Maintenance of motors?

[rupP]

I am wondering how to check and maintain my motors.
I recently bought a second hand Tarot 810 with the Tarot 4114 motors.
Now, I'm unsure of how much flying time this machine has clocked up and know that at least one of the motors has been changed so possibly high mileage?
Non of the motors have any noticeable end play in the spindle but three do have some lateral play that can be felt when the prop tips are raised/lowered. How much and what sort of wear is acceptable/safe before replacement is required? Some heat is generated too but never too hot to touch.
Also, I see that Tarot do a high speed motor lubricant, should I be lubing the bearings? Maybe dry lube as my practice site has been quite dusty recently.
Seems to be very little info on this subject, any advice/links greatfully recieved.
Rup

 

[Old Man]

Bearing condition and keeping motors clean are big items. Many fail to recognize that when departing and landing in a dusty environment all that kicked up dust gets into the motors, which causes wear and binding. Really hard on gimbal motors since they are right next to the ground.

Most motors use sealed bearings. There's been a running debate about lubricating sealed bearings for a long time. A bearing is sealed to keep the factory lubricant from getting out of the bearing. Stands to reason you won't get any lubricant in the bearing without first removing the seal, in turn likely damaging the seal. IMO buying Tarot bearing lube is like responding to an ad for a bridge for sale in a swamp. Instead replace them after they indicate wear, and examine wiring and connections during pre and post flight inspections.

 

[violetwolf]

What he said

 

[rupP]

Thanks for the reply, I appreciate that opinions may be divided on lubrication.
Looks to me as though the Tarot motors have dust covers, not seals. May be wrong though.
It's the "indicate wear" bit that I'm unsure about. They run smooth but I am unsure wether to be concerned about the play that I described above. Being a newbie, I may well be being over critical.

 

[violetwolf]

Bearing replacement isn't that hard, or too expensive. If it helps you sleep at night it might be a good investment

 

[violetwolf]

Bearings should be replaced every 100 hours anyway. So if its a few hours early it can't hurt.

 

[rupP]

Ha, I wasn't aware that the bearings could be changed on what I suppose are budget motors. I'll look into it.
Still need some idea of how to assess wear. Does this type of motor exhibit any signs before failure? They seem to run smooth enough. Could be that some motors have a little play from new?

 

[rupP]

For peace of mind I'm going to take advice and change the bearings.
These are the only ones I have been able to find so far. http://www.acerracing.com/ball_bearings/4x11mm_CERAMIC_BALL_BEARING-1200-30.html
Are they suitable? Looks like they need lubrication.
Also Barts bearing press looks useful but links to his website don't seem to be working.

 

[Old Man]

Also check www.bocabearings.com for what they might carry.

 

[Chalagi]

I usually get mine from this place and it looks like I might have to buy some now.
http://www.avidrc.com/

 

[rupP]

Thanks for the links, I'm really confused by all the choices now :-}
Rubber seal, dust seal, rubber seal on one side and open or shielded on the other. Heavy steel, ceramic coated or full ceramic lightweights with all the side protection options already mentioned......
Is there a bearing expert in the house that can shed some light on best options for MR needs?
Maybe just buy cheap ones and replace often..... Don't like that option.
I'd like to get this right first time or I may be better off with the tiny bit of play in my existing bearings

 

[Old Man]

Easiest way to qualify a bearing is to find a number on the old bearing and contact a bearing supply to have them look it up in their inventory for a cross reference. Failing that you have the following.

Next way is to measure a bearing to obtain all the dimensions like thickness, outside and inside diameter and note seal type, If you intend to use a permanently lubed bearing you use a seal, not a dust cover. Estimate the speed in revs/min and have that ready if asked. An alternative is terms like high speed and very high speed.

Sealed one side is useful in small engines where the seal assists maintaining engine case pressure and preventing oil leaks while the engine crankcase lubricant keeps the bearings lubed. Not a good idea for an electric motor where oiling up the inside of the motor is not going to make it go faster.

Ceramic bearings are very, very nice. They handle heat extremely well but cost more than steel bearings. They also don't rust and are not as resistant to impact.

The best bearings are rarely found in Chinese made hobby level products. There is a tremendous amount of historical evidence for that. You will find that if you buy higher quality bearings the replacement intervals will become much longer.

As for a tiny bit of play, at our price points there's no such ting as "zero tolerance". That sits up there with "not affordable". There will always be some amount of "play" but the amount is subjective. You want as little as possible.

