STOP Saying Lower Kv Motors Produce More Torque 

I think this video may lead to misunderstandings. Pure theory and practical application rarely lead to the same conclusions. I’ve been working with motors and electronic drives for decades and I’m still trying to get my head around the implications from this video. In industrial motion control, our Kv is volts per 1000rpm, not KV in RPM per volt, and if you convert Kv to volts per rad/s then Kv = Kt which is the torque constant in Nm per amp. That’s equivalent to the Kt = 1/KV relation you give in your video. It’s true that the peak power output in watts from the same frame size motor is the same, regardless of the windings, but changing the windings changes the voltage-current relationship at peak power. In the real world we are faced with practical limits of voltage and current, either ESC current rating or battery voltage. So showing a white board with a sixfold range of Kv and suggesting that all these motors are practically equivalent is rather unhelpful to the practical modeller. In the real world, where resistive losses are present and practical available battery voltages do not range anything like 6:1, the question becomes _for my practical setup, with say a 6S battery at 22V, what is the optimum KV (RPM/V) to choose for my hull type, size and prop?_ And the helpful answer to _that_ question is certainly not “it doesn’t matter, all motors produce the same max torque and speed with unrestricted electrical parameters”. For practical purposes in a real world situation, with _a fixed battery voltage,_ to increase torque at lower RPM you do need a lower KV motor and possibly a higher current ESC. And with _a fixed battery voltage,_ to increase RPM at reduced torque you need a higher KV motor. But in practice it’s far easier to change a prop size/pitch to better match the hull, motor and voltage than to change the motor KV, which is how things work in the real world, once the motor is correctly sized. I need to think more and do some math to check, but I think showing how the torque-speed curve changes with KV, in a real world system with fixed battery voltage, may be illuminating here.

Outstanding work. I had suspected this from experience. fascinating numbers thanks man

Didn't you explain in previous video, lower kv having more torque was a myth , but is alot more efficient, less heat transfer

Another great presentation. Also, I got my t-shirts in the mail! They look great with the new logo~ Thanks!

Thank you for this video! Now everything is clear for me!

Thanks man ! It was a good explanation but I can see that everything is related to the windings and the copper wire ! It’s obvious that if you choose a low kv motor believing that it’s gonna generate more power toque just because it’s a los kv it’s wrong some motors have diferent gauge of wires ! There are a lot of details that we have to put in mind before we purchase any more and doing more research about it ! Thank you for the explanation once again !

Excellent explanation - that really solidified a few things for me. The issue I have is that lower KV is less efficient because the windings are smaller and resistive losses increase. So it seems like if you're chasing high torque at low RPM (and high efficiency) you have to calculate the loss of efficiency from winding resistance compared to loss of efficiency from physically gearing down. This way you can decide on how to balance electrical losses and mechanical losses.

VERY ENLIGHTENING, thanks.

NICE TUTORIAL . THANK YOU BRO❣

As a RC fan: Thank you for this super useful information. I couldent find any exact on internet

Thank you for the video. Yesterday, I bought Surpass' 550 motors 21t, 27t, and 35t and measured the stall torque. The results have similar torque in both cells 2 and 3. Throttle 30%, 60%, and 100% are all the same. It should stop now that high turn motors make more torque. ;)

This video Made brushless motors clear to me. Well explained! My conlusion to this is that a low kv motor is allowed to run at higher voltage compared to higher kv motor of the same size. I think adding the max voltage to the chart will complete your explanation.

Exactly! That's why higher kV motors produce more power!

Cant wait to use this knowledge over in my Facebook groups and show off 😂 I’ll be tagging this vid for reference though

Great video! Debunking time

I have 2 sensored 2s 3660 with 10bl120a esc. One has 6.5t and other 13.5t with same pinion,. what would be the real difference felt when driving for example? And would you say 3s on 13.5t would have nore torgue!

