Motor KV explained - KV is a lie and what you really need is a torque!

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Everybody knows that an electric motor KV is a number of RPM per 1V of the supply voltage. Right? Yeah... too bad it's a lie. Not a very big lie, but a lie after all. KV is the number of RPMs when Back EMF generates 1V on the motor coils. Almost the same, but "almost" makes all the difference.
Also, KV relates to the torque motor generates. The more KV, the less efficient the motor gets because it requires more amps to deliver the same amount of torques (in Newton-meters, Nm). On top of that, the fact that you got a higher KV motor does not mean that propeller will spin faster. Why? Because you need torque to spin the propeller faster. And more KV means, in general, less torque.
More about motors • RC motors: size, torqu...

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3 янв 2019

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Комментарии : 118

@vinz486 5 лет назад

Thank you! This channel is precious for the hobby. So, as i understood, the whole equation need to be composed by: motor size, kv, prop diameter, prop blades, prop pitch, prop exponential area. We need a software for that.

@tomkunzemann8062 4 года назад

This is a great idea, let me write an app for that over the christmas time.

@lukasznalaskowski6294 4 года назад

@@tomkunzemann8062 Hi Tom . There is already a great app. see link below : www.motocalc.com/

@mr.simulator4724 3 года назад

@@lukasznalaskowski6294 that looks like a website made in 2005. very sketchy. and the software look like it was made for windows xp, not windows 10

@samhziegler 2 года назад

The humor and understanding in your videos are subtle, but amazing.

@FPVUniversity 2 года назад

Thank you, I do my best 😁

@r4y.squared 5 лет назад

Thank you Pawel, always learning something from you 😄

@Siamect 5 лет назад

Great video as usual but i think there is a misunderstanding. High Kv doesn't mean low torque. Kv*Kt=1 is true but, you need to multiply by the current. A high Kv motor have lower Kt but uses higher motor current. So here is the example: Two drones both equal except for the Kv peacefully hovering over the Gatwick tarmac... 1. KV=1000 Current 5A Back EMF 10V 2. Kv=2000 Current 10A Back EMF 5V Power consumption is equal. 5*10=10*5. if no losses are included. Current draw from the battery is the same because of the ESC chopping. So now we add the resistive losses in the windings. The low Kv motor has twice the amount of turns compared to the high Kv motor. But the space for those windings is the same in both cases so the high Kv motor has twice the area of each wire compared to the low Kv motor. The wire is twice longer in the Low Kv motor compared to the high Kv motor. So the resistive losses are twice higher in the low Kv motor compared to the high Kv motor. So based on this there is no reason why a high Kv motor should be less efficient than a low Kv motor. Quite the opposite is true. But I high Kv motor, given full power will produce a lot more power than a low Kv motor pulling the juice out of the battery very quickly which may give the impression that a high Kv motor is less efficient.

@FPVUniversity 5 лет назад

OK, perhaps I was not 100% clear on that. Higher Kv = lower Kt so more amps are required for the same torque. And because more amps equals less voltage and more battery sag, torque is lower at the end

@Siamect 5 лет назад

@@FPVUniversity If you compare the two cases the battery current is the same but the motor current differs. So there is no difference in battery sag.

@Siamect 5 лет назад

@James smith Sure there are many parameters so it is easier to understand if only one or of them are different during a comparison.

@harynian 2 года назад

@@FPVUniversity Not really. 1000KV eats 5A with 7,4V (for example), so you need 2x 1S 1000mAh connected in series, total 1000mAh, so 5A and 1000mAh = minimum 12 minutes battery life. 2000KV eats 10A with 3,7V, so you need 2x 1S 1000mAh paraller, total 2000mAh, so 10A and 2000mAh = again minimum 12 minutes of battery life.

@analoghardwaretops3976 Год назад

In motor design..power equations are a secondary matter...torque, and speed are more important ..torque/speed curves are the motor characteristics that a motor applications Engineer refers in choosing one...

@tonysanniota4884 2 года назад

I have been trying to understand the simple basics of KV and Pawel you explained it so good. Now I know what is going on with a brushless motor when KV is mentioned. Thanks so much for the video.

@FPVUniversity 2 года назад

Glad it was helpful!

