Motors/Bearings Toast ??

[rocjock]

Hey Guys,

Quick question. Google produced nothing as it's a tricky search. Maybe pushed my motors a bit hard flying dummy weight. Anyhow, the motors came down hot to the touch but not sear my flesh hot. Motors had a mild burning smell. I've never experienced this so I'm a tad concerned. Motors are T-Motor 2814-11. What is the threshold on the bearings before they are totally destroyed / unsafe to fly? I'm assuming it's the bearing grease/lube that is starting to cook. Is this correct?

 

[Old Man]

Believe it or not all the windings in a motor are insulated with something like a thin lacquer. I don't know the exact chemical but the stuff can become hot enough to melt or char and wire shorts can occur thereafter. If things were smelling burnt I'd be concerned. If the bearings didn't push grease out of the seals (they are sealed) the bearings are ok. That smell could be burnt grease so look carefully.

 

[Pumpkinguy]

The deep groove ball bearings used in these motors are made to tolerate temps of 250F and are not likely the source of your smell. Could be winding insulation. Take ohm readings on motors if you have a good meter. They could tell a tale.

 

[cootertwo]

Ahhhh, I love the smell of burning wires in the morning! Kidding of course!

 

[Motopreserve]

I think the concern with excessive temps is also the adhesion and quality of the magnets. Overheating can degrade the magnets. Either way, may be best to play it safe.

 

[Pumpkinguy]

I think the concern with excessive temps is also the adhesion and quality of the magnets. Overheating can degrade the magnets. Either way, may be best to play it safe.

I've found myself thinking the same thing. Can the magnet adhesive withstand the same temps that the copper and bearings can. Maybe that's the weakest link.

 

[Motopreserve]

I think the temp ratings that are listed (IF they are listed) are for the magnets/adhesive. I think KDE talks about this in one of the videos or product literature? Can't recall.

 

[Pumpkinguy]

I've watched the videos. Kde talks about their high temp windings and high quality magnets but never mentions the adhesive rating.

 

[Motopreserve]

I may have heard that on a podcast then.

The guy that runs Cobra motors used to doña pretty informative podcast with some good RC tech info.

 

[learningrc]

A slight burning smell could be almost anything and it doesn't necessarily mean something is wrong. Slightly overloading a motor will not cause a motor to fail. A general rule of thumb for insulation in a motor is that for every 10 degrees C that the motor goes over its rated temperature, the life of the insulation is cut in half. So if magnet wire insulation is rated for 10000 hours at 200 C, then it would be rated for 5000 hrs at 210 C.

Adhesives don't follow this rule of thumb. They usually experience a decrease in bond strength as temp goes up. Typical magnet bonding adhesives are usually rated for around 150 C but could be more or less depending on the specific adhesive used.

Bearing temperature ratings are very dependent on the grease/oil they use for lubricant.

So without knowing specifically what materials are used, it is very difficult to know what would be the weakest point of a motor.