Nice explain

Well explained 😃

Hey! Thanks again for another great video! so I have a few questions that may or may not be directly related to this video. so I’m looking for a wall plug power supply that I can use to continuously power my Traxxas e Revo esc and 2200Kv motor. I’m using a dual motor and escs setup on my custom build Tesla Turbine/Pump. now I was just going to buy some more batteries to be able to run them but I would really like to be able to just supply the power from a wall socket so I don’t have to regularly charge it to run tests with this thing. Would you have a suggestion for a wall socket power supply for me to run both ESCs without needing batteries? On another note am I able to just power these esc’s with any old 12v battery supply? Like could I actually take a car battery and run the ESCs or would that damage them horribly? Sorry if I’m asking really weird questions that are sort of wildly outside of the scope of your video 😅 you’ve been a lot of help with answers to questions I’ve asked you in the past for my Tesla Turbine +BLDC Generator build and now I’m moving to the next phase of building a Tesla Compressor so I need to supply power to the BLDCs on my build to spin up the discs to work as a pump and I just know you’re the right person to ask these questions to too! Now I was going to post a link to the latest video of my turbine/pump but I don’t want it to seem like I’m just trying to get free promotion. So if you would are willing to take a look at my turbine/pump build to properly understand what I’m doing asking, please go to my channel and check out my latest video to see the 10in Aluminum Tesla Turbine with Dual 2200Kv BLDC motors/generators videos I just posted. I had been asking you questions on a few of your videos in the past before so if you remember me, this is the progress I’ve made with my build 😇 I could really use some advice though so I can do better tests with my turbine/generator. Thank you again for your really detailed videos! They are very helpful!

So is it same for air vs ground Vehical motors vs boat motors ?

Hi, I didn't hear you about heat. I have a problem with my RC car. I changed te stock setup to a brushless setup. 2S Lipo with 4300kv motor and 60a esc. I have replaced the standard pinion and spur to slipper. This setup requires a bigger pinion, 3T up from stock. Now the motor gets so hot, that after the 3th time running it, it is rip. I can't switch to a bigger motor.... What should I do, because what I understand from your video, going down in KV won't help on torque to get my rig easier going icw keeping mt motor cooler. Or did I misunderstand something?

Nice explanation. The only thing I would add is that the lower kV motor is much more efficient at delivering torque. If heat or battery life is a concern, then you would want the lower kV. Also... You need to be able to actually deliver the full 132A in you example vs. just 22A to get the same torque.

Well said… can you do a video or comment on the relationship between the static torsion of a rotor based on the strength of the magnet in relation to how much torque that motor will produce. Basically I have two motors of the same size from different manufacturers however one shaft spins more freely than the other. I’m assuming because of the strength of the magnet. Does this mean that motor will produce more torque over the one that spins more freely?

very informative video i watched it 3 times :-) I always thought and also heard the lower the KV the more torque but your explanation totally makes sense. So the only real factor is the form right? bigger motor bigger can/magnets => more torque or a (higher KV) motor running on higher S setup geared down really hard is this right?

So if I understand correctly the kV value you want to select is going to be solely dependent on the gearing options/ prop size and the battery voltage?

Thank you for the video. I have a question. If the amount of copper is the same, it's the same motor. but 14.4v 2000kv 2000w 28.8v 1000kv 1800w Why is the watt difference between the two motors here? 1. Are the copper weights of the two motors different? 2. The voltage and wattage increase are not proportional?

Great video. Thanks for the info. Yet I still have a confusion. Do you suggest to get the highest kv possible for the same can size? For instance, if the rpm goal is 500. In that case, do you suggest to use 500kv by directly mounting or to use a 1000kv and reduce by gears, this will also give double torque at the wheels with much less battery(weight)? Thank you inadvance.

Awesome video

Another great video! A quick question: Since the lower Kv motor produced the same amount of torque (with less amps) as the higher Kv motor(with higher amps) doesn’t this mean in real world applications where the motor is under load the lower Kv motor will have a better ability to maintain its torque output since it has more current headroom left. Thus making the lower Kv motor produce more torque under load?

would you reference the motor manufacturers data you used in the first two columns please?

I had this thought when i went lower kv and was gonna up the pinion. It still started to cogg at the same tooth pinion from stock. I hate ANY cogging so i only went up 1 tooth in the end but up 1000kv at 2 up from stock 3300 and 4300 kv motors acted the same from a stop. So high kv was my only option at power/speed. Its just more powerful all around but everyone says go the other way. Didn’t work out for me im not dealing with the stutter start for the power.

What if you replaced the magnets with stronger ones, would that change the torque?

Great video...but I'm left wondering how the "max amps" spec is determined? Is that a limit based on heat generated in the motor, or magnetic saturation of the stator limits? If it's heat, then putting 30 amps into a 22 amp max motor would make it overheat eventually of course, but with better cooling of the same motor, allow for more overall power in watts?

