Any motor experts here - Motor "breathing"?

[Rawnei]

So I've been thinking about that concept EcoDrift mentioned multiple times where they put breathing tubes on the motor due to temperature and pressure differences to let it breathe and prevent it from sucking in dirt from anywhere else.

To give some context here's a good example:

https://ecodrift-ru.translate.goog/2020/12/08/begode-ex-popytki-sdelat-dorabotki-kolesa/?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=sv&_x_tr_pto=wapp

Any merit to this? Is this really a thing that makes a difference? Besides EcoDrift I really haven't seen this mentioned anywhere else.

We have a lot of riders here in Stockholm who get noisy or busted bearings sometimes during rainy periods but mostly during winter, in Stockholm we salt the bike paths a lot so of course that is a contributing factor but I was thinking if there is also some correlation to the breathing theory, without a breather is it really more likely that dirt will be pulled into bearing? Does anyone actually know (not speculation)?

[mrelwood]

There aren’t any official investigations or scientific papers made on the matter if that’s what you’re after. But air volume does change considerably with temperature, and usually the bearing is the easiest way for the air to enter the motor. Those are facts. So yes, the theory makes a lot of sense, and I haven’t seen it being refuted anywhere. At least not with anything to back up their doubts.

 This popped up in discussions when the V11 bearing issues became widespread. Before the hollow bore motors I don’t think the bearings were open to the insides of the motor in the same way, so naturally there wasn’t any air going through the bearings.

 Making a breather tube that doesn’t allow any moisture to enter the motor is not trivial though. So for most people it’s best to rely on a well greased external bearing seal. If the motor cover is well sealed and the bearing seal does its job well, the motor would be practically a closed bottle. It would just decrease in pressure when it’s cold, and increase when it gets hot. No air would go in or out from/to the motor.

[Rawnei]

12 minutes ago, mrelwood said:

There aren’t any official investigations or scientific papers made on the matter if that’s what you’re after. But air volume does change considerably with temperature, and usually the bearing is the easiest way for the air to enter the motor. Those are facts. So yes, the theory makes a lot of sense, and I haven’t seen it being refuted anywhere. At least not with anything to back up their doubts.

 This popped up in discussions when the V11 bearing issues became widespread. Before the hollow bore motors I don’t think the bearings were open to the insides of the motor in the same way, so naturally there wasn’t any air going through the bearings.

 Making a breather tube that doesn’t allow any moisture to enter the motor is not trivial though. So for most people it’s best to rely on a well greased external bearing seal. If the motor cover is well sealed and the bearing seal does its job well, the motor would be practically a closed bottle. It would just decrease in pressure when it’s cold, and increase when it gets hot. No air would go in or out from/to the motor.

But what happens then if motor is perfectly sealed? i.e. air can not get in or out?

[mrelwood]

1 hour ago, Rawnei said:

But what happens then if motor is perfectly sealed? i.e. air can not get in or out?

I described that at the end of my previous reply already. The pressure just rises and lowers, but air doesn’t get in or out to equalize the pressure.

[techyiam]

35 minutes ago, mrelwood said:

The pressure just rises and lowers, but air doesn’t get in or out to equalize the pressure.

Even if the side covers are perfectly sealed so that they are air tight, there is no way the bearing seals are air tight. There bearing seal lip against the round axle does not provide an air tight seal.

[0000]

Coming from the ebike world, Justin at ebikes.ca (who has a nice YT channel too by the way) has published a lot of fantastic independent research over the years on the particulars of electric hub motor performance, one project showing how due to temperature and pressure differentials will suck moisture up through the phase wires regardless of how sealed the motor is. Super unintuitive I know. I'd send a link, but bad connection. You can search YT or endless-sphere.com for more info if curious. *edit I should say, this weakness isn't much of a problem on our wheels since the phase motor wires and connections aren't as exposed to the elements like they are on most ebike conversions, but it's still a good example to show how porous a seemingly "sealed" hub motor can be.

So basically moisture gets trapped and oxidation/rust will happen inside the motor over time if you frequent wet conditions no matter what.