 

[Pumpkinguy]

Is there a bearing expert in the house

You rang? Lol. I was in the bearing business for 20 years. I am a "Certified Bearing Specialist" see here: www.bsahome.org

Do not try to remove the seals and replace lubricant. These bearings are sooooo small and have a close gap between the seal and inner race. That is where you need to pry from to remove the seals and it's pretty hard to do without damaging.
Don't buy into the hype of all these different bearing materials. Ceramic, stainless etc. Industrial customers don't use them and they have bearings running 24/7/365 so why should you? I used to distribute stainless bearings for special applications mainly in the food industry but they are useless for our application. Stainless is softer than regular case hardened bearing material and usually have reduced load and speed capacities.
Regarding seal type, 99% of the motors in this hobby use "sheilded" type bearings. They have a metal seal that comes very close to the inner race but doesn't actually touch it. This is the best type of seal for having the lowest amount of drag (resistance) but it's ability to keep contaminants out is not the best. I have seen a couple brands of motors as of late that have "sealed" bearings. Identified by a rubber covered metal sheild (usually black rubber)
These sealed bearings have a rubber wiper that contacts the inner race giving the best possible resistance to contamination but this comes at a cost. Higher drag in the bearing which creates heat and efficiently loss.
There are also "low drag" versions of these rubber sealed bearings. Nsk bearings make a seal called a "VV" that could be the best compromise.

My opinion would be to buy good quality bearings and switch them out every 50 hours or so. Make this part of your preventative maintaimamce schedule. Truth is, these bearings could very well last 500 or 5000 hours or longer. The whole point of preventative maintenance is to replace wearable components when they are still good. We do this because we have no way to predict when a bearing will fail. Sometimes they will show symptoms when they are getting old and sometimes they will give no warning. Replacing them early and often almost completely eliminates the chance of your bird dropping out of the sky from a bad bearing.

A bearing change on my big hex costs about $200. That is using very good quality bearings. Cheap bearings could be $30-$40 for the whole rig. When I'm flying my movi and gh4 I have over $20000 in the air. I refuse to buy cheap bearings.

 

[Pumpkinguy]

I keep these in stock for my U7's. NSK is Japanese and make awesome bearings. Other good brands are SKF, FAG, NTN, Koyo, Nachi just to name a few.

 

[Old Man]

Pumpkinguy,

Wonderful to see we have a true expert with us and I'd like to tap your knowledge and experience if you'll permit.

Being a long time small gas two stroke RC engine guy my experience with bearings aligns more with bearings that get "wet" but something I've noticed for years is how a lot of heat is generated at a bearing. For reference I have to fall back to that gas engine experience where a running engine is hot where you'd expect it to be, at the cylinder, but cool enough to hold in your hand at the case. However, at the front of the case where the crankshaft is supported by a bearing in a machined case race the case becomes quite hot. In some cases it becomes hot enough to melt the epoxies used in carbon fiber spinners.

I have a theory that much of the heat generated by our electric motors is created at the bearings, and that employing a better bearing may well make for a cooler running motor. Eliminate the possibility of the bearing spinning in the case. What's your take on that?

 

[Bartman]

fwiw, i usually run sealed bearings on the upper bearing and shielded on the lower bearings. in a coaxial quad, motors are either right side up or upside down so upper and lower is all relative.

also, for replacing bearings, this video has helped a lot of people and I don't ever recommend leaving out the washers even though I said to leave them out in the video. plan to replace washers and snap rings whenever you replace bearings. the website i mentioned, USdrones.us doesn't exist anymore. it was changed to something else which was eventually shut down.

 

[Old Man]

Bart,

Where is the source for your new spring clips?

 

[Pumpkinguy]

Get an open bearing. No seals, no lubricant. hold it in your hand and use compressed air to spin it at a high speed. Within seconds that sucker will be so hot you gotta drop it. Yes the bearings themselves generate heat. More drag = more heat. Even grease creates drag. Super high precision bearings like in a dentists drill often use oil as a lubricant. Look in any bearing manual and each bearing will have a speed rating for grease and a higher speed rating for oil.
Getting a bearing with a higher level of precision would likely allow the motor to run a bit cooler but where these high level precision bearings shine is @ high speed. 40, 50, 60K rpm ect. I am not convinced $100 bearings would solve your problem.

I think if anything getting a standard bearings with a slightly larger internal clearance such as a "C3" would help the most. Its possible that your housing or shaft fit is too snug causing a "preload" on the bearing which could lead to heat.

http://www.skf.com/ca/en/products/b...general/bearing-internal-clearance/index.html

 

[Bartman]

Bart,

Where is the source for your new spring clips?

mcmaster.com

washers too but you have to experiment with washers to find the exact specs you'll need. there are a lot of different types to choose from and mcmaster is great about providing dimensions so it usually just takes some time to work it out.

 

[Bartman]

I am not convinced $100 bearings would solve your problem.

i'm guilty of buying stainless bearings but i've also bought cheap bearings at RC shows and they worked fine.

best indicator of bearing wear seems to be noise from motors but feeling them for wiggles in any particular direction contributes to the final decision.