STOP Saying Lower Kv Motors Produce More Torque
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- čas přidán 20. 06. 2021
- Kv vs Torque from a Motor Comparison of equal diameter and length
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Max torque of all motors of a specific motor size is the same and unaffected by turn count (Kv)
The reason they're all the same is because there is the same amount of copper loss.
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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.
I found this comment more helpful than the video. They aren’t the same……not in the slightest. You change voltage going up the car intrinsically goes fast no matter what motor, but the top end is mist definitely not the same and the efficiency of the motor is going to run extremely hot, I’ve switched from 1412-3200Kv to 1412-2100kv, and 540-1900Kv fusion. Lowest Kv always gives you more low end torque and control than a high Kv. Holmes proves it, I’ve done it myself. But what this video doesn’t account for it different sized can act completely differently, and outrunners aren’t accounted for either. Which also act completely different, a 540-1400kv is not the same as a 540 brushed at the Kv equivalent. It’s just not. There are too many variables, including the weight of your crawler. Bigger the Can, the Lower the Kv the better for crawlers.
@BillySugger1965, This comment is mostly correct, but there is one slight error. Peak power does change with windings, it is not constant. It is peak torque that is constant. Power = torque X revs. So if peak torque is the same the power must increase if the revs have increased. That's the whole point of using a higher Kv motor within the same can size. You can get more power output at the expense of efficiency.
@@JeffGoris top end and torque are always going to be the same. They just ramp up at different rates. One is more efficient the other based on what the application you’re using it for.
I think some people are focused on the wrong thing.
@@wvlfkvnt Yes, the real focus should be on power. More power means more acceleration and more ability to overcome friction and drag to obtain higher speeds. There are two ways to increase power - by increasing torque (which requires a bigger motor) or by increasing RPM. I'm not sure what you mean by "top end". But, top end of the rev range is typically where the most power is made because you have the highest RPM. A motor that gives the same torque, but at double the revs of another motor will be outputting twice the power when both are at their maximum RPM.
Yeah his math must be completely wrong. Power being the same but current increases means that we have lower voltage to reach those amps at higher KV meaning we have thicker windings and probably less poles?
Outstanding work. I had suspected this from experience. fascinating numbers thanks man
Much appreciated
As a RC fan: Thank you for this super useful information. I couldent find any exact on internet
NICE TUTORIAL . THANK YOU BRO❣
Thank you for this video! Now everything is clear for me!
VERY ENLIGHTENING, thanks.
Didn't you explain in previous video, lower kv having more torque was a myth , but is alot more efficient, less heat transfer
He most certainly did i just watched it last night. He's most likely updating the video as some wouldnt accept older information even from a year ago.
You might be thinking about a situation in which you ask the higher KV motor to spin x-many times faster - yet less than x-many times softer - than you do the lower KV one, causing it to draw more amps.
You are correct. I wasn't clear enough in that video as I received many questions about needing more torque and going to a lower Kv motor within the same size class.
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 !
Thanks for the comment xavier.lonewolf82
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!
What exactly are you trying to power? The main ESC leads or the 5v receiver lead? A car battery can be used on the main power leads if the ESC is good up to 4s LiPo.
@@RCexplained the ESC leads. I know a dc power supply would need to be HEFTY because of the 3000watts and capable 120amps these 2200 Kv rated BLDCs need.
I just want to be able to supply power to my ESC so that I can use the motors to spin the Tesla turbine/pump so that I can do all my balancing of the runner without having to charge batteries all the time just to supply the power. if I could wall power supply I could just do continuous runs and not have to stop. As well in the future I want to use the motors to run the turbine as an air compressor so it would be nice to be able to power it with the same system as I’m using for the turbine and just run a power supply to it. But I do realize that’s what is so impressive about these new lipo batteries also, the power outputs they have are rather amazing.
Yes, you can power the ESC with a wall power supply. Make certain voltage, polarity are correct and watch your current use to stay under specs.
I watched your video and don't think it would take 3000 watts to spin up your turbine to balance it.
