Brushless motor theory 01 - KV and torque efficiency

Рет қаралды 137,855

SiieeFPV

Күн бұрын

Trying to digest in a very simple form theoretical aspects of brushless motor design.

Пікірлер: 136

@onlyme3543 3 жыл бұрын

Wow this stuff is like looking for the holy grail for dummies! Thank you I’ve been searching for like forever as to why, how many turns and thickness of copper for a pancake motor! And you answered a few of my questions with this vid!

@AC-hs1sj 3 жыл бұрын

Such a shame that there isn't more in this series; so well done!

@Soaringsax 6 жыл бұрын

First? Great videos! It’s great to see the science behind all the ‘it just feels smooth’ comments about motor.

@Jrod_FPV 6 жыл бұрын

Kyle Jones from what I can tell, smooth is a fake marketing term used that means absolutely nothing. People use it when trying to promote a motor but don't have anything scientific to say. Probably invented by kabob fpv. 😄

@art.alagna.design 2 жыл бұрын

...and secondly?

@fred2108 Жыл бұрын

Brilliant just what I was looking for, many thanks 👍

@collin5353 6 жыл бұрын

This is super informational, but now I think I'm more confused XD

@joshuanorris5860 6 жыл бұрын

The Schire FPV hahaha answered a bunch of questions that just brought up even more.

@joshuanorris5860 6 жыл бұрын

Im trying to build my new heli for max flight times and smoothness. Its freaking hard as shit to pick out the right motor that will be efficient but not too much power draw overall!!!

@chrispewpew 6 жыл бұрын

A great teacher takes you to the next step in the learning process. Your algebra teacher probably wont teach you differential equations, other than rare occasions, LOL

@daviddavids2884 5 жыл бұрын

you should be. there is WONKINESS here. see my comment.

@albenpino2238 3 жыл бұрын

Lol omg just lol just same i thought xd

@popwall4297 4 жыл бұрын

on my brushed motors I have actually reduce the windings to get more RPM out of some of my Motors when I first started doing this I roasted a couple Motors took too much wire off the poles then I started using a bigger wire and less turns and came up with a pretty good motor the motors that burn up ran super fast for just a few minutes then went up and smoke but boy were they fast

@TheKlickitat 3 жыл бұрын

WOW!!! This is the best video on the topic that I have found. I instantly subscribed and I am headed to your portal and looking for more. I am only hoping there is a lot MORE.

@lukaspfitscher8737 3 жыл бұрын

I lerned it the hard way bought two motor one is 230kv one is 50kv, ends up the 230kv motor has more torque and more power consumtion, realy nice video helpt me a lot 👍

@kiley1672 4 жыл бұрын

Given Faraday's law, how could more windings decrease the back emf?

@trapsarentgay4195 2 жыл бұрын

Magic

@Kabab 5 жыл бұрын

How the hell have I not stumbled onto your channel in all this time? Fantastic explanations. Please do one on voltage and how it relates to torque. I've not got much to go on in that department. Haven't done enough research but based on real world flying I'd say as the voltage goes up and current drops for the same power output, torque goes down proportionally with the current....the math mostly supports all that but I don't know why conceptually which means I dunno anything...

@pauliman1098 5 жыл бұрын

That's THIS video Bob ;p

@Kabab 5 жыл бұрын

@@pauliman1098 yeah I watched it a few more times and got it. I'm not sure if I'm more enlightened or confused after getting it.

@pauliman1098 5 жыл бұрын

I literally just did the same thing and it's kind of clicking lmao

@daviddavids2884 5 жыл бұрын

you should FORGET everything that was said here. there were TOO MANY ERRORS in this video.

