Oil cooling your hub- NOT snake oil!

[John in CR]

...high RPM where the cooling will be most necessary.

Extra cooling is most needed at low rpm with high load, which equates to high torque needs (high current) and low power output (power = torque X rpm), so it is low efficiency (lots of heat). At high rpm the motor runs lower current and has better cooling due to higher velocity and turbulence at the surfaces where heat is transferred. The exception would be big scooter motors with high pole counts, which have high no load current. Those can create significant heat just to spin the motor at high rpm even without producing any positive torque to move the vehicle.

 

[FranBunnyFFXII]

...high RPM where the cooling will be most necessary.

Extra cooling is most needed at low rpm with high load, which equates to high torque needs (high current) and low power output (power = torque X rpm), so it is low efficiency (lots of heat). At high rpm the motor runs lower current and has better cooling due to higher velocity and turbulence at the surfaces where heat is transferred. The exception would be big scooter motors with high pole counts, which have high no load current. Those can create significant heat just to spin the motor at high rpm even without producing any positive torque to move the vehicle.

My bike's motor only heats up when it's doing high speed riding, not when I'm doing stop and go traffic.

This is where my concern for cooling is coming from in the first place. The motor heats up the most when I'm cruising along uninterpted at 30mph for long periods of time.
It gets warm enough right now to physically feel the heat bleeding off the motor case. But it doesn't really warm up even to the touch after doing a good few miles of stop and go traffic where it's having to accelerate hard to keep up with cars and keep me from getting rear ended.

Since my goal with the build is to get higher top speed, much longer cruising speed range, and better acceleration, this is where the concern for cooling is coming from.

 

[John in CR]

At those power levels it's probably just getting warm not hot. For some extra cooling add an air deflector on each side to direct more airflow toward the side covers.

 

[FranBunnyFFXII]

At those power levels it's probably just getting warm not hot. For some extra cooling add an air deflector on each side to direct more airflow toward the side covers.

Less than 5$ of oil 3$ of silicon caulk and my friend's drill would still be cheaper and more effective. :lol:

 

[Punx0r]

The biggest drawback of oil-cooling for most people is keeping the blasted stuff where you want it - inside the motor. It can be surprising the number of places warm oil can find to escape: it will travel along inside stranded wire. While the ferrofluid seems expensive for a small amount of oil, it largely solves this problem by simulataneously only requiring a small amount of oil and because it's held in place by the magnets.

 

[John in CR]

At those power levels it's probably just getting warm not hot. For some extra cooling add an air deflector on each side to direct more airflow toward the side covers.

Less than 5$ of oil 3$ of silicon caulk and my friend's drill would still be cheaper and more effective. :lol:

Owning an EV that drips oil is what's :lol:

Except to the extent that using oil makes the outside shell of the motor get hotter, a sealed motor can't shed heat any faster without doing something to improve the outside air flow. I bring fresh cool air into motors where I push performance using blades on the exhaust side and holes and/or slots on the other. That's why I'm able to push hubbies at up to 30kw peak input with no cooling issues, especially at high speed. The only way I'd go the messy oil route is for a beach bike, and the oil would be more to keep water out andd corrosion resistance than for cooling.

I was one of the earliest to use ventilated cooling and have never had an issue despite riding in rain and roads with lots of magnetic dust from volcanic eruptions. Granted, I do ride strictly on raods, but I wouldn't use a hubbie for offroading anyway. For effective and durable vented cooling, don't follow the followers. Instead use the smallest holes or slots and on the exhaust side put holes only at the extreme perimeter with blades outside to create a centrifugal fan effect. My start drawing air through the motor at about 10mph that I verified with a smoke machine.

 

[Ohbse]

It's been 2.5 years since i posted that little blurb on sealing your hub.. for anybody new to this now, much has changed - just go buy some statorade and enjoy the same result with no mess!

 

[Solar-E-Cycles]

I understand that statorade (ebikes.ca) is a ferromagnetic fluid that is attracted to the magnets and therefore fills the gap between the electric windings and improves transfer of heat through the magnets to the outside hub into the air.

 

[qwerkus]

It's been 2.5 years since i posted that little blurb on sealing your hub.. for anybody new to this now, much has changed - just go buy some statorade and enjoy the same result with no mess!

