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
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!
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.
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 RUclips. I've made a few videos myself and can definitely appreciate the time it takes. Thanks......
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. 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!
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...
Tom Reed, An electric motor will never spin any faster than the Kv value multiplied by the applied voltage. You do not ever have to worry about an electric motor over-speeding with no prop installed.
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....
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.
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!)
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.
Be careful running a motor without a prop, it can spin at too high an rpm for the ESC and jam it. And you won't get the magic smoke back inside when it comes out.
Tom Reed this is nonsense. Good esc will not jam like that. If it happens then esc is bad and should not be used with the given motor (it happens due to software bug in the esc that does not reduce rpm when it can no longer keep up with the motor)
It's not nonsense. I've designed and built BLDC motor controllers before, and the combination of the phase lag between the electrical and physical angle of the motor, and the finite amount of time that the interrupt handling routine takes to execute do indeed limit the maximum speed. In this situation, a poorly designed ESC may drive a phase at the wrong time, with no back EMF to work against, thus potentially exceeding the maximum current for the motor or ESC. It's not a software "bug", but rather poor implementation.
Actually it is a ESC design flaw, your program is in charge of the current output and frequency based on feedback. If the feedback is not in range you don't have the program increase the power you either have it maintained or drop it at a reasonable rate until it is with in range; a full power drop can produce back emf which is why you back off at a reasonable rate. Unless the motor itself is fried, it will catch up or slow down to the output; VFD's are pretty much the same thing except on a much larger scale. I have never seen a VFD drive or motor malfunction because it lost water to the pump which is the exact same as running these little motors without a prop; of course VFD's are $10k to $1,000,000 price range, they tend to spend a bit more time on the engineering side.
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.
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.
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.
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.
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!
Yes and no. Brushed motors use brushes to convert Dc to AC, after a fashion. A brushless motor needs a means to do the switching that the brushes do. An ESC is a misnomer because it's MORE than an electronic speed control. It does do that, but it also does the switching necessary for the motor to turn.
The number of "winds" of wire on the stator is a hint whether it is high or low KV. If there is extremely fine (small guage) wire on the stator, it will like have a lot of winds and be a low KV. Heavy guage wire (less winds) will be a high KV motor. so if you get a motor with a number like 35-48-10, 10 is the winds. It will have a higher KV than a 35-48-16 for example
Nice video and put in an understandable way. I didn't manage to find the video you were talking about for matching the props with the engines. Is it possible to provide me a link?
After a nearly 14 minute video, in a nutshell, kv is a motor's no-load RPM-per-volt rating. The number of RPM a motor will run at with one volt applied and no load on the motor. He could have told everyone that right away :) At 2 volts, the no-load RPM will be twice the kv, at 3 volts, three times, so on and so forth. So, a 1000kv motor at 7.4V (2 lipo cells ~1/2 charged) will run at 7400 RPM without a load on the shaft and the ESC at full throttle.
zann fox Generator constant is more accurate but few of us use it for RC applicationss. There's an offset due to the motor's windage & magnetic losses when used as a motor, but few of us use RC grade brushless motors as alternators. They're actually rather good for that! Assuming kv is a motor's unloaded rpm per volt is close enough for RC use.
Would it really be worth watching a 30s video where a guy just reads a definition from a text book. Yes it longer then it needs to be but it by design.
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.
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
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?
@RCModelReviews, did you ever put up the power video you said was coming next in this video?? I looked in your videos list and didn't see it. I'd *really* love to watch it.
Awesome videos and explanations. Been watching your vids for a while now, just only signed up with RUclips. 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.
Bruce, I've a couple questions. 1)Why 2 marks on the tape. That seems like it would give you 2x the rpm. 2)Does the thickness of your marker lines affect the accuracy of the RPM reading? I really enjoy the techy videos and all the excellent detail which I consider to be something very particular to your posts. Thank you for consistently making quality videos of this type and using language that all can understand. -Jim
GREAT VIDEO'S thanks , one thing I was wondering , on both the motors you looked at with the Tachometer , you used 2 markings. I would assume that 1 revolution was 1RPM if I did it. Obviously it is not and from the kV rating/RPM measurement the rpm is double that indicated (as I would assume using 1 mark) ?
