Science, Physics, Math, & Myth

[madin88]

sorry mate you got halfway through being right, then lost it again...

" Latter would be the better choice for performance per costs and system efficiency (less losses over phase wires)"
assuming you change battery voltage and controller accordingly, and all other wiring remains the same, yes... but the difference will be pretty minor in practice.

i think you are the one who lost it suggestion: go to the simulator and do some simulations
since P loss = I² x R it will not be only minor in practice! ähmm what do we call minor? Is it a half percent ot 2 or 3?
at twice the current we would need to lower resistance by 4 times (not only half like some may think) for same losses. where is such controller? 100V controllers are the sweet spot at the moment and theory will not change that! the other thing is most motors come only with one size of phase wires and the high kV version always have more losses there - or with other words less torque output at given batt power. I'm not talking about more heat generated in the moto because its outside, but system efficiency is worse.

teslanv and i have lots of different motors, we build bikes in practice and we know what we talking about. with the simulator it now is twice confirmed that theory is one thing and praxis another.

" And it is not the same if a controller works at 50% PWM (high kV with limited speed) or 100% (without speed limit). Consumption during acceleration (top end) is different, the 100% PWM system has higher efficiency because no additional step down losses."
Nope. sorry, but if you vary the voltage and current by the same ratio as the change in KV, then the duty cycle at a given speed/power demand will remain the same, as both motors will be spinning at the same % of their no load speed, with the same back EMF (as a % of pack voltage) same (relative) resistance and inductance. if your just comparing a high kv and low kv motor with the same battery/controller combo for each then yes, it'll have a small difference. again however you're unlikely to notice it unless the controller is struggling with the high kv motor's R and L.

"Consumption during acceleration (top end) is different, the 100% PWM system has higher efficiency because no additional step down losses."
Nope, it'll be the same, as each controller is stepping down the same relative voltage, to the same relative phase voltage, in order to generate the same phase current, and thus the same motor torque (and same motor heat). Again however if your using the same controller and battery for each motor there will be a small difference, but again, this will be small.

you may have misunderstand what i was trying to point out or maybe i have not write it that understandable.
i was talking about differences between assumed System A [18kV motor, 80V, 50% speed limit] and System B [9kV motor, 80V, 100% speed]
system A will have much more top end acceleration, and even if you would lower controller and phase wire resistance of the 18kV System (by 4 times!!) it still would be a bit less efficienct because step down conversion creates losses.
this scenario was mentioned earlier in this thread or in another one so i wanted to show this up. it is a great idea if someone wants to have later the option for higher top speed, but it is not the same thing.

As has been stated repeatedly, there's no difference in heat generation between a low and high kv motor for a given torque output.

However, in NONE of these situations will the motors torque per unit heat change.

it cant be escaped... motor continuous torque is the same for any kv (well not quite, but the difference is so small you'll never notice outside of a lab).

YES YES, i think most of us reading this thread have got it^^
the problem is if we consider about the total drive system - with currently available components, and we should do this, than torque, performance and efficiency is different.

 

[sn0wchyld]

sorry mate you got halfway through being right, then lost it again...

" Latter would be the better choice for performance per costs and system efficiency (less losses over phase wires)"
assuming you change battery voltage and controller accordingly, and all other wiring remains the same, yes... but the difference will be pretty minor in practice.

i think you are the one who lost suggestion: go to the simulator and do some simulations
since P loss = I² x R it will not be only minor in practice! ähmm what do we call minor? Is it a half percent ot 2 or 3?
at twice the current we would need to lower resistance by 4 times (not only half like some may think) for same losses. where is such controller? 100V controllers are the sweet spot at the moment and theory will not change that! the other thing is most motors come only with one size of phase wires and the high kV version always have more losses there - or with other words less torque output at given batt power. I'm not talking about more heat generated in the moto because its outside, but system efficiency is worse.

teslanv and i have lots of different motors, we build bikes in practice and we know what we talking about. with the simulator it now is twice confirmed that theory is one thing and praxis another.

" And it is not the same if a controller works at 50% PWM (high kV with limited speed) or 100% (without speed limit). Consumption during acceleration (top end) is different, the 100% PWM system has higher efficiency because no additional step down losses."
Nope. sorry, but if you vary the voltage and current by the same ratio as the change in KV, then the duty cycle at a given speed/power demand will remain the same, as both motors will be spinning at the same % of their no load speed, with the same back EMF (as a % of pack voltage) same (relative) resistance and inductance. if your just comparing a high kv and low kv motor with the same battery/controller combo for each then yes, it'll have a small difference. again however you're unlikely to notice it unless the controller is struggling with the high kv motor's R and L.

