Motor comparison spreadsheet

[John in CR]

specific Km² is the about the same, same copper loss per weight. While they are totally different as you objected, there are different ways to archive high Km² figures. Lower pole count does not automatically mean higher copper loss (due less space for copper). But this is what most people think. Or how do you explain why most hubbies have these 46 poles?

I don't think Km gives us that. It gives us only how well the copper, steel, and magnets are utilized to make torque. It's essentially the torque constant adjusted to remove how Kt changes with different windings of the same motor. I'm not convinced that squaring it leads to a more useful number. What is the resulting unit Nm squared per watt? Since early in the thread I've come around about Km's usefulness, but I agree with Wikipedia's description as the "motor size constant", and only useful in comparing motors of the same size. In this case I take size to mean diameter of the air gap. I think you'll find that your comparison actually proves the HS4080 has less copper, because it's copper has the advantage of working at a greater radius. The factory even used the fact of more copper compared to comparable power scooter motors as a selling point.

I don't know who these "most people" are, but they're wrong as proven by HubMonster's quite low phase to phase resistance. What just about everyone misses is one of the reasons for going 6 phase. That is achieving low resistance while retaining a high enough inductance, so the motor doesn't become hard to drive.

As to why the high slot and pole count motors are more common, it's because they are cheaper and lighter, since they require less stator steel and copper. In their designed use the resulting higher frequency isn't an issue at the relatively low wheel rpm. Trying to go low pole at that large diameter gets way too heavy due to the stator steel required.

seems as: my favorite motor must be a half as big one, like a 20T24P 1/2-MidMonster to gain a Km² figure of about 4 times the MXUS3000 (that is quite good on core loss too here, still not s close on being equal though) using just a 2:1 reduction to gain that figure. This motor shall be running a 26" wheel but like running like a half-midmonster in a 13" wheel and very little reduction loss, almost none. 2:1 is very efficient for chain reduction, like ~97%+ and very little vibration when using a good chain.

Anyway i dont want more than 6 maybe 7kg of motor weight in my bike. I want headroom for battery.

Linukas's bike is great, though he made the almost universal mistake of attaching the motor to the frame, but that discussion is too far OT.

Good luck finding that motor. I prefer motor headroom for a cooler running motor at the power I want, and the out of production MiniMonster I used to sell (150mm X 50mm stator) is my minimum for a mid-drive. I accept the fact that 8-9kg is as light as the motor will get. MidMonster is a good alternative for me, but that's a bit more motor 9-10kg after max weight loss, and they wound the damn thing too slow. It has plenty of inductance headroom to wind it faster to reduce Rm and eliminate the high voltage requirement to take proper advantage of the motor's capability. The Revolt160 pro clicks the right boxes, but I cringe at the price, since I can get so much more motor for less.

 

[crossbreak]

so they basically save copper in trade of core loss. thx for that insight.

Km² can reflect copper loss accurately. If you calc copper loss for different motors and same circumstances, you see that it always matches Km². I can post a derivation if someones interested. The strange unit derives from: Nm of torque per Watt² of copperloss. A bit strange i must admit. But somehow logical as you must accept 4 times the copper loss to gain double the torque

The Rv160 does not use the axle design sadly. Could be stiffer or more lightweight that way, for the kind of middrive i am after, a shaft is not required. Sure you can go for smaller sprockets that way, but that's a small advantage IMO. Very sad that MiniMonster is out of production. I'm keen for those values of the resistance and no-load values of the RV160. Let's see how it compares to MiniMonster. Mauimart posted the relevant figures for MiniMonster here: https://endless-sphere.com/forums/viewtopic.php?f=31&t=40859&p=756107&hilit=rpm#p756107
Sadly not very accurate values :/

Midmonster sadly is a bit too much for a bike that is made for soft trails. If i wanted a motorcycle then i just i'd buy an 80cc. Just not as much fun as an ebike as it is twice as heavy

 

[liveforphysics]

Only 10g, but >1Nm of torque.

http://www.hobbyking.com/hobbyking/store/__89179__Brushed_Motor_15mm_6V_20000KV_w_256_1_Ratio_Gearbox.html


I have seen some pocket watches that would also look pretty bad ass with your performance metrics.

 

[crossbreak]

yeah, if core loss and redaction loss would not exist, life was so much easier. Never told that Km² = Performance

it's like if you'd say a PC with great CPU but no physical GPU is great for video gaming.

Anyway, Km² figures below 20 at the wheel suck for going off road

 

[liveforphysics]

yeah, if core loss and redaction loss would not exist, life was so much easier. Never told that Km² = Performance

it's like if you'd say a PC with great CPU but no physical GPU is great for video gaming.

Anyway, Km² figures below 20 at the wheel suck for going off road

Someday perhaps you will learn which parts of your drivetrain are there to help you convert electricity into vehicle performance, and which parts are there to convert electricity into waste heat and failure modes.

