RC BASICS: What is KV?

[@scottmarshall6766]

I'm an electrical engineer who has worked with all sorts of industrial variable frequency drives, Pwm limited stepper motor controllers, 90 and 180vdc DC speed controls etc. for nearly 40 years. I've been baffled by all the techno-babble garbage supposed experts have been pouring onto helpless RC builders who don't know what to think. The RC forums are full of "experts" expounding on meaningless formulas which are either mis-applied or totally ficticious. It's infuriating, but I, being a gentleman, have resisted the temptation to point this out to any of them (so far). THANK YOU FOR CUTTING THROUGH THE BS!! You are the 1st person I've seen who really knows what they are talking about. Great demo and explanation! This video should be required reading for anyone buying a motor. Well done sir. Best wishes for your continued sucess. Scott Marshall Elbridge NY USA

[@technicpiledriver7732]

My uncle is machine engineer

[@jonbbaca5580]

There is no way you're getting paid for how much useful knowledge you're providing to the modern RC community. I guarantee your videos and explanations have helped SO Many modern component manufacturers to figure out how to design and build their products thatve changed the whole game in RC flight. You're like the Wikipedia for RC model designers and production companies. You're like the printed Encyclopedia for the newer generation to reference and design their next generation RC products. Without ppl like you, our generation of engineers would be totally clueless. Thanks for your service of distilling a generation of electronics and RC knowledge for us to use!

[@MidwestRob]

I learn something new every time I watch one of your videos. You explain everything in a way that is very easy to understand. Thank you for your extraordinary contribution to this hobby.

[@richardt1]

What a helpful video! I hope you still read these older comments. I'm in the U.S. when I was a kid, in th 50's, we used to have a tv program called Mr. Wizard. He would explain concepts in a similar manner. He would place it in real world applications, explain the instruments and tools, and provide great visual examples. Unlike some, when it comes to electronics I am dumb as dog food. I know how to google formulas but it's the understanding and application to RC that's the hard part. Your series is right on target for a newbie who wants to understand these things as they are used in his hobby. Please keep up the great work. You bring value. Richard t.

[@gregmcdonald5986]

I just wanted to take a moment to say Thank You for the educational videos. I'm just getting back into RC after last flying glow plug engines some 30 years ago. To say things have changed would be an understatement, to say the least. There is no local flying club so the only education I get is from a few select forums and KZbin. I've made a few videos myself and can definitely appreciate the time it takes. Thanks......

[@RaduB.]

Hello again! For some reason (...) I decided to watch all your videos chronologically. So your trade is electronics 🙂. That explains a lot... Thanks for posting! And on we go... we are still way back in the past...

[@chiro30]

Ooooh.....nicely explained and continues to be a shinny forum of info for us new or somewhat new to the hobby. Much thanks.

[@iandavis6742]

Clear and easy to follow .You and 360 painless are the best videos on u tube .Thank you

[@peterlution]

Thanks, Bruce. In order to stabilize the tachometer reading, you should avoid florescent lighting. I use an LED flashlight to override the noise from ambient lights.

[@SC-lm1dt]

After some years involved in small RCs, I now understand what KV means. Thanks Bruce!

[@agentbertram4769]

Thanks Bruce. When I was a commissioning engineer on Shell Stanlow oil refinery, a 6.6kV motor was the size of a Ford Transit van. You'd never get one to fly or if you did, you'd need one big battery and an inverter from the planet Krypton. So it's revs/minute/Volt (ish). Brilliant!

[@NicholasMorganUSA]

I know most of this stuff, but this series is still really enjoyable to watch. Looking forward to the next parts in the series. . .

[@rtonce]

The car gearing to KV rating on a motor finally made that clear for me. Thank you.

[@pufferfish0567]

Thanks for putting this series together. I have just recently started converting from glow and this is going to be a big help.

[@seattleman6297]

very interesting. Thank you for this video, subscribed and liked this is the only clear informational RC source on the internet.

[@siematumichu]

Hello i have got question. I am building an rc airplane. it is not too smal cuz it have about 1,2 m long and 0,9+0,9 wings long. what kind of motor should i use?? how much KV? ( i want to use only one motor)

[@jj01a]

I love your channel, thank you for the time you invest in sharing. You do a wonderful job of explaining complex topics, it's a gift.

[@baklazanivanovich7566]

HELP ME PLEASE! 4:32 where i can find this little speed controller? (little throttle manual regulation)

[@henri-julienchartrand3387]

I agree with Jon B. What a great teacher you are. Respectfully.