@hfsabune 3 года назад

Finally starting to make sense. Thank you!

@througheagleseye585 5 лет назад

Making long story short. There is no replacement for displacement. Or.. Take two man.. One is a skinny sprinter another strong man competitor. With empty hands sprinter will arrive at the 100m mark way sooner if just speed it self will be the factor. Now give the both guys a front loader tire to carry across.. Obviously sprinter won't even be able to carry the weight. Now give this guys a keg full of beer.. I assume they both arrive about the same time but one will be over kill for the task given. Here is why you can't install 14" prop on lets say 2215 size motor despite the KV as small motor will never have enough torque to spin large propeller to advertised KV and in result will ended up overloaded. On other hand installing 5" prop is waste of large size motor design to work with 3 times larger prop as it will never spin fast enough to generate sufficient thrust even though massive torque will allow for instant acceleration of that undersized prop. Proper ratio of motor size and KV vs prop size and its pitch is a mystery for most people. Load calculation created by installed propeller on given motor and possibility of overloading motor beyond recommended specifications (current draw) makes things even worse. I'm glad to see someone is getting down to it and I'm waiting for follow up on this story..

@ColinMill1 3 года назад

Thank you this should be far more widely understood by the quad community. I think it is possible to argue that for a quad-copter the lower the KV (and higher the Kt) of the motors the better. One can always increase the available voltage to get the RPM you need for flight but if Kt is too low you will exceed the current limit for the motor windings before you have sufficient torque to drive the propeller. Also, the higher the drive voltage the lower the current for a given power requirement. This gives smaller voltage drops in the wiring of the quad and the ESCs and/or allows lighter gauge wiring to be used thus reducing the weight. As you have said propeller efficiency increases with increasing disc area and, within reason, one can always tailor blade chord and pitch to achieve an efficient lift/drag ratio for the blades. There are other advantages - high torque applied to slow-revving, large diameter props give you more torque available to give yaw authority to the quad. About the only down-side is the tendency for the bigger props to be heavier. {One extremely minor point that could be handy for those wanting to do the sums Kt = 1/Kv when Kt is in N.m per amp and Kv is in radians per second per volt. If Kv is expressed in RPM/volt the equation becomes Kt = Pi/(30*Kv) }

@Yay-hovah 4 года назад

I believe him because he has a German accent.

@TheHarshTruth101 8 месяцев назад

Hail H🥴🥴🥴😁🤪🤪😂🤣🤣

@yeeebayeeba4268 3 месяца назад

Lol

@sunrizer 5 лет назад

Very good explanation👌, thanks

@alex1stadandfpv101 9 месяцев назад

Thanks a lot for your videos. Can i ask you for the hint, how to calculate in a right way the motors for 9 inch quad if i know the full weight of the setup with battery and i want to make it as efficient as its possible?

@EnplusX 5 лет назад

Great video we need more! But why using Amps and not a Watts for mesure?

@skynet8764 4 года назад

Question. In theory you are right. high kv = low torque. I have seen some reports, where the Motor has almost the same torque indepented from kv. It was brotherhobby T1 2800kv vs 3600kv vs 4100kv. The reason for this was that the windings are different. The KV is lower and the resistor of the windings is higher. Higher resistior less curent, less torque. If i compare at banggood for example the motorsheets from same motorsize and manufactor, low kv has most of the time an higher resistor. This brings me to my theorie: As you sad, current = torque low kv high resistor torque = torque high kv low resistor drains less current drains high current low kv low resistor higher torque > torque high kv low resistor larger motor = more torque result, if i want to buy a new motor by datasheet, i have to compare kv and internal resistor ans size for a torque compareson :)

@manuelverdugo1737 3 года назад

no. The work of a motor measured in watts is represented when a propeller is put in thrust and propeller speed. The Kv influences the% distributed. more Kv, more propeller speed and less thrust and vice versa. So to achieve this, as we increase the Kv to a constant voltage the propeller must be smaller. In a model of Rc or airplane, Jet etc. the value of Kv x Voltage in the propeller rpm must be at least 70%. The power of an engine is determined by its weight and its ability to dissipate the heat generated.

