Definitive Tests on the Heating and Cooling of Hub Motors

[liveforphysics]

I spose that stuff could happen, OR you could have 6-7 race meetings, 2 years, enough miles to wear out the average ICE motocrosser engine twice over, equal unsprung weight to a std DH bike, and still runs the original 219 o-ring chain, with the only issue being a wheel bearing failure (via corrosion) at the end of last year.

After the 40+ rear tyres that have been given back to the earth, and nearly every weekend for many years spent in enjoying the forest on a mid drive electric machine i just cant fathom the doom and gloom, destined to fail stuff on drivelines Luke. -The same type of drivelines that seem to work pretty well on nearly every bike ever made, and looking back I have way more to worry about than driveline failure from something as unlikely as crashing into a kangeroo or getting fencing wire stuck in a wheel or something.

However you must be commended in posting up the vid on a 35mm 205 stator hub motor that could manage 3.4kw output from up to 8kw power in, its getting kinda odd now with power used off the battery standard that folks around here are getting high on by increasing for little gain. visitors here are now getting quite a bum steer from as torque needs to actually get to the ground to be of any benefit. ive not seen much more than 200NM maximum for any length of time from a sub 15kg hub motor, v's double that for way less power used on a good mid drive, and half the power used again for even more torque from your deathbike.
So should we not also be trying to inform our readers of this wasteful range and development limiting fact?

I have nothing but respect for you, your amazing bike, and the awesome racing you've done that crushed gas bikes.

If you can my friend, consider thinking of any electro-magnetic combination achieved through gearing that you like, perhaps your awesome Joby motor, and look at the rate you're having magnets move passed those teeth vs a given wheel speed.

Now recognize this same magnet moving by the same tooth at the same rate for the same tire speed can be made by putting it into a direct stage. The exact same EM machine with the exact same efficiency can be made, and skip the added mass and potential failure modes of having added moving pieces.

I've got no argument that most hubmotors available today are designed around the cheapest solution to get a wheel to spin, and the efficiency and performance of most of them reflects it. It also reflects the LEAF motor's efficiency improvement coming at the cost of it's potential to over-drive it productively.

This doesn't mean a hubmotor has to suck, Mile's designed and EM simulated a direct drive hub that was lower total losses than most chain stages would be alone.

I respect your awesome work and race success, and soon enough I hope to have a hubmotor that can keep up!

 

[okashira]

We need induction motor hub motors. No more parasitic torque when your battery is dead.

Another option is Metglas. Even less potential for "overdriving" but they can cut that parasitic torque by 70%.
Metglas isn't used in EV's due to power/weight, or cost. But it makes a sense for a DD ebike.

I was planning to make a post on this.... It is a sad state of affairs for DIY/Hobby/Ebike motor and controller designs compared to industry. We have IPM motors in $100 Milwaukee hand power tools, but still use surface mount magnet designs for EVERYTHING that graces this forum.

 

[liveforphysics]

We have IPM motors in $100 Milwaukee hand power tools, but still use surface mount magnet designs for EVERYTHING that graces this forum.

I did 220miles on an IPM motor vehicle yesterday, and another ~100 today.

You're right though that we are still in a primitive
state of EV maturity.

 

[Jestronix]

So my question is, what kinda cooling could be done if these were sprayed with a bit of water mist each time u punch it ? In theory a 1 litre bottle may make a difference on those tough hills.

 

[fechter]

Preliminary testing feedback on Hubsinks:
......

Great report. I'm curious where your temp sensor is located. Obviously in the motor, but stuck to the copper? iron?

 

[liveforphysics]

So my question is, what kinda cooling could be done if these were sprayed with a bit of water mist each time u punch it ? In theory a 1 litre bottle may make a difference on those tough hills.

Member Farfle's hubmotor race bike made from cutting apart magic-pie's and sandwiching them together and making a custom rotor and re-winding it also used a water mist spraying rig inside the hub. It worked amazingly well. You need to protect everything inside the motor with some tough high temp epoxy spray from corrosion to do this, and then only use distilled water.

It was seeing how well that motor performed that interested me in buying the 273*40mm wide motor from Vito, and his "V3" level of it should have a considerable performance edge over the conventional magic pie lamination stack Farfle used.

Farfle and myself both daily-ride DSR's with IPM motors now...

 

[spinningmagnets]

IPM = "X" Permanent Magnet ?

Whats the "I"?

 

[mrbill]

Preliminary testing feedback on Hubsinks:
......

Great report. I'm curious where your temp sensor is located. Obviously in the motor, but stuck to the copper? iron?

Thanks.

The thermistor is the black bump at the end of the two thin black wires tucked between the coils and the "iron" (aluminum) near the top of the photo below.

 

[liveforphysics]

IPM = "X" Permanent Magnet ?

Whats the "I"?

 

[spinningmagnets]

Ahhh...thanks

Does this qualify?

edit:

It is a sad state of affairs...We have IPM motors in $100 Milwaukee hand power tools, but still use surface mount magnet designs for EVERYTHING that graces this forum

Found this (Milwaukee drill with IPM rotor): https://youtu.be/UBvRBvYcbs0?t=540

 

[liveforphysics]

Thats IPM for sure! I don't know how that BEMF is going to look like anything but a snarl, but it's IPM.