"Consumption during acceleration (top end) is different, the 100% PWM system has higher efficiency because no additional step down losses."
Nope, it'll be the same, as each controller is stepping down the same relative voltage, to the same relative phase voltage, in order to generate the same phase current, and thus the same motor torque (and same motor heat). Again however if your using the same controller and battery for each motor there will be a small difference, but again, this will be small.

you may have misunderstand what i was trying to point out or maybe i have not write it that understandable.
i was talking about differences between assumed System A [18kV motor, 80V, 50% speed limit] and System B [9kV motor, 80V, 100% speed]
system A will have much more top end acceleration, and even if you would lower controller and phase wire resistance of the 18kV System (by 4 times!!) it still would be a bit less efficienct because step down conversion creates losses.
this scenario was mentioned earlier in this thread or in another one so i wanted to show this up. it is a great idea if someone wants to have later the option for higher top speed, but it is not the same thing.

As has been stated repeatedly, there's no difference in heat generation between a low and high kv motor for a given torque output.

However, in NONE of these situations will the motors torque per unit heat change.

it cant be escaped... motor continuous torque is the same for any kv (well not quite, but the difference is so small you'll never notice outside of a lab).

YES YES, i think most of us reading this thread have got it^^
the problem is if we consider about the total drive system - with currently available components, and we should do this, than torque, performance and efficiency is different.

hah yea i thought after posting you were talking same voltage. apologies for the misunderstanding.

so some quick calcs, assuming 12g phase wire at 1.9m total length (so pretty close to worst case for most of us). if you compare a 50A motor to a 100A one with half the turn count, then your extra losses for the phase wire at full power are just 75w. assuming 80v for the first, and 40v for the 2nd motor, and assuming 77% efficiency at peak power output, then that extra 75w accounts for about 7% extra loss, or about 1.8% of your total power draw. 3080W power output vs 3005W.

if your cruising at about 400W power draw and about 88% efficiency then your talking about 2% extra losses, or about 0.25% of your total power draw. for a bike with a 50km range, this will knock off about 100-150m of cruising range.

Like I said, pretty insignificant, and this is considering a worst case scenario too, fairly thin, and quite long phase wires. upgrade them to 10g and that 7% becomes about 4%. copper losses even in pretty small wires pale in comparison to motor losses.

"where is such controller?"
in simple terms, rsdon of a 4110 is about 2.5mohm (iirc). a 4660? (the 60v rated ones lyen uses, i forget their code) is about 1mohm. compare a 12 fet with a 18 fet, and youre getting close to your factor of 4 (in very round terms). Traces and similar may need to be beefed up, but it really isn't hard to significantly lower the resistance of a ebike controller's power stage. Again however, we're talking a minority of the overall power losses, even the same controller will only have a similar amount extra losses as the long 12g phase wires. Less in fact, since the phase to phase resistance might be about 5-7mohm vs 10mohm for the phase wires.

So all up? maybe 10% extra power losses (note, extra power loss, not extra power use) at full power using the exact same controller and phase wires. about 2-2.5% less range at full power, and about 0.4% less at cruising speed. your 50km range bike is now 49.6km range. quite frankly I didn't think the gap would be that small myself until having just done the numbers now... I was expecting that kind of difference after having changed controllers and phase wires.

your right in that there's a sweet spot atm for 100v controllers, so specking to this is a good idea, though even then the difference isn't huge... 4115 controllers for instance have lower switching losses than 4110's, so in certain situations a 4115 controllers losses may be comparable to the more 'sweet spot' 4110. and controllers are massively efficient (mid to high 90's), so losses from stepping down voltages are pretty minimal compared to motor losses, even at low pwm values.

Appologies if i came on too strong mate. too many long days trying to finish an electric car for my final year elec eng project, and dealing with regulations that state i need to change my battery wires to ones thicker than my wrist for 400A... not to mention that my controller that'll be accepting that 400A is about as wide in total as 2 of those wires side by side lol. Just imagining trying to connect the lugs that'd fit around that 00000-ish guage wire to the controller makes me giggle heheh. Like trying to park a semi in a dog kennel.

