Oil cooling geared hub motors

[JES2020]

Has anyone had any luck, good or otherwise, partly filling your geared hub motors with automatic trani fluid ( ATF)?
Interested to find out what the cooling results were, as well as what type and how much ATF was used, any leaking issues etc?

 

[tomjasz]

Statorade for DD. Neither is appropriate for gear drive hubs.

Will this work in geared hub motors or mid-drive motor systems?
No, not really. Geared hub motors do not have their rotor shell exposed to ambient air, so increasing the heat conductivity from the motor stator to the rotor does not help get the heat to ambient air outside. Similarly, most mid-drive motors (like the Bafang BBSXX) are inrunners, where the magnets and rotor are on the inside and the heat generating stator, and conducting heat to them would serve no purpose. The benefits of Statorade are really only present for outrunner motors (magnets on the outside) where the rotor is exposed to air flow.

 

[Gearedfast]

Has anyone had any luck, good or otherwise, partly filling your geared hub motors with automatic trani fluid ( ATF)?
Interested to find out what the cooling results were, as well as what type and how much ATF was used, any leaking issues etc?

Yes, it can be done and it is quite effective using relatively small amounts of ATF low viscosity, or better yet ultra-low viscosity.
The first geared hub motor I tried oil cooling on I used no more than 100ml which kept it below the axle. It is important not to use too much not just for potential leaks but to keep friction drag in the motor low, so the less the better.
Adding small amounts I monitor no-load wattage as long as it does not go too high it is not a problem at all.
The motor which is nominal 500watts I was running at up to 1500watts and naturally it was getting hot quite fast, up to 100c and beyond with full throttle.
With the ATF spinning around and closing the air gap the highest it hit was 65c which is quite impressive.
I can monitor temps with an internal thermistor and cycle analyst so those numbers are a fact.

The trickiest part naturally is sealing the motor. A motor with a high waterproof rating would be ideal but using appropriate silicone o-rings for the axle to bearing and silicone gasket material in the rotor bolt holes (not too much) and some thread sealer, and around the motor housing cover, as well as the cable exit and entrance can work quite well if the surfaces are prepped properly.

 

[Gearedfast]

Statorade for DD. Neither is appropriate for gear drive hubs.

Will this work in geared hub motors or mid-drive motor systems?
No, not really. Geared hub motors do not have their rotor shell exposed to ambient air, so increasing the heat conductivity from the motor stator to the rotor does not help get the heat to ambient air outside. Similarly, most mid-drive motors (like the Bafang BBSXX) are inrunners, where the magnets and rotor are on the inside and the heat generating stator, and conducting heat to them would serve no purpose. The benefits of Statorade are really only present for outrunner motors (magnets on the outside) where the rotor is exposed to air flow.

True, Statorade is useless for geared motors since it sticks to the magnets so pouring it into a geared hub motor and hoping for the best would not be a good idea.

However, both types of motors geared and DD have been successfully cooled using ATF fluid. Mid-drive motors have decent air cooling the way they are built so a bit of oil may or may not be of much significance to cooling, but it certainly could be worth a try as an experiment

 

[indianajo]

I seriously don't need oil with the gears rotating around in them. If kept below that level, the armature would never touch the oil. In a direct drive the coils that produce the heat are on the outside where rotating oil would not be such a drag.

 

[Gearedfast]

I seriously don't need oil with the gears rotating around in them. If kept below that level, the armature would never touch the oil. In a direct drive the coils that produce the heat are on the outside where rotating oil would not be such a drag.

In regards to geared hub motors, the idea is to close the air gaps with the stator core and the windings with the rotating stator shell and the motor housing. You really can't have the oil, not in contact with the gears.
Just a little bit goes a long way when the motor is spinning, I have never used more than 100ml usually less does the job

 

[tomjasz]

Keeping your MAC cool with ATF​

"Warning Warning Warning...if you follow my recommendations for adding ATF to a MAC to keep it cool, eventually it will leak on the brake rotor and you will lose your back brakes.

The good news is that adding 2.5-3.5 ounces of low viscosity ATF to your MAC will keep it cool with the max temps never going over approximately 85C.