 

[spinningmagnets]

Its the Headline rotor. Found in Cyclone 500W/650W/750W, etc...also AFT and EGO. The only complaint I've heard is that the very robust steel reduction gears are very noisy, and yet they have never upgraded to a slight helical tooth...

What are the advantages / drawbacks of IPM vs SPM, since this is very pertinent to the "motor design for local production" thread.

 

[spinningmagnets]

With the laminations being laser-cut, and the shafts being made on a local CNC, a small extra cost to avoid interruptions in the non-hub motor supply is well worth it (IMHO).

ie...we should continue to leverage affordable motors from China as long as they are available, but...when the proverbial "manure hits the air circulation device", I would appreciate having an idea of what a locally-made design would look like, using best available practices and designs.

 

[liveforphysics]

What are the advantages / drawbacks of IPM vs SPM, since this is very pertinent to the "motor design for local production" thread.

I will let Biff answer that. At 15min mark IPM part begins.

[youtube]q1gjyL6vmeg[/youtube]

 

[Jestronix]

So my question is, what kinda cooling could be done if these were sprayed with a bit of water mist each time u punch it ? In theory a 1 litre bottle may make a difference on those tough hills.

Member Farfle's hubmotor race bike made from cutting apart magic-pie's and sandwiching them together and making a custom rotor and re-winding it also used a water mist spraying rig inside the hub. It worked amazingly well. You need to protect everything inside the motor with some tough high temp epoxy spray from corrosion to do this, and then only use distilled water.

It was seeing how well that motor performed that interested me in buying the 273*40mm wide motor from Vito, and his "V3" level of it should have a considerable performance edge over the conventional magic pie lamination stack Farfle used.

Farfle and myself both daily-ride DSR's with IPM motors now...

So Im running a sealed hub with trans oil, by misting just the heatsink fins I take it water would still work its way in? Or the trans oil would fend off any corrosion ? I have access to deionised water, is it all worth it ?

 

[liveforphysics]

So my question is, what kinda cooling could be done if these were sprayed with a bit of water mist each time u punch it ? In theory a 1 litre bottle may make a difference on those tough hills.

Member Farfle's hubmotor race bike made from cutting apart magic-pie's and sandwiching them together and making a custom rotor and re-winding it also used a water mist spraying rig inside the hub. It worked amazingly well. You need to protect everything inside the motor with some tough high temp epoxy spray from corrosion to do this, and then only use distilled water.

It was seeing how well that motor performed that interested me in buying the 273*40mm wide motor from Vito, and his "V3" level of it should have a considerable performance edge over the conventional magic pie lamination stack Farfle used.

Farfle and myself both daily-ride DSR's with IPM motors now...

So Im running a sealed hub with trans oil, by misting just the heatsink fins I take it water would still work its way in? Or the trans oil would fend off any corrosion ? I have access to deionised water, is it all worth it ?

It cools at some cost of refilling the bottle and having added system complexity and corrosion risks. If you value added cooling in a big way, it's really very effective. I wouldn't personally design a system around using it, but I would consider it for things like road racing or long hill climbs like Pikes-Peak.

 

[Cowardlyduck]

The other option I've been thinking of is having a refillable bottle of compressed air. There a some thin/long canisters that would fit perfectly along the top of a swing-arm.
Then it's just a matter of activating them when you need the extra cooling.
Hook up to a compressor when you get home. That would be a pretty simple, effective cooling option for racing IMO.

Taking it to the next level, you could replace the bottles with liquid nitrogen and beat some drag times.
And yeah, fully understand the limit's of saturation don't change with cooling, but it would mean you could run at that limit for longer.

Cheers

 

[spinningmagnets]

From liveforphysics:

I wouldn't personally design a system around using it, but I would consider it for things like road racing or long hill climbs like Pikes-Peak

This is an important distinction when arguments flare up in the casual discussions around here. Even if a certain design strategy is not a good long-term solution for a daily driver, it can still be very useful for specific applications.

The video: Thanks for posting this again, Luke. I now recall seeing it before (I'm sure you were the one who posted it), and I see things now that I didn't see before. The permanent magnets are often the most heat-sensitive part in a PM motor, and heat management is a power-limiting factor (Astro's use SmCo magnets specifically because they can survive more heat). The IPM configuration reduces magnetic eddy currents in the magnet, reducing magnet heat, while retaining a reasonably stable flux in the gap. 150C vs 105C (at the 23:00 minute mark)

Plus cheaper assembly (a key factor in my desire to provide local-production design specs, with labor being a major cost element)

The motor can then be run warmer (if desired) without the magnets being the limiting factor. (20:00 minute mark)

Controller limited to 70C-80C (158F-176F)
Battery limited to 54C-60C (129F-140F)...25:11 minute mark

 

[fechter]

Plus the magnets won't fly off the rotor at high RPM, which was a limitation on many inrunner motors.

