Good! Someone finally oil cooled a hubbie!! HS3540

[Spicerack]

You need some form of vent for the hub to relieve excess pressure as it heats up.

Try a little bit less oil and drill a small (1mm) hole in the cover near the axle. Angle it so that it traverses from the central axis towards the outer circumference as you go from outside to inside. That way, when the wheel spins, any oil that happens to splash into the hole will be flung back inside the hub. I've done this on my mac and had no oil leak at all from the hole or axles.

For the record, the outer cases of my mac are alot hotter than without the oil so it certainly transfers heat away from the windings.

[Burtie]

Thanks andy, sounds like a good idea.
I will try drill a small angled vent in the opposite side, behind the sprockets.

[bigmoose]

Thanks for the great data on oil cooling Burtie! I think this will become standard practice for high performance motors as we go forward. I saw how much this improved the "Power Dense" motor system developed at Bowling Green State University about 10 years ago, and strongly felt it was applicable to hub motors. Your data now proves the point.

This should now end any lamination/magnet corrosion issues, and bump power handling a bunch. I will also bet thermal soak hall failures are a thing of the past also.

[Arlo1]

Thanks for the great data on oil cooling Burtie! I think this will become standard practice for high performance motors as we go forward. I saw how much this improved the "Power Dense" motor system developed at Bowling Green State University about 10 years ago, and strongly felt it was applicable to hub motors. Your data now proves the point.

This should now end any lamination/magnet corrosion issues, and bump power handling a bunch. I will also bet thermal soak hall failures are a thing of the past also.

WHat about drag at hi rpm??

[bigmoose]

WHat about drag at hi rpm??

You do the system analysis and see if you have enough AHr to overcome it. It is my opinion that we now have the capacity to accept some losses that were not acceptable just a few years ago. Using gears in the reduction of mid drives is the next area I see coming...

One thing I harp on at the "big lab" all the time is "It's all about the system..." Maximizing individual component efficiencies and capabilities does not always increase the efficiency and capability of the system. It is ALL about the system... hence my support there for multivariate optimization routines and Monte Carlo simulations.

[itchynackers]

I still don't quite understand whether the oil is just delaying thermal soak (by the oil storing the heat), or if the oil is allowing the hub to dissipate more heat.

Edit: After re-reading the thread, it seems as though the oil transfers the heat quicker to the covers (making them hotter) so more heat is carried away with the same amount of windage. Is this correct?

[parabellum]

I still don't quite understand whether the oil is just delaying thermal soak (by the oil storing the heat), or if the oil is allowing the hub to dissipate more heat.

Edit: After re-reading the thread, it seems as though the oil transfers the heat quicker to the covers (making them hotter) so more heat is carried away with the same amount of windage. Is this correct?

The second. Oil helps transferring heat to covers and they dissipate it to ambient.

[parabellum]

Try a little bit less oil and drill a small (1mm) hole in the cover near the axle. Angle it so that it traverses from the central axis towards the outer circumference as you go from outside to inside. That way, when the wheel spins, any oil that happens to splash into the hole will be flung back inside the hub

I did exactly this on Mxus DD inside disc brake screw hole with inclination to outside D inside, then tightened a screw with sprung washer (sprung part in axle/center direction), I only have 150ml of oil but it gets out of the vent anyway(maybe few droops per ride).

[Burtie]

I cleaned the oil off the disc and pads with caustic soda, and drilled a small vent on the opposite side of the hub, close to the axle.

It all works well, the brake stays clean
Just a small drop escapes from the vent each use, so will have to wipe it over occasionaly to stop things getting too messy.

Oil Cooled Test Rig.jpg (154.03 KiB) Viewed 729 times

This seems to me like a massive step forward. I can now practicaly ride this 4kw bike as hard as I like, for the whole duration of the battery pack, with no more worries about cooking the hub!

Thanks to everyone here for their ideas and suggestions
Well pleased
Burtie

[Spicerack]

Good to see. I was going to liquid cool my 9C 8x8 and run quite a few amps through it. The initial plan was copper cooling pipes around the inside of the hub, going out through a modified/fabricated side cover to a little radiator etc etc but I'll just do the oil bath first and see how I go. It only helps a little bit on my current MAC hub but that's because the windings are damaged from overheating them so a large chunk of the amps get converted to heat!

[Burtie]

I guess the MAC would suffer more loss from the viscous drag of the oil, since its rotor spins at 5x the wheel speed.

This loss might be significant enough to offset the gains (of improved thermal conductivity) somewhat?

[Spicerack]

I wondered about that too as the planetary gears will be spinning through the oil as well- but it didn't seem to make much difference during testing. Not that valid a test though as the windings are damaged- I'm putting a new 10 turn stator in it soon so will do thorough dry and wet tests with a set route, amps etc.

