Motor 3 is always better overall from what I have learnt. Because lower amps at higher voltages equals much lower heat losses and less damage to battery
Hey Greg, thank you for your comment. Here's the perfect video that talks to the high voltage vs high current setup. What do you think? ruclips.net/video/x44GB5zbOSI/видео.html
It took me a few watches but I think I'm beginning to understand. So if I want torque and don't need speed, I would pick Motor 3 in this list not because it offers any more torque than Motor 1, but because it offers that torque while pulling less amps - is that correct? I should add that this hypothetical is assuming that everything else in the system is fixed.
Can this be applied directly to the motor being used as a generator? That the Kt value can determine how much torque is needed to be put in to generate that many amps?
RCexplained no man, thank you for putting together very informative videos in a simple, straight forward format. Your videos are great, I can’t wait to see what you cover in the future. Could you do a future video on suspension setups & spring rate? I don’t mean an explanation on how the suspension system functions, there are videos covering that topic. I mean how different suspension setups influence the steering characteristics, for example, hard rear springs with soft front, or vise versa. I also think it would be cool if you could talk about ideal suspension setups for different driving styles. For example, setups for a speed run car, versus a track/touring setup, versus a drift car setup. Just some ideas, you seem to be very knowledgeable & I appreciate how you take a scientific approach to your videos. Keep up the good work!
@@BMR3 , yes I can create a video talking about suspension setups on RC Cars. My video queue is at least a few weeks out, I'll see when I can slot it in. Thanks!
That's a fantastic video. I always thought that it would be almost the same. The way I see it, it's the size off the motor and what it can handle. So a 5000kv vs a 500kv can be geared to do the same thing... as long as they are the same can size from same manufacturer.
Does that mean a 12s motor for my 90mm edf with 1200kv would be so efficient using lower amps but still producing great torque. 100amps with 50 volts = 5000 watts as oppose to my 2400kv 200amp 25 volts setup. They both produce 60,000 rpm at full power
Hi, Great vids on the dynamics of brushless motors.. I have a question, and need to know which motor to choose.( 1) TP 3640,-1570 K ,max amps-75, max volts-38, Resistance-0.014, idle amp-1,7,, (2),Tp 3650-1680K, max. amps-189, Max volts-35.7,Resistance-0.0089, idle amp-2.9. Running a 180A esc. on 6S. Which of the 2 motors would be best overall in my boat for heat control, performance ,run time? Any help would be appreciated..Thanks
That's alot of info. The information that I have gained is: 4 pole lower Kv equal to more duration and power. 2 pole high Kv is for airplane use. Better cooling required. Which If I understand you is not really true. My model boats run an 4 pole 1200Kv 11.1 volt for 7.5 cc applaction to a 4 pole 1800 11.1 550 type can size 4 pole configuration for 3.5 cc. Just smoked the 1800 550 can but it was really fun. I have a 1/8 scale hydro F1 Miss Circus Circus with a Neu 850 delta which I haven't finished so I am in uncharted water here. Am I somewhat correct here or just plan wrong.
Here are some of my comments on the points raised in the video: 1) "Continuous" current or power as provided by the manufacturer may only be sustainable for 30 seconds. If you run the motor at that "continuous" current for a couple of minutes it will damage the motor. 2) I would say a more common (peak) efficiency in brushless motors for the RC hobby is 80%-90%. 3) Torque increases with increasing load, yes, but rpm and efficiency drop. And this can be quite significant. You can easily lose 10% efficiency and more. So it is very important to match load and motor and not just load down the motor. 4) Depending on how your application looks like this matching can be quite different: a) If the used throttle is around 100% most of the time then you want to hit that efficiency peak. b) If the range is wider with an average at 50% then you want to go past that efficiency peak at full throttle. 5) Keep in mind that efficiency drops very quickly below its peak but rather smoothly and much slower above its peak. 6) I don't see the problem with comparing different motors. It will still be an apples-to-apples comparison. The comparisons only break down when you use values that are meaningless in isolation such as Kv or Kt. 7) This is nitpicking, I know, but Kv is not the no-load rpm given 1V input. It's the RPM needed for the motor to produce 1V back-emf. 8) I know that the motors are made up for easier comparison, but if you look at actual motors of the same size/weight class from some manufacturer you can often see something like this: Kv 980 ... about 25 A Kv 1250 ... about 35 A This is because the lower Kv model has higher resistance, more windings, thinner wires .. resulting in lower sustainable "continuous" power. This is not a problem though, as the same propeller at 100% throttle with the Kv 1250 motor will draw 30A while it will only draw 15A with the Kv 980 motor. And since the load might be better matched to the low Kv motor, half the current may still result in more than half the thrust. This is also why I'd start sizing/matching components with the propeller based on the requirements (thrust or pitch speed). Then match the motor, esc, battery.. to it.
