Oil cooling your hub- NOT snake oil!

[Punx0r]

When I looked at doing a submerged PC years and years ago all I could find was a purpose-made product by 3M for cooling supercomputers. The spec was great, but was about $300 per gallon.

A few people were using straight mineral (baby) oil, but there were warnings that it would eventually cause failure of the electrolytic capacitors.

A product safe for a motherboard is probably unnecessary for a simple hubmotor

 

[bowlofsalad]

http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=37972&hilit=snake+oil&start=210#p606917 This earlier post from this thread inspired a train of thought.

A lot of people have the issue of having a lot of leaking through the bearings. Typically the solution is to fill the hub motor with an appropriate amount of fluid, not too much or you'll leak, not too little or you won't get a lot of thermal advantage. What I really like the idea of is using extremely well sealed bearings as the outer bearings (and unsealed bearings for anything inside the motor). However, what I like even more is the idea of using well sealed cartridge bearings that have just one external seal and no internal seal so the bearings has a little ATF splashing around a tiny bit on the bearings themselves. This translates to extremely clean and well lubricated bearings for a long time, rolling super smoothly. In my imagination, I think that bearings can last an insanely long amount of time if they are well maintained, which to me, keeping the bearings clean and well lubricated is what well maintained is all about. According to the post I linked to, 'DU' or 'DW'(I am assuming this means sealed on one side rather than both) cartridge bearings might be the ticket, but I don't know what they mean by torque and constant revolutions. I also don't know if you can get any cartridge bearings that may have excellent seals that would prevent fluid from leaking on both sides and simply remove one of the seals so the bearings are exposed to the inside.

With these leak prevention bearings you might be able to add a bit more fluid (I am not suggesting anyone consider doubling their fill volume because of this type of setup) which would improve thermal capacity and help lubrication of the 'external' bearings. I have no idea how it would work out in practice though, what an exciting parameter for experimentation. This makes me wonder if there is any chance for leaking from between the axle and the cartridge or the cartridge and the hub motor body. I imagine the placement with needle point accuracy of some ATF compatible sealant might help. I doubt this would give me confidence to place the motor on it's side and not expect leaking, but it probably wouldn't hurt.

I suppose, if this all works out how it is supposed to, the question to ask would then be, how long would the DW or DU cartridge bearing seal last? This is probably a question best directed to an engineer that works at a company such as NSK or SKF under various parameters (temperature, torque, RPM, and so on). Maybe there is a way to gain some level of understanding on this subject without consulting someone directly.

 

[GCinDC]

fyi, from here:

Bearings with seals

Bearings with seals, designation suffix 2RS1, use a acrylonitrile-butadiene rubber, sheet steel reinforced seal that fits against a recess in the inner ring side face (fig 3). The lip of the seal exerts a light pressure against the inner ring for a positive seal. The periphery of the seal engages in a recess in the outer ring to provide a good sealing. The permissible operating temperature range for these seals is –40 to +100 °C and up to +120 °C for brief periods.

my bearing seals leaked after i surpassed this limit...

here after i removed the seals, showing ATF that got in, from page 9 in this thread:

 

[macribs]

fyi, from here:

Bearings with seals

Bearings with seals, designation suffix 2RS1, use a acrylonitrile-butadiene rubber, sheet steel reinforced seal that fits against a recess in the inner ring side face (fig 3). The lip of the seal exerts a light pressure against the inner ring for a positive seal. The periphery of the seal engages in a recess in the outer ring to provide a good sealing. The permissible operating temperature range for these seals is –40 to +100 °C and up to +120 °C for brief periods.

my bearing seals leaked after i surpassed this limit...

here after i removed the seals, showing ATF that got in, from page 9 in this thread:

Your bearings leaked after you hit a temperature higher then 120 °C, while your hub motor was filled with ATF oil?
Did you go "pikespeak" steep and long to reach that high temperature? Or is this form of cooling not removing heat fast enough?

Did you have thermal sensor on the hub so you could monitor the temp?

 

[Howlermonkey]

Most speedometer gears are "plastic" in automatic transmissions.