The leakage didn't occur while riding on relatively smooth paved surfaces but over the last couple days I have ridden off road on some pretty rough ground with exposed roots and rocks...my guess is the rough surfaces caused the ATF to splash around inside the motor more, therefore it came in contact with the opening in the axle where the wiring exits...and eventually started to seep out of the left side of the axle and onto the brake disc.

For anyone riding off road at relatively slow speeds and needing high torque...my recommendation is to go with a Mid-Drive motor like the Bafang BBSHD because you can utilize the bikes gearing as well as the motors gearing to keep the motor spinning at an efficient rpm and produce less waste heat.

What seemed like a great idea has its limitations...whatever you do, have fun, be careful and try to learn from my mistakes."

 

[JES2020]

Yes, it can be done and it is quite effective using relatively small amounts of ATF low viscosity, or better yet ultra-low viscosity.
The first geared hub motor I tried oil cooling on I used no more than 100ml which kept it below the axle. It is important not to use too much not just for potential leaks but to keep friction drag in the motor low, so the less the better.
Adding small amounts I monitor no-load wattage as long as it does not go too high it is not a problem at all.
The motor which is nominal 500watts I was running at up to 1500watts and naturally it was getting hot quite fast, up to 100c and beyond with full throttle.
With the ATF spinning around and closing the air gap the highest it hit was 65c which is quite impressive.
I can monitor temps with an internal thermistor and cycle analyst so those numbers are a fact.

The trickiest part naturally is sealing the motor. A motor with a high waterproof rating would be ideal but using appropriate silicone o-rings for the axle to bearing and silicone gasket material in the rotor bolt holes (not too much) and some thread sealer, and around the motor housing cover, as well as the cable exit and entrance can work quite well if the surfaces are prepped properly.

Thank you for this very clear explanation !
I have a couple of questions:
Do you need a breather port for the air in the motor as it expands and contracts with the heat cool cycle?
How did you introduce the ATF into the motor?
Do you have a pic of the o rings for the bearings?
And finally, did you just smear the sealant on the outside of the motor cover or remove the cover?
Thanks

 

[JES2020]

True, Statorade is useless for geared motors since it sticks to the magnets so pouring it into a geared hub motor and hoping for the best would not be a good idea.

However, both types of motors geared and DD have been successfully cooled using ATF fluid. Mid-drive motors have decent air cooling the way they are built so a bit of oil may or may not be of much significance to cooling, but it certainly could be worth a try as an experiment

Right, I understood long ago that Statorade is for DD motors NOT GH's. Besides sticking to the magnets it also has iron partials ( I think) which would not be good with the gear teeth. Someone dosn't understand that ATF and Statorade are two totally different animals, so naturally they are confused.

 

[indianajo]

For anyone riding off road at relatively slow speeds and needing high torque...my recommendation is to go with a Mid-Drive motor like the Bafang BBSHD because you can utilize the bikes gearing as well as the motors gearing to keep the motor spinning at an efficient rpm and produce less waste heat.​

Speed reduction with bike sprockets is a complete myth on 99% of bikes. Bike sprockets speed up the wheel. A very few bikes have a 36, 40, or 46 tooth rear sprocket to torque multiply. Very rare,however. My most expensive bike has a 32 rear sprocket which gives me 1:1 ratio for hill climbing. I climb >77 hills @ 8 mph in my 30 mlle commute with a geared hub motor. Does not overheat. Do not try to climb 1000' in an hour; it will overheat a geared hub motor.
IGH shimano alfine & nuvinci will reduce speed & multiply torque. The IGH sturmey archer S80 & SA 3 speed do not.

 

[Gearedfast]

Thank you for this very clear explanation !
I have a couple of questions:
Do you need a breather port for the air in the motor as it expands and contracts with the heat cool cycle?
How did you introduce the ATF into the motor?
Do you have a pic of the o rings for the bearings?
And finally, did you just smear the sealant on the outside of the motor cover or remove the cover?
Thanks

 

[Gearedfast]

A properly sealed electric motor requires no vent only cooling, in this case, it is probably not a good thing at all, in the long run, to have a vent since it will lead to a bit of fluid leakage which no one wants.