"1) "Continuous" current or power as provided by the manufacturer may only be sustainable for 30 seconds. If you run the motor at that "continuous" current for a couple of minutes it will damage the motor." How much derating is usually required for safe continuous operation? It seems like most manufacturers quote Max. Power, Current, Volts, Torque, etc., rather than "Continuous" values. What isn't clear is if those values are for the same motor operating point (is it /should it be?) Nor is it clear how to generate a speed, torque, efficiency, and power curve for these types of motors. (Divide "Max. Volts" by "Motor Resistance" and multiply by KT for stall torque?) If so, that would mean that the "Max. Power" would be proportional to speed because "Max. Torque" is essentially constant over the speed range, and that the highest efficiency would be with the motor running near its maximum speed (KV times "Max. Volts"?) "2) I would say a more common (peak) efficiency in brushless motors for the RC hobby is 80%-90%" So a motor with a "Max Power" = 2000 Watts, would produce at most 160 Watts of heat. Couldn't that be handled by adequately decreasing thermal resistances? That shouldn't be too difficult with a properly designed in-runner operating with an effective heatsink, should it?
@@gmack4097 >"How much derating is usually required for safe continuous operation?" This depends on many variables, including if the manufacturer's numbers come from the marketing rather than the engineering department and also how much (cool) air is flowing over/through the motor. But I can give you some random, concrete examples of airplane outrunners that depend on that airflow for cooling: 30g, 1500kv, 10A for a few seconds, 6A continuous 75g, 1000kv, 25A for a few secs, 15A continuous 200g, 500kv, 48A for a few secs, 28A continuous All of those continuous numbers are about 60% of the short term max current. But this may be significantly different for other manufacturers, motors, applications.
@@gmack4097 The motor stops speeding up when the applied voltage (including all the voltage drops over internal battery resistance, wire resistance, ESC resistance, motor coil Rm) equals the back-EMF (which you get through Kv). Torque is approximately proportional to current/Kv. (Hint: use SI units, so Kv*2pi/60 to get [rad/s], then you get results in [Nm]) Remember that there is a no-load current, and that V=R*I. So it seems like an unloaded motor produces some torque but that torque is required just to spin the motor itself. No "usable" torque is being produced at the shaft yet. As you load the motor down, more current flows and more torque is produced. But because V=R*I, the voltage drop across every component also increases (including the motor coil Rm). This results in lower RPM (see first paragraph). Efficiency is simply mechanical power divided by electrical power. Pel=V*I, so the voltage applied to the motor, or ESC if you want to include that, times the current flowing through the battery. Pmech=Torque*Revs/time Efficiency drops at some point because the dissipated power through the motor's coil alone is proportional to I^2 while torque produced is only proportional to I. And at no load you got the no-load current but zero usable torque, so zero mechanical "usable" power, and therefore zero efficiency. This is why you get this rapid increase in efficiency graphs as current rises over the no-load current.
@@gmack4097 >"So a motor with a "Max Power" = 2000 Watts, would produce at most 160 Watts of heat. Couldn't that be handled by adequately decreasing thermal resistances? That shouldn't be too difficult with a properly designed in-runner operating with an effective heatsink, should it?" No, that would mean at 80% efficiency the motor would produce 1600 W mechanical power. 400W would be dissipated as heat. Yes, you can decrease thermal resistance of an inrunner ... of the case to ambient, but much less so of the coils to case or magnets to case. Also, all of the things I've described in my previous post are "idealistic". In reality, there are many other sources of losses that increase with current, temperature and RPM. So the 80% efficiency on paper may in reality degrade into much lower efficiency.
Very good explanation! So we can say if you gear up two vehicles with motors of the same size but different KV values to the same max speed, the car with the lower KV motor accelerates slower, because the wheel torqe is reduced. The only downside of a high KV motor is the lack of cooling and only because of this, we have to find the sweet spot for our given application.
Thanks for your comment! This is true, however the lower kv motor should be selected based on requiring a higher input voltage. The overall output motor RPM would then be equivalent.
I would very much like to know the math that you skipped over(How you got from 1/Kv to Kt in SI units). As I can't figure it out without that part. Is there a formula that I can plot into a spreadsheet?
@@RCexplained Thanks, I think I got it now. When I plot in 1/790kv I get 0.0012658. Then 0.0012658 is divided by 1 RPM converted to rad/s(0.10472) and you get 0,01209 Nm/A or 12.09 mNm/A. That's the part I couldn't find the explanation for.
Hey Ryan, I've been rewatching some of your videos today related to kv and torque. It seems to me like it might be the most misunderstood topic in RC. A Brit RUclipsr with almost a million followers recently stated "... lower kv motors have got less rpm but alot more torque.". I'm wondering what the torque values would be with an even closer comparison. I'm invested in 3s for my 1:10 rigs so my voltage is locked there. What would the torque values look like for something like a 1406 slate that comes in 1900, 2280, 2850, and 3800kv? Sorry, long post. Thanks for the informative videos.
