Definitive Tests on the Heating and Cooling of Hub Motors

[spinningmagnets]

From "bullfrog" posted with his permission:

Just a little data on my latest experiment...I tried to cool a MAC using a mixture of distilled water and Motul brand MoCool. The MoCool is a corrosion inhibitor and used in mainly motorcycle cooling systems to help prevent corrosion when ethylene glycol is not allowed...i.e. when race tracks will not allow the ethylene glycol to be used because it is slippery and a spill on the track would be extremely dangerous as well as take a long time to clean up.

Total volume of fluid used in my MAC was about five ounces...just enough to thermally connect the motor to the housing.

Well after running it for about four months, I thought my clutch was acting up...it was not freewheeling and would go back and forth between normal operation and not freewheeling. Disassembled the motor yesterday and it turns out the failure mode was the bearings in the planet gears. The gears themselves were fine. Just FYI, the planet gears and their bearings are the highest stressed portion of a planetary gear train...learned that a long time ago while doing accident investigations on helicopters.

As far as better...the water/MoCool had about the same core temps as the ATF so from a cooling perspective they work about the same.

The ATF lubricates the planetary gears and doesn't affect the the planet gear bearings BUT it can be extremely dangerous if you get a tiny amount on your brake rotor. I was riding along after running the ATF for a few months and all of a sudden I had no rear brakes.

The water/MoCool does not cause a problem if it gets on your rotor but it washes the lubricant out of the planet gear bearings so they eventually fail.

Turns out the bearings in the planet gears are "608" bearings and the same ones used in skateboard wheels. I have been researching options this morning for ceramic bearings produced for skateboard use in an attempt to find some good ceramic bearings at a reasonable cost.

As far as the water mixture affecting other parts of the motor, the only thing I noticed was that the copper windings had a dull appearance compared to when they were new and shiny. I never had any problems with any part of the motor, hall sensors, temp sensor, or anything not working due to corrosion or issues from the water mixture. I must qualify that with I only ran it for approximately four months so I can't really comment on the "long term" effects.

I did absolutely nothing to prepare the motor before using the water mixture...Justin at Grin Tech suggested coating the electronics to prevent problems but all I did was orient the axle so that the Hall sensors were at the highest elevation possible so that when I used about five ounces of cooling fluid, they did not sit in the fluid when the bike was stationary.

IMO the best thing to do for most people is to run either a 10T or a 12T MAC depending on how much you weigh and how many hills you have as well as use a wheel/tire no larger in diameter than a 26" Maxxis Hookworm and don't more than a 14s battery. That way overheating is never an issue.

I really wanted to try my 12T MAC with a 72v battery but it will definitely require some auxiliary cooling. I know the best bet for hot rodding like I am doing is a DD motor but I really like the small size and lightweight of the MAC.

Thanks for the recommendation on the ceramic bearings.

 

[John in CR]

I'm running dual 12F Nucular controllers on a stock sealed HubMonster at 20kw peak input (pushing a 110kg bike geared to a max speed of 130kph), and a single 12F Nuc at 10kw peak on my son's MUXUS 3k speedier wind in a 23" OD 18" moto tire (geared to a 95kph top speed). Both bikes have 21s packs, and both are running markedly cooler with significantly lower wh/km than they did at lower power and lower performance than they did with common controllers. Note that like with all controllers I've used, speed settings are always set at 100% with 0 field weakening, because increases in either significantly impacts energy consumption, therefore heat. If your bike isn't fast enough, then you're running the wrong voltage or use the wrong motor.

IMHO the best and first thing anyone should do in terms of motor heat is to upgrade to a modern controller with FOC, hall sensor position correction and variable regen braking such as a Nucular controller. I assume that other FOC controllers have similar benefits, but the Nuc controllers are the only ones that I've seen other users comment about the remarkable efficiency and range increase.

 

[Hardergamer]

Update. I have been running ATF for over 2 years in an MXUS 3K 4T turbo without any leaks. The motor has internal-external cooling fins and a 0.7mm air vent hole on the sprocket side with bigger windings and phase wires, etc. I'm running 108mm of ATF Dexron 2 at 96v 220a 500pa, 24s 27p 648x Samsung 30Q cells. Sabvoton 72200, with motor temperature rollback set at 105c. Max temperature I get to is around 92c, and after a 30-mile ride at 40-50 mph, the motor temperature is only 60c. Mods I did to stop leakages is when adding new thicker phase wires is to add silicon around them in the Axl. I added new crank seals with sealed bearings and soldered the phase wires solid in the ends inside and outside of the motor, I have the phases going into xt150's 130mm outside the motor.

