Definitive Tests on the Heating and Cooling of Hub Motors

[Obiwan007]

Nice work pendragon. I have also just recently vented my side covers. Because of an AWSOME list member I had the luxury of doing the milling on a spare set of covers so that my down time will be limited. I like that you went with a different vent design, results will be interesting. My vents are similar to what Justin used in his tests. We will see if they remain strong enough. Are you planning to install vanes on the inside? I am going to get some ready to go and then assess it after opening it up. I think my little 408 is going to have considerably less room than other motors. I'll try to get some pics out of the side covers. Also I want to do some controlled tests of the heat accumulation in my current motor before making the switch and then again after so I can accurately compare results.

 

[methods]

I have not been keeping up with the thread but when I saw Justin at the end of his last trip he had some really fascinating findings from the different cooling methods they tested. It will put some of the back and forth to rest.

-methods

 

[pendragon8000]

Thanks Obiwan007,
The thin vents were from a previous attempt that I thought I might as well leave as is and add more holes as shown to be the second best method - lots of large holes around perimiter of one plate and a few around the axle of the other.

My only concern is the small amount of metal I left holding the bearing on the 4 x 19mm holes.
This method works really well. Thanks again to those who contributed to the test results.

Edit oh yeah, no vanes. Its low rpm that's the issue anyway and its fine now (in cold weather anyway)

 

[John in CR]

Lower rpm is even more reason to include blades. Justin's cooling results were pretty weak until he added the vanes, and he was running 300rpm. I still suggest angled blades rather than straight radial vanes, so you push some air at the stator and end windings.

BTW, the bearing is supported just fine. I'd be more worried that entire side supported by only the 6 spaces between the inner holes. Others have said that is plenty, but I'm not so sure. Look how thick the spokes are on aluminum mag wheels, and it's far better metal.

 

[Obiwan007]

Here is a pic of my venting effort on my teenie, tiny 408 side covers. Once I get the vanes ready I will try to do the change over in one brief go.

 

[Ypedal]

nice job !!..

i really need to get myself a proper end mill..

:lol:

 

[Obiwan007]

So, Ypedal, are trying to imply that you drilled out those covers without a rotary table? If so, wow! Nice work given the asymetrical requirement of leaving the logo intact. I'm envisioning a smoke filled room with a single bare light bulb hanging down over cluttered workbench strewn with scratch pads, dividers, compasses, broken pencils and an overheated 1975 TI calculator. Chalkboard in the background with esoteric formulas, etc. OK, probably not that hard but the result speak...skill. :wink:

 

[pendragon8000]

Looks good Obiwan

Ypedal, don't forget about Dr Bass doing the Harlem shake at 2:20 lol
[youtube]J-xUP4t35L8[/youtube]

 

[methods]

I dont think there is any worry what so ever about placement of the holes and balance. With all those spokes, the rim, the tire, the tube... so much further out... those will have orders of magnitude more impact on the balance of the built wheel.

Even if it did - a gram between the tube and the tire would solve it.

-methods

 

[John in CR]

The funnier part than balancing was the idea than someone could drill holes with the covers still on the motor. I don't care what kind of vacuum or pressure hose you have, that's a terrible idea.

 

[Arlo1]

The funnier part than balancing was the idea than someone could drill holes with the covers still on the motor. I don't care what kind of vacuum or pressure hose you have, that's a terrible idea.

THE aluminum going into the motor doesn't scare me as much as the drill bit hitting a winding lol.
MAN if anyone does that they would be in the lower half of the smart/energetic part of the population for sure LMFAO

 

[pendragon8000]

The funnier part than balancing was the idea than someone could drill holes with the covers still on the motor. I don't care what kind of vacuum or pressure hose you have, that's a terrible idea.

THE aluminum going into the motor doesn't scare me as much as the drill bit hitting a winding lol.
MAN if anyone does that they would be in the lower half of the smart/energetic part of the population for sure LMFAO

LOL I was waiting for that
I don't know what Dr bass was thinking that night. Funny in any case.

 

[Hyena]

So, Ypedal, are trying to imply that you drilled out those covers without a rotary table? If so, wow!

You dont need a rotary table, or even a drill press! I've done dozens by hand with a battery drill but use a press now as it's easier with the slow speed. I use a normal drill bit for the holes and then finish off with a step drill for a nice chamfered finish.