When the setup is optimized the torque output of a constant motor size is essentially the same in all kv options. What changes with lower kv is the torque constant increases. However, with lower maximum current capabilities that motor delivers the same output torque as a higher kv motor. If you are looking for maximum performance on 3s and you are stuck with 3s, you will want to look at how high you can go with maximum RPM of the motor in your application.
@@RCexplained No worries there. My Bomber with the 3800kv 1410 castle gets a theoretical top rpm of 42180 and that is more than enough wheel speed, even with underdrive gears in both diffs and the smallest possible pinion gear. Would you be able to point me to where I can find the formulas to calculate the torque value for a brushless motor? I'm really curious to see how these 4 motors compare to each other when they are given the same voltage. I checked your website today but didn't have any luck. Thanks
So Motor 1 pull 165a and Motor 3 pull 46a this means the battery connected to motor 1 will discharge quicker than the same battery if it was connected to motor3??
Question. Everything else being constant (terrain, top speed, acceleration) except KV and gearing. Should i pick a low kv and load with tall gearing or high kv and short gearing?
Torque produced by the motor depends on the current that is drawn. If you draw the same current regardless of your battery or RPM, you will produce the same amount of torque output.
If the motor draws the same amount of current, RPM and battery does not matter. 100A at 20k RPM vs 100A at 5k RPM is the same torque output. Battery does not matter.
@@RCexplained Oh wait, I mean when it is the exact same motor but just another KV. The Higher KV will always take more current on 3S as a lower KV right? At least that is what i have seen in the specsheets of the motors. And if you see both motors the same power (like 800W), then the lower KV can only reach that with a higher voltage than the high KV one, wich would mean the power of a lower KV motor will be lower on the same voltage (what i meant with battery, like 3S). Or am i missing something. Isn't it so that a lower KV motor can only come to its fullest potential at a higher voltage than an High KV motor?
@@RCexplained no, not all. But it seems intuitive that a higher rpm turning something would have greater force behind it than a slower rpm, assuming mass weight is the same.
Hi Ryan, maybe a dumb question but I'm trying to replicate your table and the kt seems to be off by an order of magnitude, e.g. 1*1000/2830 = 0.35335689 mNm/A. Is this correct?
True, but it takes 3x the volts on a larger KV motor to produce the same torque as one with a much smaller KV value, no? So the conclusion seems to be what you stated in one of your other videos (Yes, I enjoy mostly all of them :)) is that you have to balance low kv with a ton more volts vs selecting a high kv motor with run on a lot less volts. Would the heat produced roughly be the same or would I select a higher kv with a lower voltage for less heat (since less stress on the motor)? I'm trying to put together a basher setup where top speed isn't as important as torque for maneuvering the rc mostertruck while in the air off a ramp, pop wheelies and to more easily run through off road terrain like grass. Thoughts? I did watch you other video about selecting a KV based on RPM need and expected volts. I came to 50k RPM / 11.1 = 4500kv but wondering how to balance that with your topic in this video. My current motor's physical size is quite small at 2435 and not much room to make it much larger. 3900kv.
The kt constant multiplied by amps gives you the torque output. In general i prefer lower kv motors, however only if I am able to increase the cell count I run to them. This is where I am able to maximize the setup. Going with a larger motor also helps out as well. It generally provides a lower Rm value at the same kv and as you mentioned previously, there is more surface area for heat dissipation.
@@RCexplained Thanks. I'm not able to increase my cell count, so I used the formula you shared about RPM/V to determine the "ideal" kv. As you taught me, that'll maximize the RPM's while still staying within the range with use of the voltage I plan to equip my power system with. Thanks again. Keep up the good work. I'll be watching.
@@RCexplained A smaller physically sized motor with the same KV generally has a much lower amperage rating, meaning I can run it through a much smaller ESC and still achieve the same RPM. Is there a reason I wouldn't select a 2435 4500kv motor running on 3S vs a 3650 4500kv also running on 3S? 3650 would get less hot b/c of the surface area? So advantage of 3650 is that it's less stressed than the smaller 2435 at 50,000 RPM?
@@Funcentric Keep in mind that if you load the motor to 200A it doesn't matter what the rating of the motor is. It's going to pull the 200A. The rating is a limitation and not an indication of how many amps your setup will pull. The smaller motor has much less power potential. How many watts are you planning to pull from the motor?
After introducing Kt into explanation of brushless motors characteristics it get clear now. What about providing the same torque by motor with the higher Kv as provided by one with lower Kv - in theory yes, as I understood from your explanation, we can provide more current and thus get more torque. I.e. we can obtain the same torque from two motors with different Kv, but at cost of providing higher V/A for motor with higher Kv (and, probably, more heat on it). But, in practice we are usually bounded by ESC, which has some limit regarding max voltage/max current for two ones with lower and higher Kv (assuming that we use the same ESC model for each of two motors). In this case one with lower Kv will provide more torque than one with higher Kv. Is my understanding correct? I.e. if we choose motor with higher Kv, we obtain higher RPM, but lower torque, and vice versa for one with lower Kv. Thank you.