 

[madin88]

i'm fine with it snowchyld..

Mxus only has 13GA (2,6mm²) wires and the 3T would laugh over 200A peak, but losses than grow above 500W this would mean noticeable less thrust during hard acceleration.
4T mxus at same torque only would have about 200W loss in the wires. Im not sure how justin implemented all the motors into the simulator. did he measure resistance with or without phase wires or how long they have been would be useful to know. or are they even not considered at all. i mean at 3T motor the wires alone (stock and not shorted) would make 15-20% of total copper losses.

wires thick as a wrist for 400A? sounds overkill but it makes sense for continuous flow^^ I wish you success with that project!

 

[zombiess]

Don't forget that 3 phase only uses 2/3rds (66.66%).

The losses also occur on 2 wires. If you have 2M of wires and they have a resistance of 10mOhm, then the loss needs to be calculated on 20mOhm

I'm not sure if the people running loss numbers are taking this into account, if you are then just ignore this post.

 

[John in CR]

i was talking about differences between assumed System A [18kV motor, 80V, 50% speed limit] and System B [9kV motor, 80V, 100% speed]

Look who can't think outside the box. You present a set of ridiculous settings that no one would run and still come up with the wrong conclusions, because you base your view on experience with generic parts motors that anyone in China can easily get the parts to assemble, and then run them with an absurd controller whose speed limiting function just chops a percentage off of the throttle voltage instead of just capping the top speed. In the real world that fast wind motor will have greater acceleration at everything other than 0 rpm, which when running the same voltage is the only point the slow wind will have the same torque as the speed wind supplied with the proper current. Then as the artificial speed limit is reached acceleration quickly tapers off like it would if you were doing the same with manual throttle control. Of course it will make more heat making that greater torque.

Good manufacturers always use larger phase wires on motors expected to be run at higher current.

 

[John in CR]

Telsanv,

You can't say I didn't warn you. Anyone selling 6fet, 12fet, and 18fet controllers for $90, 150, and 220 respectively obviously isn't concerned in the least regarding cost of their customers' systems. Much better controllers than Infineon leave plenty of room for profit at retail prices of half that.

Also, it's getting old repeating myself that there's nothing wrong with slow low powered systems. I'm not interested in those systems and don't comment on them, but go ahead and keep suggesting that I've made incorrect statements in this thread and don't know what I'm talking about.

 

[sn0wchyld]

mate, if your launches are feeling more slugish, then your motor is producing less torque. if its producing less torque then its producing less heat. if its producing less heat its going to overheat slower.

if the wires are 13g yet meant to take 200a, then the motor's, quite frankly, are crap. alternatively your pushing more current than they were designed to take in which case its no surprise that your getting hot wires... your windings are likely even hotter.

i know the regs that i apparently have to use are overkill, but that's taking it well into the realm of underkill. my guess is that thats all they could fit through the axle, so to save money on a larger axle and larger bearings they just underspeced the phase wires to the point that they'll fit. alternatively that 200a is only for a few moments at launch.

you demonstrate yourself that the wires are well underspec... imagine if you used a thicker axle that allowed 10g wire? those 500w loss would become about 250w, and again a pittance compared to motor losses (at launch your talking 8000w loss). all for the sake of a bit more steel and a larger bearing. Yet even if we take those 500w wire losses we see that its still 7% of your total losses, or just 4% more than a 6t.

And no, it wouldn't mean less torque during hard launches. Common mate, its not hard.. 200A into a 3t will produce the same torque as 100A into a 6 turn. The fact that you loose 300w more in the wires is irrelevant to the torque produced. you draw 300w more power to produce that torque, yes. but again, its 4% extra power use, in the worst case scenario. other than potentially frying your underspeced wires your not going to notice that difference.

alternatively if you want to look at it as your controller drawing the same power from the battery, then the 3 turn will heat up slower than the 6 turn. Why? because its drawing less current per turn, less torque means less heat.

it still comes out almost the same... if you compare apples with apples (same torque output) then your talking a 4% increase in power use (at 8kw), even for grossly undersized wires. if your comparing the same power input for the same controller and phase wires, then your talking 4% less torque. 100nm vs 96nm, for example... with a 26" wheel that equates to a 1kg difference in thrust. in other words, if your buddy weighs just a few kg more than you then his 6t will be slower than your 3t, and overheat sooner too, if your phase wires through the axle dont first...

you can do the same calcs with lower power draws too, and the numbers still come out largely the same. even at 2kw draws your still only up to a 15% difference in torque. and again, a 15% difference in time to overheat. this is all at 0rpm though... in reality the difference in torque will be smaller (or in favor of the 3t in short order) as will the difference in time to overheat.

i'm fine with it snowchyld..