[parabellum]

I wondered about that too as the planetary gears will be spinning through the oil as well- but it didn't seem to make much difference during testing. Not that valid a test though as the windings are damaged- I'm putting a new 10 turn stator in it soon so will do thorough dry and wet tests with a set route, amps etc.

Few nice words from 2009 by the pioneer of oil filled geared hubs practice Reid Welch.

WHAT: running geared transmissions in light oil is a universal practice...except in these new, geared-type hub motors.
WHY: light oil cushions gear teeth, actually preventing contact of the pressure surfaces, through a phenomenon known as
hydrodynamic lubrication: the parts surf upon each other, oil as the separating agent. This form of lubrication prevents all wear
((think of your auto's automatic transmission, how quiet its helical gears run, and with no wear-out))

IS THERE LONG TERM HARM? Ans: No, not unless the oil were to somehow degrade hall sensor adhesive (unlikely, it seems)

Q: How much oil to be installed? A: Enough to fill the motor about one third full. Then, when running, centrifugal force
throws the oil at the perifery of the gear casing, bathing the soft steel ring gear and the plastic planets. Plus, oil contantly
washes all the bearings and constantly wets the lip seals of the axle. Some slight weepage at the axle "seals" is inevitable.

About heat and expansion: when the motor warms up, its contained air expands, and will push out a minute amount of oil.
Upon cooling down, the motor will slightly inhale some of this weeped oil.
Now, consider the stock (dry, not oiled) run in the rain: it will gradually ingest small amounts of water, eventually rusting internal parts to some small extent.

Oil is dielectric and has no effect on nylon gears nor synthetic rubber seals, which are DESIGNED to run in oil.
Oil, sloshing around the inside of the hub motor, is not of sufficient quantity to drown the rapidly spinning central rotor
of the motor, itself, so no fluid spray/strain/churn on the copper windings.
The oil will all be at the ring gear, surfing the planet gears, dampening noise, and fluid polishing the parts over time (perhaps)
to make, in time (thousands of running miles) a super quiet motor, with each planet gear tooth of the three planets, shoulder exactly the same amount of the load.
Benefit accrued: maximum robustness of the geared motor: it should never "peanut butter" any teeth, until some long-away day, when plastic fatique finally breaks off a tooth, which then spells instant destruction for all the remaining planet gear teeth.

[gogo]

Gotta love Reid's nitty gritty. I'd love to see some hard numbers on the cooling benefit and the amount of torque that oil cooled gears can take before failure in an oil bath.

[Farfle]

I know with my rc car, (pre 2004 traxxas rustler) the first time I put a brushless motor in, it lunched the Metal idler gear I bought specifically for that motor in less than 3 mins of bashing, in desperation I put the nylon gear back in, and in the process of trading gears I had to refill it with oil, I put some stihl chainsaw gearcase oil in it, and it ran for several weeks like that so imho, a good oil adds alot of durability and longevity to a gearbox.

[Burtie]

A breather without leaks ...

Have found an easy way to modify the vent hole, to prevent any loss of cooling oil.

Cut about 1/2 inch length of the plasic tube that is sometimes used as extensions on aerosol can nozzles.
(It has about a 1mm bore and a 2mm OD.)

Use silicone gasket sealent to bond this into the angle vent hole (angle described by andynogo at the top of the previous page), so that it is almost flush with the outside surface of the hub, but protrudes inside the hub by about 5 or 6mm.

In my experience, this is sufficient to prevent any oil which is running down the inside of the cover, from leaking through the vent hole. But still allows the hub to breathe, preventing leakage through the axle seals, and thus avoiding oil contaminating the brake disc.

Burtie

[sn0wchyld]

if your going though all the trouble to liquid nitrogen cool, may as well use a high temperature superconducting coil too

im rooting to discover one that works at room temp. solve all our problems.

mike

hehe... wont that just offload all the issues with heat in the motor to exploding fets in the controller? sorta the same reason why no ones been able to run Hobbykings new giant motor under any sorta load?

but yea... i've been dreaming of the same thing... it'd also make getting nice high amp wires in via teh axle a snap... just use the same guage as your hall wires or less! lol.

edit
all in all great to hear the successes with this... has anyone thought about doing some custom or modified side covers with a enlarged surface area? ie make the covers look more like heatskinks? that should improve things even more...

[PeeHell]

The real world data from Burtie seems great (~70c cooler !). Could some of you who tried this great mod detail this procedure in steps ?

I mean:
What are the specifics area that you sealed ?
What size of bit did you use to drill the vent so it can fit the venting "straw" perfectly ?
Could you use the "venting" hole to fill the hub with oil so you'd only have one hole to drill ?
Is the "Zzzz" sound heard when accelerating attenuated ?