Can’t say for sure, but perhaps there is a setting on the tach that allows you to set the number of “timing marks”? He did mention that this particular tack is often used with two and three bladed props. Just my guess. It may also be that he should have split the reading in half.
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 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
Hi Bruce!!! Love the videoes... I do have a question you didn't mention in this video... What about the number of poles?? what would be the most efficient for multirotor platforms...
BasementEngineer, good video, with some figures, even not precise to third digit, to provide useful guidance.You say that brushless AC can be used as generators, I suppose with a rectifier, condenser and voltage regulator downstream to get stable voltage. Dis I understand correctly?
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
Great video, thanks. Does that mean for instance if were using a 500kv motor with a 15 inch prop and then wanted to use a 16 inch prop efficiently you would be better off getting a motor with less than 500 kv?
Great video explained very well. Tell me though, what is the name of the device you used to adjust the speed of the motor and where did you find it? That would make balancing very easy as well
Hi there Bruce who makes the speed controller you are using in this informative demonstration? By the way after a mind numbing couple of late night knowledge quests I have found all that I need to know about motors.As a rank newcomer I just ordered a good cross section in the trainer range. I will do the tests myself :) Thanks
Thank s for a great and informative video, do you have any video explaining the relationship between brushless motors, selecting appropriate ESC's and batteries? This is something I am trying to understand in terms of matching the electronics on my planes.
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?!!!
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?
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?
nice explanation i was messing with those motors..and finally its clear. but still i have a question which is, how does the kv affect the mah of battery? i mean the flight time of a quad or plane?
A question for your next video (I apologize for jumping the gun): does field altitude (air density) affect prop selection? I live at 1500 feet ASL (about 460 meters). Denver Colorado - 5280 feet ASL (1600 meters) - is a 7 hour drive from my house. If I fly there, would I need to change props to avoid over revving the motor and overheating the battery?
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!
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.
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 RUclips. I've made a few videos myself and can definitely appreciate the time it takes. Thanks......
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. 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!
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...
After some years involved in small RCs, I now understand what KV means. Thanks Bruce!
The car gearing to KV rating on a motor finally made that clear for me. Thank you.
I know most of this stuff, but this series is still really enjoyable to watch. Looking forward to the next parts in the series. . .
Thanks for putting this series together. I have just recently started converting from glow and this is going to be a big help.
Clear and easy to follow .You and 360 painless are the best videos on u tube .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.
very interesting. Thank you for this video, subscribed and liked this is the only clear informational RC source on the internet.
Tom Reed,
An electric motor will never spin any faster than the Kv value multiplied by the applied voltage. You do not ever have to worry about an electric motor over-speeding with no prop installed.
I agree with Jon B. What a great teacher you are. Respectfully.
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.
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.
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....
Thanks a million for telling us what a KV stand for ..Regards from California
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.
You sir, are a great teacher!!! Very gifted teacher!!! Thanks!
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!)
Thanks for keeping it simple, I'm sure there's more to this subject and tons of variables.
Thank you. Simple, straightforward and amazing to a beginner. Keep it this way, thank you again :)
Great shop teacher! I feel like I'm back in technical school.
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.
Looking forward to the next video. Motor nomenclature has always had me befuddled.
Thanks for the very informative videos Bruce.
Thanks again Bruce for offering up such great essential information for so long!
Excellent job Bruce.
Many thanks for this well done video.
You've guided me from ignorance to knowledge !
I love it when you start looking for things... :D
Great vid as ever Bruce,looking forward to the follow up vid ,you explain it so well.All the best Jez
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.
Be careful running a motor without a prop, it can spin at too high an rpm for the ESC and jam it. And you won't get the magic smoke back inside when it comes out.