For myself it took spending a lot of hours playing with dyno tuning and racing before I realized if it's not iron or copper, it's parasitic loss overhead standing in the way of your vehicles performance. Prior to many hours on a dyno and racetrack, I was also an outspoken advocate of adding stages of series loss to my drivetrain, including multi-speeds etc.

 

[crossbreak]

great, plz show me the sub 10kg hub that has a Km² of >20. For onroad lower Km² maybe usable, not if climb hills all day. If you calc hysterisis loss of a 10kg hub while climbing a 20% you may notice that there is 90% copper loss

 

[liveforphysics]

great, plz show me the sub 10kg hub that has a Km² of >20. For onroad lower Km² maybe usable, not if climb hills all day. If you calc hysterisis loss of a 10kg hub while climbing a 20% you may notice that there is 90% copper loss

What I'm making at the moment, is a reasonable mans hubmotor ebike based on a Nyx frame. On paper at least, it will be capable of >100mph, capable of power wheelies up to ~70mph, and with luck it will have enough copper and iron to stay together in a non-plasma state while eating >650A of phase current.

I don't know what it's Km^2 will happen to be (though I could calculate it if I cared enough). What I do know, is that it should deliver more torque than the chassis is capable of using up to a speed beyond what I want to going, and if I'm lucky it won't melt down or ever need repairing. Those are the metrics that matter to me in a vehicles powertrain now, as everything else seems like a calculator circle jerk.

 

[crossbreak]

weight?

 

[liveforphysics]

weight?

Total vehicle should be ~88lbs with 1.8kWh of cells onboard.

 

[crossbreak]

sounds goog. whats the estimated weight of the bare motor?

 

[John in CR]

sounds goog. whats the estimated weight of the bare motor?

Better questions are what's the pack voltage and motor wheel diameter.

That kind of torque and top speed + only 40kg all up bike + and Luke so much lighter than I am = a daily rider to make Luke smile for a long time and embarrass an awful lot of vehicles that pull up next to him.

 

[speedmd]

What I'm making at the moment, is a reasonable mans hubmotor ebike based on a Nyx frame. On paper at least, it will be capable of >100mph, capable of power wheelies up to ~70mph, and with luck it will have enough copper and iron to stay together in a non-plasma state while eating >650A of phase current.

YES you have our attention. Big QS? Controller?... Looking forward to seeing the build.

 

[crossbreak]

sounds like much more than 10kg for that motor 1.8kwh for a 88lbs vehicle isn't that much actually

 

[madin88]

for daily use on normal roads such heavy hubmotor is a pain in the ass, but it will shine on smooth roads and race tracks for sure

personally i really like the design of the MXUS. there is almost no useless steel on the stator (at least it looks trimmed down well to me) and it still has a good amount of copper.
with a spokeflange made of aluminum (separated from the back iron) the weight probably could be lowered by 1,5kg or more turning it into a 7,5kg motor.
I already thought of asking my friend the CNC machinist for fabricating such sidecovers and machining down the steel ring, but than i think all the effort is not worth for only one or a few motors and much less if in the next one or two years there comes such motor on the market..

 

[liveforphysics]

sounds like much more than 10kg for that motor 1.8kwh for a 88lbs vehicle isn't that much actually

The motor is 17.7kg. Definitely a big heavy motor, but if it delivers the crushing performance Im looking for without turning to plasma, I'm OK with it being heavy in the rear wheel of my bike. Riding my wifes bike that has a 9kg hubmotor in the rear wheel seems to work surprisingly well off road. My own bike will be about double the rear wheel mass.

I will find how how it handles offroad soon enough.

 

[crossbreak]

ok then please post a video! this all sounds awesome. And still... i'd be happy to be the first to compute Km² in the end how will this compare to LMX P2 that is Km²=25 with the cheap BHT 1000W motor and 6:1 chain reducion. With almost 18kg it seems you can be the first who can strike that Km² 20 barrier as Hubmonster has Km²=17 and weight=15,4kg

personally i really like the design of the MXUS. there is almost no useless steel on the stator

yep, it unfortunately there is no 2T model that would make it preferable for middrive. Just as middmonster kV is too low. That's the main reason i think so much about the leafmotor, even if 205mm stator dia seem too large and 35mm width seem too small

 

[John in CR]

Crossbreak,

A gear reduction doesn't change anything about a motor itself. What you're saying essentially is that changing wheelsize of a hubmotor changes it's Km, which it obviously doesn't. I also don't get to increase my motor constants by taking one of my motors out of the wheel and gearing it down for a mountain trail bike. No, torque of the motor doesn't change, just thrust at the wheel. By your methodology even changing wheel size on a hubmotor would change it's motor constants.