@@RCexplained good to know! And yeah currently I’ve only gotten the 10in turbine up to 3000rpm but she’s safe to spin up to 15,000rpm and at those high of rpm the runner acting as a pump will be moving A LOT of air. I would like to think 3kw or even the dual 3kw I’ve got would be enough to make a VERY powerful centrifugal compressor but I’m very much still in the R&D phase. It’s really more of can the motors supply enough torque for the mass flow rates and the gear ratios I’m using.
The first runs I did with my setup to spin the turbine were half successful and half a train wreck. I had it way over geared for what is needed on start up and it was cogging like crazy. The polycarbonate I’m using was flexing out of the way and the spur gear was just bouncing all around on the gear. It sounded horrible lol but I got it to start spinning and once it did she sounded super smooth. But I had my esc set in training mode for some reason and I was only getting half throttle. I couldn’t get it started spinning again after I stopped it as the cogging and skipping just wouldn’t stop. Which just tells me I need to go back to the drawing board with my custom turbine bearing and BLDC motor mount plates. I also think I’ve got my pinion gear a little bit too far out on the very edge of the motor shaft. I needs to be to fit around the turbine bearing but I think being so cantilevered like that is providing some issues. I’ve got lots of ideas to fix all this though. Just gotta keep testing.
Any suggestions for getting passed the initial start up torques? Everything runs smoothly once it’s going I just gotta get it going.
We will see!
Thanks again for your help!
If you are a bit over geared to rotate the turbine assembly with the motor, it may be difficult. Can you re-gear your motor? Using the highest output batteries will help as there is a very high power transfer during startup.
You could also apply some high pressure air in the turbine to assist start the motor.
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!
So is it same for air vs ground Vehical motors vs boat motors ?
Reason I ask as I know kv rating on a drone vs ground gear vs a blade does it matter ?
I think it is the same thing
@@earlmoorhead5555 It goes for all brushless motors regardless of what it's used for. The only thing that will change is resistance against the motor from accelerating (wheels gripping, water being pushed, air being pulled/pushed etc). More stress = more heat = less efficient.
@@TR.Pixels nice 👍
So basically earl, I’m your last losi video, the stock 6500kv motor in your losi will not produce anymore torque then the Castle 7700kv(I believe it was)? @Earl Moorhead
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.
Yes. Just keep in mind the maximum amps your ESC and battery can handle not to overheat.
always use lowest possible kv and highest possible voltage.
@@johannapoder2843 So then, in trying to choose between a 2100kv and a 3200kv at a GIVEN, identical voltage of 14v, with both options falling well under the max RPM of say 75K, the lowest kv option should be should be chosen as long as the Final Drive Ratio can still be attained using that lower kv motor through gearing?
Cant wait to use this knowledge over in my Facebook groups and show off 😂 I’ll be tagging this vid for reference though
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.
Thanks for sharing
Great video! Debunking time
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.
"The issue I have is that lower KV is less efficient because the windings are smaller and resistive losses increase"
Not really. As torque is a function of induction and some other parameters that doesn't change with the winding (like the core geometry, permeability and the length of the core) if you double the turns of the winding you need half the current for the same amount of toqrue. Let's get the kV get halved! For the same coil size but double turns you need a wire with half the cross section. Your wire has 4 times more resistance but the coil needs half the current for the same inductance. (B=u0*ur*N*I/l. where u0*ur is the core permeability, l is the core length, N is the number of turns, I is the current)
P_loss=I^2 * R_loss = 0,5^2 I * 4R. The losses are exactly the same if the amount of copper used for the winding is the same. The only thing that really changes is the amount of resistive losses of your ESC which is better with lower kV motors due to lower current draw.
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?
No, there is little relevance to torque based on how freely the motor spins in your hand. The torque required to rotate an un powered motor is known as the cogging torque.
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?
First of all, brushless motors draw a lot of more current and produce a lot of more heat. Its hard to burn brushed motor, but burn brushless is very easy.
