Left side drive: what's current?

[BalorNG]

Hi TorontoBuilder

The rear 55 tooth cog has the same 190 mm diameter as the cheap system from aliexpress while the drive cog is ~80 mm versus the 39 mm of the aliexpress system. The gates drive belts are far superior and cogs are available up to 243.2 mm in diameter.

Pair that drive system with an alien power 30KV 2800 watt APS 6374S motor and you've got a sound ratio to deliver a lot of torque and do about 50 mph using 29" wheel. If you want more power then there is the 50KV 4000 watt APS 6384.

The belt drive you are describing has a gearing ratio of about 1:2.4...
I think that at this low reduction, the 6374s will not be spinning nearly fast enough to produce the 2.8 kW it's supposed to. (You have to spin a motor it in its optimum RPM range to get the nominal power, regardless of kV.) I am aiming for gear ratio in the vicinity of 1:8 for a 20 inch driven wheel (or ~1:10 for a 26 inch wheel, but this is utopia). 1:2.4 is far far too low to get decent power from small motors.

But yeah, your tooth profile point is valid though, no objection there. It will be a much better overall belt drive than the aliexpress one, especially for regen braking. But then I'd need another reduction stage.

....

Still hoping somebody will prove I'm a total idiot who can't google by posting a link to a 219 sprocket for axle mounting on a 12mm or 14mm axle .

Br,

Just draw it in CAD and have it laser cut, are you an engineer or... what, nevermind

 

[TorontoBuilder]

Hi TorontoBuilder

The rear 55 tooth cog has the same 190 mm diameter as the cheap system from aliexpress while the drive cog is ~80 mm versus the 39 mm of the aliexpress system. The gates drive belts are far superior and cogs are available up to 243.2 mm in diameter.

Pair that drive system with an alien power 30KV 2800 watt APS 6374S motor and you've got a sound ratio to deliver a lot of torque and do about 50 mph using 29" wheel. If you want more power then there is the 50KV 4000 watt APS 6384.

The belt drive you are describing has a gearing ratio of about 1:2.4...
I think that at this low reduction, the 6374s will not be spinning nearly fast enough to produce the 2.8 kW it's supposed to. (You have to spin a motor it in its optimum RPM range to get the nominal power, regardless of kV.) I am aiming for gear ratio in the vicinity of 1:8 for a 20 inch driven wheel (or ~1:10 for a 26 inch wheel, but this is utopia). 1:2.4 is far far too low to get decent power from small motors.

I can't concur with your thinking because I've actually done calculations rather than made an assumption. I am also sure that you're thinking of the typical performance of RC motors with high velocity constants used in quad copters and planes. Not all motors are alike, hence my specifically saying a 30KV motor.

The maximum rpm of the motor I mentioned is only ~1200, unlike the typical RC motors of this range that have maximum rpm ratings between 7,000 to 12,000 rpm.

The 30 KV APS 6374S is designed to operate at a much lower rpm so that the corresponding power, torque and efficiency curves will also be lower and suit my usage very well. I know this with confidence from the manufacturer's specifications even without looking at performance curves. I know this for another reason as well.

There is a calculation to assure that ideal operating rpm of the bike drive system will fall within the peak power range of a motor.

Tom Stanton defines the output of his version of this type of calculation the 'golden ratio" and quantifies it as a numeric value of approximately 10. Nice, round and convenient eh.

Check out his video response to everyone asking how to select the correct RC motor for use on an e-bike. His comment starts at the 11:47 mark of the following video:

[youtube]https://youtu.be/1pm1RtCuE3A?t=707[/youtube]

The gist of Tom's calculation is to multiply motor KV by the drive system ratio.

Regardless of how the power is transferred to the wheel, direct drive, friction drive roller, pulleys, or sprockets you calculate the ratio, and then multiply that by the motor velocity constant KV.

My result is well within the parameters: 30 KV x (22 tooth / 55 tooth) = 12 or;

30 x (75.3 OD / 109.7 OD) = 11.84



The calculation is at the 12:49 mark of the video.


Hub motor typical KV is 8.7:

8.7KV x 1 (direct drive) = 8.7

IF I was designing a friction drive using the exterior can of a 63 series motor as the drive roller I'd choose a 130 KV motor:

130 x (197.92 mm drive wheel circumference / 2268 mm driven wheel circumference) = 11.3 or;

130 x (63 mm diameter drive roller / 736 mm wheel diameter) 11.12

This is a whole numbers game... 9, 10, 11, 12 all acceptable outcomes. The higher the value the lower the low end torque.