Mine in my worked 3n71b are 35 years old and are not degraded into goo....... But they were formulated for thier intended purpose of living in atf.

If ATF is ruining adhesives that bond magnets, use an oil free of the crazy levels of "detergent" that are in most atf.

 

[Marc S.]

What I really like the idea of is using extremely well sealed bearings as the outer bearings (and unsealed bearings for anything inside the motor). However, what I like even more is the idea of using well sealed cartridge bearings that have just one external seal and no internal seal so the bearings has a little ATF splashing around a tiny bit on the bearings themselves. This translates to extremely clean and well lubricated bearings for a long time, rolling super smoothly. In my imagination, I think that bearings can last an insanely long amount of time if they are well maintained, which to me, keeping the bearings clean and well lubricated is what well maintained is all about...

I suppose, if this all works out how it is supposed to, the question to ask would then be, how long would the DW or DU cartridge bearing seal last? This is probably a question best directed to an engineer that works at a company such as NSK or SKF under various parameters (temperature, torque, RPM, and so on). Maybe there is a way to gain some level of understanding on this subject without consulting someone directly.

I had setup my Bafang BPM2 in 26" wheel in this manner. Had removed the inside facing seal on both new RS2 axle bearings. Lasted about 4,500-5,000km till some small amount of ATF leaked through occasionally. I'd used that Bafang usually with 15s LiPo at 35A on my 20km commute, but flogged it sometimes with 20s as well till the planetary gears shredded.

Guess what, I'm currently using a vanilla direct drive hub at 20s/40A without issues for 4,500km... (MXUS 1307 = 9C 2807 clone)

 

[bowlofsalad]

I had setup my Bafang BPM2 in 26" wheel in this manner. Had removed the inside facing seal on both new RS2 axle bearings. Lasted about 4,500-5,000km till some small amount of ATF leaked through occasionally. I'd used that Bafang usually with 15s LiPo at 35A on my 20km commute, but flogged it sometimes with 20s as well till the planetary gears shredded.

Sealed bearings require lubrication on both sides of the seal, without this lubrication the seal will burn (friction) and break. If you don't have seals on both sides with grease or oil inside the bearing, it's pretty important that enough oil splashes the bearing to keep both the bearings and the seal lubricated. I am not saying this happened in your situation(anything is possible who knows), but I take it that a little bit of weeping is seen as typical. I thought I'd share that here as it's pretty useful information.

How much oil did you see leaking through your bearing seals?

I am not sure what RS2 bearing seals are. http://www.skf.com/group/products/bearings-units-housings/ball-bearings/deep-groove-ball-bearings/single-row-deep-groove-ball-bearings/sealed-bearings/bearings-with-contact-seals/index.html This page gives a good explaination and illustration of bearings with seals, 2RSH, RSH, RS1, who makes RS2? My first guess was you meant 2RS, but I'd rather ask.

Guess what, I'm currently using a vanilla direct drive hub at 20s/40A without issues for 4,500km... (MXUS 1307 = 9C 2807 clone)

I am happy for you if you are happy. I've ridden direct drive hub motors for 1000s of miles, they work great in many respects. What I don't enjoy is the extra size and weight. I don't want to break more spokes than I already have, which is why I often find myself leaning towards preferring the idea of using a geared hub motor. There are some very small and lightweight geared hub motors.

 

[The Stig]

BTW welcome to the forum Howlermonkey

 

[Howlermonkey]

Thanks for the welcome.

Pretty cool forum full of smart people who are willing to experiment.

 

[richdeloup]

Hi, I posted this somewhere else but its probably more specific to be on this thread
I haven't had time to read through the full thread, so apologies for any repeat findings etc, having a read tonight ...

 

[richdeloup]

9c clone running at 100v 60amp, tested to 90 degrees overheat temperature.