[@mohamedsheikh2502]

Thanks a million for telling us what a KV stand for ..Regards from California

[@Just_Jeff_Tunes]

These are incredible helpful! Please keep going! I'm going to share these around to make sure that people just starting like me get your awesome help.

[@StonyRC]

Excellent video - many thanks for helping me to understand. We need more people like you to help newbies like myself.

[@xnoreq]

Kv is the reciprocal of the back-emf constant. A 500 Kv motor will generate a 1 V back-emf when the motor is rotating at 500 RPM. At 3700 RPM that motor will generate 7.4 V. Applying it the other way around ("7.4V will make the motor rotate at 3700 RPM") is only an approximation and technically wrong. This video is actually full of misinformation because RCModelReviews relies on the latter understanding of Kv which is wrong. The motor RPM is NOT calculated by V*Kv. The actual RPM = (V - R*Io) * Kv = (Voltage - Motor Resistance * No Load Current) * Kv. So given the above motor with R=0.5, Io=1, we get 3450 RPM at 7.4V. Also, Kv tells you nothing about how powerful or efficient the motor is. That's another point where RCModelReviews is wrong. High Kv does not mean the motor has low power. You can get high Kv motors with higher power than low Kv motors....

[@ScottGinn]

Hey jfan4reva! I am down here in Colorado Springs, and you do in fact have to go larger in prop to compensate for air density. I end up just going a prop size larger or pitch depending on the model type. Having too small of a prop will not "over rev" a brushless motor as you see by the bench test, it maxes out and that is it. Running a small prop means less wattage.. that simple. Just keep your manufacturers specs in mind and match a prop accordingly (which I am sure we will see next!)

[@moonchildoforcamoon6272]

I noticed you say "Rule of thumb" a fair bit. For those who do not realize this term was coined in the before time when people would brew beer and without thermometers would use there sensitive thumb to test if the temperature was right to add the yeast for the fermentation process hence rule of thumb. Great channel, I always thought of Kv as Kilo volts also before watching this :)

[@vertigo6982]

In the movie Boondock Saints a huge man-hating feminist lesbian pointed out that saying meant back in the medieval times or earlier a man was legally able to beat his wife with a stick no bigger than his thumb. One of the Irish twin brothers who are the lead characters who was training the huge woman with on-the-job training in some meat warehouse then jokingly replies( knowing the woman hates men by the "Never touched by man" tattoo under her chin) , "Rule of thumb? Well what's that gonna do? Perhaps it shouldve been rule of wrist?". Which of course led to a fight where the boys convinced the woman to keep her comments to herself with a right hook to her chin. Damn good movie.

[@SergioNayar]

You sir, are a great teacher!!! Very gifted teacher!!! Thanks!

[@martienl]

Where to buy the speed controller that he shows at 4:32?

[@MrGpse]

Thanks Bruce, this video has been more informative than the past dozen hobby shops in my area. Looking forward to pt. 3 of the XG8 review.

[@wendtb]

For all those wondering what was used to control the esc it was a servo tester. Bruce, when an engine specs would say 600w for an engine on 3s so 54 amps is it safely able to increase power through voltage instead of current? Such as a 4s battery running 50amps?

[@DobyxRC]

Thanks for keeping it simple, I'm sure there's more to this subject and tons of variables.

[@catamaranman333]

Thanks again Bruce for offering up such great essential information for so long!

[@oldiron1223]

Big thanks Bruce! My background is in radar and I couldn't understand why a tiny motor would need several hundred to thousands of KV (kilovolts) to run and how that voltage was being developed off such tiny batteries. RPM X 1K per volt makes a lot more sense.

[@dhirendra876]

Whats the device you have hooked to the power elimination module of the ESC with which you are actually controlling the speed?

[@samacumen]

Thank you. Simple, straightforward and amazing to a beginner. Keep it this way, thank you again :)

[@sonickalbright]

What is the little controller board connected to the ESC?

[@Torcika]

hello I'm looking to build a model for a project.Problem is,the project I'm trying to do implies an empty motor shaft.Do you know if there are any such models of motors or if I can let's say drill inside the shaft myself,without causing major structural damage.I haven't had any luck searching for similar projects on google

[@nisalanadeera3881]

I can't figure how may I calculate motor A. I got thr motor n looking for how many A's can use that motor. bt didn't have anything about A. please help me to figure that.

[@TilmanBaumann]

Great series. I hope in the end you can make a guide on how to select a powertrain for any model. Like, how does it fit together, how can I apply all those basics to buy the right motor/prop/ESC/battery the first time round for a new model. I tend to go with, what did others use for similar planes or what does the ARF version use. But I never feel like I know really why this combination is right. I just improvise.