Mxus only has 13GA (2,6mm²) wires and the 3T would laugh over 200A peak, but losses than grow above 500W this would mean noticeable less thrust during hard acceleration.
4T mxus at same torque only would have about 200W loss in the wires. Im not sure how justin implemented all the motors into the simulator. did he measure resistance with or without phase wires or how long they have been would be useful to know. or are they even not considered at all. i mean at 3T motor the wires alone (stock and not shorted) would make 15-20% of total copper losses.

wires thick as a wrist for 400A? sounds overkill but it makes sense for continuous flow^^ I wish you success with that project!

 

[markz]

https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907&start=25#p975389

http://www.ebikes.ca/learn/hub-motors.html

Crystalyte Hub Motors in Depth


At the moment, the only hub motors on which we've worked extensively are those from Crystalyte. These motors are of good value. They are manufactured with nowhere near the polish and precision of Heinzmann, for instance, but for 1/5th the price you get reliable performance and an appreciable power output. They offer a large selection of different configurations, and Crystalyte openly publishes the technical specifications of their motors, while most other companies don't let you read past the marketing department.

On the Crystalyte website, you'll see a large number of motors listed and characterized like 406, 408, 409, 4011. The last digits refer to the number of turns of copper around each stator pole. So for instance, a 406 has 6 turns, the 4011 has 11 turns.

The torque that is produced by one of these motors varies in direct proportion to the total current flowing around each pole. So in the above case, a 406 motor with 15 amps flowing through the winding has a total of 90 amps around the pole. The 409 motor would need just 10 amps to have 90 amps around the pole and hence the same torque output.

One false and oft-repeated conclusion is that therefore the 409 is a higher torque motor than the 406 because it can produce the same torque with fewer amps, or likewise more torque with the same amps. This is not the case. All 400 series motors can deliver exactly the same torque at exactly the same efficiency. The lower winding count motors just need more current to do this, but because they have fewer turns of a shorter length of heavier gauge wire, they can handle high currents with minimal loss. To use a concrete example, lets compare a 404 with a 408. The 408 has twice the number of turns than the 404, so the copper wire in the windings has 1/2 the cross sectional area and twice the length, for a total of 4 times the winding resistance of the 404. For a given torque output, the 408 needs only 1/2 the amps, but because it has 4 times the resistance the net electrical loss (I2R) is exactly the same.

Another consequence of having a larger number of turns around each stator is that the voltage induced in the winding by the passing magnets is increased in direct proportion to the number of turns. So for instance, at a certain speed of rotation, the 408 motor will produce twice the back-emf voltage as a 404 motor rotating at the same RPM. To power a motor, the battery pack voltage needs to be greater than the back-emf voltage, and so the 408 motor needs twice the voltage to spin at the same speed as a 404. However, it will only draw 1/2 the current, and you can see that the net power input (Volts * Amps) remains the same.

 

[teslanv]

Telsanv,

You can't say I didn't warn you. Anyone selling 6fet, 12fet, and 18fet controllers for $90, 150, and 220 respectively obviously isn't concerned in the least regarding cost of their customers' systems. Much better controllers than Infineon leave plenty of room for profit at retail prices of half that.

Whether or not a customer chooses to buy my Infineon controllers or some other less expensive controller is irrelevant to my argument. My point is that a higher current controller from any manufactured will be more expensive than a similar lower current controller from the same manufacturer.

I don't question your knowledge, John. Clearly you already know it all.

 

[zombiess]

Whether or not a customer chooses to buy my Infineon controllers

I don't think you are selling Infineon controllers, they look like the Xie Chang controllers and don't contain any parts by Infineon.

 

[teslanv]

I don't think you are selling Infineon controllers, they look like the Xie Chang controllers and don't contain any parts by Infineon.

I stand corrected, Z.

Yes my controllers are Xie Chang.

