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Old Nov 08, 2007, 04:35 PM
Chophop is online now
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Discussion

Brushless Motor Life Expectancy


I am looking at a BLDC motor for my tail and found this description I will link. It says this motor (BLDC) has 5 - 6 times the life expectancy of a brushed IPS motor. Only 5 - 6 ? Doesn't seem like much.
Maybe the magnets or bearings go bad. Anyone know these Feigao 120 sized BLDCs ?

http://www.bphobbies.com/view.asp?id=V001105

CH
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Old Nov 08, 2007, 05:49 PM
ChrisWNY is offline
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On an inrunner or an outrunner, the life expectancy is limited by the bearings. Outrunners can last forever if you don't pump too much power through them, burning out the motor. Even an inrunner, however, should last many, many years before you'd need to replace the bearings. You can even apply very light-weight oil on those bearings to extend their life.
Last edited by ChrisWNY; Nov 08, 2007 at 08:19 PM.
Old Nov 08, 2007, 06:02 PM
Ron van Sommeren is offline
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OUtrunners have bearings too.
Old Nov 08, 2007, 06:34 PM
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I would think the inrunner bearings would be subjected to more heat, throw the lube, and fail sooner. The outrunner's bearings would be enduring more shock vibrations from the significantly higher centrifugal force in an outrunner. The outrunners have several advantages in cooling, the "fans" built into the can, and the exposed magnets do not sit in stagnant air.
Maybe it evens out. Could be the description is wrong. People who used the short can version for a tail motor on a 300 heli said they had over 350 flights and still running.
I am deciding on a belt conversion for my little 300 and need to decide if I want to gain 60 to 80g on a belt tail, or about 15g for a brushless tail drive system. That 300 does not even like +26g from a heavier battery. It gets mushy and does not turn as well.
This is only a little heli for gentle graceful flying and I really don't have a need for high performance tails. Reliability and weight is my concern. I think the simple BLDC tail will do the job and be much more reliable if the description is wrong. I have some 400 helis for the wild stuff.



CH
Old Nov 08, 2007, 06:54 PM
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A bearing is a bearing. You treat it poorly it will treat you poorly no matter what the application is - inrunner or outrunner.

I don't understand the recent amount of backlash against inrunners.

They are more efficient, can cool through the entire length of the case, can put out the most amount of powerout per weight. They each of their own uses and if you don't like a gearbox application then you have a choice.

Old Nov 08, 2007, 07:00 PM
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But how long do the Feigao IPS replacement BLDCs last ?

CH
Old Nov 08, 2007, 08:02 PM
Challenger 413 is offline
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Depends on the running conditions such as amperage, volts, crashes, etc. I have one going on 2+ years. the first thing I did was to use some goop where the wires exit in the back. I ran it geared for the first 150 flights, have been running it in a small wing direct drive for the last 75 flights, I have been using a heatsink though. (4100 KV)

Challenger413
Old Nov 08, 2007, 08:16 PM
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Is it good practice to lube the bearings? If so, what? 3in1, mmo???
Old Nov 08, 2007, 10:57 PM
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Most, if not all, of the motors we use have sealed bearings, so all using lubricants, even thin oil like sewing machine oil or 3 in 1 Oil, does is gunk up the shaft. Unless you know that the seal has failed, you are better off to not do anything at all to it. If the motor augers in from a crash, blow it out with compressed air.

If you feel you must lube it, use a silicon based lube that will not attract as much dirt as grease or oils do.

FC
Old Nov 09, 2007, 05:44 AM
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Most bearing seals can be removed and replaced. Fasten it down in a bearing block, use a sharpened needle under a magnifier, gently pry the tiny C retainer ring out. Of course you all KNOW it is probably going to fly, so be ready for that.
I had some loctite in some heli blade grip bearings. I soaked it in acetone a few days. Acetone is not a good solvent for loctite but that's what I had. The loctite crumbled and fell out in specks. I put red lithium #2 back in, reinstalled the shield and it's been great ever since.

BTW , loctite does not always set if it is not in a confined application, so be sure to soak up any loose loctite in crevases etc.

CH
Old Nov 09, 2007, 10:09 AM
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Shields not Seals

I have yet to see a brushless motor with sealed bearings. They have all been shielded instead.

Sealed bearings require no periodic or additional lubrication.
Shielded bearings do. They can also be contaminated by small particles that get by the shields. If contaminated, they should be replaced.

The main advantage of shielded bearings, as we use them, is reduced drag.

Joe
Old Nov 09, 2007, 11:53 AM
Bare is offline
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From Experience: Feigaos are ..Junk
their bearings are v often Bad , fresh from the box, the windingwires on the teemy F's break .. often.
Only advantage is their 'lowish' price..
Old Nov 09, 2007, 12:02 PM
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For 12mm motors Medusa are head and shoulders above the rest.
Old Nov 09, 2007, 12:17 PM
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Bearings should not be lubed without first cleaning them out. New oil or grease no matter what type, may not be compatible with what's already in the bearing. Once contaminated the lube can break down and will not do its job.
Old Nov 09, 2007, 12:41 PM
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the bearings used in many motors running 3mm shafts are so small that they are simply not capable of withstanding much of a shock load especially down the axis of the shaft. If you drop that little motor from even a few inches and it lands on the shaft the tiny little balls will get dented also the ball races will be dented, its down hill very quickly from this point and the bearing will eventually self destruct.
This is why it is so important that the bearing (during assembly) is pressed into its pocket using force applied only to the outer race. some of these bearings will become damaged if we allow the bell to "snap in place" under the magnetic attraction.
Dan


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