 

[Bullfrog]

I would NOT change cooling fluids if what you are running is working but if you have your motor open switching to a Low Viscosity Full Synthetic ATF like Dexron VI or the "Super Tech" brand of Low Viscosity Full Synthetic that Walmart sells will do three things for you...
A. It will go to a higher temperature without degrading...which you probably don't need :lol: .
B. The low viscosity will have less drag...which you probably won't notice in the big picture .
C. It will lubricate better...which doesn't matter in a hub motor since there isn't anything to lubricate :wink: .

Most electric motors can run 150C without any damage...not sure I'd want to push it that hot unless you can verify it with the manufacturer but going to 120C should be no problem whatsoever. Only reason I bring this up is you could run a little less cooling fluid which would give you less drag as well as a lower chance of leakage but just like the comments above, if what you are doing is working there is no need to change anything :thumb: .

Controllers...I agree FOC is the best. All the commutation strategies have advantages and disadvantages and the FOC is more complicated and challenging for software/hardware as far as getting it to work properly. Although trapezoidal is not very good at low speeds it is about as good at high speeds as FOC. Check out this article and you can jump to "Table 2" in the article for a summary that helped me: https://pdfs.semanticscholar.org/40ac/06d3db0b82242038c2dcd20c433d5d1c74f6.pdf

 

[Cowardlyduck]

Long term testing results...I've been running Ferro Fluid (Statorade) in this cheap golden motor for about 5+ years and over 15000km. It is vented on one side also and I've topped up the Ferro Fluid with around 3-5ml twice in that time, but never opened/cleaned it.
Yes it's a bit dirty which is to be expected from it being vented, but overall not that bad!


This motors stator was painted with insulating varnish, and the inside of the side plates with black paint prior to the Ferro Fluid being added.


After cleaning up, which took some of the paint with it (I guess due to the abrasiveness of the FF mixed with dirt), it still looks great underneath!


The only repair needed was some additional epoxy on one of the hall sensor legs that became exposed when the heatshrink moved back, but it is (and was) still working fine.

After putting everything back together with a new freewheel side bearing (other side is too hard to access with the upgraded phase wires), I will add more Ferro Fluid (probably only about 3-4ml this time) and should get another 15000km out of it.

Thanks again to Justin for finding/marketing and selling Statorade. What an awesome product!

Cheers

 

[DasDouble]

Long term testing results...l
...

Cool!! Thanks for sharing!!

 

[ZeroEm]

by Cowardlyduck » Sep 04 2021 10:22pm

Long term testing results...I've been running Ferro Fluid (Statorade) in this cheap golden motor for about 5+ years and over 15000km. It is vented on one side also and I've topped up the Ferro Fluid with around 3-5ml twice in that time, but never opened/cleaned it.

No real drawbacks from running FF. I have read of lose/falling off magnets, attack's seals and other materials. None of that seems real now. I'm a FF fan, even thought I don't over heat my motor, why not keep it as cool as possible.

Do have one question for everyone. Don't have a dipstick for FF. The only way to top it up is do the watt test or any other way this is done that I have not heard about?

 

[Bullfrog]

by Cowardlyduck » Sep 04 2021 10:22pm

Long term testing results...I've been running Ferro Fluid (Statorade) in this cheap golden motor for about 5+ years and over 15000km. It is vented on one side also and I've topped up the Ferro Fluid with around 3-5ml twice in that time, but never opened/cleaned it.

No real drawbacks from running FF. I have read of lose/falling off magnets, attack's seals and other materials. None of that seems real now. I'm a FF fan, even thought I don't over heat my motor, why not keep it as cool as possible.

Do have one question for everyone. Don't have a dipstick for FF. The only way to top it up is do the watt test or any other way this is done that I have not heard about?

