I feel like this has been disproven in the past, but people still continue to claim a lower kv motor have more torque and a higher kv motor having less torque. Is this really the case or does motor torque come down to the mass of copper windings and stator size?
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I am currently using a tacon bigfoot 295kv, and I can climb hills larger than I ever imagined. I wrote about it here
So in my opinion, no lower kv does NOT mean more torque, it is in the gearing. On the other hand hub motors may be different, I have no expirence with them.
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In a motor more than anything to create torque, in a small package especially, you need iron. nothing is as important for torque as iron. The iron greatly enhances the windings magnetic field and u get a greater magnetic strength. At some point trying to get more and more magnetic strength from the electromagnet, pumping in more amps, the iron enhancer becomes magnetically saturated and the more amps u give it isn’t increasing the strength of the iron’s magnetic field. More iron, or more importantly more iron on the end of the stator tooth, where its used, and eventually gets saturated given too many amps. Adding gearing is a huge way to get torque. Kv doesn’t matter as even with a really high kv u can give it more amps and run a low voltage system and get exactly the same power output and the same torque output. Gets just as hot as the low kv in the motor. And the same size battery and watt hours. Why no one runs on 4s or even 2s…I don’t know. If the controller can do it that’s the only limitation. The motor sees either the high voltage or low voltsge systems the same and the volts are converted to amps as far as the motor sees it. Just as much torque or watts output before overheat in the motor with either system
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That seems like the most unscientific explanation. Gearing obviously changes the characteristics. You can get any torque or speed output you wamt by adjusting the gearing accordingly. To answer that question fairly no gearing has to be used and then the output can be compared.
Don’t forget the vesc limitations on 12s. We should only use about <220KV at 12S unless we limit the vesc rpm
Your right, the gearing does change it. But everyone uses gearing…
I also didn’t know this was a science competition. I was just giving my input
Well this is ultimately physics that we are talking about - and misleading headlines like “torque misconception” should not be used for this type of thing. If you want to do it right you need to get rid of gearing, test the motors and only then tell the differences between high and low kv motors.
As @Hummie said as long as the copper mass, iron and magnets are all the same the output of the motor is the same. Kv is about at what voltage is the motor efficient before drawing To many amps.
Some one correct me if I’m off base!
You need to calculate what speed you want to be riding at 80% of the time and then try and get the motor spinning at about 5-8000rpm at this speed with the highest voltage you can.
Sadly this doesn’t work so well for hub motors as you can’t gear so you have to reduce your kv.
Boosted use a 1:3.12 gear ratio with a 190kv motor and 43.2v battery. So in turn they have a low top speed but at 20-30km/h they have a really low amp draw and good efficiency, if they used a higher kv motor that efficiency would be at a lower speed and at they would want to use a gear ratio of 1:26 to get the efficiency back up to that speed sweet spot but would loose some low end torque (which they need with such small motors)
Raptor has a bigger motors so can use a 1:26 gear ratio with similar voltage same kv and bigger wheels. So it’s efficiency is between 30km/h to 45km/h at its top speed. So for a rider like me who doesn’t go faster then 30km/h then the setup is not going to be good for me.
My opinion is we need split gears.
Read more: http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/
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The sweet spot is between 190kv and 300kv Outside of that, your speed will suffer. Too fast or too slow.
No groundbreaking tech speak here…just tried and true results.
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A lower kv motor does have more torque… per amp!. This is the thing people always leave off or forget or don’t understand. The lower kv motor will make more torque at a given current than a higher kv motor all else being equal (i.e. You are comparing motors that are identical aside from how they are wound).
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People would use 2s or 4s if they could. But you do know! Yes, the limitation is the controller. No controller can currently drive the kind of current that would be required to run 2s or 4s.
Here’s my understanding: a 3,000W motor will get me to 30mph without overheating. 3,000W is 4 horsepower, and the scooters here in LV are limited to 2HP (supposedly) and can do 35 with 1/2 mile of runway.
That’s 4 “MECHANICAL HORSEPOWER”, so as long as my gearing sets my top speed reasonably, a 30% reduction in KV will equate to 30% reduction in top speed, BUT, 30% increase in motor gear teeth will compensate perfectly…
IF the motor has the same WATTAGE. So, 4HP from 245kv is exactly the same as 4HP from 190kv or 149kv… Right?
No, because the efficiency of the motor depends on the RPMs. I changed my 10s, 245kv, 83mm, from 12t to 15t, and although I did get (exactly) 25% increase in speed, my braking torque was almost gone and because of the increase in current required to do 25% more work, my range seemed to decrease also, but I was probably hot-rodding around. I’ve ordered a 190kv so I can compare my braking power with electrical torque (low KV) vs mechanical torque (high KV), keeping in mind that I use a K-force that has a drag brake, meaning my brakes are always using exactly the same current.
I think we need to figure out which type of breaking torque kills motors, and gear accordingly.
3,000w is around 4HP but depending on your motor as some suck, and the drive train you might only get 3HP.
Damn entropy and capitolism, and gravity…
Always gettin me DOWN, man.
^this
thats what i wrote a while on ES when contemplating about 190KV 6355 rspecc to 168KV SK6374 switch:
Im not actually sure what I can expect from a lower KV motor except for a better torque per current ratio. to ride the same speed will cost the same power (naturally, since the same work has to be done). a nice graphic to understand that can also be found here: mabuchi motor tech → same speed = horizontal line = same current for identical motors with different winding numbers.
at the same time, for a constant torque you can see that different winding numbers produce the same torque with different currents (vertical line): more windings = lower KV = more torque per current.
when I ride with a constant 35kph, the only difference I will notice coming from my 192KV r-speccs, is the simple copper increase from 6355 → 6374. the KV change from 192 to 168 wont make a difference, except for my top end power: higher KV = higher power output, since its running at higher speed and power is basically rpm x torque.
so, the only thing Im hoping for with the KV downgrade is less heat in my vesc when I really need just torque and still sufficient speed on the straights, since with 16/36T, the setup can still reach up to 45kph.
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wait wait wait, what about the controller limits 4s from happening? I’ve never heard anything about this before, I’ve been browsing this place for about 2 months now and just thought everybody wanted to go super fast. I have 3x 4s batteries, is it not possible to use just one?
Lower voltage = Higher amps. The more amps you pull through your esc the greater chance it will say uncle.
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oh no! my set-up is gonna be 12s 6.6ah @ 60C constant. Did I just royally screw up with the massive discharge rate from my 3 4s batteries?
The reasons to not use one of those batteries…from the battery perspective it would need to be a really high c rating and be able to discharge what’s asked of it or it will have few life cycles and also suffer voltage sag in use and keep u slow. From the perspective of the motor… As long as the kv is increased by 3x it wouldn’t notice and you’d go just as fast and just as much torque. From the escs perspective…it now has its power coming from the battery with a much thicker mix of amps than would be the case with 12s. It will get hotter. Making 1000 watts from 16volts u need to multiply like 70 amps((too many for the vesc but there are escs that will do that)). Or making 1000 watts from 45 volts and multiplying with that you only need like 25 amps and that’s no problem for the vesc or a lot of controllers.
No. 12s is high voltage. (lower amps)
Think about it. Most 6s ESCs can handle 120a. Some 6-8s esc can handle 180a-200a.
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