If I was not a fair weather rider and used my wheel for commuting, there's a few motor mods I would do to ensure the laminated steel stacks + magnets don't rust out and improve performance depending upon motor wind config (assuming I'd want to keep the wheel long-term):

1. Disassemble the motor and spray coat the stator and magnet ring with electrical insulating varnish. Forgot the brand, but the red/orange stuff is what everyone uses on endless-sphere. I've done it with my ebike MXUS motor with success.
    
2. I don't know about the breather tube mod, but considering these motors are functionally the same as e-bike hub motors I would drill some small holes on each side of the motor cover plates near the windings to allow for moisture to dry/escape from motor case after wet rides when the wheel is just sitting there.
    
3. Might as well add ferrofluid from ebikes.ca if using fast-wind motor to improve heat transfer and cooling for better efficiency while you got the thing open too.
    
4. With the bearings, assuming the seals are good (inspect), clean out the presumably sub-par random grease and replace and pack with quality marine grease.

That's what I'd do anyway if I wanted a bulletproof all-weather commuter I want to keep for a long period of time. Also, I'd probably make a spray station and routine to gently hose the wheel off if exposed to winter salts.

Edited March 3, 2023 by Vanturion
link

[alcatraz]

That's an interesting theory. Clean out some of the goo around the power cable entry hole into the motor and you've started the experiment. Let us know how it went and after a few thousand kms.

[mrelwood]

8 hours ago, techyiam said:

Even if the side covers are perfectly sealed so that they are air tight, there is no way the bearing seals are air tight. There bearing seal lip against the round axle does not provide an air tight seal.

Absolutely, it doesn’t. But when there’s only grease against the bearing, pulling the grease through the bearing’s internal seal requires a lot of force. So it allows for the pressure in the motor to increase and decrease by a certain amount in relation to ambient.

 

7 hours ago, Vanturion said:

1. I would drill some small holes on each side of the motor cover plates near the windings to allow for moisture to dry/escape from motor case after wet rides when the wheel is just sitting there.

That’s a really bad idea for EUCs though. Unless there’s something wrong with the motor cover edge seal, water doesn’t get into the motor. But it absolutely would if there were holes on the motor cover near the tire.

Riding on wet ground makes the whole wheel well a shower, which would definitely push some water in through the holes. And due to surface tension of water, it wouldn’t drip out after a ride. And considering that it takes a few days for the tire to dry out inside the wheel well, the water inside the motor would take very long to evaporate through the holes.

Carefully adding a layer of silicone between the motor cover edges and the rim is a good idea on some wheels though.

[EUCzero]

Too compensate for variable air pressure, a membrane could be used. Already in use in many places for this application.
Not sure how to do in on the motor and still maintain long life as well as not fucking up the balancing of the wheel. But...
 

On the motor cover..... a small hole could be made. But on the inside a large volume made by a rubber membrane should cover the hole. That way it would "breath" without letting air/moisture into the wheel itself.

 

Edited March 3, 2023 by EUCzero

[Rawnei]

The discussion is very focused on different technical solutions, but do you guys think this might be one reason why bearings break down?

[EUCzero]

Sure.
But only if there is water clinging on the outside of the bearing when the motor is cooled down.

This could happen on a warm motor ridden thru a long deep puddle, cooling the motor down fast as the outside of the bearing is soaked.
But it is just a theory. And the motor needs to be cooled at the same time as the bearing is very wet for it to actually suck in water.

Edited March 3, 2023 by EUCzero

[Rawnei]

21 minutes ago, EUCzero said:

Sure.
But only if there is water clinging on the outside of the bearing when the motor is cooled down.

This could happen on a warm motor ridden thru a long deep puddle, cooling the motor down fast as the outside of the bearing is soaked.
But it is just a theory. And the motor needs to be cooled at the same time as the bearing is very wet for it to actually suck in water.

Any theory as to why we see more bearing problems during the winter? Salt shouldn't make water and dirt more likely to penetrate bearing seals should it?