Not sure how to answer your question. If your ESC does not work for the higher Kv motor, the ESC was not selected correctly. Same thing with the lower Kv motor. If it does not allow the voltage you need to run the motor, efficiency is going to be effected and the resulting torque will not be accurate. Best bet is to match the ESC for the setup you sre building. If the motor is going to pull more current, an adequately rated ESC is necessary.
@@RCexplained What do you mean for "ESC does not work"? Per my understanding, it works while amount of pulled by motor current doesn't exceed its limit.I'm not sure that understood point about voltage. Voltage is the same (at lease for those two motors) any time, irrespectively to load, and depends on battery we use. For example, 11,1V (3S LiPo).
You said "But, in practice we are usually bounded by ESC, which has some limit regarding max voltage/max current" When selecting a power system you need to select the correct ESC to match your requirements.
Yeah I think this point is “moo” because of course the manufacturer do not want to have a bunch of claims or returns and is going to put low numbers yet subliminally advertise a lot of power. You should multiply by same amperage and that would have the lower kv equal more torque.
Thanks for the comment Lazy Man. RPM / torque curves would be tough as with an electric motor I can give you what ever shape of a curve you want. Shape of the curve depends on the load and control settings put in place.
@@RCexplained I think I'll have to learn more. But now I find you and will abo you to watch relaxed some old vids and of course the new ones. Have to read more about the topics, I new start RC Hobby.
Finally someone speaks the truth! Same basic principle applies to brushed motors too all else being equal. You might get an advantage in the brief transition between zero and a few RPM but that's it.
@@RCexplained Thanks for the reply - could explain this is another video perhaps - the maths of how to get to gearing from Kv, via Kt? Perhaps others, like me are intruiged as to how to choose the optimal gearing - I race 1/12 pan cars in stock 13.5 turn bsushless motors. 1s Lipo, 1s specific ESC (120amp). Each race is between 4 and 6 minutes so I want the best performance for that duration. I liked your video on designing/ choosing your power system - would be great to see a more in depth one for my case (although I don't have much choice), and perhaps specific examples of the other two? Great work - I've learnt a lot - I'm just missing a few details. Thanks
@@xaviertaylor759 the best way to further optimize gearing and other choices is by testing different combinations and measuring performance, power output and heat. The theoretical side will only get you so far.
Hey Xavier, just an update. The recently uploaded video shows the math on Kv vs Kt to answer your question here. Also the video planned for next week will look at gearing and kv selections to a degree.
@@RCexplained Do you have a link to this? I am curious to know how to convert Kv to Kt too. Came across this channel today, absolutely amazing. Liked and subscribed!
This series is the best explanation of the various motor parameters I've seen. Unfortunately, it's still not quite explaining what the advantage of bigger motors is (in my specific case, on fixed wing aircraft). Does more KV mean more speed? Why, if the total torque is always the same? Also how does motor size affect things, how is a larger motor better than a smaller one (I know it's more heat dissipation, but what does that mean in practice? More speed? More efficiency?). I am hopelessly confused on this subject, alas.
Larger motors mean more power output potential. With more power output you can set your airplane up to go faster. More kv can mean more speed if your motor and power system is able to deliver the increase in power output.
@@RCexplained I see, thank you, so basically what we care about is the wattage, not so much the size (except for heat dissipation, I guess), is that correct? Ie I can just look at the wattage to figure out how much power the motor can deliver and the amperage to figure out if it'll burn? Also, why does more KV mean more speed, since power is constant? Wouldn't more KV with a smaller pitch prop be the same power as less KV with a larger pitch prop (since more KV = less torque for the same power/size motor)? Sorry for all the questions, I'm just a bit confused because all the explanations I've seen tend to change more than one variable at a time, and not say "more KV means this, more power means this, more size means this, all else being equal". Thank you!
very good explanation, and professional talk! in the next video please explain how KV and torque will be affected by the gearing ! for example, a 2200kv will use a 16T pinion and a 1480kv will need a 19T pinion on the same car to achieve the same end speed
Whilst this is theoretically true I'd argue that in practice we don't scale everything appropriately, smaller than equivalent cells, same connectors and wiring etc. In practice I would argue that lower kv motors DO produce more torque because the system usually restricts the amp load for an equivalent high kv motor.
Hi Fraser, thanks for the comment. If we don't pick our power systems correctly and as a result restrict the amp load, that's on us. It's not the higher kv motors fault.
@@RCexplained 100% My point though is that it's rarely, if ever, done in practice. Even if you wanted to, there is so much that is standardised. Typically moving to higher voltage is something we do to prevent having to deal with huge current amounts that would be problematic. Often it is not really feasible to go the other way. BTW your videos are spectacularly good. I'm somewhat honoured that you responded to a comment on a year old video.