However, with decent motor controller and a high peak current a motor can achieve higher torque/power output at lower rpm. My selection will have ample low speed power and torque.

 

[TorontoBuilder]

Just draw it in CAD and have it laser cut, are you an engineer or... what, nevermind

I'd ask what is wrong with the dozens of 415 chains, sprockets and adapters on the market...

If I could figure out how to attach a file I'd be kind enough to upload a dxf file for an adapter to allow six hole mounting 219 sprockets to be mounted on a 6 hole disc brake hub.

View attachment 6 hole disc brake to 219 chain sprocket.dxf

 

[BalorNG]

Hi TorontoBuilder

The rear 55 tooth cog has the same 190 mm diameter as the cheap system from aliexpress while the drive cog is ~80 mm versus the 39 mm of the aliexpress system. The gates drive belts are far superior and cogs are available up to 243.2 mm in diameter.

Pair that drive system with an alien power 30KV 2800 watt APS 6374S motor and you've got a sound ratio to deliver a lot of torque and do about 50 mph using 29" wheel. If you want more power then there is the 50KV 4000 watt APS 6384.

The belt drive you are describing has a gearing ratio of about 1:2.4...
I think that at this low reduction, the 6374s will not be spinning nearly fast enough to produce the 2.8 kW it's supposed to. (You have to spin a motor it in its optimum RPM range to get the nominal power, regardless of kV.) I am aiming for gear ratio in the vicinity of 1:8 for a 20 inch driven wheel (or ~1:10 for a 26 inch wheel, but this is utopia). 1:2.4 is far far too low to get decent power from small motors.

I can't concur with your thinking because I've actually done calculations rather than made an assumption. I am also sure that you're thinking of the typical performance of RC motors with high velocity constants used in quad copters and planes. Not all motors are alike, hence my specifically saying a 30KV motor.

The maximum rpm of the motor I mentioned is only ~1200, unlike the typical RC motors of this range that have maximum rpm ratings between 7,000 to 12,000 rpm.

The 30 KV APS 6374S is designed to operate at a much lower rpm so that the corresponding power, torque and efficiency curves will also be lower and suit my usage very well. I know this with confidence from the manufacturer's specifications even without looking at performance curves. I know this for another reason as well.

There is a calculation to assure that ideal operating rpm of the bike drive system will fall within the peak power range of a motor.

Tom Stanton defines the output of his version of this type of calculation the 'golden ratio" and quantifies it as a numeric value of approximately 10. Nice, round and convenient eh.

Check out his video response to everyone asking how to select the correct RC motor for use on an e-bike. His comment starts at the 11:47 mark of the following video:

[youtube]https://youtu.be/1pm1RtCuE3A?t=707[/youtube]

The gist of Tom's calculation is to multiply motor KV by the drive system ratio.

Regardless of how the power is transferred to the wheel, direct drive, friction drive roller, pulleys, or sprockets you calculate the ratio, and then multiply that by the motor velocity constant KV.

My result is well within the parameters: 30 KV x (22 tooth / 55 tooth) = 12 or;

30 x (75.3 OD / 109.7 OD) = 11.84



The calculation is at the 12:49 mark of the video.


Hub motor typical KV is 8.7:

8.7KV x 1 (direct drive) = 8.7

IF I was designing a friction drive using the exterior can of a 63 series motor as the drive roller I'd choose a 130 KV motor:

130 x (197.92 mm drive wheel circumference / 2268 mm driven wheel circumference) = 11.3 or;

130 x (63 mm diameter drive roller / 736 mm wheel diameter) 11.12

This is a whole numbers game... 9, 10, 11, 12 all acceptable outcomes. The higher the value the lower the low end torque.

However, with decent motor controller and a high peak current a motor can achieve higher torque/power output at lower rpm. My selection will have ample low speed power and torque.

It is not the first time I see APS motors having *much* lower KV (though, much higher no-load current too, no free lunch) ratings but 'typical' motor resistance (phase to phase) values. Did you look inside? Are they using double the number of magnet poles or just much stronger magnets?

 

[TorontoBuilder]

It is not the first time I see APS motors having *much* lower KV (though, much higher no-load current too, no free lunch) ratings but 'typical' motor resistance (phase to phase) values. Did you look inside? Are they using double the number of magnet poles or just much stronger magnets?