@harynian 2 года назад

@@manuelverdugo1737 You didnt tell what do you want to achieve with changing to high KV motor with the same voltage, but with smaller propellers. You gave only a little details. Those cases are more complicated. You have to know electric motors characteristics. Motors have constant torque till the certain RPM, then, they losing a lot of torque. When you change low KV motor to the high KV motor with the same voltage, you can overvoltage it and mess with torque. Thats why you have to decrease load with smaller propeller, motor doesnt have enough power for big propeller or overheat too fast.

@MCsCreations 5 лет назад

Pretty interesting stuff, man. 😊

@kermets 5 лет назад

Pawel are there Micro Brushed Flight Controllers for micro quads like the whoop that can take iNav ?

@Rohit-oz1or 4 года назад

Made absolutely clear. Thanks

@rivenmain2175 3 года назад

so if i have an electric skateboard with low KV it will drain the battery slower and can go up hills better?

@DeMoNSe3d 3 года назад

I've always had my doubts about the use of KV as a linear indicator of speed, I guess I was'nt far from the truth, great video, subscribing!

@fpvarborist7436 5 лет назад

What motors would u recommend on a 7" source one

@BuZZarDFPV 5 лет назад

Again I have been lied to! Dammit!

@Subscribe_Mr Год назад

Just please explain how to find perfect motors+Propellers. If it's connected with battery, then do recommend that also.

@stelic9515 3 года назад

Thank you alot. Wery good explanation.

@justainchoe6141 2 года назад

This was pretty good because it does have a good thesis, but this could’ve been explained in 3-4 minutes. It took too long and felt redundant to tie it all and explain that kv misconception is that higher kv means faster quad but the inverse is true. There definitely were informative parts that you should take time to explain, but more than half could be left out. Thank you for explaining it.

@Funcentric 4 года назад

Interesting concept. Thanks for sharing. Question for you. This seems similar to my thoughts on Led Acid batteries on electric scooters. Since empty batteries don't weigh any less than a full battery, there's a point where the efficiency drops in a big way. The larger the battery, the more "juice" it needs to carry itself before showing any real benefit for the rider/scooter. I find that 36v is the best balance for speed and range. So is there an ideal balance you'd consider optimal for motor KV? I realize there's tons of other aspects like number of turns, the battery running through the motor, the amp rating etc. A lot of people seem to want high speed for RC cars, but it takes longer to get to the top speed. The distance is too extreme, further than anyone would really drive. I figure torque is more important in RC bashing and just messing around. How low of a KV would be "too low" if there's such a thing. Super low for crawlers, but a basher needs speed to take jumps and torque to control it in the air. Curious of your thoughts on "ideal/efficient kv" on a basher RC.

@xnoreq 3 года назад

I have no clue about RC cars, but the way to do this is to always start at your design goal and figure out what the load for the motor will be. Then you pick batteries and motor. For example if your goal is to drive at 100 km/h then you should figure out the required RPM that your wheels need to spin at. This will limit your choice of battery voltage, motor Kv and gear ratio. Then, if possible, you should calculate the torque required at that speed. This will mainly be drag of your vehicle, any resistances in the bearings and gears. For the motor itself the specs usually contain Io (no-load current) which can be used to derive the extra torque required just the spin the unloaded motor. Given required torque and some Kv, you can easily calculate the min current. Note that voltage drops over battery, ESC, and motor coil resistances add up and are proportional to that current, so the motor RPM will drop more and more with higher current. Higher amp ratings usually mean lower resistance (in the batteries, ESC, and even the motor). This usually needs to be paid with extra weight and money. In RC airplanes weight is a huge problem. For my example of just driving at some top speed it doesn't matter that much. You can of course also make acceleration at some velocity your design goal, and calculate required torque from that. Because as you said correctly, with the minimum acceleration to reach the top speed it will take huge distances to accelerate the car. Since F=ma it is clear that a higher mass needs higher force. But since you know the torque required you can simply lower motor Kv (and raise battery voltage) and therefore increase acceleration as much as you want. Finally, you can "score" potential combinations e.g. by calculating mechanical power/electrical power (= motor efficiency), or by motor run time given your choice of battery, etc.