And yeah I've heard doc talk about drilling motors with the covers on before, madness! You certainly can't do it with the step drill he showed, you'd be 3/4 of the way through your windings before you got a 10mm hole in the cover! :lol:
If you had a good mill or CNC that was depth accurate to 1mm you could arguably get away with it but using average tools is asking for trouble, especially on the newer crystalytes where the tolerance is so close they actually machine a channel in the side covers to clear the windings

Ypedal, don't forget about Dr Bass doing the Harlem shake at 2:20 lol

Did you link the wrong vid ? There's nothing out of the ordinary there at 2:20?

 

[pendragon8000]

Ypedal, don't forget about Dr Bass doing the Harlem shake at 2:20 lol

Did you link the wrong vid ? There's nothing out of the ordinary there at 2:20?

yeah when i first saw him imitating being on a bike with unbalanced wheel i thought it was really funny so i put it up anyway even though it's not necesarily that funny now that I've seen it a few times. to be honset my drunk rambling videos are probly on par or worse.

 

[nicobie]

The funnier part than balancing was the idea than someone could drill holes with the covers still on the motor. I don't care what kind of vacuum or pressure hose you have, that's a terrible idea.

I watched LFP and Thud attempt exactly the same in the parking lot of some scuzzy whore infested motel in Tucson. Did the work on the ground, in the sun in 100F weather. I thought that they were crazy, but they did get a few of the 1½" holes successfully drilled before giving up and taking the side covers off.

It was a good trip....

 

[dan974]

Hey,

what you guys think about adding rad like this one, curved on the outside hub behind the magnets ? dissipating the heat of the magnets would help cooling or is the heat mainley on the windings?
100x30x22 or 132x22x30

and do you think that doing some small slots in the hub would work as venting out near the magnets/windings ?

 

[amberwolf]

what you guys think about adding rad like this one, curved on the outside hub behind the magnets ? dissipating the heat of the magnets would help cooling or is the heat mainley on the windings?

The heat *starts* at the windings, but is radiated and then conducted out everywhere, albeit not evenly.

Radiators may help the magnets stay cooler, which if you are really overheating the motor a lot may keep them from losing strength--but under normal circumstances and usage there's not much need to worry.

Unfortunatley the place that really needs a radiator wouldnt' help to have one, because it's inside all the covers, and that's at the windings themselves, and the stator laminations.

and do you think that doing some small slots in the hub would work as venting out near the magnets/windings ?

[/quote]

Holes at the magnet's backing ring (the rotor) might well help the airflow a bit, but they will also compromise the magnetic flux ring that the magnets are on, and this may (or may not) affect the motor's performance. You'd have to test it before and after, to see if there is any change in performance or efficiency or heating because of it.

 

[John in CR]

I agree with AW. You don't want to cut into the magnet backing ring so close the the magnets. It's much easier to make holes in the cover.

With effective ventilation you don't need any extra heat sink to cool the motor. As Justin proved earlier in the thread, holes or slots alone are relatively ineffective. I've always used some kind of interior blades, which explains the success I've had. More recently though I added some exterior blades to a hubbie with exhaust slots only on one side, and now the motor moves a tremendous amount of air. I started with a many slot approach to keep debris out, and my thought was the material between each slot would act like a centrifugal blade. It did work and flows some air, but I'm sure less than 5 or 10cfm, which can't take much heat out with it by my calculations. That changed with the blades and I can feel so much wind off of that side of the wheel that it has to be moving hundreds of cfm through and across the outside from left to right. I tested it with smoke and it sucked smoke both inside and across the outside quite strongly even at mid hundreds of rpm. My next iteration will be just 6 larger exhaust holes with a slightly angled blade in front of each instead of just straight radial like I did here. The slight angle will be so the blade covers the hole to some extent. With a more typical hubbie there's more room between the cover and the stator, so the narrow slot cut for the blade will allow a significant amount of blade on the inside to, which will create more turbulence at the stator for better cooling. Drilling bolt holes and tapping threads allows the blades to be fit perfectly from the outside with the motor assembled. I didn't even take the motor off the bike to install my blades. I used a piece of cardboard in the slots to get the interior amount of blade just right before cutting the metal ones. :
View attachment 2

 

[docnjoj]