Only one smoke charge
Tom Reed this is nonsense. Good esc will not jam like that. If it happens then esc is bad and should not be used with the given motor (it happens due to software bug in the esc that does not reduce rpm when it can no longer keep up with the motor)
It's not nonsense. I've designed and built BLDC motor controllers before, and the combination of the phase lag between the electrical and physical angle of the motor, and the finite amount of time that the interrupt handling routine takes to execute do indeed limit the maximum speed. In this situation, a poorly designed ESC may drive a phase at the wrong time, with no back EMF to work against, thus potentially exceeding the maximum current for the motor or ESC. It's not a software "bug", but rather poor implementation.
let the magic smoke out.. watching too much AvE channel lol
Actually it is a ESC design flaw, your program is in charge of the current output and frequency based on feedback. If the feedback is not in range you don't have the program increase the power you either have it maintained or drop it at a reasonable rate until it is with in range; a full power drop can produce back emf which is why you back off at a reasonable rate. Unless the motor itself is fried, it will catch up or slow down to the output; VFD's are pretty much the same thing except on a much larger scale. I have never seen a VFD drive or motor malfunction because it lost water to the pump which is the exact same as running these little motors without a prop; of course VFD's are $10k to $1,000,000 price range, they tend to spend a bit more time on the engineering side.
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.
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.
Lol, I wish this vid was available 5 years ago :)
Thanks for sharing Bruce!
J
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.
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.
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.
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 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.
Brushless motors are 3 Phase DC, BLDC motors are not exactly the same as AC induction motors
Yes and no. Brushed motors use brushes to convert Dc to AC, after a fashion. A brushless motor needs a means to do the switching that the brushes do. An ESC is a misnomer because it's MORE than an electronic speed control. It does do that, but it also does the switching necessary for the motor to turn.
The number of "winds" of wire on the stator is a hint whether it is high or low KV. If there is extremely fine (small guage) wire on the stator, it will like have a lot of winds and be a low KV. Heavy guage wire (less winds) will be a high KV motor. so if you get a motor with a number like 35-48-10, 10 is the winds. It will have a higher KV than a 35-48-16 for example
I think you might find the opposite, less larger windings mean more current and more torque so lower KV
Nice video and put in an understandable way. I didn't manage to find the video you were talking about for matching the props with the engines. Is it possible to provide me a link?
Fantastic explanation by referring to gears in a car. Just made it instantly sink in for me.
BRAVO! Once again, informative and complete in (The King's) English. I always enjoy your videos. Keep up the fine work.
excellent video bruce!
After a nearly 14 minute video, in a nutshell, kv is a motor's no-load RPM-per-volt rating. The number of RPM a motor will run at with one volt applied and no load on the motor. He could have told everyone that right away :)
At 2 volts, the no-load RPM will be twice the kv, at 3 volts, three times, so on and so forth.
So, a 1000kv motor at 7.4V (2 lipo cells ~1/2 charged) will run at 7400 RPM without a load on the shaft and the ESC at full throttle.
+BasementEngineer No
Kv = "Generator Constant, Dynamo Constant"
astrobobb.com/electric_motor_handbook.pdf
zann fox Generator constant is more accurate but few of us use it for RC applicationss. There's an offset due to the motor's windage & magnetic losses when used as a motor, but few of us use RC grade brushless motors as alternators. They're actually rather good for that! Assuming kv is a motor's unloaded rpm per volt is close enough for RC use.
You're forgetting some people learn visually
I learned by touching the video
Would it really be worth watching a 30s video where a guy just reads a definition from a text book. Yes it longer then it needs to be but it by design.
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.
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
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?
This was so so informative. To the point. thank you.
@RCModelReviews, did you ever put up the power video you said was coming next in this video?? I looked in your videos list and didn't see it. I'd *really* love to watch it.
Thanks for sharing your wealth of knoledge with us and taking the time to simply explain so everyone understands i love your vidios
I really like this RC basics series!
Great video - so clear - thank a lot. BTW, did you make a video about choosing the right prop for e-motor?
thank you so much for these videos. you really helped us in preparing for SAE competition
Hi. A great explanation, thank you. Since kV is quoted at no-load how can I know what the rpm will be when a prop is fitted ? Regards John McClean
Awesome videos and explanations. Been watching your vids for a while now, just only signed up with RUclips. 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.
Bruce, I've a couple questions.
1)Why 2 marks on the tape. That seems like it would give you 2x the rpm.