Your comments while welcome are immaterial to the points being made. Those points are that the motor mentioned is well suited to the application that it was specified for, and the methodology used to specify the motor assures that the drive system will operate at or near the nominal operating point and will operate well within the continuous operating region except during times of hard acceleration as with most any bldc ebike motor

The methodology does not care how the manufacturer has designed or built the motor beyond the max voltage, amperage and the velocity constant of the motor. The methodology has been validated repeatedly in real world builds.

But in regards to your question, no I have yet to receive the motor so haven't peered into its guts yet. When I can I might include such observations in my own thread build as an aside. In my case the 30 KV motor is merely a temporary motor* while I build my own. But I will likely not because if it works everything else is immaterial really. If it is not as efficient as it could be I'm not overly concerned.

I mean sure, I could (and assuredly should) shit on a 1986 Lamborghini Countach as a vile anti-social piece of engineering targeting aholes with limited endowments, but no one can argue the point that its engine will get a person from point A to B.

Just in case it is not coming across, the above is all meant tongue in cheek.

Edit:

Maybe I should have shit on the 1973 Lincoln Continental instead? It had the same staggering 7 mpg combined fuel economy rating (inconceivable during the 1973 OPEC oil embargo) AND it had the looks of a rolling hemorrhoid to me.

*Thanks APL for making me decide to spend over $200 bucks on a non-necessity. I intend to blame you when my wife finds out.

 

[BalorNG]

It is not the first time I see APS motors having *much* lower KV (though, much higher no-load current too, no free lunch) ratings but 'typical' motor resistance (phase to phase) values. Did you look inside? Are they using double the number of magnet poles or just much stronger magnets?

Your comments while welcome are immaterial to the points being made.

Erm, not sure what I've said to deserve such a reply. That is really just me being interested. I can use a light motor in e-board form-factor with massive torque capacity for the weight!

 

[TorontoBuilder]

There was no disrespect or rudeness implied, I merely meant that your comments had no bearing on whether the motor would operate as intended.

The beauty of this methodology is that without spending a dime to buy and try motors, you can use an iterative process and a spreadsheet as I have to plug in many drive system variables in order to evaluate the components.

The one item I put far less weighting on in my criteria was motor mass, since most of these RC inrunner and outrunner motors will all be similar in mass for a given can length and diameter from my experience.

Case in point, APS has a 400KV and a 30KV 6374 outrunner motors both of which have the same 850 gram mass. So how the motors are different is not readily apparent to me. But as I said, I can still use the methodology to know that the 400KV one will be crap in my application.

Oh and the KV30 motor just as light and has massive torque (over twice the torque) in comparison to the typical 130 KV skateboard motors. You just wont like the lower top speed using it on a board

 

[BalorNG]

There was no disrespect or rudeness implied, I merely meant that your comments had no bearing on whether the motor would operate as intended.

The beauty of this methodology is that without spending a dime to buy and try motors, you can use an iterative process and a spreadsheet as I have to plug in many drive system variables in order to evaluate the components.

The one item I put far less weighting on in my criteria was motor mass, since most of these RC inrunner and outrunner motors will all be similar in mass for a given can length and diameter from my experience.

Case in point, APS has a 400KV and a 30KV 6374 outrunner motors both of which have the same 850 gram mass. So how the motors are different is not readily apparent to me. But as I said, I can still use the methodology to know that the 400KV one will be crap in my application.

Oh and the KV30 motor just as light and has massive torque (over twice the torque) in comparison to the typical 130 KV skateboard motors. You just wont like the lower top speed using it on a board

Well, yea, good point. I'm just curious - one may never know how a piece information you gleaned somewhere may come crucial in an other, possibly unrelated, project.

 

[sleepy_tired]

After looking at RC motors with especially low KV ratings I always wondered what the penalty for this is. Everything has a trade off. Doing the math on the Kv and deriving the rpm/A says that this setup should work.

But I don't know if the motor can handle the power required for minutes at a time when it's rated power level is probably assuming that 'continuous' is less then 180 seconds while behind a propeller wash.

 

[TorontoBuilder]

After looking at RC motors with especially low KV ratings I always wondered what the penalty for this is. Everything has a trade off. Doing the math on the Kv and deriving the rpm/A says that this setup should work.

But I don't know if the motor can handle the power required for minutes at a time when it's rated power level is probably assuming that 'continuous' is less then 180 seconds while behind a propeller wash.

These are eskate motors. "Continuous" in the industry means continuous duty otherwise it is consumer fraud.

The trade off is ~17% lower maximum power output for sub 100 KV motors in comparison to their higher KV motors in the same form factor.

