Air-cooling the moving hub motor

[John in CR]

Since you want to get a lot out of a little, you'll want to motor temps. For 4 or 5 years I just used the feel my motor with my hand approach after stopping immediately after more and more demanding use...longer steeper hills. That's using much bigger motors, so your much smaller lighter stator will heat quickly, so closer monitoring is necessary. I very highly recommend using a Cycle Analyst V3 from Grin Tech, who pays for our wonderful forum. Once you use a CA you won't even want an EV without it, and a CA3 includes the ability to report temps and even do current limitation based on temp limits you set and thermal shutdown too. You need to plan ahead and get a 10k thermistor to install on your stator...I recommend on the stator instead of stuffed in the windings to avoid reporting of the short spikes that can occur in the copper before the heat moves to the stator steel.

Let me know by PM if you still have heat issues, because I have other ventilatated hubbie cooling ideas that I'm certain will help even though they're no yet proven because I haven't needed more. One thing I did start doing 5 years ago, even before I started using exterior centrifugal blades was to direct more air at my motor. My swingarm has 2 air scoops that direct more air toward the motor. I did it primarily for aesthetics, but functionally they definitely get more air to the motor, which has to help with cooling. I ran 16kw peak pushing my heavy load with a sealed hubbie for a year and a half in a mountainous region without a meltdown, so they sure didn't hurt. Here's the best pics I found on my computer to show what I did.

 

[Vanarian]

Ok I'll keep update for you on how it goes! I'll also check CA and thermistor.

Though I was thinking also of getting a temp gun, Justin has been using it to test Ferrofluid and check where heat applies over the motor parts. Well for ride test, it looks unusable to me , it works for bench test I suppose!

 

[John in CR]

Heat moves relatively slowly, so an IR thermometer (super cheap at Hobby King) is a worthwhile investment and can be used in real world testing. Just stop and check temps with a tool that easily fits in your pocket. I picked up a couple (I like backups) and they're about the size of a finger.

 

[Hummina Shadeeba]

The extent of my testing is to use my infrared thermometer on the top of the hill. Not a fair test really as I'm always going as fast as possible but that's fine too.

John with ur fin attachment it doesn't blow through the motor and just on the outside it seems. If they blew in the motor right at the center as you have them and then there were centrifugal blades the length of the hub...would be great.


Im getting this made. Changing it to make the inner room,without the blades, to be thinner, and add more blade width.

. I wonder what I could do to the inner empty room to enable the air up through the 6 holes and then through the big central hole and diminish the 6 bolt hole structures. .

 

[Vanarian]

Careful Hummina, from what I've understood so far there is a sweet spot in air about pressure and speed to use its thermal absorption.

Note that if you force air through instead of forcing it out and you don't have enough exhaust, you will face back pressure which will apply force through your motor + substantially heat up the air itself.

In which direction do you want to spin it?

 

[Hummina Shadeeba]

This is centrifugal. Flowing out. It will go out either way u spin it

 

[Vanarian]

This is centrifugal. Flowing out. It will go out either way u spin it

The way it looks, it looks like it will produce different results depending on the direction you spin it.

If I take the transparent pic, spin it on the left and it will cause compression in perimeter while still causing low pressure at the edges ; spin it on the right and it will cause full depression (right I don't know how to say low pressure in one word in english :lol: )

Why don't you try to straighten the edges?

 

[Hummina Shadeeba]

I'm getting a plain straight blades one made and also this curved blades one. Actually it will be with blades that sweep even more so instead of the 45 degree angle blade u see here it will be a full 90degree. I should get them today and excited to see how they all do. And I'll be able to flip the 90degree super pinwheel to have the blades sweep forward and see how that does too. If there's anything that can make up for having a motor that's too small I think it's this!

 

[John in CR]

John with ur fin attachment it doesn't blow through the motor and just on the outside it seems.

They don't blow air into the motor. They suck air through the motor, and the dense smoke test I did clearly showed that it draws air through the motor as well as over the shell from the left side. At somewhere around 10mph (above 150rpm or so), it starts to draw air through the motor, and the flow gets stronger the faster it spins. Several exhaust slots are in the low pressure region in the "shadow" of each blade. The pics of the swingarm air scoops are from before I vented the motor. Those are just the best pics of the scoops I had.