@@RCexplained let me phrase the question slightly differently: In what practical rc application would you be able to halve the voltage/double the current and still have the same amount of torque? I'm saying you practically can't because the requirements of the increased current dramatically change properties the system. If you don't change it, you suffer losses that will suck power out leading to lower torque. For example xt30->xt60.
Thanks for the comment Fraser. I respond to all new comments on the channel. It pops up in my feed as long as there arent too many all at the same time. I understand your point, and I guess it would really depend on the power system and the application.
Please lend some advice to a newb! Just got a limitless. It came with a 2650kv motor and mamba (something) esc! I just bought a hobby wing Max 6 combo with the 1650kv motor. What am i to expect? I'm running 6s (2 3s lipos) Thanks just subscribed!
Have you tried entering this combination on the radiocontrolinfo website? There is a calculator that will estimate the potential speed that you may be able to hit.
Hi Fritz, thanks for the comment. Once I move, I'll be able to focus on the background and completely change it. Until then, there's not much I can do.
I have a 2000kv motor and a 70kv motor, weight is the same, but i get much more torque output out of the 2000kv with a 7:1 gear ration in comparison to the 70kv motor with no gear why is this? (Voltage is the same) and good video 😉
Hi Lukas, just curious how you know you are getting less torque? What are the continuous wattage rating of both motors? What is the maximum RPM spec of each motor? What is the voltage you are operating on? What is the max continuous current spec of each motor?
Thanks Ryan a lot! Shame on me I haven't learnt physics at school so now it takes so much time to understand all this things..... It's mindblowing for me right know but interesting at the same time....Like learning magic xD Am I right with my current situation (my 1:10 truggy that has 3100 KV motor (size 3650), 60A Esc and 3s lipo battery) and I want this car to climb better at low speed (or rotate slightly larger and heavier wheels without noise and vibrations at the start), that swaping to 2400kv motor only(!) I will not reach my goal? I guess, I need a bigger motor (for example 3660 or 3665) with the kv matches my battery (already put a smalest pinion gear on my 3100kv motor). Is there a solution to reach my goal without changing (at least) my battery?)) Thanks in advance a lot! :] Keep it going! P.S: I found the answer from two (or more) of your videos: - it is better to use sensored brushless motor for this type of riding..... Thaaaaanks!!)
Hello, if you are not looking to go faster a kv drop will help with more power for going up hills and accelerating. A sensored motor will help with extremely slow speeds.
You missed the most important aspect of this, which is the fact lower KV gives you better torque at lower rpm, and higher KV gives you better torque at higher rpm.
You fail to mention that the torque value max is reached much quicker at 790kv than 2830kv which is really the point in going lower kv, the way you've presented this is a little misleading.
I'd say you'd need to look at the whole system to choose the correct motor. A low kV motor will require less amps but more voltage for the same power, while a high kV motor will require less voltage, but a lot more amps. Generally it's more difficult to get high amps delivered (need bigger wires, batteries with high C rating and beefier ESC), but you probably also don't want to use batteries with a lot of cells. To get the most torque and power out of the motor, you need to max out voltage and amps as best as you can with the space and money you have available.
Hi Razor Blade, that's very true. This video is specific to torque vs kv, if you are interested in how to choose a brushless motor there is a separate video for that on the channel. This video in no way covers how to select a brushless motor.
You say Kt is the "torque constant" of the motor, that is fine. You say (like 95% of the Internet) Kv is RPM/volt. Shouldn't that be Kv is the "voltage constant" of the motor? That is the relationship between rotational speed and back e.m.f. produced by the motor, it has nothing to do with the voltage applied to the motor. There is only an approximate relationship between this and RPM/V, close enough for our use I guess but this is just another example of inaccuracy being perpetuated across the internet.
Hi Don, thank you for your comment. I'm not exactly sure what you are after here as it seems you fully understand why Kv is used. But either way, please let me try to explain. Similar to Kt, Kv has been defined for the sole purpose of providing us with a standard to determine a mechanical property we get out of the motor for an electrical input. Kv is known as the velocity constant (upper case V is voltage) and this is very important. Like the torque constant provides us with a means to understand mechanical output torque of a motor, the velocity constant provides us with a means to understand mechanical velocity. Translating between electrical and mechanical properties will never be "exact." This is for Kv and Kt. Now if we were interested in back EMF produced per RPM of input we would use the back EMF constant also referred to as the voltage constant - Ke. Note that Kv and Ke are inverse to each other and setup for their intended use. Ke and Kt are equal to each other but use different units. Ke would be used in electrical motor calculations as standard practice. Kv would be used when relating mechanical output. As for this video being another example of inaccuracy being perpetuated across the internet - There are many sources of information out there and I understand some may be inaccurate. It's not easy explaining this stuff to a world of opinions. But at the end of the day, we are all just trying to provide free information in order to bring the hobby to another level, allow hobbyists to reach their goals *successfully* and to be able to have the most fun possible.
