Motor Bearings DO make a difference in temps

[Logan's_Rcs]

Recently, I asked TP Power to send an extra set of end caps for their 4060 line so I could test out some different bearings in my motor.. I tested the bearings by spinning my motor no load for 45 seconds at full throttle (Do not do this at max voltage of your motor, it will destroy it). After 45 seconds no load, I took the temperature.

First, I tested Acer Ceramics at 45 seconds. After 45 seconds, no load, my motor came to around 91 degrees Fahrenheit.
Next, I tested the stock NMB 688 bearings. After 45 (actually slightly less) seconds, the motor was at 101 degrees Fahrenheit!

Just by going to better bearings, my motor dropped 10 degrees in the same amount of time. There was no air flow around the motor, and all the ESC settings were the same. Only change was my bearings. I took the tests on different days inside and the ambient temp was the same. The motor started at the same temp both times.

I'm going to be looking for more bearings to test out in this regard, are there any other brands you guys would like to see me try? I was considering VXB and pro-motion rc ceramics next.

 

[Chapinb]

Interesting. Where was temp tested?
If 2 bearings added 10 degrees to the center of the can, I have my suspicions. That would mean the bearing itself is waaay over temp spec to push that much heat in that little time. Talking like open flame type heat.

 

[Logan's_Rcs]

Interesting. Where was temp tested?
If 2 bearings added 10 degrees to the center of the can, I have my suspicions. That would mean the bearing itself is waaay over temp spec to push that much heat in that little time. Talking like open flame type heat.

I took the temp throughout the can. It makes sense that the whole can would get warmer, as bearing friction is part of the no load current. If there is more resistance, more amps need to be drawn to get the motor going, therefore warmer motor.

 

[Chapinb]

Bearing friction is def part of the rotational friction. But the amount of heat produced by the bearing I have trouble believing.
In no way am I suggesting you didnt get the numbers posted. But having a hard time swallowing the heat and time required to transfer that heat came from just the bearings.

Some rough napkin math means each oem bearing produced ~12w of heat more than the ceramic if heat transfer was immediate and if none was transferred to the rotor. If 12w is the difference, meaning the bearing itself produces significantly more heat. Thats a cooked bearing.

 

[Logan's_Rcs]

Bearing friction is def part of the rotational friction. But the amount of heat produced by the bearing I have trouble believing.
In no way am I suggesting you didnt get the numbers posted. But having a hard time swallowing the heat and time required to transfer that heat came from just the bearings.

Some rough napkin math means each oem bearing produced ~12w of heat more than the ceramic if heat transfer was immediate and if none was transferred to the rotor. If 12w is the difference, meaning the bearing itself produces significantly more heat. Thats a cooked bearing.

I mean it's possible the OEM bearings had an issue, but I ran the motor in my MT410 without too much of a problem. Granted, it did get warm decently quick, but I've had the same result with other motors too. The OEM bearings spun freely, weren't jammed and I didn't see any damage. I could try takin ga video of the test and posting the results?

 

[Chapinb]

Not needed, don't doubt the results you got. I think some other variable not accounted for is at play. What it is, no idea?
I would be curious as to the amps drawn from the lipo, or better yet a power supply, how that would change. Or the temp directly on the bearing. Hmm, now you have me thinking on this, might need to order a few lil bearings for myself.

Side note - ceramic bearings don't deal with shock/impacts well. Is there enough shock in an rc to cause an issue? Never played with ceramics due to the cost.

 

[Logan's_Rcs]

Not needed, don't doubt the results you got. I think some other variable not accounted for is at play. What it is, no idea?
I would be curious as to the amps drawn from the lipo, or better yet a power supply, how that would change. Or the temp directly on the bearing. Hmm, now you have me thinking on this, might need to order a few lil bearings for myself.

