wore in and has stayed the same after that.
While they run in water there is no noticeable heat generated. But while running them dry at max rpm for somewhere between 30 and 60 seconds they started getting slightly warm.
However, even Bluerobotics does not recommend running their thrusters dry for more then a short while.

I will improve my test setup, put a prop on it an lett in run for a few days or until they brake. Because why the hell not?

Wow! "why the hell not" a bold experiment. "only 5 hours"?? Very impressive.

olegodo you are my kind of guy! I will check out Igus. I was thinking of making bushings from Nylatron which is a graphite filled Nylon. I think Nylon is hygroscopic and I will need to attend to tolerances so it can swell naturally without binding the shaft. Another thought is a ball bearing with glass balls and a plastic race. I am maybe a week away from testing my Textronic DT700 for thrust. Then I will do testing in salt water.

Let us know how testing continues with your printed materials. Do you have any other info regarding measures that Bluerobotics takes to make their motors usable in salt water? I am pretty sure they use a brushless DC motor and run it totally submerged without trying to seal it from water.

Randy

Ran the motor for another 2 hours yesteday with no change. Still runs fine and no noticeable wear, friction or noise change.

The nylon will absorb moisture and swell for sure but I'm not sure how big the effect will be. So I have the motor sitting in water now to see if it there is any notable difference in friction after one day in water.

I do believe the Bluerobotics thrusters are encased in some sort of epoxy to protect the winding of the motor. I plan on doing the same, but I'm not sure exactly what epoxy to use yet.

Not sure of a potting epoxy either. I think it should be slow cure and low viscosity. Anything I have found so far is very expensive as you must buy a quart or more. I just bought some Loctite marine epoxy from Lowe's with a 2-3 hour cure but haven't tried it yet. Currently I am building a small vacuum chamber based on a cooking pot with a glass lid. Vacuum is important to remove air from the potting as it cures so that you get complete saturation, but vacuum level must be regulated or you will pull out components of the epoxy such as the catalyst, or so I am told.

Randy