Homebuilt ROVs Forum

Just thought I'd post some observations. After reading endless online posts stating that "yes brushed motors work fine underwater" or "never use brushed motors underwater". I got tired of all the endless debate and desided to conduct my own real life tests. I purchaced a 12v brushed motor from a surplus store for $12.99 (they are automotive rad fan motors) so lots of power for a thruster and with 5/16 shaft. I filled a bucket with water and wired up the motor and droped it in and let it run for about 30 mins. For starters it ran fine underwater. I never had a multimeter hooked up but the resistance from the water seemed minimal.(the shaft end of the motor has big holes). So i kept putting the motor in and out of the water for the another 30 mins. Still no effect motor running fine. Then i let the motor sit for a couple of hours and tried it again still fine. So next i removed the screws and pulled the motor apart to check out the inside.

The first thing i noticed was there are no bearings only a bushing at either end. So there goes the greese out the bearings argument. i checked out a few other dc motors around the garage and noticed very few actually have bearings. Ok moving on to the brushes they where all clean with no buildup or corrosion. But i thought 1 day might be a little short for corrosion. So I repeted the water testing over 3 days with no drying or cleaning of the motor. Just ran the motor in the water for 20 mins and then pulled it out and threw it on the floor. After the third day pulled the motor apart again and still no corrosion.

So to conclude, I think im going to use these motors for my thrusters unsealed (not the trolling motors in my other post) they should be very robust. Think about a car rad fan they run very hot exposed to dirt and moisture and run forever. I think after each use i will spray the inner workings of the motors with a quality spray lube rust inhibiter. Keep in mind that i plan to run in freshwater only salt water will be hard on anything you use.

I know this post is a little long. But thought it might be useful to someone. Sometimes forums get full of speculations and theorys with out any hands on testing. Not trying to step on anyones toes just wanting to put some real life abservations out there.
thanks again for the good info on this forum
karson

After spraying the anti corrosion fluid, and throwing the motor back in the water, did you see a shiny slick spreading on the surface? I think, and yes, I should really try it out, that running the motor once out of the water, for a period of time, would dry it enough to ward off most corrosion problem.

I do like your methods, nothing like "doing it".

Salt water will be near a dead short to the small gaps in the motor. And the different metals coupled with the salts and the electricity will make short work of the assembly. Some parts will literally "melt", that is one of the reason they use zinc anodes on industrial ROVs, as well as on boats. The zinc takes the hit, chemically ("ionically"?)-wise, and disintegrate, slowly if there is no electrical fields around, quite rapidly if there is. Then you replace it.

Keep an eye on the test subject, and see if time has an effect on corrosion potential. Ans thanks for sharing the experiment with us!

Let me start by correcting my self. Ment to type observations not abservations. Ok back on topic.

Still running the experiment day six. Same results no loss of power no corrosion. I havent used any sort of lube yet just bare motor for the experiment. I think at this point I'm probuly pushing the motor harder than normal use and giving it absolutly no care. Not removing no water just out of the bucket and onto the garage floor and let it sit.

I'm getting more and more confident by the day. In reality it no diy type thruster is going to last forever anyways so if I can get a fair amount of use out of these. I will be happy.

I will keep the experiment going and keep you posted. Maybe if i get time a youtube video.
thanks karson

I guess you didn't use saltwater? Perhaps then there will be some corrosion?

Still running the test. No change as of yet. Lost track of how many day must be around 10 or 12.
And no i am not using salt water. Fresh water only. Yes i would imagine saltwater would have drastically differn't results. But then again there is the speculation again!. Maybe someone on here should do some hands on testing of a brushed motor in salt water
karson

I want to be able to run my ROV in both salt and fresh water. And I think I've got a brilliant idea, folks!

I got this idea after seeing all the problems people had getting their engines waterproof - even bilge pumps got into problems when they started to hit some depths. The seals that makes them waterproof actually became a problem because they were pressing against the drive shaft, generating heat and slowing the motor down.

Then the bad part of me thought: "Why not leave out the waterproof-capsule-thing?"
But the good part replied: "But how are you going to protect the engine parts from the corrosion?"
Then the bad part said: "Uh, well.. Thats right... Just paint it!"

You see, unlike the brushed DC motor, the brushless has no need for any electrical connection between moving parts. So I thought about giving all the externals and internals a nice coat of clear paint. You see, the power transfer is magnetic.

The only problem I saw arising is that the paint could make the stator and rotor touch eachother, and thereby the paint will scratch off and the engine will rust. To counter this, I would like to give the parts a small finish in red color. This way I see if the stators and rotors are touching and judge if the engine is capable of living when I test them.

I would like to try this out one day.

Bingo!

Yes, people have tried things like this before, but what I've seen was more along the lines of removing the core of the motor and basically just covering it in some type of epoxy or something. The only problem I forsee is that taking the motor apart, depending on your motor, might not be too easy. It would be would be a good solution for some of us if it worked.

Some people use clear nail-polish for added protection. I will run my brushless motors in salt-water openly (sand protection only) and according to the famous German ROV site you only need to wash the engines in fresh water after each dive. I dive for a living with “rust-magnet” equipment such as firearms and we just flush/lube them after each dive.

Green – I don’t think you will see any rust anytime soon but if corrosion is your concern connect through a wire a sacrificial zinc anode, they do miracles…