I seem to remember a discussion about the need to oil the motor bearings every 6th flight.

OMG!

I was on the phone with 3DR about another subject and when finished I said  "oh by the way"

blah, blah, need to Lube? and the answer was yes, I will send you the directions. 

I did not receive the information as of 2 weeks later.

How often to do oil the bearings?

with what oil?

and how?

Decades ago I built anemometers for a research project and calibrated them in a wind tunnel. I found that

it was better to run the bearings dry as it did not collect dirt as well. The bearings were very lightly loaded

so it seemed to work. It seems to me that when I fly and apply vigorous attitude adjustments the bearings are sufficiently loaded to require Lubrication.

Can I get a witness?

How about, how often and the technique.

Safe landings

Dan

 

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Replies to This Discussion

Sorry I wasn't clear, possibly I misunderstood what you were saying.

Conrad style pressed ball bearings are what are used in all the brushless electric motors that are available to us from all manufacturers.

These can either be shielded or sealed or not.

Sealed bearings have side wipers / seals on them and these can be either plastic/rubber or stainless steel.

If you look at both sides of the bearings and it appears to be closed by a plastic or steel ring and you cant see the individual bearing balls at all, it is a sealed or shielded bearing.

These bearings are prelubricated but many of them can benefit from adding a little high quality oil or grease to the shield area which can "wick" into the bearings.

Here is a picture of some very high quality ABEC-7 style Conrad style sealed ball bearings for a top quality KDE motor:

and some Tiger motor shielded bearings:

Tiger Motor and KDE and other motor manufacturers use shielded and sealed bearings which are designed to be used and then replaced.

However because of the shielding and the use of a top quality lubricant they out last unshielded ones even if you don't relubricate them at all.

Sealed bearings are designed to be used for the life of the bearing without any relubrication.

Generally shielded bearings can accept additional lubrication around the shield with it wicking into the bearing.

Sealed bearings are less likely to be re-lubricatable by this method.

In practice, you will probably not be able to determine whether you have a sealed or a shielded bearing so it is best to treat it as shielded and add a bit of lubricant to the seal/shield area once or twice a year (more under use in severe weather or dust conditions).

Some of the cheapest Chinese motors that we use have ABEC style open ball bearings which do not have side seals at all (open bearing)

These definitely can and need to be relubricated (and even cleaned if necessary prior to relubrication).

These are still a Conrad style pressed bearing but they do not have side seals and so are open for relubrication.

For small, high speed electric motors (like our brushless ones) synthetic oils/greases containing PTFE additives will generally provide the longest smoothest operation with the least bearing wear.

Big heavily loaded applications like automobiles, trucks and heavy equipment require higher film strength, but for our little high speed motors, film strength is not so important as having a wide load operating range.

Basically with the normal shielded ball bearings an occasional (once or twice a year) application of a small bit of lubricant to the shields themselves is a good idea and for unshielded bearings bimonthly cleaning and relubrication is probably a good idea under moderate use.

(The effectiveness of lubrication will vary for shielded / sealed bearings, some are simply so well sealed that no lubricant will seep into the bearing.)

Hope this helps, this is a matter of considerable contention, but this is the best I have been able to make of it over the past 5 years.

Best Regards,

Gary

Attachments:

Thank's Gary to this complete explanation, I'm in the correct way with incorrect grease, I'm going to find you recomended one.

I don't have much experience with the bearings in the brushless RC motors, only 608 size. Usually these have a circlip that can be unclipped to allow removal of the shields and then you can use acetone to properly clean the bearing and apply oil inside. I wouldn't apply oil to the outside for it to seep inside through the shields, unless you wipe the bearing dry before taking it out in the wild it'll just attract dirt/dust that sticks on to the oil.

If you can do maintenance on the bearings, I'd have two sets of motors to swap in and out as needed for maintenance without being grounded.

I find this Super Lube here, it's correct?

(second one)  https://www.deere.com.ar/es_AR/parts/featured_parts/general_use/lub...

At conferences I go to, when a group explores a subject often times, a good deal of experience and knowledge happens rapid fire. At some point, the moderator or person who brought up the discussion, gives a first summary that may fire up some more exchanges or the group refines and agrees on the current understanding. Lets try this now.

The question:  How often, with what lubricant, and technique should I tend to my Iris motor bearings?

Summary of discussion to date:

Not everyone in this group fly the IRIS and those who do, in time or have may already, switched to a different motor than stock.

The stock motor as supplied did not come with recommendations that I can find in writing yet some have suggested that a 6 flight maintenance schedule is best.

I do not know if over time, the stock motor has evolved and what the configuration is.

So, in general, depending on the specific bearing design, lubrication if at all, cleaning may or may not be required or in the case of some sealed bearings, not effective.