[@PugetSoundFlyer]

Many thanks for this well done video. You've guided me from ignorance to knowledge !

[@pyrexia2]

Great vid as ever Bruce,looking forward to the follow up vid ,you explain it so well.All the best Jez

[@MrDieseltwitch]

where can i get one of those esc manual controllers? I want to be able to test motors without hooking up all the radio gear.

[@ElPePe10300]

so for multi-rotor world...if im trying to carry a payload and not too worried about speed, i need to use low KV motor with larger prop and if i want to do FPV flying which i need speed, i need to use higher KV with smaller props...do i have this correct?

[@wnleon]

Great introduction to KV. Sure it will set off the EE guys, but this is a very practical explanation that is clear and easy to follow. Good job.

[@glenkisela8550]

CAN I put a Brushless Motor in a v262 Quad? and what do I need to install them??

[@RGCbaseace]

Hello bruce i have a question what motor/prop would give me the longest flight and lift the most based on a 650 quad frame(hk predator) 3-4 s lipos5000mah using simonk flashed 30 amp escs

[@deltajegga]

what size prop would you run on a dt700 for a tricopter?

[@LordKaos666]

Hi! What is the name of the manual controller you use to control the speed? Thanks!

[@0917bobb]

Excellent job Bruce.

[@TheCorvairGuy]

Does a speed controller only supply power that the motor requires?

[@davidrotor]

ive got a question how do i know how much thrust the motor delivers if i know the KV?

[@Cyberdactyl]

Looking forward to the next video. Motor nomenclature has always had me befuddled. Thanks for the very informative videos Bruce.

[@yetanotherproject-ce2nm]

Great shop teacher! I feel like I'm back in technical school.

[@LordKaos666]

What is the name of the analog variator you´re using connected to the ESC? Thanks!

[@michaelgrossman5528]

Thanks for sharing your wealth of knoledge with us and taking the time to simply explain so everyone understands i love your vidios

[@tomaswolsink7620]

Hi i have a question some of those outrunner motors believe to have more then 1500 watt of power is that a peak current ore continious power?

[@chuckbear1961]

Where do you get the speed controller with the knob?

[@shannonlaramie8712]

Whats do you call the speed controller unit that you plug the ESC into to adjust the speed for testing?

[@superdau]

Servo tester.

[@shannonlaramie8712]

Thank You!

[@Rcd872]

I’m an rc car enthusiast. 3 years ago I made the switch to battery and these small dc motors. I’m trying to learn the theory, terminology and practical from using chemicals to generate electricity (to more clearly understand the battery) to the use of electromagnetically spinning a rotor to power my rc trucks. Please continue your series and do you have a book you could recommend to a beginner to teach the basics. Thanks

[@pvantuel]

Thanks Bruce. I've been flying for donkey years, but never understood the motor sizes... This video is very helpful. I'm looking forward to your next video about props in relation to motors. Cheers.

[@sas2dj]

Is it possible to mix different kv motors? For instance for a hexacopter, 2x 950 kv and 4x 1000 kv. 0r the other way around: 4x 950 kv and 2x 1000 kv

[@HowtoStopMice]

Could you please tell me "what is that device that is plugged into where the receiver goes that has the adjustable knob on it?"

[@WeTrudgeOn]

+Mitch Livingston You can buy a digital servo tester, typically used to test that servos are running the right direction, they will also work for testing motors all you need are the signal and ground wire from the ESC, They typically need a 6 volt battery or wall wart DC power supply then you just plug the ESC leads into the other end, the pins will generally be marked with a +, - and a squiggly line you just plug in the - and the squiggly line from the esc and away you go.

[@HowtoStopMice]

+fabricator Thank you very much for taking time out of your day to answer my question!

[@WeTrudgeOn]

No problem.

[@bernhardlehder]

Hello, Can you please tell me what are you using to control the ESC, yes its a potentiometer but there is more to it then just that. I would like to buy one for myself, if anyone can please tell me. Many thanks

[@davemarshallmusic]

Bernhard Lehder what he’s using is a servo tester. They’re very affordable. Here is the one I use: www.banggood.com/Wholesale-EK2-0907-Updated-Version-Servo-Tester-Server-Electronic-Speed-Controller-p-66240.html - just be careful hooking up the battery, you can use the balance plug on a multi cell lipo to power it up but you only want 1 cell. Or use a receiver battery pack for gas planes. Hope this helps!

[@alexandrugroza839]

Does the Esc amperage need to be bigger or lower than the batterys amps. ? If i have an instalation that require 60A , 60/4 =15A about an 20A Esc will work but the battery amperage need to be bigger or lower than 20A Required per motor ? The battery will need 60000mAh or the mAh multiplyed by C rate need to be 60A?