[techyiam]

35 minutes ago, mrelwood said:

Absolutely, it doesn’t. But when there’s only grease against the bearing, pulling the grease through the bearing’s internal seal requires a lot of force. So it allows for the pressure in the motor to increase and decrease by a certain amount in relation to ambient.

Even if the grease in the bearings is properly packed (25%-30% grease fill), the grease can barely support shear, and thus, while the bearings are rotating, air molecules can get through. If there is any appreciable pressure difference, the grease will yield. Then there is a matter of the air gaps between the bearing and the housing, both are not perfectly round. Coming from the factory, there is no sealant there. Generally speaking, a cartridge bearing is not considered to have hermetic sealing.

Here is a link to a hermetically sealed hub for a trailer. The hub is pressurized to 5-10 psi internally.

Hermetically sealed hub.

[techyiam]

1 hour ago, Rawnei said:

Any theory as to why we see more bearing problems during the winter? Salt shouldn't make water and dirt more likely to penetrate bearing seals should it?

Based on my own experience with my T3, my guess is that it takes much less saltwater than plain water to cause corrosion. Saltwater is very corrosive for steel (iron).

And when I remove the wheel and remove the seal, I saw no pockets of water. It was just discolored factory grease packed normally. Rusted rolling elements and races were evident. 

I believe regularly packed bearings can tolerate a small amount of moisture. But if the rolling elements and races are not lubricated in a quality marine grease, that small amount of saltwater inside the bearings will be enough to cause corrosion in quick order.

Quote

Saltwater corrodes metal five times faster than fresh water does and the salty, humid ocean air causes metal to corrode 10 times faster than air with normal humidity. Bacteria in ocean water also consumes iron and their excretions turn to rust.

Effects of salt water on metals

Edited March 3, 2023 by techyiam

[Punxatawneyjoe]

2 hours ago, Rawnei said:

Any theory as to why we see more bearing problems during the winter? Salt shouldn't make water and dirt more likely to penetrate bearing seals should it?

I'm guessing temperature can play a role here as well, my guess is most greases used in these machines aren't for extremely low temperature and don't provide adequate lubrication under cold temperature conditions. Just my 2 cents. I recently cooked the bearings on my v11 with one 4 mile ride in -7°f temperature and no moisture. They were fine beforehand and noticed them getting loud on the way back.

[Cerbera]

25 minutes ago, Punxatawneyjoe said:

my guess is most greases used in these machines aren't for extremely low temperature and don't provide adequate lubrication under cold temperature conditions.

I guess that might explain why my bearings seem to be doing OK in the cold and wet - that LiquiMoly stuff I filled mine to the max with is designed for the freezing seas !

Edited March 3, 2023 by Cerbera

[mrelwood]

3 hours ago, techyiam said:

And when I remove the wheel and remove the seal, I saw no pockets of water. It was just discolored factory grease packed normally. Rusted rolling elements and races were evident. 

When I opened my bearings that had been extremely loud for months already, I also saw discolored grease, but no signs of rusted surfaces once I washed the grease off with acetone. My guess was that the noise and colored grease came from tiny sand particles that the bearing had been grinding over and over.

 After a wash and new grease the bearings were silent and worked normally.

[techyiam]

13 minutes ago, mrelwood said:

My guess was that the noise and colored grease came from tiny sand particles that the bearing had been grinding over and over.

Interesting that sand particles got inside. Did you ride in muddy water? Usually riding in just rain doesn't result in getting sandy particles inside the bearings. 

Wait a minute, were the bearings packed in marine grease? 

Edited March 3, 2023 by techyiam

[mrelwood]

1 hour ago, techyiam said:

Interesting that sand particles got inside.

Sand, mud, dirt, or other natural contaminants. While rain water is pure, if you ride on a wet ground the wheel well is a shower full of dust and dirt from the ground.

I did ride the wheel pretty freely everywhere, and got caught up in a few strong rains as well. But at that time the V11 had no bearing protectors whatsoever.

1 hour ago, techyiam said:

Wait a minute, were the bearings packed in marine grease? 