@@RCexplained I'm trying to wrap my brain around all this R/C electrickery, I think I'm getting there but it is difficult as there's so many and differing explanations for things like this on the Internet. There are so may threads (and as you say, opinions) on so many forums on this subject. I must say your videos are proving to be the easiest way to learn this stuff, thanks for that. I hope you don't think I'm saying you or your video are wrong coz I'm not haha, apols if you got that impression. It's caused by my remaining but diminishing confusion, haha again.
Motor 3 is always better overall from what I have learnt. Because lower amps at higher voltages equals much lower heat losses and less damage to battery
Hey Greg, thank you for your comment. Here's the perfect video that talks to the high voltage vs high current setup. What do you think?
ruclips.net/video/x44GB5zbOSI/видео.html
It took me a few watches but I think I'm beginning to understand. So if I want torque and don't need speed, I would pick Motor 3 in this list not because it offers any more torque than Motor 1, but because it offers that torque while pulling less amps - is that correct? I should add that this hypothetical is assuming that everything else in the system is fixed.
Finally, good and simple explanation how to calculate torque.
Right on, thanks for the comment!
i ber you has already forget the fomula by now, if not than plz write it!
Can this be applied directly to the motor being used as a generator? That the Kt value can determine how much torque is needed to be put in to generate that many amps?
Yes this would be a great starting point.
@@RCexplained awesome! That’s what I thought but didn’t want to assume. Thank you for your response!
i understood everything you said, and am no closer to understanding which motor to choose
sir, which one is more suitable for rc boat, outrunner motor with low kv or inrunner with high kv?
Inrunner with accurately selected Kv. ruclips.net/video/2tuvoAfPMYU/видео.html
Why would someone give you a dislike? Your dropping some hot knowledge
Hey BMR 3, I didn't even notice that. Thank you for the support and I greatly appreciate you taking the time to leave an awesome comment!
RCexplained no man, thank you for putting together very informative videos in a simple, straight forward format. Your videos are great, I can’t wait to see what you cover in the future.
Could you do a future video on suspension setups & spring rate? I don’t mean an explanation on how the suspension system functions, there are videos covering that topic. I mean how different suspension setups influence the steering characteristics, for example, hard rear springs with soft front, or vise versa. I also think it would be cool if you could talk about ideal suspension setups for different driving styles. For example, setups for a speed run car, versus a track/touring setup, versus a drift car setup.
Just some ideas, you seem to be very knowledgeable & I appreciate how you take a scientific approach to your videos. Keep up the good work!
@@BMR3 , yes I can create a video talking about suspension setups on RC Cars. My video queue is at least a few weeks out, I'll see when I can slot it in. Thanks!
RCexplained awesome thank you sir!!
Because some people are in denial because they've grown up believing slower motors have more torque.
So what do you recommend for say a monster truck application? 1 I'm referring to a ClodBuster or Axial SMT10
That's a fantastic video. I always thought that it would be almost the same.
The way I see it, it's the size off the motor and what it can handle. So a 5000kv vs a 500kv can be geared to do the same thing... as long as they are the same can size from same manufacturer.
Would a motor call for more amps if a higher mah batery is supplied both having the same gearing and load
If both batteries are healthy, you may only see a small bump in current. A few percent.
Does that mean a 12s motor for my 90mm edf with 1200kv would be so efficient using lower amps but still producing great torque. 100amps with 50 volts = 5000 watts as oppose to my 2400kv 200amp 25 volts setup. They both produce 60,000 rpm at full power
Hi, Great vids on the dynamics of brushless motors.. I have a question, and need to know which motor to choose.( 1) TP 3640,-1570 K ,max amps-75, max volts-38, Resistance-0.014, idle amp-1,7,, (2),Tp 3650-1680K, max. amps-189, Max volts-35.7,Resistance-0.0089, idle amp-2.9. Running a 180A esc. on 6S. Which of the 2 motors would be best overall in my boat for heat control, performance ,run time? Any help would be appreciated..Thanks
change motor timing is also another way to get more torque, right ?
Yes, you can think of it as that. There will be a tradeoff.
That's alot of info. The information that I have gained is: 4 pole lower Kv equal to more duration and power. 2 pole high Kv is for airplane use. Better cooling required. Which If I understand you is not really true. My model boats run an 4 pole 1200Kv 11.1 volt for 7.5 cc applaction to a 4 pole 1800 11.1 550 type can size 4 pole configuration for 3.5 cc. Just smoked the 1800 550 can but it was really fun. I have a 1/8 scale hydro F1 Miss Circus Circus with a Neu 850 delta which I haven't finished so I am in uncharted water here. Am I somewhat correct here or just plan wrong.