 

[ferret]

Telsanv,

You can't say I didn't warn you. Anyone selling 6fet, 12fet, and 18fet controllers for $90, 150, and 220 respectively obviously isn't concerned in the least regarding cost of their customers' systems. Much better controllers than Infineon leave plenty of room for profit at retail prices of half that.

Also, it's getting old repeating myself that there's nothing wrong with slow low powered systems. I'm not interested in those systems and don't comment on them, but go ahead and keep suggesting that I've made incorrect statements in this thread and don't know what I'm talking about.

John,
can you post a link to these better controllers?

Thanks,
Avner.

 

[madin88]

Also, it's getting old repeating myself that there's nothing wrong with slow low powered systems. I'm not interested in those systems and don't comment on them, but go ahead and keep suggesting that I've made incorrect statements in this thread and don't know what I'm talking about.

thank you for that^^
nobody says you have made incorrect statements here. quite the opposite is true because you have been the one that started to tell everyone here that there is no HT or HS motor (referring to how Clyte names theire motors or also BMC)

As already said the problem i have is when it comes to ebike with 3000w or below. there is no need for a very fast motor because with our 100V sweet spot of controllers it is better to up the voltage rather than using lower volt and unreasonable higher current. it is the better choice in terms of overall SYSTEM efficiency and component costs. additionally its more easy to deal with smaller wires and stock components doesn't need to be upgraded.
If we keep talking about hubmotors like MXUS 3k, the 9kV can take about 40A continuous. with 80V battery this already would be 4kW. it would not make sense here to use a 2T motor (if it would be available) and go with 40V and 80A. thats the point. Most builders work with components in this power region and many are not shure what type of winding they should choose, so i think its good to talk about this.
If we talk about higher power hub's like your Hubmonster than higher kV is needed to make use of the power.

mate, if your launches are feeling more slugish, then your motor is producing less torque. if its producing less torque then its producing less heat. if its producing less heat its going to overheat slower.

absolutely right. heat in the motor is lower but in other areas its higher.

And no, it wouldn't mean less torque during hard launches. Common mate, its not hard.. 200A into a 3t will produce the same torque as 100A into a 6 turn. The fact that you loose 300w more in the wires is irrelevant to the torque produced. you draw 300w more power to produce that torque, yes. but again, its 4% extra power use, in the worst case scenario. other than potentially frying your underspeced wires your not going to notice that difference.

you have two systems: both have same battery amps and same phase amps, but on system A you have 500W loss over phase wires and on system B only 100W as example.
what happens now: as you have less voltage at the windings beacause of the sag, the torque AT GIVEN RPM is different. the less sag the stiffer the motor. therefore system B will accelerate faster than system A. same happens if the motor gets hot and resistance increase: it will have more voltage drop between the phase wires so it has less stiffness.

if the wires are 13g yet meant to take 200a, then the motor's, quite frankly, are crap. alternatively your pushing more current than they were designed to take in which case its no surprise that your getting hot wires... your windings are likely even hotter.

these motors are one of the best available at the moment and more and more use them so i would no call them crap. The 3T never was planned by MXUS it was made by request (i was one of the guys that have asked them to produce them, i remember when they said they first need to try it out and i needed to wait a few weeks for their approval).
but if you look at other brands its almost always the same. only one size of phase wires for every type of winding.
from what i know MXUS is working on a V3 and at the minimum the phase wires and axle will be different. looking forward to the release

 

[sn0wchyld]

mate, if your launches are feeling more slugish, then your motor is producing less torque. if its producing less torque then its producing less heat. if its producing less heat its going to overheat slower.

absolutely right. heat in the motor is lower but in other areas its higher.

higher in areas that are generally well vented... so other than a small range reduction (<10% at 4kw) there's very little difference.

And no, it wouldn't mean less torque during hard launches. Common mate, its not hard.. 200A into a 3t will produce the same torque as 100A into a 6 turn. The fact that you loose 300w more in the wires is irrelevant to the torque produced. you draw 300w more power to produce that torque, yes. but again, its 4% extra power use, in the worst case scenario. other than potentially frying your underspeced wires your not going to notice that difference.

you have two systems: both have same battery amps and same phase amps, but on system A you have 500W loss over phase wires and on system B only 100W as example.
what happens now: as you have less voltage at the windings beacause of the sag, the torque AT GIVEN RPM is different. the less sag the stiffer the motor. therefore system B will accelerate faster than system A. same happens if the motor gets hot and resistance increase: it will have more voltage drop between the phase wires so it has less stiffness.