[@ralphd204]

Hi, I run a 9,000 kV brushless motor with 2 cell lipo on my Tiny whoop and get around 3.5 mins of acro flight time (4.5 mins if cruising). How do you think would swapping it with a slightly higher kV motor, let's say 12,000kV, theoretically affect the flight time and acro performance of my tiny whoop? Thanks in advance!

[@stukingman6438]

BRAVO! Once again, informative and complete in (The King's) English. I always enjoy your videos. Keep up the fine work.

[@laharl2k]

but wouldn't upping the voltage saturate the motor's core? or are they prepared so that they can withstand a little overload for a short period? Because i cant see the rpms having a linear relation to the voltage :(

[@dipeshshrestha1895]

what is the minimum kv required by any models for it to be flown and can the motors from radios , computers has that ability ?

[@etopsflight]

any brand/part number for the speed controller used in the video to change the speed of the motor?

[@jpsalis]

I've heard the tearn inrunner motor a few times from hobbyking... what is the difference between an inrunner and an outrunner? also what advantages could an inrunner have over an outrunner?

[@MsSomeonenew]

Out/In runner only means which part is moving, the outer shell or the inner shaft.

[@stavart13]

how do work out how many amps a 21.5t/1600kv motor will need? This is for choosing an ESC/battery etc.

[@TomReed95]

You cant work out the current draw using only the kv. It is a function of the load on the motor and the voltage you run.

[@bbab9051]

i know its an old video but I just started to learn and have a question please I would really appreciate if I can get the answer one of the motors in my drone burned and I can not find the exact same size with exact same kv, the closest motor I can find is same size but slightly different in kv, I would love to be just change that motor so I'll be able to fly my drone again, is there any chance I can use one motor with 3600 kv and 3 motors at 3800 kv but both same size in one drone ? thanks alot

[@mikemike457]

I have 80/100 130kv outrunner knead to know what esc to get if you can help me pls thanks

[@martinwhitehurst9893]

Hey i have a question i hope you can help me with please...... i want to take everything out of a cheap RC tractor and put all components in a Custom one im trying to build..... Can i use another remote and how would i do that???

[@eirenwhelan3312]

Would it be possible to use two different motors for something like an electric skateboard? As an example, 130kv for torque and 220kv for speed? Would you need a slipper on the lower kv motor for when the speed goes over it’s limit? Thanks

[@ADVscooter]

I really like this RC basics series!

[@piyushmahajan5867]

which instruments are used in this video?

[@fluttershy77x]

I want to build an 900 mm EPP wing and was looking for motor options. It is suggested to use a 2822 1450 kv motor. Though, when I look at these motors, their thrust seems very low, even with big props, compared to the 2205 or 2206 motors used for quads. I'm now wondering: what is the benefit of using a large motor, with low kv, which has not very much thrust?

[@johnconrad5487]

what do the signals to the motor and the servos look like? are they just varying DC levels or pwm or what?Thanks

[@samadvanes8711]

I love it when you start looking for things... :D

[@pyramid360]

thank you so much for these videos. you really helped us in preparing for SAE competition

[@MagicSteve46]

can you explain how watts relates to voltage and amps?

[@reeceengineering]

Seems like to increase EDF jet efficiency I would want to pair a low KV motor with a high # of blades that use an aggressive pitch angle. This should allow the plane to hit significant speeds at a lower rpm. Is this correct?

[@travispratt6327]

I'm still trying to figure these types of questions out, I believe the defining factor is propeller stall, if you go too high of a pitch for your model your propeller will be stalled for too much of the flight envelope, so with too high a pitch you'll be very innefeciant at low airspeeds. I think this is a safe assumption but I'm still learning myself so could be off here. Also the answer I always get when asking a similar question is "it depends on the model" but no one has fully explained why. Hard to research this stuff cause it's hard to know exactly what you need to learn.

[@reeceengineering]

Travis Pratt A motor will be most efficient at a given rpm. Say with the given pitch of blades and # of blades that rpm would push an F16 (or similar plane) to 60mph. Well if you put that same motor in something shaped like a B57 Canberra then that same peak efficiency motor RPM would have the plane going much slower, and this would lead to a higher amp load on the aircraft with more drag. Hence the "depends on the model" its drag/power ratio. As you mentioned the low KV motor and high pitch blades would require a higher minimum speed. Thats what im after. High speed efficiency. Im theorizing that running the same Jet on a higher KV motor, (requiring lower pitch blades and higher rpm at the same speeds) would net more drag because friction gets exponentially worse with rpm.