@jonbigman9723 6 жыл бұрын

Actually the resistance is not related for the most part. The more turns the coil has the less current goes through due to cemf, self inductance is also related. This is due to a rule that a coil as you put more turns on, it resists *any* change in current more efficiently(same thing that happens in a choke, it is also a fact that as you add more turns the voltage out of the coil goes up, if the current gets choked it forces the voltage up. The coil also has a core which amplifies the reluctance of current change in the coil as it concentrates the magnetic field. If you take the wire out of the pole and measured the resistance of the wire straitened out it wouldn't be very much. anyways the resistance actually is only related to the heat made while current goes through the wire. Current might be lowered but only a fraction of what you are suggesting. For the most part cemf and self inductance chokes the current and raises the voltage out as a result.

@Powerpickle68 5 жыл бұрын

What you described is something that takes place in a generator application which means there is a voltage and amperage output. That is not how an electric motor operates.

@TheTechnicalTraders 4 жыл бұрын

Question on Motor Poles and current need help understanding please! Given the same motor dimensions, kv, volts, and propeller/wheel how does the number of poles affect the amps/current under load. one motor has 6 poles, the other motor has 10 poles. how would the 10 pole perform? smoother rotation? more torque for sure, but would it draw fewer Amps with same load and RPM as it does not need to work as hard?

@SiieeFPV 4 жыл бұрын

more poles gives you more torque and lower speed for the same ERPM. Smoothness is more of a function of tooth design than pole count. I haven't looked a lot into the pole count side of things since most motors as small as what I work with all come in the same count.

@ChiefRickyRC 3 жыл бұрын

So a higher kv motor of same size, just different kv values will have more torque then the lower kv motor on equal voltage and current? Or it only changes the rpm, which is the cause of more power? I'll watch the video now, but I've been trying to find the simple answer

@sneakyfpv8914 2 жыл бұрын

So, at the same KV, the bigger the wire mean more torque than smaller wire??

@michaelinzitari 3 жыл бұрын

Going by this, when a manufacturer releases a new motor, they all have the same torque for a given can size. Wow who would have thought

@nikleiser5888 8 ай бұрын

Is it possible to estimate the number of Poles (4), Size (3656) and KV (4000) ? Cheers (from freezing cold Germany) Nik

@cesitli5615 2 жыл бұрын

A 3 phase brushless motor has the following values. The maximum current drawn from the battery is 4.62 amps.. The thrust is 4025 grams with a three-bladed fan 18 * 8.. The speed at the maximum lifting force is 2780 rpm. The battery voltage is 23.46 volts. How much is the output power? How much is the efficiency?

@jandonker3587 4 жыл бұрын

This is incorrect. A motor acts more like a transformer than like a resistor, which is like you present it. It is not the resistance that limits the current. Resistance is a factor in the motor-losses, which limits its power. But the core has losses as well, i.e. magnetic losses. These losses are 2 times bigger than resistive losses. So the core limits the max torque, but it also limits the speed, as core-losses increase with frequency. Third factor are the mechanical losses in the bearings and in the air that's moving inside the motor-housing. The thruth is : the faster you want to fly, the shorter the life of the motor will be and the more you pay for high-tech materials.

@dimtass 4 жыл бұрын

Indeed. I guess the motor equivalent circuit is too complex to explain and it's sometimes better to simplify the explanation by referring to the equivalent impedance. On the other hand, it's quite common for hobbyists to get confused with impedance and resistance, but still it's the more simple way to explain motor losses.

@rangkara7201 3 жыл бұрын

this should be pinned

@youeladamas7840 6 жыл бұрын

nice you explain it very well I'm winding motors and you hit the nail on the head Mr Miyagi style. You should go in to materials used like silver coated vs copper if you have data lamination sizes ceramic vs steel bearing all the details. I think we should go back to self tuning motors though its harder matching 4 for kwads. also do you oil motors before test if not could you do test to see if it helps overall efficiency/power

@SiieeFPV 6 жыл бұрын

I don't think my stand is sensitive enough to pick out differences in bearings and oil above the noise. That might show up better if I had a way to characterize the vibration of the running motor, but I haven't built that kind of test rig yet.

@superdon1chw Жыл бұрын

All right so I think your saying KV 850 and 2200 has the same performance ?