Some things you can't tell from the earlier pic with the blades are:
- The blades extend inside the motor almost the length of each blade, and the resulting interior blades run as close to the stator as I dare. That's to ensure as much of the air inside the motor as possible is spinning at motor rpm, and to create turbulence at the end windings. The interior portion of the blades has minor effect on flow compared to the outside portion of the blade that is much larger and at a greater radius.
- The sides that give structural rigidity to the radial blades and a way to bolt them onto the moto, also block air rushing in to fill the low pressure behind the blades to a large extent. Instead of perfectly flat against the side of the motor, they're bent outward slightly to both open more of the slot to flow air through, and to push air away from the side.

The blades were simple to make by hand to test, and easily modify as needed. It worked so well that I only unbolted them twice. Once to change the tire, and once right after initial tests to make the rounded corners since the original square corners were pretty ugly. They aren't beautiful now, but function rules the day for me. Maybe someday I'll throw on a full side plate, but with no heat stress even jamming up a solid 20% grade to the wind turbines on the mountain ridge above my house, pumping 28kw through the motor accelerating out of every curve during the climb, it's hard to get motivated to change anything. I've been waiting almost 4 years for someone to catch up, so I can crank it up more to explore the power limits, as well as enhance the cooling system that may be needed at higher current.

 

[Hummina Shadeeba]

After trying a radial bladed version and a swish blades version I'm disappointed. It shows to pull air through but the temps
I'm hitting are pretty much the same. But the new motors I got made of steel and with a smaller airgap, yet almost everything else the same, in fact they have weaker magnets so the pull force is equivalent with the smaller airgap, but the motors stay way cooler! I've stuck my infrared thermometer everywhere I can to find the heat and it's not there anymore!

I'm going to do more testing but do you have any theories how the motor design I have above can show a huge temp drop for a given load with only the modification of replacing the n50m magnets and .5mm gap with weaker n45sh and a .4mm gap? My first motors were .4 and heat wasn't an issue and never thought about it, then the change to .5 and things get hot, back to .4 and with testing they show much cooler.

 

[Vanarian]

At this size and space I think it is a matter of your motor being able to cope more easily with rotation.

Stronger magnets will give more flux but also add drag. You gain torque but you need more energy to move this torque. So maybe your motor reads more phase amps through windings?

Plus neodymium magnets will absorb heat more easily when you raise rating so it could be a backlash? I guess that's a huge difference

Just a silly idea, have you tried wider blades as "covers" for your hubs? Like Knight Rider I mean.

Your wheels stay flat so you can do better than I can afford since I tilt mines.

 

[Hummina Shadeeba]

At this size and space I think it is a matter of your motor being able to cope more easily with rotation.

Stronger magnets will give more flux but also add drag. You gain torque but you need more energy to move this torque. So maybe your motor reads more phase amps through windings?
i imagine when a motor uses a stronger magnet which may add a cogging effect when unpowered it wouldn't have that resistance when powered. Also the pull force of the magnets is the same when the distance is factored in

Plus neodymium magnets will absorb heat more easily when you raise rating so it could be a backlash? I guess that's a huge difference
what do you mean by they would absorb heat more easily. The magnets are rated to different temps, they have different temp opperating and Currie numbers but their ability to absorb or conduct heat would be pretty similar.

Just a silly idea, have you tried wider blades as "covers" for your hubs? Like Knight Rider I mean. they were covers that replaced the bolt-on flange.

Your wheels stay flat so you can do better than I can afford since I tilt mines.

. id think tilting would allow more airflow.

 

[Vanarian]

To my understanding the resistance remains, so there is actually also a sweet spot for the choice of your magnets strength. Your n45sh magnets should be the sweet spot for this size of motors, for bigger ones like found on e-bikes it might be a lower rating.

The more strength you get, the more drag thus less efficiency you get while you gain torque in exchange.

For neodymium magnets, I'm pretty convinced they don't absorb heat the same way. They may heat similarly but weaker magnets will release more of the circulating heat while stronger magnets will keep it caged for a longer time. I'd like to experiment this with a temp gun.

For the covers, I saw it but can you do it bigger (same diameter but larger)?

tilting by itself won't do much, but on the contrary it will prevent me from putting bigger blades because of ground clearance.

 

[Hummina Shadeeba]

I'd think that with the motor in use a stent magnet could only be a boon. ?

When u say the temp will be contained within stronger magnets I've never heard of that or any interaction between heat and magnetic strength. ?

I get what u mean by tilting now. I could go longer but lately haven't felt a need!