I've thought about a water spray system for the long hill climbs I like to do. One idea was to wrap the hub with some kind of fabric that would soak up the water then evaporate in the wind. Sort of like an evaporative cooler. Otherwise a lot of the water might just bounce off. This would be on the outside, with ferrofluid in the gap to send the heat out that way. It would go in the same space as the hub fins. The spray would just be intermittent as needed to keep the fabric wet.

One downside of this approach would be impaired cooling if you ran out of water, which would be foreseeable.

 

[fechter]

The thermistor is the black bump at the end of the two thin black wires tucked between the coils and the "iron" (aluminum) near the top of the photo below.

That's helpful to interpreting the temp readings. I'd guess that spot would be slightly hotter than the hall sensor location if using ferrofluid.

 

[macribs]

We have IPM motors in $100 Milwaukee hand power tools, but still use surface mount magnet designs for EVERYTHING that graces this forum.

I did 220miles on an IPM motor vehicle yesterday, and another ~100 today.

You're right though that we are still in a primitive
state of EV maturity.

You got the new Zero motor? From what I can gather from memory from a youtube posted here showing the Zero's new motors those where IPM's?

 

[macribs]

Plus the magnets won't fly off the rotor at high RPM, which was a limitation on many inrunner motors.

I've thought about a water spray system for the long hill climbs I like to do. One idea was to wrap the hub with some kind of fabric that would soak up the water then evaporate in the wind. Sort of like an evaporative cooler. Otherwise a lot of the water might just bounce off. This would be on the outside, with ferrofluid in the gap to send the heat out that way. It would go in the same space as the hub fins. The spray would just be intermittent as needed to keep the fabric wet.

One downside of this approach would be impaired cooling if you ran out of water, which would be foreseeable.

I don't think your idea rule out the use of a heat sink. If you find a way to attach the cloth to cover just part of the heat sink you could harvest the benefits from both. Ie if you fitted some spungie material in the middle of the fins, or on the outside. And a wrap with a cloth or whatever to feed moisture to the spungie parts. As long as you leave some room for air to cool the heat sink as well I think you will be well set.

That said heatsink 2.0 with embedded heat pipes would take things yet further to a whole different level. A closed loop liquid and air cooling system that would cool faster the hotter the motor is running. Meaning if you do a long climb the higher the motor temps get the faster the transformation from liquid into gas will occur and as the gas rises in the pipes the cool wind to the fins will convert gas back into liquid and create circulation inside the heat pipes, bringing cooled down liquid close to the heat source, that liquid will do a phase transition into gas and rise backup the pipe and get cooled down converted into liquid again. Below you can see how the liquid inside the heat pipes are transformed into gas at the evaporator and turns liquid at the condenser.




So what does heat pipes add to the already great working heat sink? Well first and foremost they increase the thermal disposal capability. More heat can be transported faster from the source of the heat to the heatsink fins where the cooler air got a large surface of fins to work with. Because it is a closed loop system to some degree the heat transfer will remain decent even at low speed with little air flow across the fins, cos of the heat pipes circulation.

Depending on the design, sizes and numbers of heat sinks I do think heatsink 2.0 would cater for all situations, although if you find yourself in extreme conditions where you think v2.0 might be inadequate user your fluid mist, damp cloth or nitrogen spray idea to add even more ludicrous cooling.

 

[liveforphysics]

We have IPM motors in $100 Milwaukee hand power tools, but still use surface mount magnet designs for EVERYTHING that graces this forum.

I did 220miles on an IPM motor vehicle yesterday, and another ~100 today.

You're right though that we are still in a primitive
state of EV maturity.

You got the new Zero motor? From what I can gather from memory from a youtube posted here showing the Zero's new motors those where IPM's?

Look a couple posts up.


Also, water works well for cooling because of the phase change between liquid water to vapor water consuming a bunch of energy. While things like dry ice or liquid N2 have very low boiling/sublimation points, they don't actually absorb diddly squat for thermal energy compared to water. Likewise a compressed air blast would give you a couple seconds of slight cooling but any size air tank you could carry would not be as useful as even a tiny couple fluid oz bottle of water.

 

[liveforphysics]

Increased cost, more efficiency? I saw a 30% figure floating around, so a 90% efficient motor could be 93% efficient?

For the Zero SPM to IPM it was ~95.3% measured peak as an SPM and ~96.6% measured peak as IPM if I recall correctly. Ryan would obviously know better.

With respect to range, that is almost unnoticeable, with respect to this threads topic on cooling, it means ~38% less heating (while at peak efficiency).

 

[okashira]

Increased cost, more efficiency? I saw a 30% figure floating around, so a 90% efficient motor could be 93% efficient?

For the Zero SPM to IPM it was ~95.3% measured peak as an SPM and ~96.6% measured peak as IPM if I recall correctly. Ryan would obviously know better.

With respect to range, that is almost unnoticeable, with respect to this threads topic on cooling, it means ~38% less heating (while at peak efficiency).

I bet the efficiency difference is even greater at torque levels above the peak efficiency point.