@alexandrugroza839 4 жыл бұрын

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?

@philippelevesque9845 4 жыл бұрын

Thanks man, really appreciate your video.

@mybluebelly 4 жыл бұрын

Magnetos ftw !

@tomcypher3864 3 жыл бұрын

You forgot to mention, that with lower kV the max torque is achieved at lower power draw.

@avecforte8851 4 жыл бұрын

Great video

@siyahgercek 4 жыл бұрын

If we cut the wire diameter in half and double the number of turns, do we get the same torque? If we do so, wouldn't it be less to withstand high currents since the wire is thin compared to thick wire?

@mytehmvtchannel2337 4 жыл бұрын

Then, less kV is needed for generating enough electricity, right ?

@luongmaihunggia 4 жыл бұрын

Yes

@abhishekpavani1779 5 жыл бұрын

Hey This was unlike any other video explaining the same topic. Great job! Can you please share some references here so that I can look into the matter in much more detail. Any useful links on the subject would be superhelpful. Thanks! P.S I immediately subscribed after watching just this 1 video! Great stuff

@SiieeFPV 5 жыл бұрын

Look up some of the books by Dr. Duane Hanselman, they're a great place to start

@xXBallsackGamingXx 6 жыл бұрын

Im looking for a quite fast combo but i am wondering if i should go with a 3500kv or 2950kv. Because i want about 50mph but since i have a buggy i also need decent to good torque.

@SiieeFPV 6 жыл бұрын

kv on it's own is meaningless. You need to take into account the motor torque, your drive voltage, and on a car other things like your gearing

@joannot6706 3 жыл бұрын

Thank you!

@ParadoxAzuremyst 4 жыл бұрын

I learnt something. Thank you

@hoofheartedicemelted296 3 жыл бұрын

So if I have 2 devices that would benefit from what you have just explained. First a vertical axis wind turbine and second a one wheel XR tpye electric vehicle, what configuration would be more suitable for each device. Great video sir thank you.

@ClericChris 2 жыл бұрын

What happens if you increase the wire size as you go out? Say 22 awg near center and 14 awg near magnet's? Also what if you use square wire or just shapes?

@SiieeFPV 2 жыл бұрын

I would guess that you'll just be bottlenecked by whatever the thinnest wire you have in the loop. The thicker windings may be able to handle more current, but the thin windings will die before they can be fully utilized. I would expect that you'd be better off just using entirely a single gauge between the two extremes, plus it would make managing your KV much simpler. I also guess that wire shape wouldn't have a particularly significant effect. Perhaps it changes how things work with the skin effect, but if skin effect is a major contributor I think you'd be better off by going stranded than trying to find some other shape of wire, as a circle would have the best ratio of enamel surface vs. copper volume. It would certainly be interesting if you could find any examples of high performance or maybe large industrial motors that use anything other than typical round conductors.

@biggityboggityboo8775 6 жыл бұрын

So the voltage that you're talking about is it the peak-peak sinusoidal voltage or the RMS value?

@SiieeFPV 6 жыл бұрын

RMS

@tapas1505 4 жыл бұрын

How to calculate the torque figure for example of a 3200KV brushless motor?

@furiouswolf777voodoo4 4 жыл бұрын

So, to help my limitless hit 120 mph I need ???🤔lower or higher kv for a 14 pound car?? Thanks

@joshuanorris5860 6 жыл бұрын

These videos helped me a lot. I like the voltage ones too. You should make some better playlists on your channel so people can find the related videos :) and mention that you made another video at the end of course ;)

@SiieeFPV 6 жыл бұрын

Thanks, I've been meaning to update the playlists, it's just so easy to forget.

@eleftherioskarakostas7191 6 жыл бұрын

very informative video, I like the new blue and white drawings. So , the more copper packed the higher the efficiency?