if you have 2 systems as you suggest, with the same phase amps, then yes, the high turn count motor will produce allot more torque. And a lot more heat. and guess what? the same heat in the phase wires, because as you state they're transmitting the same phase currents!!
What happens now? you have the SAME sag in the phase wires. because as you say phase amps are the same.... so the SAME losses in the phase wires.
so ill ask, whats your point? Of course system B will accelerate faster (at least until back emf clamps down on available power), and it'll produce far more heat doing it.
I also address the 'same power in' later in my last post... so im doubly puzzled why you bothered posting this...

if the wires are 13g yet meant to take 200a, then the motor's, quite frankly, are crap. alternatively your pushing more current than they were designed to take in which case its no surprise that your getting hot wires... your windings are likely even hotter.

these motors are one of the best available at the moment and more and more use them so i would no call them crap. The 3T never was planned by MXUS it was made by request (i was one of the guys that have asked them to produce them, i remember when they said they first need to try it out and i needed to wait a few weeks for their approval).
but if you look at other brands its almost always the same. only one size of phase wires for every type of winding.
from what i know MXUS is working on a V3 and at the minimum the phase wires and axle will be different. looking forward to the release

Best available doesn't mean squat if they're expecting 13g wires to handle 200A for more than a second or two. The rest of the motor may even be excellent, but the fact remains that its 13g wire transmitting 200A. its like buying a 1000 liter a second pump then trying to force that water through a common garden hose. Defeats the whole purpose by hampering its potential performance. That said, its still only 10% lower efficiency at peak current draw, so far less than 10% extra loss in general usage.

Seriously, it'd be so easy to get the 3t to work well (assuming the rest of the motor is good, i dont follow hubs much any more)... change the axle to a 30mm OD, use a 30MM ID bearing and run 10 or 8G wires. presto, all that extra power loss is gone and you can have crazy torque that doen't fall off a cliff at 40km'h (talking compared to a 6t here).

 

[madin88]

you have two systems: both have same battery amps and same phase amps, but on system A you have 500W loss over phase wires and on system B only 100W as example.
what happens now: as you have less voltage at the windings beacause of the sag, the torque AT GIVEN RPM is different. the less sag the stiffer the motor. therefore system B will accelerate faster than system A. same happens if the motor gets hot and resistance increase: it will have more voltage drop between the phase wires so it has less stiffness.

if you have 2 systems as you suggest, with the same phase amps, then yes, the high turn count motor will produce allot more torque. And a lot more heat. and guess what? the same heat in the phase wires, because as you state they're transmitting the same phase currents!!
What happens now? you have the SAME sag in the phase wires. because as you say phase amps are the same.... so the SAME losses in the phase wires.
so ill ask, whats your point? Of course system B will accelerate faster (at least until back emf clamps down on available power), and it'll produce far more heat doing it.
I also address the 'same power in' later in my last post... so im doubly puzzled why you bothered posting this...

again here is some misunderstanding. Both systems are exactly identical in components and have exactly the same current settings. only one has upgraded phase wires and the other uses stock. as example mxus 3T. wasn't that evident?
now what happens during acceleration:
at the very beginning the controller operates in phase current limit, right? here is no difference in torque (controller only takes more power from the battery so losses are compensated automatically).
after that controller will change from phase amp limit into battery current limit, right? (thats when we see full power on the display, happens pretty soon) from than on torque and acceleration will be lower because losses are no more compensated.
you understand now!? if you would have done some simulations you would know already or tests in parctice like teslanv who noticed a bit better acceleration after the wire upgrade.

resistance needs to be 4 times lower if you double the amps and want to keep losses similar - thats what we do not have in practice.
so tell me what speaks for high current / low volts if you also could achieve the top speed you looking for with higher volt and lower amps?

 

[John in CR]

Madin88,

There's no 100V sweet spot for controllers. Running fresh off the charger voltages at the components' limits is against standard engineering practice, yet 24s is all too common. That's because people want more speed and power...Yet they still fall short with 24s, and end up with less reliable systems going that route.

Then there's the infatuation with running the largest diameter wheels possible, which is fine at low power and low load where anything works, but it just doesn't work for high performance with a hubmotor. In every other electric motor application proper gearing for a given speed and load is understood as just common sense. With direct drive hubmotors that common sense goes out the window, so they're somehow magical devices not bound by the laws of physics. That's where "the myth" comes in and gains such a strong foothold, since it seems logical almost everyone easily falls prey. Unfortunately there are people on the forum still pushing it, but they use different language than the old "high torque wind vs speed wind". Instead it's become "slow wind motors are better on hills", which is complete BS.