Actually statorade still requires proper motor sealing if you don't want the stuff to leak through the edges of the side panels at high rpm.

 

[Emmett]

It's been many years since I posted in this thread, but thought I'd share a little update in case anyone is having issues...

Oil cooling is awesome. I have a castor oil cooled H4040 with hubsinks and MC rim and 3" fat tyre pumped at 6400W peak with 18S2P (73V) and riding lots of tight to medium speed bush trails and hills at full power very often. Speeds usually in the range of 10 to 50km/m. Lots of dirt and mud everywhere. Super easy to clean and low maintenance bike setup. Riding like that for usually 4x20 minute bursts with about 5 min gaps inbetween each 20. I've never ever had to worry about cooking this motor in this config. Without the oil, the stator would be cooked in 10 minutes.

My fill/drain hole is a threaded hole close to the magnets with a stubby M5 plug bolt and fiber washer seal around the Phillips head. I use 80ml of oil.

Almost zero leaks. Sometimes a little out the bearings or via the 1.5mm breather on the sprocket side near the axle, but hardly noticeable.

For any leakage, I water wash and wipe it off. I use odourless castor oil. The trick with castor oil is to replace it often enough because it thickens with heat, as the molecules grow larger.

The trick with sealing the motor side covers is two things:
A. Using an oil-resistant sealant like ThreeBond on spotlessly clean surfaces.
B. Loctite the bolt fasteners in with clean threads.

This requires a two step process. 1. bond side plates on and do the bolts up. Allow curing. 2. Remove all bolts and clean threads and reinstall with loctite. It takes a while. I "waste" a set of bolts for step 1. and clean the threads in the hub ring using brake cleaner, a thread tap and compressed air. Takes some time but it's all worth it when I can smash the wheel and it takes it.

 

[caseylain]

Sooo...I thought this all sounded pretty cool but I'm not wading through 25 pages to get all the relevant info I need. I had a spare swx02 motor and some silicon glue and decided what the heck. I used a unmarked dispenser bottle to inject oil through the disc brake hole. On the swx02 at least, the brake holes go all the way through so you don't need to drill anything. Squirted like...half a bottle, till it started dripping out the lowest brake hole and sealed it up.

Now I read the atf will attack the wire insulation and stuff. Is that for real? If so can I just drain the atf and replace with something nicer, like silicon oil?

 

[fechter]

The wires should be OK with ATF depending on what kind is insulation is used. The transmission on a car has all kinds of wires inside it.

 

[caseylain]

Ok thanks I'm liking it so far, I have it hooked to a 48v 38 amp Xunlida sine wave controller and it really goes now. It gets almost hot on the outer shell, which I suppose means the oil is working. It's not leaking anywhere either, other then where the wires come out of the axel.

 

[JES]

Hello
Now that it's been a couple of years, how is your experience with the oil cooled geared hub?
Any issues with leaks magnet glue etc?

 

[markz]

This talks about using water to cool the inside the motor (like atf) but using water rust inhibitors.
Prior in the video, he talks about Statorade and cooling holes.

https://youtu.be/c96n0Ma2rLY?t=6288

 

[JES]

Thanks
That guy seems brilliant !

 

[TDB]

A little trick I use to eliminate pressure relate leaks with oil cooling is to let the motor breath. I lay in small bore copper tube with the wire bundle (easier if the cables enter through the side cover) and connect it to the bottom (through the top) of a small PE bottle. Bottle has a small vent hole. Oil that is vented is trapped in the bottle and pulled back to the motor when it cools... same as a radiator overflow in a car.

 

[JES]

Hey TDB ,
How long have you have it set up like this?
Can you post a photo and
what did you use to seal the motor?
Thanks

 

[mcfizzlestag]

I've been contemplating using Dexron III in my CYC x1 Stealth gen 3 mid drive to help deal with some thermal throttling i encounter in long climbs (85C peak). The heat drops really quick once the load lessens, so i suspect it is the ~1-2mm air gap between the outer casing and the motor casing trapping heat and 4mm gap on the cover side. Since its an enclosed outrunner motor, statorade wont do much to bring that trapped heat out,