@SiieeFPV 6 жыл бұрын

Yup, the higher the cross section of copper the better, having too thin a wire and a lot of unused space or too thick insulation (either on the wire or over the stator laminations) will hurt

@BR. 6 жыл бұрын

I need a motor that can have fairly high torque at ~100 RPM because I want to use it for a DIY ceiling fan and I am thinking brushless would be nice becuase it's very quiet. What is the KV range I should do you think be shooting for?

@SiieeFPV 6 жыл бұрын

rpm = kv * voltage But kv doesn't say anything about torque, so it doesn't really help all that much. for only 100 rpm you're going to need to find as low a kv as you can find if you're looking at only hobby motors, but the question as to how big a motor you need to find for that application is still really open.

@miyamotosan972 4 жыл бұрын

So does this mean the more kV a motor has the faster/better it is?

@TheThemrdomi 6 жыл бұрын

Hey! Nice and informative video! You told that the copper volume is the same if we decrease the number of turns by 2 but increase the diameter by 2 right? Isn't it not proportional since the area has the diameter squared? A=(3,142/4)*D^2 Just a deliberation I had while watching. Keep up the good work!

@SiieeFPV 6 жыл бұрын

if I said diameter I certainly meant area. cross sectional area is all that matters for slot fill %. The correct equivalence is wire gauge, every 3 points of wire gauge is double the cross section. So if you've wound with 12 turns of 30awg wire, to double the kv and keep the same slot fill you need 24 turns of 33awg.

@TheThemrdomi 6 жыл бұрын

Thanks, makes sense!

@dwayner2518 6 жыл бұрын

so basically 6 turns uses half the current to output same amount of torque as 3 turns???

@SiieeFPV 6 жыл бұрын

yes, but since the 6 turns is longer wire it requires more voltage to run half the current, so total power remains the same.

@thagrit 6 жыл бұрын

you get higher torque but lower speed.

@dumitru5061 5 жыл бұрын

Bravo!

@sippeyxp 5 жыл бұрын

Thermal power is current*current*resistance, the 6 turn winding end up wasting half the energy to heat and that is the point of low KV.

@SiieeFPV 5 жыл бұрын

Lets take a hypothetical micro motor, say it's wound with 5ft of 33awg wire, and uses 50W on our test prop, for a total amp draw of 6.25A. Our total winding resistance is 1.035ohm, and we can calculate the I2R losses as 40.4W, or 80.8% (it's just made up) Now let's halve the kv of the motor by doubling the number of turns, now we have 10ft of 36awg wire, for a total resistance of 4.15ohm. To hit our 50w draw point we're now down to a nice 3.125A. And now you can calculate that our I2R losses in this case are 40.5W, or 81.1% Consider the difference just from rounding numbers along the way. You can run that simple math with any combination you like.

@dragan3290 5 жыл бұрын

How dou test with a multimeter for kv when you have 3 wires and 2 probes on the multimeter? Any reply appreciated thanks!

@SiieeFPV 5 жыл бұрын

fishpepper.de/2017/10/17/tutorial-how-to-measure-the-kv-of-a-brushless-motor/

@daviddavids2884 5 жыл бұрын

since kv IS a rotation rate value, the use of an optical or electrical TACHOMETER is necessary. see my comment.

@Cam-el8cr 6 жыл бұрын

So would this mean that a lower KV motor has higher torque at lower RPM levels than a respective high kv motor? Or does it really not make a significant difference?

@SiieeFPV 6 жыл бұрын

For the same drive voltage the higher kv motor will be capable of producing more torque at all rpm, up until the thermal or magnetic limits of the stator. For a quad this means more torque for dealing with inertial loads (acceleration and deceleration of the prop) since the torque demand from the prop stays the same for the same speed. If you compensate the voltage proportional to the KV (more voltage with lower kv) then the torque available stays the same. If you want more torque out of a motor you need to play with the pole count, stator size, flux density, or delta vs wye windings

@harynian 5 жыл бұрын

@@SiieeFPV "For the same drive voltage the higher kv motor will be capable of producing more torque at all rpm, up until the thermal or magnetic limits of the stator." You don't know what you are saying. On video you said something else...