The stock bearings? No no, just the same lumpy see through grease that I believe most wheels come with. I only put the Marine Grease on afterwards. I actually tried automotive Mos2 bearing grease at first, but it lowered the range too much for my liking. Only then did I learn about the huge differences in viscosity, so I got the Marine Grease.

Edited March 3, 2023 by mrelwood

[Rawnei]

2 hours ago, Cerbera said:

I guess that might explain why my bearings seem to be doing OK in the cold and wet - that LiquiMoly stuff I filled mine to the max with is designed for the freezing seas !

Just a heads-up if this is what you meant but you don't want to pack the bearings full of grease it can lead to serious issues over time, around 30% is normal fillrate.

[Cerbera]

22 minutes ago, Rawnei said:

Just a heads-up if this is what you meant but you don't want to pack the bearings full of grease it can lead to serious issues over time, around 30% is normal fillrate.

Lols - yes I was in that thread too; in fact it might even have been MY thread about knocking bearings ! 

[Tasku]

I hope the these devices would look more like this when they come from factory(video). Also I would not make holes, but rather use the blackmatte paint trick(cover) to make the aluminium covers take the heat and dissipate it.

Using silicone is good idea(at edge of covers, avoid it bending or leaking) but like said, it is still possible water to get in.

Also, you don't even have to "paint" anymore(the motor), there is simply sprays that you can use to protect motors, making it very easy, as long as you can assemply the motor right. (apply like every 2-years.) If you do plan to protect your motor, make  sure the products are for electric motors use case.

For bearings, as long as they have right grease, they will not overheat, do not make sound or noices, and will resist water. That is not given on stock wheels. But I would say that the stock wheels are "summer-wheels" and you will have bad experiences, well unless you protect the wheel in so many ways better all around.
(also the boards should be protected with coating(on factory) and wires as well, lids(silicone) and such so, water would not get in.)

Just my 2cents what I would like to see euc build quality going for.

 

[Eucner]

I would look a way to put Gore vents to motor side covers or hub. They might clog in use, but are cheaply replaced.

https://www.gore.com/products/categories/venting

[Tasku]

When air passes I assume the air can be humid enough to form water inside motor? Leaving me thinking the waterproofing is very cheap way to have some peace of mind. I do use cloth(treated with repelling water treatment) to filter water from air that my device needs for airflow as it is.

Edited March 3, 2023 by Tasku

[0000]

On 3/3/2023 at 8:02 AM, mrelwood said:

That’s a really bad idea for EUCs though. Unless there’s something wrong with the motor cover edge seal, water doesn’t get into the motor. But it absolutely would if there were holes on the motor cover near the tire.

Riding on wet ground makes the whole wheel well a shower, which would definitely push some water in through the holes. And due to surface tension of water, it wouldn’t drip out after a ride. And considering that it takes a few days for the tire to dry out inside the wheel well, the water inside the motor would take very long to evaporate through the holes.

Ah yeah that's true, wasn't really thinking how much closer the hub motor is to the ground on a wheel vs the e-bike hub motors in ~26" rims. Although, from the threads I recall perusing years past, it was surprising to see, even the hub motors with almost comically large cooling holes drilled into the motor cover plates near the windings, these motors didn't seem to accumulate water or dirt with regular riding based on the posters' claims.

Another somewhat haphazard idea that comes to mind - one could drill somewhat larger diameter, in-line holes near the windings on opposing sides of each of the side thin-wall cover plates, then tap these holes for QD air hose fittings (which would only be temporarily attached after a wet ride to use compressed air to blow out any water if an amount that can be affected by gravity has accumulated). Needless to say, you probably wouldn't want to run ferrofluid with this approach.

Even using compressed air thru the QD fitting in this way probably won't reach small amounts of moisture trapped in the magnet ring and other crevices which is where the red varnish @Tasku linked in the video above comes in.  Then to finish the job, install low-profile threaded plugs with o-ring seals in each tapped hole for regular use.

Not saying it's a good idea, but it is an idea.