Here are some of my comments on the points raised in the video:
1) "Continuous" current or power as provided by the manufacturer may only be sustainable for 30 seconds. If you run the motor at that "continuous" current for a couple of minutes it will damage the motor.
2) I would say a more common (peak) efficiency in brushless motors for the RC hobby is 80%-90%.
3) Torque increases with increasing load, yes, but rpm and efficiency drop. And this can be quite significant. You can easily lose 10% efficiency and more.
So it is very important to match load and motor and not just load down the motor.
4) Depending on how your application looks like this matching can be quite different:
a) If the used throttle is around 100% most of the time then you want to hit that efficiency peak.
b) If the range is wider with an average at 50% then you want to go past that efficiency peak at full throttle.
5) Keep in mind that efficiency drops very quickly below its peak but rather smoothly and much slower above its peak.
6) I don't see the problem with comparing different motors. It will still be an apples-to-apples comparison. The comparisons only break down when you use values that are meaningless in isolation such as Kv or Kt.
7) This is nitpicking, I know, but Kv is not the no-load rpm given 1V input. It's the RPM needed for the motor to produce 1V back-emf.
8) I know that the motors are made up for easier comparison, but if you look at actual motors of the same size/weight class from some manufacturer you can often see something like this:
Kv 980 ... about 25 A
Kv 1250 ... about 35 A
This is because the lower Kv model has higher resistance, more windings, thinner wires .. resulting in lower sustainable "continuous" power.
This is not a problem though, as the same propeller at 100% throttle with the Kv 1250 motor will draw 30A while it will only draw 15A with the Kv 980 motor. And since the load might be better matched to the low Kv motor, half the current may still result in more than half the thrust.
This is also why I'd start sizing/matching components with the propeller based on the requirements (thrust or pitch speed). Then match the motor, esc, battery.. to it.
Hey John,
Thank you for your comments!
"1) "Continuous" current or power as provided by the manufacturer may only be sustainable for 30 seconds. If you run the motor at that "continuous" current for a couple of minutes it will damage the motor."
How much derating is usually required for safe continuous operation?
It seems like most manufacturers quote Max. Power, Current, Volts, Torque, etc., rather than "Continuous" values. What isn't clear is if those values are for the same motor operating point (is it /should it be?) Nor is it clear how to generate a speed, torque, efficiency, and power curve for these types of motors. (Divide "Max. Volts" by "Motor Resistance" and multiply by KT for stall torque?) If so, that would mean that the "Max. Power" would be proportional to speed because "Max. Torque" is essentially constant over the speed range, and that the highest efficiency would be with the motor running near its maximum speed (KV times "Max. Volts"?)
"2) I would say a more common (peak) efficiency in brushless motors for the RC hobby is 80%-90%"
So a motor with a "Max Power" = 2000 Watts, would produce at most 160 Watts of heat. Couldn't that be handled by adequately decreasing thermal resistances? That shouldn't be too difficult with a properly designed in-runner operating with an effective heatsink, should it?
@@gmack4097 >"How much derating is usually required for safe continuous operation?"
This depends on many variables, including if the manufacturer's numbers come from the marketing rather than the engineering department and also how much (cool) air is flowing over/through the motor.
But I can give you some random, concrete examples of airplane outrunners that depend on that airflow for cooling:
30g, 1500kv, 10A for a few seconds, 6A continuous
75g, 1000kv, 25A for a few secs, 15A continuous
200g, 500kv, 48A for a few secs, 28A continuous
All of those continuous numbers are about 60% of the short term max current.
But this may be significantly different for other manufacturers, motors, applications.
@@gmack4097 The motor stops speeding up when the applied voltage (including all the voltage drops over internal battery resistance, wire resistance, ESC resistance, motor coil Rm) equals the back-EMF (which you get through Kv).
Torque is approximately proportional to current/Kv.
(Hint: use SI units, so Kv*2pi/60 to get [rad/s], then you get results in [Nm])
Remember that there is a no-load current, and that V=R*I.
So it seems like an unloaded motor produces some torque but that torque is required just to spin the motor itself. No "usable" torque is being produced at the shaft yet.
As you load the motor down, more current flows and more torque is produced. But because V=R*I, the voltage drop across every component also increases (including the motor coil Rm). This results in lower RPM (see first paragraph).
Efficiency is simply mechanical power divided by electrical power.
Pel=V*I, so the voltage applied to the motor, or ESC if you want to include that, times the current flowing through the battery.
Pmech=Torque*Revs/time
Efficiency drops at some point because the dissipated power through the motor's coil alone is proportional to I^2 while torque produced is only proportional to I.
And at no load you got the no-load current but zero usable torque, so zero mechanical "usable" power, and therefore zero efficiency.
This is why you get this rapid increase in efficiency graphs as current rises over the no-load current.