You have to deliver a proper cooling system or make a bigger gear ratio which will make your car slower and reduce load on your motor.
You can program your ESC to use less power and make your car slower or buy lower KV motor which will be underpowered by 2S.
@@harynian ok,
Now I bought a 3800kv motor but this time a bit longer can. The 3660 size. I didn't have the chance to run it yet, because I'm also waiting on an 80A ESC. The 60A must have got a glimp from the previous 3650 motor going so hot because it's also rip now.
Car is just a 1:10 scale buggy. Nothing heavy with big tyres or so.
@@Daniello84 you should also buy cooler fan for motor, it helps a lot.
@@harynian I did, but I can't get it to fit underneath the body 😭
would you reference the motor manufacturers data you used in the first two columns please?
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.
Kt is correct at 100% throttle for all voltages. That is correct Current gives you torque, voltage is RPM. Efficiency plays in to this as well
@@RCexplained awesome thank you. So does that means since I’m using this motor as a generator if I supply too much torque to the shaft, even at low RPMs I could very easily go well over the rated amps for the BLDC then?
Like say since I’m at Kv=2200 and Kt=4.34mN•m/amp and my BLDC can handle a max of 120amps. So If I supply anything over 520.8mN•m to the shaft it would gravely go beyond the 120amps the BLDC was rated for then right?
Yes, however, your charge controller would have to be able to handle / draw the >120A.
@@RCexplained sound good! Yeah I’ve got a 4000watt /8000watt peak 12VDC->120VAC 60hz. That should be able to handle everything I’m pushing at the moment. Thanks a lot for all the help!
Also, just FYI, I NEVER get a notification when you respond to my comments. I don’t know why when I get notifications for replies on other comments I make on other channels. Like I have to go back to your movie and find my comment to see your replies. Idk if maybe thats something you want to speak with CZcams support about because people should def be getting notifications when you reply because it helps get them back to comment more helping the engagement rates on your videos to go up. Just something I thought you might want to know. Thanks again for all your help!
No problem Charlie. You may also drop links to your video, not a problem. All I ask, is that your video has a link to RCexplained if something was able to help and a link would fit.
Also,
Turn on "Activity on my comments" in your settings. You must have them off, I think it does default on.
Well explained 😃
Thank you 🙂
Can I calculate it like this?
9500 / kv = kt
Nice explain
Thanks !
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?
Yes, primarily Kv varies for users to be able to run different voltages on the same size motor.
It would not be good practice to take a 60,000RPM capable motor and run this on a prop at 8,000RPM. Motors designed to operate at 60,000RPM will not be able to make maximum power at 8,000 RPM.
No, it depends on the rpm you want to run your motor as well. Lower KV if you’re running at lower rpms, higher KV if you’re running at a higher rpm.
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?
Correct, the only real factor in theory is form. In one physical size all motors of all different Kv values are limited to the same value for maximum torque and horsepower.
@@RCexplained love your vids
thank you
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. ;)
Dont understand you at all.
He means that higher turn motors produce the same max torque, as explained in the video. What they produce more is the amount of torque per unit amount of the current.
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?
Max Current is determined by heat. If you cool the motor more, it can handle more waste heat and thus more power.
@@RCexplainedso in relation to what you’re saying it means that the lower kv motor has more room to run a higher gearing and will only then produce a higher amp rate due to the waste heat?
@@zacmcdonald80 Nah, lower kV motors don't have more room for higher gearing. They are just good at producing more torque per unit current. In higher kV you will be drawing a lot of current from the batteries.
What if you replaced the magnets with stronger ones, would that change the torque?
It would increase Kt the torque per amp while the measured Kv would decrease.
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?
How much power in watts do you need and at what rpm? When you know bit of information it's quite easy to select the kv along with the cell count you wish to use.
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?
This video is totally misleading. kVis the offload speed at different voltages, it is not the load speed. All that tells you is ‘is might it be fast enough?’ . It doesn’t tell you if it is powerful enough. The power, or torque depends on the Volts x Amps principally and for how long that power can be maintained without burning out the motor.