@andyvannort2743 3 года назад

Well i have a traxxas xmaxx. One of the largest heaviest monster trucks. Probably best basher out there. Original model came with a 1600kv 6s motor, my model has 1200kv 8s motor. The upgrades most people choose are either an 1100kv or 800kv motor and gear it through the roof to obtain the same speeds as the higher kv motors at much lower temps. 800 seems to be the biggest can motor people are using. The 800 and 1100 have roughly the same top speeds with the 800 being a bit more torquey. The 1600kv ones have a little bit higher top speed but you sacrifice alot of torque and deal with high temperatures

@xymaryai8283 Год назад

from what i understand, a synchronous ac motor like we use, responds to voltage or duty cycle of the sine wave. i don't understand how, because voltage only affects the power of the motor, so the speed controller must also be varying frequency. but then we run into why the frequency generated be higher with a higher voltage? if it can control frequency, does that mean the only reason we pulse width modulate voltage is for current limiting? have we all been running those special KISS escs this whole time? if motors are controlled by frequency, then what is stopping motors from spinning at low RPM with high force, and therefore preventing desyncs?

@FPVUniversity Год назад

That's a very good question. And the answer is that if we refer to "ESC frequency" as a PWM frequency at the output that this has nothing to do with the motor speed at all. It's just an information how fast ESC can drive a phase high/low for desired duty cycle. ESC is either fully LOW or fully HIGH and PWM. So if 16V is applied then it's either 16V or 0V on the motor phase. With variable duty cycle we indeed limit the average voltage and average current. And thus, drive the strength of magnetic field and momentary torque. In fact, there are 2 frequencies on each phase. One that depends on the RPM when the phase is energized and the second that depends on the ESC PWM output frequency. First one changes with RPM directly, the sencond one changes only if variable PWM frequency is used. If it's not used, it's a constant 24/48/96 kHz. And motors stall on low RPM for 2 reasons: - on low RPM fast motor need low current and torque to spin, so it's probable that momentary load torque is more than momentary motor output torque - ESC needs to detect zero crossing with back-emf detection. If RPM are too low, back-emf is low and ESC fails to detect, loses the info how fast motor is rotating, does not energize the coils with enough precission and has to switch to low-torque startup phase when it just tries to keep motor rotating fast enough to be able to detect zero crossing. Then motor has vary little torque and can stop easily.

@JGnLAU8OAWF6 Год назад

With proper motor control you can achieve full torque from standstill.

@robertgubberiksson2068 5 лет назад

I really likte your sense of humor, Laughing my ass of in the first 30 second.... Thumbs up for you my friend

@FPVUniversity 5 лет назад

thanks man

@p.i.engineer398 5 лет назад

I lol'd on the treadmill, thank you for that

@thestrongestavenger1 3 года назад

Essentially find the drag first, then choose how fast you want to go, and get a motor that will meet the first criteria and the second at the lowest kv possible to be the most efficient?

@ChrisRiley3D-Everything 2 года назад

HI, would 1806 2700kv motors give me any more power or speed on my 3 inch quad than say the normal 1407 3600kv motors. im trying to decide what to use in my heavy 360 gram 3 inch build. im running a gopro session and large lipo , thats why its so heavy. What are your thoughts? which would be better for my setup? thanks brother.

@FPVUniversity 2 года назад

It's not that simple. You can try www.ecalc.ch/xcoptercalc.php to simulate

@dougwhitman3056 Год назад

I am working on a boat project, but I wonder if it isn't it easier to match the propeller to the motor rather than to match the motor to the propeller? Can't we just change the pitch and/or diameter?

@FPVUniversity Год назад

It really depends on what you build. If a 5 inch drone then you are left with 5 inch propellers. Plus pitch is not all. Or rather it's a more complicated relationship

@mehimrc1314 3 года назад

So is this why you go lower the kv the hight the battery input such as the value 1v=1full rotation. You blew my little mind man

@lochalianilkumar5721 2 года назад

Plz make one video on how much torque requred for 150kg weight lift,,and what types of factors mainly consider to drone lift,and how to calculate BLDC motor torque plz plz make video sir

@rileylowe8039 3 года назад

Amazing explanation, thank you.