Side note - ceramic bearings don't deal with shock/impacts well. Is there enough shock in an rc to cause an issue? Never played with ceramics due to the cost.

yeah they don't do great with that, the ones I'm using are hybrid ceramics. They have a metal cage, but ceramic balls. Plus, the motor shouldn't be getting that much impact anyway, if it is, I think there are larger problems lol.

I'm gonna order some VXB bearings soon and try the test with them again, probably post it in the thread later. It would be pretty awesome if I could find a bearing that would drop 15-20 degrees on the temp over the OEM. Doubtful, but it would make a huge difference when bashing.

 

[Chapinb]

Post the results please.

@LibertyMKiii Any experience with changing bearings and seeing a difference?

 

[Logan's_Rcs]

Post the results please.

@LibertyMKiii Any experience with changing bearings and seeing a difference?

Alright, I just ordered two VXB's highest quality ABEC7 ceramic bearings. They'll be here in about a week, I'll update the thread then!

 

[Logan's_Rcs]

Recently, I asked TP Power to send an extra set of end caps for their 4060 line so I could test out some different bearings in my motor.. I tested the bearings by spinning my motor no load for 45 seconds at full throttle (Do not do this at max voltage of your motor, it will destroy it). After 45 seconds no load, I took the temperature.

First, I tested Acer Ceramics at 45 seconds. After 45 seconds, no load, my motor came to around 91 degrees Fahrenheit.
Next, I tested the stock NMB 688 bearings. After 45 (actually slightly less) seconds, the motor was at 101 degrees Fahrenheit!

Just by going to better bearings, my motor dropped 10 degrees in the same amount of time. There was no air flow around the motor, and all the ESC settings were the same. Only change was my bearings. I took the tests on different days inside and the ambient temp was the same. The motor started at the same temp both times.

I'm going to be looking for more bearings to test out in this regard, are there any other brands you guys would like to see me try? I was considering VXB and pro-motion rc ceramics next.

Also for anybody interested, here is the link to the ACER bearings I picked up: https://www.acerracing.com/products...oaiG4rmqAgQXa3SRJaq-MzGWgP6WHPdBoCdOAQAvD_BwE

 

[#ARRMArcfanboy4life]

At a glance, a 10º difference doesn't seem likely. I would be curious to see what current draw, battery voltage, temp sensor readings, across different motors with a variety of bearings.

 

[Logan's_Rcs]

At a glance, a 10º difference doesn't seem likely. I would be curious to see what current draw, battery voltage, temp sensor readings, across different motors with a variety of bearings.

I agree, I think that would be really interesting. I would love to get a motor analyzer to look at the current draw and such.

 

[ih8nixon]

Hate to be the turd in the punch bowl, but I don't think this is the best way to get realistic results. You're operating a brushless motor at pretty much its worst efficiency point (Full RPM, Pretty much no torque) with no measured RPM to test the effects of pretty much an unloaded bearing. I know a seemingly good unloaded bearing can go to crap with a load placed on it. Also I might be wrong, but I think it's possible the NMB bearings could actually be spinning faster pushing the motor into a worse efficiency point thus creating more heat.

A gear train driving a propeller (or some other load) with a tach would probably show a more realistic response and give more meaningful results.

 

[Logan's_Rcs]

Hate to be the turd in the punch bowl, but I don't think this is the best way to get realistic results. You're operating a brushless motor at pretty much its worst efficiency point (Full RPM, Pretty much no torque) with no measured RPM to test the effects of pretty much an unloaded bearing. I know a seemingly good unloaded bearing can go to crap with a load placed on it. Also I might be wrong, but I think it's possible the NMB bearings could actually be spinning faster pushing the motor into a worse efficiency point thus creating more heat.

A gear train driving a propeller (or some other load) with a tach would probably show a more realistic response and give more meaningful results.

Interesting thought! I was thinking about getting a motor analyzer that would show the current and rpm as well. That would probably be the better way of doing it.