@SiieeFPV 5 жыл бұрын

@@harynian In this video I'm talking about motor constants, not peak torque production. I'm not sure what you're talking about.

@srnunan4783 5 жыл бұрын

You speak about torque efficiency.. . But what about the copper losses of that high kv example? A low turn motor has a low winding resistance which leads to high "no load current" and lots of heat/short battery runs.

@SiieeFPV 5 жыл бұрын

Current increases with fewer turns, but since the wire size also increases which decreases copper losses it all cancels out assuming that everything stays in proportion. High kv has lower losses but higher current, and low kv has higher losses but lower current, so your total losses end up basically the same

@joewoodchuck3824 4 жыл бұрын

I don't understand why the industry places so much emphasis on the kv ratings. We know that motors in general go faster with higher voltage and to a lot of people is intuitive. So if we know the kv rating, so what? Yet the motor power information is only listed in a spec sheet which may or may not even be available. So if I have a diy airplane of certain size and especially of a certain weight and know how I wish to operate it, why is it such an arduous task to find a motor to use? It seems backwards to me to have to page through so many models to even get in the ballpark of what I want. It seems like it all became so needlessly complicated compared to the size selection of glow and later on of brushed motors. It's all very frustrating and it just makes me want to use a brushed motor and live with a little less efficiency.

@iamameend9695 4 жыл бұрын

i have bldc... and i try to run it without esc... please...i dont know how... i just have 2 electric dc cable, but motor have 3 cable...

@bagibadoo439 4 жыл бұрын

It is not possible, to run BLDC motor you need ESC.

@jvinsnes 5 жыл бұрын

i am buying a brushless motor for a 7.4v esc and one is kalled 4800kv, one is called 4600kv and the third is called 7300kv. which will go fastest? which will be most efficient? which will have the highest torque? thank you

@discord2000 5 жыл бұрын

It depends on the size of the motor and the load on the motor. There is no simple answer.

@PK-zf9wm 6 жыл бұрын

Does changing a bell from 2600kv to 2400kv with different air gap, flux, magets. Change the overall kv to 2400kv?

@SiieeFPV 6 жыл бұрын

Getting a higher flux density (either through stronger magnets or smaller air gap) will lower the kv, but kv strongly depends on the winding of the motor so there's really no such thing as a "2400kv bell" Generally if you're looking at different kv variations for a single model of motor the only difference will be the windings, the bells would be identical (except for the label) and interchangeable. You can swap bells between different models and manufacturers and get different results. Ryan at MQTB has played with this a little bit in one of his articles.

@PK-zf9wm 6 жыл бұрын

SiieeFPV ok well that sucks I just bought f40 pro ii 2600kv to try out higher kv and it's not for my type of flying was hoping I could change out bells with 2400s. My friend done it with racerstar 2205 2300 and 2600 and it worked he says. I had my doubts. Thanks man

@SiieeFPV 6 жыл бұрын

It's not a rule by any stretch, there could very well be a difference, I just think it's very unlikely. Placebo effect is very strong in this hobby, and even being aware of it does not make a person immune to it unless there is some real rigor in the testing. For lowering your kv you can accomplish basically the same thing by changing your throttle endpoint in your radio. The bulk of the "feel" difference is just in how the higher kv motor will compress the response range of your sticks, anything you can do with the 2400kv F40 you can do exactly the same with the 2600kv

@PK-zf9wm 6 жыл бұрын

SiieeFPV that makes sense I'll try changing my thottle end point. Thank you for dumbing it down perfectly for me

@wallybaldemor8523 4 жыл бұрын

Is it 3phase?

@bpt1231 6 жыл бұрын

Hi, how can we find how many poles are there in Brushless motor. Thanks.