@Banana_Chris 3 года назад

Does that mean, that the moving magnet produces 1V in the coil, that voltage produces a current, that creates a magnetic field which is in the opposite direction. So, when the magnets moves faster and faster, the back emf increases until it has the same value like the supply voltage and the motor can't turn faster? Is that right? So that mean when an motor has an higher kv factor, the opposite magnetic field increase not as fast as the low kv motor with rising rpm? And that is the reason why it can turn faster? In my imagination it's a bit like falling from the sky, the force of the wind is increasing until you get an steady state , because the wind force got the same value as the gravity force? 🤔

@vladyslavlesyk5483 4 года назад

So, from this video understood that if we take the same motors but one is lower kv the other is higher kv, the lower kv one will be better because with the same torque on both motors the lower kv will consume less current and the higher kv will consume more, there is some gap here I guess or I don't understand something completely, it also makes me think we should never aim for higher kv motors, because what is the reason for that if lower kv will consume less but give the same torque, something isn't right here or I did not get something completely, because higher kv will definitely make your quad more aggressive in terms of speed changes and top speed should be higher than with lower kv

@hansleatherby1032 5 лет назад

more please!

@lucianvasile7300 3 года назад

Kt~ 1/kv, not "=" . Kt=1/kv for a given size with same configuration of motor, not for different motors. The required power is going up by cube. On one hand the drag proportional u * v= friction coefficient x speed , on the other hand the energy applied to the moved air is squared E = m*v*v/2. Ofcourse this is very said. Kv it's not a "lie" it's like rpm on cars, it's nobody's fault if you want to put a formula one engine on a truck, keeping the original gearbox of either one (truck or f1 car). You have to mach the rpm/torque of engine with the one of the load. Same with kv and propeller you have to match propeller size&pitch with kv&kt&voltage. Usually for a given propulsion system there is some spare torque (which is used during acceleration mostly, but not used during steady load) , so there is room for a little higher kv.

@carnagefpv8256 3 года назад

Am I the only one who got the joke about the little black couch? 🤣

@MaxBeamer 5 лет назад

Kv only applies to rotations at 1V and the relationship with V is not 1/1 everyone should know this..KV is useful for so many calculations including where torque will be in the throttle range.. not how much torque there is

@MaxBeamer 5 лет назад

Good video

@dweight1990 5 лет назад

So, what are we gaining from higher KV of motors? Aren't they accelerating faster because they have more amps to work with?

@FPVUniversity 5 лет назад

Higher KV = higher max rotation speed if there is enought torque to spin the prop that fast

@johnchurch2321 Год назад

"a certain black couch!!" 🤣

@howintesting940 11 месяцев назад

Good effort trying to explain, but sorry to say it is wrong. Kv is not a lie; it is just a specification of brushless motors. It is always a misconception by many people though. High Kv motor does not mean it has low torque. Same size motor theoretically has same nominal power ratings by design. High Kv motor need less voltage to achieve that power ratings, but more current; conversely, low Kv motor need high voltage to achieve the same power ratings, but less current. When they both achieve that ratings, power delivered is the same and thus same revolution and torque, even same heat generated. Using high Kv or low depends on application scenarios: high voltage application chooses low Kv motor and low voltage one chooses high Kv motor. People tend to have misconception high Kv motor deliver less torque is because: when user chooses high Kv motor in hope of high power to deliver they ignore power supply voltage, keeping the same voltage as in low Kv scenario, thus causing motor overloaded. From the motor power curve it can be observed motor's efficiency drops sharply after passing nominal power ratings, generating less torque but more heat. In many cases, in the RC world, devices are used to the extremity, to name some: Lipo battery - lifespan is much shorter than nominal case because people are power-hungry; FPV video transmitter - for small form factor and more power, design is not good enough to handle signal integrity and delivery, thus generating a lot of waste heat ...

@wizardOfRobots 2 года назад

15:50 increasing KV doesn't lower torque...I read that for same size motors, all KV will have roughly same max torque due to same copper loss

@harynian 2 года назад

Yes, but you have to deliver max voltage for individual motor.

@Sebijr 5 лет назад

I get lost at the first formula !

@edouardmalot51 4 года назад

Great video. One more point is in 4S, batterie limit the max current/torque. That is why 6s have dooble avantage : better Kt and curent (not) limit by batterie

@paulhope3401 2 года назад

Not quite. A 6S Lipo of the same C rating and weight as a 4S, will have aprox 1/3 less Capacity... and so will not be capable of supplying the same amperage as its 4S counterpart.