2)Does the thickness of your marker lines affect the accuracy of the RPM reading?
I really enjoy the techy videos and all the excellent detail which I consider to be something very particular to your posts.
Thank you for consistently making quality videos of this type and using language that all can understand.
-Jim
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 !
@biggavdemille
That particular tachometer is designed for measuring the speed of "two or three blade props" It probably doesn't have a 1:1 option.
he had 2 marks on the tape,, I use this method all the time
larz0001 sorry I didn't read everything ignore last comment
Bruce, You mention the trial and error approach to motor/prop selection. Have you tried using Webocalc?
Finally this is explained, thank you! No to go find the prop video!
GREAT VIDEO'S thanks , one thing I was wondering , on both the motors you looked at with the Tachometer , you used 2 markings. I would assume that 1 revolution was 1RPM if I did it. Obviously it is not and from the kV rating/RPM measurement the rpm is double that indicated (as I would assume using 1 mark) ?
thats what im confused about too
Can’t say for sure, but perhaps there is a setting on the tach that allows you to set the number of “timing marks”? He did mention that this particular tack is often used with two and three bladed props.
Just my guess. It may also be that he should have split the reading in half.
Whats the device you have hooked to the power elimination module of the ESC with which you are actually controlling the speed?
Where to buy the speed controller that he shows at 4:32?
Crystal clear now thnx. Waiting for the next installment.
Thanks Bruce you answered a few questions,what was the device you used to replace the receiver ?? and where did u get it from??
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
Awesome video! Am really enjoying your newest stuff. Looking forward to more. Keep em coming! :)
HELP ME PLEASE! 4:32 where i can find this little speed controller? (little throttle manual regulation)
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
Great Work! Can you possibly post a link of the potentiometer you used?
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
Hi Bruce!!! Love the videoes... I do have a question you didn't mention in this video... What about the number of poles?? what would be the most efficient for multirotor platforms...
BasementEngineer, good video, with some figures, even not precise to third digit, to provide useful guidance.You say that brushless AC can be used as generators, I suppose with a rectifier, condenser and voltage regulator downstream to get stable voltage. Dis I understand correctly?
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
Awesome, thanks very much for clearing this up!
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.
Great video, thanks.
Does that mean for instance if were using a 500kv motor with a 15 inch prop and then wanted to use a 16 inch prop efficiently you would be better off getting a motor with less than 500 kv?
Great video explained very well. Tell me though, what is the name of the device you used to adjust the speed of the motor and where did you find it? That would make balancing very easy as well
Hi there Bruce who makes the speed controller you are using in this informative demonstration? By the way after a mind numbing couple of late night knowledge quests I have found all that I need to know about motors.As a rank newcomer I just ordered a good cross section in the trainer range. I will do the tests myself :) Thanks
Great video, keep up the good work. Am looking forward to the power video
Thank s for a great and informative video, do you have any video explaining the relationship between brushless motors, selecting appropriate ESC's and batteries? This is something I am trying to understand in terms of matching the electronics on my planes.
Thanks for the Vid! It has helped me to understand the basics. Top Job!
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?!!!
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?
I'm interested in that little controller with a knob, too. What exactly it is ? Where can I get one like that ?
Hi! What is the name of the manual controller you use to control the speed? Thanks!
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?
Hey!! Nice video, thanks. Can you tell me where you got the manual pulse generator for the ESC? I really like it compared to mine.
nice explanation i was messing with those motors..and finally its clear. but still i have a question which is, how does the kv affect the mah of battery? i mean the flight time of a quad or plane?
A question for your next video (I apologize for jumping the gun): does field altitude (air density) affect prop selection?
I live at 1500 feet ASL (about 460 meters). Denver Colorado - 5280 feet ASL (1600 meters) - is a 7 hour drive from my house. If I fly there, would I need to change props to avoid over revving the motor and overheating the battery?
hey where did you get that variable controller from? please advise. thanks. nice job
Great info ! Thank You. And the best is there were no baby's killed in the making of this lesson !
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?
receiver?
+Ryan Ellul Its a servo tester that is used in the video.