The maximum speed is limited by the back emf generated by the rotation of the rotor and kV is a hangover from the days of brushed motors when the speed was limited by the applied Voltage, the higher the Voltage the faster it went until the back emf was nearly the same as the input voltage and there was no more power left to keep the motor turning. BLDC motor speed is governed by the electronics. All is governed by the heat generated in the windings. Hence the standard for rating motor outputs is based on specific ambient temperatures.
And as for the elegant mathematics what you need to know is the output power, which is easily specified in Watts, just like light bulbs or cookers. You know the speed that you want your shaft to drive and you want to know the power that is available. The more power you have the more likely it is that your plane, car or boat is going to run. kV doesn’t tell you that.
Torque is power per rev. and apparently mistaken for power. There is of course the relationship, but it is power that drives your car, torque allows it to carry heavy loads but at lower speeds
Would the battery last longer on the motor with the lower Kv value while maintaining the same amount of torque?
Yes, because the same amount of torque is only applied at a lower speed, and therefore lower power. In most applications, speed is just as relevant of a parameter as torque.
Awesome video
Thanks!
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?
Hello where does the increased headroom come from for the lower Kv motor?
@@RCexplained for example the max current you have rated for a 660kv motor is 32A @ 314 torque, when looking at a higher Kv motor the amp draw is much higher for a given torque output. My thoughts probably don’t line up with you chart but I’m just trying to find out if there are any benefits of a lower Kv motor. Other then making sure you don’t go under or over your RPM limit(Kv)… the calculations are great but I think we need a real world test where the motors can be loaded. Thanks!
@@crimsonspan9750 benefits to a lower kv motor is requiring less energy to produce the same amount of torque, reducing heat, wear, and tear on the system. Typically you can adjust final drive ratio through gearing, similar principle in rc cars. Higher kv motors are recommended for lighter weight 2wd vehicles, lower kv motors for heavier 4wd vehicles. Also lower kv typically means higher voltage, as most motors have rpm limits and the higher the kv the lower the voltage ceiling
@@tylercampbell6301 thanks! I am aware of all of that, I was referring more to the torque vs RPM ratio under load of the same size motor with different Kv values.
You are right, for a given amount of current you will have more torque per unit current in a lower kV motor. That is why lower kV motors exist. Otherwise they have a drawback of back emf requiring more voltage for higher rpm, due to increased number of turns (Just like an electric transformer). This increase in voltage will result in slight heating. I suspect wires are also thinner (inverse root to the Turns) in lower kV motors due to lack of space, but not ever checked.
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.
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.
Very interesting. I have a similar video topic somewhere in queue for this.
Ty big bro
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?
If you could increase the efficiency of the motor, there is potential for additional torque. An increase in efficiency could also decrease your Kv allowing you to run a potential higher voltage.
@@RCexplained Thanks for your reply! Much appreciated.
Does a 12t rc brushed motor have more Torque then a 21T motor
If all other specs are the same, they should be equal. 21T will have more torque for the same voltage as the 12t will require higher voltage.
errrr....brrrr... errr.... bzzztt. brain just short circuited. LOL
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?
It's in the description.
@@RCexplained I saw the link to the Astro flight website but I didn't see any listing for motor options or anything like that. Maybe it's changed since you created the link?
Look up Neu Motors or leopard motors and pick any motor can size.
Exactly! That's why higher kV motors produce more power!
You got it
But one thing I always wondered, the lower turn wires are also thicker, right? Since they will have much more volume to fill and therefore should be the reason for the higher current capacity, along with shorter solenoid length.
That is correct
Doesn't more wats mean more power. Because when you decrease the kv it jas more wats?(can you explain?)
All Kv's have equal watts. Watts = Power . RC explained as requested :)
I'm confused....I'm running a 2200kv motor at 2x5000 milliamps. Where that 73 is coming from? How can you run such high amps? Thanks
A motor data sheet for current.