I may have missed it but is it assumed that the Kt is correct at all voltages/RPMs? Mainly, I’m using my BLDCs as generators so Like for a Kv=2200rpm/volt and Kt=4.3mN•m does that really mean that regardless of the rpm, if I supply the same torque to the shaft at the different rpms it will always put out the same current but it will do that current at different voltages depending on the rpm? because if I understand it correctly both these values are actually for if you supply a torque of X value at rpm of Y value you will get A amps out at V volts and not necessarily directly correlated to what power is put in using it as a motor. Is that correct? Something just seems to not fit with that to me for some reason.

Ty big bro

Wow, this video was awesome, but now I'm even more lost then I was before. I'd like to build a diving scooter, but selecting a correct motor is a nightmare. Does anyone have any tips for me? I was thinking I should go with the Flipsky 65111 160Kv 3000W because of the low Kv, but does it even matter?

Let's say I have a motor and I want to increase torque. However, im restricted by the physical size of the motor. As in, I cannot change diameter or length of motor. Im also stuck to using stock magnets. They cannot be changed or made stronger. The only variable I have the ability to change is the winding of the motor. So I can change the amount of turns and guage of wire. So my question is... if I were to rewind a motor and keep the amount of turns exactly the same but increase the thickness of wire used, would this alone create more torque?

Can I calculate it like this? 9500 / kv = kt

Would the battery last longer on the motor with the lower Kv value while maintaining the same amount of torque?

Maybe because MOST lower KV motors are in much larger cans so they WILL have more torque? Don’t ya think that of course a smaller magnet isn’t going to have as much torque?

Ok so the *motor* can in theory produce the same torque but I argue that is practically irrelevant. High current is harder to manage than high voltage in any situation that matters for us. Losses to current will almost always mean lower kv = more torque.

I have both 1400kv and 2200kv motor which one will drain my battery faster

Doesn't more wats mean more power. Because when you decrease the kv it jas more wats?(can you explain?)

Quick random question: I run surface and I’ve noticed and heard from others the same Why is it that a 4000 mah 3s would last longer than a 4000 mah 2s C rating should be the same With the 3s , the motor is having almost twice as much amp pull so you think it’d be less run time but ??

Does a 12t rc brushed motor have more Torque then a 21T motor

I'm still confused then as to why they would even offer 7 different versions of the same motor. If I'm limited to low voltage, would I still look at choosing a lower KV? I'm guessing that limits the current, which limits the RPM?

If my motors were the same size producing the same amount of torque, would the one with the higher KV go faster?

If you keep the same battery for both motors in different kv's will you see a difference in torque?

I posted this in an RC car group and someone replied saying they didn't believe you because I didn't think that it was possible to get that wide of a KV range from a single size of motor. Would you be willing to share your source for the motor information so I can clarify to them?

hi very good video i have one question : i making elektrique motorbike (i have 1 year to finish) i dont have lot of money to buy 100Kw motor .... but previusli i make elektric scooter of 1500W but the motor have 30kv and 66V battery (13+6s) the max speed is 45km/h but 45kmh is max out du to kv limitation not power because with the oter gear ration i go 55km/h... for the bike i use 10-20Kw motor but there are the PROBLEM if i want to have high torque mi speed by slow if i want high speed mi torque by low or the power hangry will by over kill for my battery .... so i dont have lot of money tu buy very powerfull battery and motor and esc (800-1200€ esc+motor) but i want to use gear ratio (gearbox of 3to5 gears) 1 gear slow mode high torque laste gear high speed low torque ... this methode will be good because i dont need owerprice extra powerfull motor ... (sory for long text and error i have bad uk) is this idea good idea ??? or not ???? thanks for your video is very interesting

Does lowering kv increase efficiency?

And its not just the the area amount of copper windings torque changes with where the windings are on the stator

I'm finding opposite results with my Surpass 1410, 2500kv 8A, .00382kt x 1000 = 3.82 x 8A = 30.56mNm 3500kv 9A, .002728kt x1000 = 2.728 x 9A = 24.55mNm 5500 kv 10A, .001736kt x 1000 = 1.736 x 10A = 17.36mNm 9500kv 12A, .001005kt x 1000 - 1.005 x 12A = 12.06mNm Did I mess up the calculations?

