Homebuilt ROVs Forum

We all know that running a brushed DC motor in oil works, but is generally a bad idea. As the brushes get worn, carbon and dirt gets mixed in with the oil and would cause it to fail sooner or later.

My question is, how long would it last? Could you expect only a couple of hours or days of operation?
Maybe someone here have some experience with this?

I dont know what motor you use ... is it right it loses parts in oil?

I'm using brushless-motors in oil and there is no dirt... nothing which will cause failure.
The only problem is the temperature of the oil. You cannot use this in sealed cases because of rising oil pressure will crack every case. So use a equalization of pressure...

Brushed motors is the way to go, thew work pretty much flawlessly in oil.

The thing is that I already have a bunch of brushed motors, and controller boards for them.
Brushed DC motors give off a fine dust from the brushes when they run. its not much, but over time it will accumulate in the oil, and in the end make the oil both conductive and even ruin the bearings.
Since I already have the brushed motors and drivers, I just wanted some input if it's a good idea to just use them in the beginning, until they eventually die, or spend some extra cash and go brush less right from the start.

.. spend some extra cash and go brush less right from the start.

Do this. You will NEVER regret.

I still think mag-coupled thrusters is the way to go.

If the oil heats up doesn't that mean that your motors are working too hard to turn in the added viscosity of the oil (rather than air)?

Of course you are loosing power because of higher friction. But you are not running at high power all the time so ... this is not an option for (underwater)-microcopter

a_shorething wrote:I still think mag-coupled thrusters is the way to go.

If the oil heats up doesn't that mean that your motors are working too hard to turn in the added viscosity of the oil (rather than air)?

It doesn't necessarily mean anything is wrong - brushed dc motors can get hot even under normal operation in air. Regardless, brushless motors would work better in this application.

Way to wake up an old thread, but today I actually tested a cheap brushed 12v dc motor running in mineral 10W-30 motor oil.
Note that I will be using brushless motors on my rov, this was just for fun

The result?
~40mins and it was completely dead.

I have a few more of these motors if someone wants me to test with different oils?

Interesting post Olegodo. Have you pulled the motor apart yet to check out the brushes and commutator? I'm wondering whether the oil softened the brush material and caused it to clog up and short out the insulating space between the commutator segments, or if the oil soaked into the brushes and caused them to go high-resistance?
Regarding the other oils to try, i don't have any suggestions, but was interested in Dressur4's mention of glycol used in pressure-compensated pump motors (induction, not brushed). Those pump motors I think used sleeve bearings, or bushes. Not sure what material. Maybe the hard plastic stuff used in boat skeg bushes?? The motors you are testing i guess would be bronze bushed. I did some internet searching on glycol/antifreeze/corrosion inhibitor (concentrated it has an oily feel) wondering whether it could be used as a lubricant for brushless motors. No good for ball-bearings apparently, but bronze bushes?..... Maybe glycol wouldn't affect the brush material, but if conductive at all would cause corrosion problems for the dissimilar metals in the bush and shaft?

I did not pull it apart. these motors are small and let's face it, full of oil
After it died, I did measure the leads to the motor and there was no contact, so I guess the brushes burned up or something.
I should also note that these are very cheaply made motors. Also, I don't really thing they last too long running in air at 12v either.

Your glycol/antifreeze idea sounds interesting. I might try that.

If anybody else has some input, please let me know.