Also, about the bearings spinning faster and creating more heat... I don't think that's how it works. I should've stated this before, but the Acer bearings I got weren't broken in. I just did the test again and I got a couple degrees cooler, this time 89 degrees instead of 91, again measuring the whole can for the same time.

According to the theory, once the Acers broke in and spun faster, I should've got warmer temps since the motor is spinning faster. However, I actually got cooler temps this time! Still, maybe this is worth the purchase of the SKYRC Motor Analyzer. If we know which motor bearings are super efficient, maybe we could get away with smaller motors in rigs that we think require larger ones. Probably not, but it would be interesting to test!

 

[LibertyMKiii]

Post the results please.

@LibertyMKiii Any experience with changing bearings and seeing a difference?

I put synthetic bearing oil in my motor bearings every 2 runs so they never went bad

 

[Chapinb]

Brushless motors produce more heat, or run less efficient at higher rpm, and that gets exacerbated after ~30k rpm. But the motor efficiencies dosent play a roll here. Unless the bearing provides so much bearing resistance it slows the rpm significantly and raises amp draw - and thats worth verifying rpm so good point there. That would be a very large resistance to have a significant change. Higher rpm may even be preferred as that would stress the bearing more.
I don't have a motor analyzer but can monitor rpm, volt and amp draw. When I get home I plan on ordering a set of ceramics to try for myself.

Surpass does offer ceramic bearings for their rocket motors for what its worth.

Poking around at some studies, if the only change is steel balls to ceramic, you can gain upwards of 40% efficiency, usually closer to 20%. That differential decreases as you add shields and oil to <10%. I don't expect any noticeable difference in performance between them in this case. More testing needed!

Id suspect type of bearing shield (sealed vs shielded) and oil (thin vs thick) has a much bigger role to play.

 

[Logan's_Rcs]

Brushless motors produce more heat, or run less efficient at higher rpm, and that gets exacerbated after ~30k rpm. But the motor efficiencies dosent play a roll here. Unless the bearing provides so much bearing resistance it slows the rpm significantly and raises amp draw - and thats worth verifying rpm so good point there. That would be a very large resistance to have a significant change. Higher rpm may even be preferred as that would stress the bearing more.
I don't have a motor analyzer but can monitor rpm, volt and amp draw. When I get home I plan on ordering a set of ceramics to try for myself.

Surpass does offer ceramic bearings for their rocket motors for what its worth.

Poking around at some studies, if the only change is steel balls to ceramic, you can gain upwards of 40% efficiency, usually closer to 20%. That differential decreases as you add shields and oil to <10%. I don't expect any noticeable difference in performance between them in this case. More testing needed!

Id suspect type of bearing shield (sealed vs shielded) and oil (thin vs thick) has a much bigger role to play.

Shielded vs sealed and the type of oil definitely play a larger role in how free the bearing spins. From what I've noticed, NMB and Acer seem to use really thin oil, while other brands like Avid and FastEddy use heavier amounts of grease.

 

[Xjeepguy]

Really cool test, and interesting results.

I will say this, I'm an industrial maintenance technician, and I typically use a heat gun to identify when motor bearings are going bad. You can literally measure a drastic difference in temperature between each end of the motor, to indicate if a bearing is starting to go out, and the overall temperature of the motor to indicate there's a problem in the first place. So it stands to reason that our RC motors are just a scaled down version of this. So it comes as no surprise to me that a higher tolerance/quality bearing would lower the overall temperature of the motor. Under load it would likely be amplified, maybe install a balanced flywheel?

 

[Ghast]

Good info in here, friction causes heat so I can see it affecting motor temps but I'm surprised by how much.

Looks like I'll be adding motor bearing maintenance higher on the list

 

[N.Mango]

I have always kept my motor bearings clean and lubed...but only because of the thought of dirt would drive me nuts.
I never thought about the heat aspect of bearings.

I guess it wasn't being done JUST for ocd/shelf queen reasons.