It's you and Teslanv who need to get your heads out of the box, and learn how to use simulations to compare systems, especially if you want to talk about the system as a whole with performance and/or efficiency as a goal. eg Take your precious slow wind 6t vs the fast wind 3t to highlight the real differences. Run the 6t at your "sweet spot" unstable 100V and the 3t at a perfectly safe 75V. Use a 40A for the 6t and 60A for the 3t, and put the 6t in a 26" wheel with the 3t in a 20" wheel. What you'll find is that at every speed the rig with the 3t has greater efficiency, especially under the higher load of hills. It also has a higher top speed with greater acceleration at every point getting there. Then if you throttle back to cruise at the same speed as the slow wind the efficiency advantage really stands out, especially at higher loads.

You might at well stop bringing up HubMonster, because that's a completely different class of motor that gives me a 100mph bike no one has matched with a hubmotor, and at 20s I was able to run it at 16kw peak with a near 70mph top speed in bone stock form even pushing my 100lb heavier load compared to more typical ebikers. We can discuss why those 20s results are possible if you like, but it's not because it's a heavier more powerful motor. It's due to the efficiency advantage, which isn't size dependent. HubMonster's size is what permits me to go to 25-30kw with easy cooling mods.

There's no need to bring up HubMonster anyway. Since 2009 I've always had 60mph ebikes with my outside the box approach using 20s and a 40mm wide stator motor from the factory that originated the 51 tooth 46 magnet design so widely copied now. Despite my much heavier total load and 11% lesser motor, my old cargo bike, built for well under $1000 in the days when batteries cost and weighed double, still outperforms what you guys are building with the MXUS 3000. That's because I have a speed wind motor running in a small wheel. I was forced to learn this lesson due to heavier loads and mountainous terrain, while you lighter guys are able to get away with running at the margins with less optimal setups that have lower efficiency (more heat problems) and don't take full advantage of the motor's capability.

You seem to accept that different windings of the same motor make them no different if voltage and current are variable, and we agree that voltage is limited at the top end. The part you're missing is that DD hubmotors are all too steeply geared in normal bicycle size wheels. Sure the difference is small enough to ignore with flat land riding up to moderate speeds, but on hills or with the wind load of higher speeds a smaller wheel is significantly better in terms of gearing. When you add in the upper voltage limitation before prices go way up and controller selection evaporates, it makes the fast wind motor in a small wheel the clear winner.

 

[flathill]

I don't agree a smaller wheel is always better. For a vehicle with a given direct drive hub motor, you do in a way select your gearing by selecting your wheel size. For maximum torque, select the smallest possible wheel that will fit the hub motor. For maximum efficiency you select the wheel size such that the motor is operating at max efficiency at cruise speed. Cruise speed might be 65-75mph for a car or motorcycle, or 20-30 mph for a common ebike, or 35-50mph for a high performance ebike. A 40mm 273 motor will have more than enough torque to wheelie even with a 700c rim, but yeah if you are hill climbing or hauling heavy loads, most of the time, you want a smaller rim.

 

[madin88]

John it really makes no sense to talk with you since you do not understand what i'm trying to point out.
I have never said that one should use 100V battery together with 100V controller. please correct me it should be "up to 100V sweet spot"
Most of them what you said at last you already have repeated three or more times.. Everyone now knows that hubmotors perform best with smaller wheels. Did anybody miss that part? NO!
What you do not see is if someone builds powerful e-BICYCLES (no scooters or motorcycles) for customers to theire specifications (top speed and power) it doesn't require to use the fastest wound motor and if we would make use of it there would be higher controller costs and more system losses.
Thats what i was trying to bring up and i believe also teslanv.

how hard is it to understand?

you are always talking about your great stuff and that you have the best motors.
well, where is that more realiable controllers for half the price, why not tell us more?
or where is that 40mm high kV motor that eats all of the MXUS 3k builds here? i doubt it will eat ALL :wink:

honestly, if i look at your bike with hubmonster motor i must :lol:
yes it will perform great on that straight highway in front of your house, but you can be happy that you never have hit a pothole with it or never had to deal with the unsprung motor mass in other situations.
If you would have, you would think more about wheel size and making COMPROMISES. A heavy motor in a small wheel together with a lightweight bike + rider is the worst thing for traction and handling, but as you are a heavy guy it will turn things better because sprung to unsprung mass ratio is higher^^