A motor with a lower KV has better torque at low rpms, so it accelerates faster, but reaches a lower top rpm. A motor with a higher KV has better torque at higher rpms, so it accelerates slower but can reach a higher top rpm.

Great video! even the torque of those motors are the same, I wonder what's the torque curve actually looks like. Will the lower Kv motor produce maximum torque much sooner in the rev range?

I have a 3000.00 $ dyno that says different indeed lower kv motors spin my load wheel up to speed significantly faster than the same size motor at a higher kv if that isn't more torque what is?

To load 100 kg how many kv motor required?

Although I can't disagree with what you're saying, this is on the basis of the same motors from the same manufacturer. I believe the inherent concept of when people saying "use x motor as an upgrade as it provides more torque" in the hobby is usually because people are upping the general can size. Example, Arrma vehicles. The 1650kv HW unit is a very popular 6s line upgrade, but also has a bigger diameter. I'm no where near technically in tune as you, but I think that's where the notion of "this lower kv system (compared to the factory 2050kv 6s system) has more torque". I'm not a maths whiz but surely the 1650kv system produces more torque than the smaller can 2050kv Firma?

Sorry for this comment haha you prob don’t have the time to answer But I have a truck I’m deciding between 2200kv motor And 2400 I only have 4s batteries and I would prefer to go faster What would be the better option gearing up the 2200 or going 2400, I like the 2400 because I would save about 4 oz Also the truck is light enough that either would work. Probably a very open ended question with not enough detail haha

so a higher kv gives better efficiency... so why wouldn't I go with a high kv that can give more top speed

Questions, Does Running A Lower Kv Motor Runs Cooler & More Torque Means More Hp Meaning More Speed?

okay, so if you push a low KV motor beyond its limits, you can get more torque for the same current, but at risk of burning it out. so you should always match the motor to the current output, theres no reason to under spec if you have the available current.

Ok everything looks good on that paper. tell me then why motors sensorless of course with high kV have coging on small throttle but those with smaller kV ratings not have that problem. you have said that torque will be the same but in life I can see something different. Please explain me that fact. on you white board you have calculate on max load what for me is not right.

Could you not buy a higher kv motor of the same size and manufacturer gear it down to maintain the same wheel speed but produce more torque at the tires of the vehicle as long as heat isn't an issue and the rc car can accept the lower gearing? Making the higher kv motor the choice to produce more torque at the tires by gearing lower and maintaining the same topspeed?

HELP ~ 3960kv x 2pi / 60 = 414.69023rad\s x 1000 = 414,690.23mNm ~ so how are you getting 2.14mNm ~ what am i missing or what are you leaving out?

gotcha "bigger the better" 😂

under same contitions (amp and volt) higher kv will have more rpm and lover kv will have more torgue ;)

this is misleading. there is no motor with that kv range . a 3960 usually is a small motor , where as a 660 kv is usually a soda can size motor. so motor size make the difference in torque!

Unfortunate I can only hit the like button once

But the the 3960kv would blow up first under high load than that of the lower kv motor fact’s

💯🏎🏁

we call that watt not torque

To sum up: for one size, just buy higher kV and play with throttle limit to have which kV you want... Is it correct?

Why does RU-vid decide subtitels should be in Vietnamese in this video?

missing a lot of information

good video thanks

You talk about all the various motors there being able to deliver the same maximum power and RPM (~7:45), but to do that, they need different voltage supplies. The lower KV motors will need higher voltage input. Obvious? Sort of, but should be said. And does the manufacturer specify that the motors are good to use at the higher voltages? Really interesting.

So please correct me if im wrong ...... Thats why a drag break works better on lower kv bc the esc doesnt have to work as hard?

Please have hard fax not fax on a chalkbord invest in a dyno and you will see this video is a bunch of numbers on a paper but does not have any real world meaning

Electrical engineer here, well without going into a long detailed explanation on on why some of the concepts are only partially correct. Why don't you prove your theory??? Purchase an accelerometer and measure the efficiency curve at a given RPM. And not the theoretical amperage but how much power the motor actually produces based on its KV. This will be a learning opportunity for you. I promise, and you will have to eat some Crow... But it's okay... We're all in the process of learning.

Would be nicer if you took a breath at the end of your sentences. Non stop talk no pauses in exhausting and irritating.

First! Ha