If you could determine the height of the FF when the bike is sitting still then you could drill a "check" hole in the cover, thread it and put a pipe plug in it...when you pull the plug FF should not run out but if you lean the bike just a tiny bit, FF would start to show. I'd drill another hole 180 degrees out from the first one and plug it as well so air can get in/out when you are doing the check and you can also use it to add FF. What I am describing is how I check the oil level on my KTM motorcycle and how I checked the cooling fluid in my MAC but I used a brake rotor bolt hole...just FYI, I ran a LOT higher fluid level in my MAC :wink: .

 

[Cowardlyduck]

Another easy way to determine the need for more FF is by the lack of thermal cooling and noise.
As I initially discovered on this same thread back in 2016, there is a noise when reaching a certain amount of FF inside hubs that can easily be heard when they are vented:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=48753&p=1149900#p1151002

When I can no longer hear any noise and the cooling effect seems diminished I know it's time to top it up. As mentioned, in about 15000km and 5 years this was only needed twice.

Cheers

 

[ZeroEm]

Well i'm just going to read your whole thread. That is fascinating, have so much to learn.
Thx.

 

[DogDipstick]

I like my ATF. However I have stopped using it. Hubsinks only. The ATF let no oil out.. but... Water got in. Messy emulsion. Did not rust... But... Was creating drag, the half a litre in there. I am gonna try again with a brand new hub.

Yes these thing are strapped in multiple temp sensors.

 

[ZeroEm]

Automatic transmissions don't seem to have an emulsion problem. not that I remember. Have worked around equipment that the oil would turn milky and need changing. Most of the time it would mean a leaky seal to some water source. It odd that just humidity is such an issue. Here there is high humidity all the time so may need to keep a closer check on what's going on in side. To me FF is great. Can not see putting in to much unless other mods are done. Everyone's testing is great. Just need to dig and read. Don't really have it figure out how to navigate the site that well.

 

[Bullfrog]

The problem I had with Automatic Transmission Fluid is that it is slippery and if any leaks on your brake rotor, your brakes stop working.

I tried a mixture of distilled water and Motul MoCool (corrosion inhibitor) in my MAC for about a year and it worked well plus leakage on the brake rotor did not affect my ability to slow down :lol: .

Seems pretty strange to be pouring water in an electric motor but it worked for me and my MAC. I used ~4.5 ounces total volume for the distilled water/MoCool mixture.

 

[Kodin]

Here's a question - I have some Maytech 6396 outrunners on a mountainboard that are sealed with a 3rd skirt bearing around the open end of the can. As such, they have no air circulation path as far as I'm aware. While they are 0.2mm lamination stators and have good winding lays, they can still overheat at the 80+ phase amps they tend to be run at. Especially in the summer. Anyone have an idea of how much statorade I'd need to add or will I need to do the usual current draw test? I realize not many people have played with hobby outrunners, but figured I'd ask before I start down that road myself. Furthermore, what's my best option for insulating the hall sensor board in my motors since the halls tend to have exposed contacts? Is Statorade electrically conductive? I completely forget at this point... Also other data that might be useful - running 8S and 190KV so ~6000 RPM max. Curious to know how much the statorade flattens out or pushes elsewhere at that RPM...

 

[ZeroEm]

Don't have any easy answers. Even with a well known motor there is discussion on how much to use. To bad no one has come up with a formula to calculate how much a motor could use by the dimensions and stator/magnet gap.

The purpose of Statorade is to reduce heating. If to much is used you create drag which causes heating. Then there is the aerating of the oil which in a slow turning DD motor is not an issue, just not sure about a mid drive.

The Statorade only needs to fill the gap above the magnets to work. You can gauge it by the watts or the cooling effect if you know your motors normal temperature range.

I run a 1500w leafmotor and can guess because it is so well known. 5ml on this motor. I do know the range is between 4.5ml - 6ml. Statorade needs to be checked and refilled. This is another issue with an unknown time/miles. So if its over filled a little to much then it may last longer. Just watch for the cooling effects to go away.

Someone else may have better answers, more than welcome to chime in.

by Kodin » Oct 06 2021 11:15pm

Here's a question - I have some Maytech 6396 outrunners on a mountainboard that are sealed with a 3rd skirt bearing around the open end of the can. As such, they have no air circulation path as far as I'm aware. While they are 0.2mm lamination stators and have good winding lays, they can still overheat at the 80+ phase amps they tend to be run at. Especially in the summer. Anyone have an idea of how much statorade I'd need to add or will I need to do the usual current draw test? I realize not many people have played with hobby outrunners, but figured I'd ask before I start down that road myself. Furthermore, what's my best option for insulating the hall sensor board in my motors since the halls tend to have exposed contacts? Is Statorade electrically conductive? I completely forget at this point... Also other data that might be useful - running 8S and 190KV so ~6000 RPM max. Curious to know how much the statorade flattens out or pushes elsewhere at that RPM...