@SiieeFPV 6 жыл бұрын

for a simple hobby motor you can count them, each cog on the stator is one pole

@williamedwards6519 3 жыл бұрын

you guys never explain what torque efficiency is. and , if you are putting 3 amps thru3 turns x1 amp = 3 amps, 6 turns x .5 amps, its still 3 amps, the KV is lowered but the torque remains the same. How are you putting less amps thru? that's the gain?

@joaomariaalpoimcolaco5049 6 жыл бұрын

so... if i get a 3200 kv motor its not going to have less torque than a 2500 kv motor? im just concerned about that

@SiieeFPV 6 жыл бұрын

For an otherwise identical motor the motor constant will be the same, so the amount of power you need to make the same torque doesn't change. But when the only thing you're comparing is the motor and the rest of your setup is the same you need to consider that that is a partial throttle comparison. We should have a good practical look at that soon, once we start looking at dyno results some of the first things we'll look at is the same motor at different KV

@joaomariaalpoimcolaco5049 6 жыл бұрын

SiieeFPV so... if its using the same battery and the ESC is the same on both cars but kv different we need to test it still? Because thats a dealbreaker because the two models im compraring have same ESC but different motor and i love the torque already from the lower kv... and if only top speed is increased and torque reduced its kind of a dealbreaker for me.

@SiieeFPV 6 жыл бұрын

If I understand it correctly it should be exactly the same, the KV just pushes the rpm range up and down based on voltage, I just don't want to commit to that. Torque comes from the flux density and pole count and the stator design. A higher KV motor should be able to do everything that a lower KV motor can, but that also ignores other things that may effect it like how the ESC will behave. To get the same torque from the same voltage a high KV motor is going to run at a lower duty cycle

@xXDarkKisukeXx 6 жыл бұрын

I know this is kind of old, but if you`re still interested: A higher kv motor needs more current for the same torque. Your battery, and esc must be able to supply this increased current. This extra current also results in higher I^2 * R heating in your motor, esc and battery. This reduces your efficiency.

@artcodezen 5 жыл бұрын

Excelent Video. Thank you!

@t.hussain6278 5 жыл бұрын

Thanks

@thou_shalt_kill1355 6 жыл бұрын

More turn more volt will produce in the motor if you spin it you are wrong

@SiieeFPV 6 жыл бұрын

I'm sorry, you're totally right I don't know what I was thinking. I'm mixing up terms and values in my head. more turns/low kv requires a higher drive voltage to reach a certain speed precisely because the BEMF is higher

@luongmaihunggia 4 жыл бұрын

Yeah, that's exactly what Kv means

5 жыл бұрын

Very important information thanks for your time :)

@donnymontreano9235 3 жыл бұрын

i need part 02

@johncgibson4720 4 жыл бұрын

All these is much more straight forward to optimize if you fly helicopter with a constant RPM. If you never know what RPM you want to fly your drone with, you never know what Kv motor you want to buy.

@user-sb3hp5qu7b 4 жыл бұрын

More kv =more rpm ??? Or no?

@PanDiaxik 4 жыл бұрын

Without load yes, if you load the motor much, you'll need rather higher KT

@taiwoolaleye6333 6 жыл бұрын

what did you study, to know this electric engineering or physics

@SiieeFPV 6 жыл бұрын

I've never studied any of this, just do my own research and reading books and technical papers. If you're looking for what to study I think this is more of an EE topic than physics

@wntu4 5 жыл бұрын

@@SiieeFPV I assure you it's covered in physics too. It's electro-magnetism and basic circuit theory. Maxwell lead the way into modern physics.

@daviddavids2884 5 жыл бұрын

the back of a cereal box

@smitgee 5 жыл бұрын

what happend to the series

@SiieeFPV 5 жыл бұрын

Been too busy with work and other projects for the regular type of postings, and these take a lot of time to research and figure out how to explain simply. Hopefully should get back to them in the next few months as I can clear out the backlog and find some more time for research.

@daviddavids2884 5 жыл бұрын

this guy was so wrong, just be glad there were not More such videos.