 

[miuan]

John is sure good at proving that 20" wheel is more efficient than a bigger wheel under pretty much any riding condition. This is obvious.
However, saying that this is "taking full advantage of the motor's capability" is just like assuming I did my best at the exam because I had been preparing for 7 days.
It may have been the longest preparation for an exam I'd ever done, but it wouldn't make me any better prepared than someone else after 14 days, or 20 days of study, does it. One could argue that using a tiny cast 16" rim assembly bolted to the motor would be even better for climbing steep hills than lacing it to a spoked 20" rim.
So where does this end? Just like there may be even more efficient mosfets for 150V or 200V systems (if not in TO220 package), there may be better ways of having the motor spin at even higher RPM, like putting the motor in the frame and using a 2.5:1 chain transmission or employing a smaller front drive motor.

 

[miuan]

.

 

[John in CR]

For maximum efficiency you select the wheel size such that the motor is operating at max efficiency at cruise speed.

This would only be true if your riding is all long constant speed cruising, and even then it's questionable that peak efficiency ever is reached. You need to look at overall efficiency and at common ebike speeds the rpms are so low that the iron core losses are in the tens of watts, and copper losses are greater. That means reducing copper losses puts you ahead, and that's exactly what running a smaller wheel does.

Look at Miles spreadsheet, and look a columns AD thru AJ with the 4 hubbies that Justin provided full details. You can even vary AD and AE to see results at different speeds and power. Then you'll come to the realization that what I'm saying is 100% true.

 

[John in CR]

Actually the advantage disappears for the common high pole and slot count hubbies around the 1000rpm range. Like Flathill learn to make use of Miles' Motor Comparison Spreadsheet, and keep in mind that the rpm based iron losses occur whether you're on the throttle or not. That means just like the simulations lead people astray about large wheels, you don't want to go too far with smaller wheels and shoot for peak efficiency at cruise with stop-n-go riding. BTW peak efficiency at a given rpm is when copper losses and iron losses are equal.

I didn't say running any size wheel was taking advantage of the motor's capability, just that running the big wheels leaves a lot on the table. It's not only that though, because big wheels also make motors more prone to heat problems.

Your examples of test prep might as well be greek to me. I never studied more than the night before and day of an exam, if at all, and always outperformed those who prepared for a week or more. 8)

John is sure good at proving that 20" wheel is more efficient than a bigger wheel under pretty much any riding condition. This is obvious.
However, saying the this is "taking full advantage of the motor's capability" is just like assuming I did my best at the exam because I had been preparing for 7 days.
It may have been the longest preparation for an exam I'd ever done, but it wouldn't make me any better prepared than someone else after 14 days, or 20 days of study, does it. One could argue that using a tiny cast 16" rim assembly bolted to the motor would be even better for climbing steep hills than lacing it to a spoked 20" rim.
So where does this end? Just like there may be even more efficient mosfets for 150V or 200V systems, there may be better ways of having the motor spin at even higher RPM, like putting the motor in the frame and using a 2.5:1 chain transmission or employing a smaller front drive motor.

 

[John in CR]

John it really makes no sense to talk with you since you do not understand what i'm trying to point out.

There's not be a single thing you've posted that I haven't understood. Since you don't know how to tune your suspension, I'd suggest getting with MadRhino, who on one of his bikes runs an Xlyte 54xx which weighs about the same as HubMonster. For offroad, MX motos run a smaller wheel on the rear for better traction, so you've got some learning to do there too. Regarding potholes, sure I've hit a few, but frankly I ride with focus and avoid them, so maybe you should pay closer attention while riding.

Back and forth with you is exhausting. There's nothing I can learn from you, and you think a bit too highly of yourself to learn anything new, so I won't waste any more time.

 

[markz]

I have never hit a pothole in my life! EVER!
And I ride a lot!

 

[Rix]

I have never hit a pothole in my life! EVER!
And I ride a lot!

You smell that stink? That's you Markz because you are the $h!t :lol: Same here with the caveat that I did hit pothole, but it was dark and I didn't have a light. Issue has since been corrected.