In a brushless outrunner motor, the parts that generate friction is the shaft bearings. After some usage it might get dry and start making noise, lubricant can help improving the smoothness and efficiency.
https://oscarliang.com/oil-micro-brushless-motors/
Lubricating your motor bearings is an important part of motor maintenance and in the long run can lead to extended life. more flying == greater happiness
Choosing the right oil/lubricant
Choosing the correct oil to use for your motors can be tricky if you don’t know what to look out for. You want to find an oil/lubricant that can handle parts moving at a high RPM, heavy-duty, high temperatures and humid environments. Knowing all of this you MUST NOT USE WD-40.
WD-40 is possibly one of the worst things you can put on your motor bearings. It is fantastic for applications such as freeing up hinges, locks, cleaning and rust-prevention but it is not marketed or sold as a lubricant. lubricants must have good oxidation resistance to resist sludge build up at operating temperatures (in our case, this can be quite high) and most lubricants are formulated with antioxidant additives to provide this protection. However, WD40 does not contain such additives and would likely degrade to form sludge fairly rapidly.
A good choice of lubricant would be one that is specifically designed for the lubrication of high speed parts at higher temperatures. I’ve found that one of the best choices for this is Singer Super Oil which is a good cheap universal lubricant.
Singer super oil
This oil is specially formulated for lubricating sewing machines which have a lot of small fast moving parts that generate a lot of friction and heat. This oil is perfect for our application and can be found online for around $5 (£3) for 125ml.
Another alternative oil is the Tarot High-Speed Bearing Oil that can be found on banggood for about £7 (£5).
What parts to lubricate
Within the typical brush-less motor designed for use on a quadcopter, you will typically have 2 bearings. See below at the stator of a DYS 1806 and cobra 2204 motor, one bearing is on the top of the stator, and the other is on the bottom.
Top bearing on motor stator (Left is cobra 2204, right is DYS 1806).
Top bearing on stator
Bottom bearing on motor stator:
Bottom bearing on stator
These types of bearings are called shielded bearings and are designed to keep the majority of the grime and rubbish out of the bearing enclosure, unlike sealed bearings which are used on higher quality motors and keep everything out of the bearing enclosure.
Method
I tend to lubricate my motor bearings each week after heavy use, its best to do this after cleaning all the dirt off and out of your motors (crashing is a big part of 250 flying!) and I’ve discovered a little trick that I’ve found works really well.
Hypodermic Needle
You will need to get hold of a hypodermic syringe and rounded needle (or any needle, I prefer to not have sharp things with oil in them lying around on my desk!) for the application of the oil. You don’t need too much, just a few drops on each bearing and then spin the motors to make sure the application is even. Once done, I leave them for the night until I’m ready to fly again the next day! simple right?
How to reach inside motor
You can pick up a pack of hypodermic syringe and needles on ebay for a few $ http://www.ebay.co.uk/itm/231080683351