[Burtie]

Seal both covers and the axle slot.
Drill the vent hole opposite side to the disk, close to the axle, just big enough to insert the aerosol tube (perhaps 2 or 2.5mm diameter).

I think it probably best to drill a separate filler hole big enough to sensibly inject the oil with a syringe (maybe M3 or M4), thread it and fit a bolt with an 'o' ring under the head, to seal it.
Position the filler hole to make sure the protruding bolt head will not interfere with the derailleur or the disk brake caliper.

Yes, the resonant audible buzz I experienced, seems to be attenuated significantly by the presence of the oil.

I am still amazed at how well this oil bath mod cools the windings, removes all the 'temperature anxiety' from my hub motored ebike riding

Thanks to bigmoose for bringing this technique to our attention at ES.

Burtie

[dfar]

Just wanted to state that I tried the ATF cooling method and am really impressed with the results.

Before the introduction of the oil my HS3540 would get up to 90 Celsius +++ within 15min of heavy riding. With the ATF I cannot get the temp over 55 Celsius with full throttle riding. Overheating is now not the limiting factor in the performance of the bike.

I did not drill any vent wholes in the hub motor and sealed the sides with silicone. It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket. This unintended leak effectively "oils" the chain therefore I don't really have a problem with it.

The only thing I am thinking about altering is drilling and tapping a filling valve so one could top up the ATF without taking the side cover off the bike. Maybe make it into a filing/venting valve.

[sn0wchyld]

Just wanted to state that I tried the ATF cooling method and am really impressed with the results.

Before the introduction of the oil my HS3540 would get up to 90 Celsius +++ within 15min of heavy riding. With the ATF I cannot get the temp over 55 Celsius with full throttle riding. Overheating is now not the limiting factor in the performance of the bike.

I did not drill any vent wholes in the hub motor and sealed the sides with silicone. It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket. This unintended leak effectively "oils" the chain therefore I don't really have a problem with it.

The only thing I am thinking about altering is drilling and tapping a filling valve so one could top up the ATF without taking the side cover off the bike. Maybe make it into a filing/venting valve.

sounds good! what sort of power levels are you running/what size wheel? and when you say heavy riding, do you mean riding WOT lots with no pedalling?

Im getting more and more tempted to do this, since I have a spare set of side covers sitting on my desk. I'm trying to think of a way to increase the surface area of the covers though... probably overkill for sub 5kw levels by the sounds of things but I'd rather go too far than not far enough...

Does anyone have any CAD or 3d drawings for the sidecovers by chance? Speaking to the guys at my uni workshop about this, they mentioned that I might be able to get some free CNC time to make some custom sidecovers with enlarged surface areas... my cad skills are pretty non existant atm though, so a template to work off would be a big legup...

[dfar]

sounds good! what sort of power levels are you running/what size wheel? and when you say heavy riding, do you mean riding WOT lots with no pedalling?

heavy riding = lots of starts and stops with relatively heavy acceleration to keep up with traffic (0-60km in 7-10sec)

82 volts hot off the charger. pulling upwards of 5-6k from dead stop to max speed, also using in the city with regen activated for breaking. Wheel is 26 inch, and as previously stated using a HS3540. With stop and go using 5k (not sure of the avg) to accelerate up to a max of 65-70km/h avg 35-40km and using regen for breaking motor has only been as high as 60 Celsius after 25 km of riding. I like to pedal when riding but even when using only the motor I can't seem to get the temps past 60 Celsius. *note ambient temps are avg 8 Celsius (sweater weather) when riding, The real test will come mid summer but so far I'm really impressed with the results.

Can't comment on long term impacts but I will post back if I have any issues.

[kfong]

This is really good news, nice hearing the actual field reports from Burtie and Dfar. I will seriously consider doing this.

[bobale]

It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket.

Wait a second. Bearings are usually greased with thick grease. How will introducing light oil affect their life? Will ATF wash off thick grease, and leave bearings dry if you decide not to put any more oil into the motor?

[parabellum]

It seems a small amount of ATF leaks out through the bearings and axle and onto the sprocket.

Wait a second. Bearings are usually greased with thick grease. How will introducing light oil affect their life? Will ATF wash off thick grease, and leave bearings dry if you decide not to put any more oil into the motor?

Mxus, GM, Hx have sealed type bearings, so even if thick grease is replaced with ATF (with created pressure), oil is being retained inside the bearing for quite a while.
I have different problem, my phase wires are drooping oil constantly. It may be because of gravity, my wires are tied on axle height and bike is leaned to wire side if parked or capillary action since I do not think that even parked oil level comes to the axle.
Pressure must be discarded, breathing tube/hole is present.