 

[Hummina Shadeeba]

Why don’t they make a hub motor that has a wide enough stator that the side plates crush the winding end turns on both sides? The magnet insulation is really durable and the manufacturer of square magnet wire..they add the insulation to round wire first then squeeze it rectangular


Maybe would need some material between the motor plates and wire so thermal expansion isn’t a problem.

 

[ZeroEm]

The side plates are turning and the Windings are not. If they touch the insulation would not last.

 

[Hummina Shadeeba]

The side plates are turning and the Windings are not. If they touch the insulation would not last.

Another duh moment. I thought I had a great idea till ruined by reality.

 

[ZeroEm]

That is why I post any idea's on here to get a reality check. Always hope that when I state something and my brain is off track it gets checked.

Hummina Shadeeba » Nov 02 2021 12:09pm

ZeroEm wrote: ↑Nov 02 2021 11:51am
The side plates are turning and the Windings are not. If they touch the insulation would not last.
Another duh moment. I thought I had a great idea till ruined by reality.

 

[Hillhater]

I like my ATF. However I have stopped using it. Hubsinks only. The ATF let no oil out.. but... Water got in. Messy emulsion. Did not rust... But... Was creating drag, the half a litre in there.

Two points....
1) ..”half litre”.. seems way too much compared to other users of SA. Hence the high drag. It is acting like ATF is designed to do and acting like a torque converter unit !
2)..if its emulsifying it is not getting hot enough to drive out the water. Less fluid would get hotter maybe ?

 

[DogDipstick]

Two points....
1) ..”half litre”.. seems way too much compared to other users of SA. Hence the high drag. It is acting like ATF is designed to do and acting like a torque converter unit !
2)..if its emulsifying it is not getting hot enough to drive out the water. Less fluid would get hotter maybe ?

IDK. I suppose so. Bearing is going out on the brake rotor side too. I am gonna go in there again and fix the bearing, I'll report back.

I am also increasing the battery by some 10Ah and installing a much more powerful KEB in the same spot.. 4500w contin instead of 33oow contin... 220A phase vs 100A phase... and then Imma gonna take more pictures. See a difference. Hope the hub survives. You can see int hat pic the temp reached 110*F+ on the cover face of the hub. There must be some heat transfer happening. Lol.

 

[Logic11]

hi everyone.

Lurking nd learning atm, but have a question:
How come no one has turned Motor side/end covers out of old (the clutch inside is always breaking) Viscous fan couplings from cars..???

Tons to choose from:
https://www.bing.com/images/search?q=FAN+VISCOUS+CLUTCH&form=QBIR&first=1&tsc=ImageHoverTitle

Even if you dont want to drill holes; having radial fins on both sides of the covers will help IMHO.

I woulda thought that more people who'd also 'swung spanners' at cars would be here?

 

[DogDipstick]

hi everyone.

Hi there !


We cannot use those because often on bicycles, the brake clearance in the rear fork dropout is very small.. and the sprockets and chain will get in the way, also.

Also, These guys ( everybody who posted here for years before you and I) did all the could years ago, with cutting machined holes in side covers to get the convection to carry the heat away: Problem with cooling side cover is there is not alot of heat transferred to the side cover with conduction in the hub when hot, and the convection does not exist, and the radiation is minimal gain to be had. It would be weight and if you did the fin equations you would see the space to gain a good transfer is limited to the point og negligible gain.

Well, I happen to have an extensive heat sink collection. One of the strange things I focus on. One day started collecting, and it grew, and it hasn't stopped. It occupies a large amount of two shelves, in my garage. Huge, small, med. Aluminum copper, steel, new old exotic, normal. Ect. You name it.

Lol. :lol: :lol: :lol:

 

[kk64]

I am a fan of gear motors. Liquids cause a lot of problems for electronics and leaks. Air seems to be the 100% solution - at least for now. Air has its disadvantages - it absorbs heat less than liquid, but it does not cause as much trouble as liquid.

