RC BASICS: What is KV?
ฝัง
- เผยแพร่เมื่อ 19 ม.ค. 2013
- When using electric motors to power RC model aircraft you'll often hear the term KV - so what is it?
In this video, I explain what KV is and how it can be used to calculate the RPMs of a motor when powered from a battery of a known voltage. I also demonstrate how to measure the KV of a motor when it is unknown -- although you can buy a KV meter which will do the job much more simply if you want.
I'm sorry that this video is a bit long -- I may re-edit it later and shorten it up a bit. - วิทยาศาสตร์และเทคโนโลยี
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
My uncle is machine engineer
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!
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.
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 TH-cam. I've made a few videos myself and can definitely appreciate the time it takes. Thanks......
Awesome, thanks very much for clearing this up!
Thank you. Simple, straightforward and amazing to a beginner. Keep it this way, thank you again :)
Thanks for keeping it simple, I'm sure there's more to this subject and tons of variables.
You sir, are a great teacher!!! Very gifted teacher!!! Thanks!
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.
I agree with Jon B. What a great teacher you are. Respectfully.
Thanks again Bruce for offering up such great essential information for so long!
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.
Thanks for putting this series together. I have just recently started converting from glow and this is going to be a big help.
The car gearing to KV rating on a motor finally made that clear for me. Thank you.
After some years involved in small RCs, I now understand what KV means. Thanks Bruce!
very interesting. Thank you for this video, subscribed and liked this is the only clear informational RC source on the internet.
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.
Thanks for the Vid! It has helped me to understand the basics. Top Job!
Thanks a million for telling us what a KV stand for ..Regards from California
Excellent video - many thanks for helping me to understand. We need more people like you to help newbies like myself.
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....
Many thanks for this well done video.
You've guided me from ignorance to knowledge !
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...
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!
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.
Thanks Bruce! I love this series, keep them coming.
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.
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.
Great vid as ever Bruce,looking forward to the follow up vid ,you explain it so well.All the best Jez
This was so so informative. To the point. thank you.
Ooooh.....nicely explained and continues to be a shinny forum of info for us new or somewhat new to the hobby. Much thanks.
Clear and easy to follow .You and 360 painless are the best videos on u tube .Thank you
I really like this RC basics series!
Great video, explanation and demonstration. Thank you.
thank you so much for these videos. you really helped us in preparing for SAE competition
I know most of this stuff, but this series is still really enjoyable to watch. Looking forward to the next parts in the series. . .
Lol, I wish this vid was available 5 years ago :)
Thanks for sharing Bruce!
J
Thank You ,great job very informative and easy to understand.
BRAVO! Once again, informative and complete in (The King's) English. I always enjoy your videos. Keep up the fine work.
Good stuff. Thanks for taking the time.
I love it when you start looking for things... :D
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.
Thank you!!! Best explanation I have seen!!!!
Thanks for the information. Very well explained.
That clarified everything. Thank you very much!
You're a genius. Another excellent video! Thanks.
What a bunch of great, entertaining and informative videos you have. I subb`ed as soon as I was done watching the first vid (explaining KV ratings).
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.
I've learned quite a lot from you and the videos always very enjoyable to watch. Hope you continue making more great videos. Thank you.
Awesome video! Am really enjoying your newest stuff. Looking forward to more. Keep em coming! :)
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!
Came here for the exact same reason.
Thanks for sharing your wealth of knoledge with us and taking the time to simply explain so everyone understands i love your vidios
Looking forward to the next video. Motor nomenclature has always had me befuddled.
Thanks for the very informative videos Bruce.
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 :)
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.
Great shop teacher! I feel like I'm back in technical school.
great and very easy to undrstand info bruce thanks for shreing
Great video, keep up the good work. Am looking forward to the power video
Great video thank you for taking the time to make it
great vid, awesome, I had no idea what kv meant. Thank you!
really instructive, NOW I UNDERSTAND KV !! thanks !
Thank you I'm quite new to this and your video really helped
Crystal clear now thnx. Waiting for the next installment.
Excellent job Bruce.
Excellent video, thank you very much.
Great video very informative!!!!
awesome video! I wish u could explain about thrust as well n how to choose the right motor for our model n how to match it with ESC n battery
Brilliant! Thank you Bruce!!!
Finally this is explained, thank you! No to go find the prop video!
Awesome videos and explanations. Been watching your vids for a while now, just only signed up with TH-cam. And fairly new to the quad scene, been an electric off road car hobbyist for years. Hopefully you have your "wings" back by now officially.
Very coool ! Good explaining.
Well done! Makes it easier to understand for sure!
How about a vid on ESC TIMING ISSUES AND MULTICOPTER ESC TIMING
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.
Great videos!
Btw, can you tell me where did you get that little speed control that connects to the ESC? I need one just like it! Thanks !
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.
+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
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.
Good detailed videos sir, subbed.
Great video! Can't believe I am just now finding your channel...I have only myself to blame :(
Thanks for all the info!
Great vid , thanks Bruce.
When you do your power vid will this also include "timing", I comprehend what this does but have difficulty in explaining.
The question arose on the RCMR forum but my explanation was anything but helpful.
thank you very much.....no words to say you are simply awesome....
These are great videos!
thanks for that. very useful. keep up the good work
Amazing video .
very helpful. thanks mate. :-)
Thank you. Nice and clear
Tanks for sharing, greetings from Mexico.
core blimmy rating. these videos ill become the core literacy for the general population. i love learning what would have facinated Tesla and Edison in the USA as AC and DC dueled out for supremicy. well done bruce.
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!)
Very helpful thanks! 👍🏽
Thanks again, Bruce!
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.
Thanks a million for this!
Thank you for a great presentation. Its very helpful to actually understand this as I am new to flying Quad copters and currently using brushed motors in low cost quads. Ive been considering converting a Syma X8C to brushless motors and now I better understand the theory of operation. For the X8C what KV motor rating would you recommend? As you have the 40 yrs in this and can make the best estimation off the top of your head. My 40 yrs experience is in Mercedes Benz and BMW cars. Thanks again!
I understand you are a very good teacher.
Outstanding, Thank you
Love your reviews my English friend!
Bruce, great video as always.
Can you please do a video explaining the effect of pole count and star vs delta windings on output RPM and torque
Excellent as usual!!
Bruce:
Thanks for explaining this and I am waiting for the rest of the videos. I hope you can explain the number of wraps on each pole and how the number of poles effects the power and or rpm.
Thanks again.
Don
Very nice explanation thank you sir
Hi, great video! I'm just wondering what "speed controller" you are using in this video? and where can you buy this simple turn-dial variable speed control? Thanks. Dave.
I had the same question.
I think I found this... It looks like it is just a servo tester... Like:
www.hobbyking.com/hobbyking/store/__17143__Simple_Servo_Tester.html
but I think this one looks better:
www.hobbyking.com/hobbyking/store/__8296__Turnigy_Servo_Tester.html
Very helpful thanks!
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.