@pjak2000 5 лет назад

To nie kłamstwo - tylko brak wiedzy jak działa fizyka silnika... i to że dla pewniej "objętości" silnika/statora z KV jest bezpośrednio związana wartość rezystancji wewnętrznej silnika. A wynika to z innego nawinięcia cewek. Wniosek taki, że silnik o tym samym rozmiarze o mniejszym KV będzie miał większy moment obrotowy od takiego samego silnika o większym KV. To nie kłamstwo tylko dyletanctwo.

@FPVUniversity 5 лет назад

oj taki mały click bait. Dobry nagłówek lepiej sprzedaje treść :)

@harynian 2 года назад

Nie rozumiem na jakiej podstawie twierdzisz, że mniejsze KV ma więcej momentu niż większe KV? Nie podałeś absolutnie żadnej kluczowej informacji, chociażby przy jakim napięciu porównujesz dwa silniki (czy jest ono takie same czy maksymalne dopuszczalne). Moment obrotowy można wyliczyć tylko i wyłącznie z KV i prądu, a wzór to: (prąd * 60) / (2 * PI * KV). Taka relacja pokazuje jasno, że zwiększenie KV np. 2 krotnie, wymaga zwiększenia prądu też 2 krotnie aby zachować ten sam moment obrotowy, a wystarczy sprawdzić specyfikacje silników, że praktycznie w każdym przypadku 2 razy większe KV oznacza 2 razy większy prąd. Nie wiem po co w tym przypadku mącić zagadnieniem "rezystancja", bo rezystancję definiuje już prąd i napięcie, a tylko one nas tu interesują.

@randomdudefpv4927 5 лет назад

let's make black notebook more famous than black couch!

@ruzzcraze1862 2 года назад

🥶😳

@fernandohood5542 4 года назад

I am not in the hobby but need a high rmp(15000rpm) and high torque to generate 15000 wats...The kv thing makes it difficult

@RobotoForgoto 3 года назад

How hard is it to describe an electric motor like an electric motor eh? I hate KV nonsense too! Cheers for the video! P.s. i like your white-board...no nead to get all self concious!

@Scyth3934 Год назад

I just looked up what KV was and I was really confused to see that it is the revolutions- you could just add a gearbox and change your motor's KV! What a terrible "unit"!

@FPVUniversity Год назад

No, gearbox does not change the KV. KV is a property of a motor only. And no, it's not even RPM per volt. It's Volts per RPM. The other way around

@rahultej2248 3 года назад

great video! really helpful for those who are being lied to by dumb noobs

@kwikfix69 2 года назад

I agree

@haley8004 3 года назад

It's a lie! ...It's more or less true. This isn't even my hobby and I already know all this. I want to hear a good reason why high KV is less efficient, despite changing the prop size or gear ratio.

@tankogenonrcgroups9750 4 года назад

Wonderful video. Thanks so there wasn’t made hundreds of motors to confuse us just lots of folks drinking that kv kool aid lol

@calisti9308 Год назад

Wait, did you say you’re in Berlin?

@FPVUniversity Год назад

Sometimes I am 😄

@jackevans2386 2 года назад

Larger magnets and larger diameter copper windings = higher torque = higher power = more drain on batteries.

@bvanlaer 5 лет назад

So! A wider stator (1403 motor) will give more torque per amp than a narrower stator (1103 motor) and thus be more efficient. And, if i've understood it correctly, the relationship between torque and stator width is linear.

@chriscflint 3 года назад

Very well explained.

@MrfB-br6yh Год назад

I like that guy

@garypaisley 10 месяцев назад

No, what you really need is power, the multiple of torque and rpm

@TheMadmacs 5 лет назад

this was pretty awful man, i dont recall anybody ever saying high kv had more torque, i do recall people saying it had less torque, i had hoped to learn a bit about actual kv and torque ie. how kv relates to copper windings and magnets, the ability to change speed rapidly or have a higher final speed per volt is not a problem for us, there is enough torque from 16v and the magnets for our motors to perform very well, all of them. higher kv motors just have a higher final running frequency per volt. the mystery for all of us is why we have kv at all, we all know it relates to windings and is slight trade off to torque, and other than some motors feel slightly sluggish to wind up, and us saying use a lighter pitch prop we rarely experience any lack of torque, apart from the magnet strengthi thought torque was pretty much a set thing, big large diameter motors give big torque,

@jamich1 5 лет назад

he did not say that

@harynian 2 года назад

Why we have KV at all? To calculate RPM, torque, propeller size? But other specs like max amps and volts are as important as KV.