Where does your 2 x 5000mA come from? What RC are you running? This is not a commonly measured value of current in an RC vehicle. Also, measurement tools do not specify current drawn as a multiple - 2x. The measurement tool you are using is way off I'm sure.
Looks like the torque (and by its nature the max applicable current) is limited by the core saturation, and not the winding.
I have both 1400kv and 2200kv motor which one will drain my battery faster
With all else equal and using 100% throttle, the 2200Kv Motor will.
If you keep the same battery for both motors in different kv's will you see a difference in torque?
Same battery (voltage) will result in equal torque, but the low-Kv motor will have lower speed. On low Kv motor, you can increase the voltage enough to result in equal power. This will occur at lower speed, and higher torque than the high Kv motor.
Equal speeds would require even greater voltage. In this case, the low-Kv motor would then have greater torque, voltage, and power, so it might fail due to excessive torque, heat, or electrical arcing. Even though the current is equal, low-Kv motors have more (i.e. thinner) windings so the same current causes more resistive heating, assuming the same size motor.
@TheBenware81, that is a really good question because that is the situation that people are referring to when they say a higher Kv motor has less torque. You typically can't change the voltage in racing as you are restricted to a specific battery type. Also, even if not racing you can't fine tune the voltage, you can only make step changes of typically 3.7V with LiPos. If all you change is the motor, the car with the higher Kv, at a given speed will have less torque and will accelerate more slowly than the lower kV motor because at the same RPM the lower kV motor has more torque. The higher Kv motor should, in theory, obtain a higher top speed.
The reason for using a higher Kv motor is for more power, but you will only get this at higher RPMs. So, when you drop in a higher Kv motor, if you want more acceleration then you must reduce the gearing appropriately (eg, smaller pinion, bigger spur, reduce prop pitch, etc.). If you adjust the gearing correctly you can obtain both more power across the entire rev range and a higher top speed with a higher Kv motor. Downsides are that the battery depletes faster (obviously) and the motor runs hotter.
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 ??
Because voltage, you have an extra 3.7v going into your car
An important battery specification you are missing is watt hours. For example, a LiHv with the exact same mah and C rating to a LiPo will have a higher wah rating thus lasting longer.
Because when you use the 2S to go lets say 50km/h you need 50% throttle and with a 3S you would need 30% throttle , so you are using the same amount of energy but you are drawing it from 3 cells not from 2. 2S has 2 cells each with 4000mah and 3S has 3 cells with 4000mah each , that's why the 3S is also significantly larger in size.
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?
Curves should be very similar.
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?
Kv options are available to match the voltage a user will run. With motor RPM constant, a lower voltage will need a higher kv to get back to the same overall rpm as a higher voltage setup.
@@RCexplained Awesome. Thanks very much!
If my motors were the same size producing the same amount of torque, would the one with the higher KV go faster?
no. because higher KV has a lower voltage capacity. lower KV accepts 4s-6s. a 3000kv @ 15v = 45,000 rpm. 2200kv @ 22v - 48k rpm.
Does lowering kv increase efficiency?
it can but won't if as a result you need to pull more current using the same voltage
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
for the bike the max speed will be if posible 140km/h+ and start torque (torque at lower speed) high to klimb every road (12%+)
for theoretical power 15kw is the max power of 125cm3 this bike go over 120km/h (140) i think with 15kw brushless motor the speed will be similar
last comment sorry.... if i use 1 gear (no gearbox) with 15kw the max speed will be 90km/h for mi is not bad but at this speed 8kw is good to ... THE SAME IS WITH INWEELS MOTORS 3KW GO 70KM/H 4KW GO 85KM/H AND THE 27KW GO 120KM/H THERE ARE BIG DIFFERENCE IN POWER BUT NOT IN SPEED ....??????......,??????
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?
Note that the 9500Kv motor is 3.8x more Kv then the 2500Kv motor. However, current only goes from 8A to 12A or 1.5x higher. I haven't looked at the calculations as these specs are the area of concern. The max current specifications suggest that there is a problem with the copper mass of this motor series.