 

[LewTwo]

If I might be allowed to interject another question into this ....

I have always (perhaps incorrectly) that these small high RPM motors would produce an unpleasant and annoying sound similar to a run-away sewing machine. For the most part, DD hub are nearly silent and small geared mid drives and hubs are usually not very loud .... or even close to silent if they incorporate helical cut reduction gears.

 

[sleepy_tired]

These are eskate motors. "Continuous" in the industry means continuous duty otherwise it is consumer fraud.

That never actually stopped anybody, though. I have zero faith that the hobby RC/eskate/drone numbers they site, continuous/max/otherwise, is anywhere close to reality. I'd like to see somebody try to sue Turnigy because their 170 dollar motor burned out on a ebike after 20 minutes. Impossible to enforce laws are the same as not having those laws at all.

I really need to get my hands one, I guess, and figure out what their specs really are. That way I don't have to speculate.

The trade off is ~17% lower maximum power output for sub 100 KV motors in comparison to their higher KV motors in the same form factor.

Very good. Thank you.

 

[sleepy_tired]

If I might be allowed to interject another question into this ....

I have always (perhaps incorrectly) that these small high RPM motors would produce an unpleasant and annoying sound similar to a run-away sewing machine.

It expect really depends on the motor and the controller you are using with these things. Like how many pole pairs, what the erpm limit, the ability of the controller to keep a nice sinewave shape and such things.

We are talking about motors with Kv less then 100, which means that they are only spinning 5200 rpm or less, generally.

If you want a comparison check out the videos and reviews X1 Stealth mid-drives from Cycmotors. They are using essentially the same type of motors. Small SPM outrunners with Kv of 150 with a ASI FOC controller.

https://www.youtube.com/watch?v=KpiVs5vENU8

Some of that is going to be the motor. Some of that is going to be the gearing. It has to have more layers of gear reduction (planetary gear set + 2 sets of chains to get to the rear wheel) because they need to reduce the speed to a reasonable cadence for a rider and then from the crank to the rear wheel.

It doesn't seem any worse then any other mid-drive.

A left-hand drive with a sub-100kv motor should be quieter because it's slower and only has one layer of speed reduction. If you keep the motor sprocket 11 tooth or higher you can get a 100 tooth 219 sprocket pretty easily for the rear wheel then that will help a lot with the noise. (I hope) Once you get smaller then 11 it makes chains a lot noisier. At least that is my limited understanding.

They even make polymer rear 219 sprocket that would eliminate some more of the noise. It should hold up OK, I think if you want to stick to 1500 watt or lesser power levels. Not that I ever tested it.

 

[TorontoBuilder]

If I might be allowed to interject another question into this ....

I have always (perhaps incorrectly) that these small high RPM motors would produce an unpleasant and annoying sound similar to a run-away sewing machine. For the most part, DD hub are nearly silent and small geared mid drives and hubs are usually not very loud .... or even close to silent if they incorporate helical cut reduction gears.

certainly.

the noise is more a product of how the controller. Kepler did a few videos of his friction drive in foc mode illustrating this

[youtube]https://youtu.be/6F8xD2zRV_0[/youtube]

 

[BalorNG]

After looking at RC motors with especially low KV ratings I always wondered what the penalty for this is. Everything has a trade off. Doing the math on the Kv and deriving the rpm/A says that this setup should work.

But I don't know if the motor can handle the power required for minutes at a time when it's rated power level is probably assuming that 'continuous' is less then 180 seconds while behind a propeller wash.

Of course, their max power is defined at max RPM - that is usually at 50v. This is, indeed, countinous power - especially when riding at high speed and having the motor bolted to a mount that has considerable heatsinking potential.
Do not expect 2kw rated motot to output more than 200w continously at 10% duty cycle, and with low efficiency to boot.. but that it applied to bike motors as well, they just have more thermal mass and can take more abuse.

By using forced air cooling solution (running air from a fan though the windings) howefver, yon can run them at 1.5 stated amps indefinetely and at low RPMs too - still, there is a limit of course.

 

[BalorNG]

A left-hand drive with a sub-100kv motor should be quieter because it's slower and only has one layer of speed reduction. If you keep the motor sprocket 11 tooth or higher you can get a 100 tooth 219 sprocket pretty easily for the rear wheel then that will help a lot with the noise. (I hope) Once you get smaller then 11 it makes chains a lot noisier. At least that is my limited understanding.