But... If you can afford it you can test it with very good results, which is all you really want who really cares about a tiny amount of seepage.
Open a motor up and seal it as best you can from the inside out and get great results with minimal seepage using a small 1 or 2 mm vent hole near the axle, preferably with some absorbate material covering it.
Just make sure your vent is not on the rotor side, as it suggests a vent is basically a leak don't put it on the rotor side as some unfortunates have done.

I filled the motor I have experimented on with a drilled and tapped hole in the outer shell using a brake bleed kit, putting the hole there also makes it easier to drain, you could use one of the rotor bolt holes you left unplugged as well, not so easy to drain through though.
By the way, your motor probably has grease on the parts it will dissolve with the ATF sloshing around so you will want to change it after a while, that's if you did not bother to clean off with mineral spirits prior.

Instead of putting o-rings which most motor axles don't have channels for... and if you don't have the means to cut your own to put o-rings in, you can put silicon sealant on the axle to seal the air gap between. You don't want excessive material interfering with the bearing locknut fit and be sure not to interfere with its inner and outer bearing race rotation using too much sealant!

As a more advanced option which you probably accomplished with proper sealing anyway if you don't want any leakage whatsoever from an enclosed space like a motor you really need to create a vacuum-sealed environment, it is actually easier to accomplish with the same materials plus a vacuum pump to ensure all is sealed!
Hope that helps a bit I can't write a step by step guide since there are so many motor configurations and it really is a wide-open topic with many unique solutions, only people that have failed at it will disagree

 

[JES2020]

A properly sealed electric motor requires no vent only cooling, in this case, it is probably not a good thing at all, in the long run, to have a vent since it will lead to a bit of fluid leakage which no one wants.

But... If you can afford it you can test it with very good results, which is all you really want who really cares about a tiny amount of seepage.
Open a motor up and seal it as best you can from the inside out and get great results with minimal seepage using a small 1 or 2 mm vent hole near the axle, preferably with some absorbate material covering it.
Just make sure your vent is not on the rotor side, as it suggests a vent is basically a leak don't put it on the rotor side as some unfortunates have done.

I filled the motor I have experimented on with a drilled and tapped hole in the outer shell using a brake bleed kit, putting the hole there also makes it easier to drain, you could use one of the rotor bolt holes you left unplugged as well, not so easy to drain through though.
By the way, your motor probably has grease on the parts it will dissolve with the ATF sloshing around so you will want to change it after a while, that's if you did not bother to clean off with mineral spirits prior.

Instead of putting o-rings which most motor axles don't have channels for... and if you don't have the means to cut your own to put o-rings in, you can put silicon sealant on the axle to seal the air gap between. You don't want excessive material interfering with the bearing locknut fit and be sure not to interfere with its inner and outer bearing race rotation using too much sealant!

As a more advanced option which you probably accomplished with proper sealing anyway if you don't want any leakage whatsoever from an enclosed space like a motor you really need to create a vacuum-sealed environment, it is actually easier to accomplish with the same materials plus a vacuum pump to ensure all is sealed!
Hope that helps a bit I can't write a step by step guide since there are so many motor configurations and it really is a wide-open topic with many unique solutions, only people that have failed at it will disagree

if I understand correctly ;
You are using the ATF in place of the motor grease?
You drilled a drain hole w/ plug on the very bottom of the motor,( between the spoke attach points)?

My only concern is with sealing the bearings, do you know of any pic or link that would clarify just exactly where this sealant should be placed?

Thanks

 

[tomjasz]

You are using the ATF in place of the motor grease?

NO!

you’ll only need additional cooling if you are pushing a motor beyond its specified voltages. The right motor for ones style and riding location is important, in my experience.

 

[Gearedfast]

if I understand correctly ;
You are using the ATF in place of the motor grease?
You drilled a drain hole w/ plug on the very bottom of the motor,( between the spoke attach points)?

My only concern is with sealing the bearings, do you know of any pic or link that would clarify just exactly where this sealant should be placed?

Thanks

Yes ATF is excellent for this purpose and why it is used in Transmissions the low viscosity can travel easily in the many narrow passages while still providing excellent lubrication. Don't use CVT fluid it is thicker and made for continuously variable transmissions.