@@RCexplained That makes sense, they're about as cheap as it gets.
Would that be a discrepancy in the current draw, or kv? or kinda both?
Thank you for the response, and great video, I learned a lot that I didn't know about brushless motors.
Questions, Does Running A Lower Kv Motor Runs Cooler & More Torque Means More Hp Meaning More Speed?
Not necessarily, a properly selected power system will run cooler. More torque and RPM is more power.
Wait.. then what is the point of using a high Kv motor, if it has the same RPM and torque but draws more power and creates more heat?
Different Kv options are available to allow varying voltages to be used with the same class motor and then from there RPM tweaking.
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?
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?
A motor of the same size and manufacture will have the same max RPM and Max torque output values. If you are running the motor at or approaching max RPM, you will not be able to increase the Kv operating on the same voltage otherwise you are over Max RPM.
At the same time, if you are operating a motor at 35,000 RPM with a max of 60,000RPM - You are not getting full potential from the motor. (incorrectly optimized motor) Raising the Voltage or Kv will allow better optimization.
Each motor in the same size class from the same manufacture has the exact same potential when it comes to power meaning torque and RPM.
And its not just the the area amount of copper windings torque changes with where the windings are on the stator
First off I never saw a question ask second off if you're adding batteries into the equation I don't need to have this conversation with you because you are too ignorant to know testing motors is done on constant power good day happy safe flying
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.
We have not enough details about your situation to answer.
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
Which ever motor produces the most watts has the potential to go the fastest. Generally, this is the largest motor.
@@RCexplained running same gearing in both with a setup, pretty easy on the motor which do you think would ask for more amps
Higher Kv will require more power with all else equal.
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.
Hey Fraser, copper losses due to current in a quality motor will be equal across all Kv options / winds. This comes directly from the motor manufacture.
@@RCexplained whole system vs motor in isolation. Esc, wiring and connectors rarely change to the same degree.
I also privately think that in a lot of cases (mainly outrunners) the same wire diameter is used for all kv options for cost reasons.
To load 100 kg how many kv motor required?
100kg what? Thrust??? Or 100kg/m torque??? For thrust an A2212 2200kV BLDC should produce 1.5 kg at max. For torque it is more dependent on the parameters of the motor, and gearing if any.
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?
Are the motors pulling the same amps, does your equipment allow higher amp draw by the higher kv motor?
@@tylercampbell6301 yes there is a higher amp draw on higher kv motors and yes my dyno has a magnetic flywheel I can simulate different loads on motors and see how long it takes to get to peak rpm.i used to race rc cars and adapted it to brushless outrunners.if I was better with the social media thing probably be able to have a channel to do good motor reviews. Coming from cars it shocks me there is not more good data on motors out there
Lower KV gives better torque at lower rpms. Higher KV gives better torque at high rpms. So the motor with lower KV will accelerate faster, but reach a lower top speed.
@@AlexB_yolo exactly what I am seeing on my dyno higher kv don't start making torque until higher rpm regardless lower kv spins to kv much faster than higher kv
It looks like you have high current protection, but you said nothing about your configuration, so we cant make any real conclusion.
We have to know:
- KV of low KV motor, its amp and voltage rating from specs, your battery voltage/cells and current/power draw while accelerating
- KV of high KV motor, its amp and voltage rating from specs, your battery voltage/cells and current/power draw while accelerating
Then we can talk.
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?
What formula did you use for Kt? How did you go from rad/s to mNm/A?
@@RCexplained i multiplied (414.69023rad\s) by a 1000 like you said
Kt = 1/ Kv
@@RCexplained That didn't HELP & kt = 1/kv wasn't mention anywhere in the video ~ im not a math wiz ~ i have no idea where to put kt = 1/kv in the formula ~ can u just write out the formula in English for people who are not math wiz can understand?