 

[crossbreak]

This way it's no motor constant anymore. Lets call it drivetrain constant

 

[John in CR]

This way it's no motor constant anymore. Lets call it drivetrain constant

It's incomplete then, because it doesn't factor in the last step, which is wheel size. That's partly why the puny geared hubby scores so high. Once you factor in mass, a high relative rating is logical, but otherwise no.

We should also get the no load current including the complete drivetrain along with the bare motor data. I guess we'd need 2 data points for that too, since while friction losses I think are linear, windage shouldn't be. Out of curiosity I'd like to see windage for some different tires, since the one time I had a motor come with a knobby bicycle tire and it threw off quite a bit of wind.

 

[crossbreak]

Yep. Wheel size and the specific value should then be referenced to vehicle mass rather than motor mass alone. at the end of the day, the motor has to push it all up the hill at once, no discount here.

This dKm² (drivetrain Km²) is defined as:

dKm² = Km² * i² /r [N/W²], with i being the reduction ration and r being the radius of the wheel,

Km² =Kt²/Rm, where Kt is the motor torque constant and Rm the motors terminal resistance

windage loss increases with rpm³, so we need 3 data points to include it into no load losses.

 

[jk1]

So on column R i can see the cyclone motor efficiency peaks at 89.95% and peak power at this efficiency is 5980w, is that running 72v ? wow thats a lot of power from such a small motor! and the efficiency is very similar to the ASTRO motors of 3210 8t has 93% efficient but at a low lower power of 1219 W and the 3220 4t has 93% efficiency but at low peak power of 2830w is that true ?

But also if you factor in the ASTRO motors have a higher 169 KV they will probably be running higher RPM and hence you would need more reduction and maybe another reduction stage which adds weight and hence the efficiency looses would be worse compared to the cyclone 122 kv. As others have said this can be 5 to 10% losses per reduction stage, so when used as a mid drive or direct to the rear wheel with one stage reduction the cyclone motor may have overall higher efficiency possible than these 2 common Astro motors if you add the gear reduction losses ?

Yeah that's a good point and as people have been pointing out on this thread you need to factor in gear reduction losses as every reduction stage adds weight and losses 5 to 10% per stage. So a for a mid drive or direct to the rear wheel where the Astro rpm is way above the RPM needed then the cyclone motor will need 1 less reduction stage and hence the efficiency will possibly be the same or higher depending on what it is i.e belt drive reduction on an astro being less efficient then a planetary gearbox of the cyclone etc. And as others have mentioned gearbox losses are a higher % at low power then they are at full power. Hence getting the gear reduction efficient is very important on partial load and cruise economy which is MOST Of the ride so again the less reduction stages the better and more efficient each reduction stage the better ! as you get the extra torque with less losses.

Obviously their is a balance because a hub motor has all the disadvantages of needing a very high power motor, battery and controller which all combine to add a lot of weight as well as a lot of UNSPRUNG mass. ok maybe for a drag bike but not for anything else.... 1 or 2 stage maximum reduction allows better packaging by putting the motor in the frame of the bike and remove UNSPRUNG mass as well and reduce the motor size, probably why tesla has gone that way and not direct drive.

 

[jmz]

The motor constant was only *ever* intended to provide a comparison of efficiency of torque production between motors in the same application, i.e. bolt-in replacements for the same reduction/radius. In this specific role it is perfect as constructed.

 

[bunya]

I notice the no load current isn't included in Column AJ . For example, with the cyclone figures I uploaded no load is approximately 2.85A at 6000rpm (Sinusoidal) and at no load efficiency is 0%. Yet the table shows that for 6000rpm efficiency is ~40% at 1.92A, I'm guessing this must be 1.92+2.85A for 4.77A.

The numbers also highlight the most efficient rpm to be at for the required power, for example I always though high rpm was more efficient but it seems that for low speeds low rpm is more efficient at least for the cyclone motor with its high hysteresis, iron and eddy losses. Thanks for the heads up

It will be interesting when I start using a VESC and FOC to see if I can use reluctance torque to increase the motor's efficiency under low loads.

 

[liveforphysics]

This way it's no motor constant anymore. Lets call it drivetrain constant

It's a worthless misleading metric that would lead one to believe a pocket watch is the optimal drivetrain choice.

That said, enjoy life and have fun with math as much as you like.

 

[Doctorbass]

sounds like much more than 10kg for that motor 1.8kwh for a 88lbs vehicle isn't that much actually

With ultra high C rate Lipo that exist now, the energy rating of the battery become really low for high power...

I have Lipo that has been tested really at 200C by one of the EPIC guy on NEDRA. These are rated 100C and 50 cont... I mean REAL C... these come from unclassified Military special drone projects.

I have built a 900Wh 70kW battery for my 2WD NYX and for my maybe future lightweight drag racing ebike/motorcycle trade off...