They even make polymer rear 219 sprocket that would eliminate some more of the noise. It should hold up OK, I think if you want to stick to 1500 watt or lesser power levels. Not that I ever tested it.

With a single step reduction belt drive and at lower KV motors (I'm using lower volts and higher KV motors myself due to 24v battery, but same principle) the drive is pretty much silent both at lower end of speeds and at higher speeds it is drowned by wind noise anyway.

I've tried using dual step reduction for more torque using 250kv motor and two chains (6.25 and 219) and it frankly sounded like chainsaw, highly annoing... it did feature 10T cog.

Currently I think that by using oversized and 'overmolded' in TPU cogs you can have higher efficiency than a belt, but also silent like a belt, my preliminary tests are promising.

 

[LewTwo]

... the drive is pretty much silent both at lower end of speeds and at higher speeds it is drowned by wind noise anyway.

Define higher speeds. At 20-25 MPH i have very little perceptible wind noise (and I have big ears ... think Prince Charles).

 

[BalorNG]

... the drive is pretty much silent both at lower end of speeds and at higher speeds it is drowned by wind noise anyway.

Define higher speeds. At 20-25 MPH i have very little perceptible wind noise (and I have big ears ... think Prince Charles).

Yes, above 25mph. And yes, the motor 'whine' is barely perceptible over it

 

[badgineer]

I can't concur with your thinking because I've actually done calculations rather than made an assumption.

I made the same calculations as you, based on the same assumption as you. Only to realize while the calculations were correct, the assumption was wrong...

The 30 KV APS 6374S is designed to operate at a much lower rpm so that the corresponding power, torque and efficiency curves will also be lower

--> this assumption. It is an assumption, and it's wrong.

Typically the low kV motor is the exact same motor as the 200+ kV version, just with more turns of thinner wire.

This is seriously off topic already (and the wrong forum section!), but I'll give you a short explanation of why having the same power at much lower RPM does not work on the more or less same motor with a lower kV winding:

Mechanical Power = Torque x RPM x k (k -> constant you can't do anything about if you can't alter physics)

If you want the same power at a RPM 5x smaller, you have to increase Torque 5x. So you have to increase current 5x, which is already a problem. Couple that with the fact that to achieve the much smaller kV you have much higher phase to phase resistance (many more turns, much thinner wire) that 5x bigger current will fry the little motor in a matter of seconds.

Also, that torque is probably close to impossible for the little motor to do because:
1) it's small and can't mechanically deal with it without extreme wear and early failure.
2) the stator is tiny and the current needed for that torque take it *super far* into saturation.

these are the reason why a "5kW rated motor" weighs ~2kg if it's 200kV, and ~10kg if it's 10kV.

After looking at RC motors with especially low KV ratings I always wondered what the penalty for this is.

The trade off is that you either have to raise the voltage to spin it up to the same speed as the motors faster "brothers" to get the same power, or just be content much lower power than the "rated one". Or get a bigger motor.

Everything has a trade off.

Amen to that!

Make a separate thread for small rc motors with high kv, (in the right forum section) and we can go further into details. I'm quite interested in this topic also.

Let's leave this thread to mechanical drivetrain stuff. Just sayin'

Br,

 

[badgineer]

Back on topic to drive train stuff.

I'd ask what is wrong with the dozens of 415 chains, sprockets and adapters on the market...

Well to get high reduction (~8) in 1 stage, the driven sprocket would need to be HUGE. Just this. That's why I'm looking at chains with smaller "step".

Just draw it in CAD and have it laser cut, are you an engineer or... what, nevermind

What are you implying? That I am a bad engineer? What gave it away? :lol:
To answer the question though: I'd really rather leave it to the pros. That small sprocket will see quite some action. Also, a lot of wear, so cheap replacement would be cool, and custom machining ain't cheap...
As for big sprockets, there are a few off the shelf. An adapter for them, that much I will probably manage, but a custom sprocket I would like to avoid if possible.

 

[BalorNG]

Typically the low kV motor is the exact same motor as the 200+ kV version, just with more turns of thinner wire.

I think this is not actually true in that case.
If you look at their no-load current (huge!) and (low) phase resistance, it seems what they did is installed either much more powerful, or just doubled the number of magnets compared to typical eskate motors (that's why I'm really interested how it looks inside).

This will neatly explain low Kv, moderately low resistance yet huge no-load current.

 

[BalorNG]

Back on topic to drive train stuff.

As for big sprockets, there are a few off the shelf. An adapter for them, that much I will probably manage, but a custom sprocket I would like to avoid if possible.