Hello, the formula was in the video and also written out. Kt = 1/ Kv is the formula. Convert Kv from RPM/V to RAD/s/V by multiplying 2π/60. Then place in formula. Lastly multiply by 1000 if you are looking for mNm/A. If you don't multiply by 1000 you get Nm/A.
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?
Generally speaking, torque scales with the weight of the motor, all other factors being the same. The 1650KV motors from CC and HW are, at least to my knowledge, all larger than the typical 4074 2050KV motors found in 6S vehicles. So the short answer to your question is: yes. 🙂
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?
💯🏎🏁
gotcha "bigger the better" 😂
The bigger the better. I like that.
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.
Any source? Because it is opposite to this video.
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.
You can push any motor beyond the limit by increasing the potential (voltage). More potential equals more current equals stronger magnetic field equals more torque and better rpm response. But that current will produce extra heat and most likely melt the solenoid coating resulting in short circuiting. Especially in outrunning motors!
under same contitions (amp and volt) higher kv will have more rpm and lover kv will have more torgue ;)
To sum up: for one size, just buy higher kV and play with throttle limit to have which kV you want...
Is it correct?
Hi J2, Match Kv with the battery you intend to run. The setup must be selected based on 100% throttle input.
But the the 3960kv would blow up first under high load than that of the lower kv motor fact’s
so a higher kv gives better efficiency... so why wouldn't I go with a high kv that can give more top speed
good video thanks
Unfortunate I can only hit the like button once
Thank you for the comment! 😊
@@RCexplained I used to not know the science behind it, but I always thought even if you did get more torque, it’s all lost in the gearing reduction you’d use for a faster spinning motor.
I’m surprised so many people stick to it when in 1/10 racing 17.5 and 13.5 motors are way slower than mod motors, and in 1/8 racing you use a lower KV motor if you have too much power for a certain track or surface. (Or if it would be a tall ask on a higher kv motor to last a 20min race
For sure!
we call that watt not torque
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!
Actually, the motor Kv range for this motor series runs from 660 to 8800. Why do you think there is no motor with this range? This is not at all unusual.
@@RCexplained i meant surface motors! auto motors don't have that range
Yes, these motors are used in RC cars. Actually, it's this exact series and company that helped start the entire line of castle brushless motors.
@@RCexplained wow
Why does CZcams decide subtitels should be in Vietnamese in this video?
나도 그렇다..어째서 베트남어인지...
@@rcmod642 Sometimes I watch the video's without sound, subs only.
With these subs that is really challenging. ..
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.
Hi David. Motor's are not limited by voltage. They are limited by maximum rotation speed.
@@RCexplained It sounds like you cant go over 60,000 RPM, but thats not true: czcams.com/video/1TiePd7qng8/video.html ^^
missing a lot of information
What do you mean?
@@RCexplainedfor example you didn't explain how the windings relate to Kv, or about saturation, or about the load on the motor. if i wanted to know about Kv ratings and what voltage I put on the motor without burning it up and i would watch your video i would not know anything at the end. like why do you put less current in lower Kv ratings and why can't i put the same current in it and get more torque out of it, all kind of details i'm curious about.
Ahhh. I've done videos on a few of those items already. I don't like to cram 5 topics in to one video. I tried this and I get the opposite comment of what yours is. Too much information.
@@RCexplained ok i get it. so i watched "Maximum Motor Current Specification" and it's just completely obvious stuff. that's ok though, no worries.
I think this is an interesting video for you?
czcams.com/video/r0dzdtM8Zt8/video.html
Search CZcams and send me the video you are looking for. I'd like to get an idea as to what you are after.
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.
Okay can't stop thinking about this,
a few questions that I'd like you to consider?
Do you believe that the torque output of a motor is linear?
Or do you think that there is an efficiency curve? Based on RPM and magnetic field strength?
Why does motor top out at a given KV or voltage?
You put the motor in a vacuum where there was no external drag other than the magnetism, with the RPM increase and definitely?
Where is there some other Force at play?
Pause that I'd like you to research
1. Faraday's law
2. Kershaw's law.
This will get you a little closer to the direction of real...
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