No mods overheats in 8.12 minutes
A 4mm thick aluminium disc polyurethaned on each side and filled with 200ml oil, overheats in 12.86 minutes with no leakage
A 4mm thick aluminium disc riveted on each side, with thermal grease in between for direct contact with cover and filled with 200ml oil, overheats in 19.34 minutes with slight leakage from rivets. (thermal grease melts so thermal pads or glue would be better)

As above but with a 2mm copper disc riveted inside of cover, raised approximately 2mm, with holes in cover for oil flow to contact both side of cover and one side of external disc.
Closed headed copper rivets used and external disc also raised approx 2mm from cover. max temp 73.3 degrees before out of battery at 23mins.

What I cant figure out is how exactly this is working, any suggestions welcome?

So the internal copper discs runs very close to the windings and should be taking some of the heat either directly or helped by being covered in oil.
Some of the heat should run to the external discs through the copper rivets. (going to add a whole lot more for next attempt)
Some of the oil/heat should get trapped between the cover and external disc. Maybe because the oil is trapped, it has more time in contact with the cover to transfer the heat through, rather than constantly being on the move??

 

[amberwolf]

What temperature scale are you using? Because if it's F, I get temperatures hotter than that as ambient, for wintertime on hot days.

(just trying to insure people understand it's important to use the scale or units of their measurements, or else the whole data is useless for comparison to anything other than itself).

 

[richdeloup]

What temperature scale are you using? Because if it's F, I get temperatures hotter than that as ambient, for wintertime on hot days.

hehe yes its celsius!

if it's F, I get temperatures hotter than that as ambient, for wintertime on hot days.

would have thought that that gave it away

 

[richdeloup]

980 grams added weight,
2x 2mm thick inner copper discs,
2x 4mm thick external aluminium discs
200ml ATF

Oh and rivets and gas fitting valve, so around the 1kg added weight.

 

[richdeloup]

Wow, huge interest, maybe this has already been covered?

 

[richdeloup]

Switched to coconut oil

 

[Stevil_Knevil]

Switched to coconut oil

Bonus points for experimenting, but ..coconut oil will coagulate into a hard waxy state - almost like a candle.

It would be a real bummer to jump on your eBike, grab a handful of throttle and instantly rip all of the hall and phase wires off

Maybe switch to canola or olive oil if you want a food-based coolant?

 

[richdeloup]

Yep thats all this is, random experimentation and I chose it because it solidifies somewhat.
Oil bath servers are apparently having great results using coconut oil.
If wires start ripping off, I may start mixing it up somehow??
So far things are fine and its nice to be able to throw my bike in the back of a car with no leakage
Cooling seems to be better too but ive yet to take any actual readings so maybe this is wishful thinking....

 

[Ohbse]

What is with the obsession with alternative oils?

ATF or mineral oil is absolutely ideal, I don't understand why you would even need to experiment, especially with things much better used as food than lubricant in high temperature spinning motors.

To add my experiences to this thread:

I was previously running an HS3540 in a 26" rim with Hookworms, 20s lipo running ~65 amps. Something like 6kw peaks, travelling 12.5km each way on a daily basis. Prior to oil cooling I was hitting 120c at the end of the journey. After drilling a very small hole near the centre bearing, sealing the covers with a bead of high temperature gasket silicon I injected ~100ml of very lightweight, general purpose oil.

The difference was immediately apparent - the temperature at end of journey dropped a full 40c and that was probably riding harder than I had been previously as I was less concerned with temperature. I continued to commute with this setup for a number of months and towards the end of that I found that temperatures were again climbing towards 100c. This was due to my very lightweight oil being slowly lost out of my very small vent hole. It took several months and I would estimate I lost ~70% of the oil I originally injected. There was an oily residue on the motor/spokes/rim which accumulated road scum, it was not unlike the underside of most ICE vehicles. It had also travelled and contaminated all of the wires that came out of the axle. Even 40cm away from axle exit it was evident there was oil inside the jacket of the phase wires. Re-terminating the hall sensor wires when I changed controller was a real pain in the ass as I had to de-grease all the wires before I could get a soldered joint. Definitely wasn't dripping though, volumes were very low.