The initial downside when you add the ATF and it sloshes around for a while it will combine with the grease and raise the viscosity which defeats the purpose of using ATF, it won't hurt anything but it will increase internal resistance which you don't want.
So let it do its thing and then after a bit drain it and refill with fresh ATF, you may have to do that more than once so it is probably better to clean it up, to begin with using an appropriate degreaser.
Don't use that stuff on the windings whatever you use, it is unlikely they are contaminated with grease anyway.
I still recommend a drain and refill regardless of how well it is cleaned up just to get rid of any contaminants or bits of debris.
One thing I have noticed having opened up quite a few motors is they actually use very little grease those gears are very tuff, especially the blue composite ones.
And yes I drilled and tapped an M5 .8 thread common on bikes, right next to the motor housing ring gear, there is a bit more room there and the shell metal is good for a couple of threads which is all you need, again motors vary and you will likely have to grind down a button head screw a bit unless you make a thicker fiber gasket, seal with blue Loctite.

As for the gasket material for the bearings just rub some oil-resistant gasket maker or sealer on the inner bearing surface and a bit on the axle, if the tolerances are tight which they should be you won't need much, remember to let is set for the recommended amount of time before putting the oil in.
And clean any that happens to get on threads.

This is a work in progress for me there is no manual and so just remember there is a certain amount of trial and error to all this you will have to keep an eye on things and make adjustments to how you go about it.
And as I said previously you will more than likely get a bit of seepage from any vent hole you drill, I have never had oil dripping or shooting out though.
As others have done though I just used some gasket material over the hole just to be on the safe side.

I mentioned creating a vacuum, handheld ones with gauges are common, if your motor can hold one it probably will not need a vent at all (hint). And it means you did an excellent job of sealing the motor.

To wrap it up (and probably where I should have started) unless you are like me, an enthusiast with no problem experimenting and have temp sensors installed and programmable controllers with detailed displays, etc. just to push your motor to the limits it may very well not even be necassary for you or anyone to even bother with this since many bikes and kits are most likely designed to work within a specific range and for specific weights and uses.
Electric motors can take a lot of heat we are talking over 100c to 120c and even more depending on the quality and build of the motor where your windings will likely start to burn and If you get to the 130c range you will start to have real problems with the gears, and the magnets can lose their magnetism.
When you are hitting or getting close to those numbers yeah you need cooling if you want the motor to last.
If you go for it let us know how it goes!

 

[JES2020]

Yes ATF is excellent for this purpose and why it is used in Transmissions the low viscosity can travel easily in the many narrow passages while still providing excellent lubrication. Don't use CVT fluid it is thicker and made for continuously variable transmissions.

The initial downside when you add the ATF and it sloshes around for a while it will combine with the grease and raise the viscosity which defeats the purpose of using ATF, it won't hurt anything but it will increase internal resistance which you don't want.
So let it do its thing and then after a bit drain it and refill with fresh ATF, you may have to do that more than once so it is probably better to clean it up, to begin with using an appropriate degreaser.
Don't use that stuff on the windings whatever you use, it is unlikely they are contaminated with grease anyway.
I still recommend a drain and refill regardless of how well it is cleaned up just to get rid of any contaminants or bits of debris.
One thing I have noticed having opened up quite a few motors is they actually use very little grease those gears are very tuff, especially the blue composite ones.
And yes I drilled and tapped an M5 .8 thread common on bikes, right next to the motor housing ring gear, there is a bit more room there and the shell metal is good for a couple of threads which is all you need, again motors vary and you will likely have to grind down a button head screw a bit unless you make a thicker fiber gasket, seal with blue Loctite.

As for the gasket material for the bearings just rub some oil-resistant gasket maker or sealer on the inner bearing surface and a bit on the axle, if the tolerances are tight which they should be you won't need much, remember to let is set for the recommended amount of time before putting the oil in.
And clean any that happens to get on threads.

This is a work in progress for me there is no manual and so just remember there is a certain amount of trial and error to all this you will have to keep an eye on things and make adjustments to how you go about it.
And as I said previously you will more than likely get a bit of seepage from any vent hole you drill, I have never had oil dripping or shooting out though.
As others have done though I just used some gasket material over the hole just to be on the safe side.

I mentioned creating a vacuum, handheld ones with gauges are common, if your motor can hold one it probably will not need a vent at all (hint). And it means you did an excellent job of sealing the motor.