@manuelverdugo1737 3 года назад

More Kv not is less effy. Motor work is Propeller speed + Trhust. Motor work is determinated por weight motor. in RC is around 3watts /grame In EDF around 6-10 watts /grame. Never work a electric motor below of 70% effyciency.

@jeffs7915 Год назад

Torque = work. Fxd. Force x distance. But you can't really get a useful mathematical value for any aircraft, approximate ok, depends on flying style, it's a starting point but trial flights confirm your math. I just ask a guy which motor works better.

@FPVUniversity Год назад

No. Torque is not work. Torque is force for angular movement

@johnnyjoey1487 Год назад

As an engineer, I would never use kv to select a motor for a given application. You need torque and power (ideally a torque vs rpm curve graph). Kv is meaningless.

@FPVUniversity Год назад

yes it. Unfortunately in the RC world nobody provides torque and rpm to torque curve. And nobody really gets that. So KV plus size is just "good enough" approximation of a problem

@mattivirta 4 года назад

this not havev true, if you use too high kv=rpm motor you have cavitation, mean, motor run too fasdt and propeller run but plane not move anythink because propeller run too fast, same effect have at car, you run too fast you wheel run fast but car not move anythink. rpm must be ideal at peopeller, you need know what is propeller ideal and fasten rpm.

@manuelverdugo1737 3 года назад

EDF use aroun 30,000 rpm and up. 2000, 3000, 4000 kv is ok. But if in a rc plane, a very small propeller does not help. That is why after making the model and according to its characteristics, the propeller and rpm needed are determined, and then the engine is looked for to do the job.

@lozmoss9913 8 месяцев назад

😂 I'll stick to the black book 📖

@FPVUniversity 8 месяцев назад

all praise the black book ;)

@mattivirta 4 года назад

need show example, you need fly 4 motor max 400gram drone, what motor need be, and you fly drone weight have 30kg what motor, kv and propeller need be.examples please, i want understand what i need if i build drone what weight have 10kg or 30 kg. or 300 gram, about. i think build work drone to land. agricultural.or move to tool box home to workarea. or move pizza to home.

@manuelverdugo1737 3 года назад

aeromodelismoelectrico.blogspot.com/search/label/Multicoptero use translate included.

@arendmookhoek4314 5 лет назад

Meanwhile kababfpv is claiming higger kv doesnt influence torque lol

@FPVUniversity 5 лет назад

well, in theory it does not. But higher KV requires more amps for the same torque and more amps equals higher voltage sag and, voltage drop over the lines, overheating and even less efficiency than before

@arendmookhoek4314 5 лет назад

@@FPVUniversity yrah but all else being equal ots just so obviosu thatore speed means reduced torque, you think he knows how a gearbox works?

@FPVUniversity 5 лет назад

Electric motor is not a gearbox

@arendmookhoek4314 5 лет назад

@@FPVUniversity well yeah no shit, but ehrn comparing something sith higger speed and all else being equal, its obviously going to have less torque.

@fahrero793 Год назад

no, you need power -> P = M x n = F x r x n

@botkillerfpv4318 5 лет назад

🤯

@ianchan2624 3 года назад

hahaha

@harynian 2 года назад

I cant agree with you. Torque = amps * Kt = amps / KV. Formula is very simple. If you have 3000KV and 50A, with 6000KV you need 100A to achieve the same torque and max speed. 2 times more current, not 4 times.

@jzuidema 3 года назад

Did you just start your video on brushless motor KV rating misinformation, with a casting couch joke?

@neilchoh296 4 года назад

Another waste of time video. It still does not explain why KV is a lie. The title of your video is click bait. You did not fully explain everything either. You say drag is squared. But lift force from propellers are also squared. Again Ido find some of your videos informative but I'll be careful before clicking any future videos of yours as I don't like wasting my time on incomplete and inconclusive information.