Hey John!
Is that the outside of the motor or is there another cover? Right now it reminds me of those Roman Chariot wheels with the scythe blades outside.
otherDoc

 

[John in CR]

Hey John!
Is that the outside of the motor or is there another cover? Right now it reminds me of those Roman Chariot wheels with the scythe blades outside.
otherDoc

LOL, yeah you don't want to stick a finger in there. That's it. I ride it as-is, though you could add a thin disc the diameter of the blade tips, which would probably increase flow a bit by further reducing air feeding from the right side, but the angle does a sufficient job. What surprised me was the lack of noise or rattling even at well over 1krpm. Sure there's some wind noise, but the motor is still almost as silent as in stock sealed form. It's so easy and effective, even moreso with a common larger diameter hubbie, that it's definitely my recommended method. The only approach close to as effective for going very high power is Toolman2's leaf blower.

 

[dan974]

would you show us your left side John plz ?

 

[Kingfish]

>> What AW said...

Heat is also generated in the magnets from challenge to Stator field strength, and with the back iron. I don’t know the value of that or how it factors relative to the windings and iron core issues because I haven't studied RF extensively.

As long as the holes are in the aluminum part of the periphery and not in the magnet or back iron part – that IMO is acceptable. I did a similar thing on the hub covers on my 9C 2806: Weep holes - three/side 120* apart, though for a completely different reason – to prevent moisture accumulation.

~KF

 

[John in CR]

would you show us your left side John plz ?

The left side is an aluminum cover, and all I did was cut a bunch of slots with an angle grinder and drilled a number of small holes, all as many as I dared without weakening the cover too much, but allow as free an intake as possible. The blades with exhaust holes (in this case slots) immediately behind the blades and the side facing piece of the very thin angle iron which largely prevents air rushing in from the side to fill in the low pressure region created as the blades fling air off edges are what is important. That's how centrifugal fans work. ie The blade flinging air off the tips creates low pressure behind it, and in this case a large portion of the air to replace flung off the perimeter comes from inside the motor. I can clearly feel the greater wind thrown off that side of the tire from over half a meter away.

I'm now running the hubmotor at over 25kw peak input and the stator has yet to get over 85° no matter how I ride. At some point I'll try adding a ring to block the open slots in the rim to prevent flow from the left side to the right on the outside of the motor, because that flow is substantial which I saw during the smoke test. As we got the smoke output tube near the perimeter of the side cover we could see it clearly suck the smoke outside of the shell to the other side. Blocking that should greatly increase flow thru the motor.

If I wanted even more flow, then I would install an air dam on the left side. The idea would be to slow the flow of air from the moving bike that is flowing at a right angle to the direction of intake. Slowing that air flow immediately outside of the intake will increase the pressure, making flow into the motor easier. The trick would be to make such a duct/dam so it doesn't deflect sand and rocks at the side cover to get more easily sucked into the motor.

I already have air scoops on both sides of the swingarm which direct considerable air toward the motor when riding at high speed with minimal effect on aerodynamics. I should probably block off the scoop on the right side, since I don't need to add to the outside air pressure on the exhaust side, or at least deflect it somewhat upward to create greater velocity at the blade tips at the top of the rotation. It's working so well that I'm not very motivated to make changes. The right and left scoops are identical. Here's a pic of the right side before I vented the motor:


PS- I'm about to vent a couple of more motors using what I learned on this one. I'll document it much better and give it its own thread with plenty of pics as soon as I'm sure my new adjustments are an enhancement in both ease of build and improved function. I expect it to be my recommended approach that can be applied to any hubmotor with only the high load low rpm guys needing to go with active fans in addition to these passive blades.

 

[John in CR]

Heat is also generated in the magnets from challenge to Stator field strength, and with the back iron. I don’t know the value of that or how it factors relative to the windings and iron core issues...

Since there is some heat generated in the rotor, I haven't really worried about the cross flow I'm getting outside of the motor, because there is some cooling benefit to extra flow there. However, the spoke holes are fairly small on this motor and largely restricted by the 6 phase wires, which means with intake on one side and exhaust only on the other that a lot of the air flow through the motor goes through the magnetic gap cooling both the perimeter of the stator and the magnets and back iron.

 

[dan974]

ok, John, I fully understand your exhaust side with the blades creating depressure, I just wanted to see your intake approach/positionning holes near the stator axel or near windings, I don't think I saw it on your pics...