Experience has demonstrated particulate contamination in the motors..after they are forced air cooled.

Apart from a dynamic film that reduces the stress or working of the bearing material to prevent failure, Lubrication can also transport and retain material that interferes with the rotation..binds the bearing or increases the failure rate. The Crunchy Rotation Syndrome or CRS

It was pointed out that the ball bearings used in motors for aerodynamic propulsion in the direct drive configuration have mainly an axial or thrust load. Unless specifically designed for thrust load, bearing designed for radial loads will be compromised and thus have a reduced service life if the thrust load is above some fraction of the radial load spec. An Iris with battery weighs 1.3 KG thus for a Iris without a payload, the thrust at hover will be 1.3 Kg divided by 4 per motor...does not seem like much but the bearings are tiny.

Proposed Conclusions:

* We need what is specifically recommended by the motor manufacture and published in the user guides.  By this I mean not just oil

* If a lifetime for the motor is specified then one needs to decide on the replacement interval

to satisfy lifetime requirements.  This is complicated by the flight environment. Take off from a beach? 

* Those who increase the acceleration of their drone by using different props or more battery cells should be aware that the bearing life time may not be as expected from lower thrust levels.

* number of flights may not be the best way of looking at this as for example flying at higher altitudes results in a higher rotation speed and we all know that given a bearing under a certain load, we can not increase the rotation speed above a point before the bearing fails.

Anything else?

All the motors I have seen have shielded/sealed bearings, even $10 ones from hobbyking.

Shielded bearings can be lubricated if the shields are removable like Steven Adams described. You can google "how to lubricate inline skate bearings". It's not a short process. It's probably more reasonable to buy new bearings.

Lubricating by letting oil wick into the bearing is a bad idea. It's pretty sure that you'll get some oil on the outside of the shield and this oil will only collect dust. This dust on top of the shield will unavoidably get into the bearing.

Good summary Dan, I don't know If you can move the summary at first, under your topic presentation, A thing that I look important too, is to check each motor with the hand (as someone else explain to me in this forum, im goig to try to find)) periodically doing little force to one side, if you notice something different like a crispy bearing, not fly and try to replace as soon as posible, I think that this is common to any motors. It's great if manufacturers give this information but anyone do it because of different conditions, the only thing that we can have is changuing information here with owr different experiences.

Sorry my offtopic with my no iris cuad but I didn't find many discussions about this subject.

Thanks for the recommendation. I just ordered some! First I will use alcohol to clean them up.

Just got a reply from 3DR

"In regards the motor lubrication; unfortunately we have no guidelines on this at the time, but I'll make sure to bring it up to see if there's any pointers we can share."

So my action item to find out what 3DR recommends is done, yet still no specific guidance.

Hi Cala,

Yes that is SuperLube (oil) labeled for distribution by John Deere.

And their spray should work fine, although what I might do is spray a bit on a Q-tip and rub it on the bearing rater than just squirting it into the motor.

I use the light Superlube grease myself dabbed on the bearing with a toothpick.

but the spray should work fine, this really is great stuff.

Best,

Gary

Thank's Gary, perhaps I can find that one here, I read about It and looks interesting for many uses

Almost none of the bearings used in multicopter motors have removable shields and many of them are not simply shielded, but in fact sealed.

The thinner oil or grease - (Superlube) I have recommended will in fact penetrate most shields, but generally not sealed bearings (and you do not want to inject through or under a rubber sealed bearing.

So far the only company I have seen that has any data regarding their bearings is Tiger Motor who have a bearing replacement schedule for their large motors based on hours of use.

Basically most manufacturers of quality motors supply replacement bearings and expect you to simply replace them when they become worn out (ostensibly due to the fact that they are not disassembleable).

Older motors like Scorpion recommended lubricating (and even had their own lubricant).

But almost all bearings have shields or seals now and information about lubrication has become very sparse.

I am actually glad to see the response you got from 3DR, at least they also appear to have figured out this isn't as simple as they thought it was.

KDE motors have the biggest, best bearings they can stuff in them and most of them have a 3 bearing stack (which is pretty much unique).

Some of them especially their bigger ones are sealed and the rest are shielded.

KDEs motors will outlast (and outperform) any other motor in the same size and weight class, period.

So far none of the motors have adopted proper thrust bearings which is what is really needed for multicopter use, so the best we can do is get ones with the highest quality largest conrad style ABEC bearings we can.

It is possible that ceramic or boron nitride like are available from Boca Bearing might provide extended life, but they can be fussy too.

http://www.bocabearings.com/bearing-applications/rc-bearings

Or these hybrid ceramics

http://www.trbrc.com/category-s/364.htm?gclid=Cj0KEQiAsdCnBRC86PeFk...

Best regards,

Gary

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