There are freecad scripts to make any sprocket, in any size, any shape you want (well, except asymmetric). Get DXF and send to laser cutters, problem solved (ok, you'll have to file the ends, but that is not that hard with an angle grinder).

 

[badgineer]

There are freecad scripts to make any sprocket, in any size, any shape you want (well, except asymmetric). Get DXF and send to laser cutters, problem solved (ok, you'll have to file the ends, but that is not that hard with an angle grinder).

Only ever used Tinkercad for 3d printed parts, but this is not the problem, I think I would be able to do this relatively easily.
My bigger concerns are:
1) hard to find laser cutters where I live - last time I searched.
2) the part with the teeth, lets say it's OK, but then how to I attach it to the shaft? That sprocket to shaft interfacealso needs to be able to handle the whole torque....

I think this is not actually true in that case.
If you look at their no-load current (huge!) and (low) phase resistance, it seems what they did is installed either much more powerful, or just doubled the number of magnets compared to typical eskate motors (that's why I'm really interested how it looks inside).

This will neatly explain low Kv, moderately low resistance yet huge no-load current.

Interesting. Maybe it really is different.
I read quite a few 80100 motor threads, and asked some manufacturers (about 80100 and 12070 motors), and I found no differences between the 50kV and the 180kV motors other than the windings...

But even if it has a more adequate motor design for low kV, that still only addresses some of the problems.
A small motor will still have a higher phase to phase resistance than an same kV big motor because less wire fits in it. And it will have small stator teeth that get easily saturated. And will be generally less rugged and wear faster at high torque / power. And will have smaller mass that will get hot faster from the same conduction losses...

Anyway, hope TorontoBuilder will have one soon so we can find out how the insides look like and how it performs. I'm genuinely curious.

BR

 

[BalorNG]

There are freecad scripts to make any sprocket, in any size, any shape you want (well, except asymmetric). Get DXF and send to laser cutters, problem solved (ok, you'll have to file the ends, but that is not that hard with an angle grinder).

Only ever used Tinkercad for 3d printed parts, but this is not the problem, I think I would be able to do this relatively easily.
My bigger concerns are:
1) hard to find laser cutters where I live - last time I searched.
2) the part with the teeth, lets say it's OK, but then how to I attach it to the shaft? That sprocket to shaft interfacealso needs to be able to handle the whole torque....

Tinkercad is child's toy. Fusion360 is free (well, for now at least...) and 1000x times more powerful and actually really easy to use.

I've actually meant this (sorry, not freecad, OpenSCAD):

https://www.thingiverse.com/thing:4170542/files

Download and see for yourself. There are lasercutters in our town (and the charge affordable rates), but if you do not have any in your neck of the woods there bound to be some around that work by mail.

Regarding bolting the sprocket - personally, I do that to 6 bolt interface replacing the brake. Rear brake is a 'drag brake' anyway, and regen perfectly performs that function.

 

[TorontoBuilder]

I can't concur with your thinking because I've actually done calculations rather than made an assumption.

I made the same calculations as you, based on the same assumption as you. Only to realize while the calculations were correct, the assumption was wrong...

The 30 KV APS 6374S is designed to operate at a much lower rpm so that the corresponding power, torque and efficiency curves will also be lower

--> this assumption. It is an assumption, and it's wrong.

Typically the low kV motor is the exact same motor as the 200+ kV version, just with more turns of thinner wire.

This is seriously off topic already (and the wrong forum section!), but...

After looking at RC motors with especially low KV ratings I always wondered what the penalty for this is.

The trade off is that you either have to raise the voltage to spin it up to the same speed as the motors faster "brothers" to get the same power, or just be content much lower power than the "rated one". Or get a bigger motor.


Make a separate thread for small rc motors with high kv, (in the right forum section) and we can go further into details. I'm quite interested in this topic also.

You never showed your work, so I doubt you did any calculations.

I already explained the trade off more precisely with the motor in question, and I dont keep tossing out different motor stats.

I'm very sorry that missed the concept I was trying to explain, tThe 30 KV APS 6374S is designed to operate at a much lower rpm so that the corresponding power, torque and efficiency curves will also be lower. Just like the higher KV motor, peak power comes at the half the no load speed. So in my application the peak power is attained at half the much lower no load speed, and the same for torque.

Again, sorry that you cannot grasp that this motor was selected based on it having the desired attributes and there is no need to select any other.

Feel free to start another thread. I'm blocking you because you're being deliberately obtuse without offering any merit or value. Bye now