If I was to continue riding with this motor (I still have it, I just upgraded to Cromotor) I would definitely continue to run oil cooled. Rather than a small hole and leaving it open I would drill a larger hole, tap this and thread in a shortened capscrew through which I would rill a vent hole a fraction of the size of my original. <1mm. This allows for filling relatively easily, keeps the pressure from building up too much (and forcing oil out through bearings) but should reduce the mist effect I noticed. I would run with ATF.

HOWEVER I will say that if you're pushing the motor as hard as I was or more and you're seeing triple digit temperatures (in C of course) then you're probably using the wrong motor for the job. You can bandaid this by improving the cooling, but you're going to have a vastly superior experience overall if you just buy a motor that can give what you're asking of it. I moved on to Cromotor in a 24" rim. Running the same battery/controller on the same journey but riding even faster I cannot get the motor to go over 38C with no oil. Obviously there are limits to this line of thinking, but I think the majority of the people interested in oil cooling in this thread are probably doing it to cover up the inherent shortcomings of shitty motors rather than for absolute peak performance potential. If you're oil cooling your hub monster because you're hitting 35kw peak input then carry on

 

[Stevil_Knevil]

Yep thats all this is, random experimentation and I chose it because it solidifies somewhat.
Oil bath servers are apparently having great results using coconut oil.
If wires start ripping off, I may start mixing it up somehow??
So far things are fine and its nice to be able to throw my bike in the back of a car with no leakage
Cooling seems to be better too but ive yet to take any actual readings so maybe this is wishful thinking....

I am all in for experimenting!

It does take a while before coco oil begins to solidify.

Maybe set an electric heater to preheat the oil in your hub before a ride?

 

[richdeloup]

Maybe set an electric heater to preheat the oil in your hub before a ride?

Yep ive been trying to suss out the temperature/time that it turns liquid, will test it out in the week ahead...

Rather than a small hole and leaving it open I would drill a larger hole, tap this and thread in a shortened capscrew through which I would rill a vent hole a fraction of the size of my original. <1mm. This allows for filling relatively easily, keeps the pressure from building up too much (and forcing oil out through bearings) but should reduce the mist effect I noticed. I would run with ATF.

This is what I have done, now trying coconut oil to see if there are any noticeable differences compared to ATF?

I moved on to Cromotor in a 24" rim

I have a Cromo in a 24" rim but Im experimenting with a £60 motor which I can overheat easily, in order to quickly see results on a motor that I don't mind destroying. Once happy with my preferred best cooling method, Ill prob mod the Cromo in the same way

These motors have been tested to destruction for many years in many different ways, so nothing new there. I'm mainly interested in trying to find the best way to transfer the heat through the cover.

I think the majority of the people interested in oil cooling in this thread are probably doing it to cover up the inherent shortcomings of shitty motors rather than for absolute peak performance potential

Very true, also fairly interested in the weight difference though, especially if putting less than 5kw through them.
shitty motor, cooled and on a 24" rim around 7-8kg
Cromo 2 on 19" moto rim around 14-15kg

 

[Ohbse]

Your experiments with the side covers are awesome! Awesome results and innovative thinking, all I meant by my comments regarding fluid is that's a problem that's been solved by 50 years of improvements in the ICE world. There's few advantage to further experimentation, but potentially many downsides (like the guy with mayonnaise coolant)

There's a huge amount of ground to cover in iteratively improving lightweight electric vehicles, the make-up of the lubricant and coolant seems like it's been pretty well covered.

 

[richdeloup]

the make-up of the lubricant and coolant seems like it's been pretty well covered

For sure, big companies have researched this for years.

To be honest, ebayUK was doing a deal on buy 1 get 1free coconut oil My girlfriend uses one in her stir frys, and I stuck one in my hubby, mainly because ATF was dripping out of the air hole, when I slung the bike in the car to take to the forest. Whole place now smells like the Caribbean

 

[Ohbse]

Whole place now smells like the Caribbean

Well that definitely is an advantage! Did you drain out the ATF first or running some sort of ATF/coconut hybrid fluid? That probably is covering new ground...

 

[Stevil_Knevil]

Damn, suddenly craving a pina' colada