The gear motor sheel acts as a heat exchanger between the inside and outside of the motor. What if we drill holes in it like in DD motors, but not from the side, but from the hub side - as in the picture? We can't do that because if it rains, the engine will stop working, and dirt is bad for the gears. But we can close the whole thing with disc - like on the photo. These discs aren't hard to make at all. They do not have to reach the axis of the motor at all. After such treatment - the entire disk becomes a heat exchanger. The inside of the disc is filled with heat from the motor and the surface area of penetration is much larger than the motor shell.

The second idea is to do everything as above, but in the motor housing you can drill only two holes (at the intersection of the motor diameter with the housing - the furthest apart) and put a fan on one, which would inject / extract air into / out of the motor and the other side would fly out passing through the windings. This is an idea if the heat didn't want to get enough of itself through the holes in the engine into the space between the disks. But I secretly believe that warm air will move quickly without a fan.

Of course, the discs would have to be tightly mounted to the rim and to the hub to prevent dirt and water from getting in - this shouldn't be hard.

Discs made of light material and - I don't know what kind. Of course material which is easy to penetrate by warm. It can much thinner than hub shell - in this way heat exchange will be a lot better.

Escaping heat through shell is only way to cool down, so making this heat-transfer-areas a lot bigger and thiner - then it hould work (?).

Little math :

Area of part where we will drill holes - 208 cm^2.
Two disc area total - 3845 cm^2.
So disc has 18,5 time bigger area.

Area is bigger - but next big thing is free space volume of motor hub inside for air, and volume of motor hub + space free space for air between disc. Hard to compare and calcute, because motor hub is alomost in 90% filled by parts...so I think we can't think about free space for hot air at all. But in the second example (motor hub+space between disc volume) - we have a lot of space. Summary - bigger volume should be second(next to 18,5 times bigger area) benefit for cool down motor.

What do you think?

(Of course let's talk about mtb wheel, on photo there is roadbike wheel. don't stick to that.)

 

[ZeroEm]

That area is covered in magnets! On my typical DD motors.

by kk64 » Dec 10 2022 1:09pm

I am a fan of gear motors. Liquids cause a lot of problems for electronics and leaks. Air seems to be the 100% solution - at least for now. Air has its disadvantages - it absorbs heat less than liquid, but it does not cause as much trouble as liquid.

The gear motor sheel acts as a heat exchanger between the inside and outside of the motor. What if we drill holes in it like in DD motors, but not from the side, but from the hub side - as in the picture? We can't do that because if it rains, the engine will stop working, and dirt is bad for the gears. But we can close the whole thing with disc - like on the photo. These discs aren't hard to make at all. They do not have to reach the axis of the motor at all. After such treatment - the entire disk becomes a heat exchanger. The inside of the disc is filled with heat from the motor and the surface area of penetration is much larger than the motor shell.

The second idea is to do everything as above, but in the motor housing you can drill only two holes (at the intersection of the motor diameter with the housing - the furthest apart) and put a fan on one, which would inject / extract air into / out of the motor and the other side would fly out passing through the windings. This is an idea if the heat didn't want to get enough of itself through the holes in the engine into the space between the disks. But I secretly believe that warm air will move quickly without a fan.

Of course, the discs would have to be tightly mounted to the rim and to the hub to prevent dirt and water from getting in - this shouldn't be hard.

Discs made of light material and - I don't know what kind. Of course material which is easy to penetrate by warm. It can much thinner than hub shell - in this way heat exchange will be a lot better.

Escaping heat through shell is only way to cool down, so making this heat-transfer-areas a lot bigger and thiner - then it hould work (?).

Little math :

Area of part where we will drill holes - 208 cm^2.
Two disc area total - 3845 cm^2.
So disc has 18,5 time bigger area.

Area is bigger - but next big thing is free space volume of motor hub inside for air, and volume of motor hub + space free space for air between disc. Hard to compare and calcute, because motor hub is alomost in 90% filled by parts...so I think we can't think about free space for hot air at all. But in the second example (motor hub+space between disc volume) - we have a lot of space. Summary - bigger volume should be second(next to 18,5 times bigger area) benefit for cool down motor.

What do you think?

(Of course let's talk about mtb wheel, on photo there is roadbike wheel. don't stick to that.)