To wrap it up (and probably where I should have started) unless you are like me, an enthusiast with no problem experimenting and have temp sensors installed and programmable controllers with detailed displays, etc. just to push your motor to the limits it may very well not even be necassary for you or anyone to even bother with this since many bikes and kits are most likely designed to work within a specific range and for specific weights and uses.
Electric motors can take a lot of heat we are talking over 100c to 120c and even more depending on the quality and build of the motor where your windings will likely start to burn and If you get to the 130c range you will start to have real problems with the gears, and the magnets can lose their magnetism.
When you are hitting or getting close to those numbers yeah you need cooling if you want the motor to last.
If you go for it let us know how it goes!

Very very useful information !
I will save this link for future use. I had modded my controller for more amp and was concerned about overheating the motor, but all is well.
Love to learn how to oil cool these motors though.
Thanks

 

[Gearedfast]

Very very useful information !
I will save this link for future use. I had modded my controller for more amp and was concerned about overheating the motor, but all is well.
Love to learn how to oil cool these motors though.
Thanks

I will update things down the road maybe with pics and possible video, again though there are many different motors and configurations, there is no manual no kit just ingenuity and skill.
You never mentioned the motor you had a concern with.
Anyway, I did my first motor complete including drying time in less than 3 hours, If I can do it successfully with a halfass job anyone can

 

[JES2020]

I will update things down the road maybe with pics and possible video, again though there are many different motors and configurations, there is no manual no kit just ingenuity and skill.
You never mentioned the motor you had a concern with.
Anyway, I did my first motor complete including drying time in less than 3 hours, If I can do it successfully with a halfass job anyone can

Updates will be great.
I actually don't know what brand of GH I have, as the seller will not say. I got it from Calibike, the 52v 1500w kit.

 

[Ken M]

Statorade for DD. Neither is appropriate for gear drive hubs.

Will this work in geared hub motors or mid-drive motor systems?
No, not really. Geared hub motors do not have their rotor shell exposed to ambient air, so increasing the heat conductivity from the motor stator to the rotor does not help get the heat to ambient air outside. Similarly, most mid-drive motors (like the Bafang BBSXX) are inrunners, where the magnets and rotor are on the inside and the heat generating stator, and conducting heat to them would serve no purpose. The benefits of Statorade are really only present for outrunner motors (magnets on the outside) where the rotor is exposed to air flow.

Please....you make some very incorrect statements.

Heinzmann actually makes a gear hub motor with oil bath lubrication of the planetary gears. There is no reason this could not be done in a mid drive motor given the gears are almost entirely isolated from the motor section. The main reason why none of the mid drive motor companies have done this is because they don't want to motors to be too reliable (the bike industry has too many bean counters and marketing people making design decisions so planned obsolescence is the norm not the exception).

You may have also forgot that most mid drives are in-runner designed motors where the stator does have a direct conductive heat path to the external housing of the drive unit. Statoraid in direct drive hub motor is a much improve heat path vs the mag air gap but it's never easy to know just how much stator aid is needed or when it needs to be serviced.

 

[Gearedfast]

Updates will be great.
I actually don't know what brand of GH I have, as the seller will not say. I got it from Calibike, the 52v 1500w kit.

I actually looked at that kit last year.
It is a really small-looking motor almost guaranteed to be overpowered looks more like a common 350-500watt motor.
If he is not listing the motor and he is not telling directly means he either does not know himself or you may not like the answer.
Anyway, that does not mean it is not a good motor. Look on the shell for any identifiers no matter how trivial they look, serial number prefixes are unique to manufactures.
Sometimes you just have to open them up and look for the manufacturer stamp the reason why is it may simply be rebranded or just lacking the original brand, nothing uncommon about it.
The motor looks a lot like a Bafang with the round spoke flanges.
If it has the lock spacers up against the inner race of the sealed bearings it is a good candidate for easy sealing, most likely it does.
And if you open it up and see tiny orange o-rings where the bearing slips over the axle that's even better as that means it is designed to have a waterproof rating, you may be able to add better larger ones just look on Amazon for metric sized silicon o-rings they sell kits cheap.
Most side plates have a large o-ring around them but don't count on it being oil tight