[@travispratt6327]

Its rpm that determines motor efficiency? Will rpm always be the same for a given watt draw with the same motor?

[@reeceengineering]

Travis Pratt I am unsure if rpm nets efficiency as it does in Airsoft. The rpm should be the same at a given wattage, if the plane is doing the same thing at that given time. Climbing vertical will hit a higher wattage at the same rpm than level flight

[@MattNicassio]

I went through your WHOLE video history but never found anything about Prop size or 2 vs 3 blade or how to pick a prop for a motor, or a motor for a specific mm size quad. Your videos are the best on YT for RC, but have you done a follow up for your RC Basics series on motors / KV / ESC's - you mentioned next would be about props and how to combine it all? I'm interested for QuadCopters mostly but fixed wing is something that will interest me in the future certainly.

[@jchtr3ac]

Thanks Bruce. That cleared up a lot of my questions. The analogy you did with the car gears brought it into focus for me very well. I get it! Cheers.

[@DrBleck35]

Thank you very much for clarifying the KV vs. kV thing. I used to work with high voltage stuff and the term "KV" used to confuse the heck out of me. Not any more, thanks to you.

[@BenjaminEsposti]

+DrBleck35 They should have used "KRV" ... then again, as you say you used to work with high voltage stuff, I'm guessing it was something to do with power distribution? Then you'd probably confuse "KRV" with "kvar" XD

[@DrBleck35]

Nope about power distribution. Capillary Electrophoresis. Also, "KRV" would always remind of the time I met Stevie Ray Vaughn's illegitimate (and fictitious) brother Kevin.

[@CrucialStuff]

Just for you'r info. Your video helped me to learn even throught i'm not interested in RC and more on building a electrical skateboard! Greetings from Spain!

[@chrisvanhouten6348]

Came here for the exact same reason.

[@DusanHlavaty]

I'm interested in that little controller with a knob, too. What exactly it is ? Where can I get one like that ?

[@Tijdperkzuid]

Hi, What kind of esc did u use? with the potentio on it.

[@ExperimentalPlasma]

I am a electrical engineering student ...I am longing to know how the direction of rotation of motor in remote control car changes...plz help me...

[@gambulgambula]

Hi Iam just asking if I can modify the hard drive motor to work on rc plane? Theoratically I find more topics on the web but no vedios showing that.

[@ChrisBlackburn]

what's that little device you used to control the speed controller? I get fed up of ripping my RX out of my planes in order to test new motors using my 9x

[@MarkoKukovec]

I always thought that speed of the BLDC motor is defined by the ESC by how fast it changes between the energizing coils. So always with full nominal voltage. Like speedy stepper motor. So what has number of windings has to do with speed except it affects torque?

[@MrEzplay]

What kind of connector do use the most, banana plug, deans, Ec3 or hobby kings....??? Im kind of confused, Can you help? You are very helpful

[@sicroly]

Sir Bruce !! i would like to know what do you call that controller from ? dopes hobby king sell it ? what's it called ? advise advise... thanks !!

[@unitedforhelp]

Great video, can someone let me know what is the small device called or the model name of that thing which is controlling the speed fed to the ESC?

[@EthanHeffernan]

receiver?

[@jpstroebel7253]

+Ryan Ellul Its a servo tester that is used in the video.

[@guloguloguy]

ARE THERE ANY GOOD REFERENCE BOOKS, ETC., TO HELP IN SELECTING R/C ELECTRIC MOTORS, FOR VARIOUS MODEL PARAMETERS,... OR, ON HOW TO TRANSLATE/COMPARE SMALL FUELED ENGINES (BY DISPLACEMENT SIZE), TO THE EQUIVALENT ELECTRIC MOTOR SIZE?!!!

[@ronwatt1042]

Please advise what small device (has a grey/red knob) are you using to vary the motor speed thru the ESC. Regards, Ron

[@ronwatt1042]

Discovered device is a servo tester. Can you advise brand and model type that you used? Thanks, Ron

[@travispratt6327]

I'm still having a hard time figuring out how the winding affects motor power and efficiency with a direct drive propeller. It seems with the same motor if you go up in kv you get more watts at a higher efficiency, which means in any application going for the highest kv motor then adjusting prop size and pitch seems to be the best use of the motor. Am I wrong? What would be the point of choosing a lower kv winding of the same motor instead of a higher kv and lower pitch to get your torque?

[@yorkie478]

can one use a brushless set up with 35 mhz radio ie esc etc

[@maaz.uae6738]

hi thank you for this clip. i want to know what type of speed control for switch on and off in this clip

[@it-diagnostyka859]

which motor you recommend for replacement after the original disaster in parrot disco ?