@@gmack4097 >"So a motor with a "Max Power" = 2000 Watts, would produce at most 160 Watts of heat. Couldn't that be handled by adequately decreasing thermal resistances? That shouldn't be too difficult with a properly designed in-runner operating with an effective heatsink, should it?"
No, that would mean at 80% efficiency the motor would produce 1600 W mechanical power. 400W would be dissipated as heat.
Yes, you can decrease thermal resistance of an inrunner ... of the case to ambient, but much less so of the coils to case or magnets to case.
Also, all of the things I've described in my previous post are "idealistic". In reality, there are many other sources of losses that increase with current, temperature and RPM.
So the 80% efficiency on paper may in reality degrade into much lower efficiency.
Very good explanation! So we can say if you gear up two vehicles with motors of the same size but different KV values to the same max speed, the car with the lower KV motor accelerates slower, because the wheel torqe is reduced.
The only downside of a high KV motor is the lack of cooling and only because of this, we have to find the sweet spot for our given application.
Thanks for your comment! This is true, however the lower kv motor should be selected based on requiring a higher input voltage. The overall output motor RPM would then be equivalent.
@@RCexplained Thanks! Now the puzzle is completely solved. :-)
I would very much like to know the math that you skipped over(How you got from 1/Kv to Kt in SI units).
As I can't figure it out without that part.
Is there a formula that I can plot into a spreadsheet?
1 RPM = 0.10472 rad/s. This is just a unit conversion. Then Kt = 1 / Kv. Kt would then be measure in Nm/A.
@@RCexplained Thanks, I think I got it now.
When I plot in 1/790kv I get 0.0012658.
Then 0.0012658 is divided by 1 RPM converted to rad/s(0.10472) and you get 0,01209 Nm/A or 12.09 mNm/A.
That's the part I couldn't find the explanation for.
Hey Ryan, I've been rewatching some of your videos today related to kv and torque. It seems to me like it might be the most misunderstood topic in RC. A Brit RUclipsr with almost a million followers recently stated "... lower kv motors have got less rpm but alot more torque.". I'm wondering what the torque values would be with an even closer comparison. I'm invested in 3s for my 1:10 rigs so my voltage is locked there. What would the torque values look like for something like a 1406 slate that comes in 1900, 2280, 2850, and 3800kv?
Sorry, long post. Thanks for the informative videos.
When the setup is optimized the torque output of a constant motor size is essentially the same in all kv options. What changes with lower kv is the torque constant increases. However, with lower maximum current capabilities that motor delivers the same output torque as a higher kv motor.
If you are looking for maximum performance on 3s and you are stuck with 3s, you will want to look at how high you can go with maximum RPM of the motor in your application.
@@RCexplained Thanks for the reply. The 540 slate motors are rated at 100k rpm so I'm safe there.
Your RC vehicle may not be able to handle anywhere close to 100K though.
@@RCexplained No worries there. My Bomber with the 3800kv 1410 castle gets a theoretical top rpm of 42180 and that is more than enough wheel speed, even with underdrive gears in both diffs and the smallest possible pinion gear.
Would you be able to point me to where I can find the formulas to calculate the torque value for a brushless motor? I'm really curious to see how these 4 motors compare to each other when they are given the same voltage. I checked your website today but didn't have any luck.
Thanks
Kt x current = torque. Kt = 1/kv. Kv need to be in rad/s.
So Motor 1 pull 165a and Motor 3 pull 46a this means the battery connected to motor 1 will discharge quicker than the same battery if it was connected to motor3??
Yes, but typically you would be using a very different battery to match each motor.
as my sir said lower kv have more torque in it, is it?
Excellent info. Thanks Ryan!
Thanks!
I've been searching for this answer for weeks lol. Big thank you!
Happy to help!
Question. Everything else being constant (terrain, top speed, acceleration) except KV and gearing.
Should i pick a low kv and load with tall gearing or high kv and short gearing?
Hey James. Motor Kv is selected based on the voltage you plan to run to hit the same RPM at the motor.
@@RCexplained oooohhh.
Thank you. I find your subjects interesting. Can you givw me advise the needed electronics for twin engine 36" catamaran. Fan from the philippines
Hi Boni, what are your goals for this build? Is there a targeted speed you are after?
@@RCexplained i am looking at not so fast and neither too slow. Maybe 40-50kph is enoigh
Thanks for your video got me to hit the subscribe button
Thank you!
So does de lower kv have the same torque at lower Rpm? Is it the same torque when you use the same battery?
Torque produced by the motor depends on the current that is drawn. If you draw the same current regardless of your battery or RPM, you will produce the same amount of torque output.
RCexplained but at the same battery, that means on a lower rpm right?
If the motor draws the same amount of current, RPM and battery does not matter.
100A at 20k RPM vs 100A at 5k RPM is the same torque output. Battery does not matter.
@@RCexplained Oh wait, I mean when it is the exact same motor but just another KV. The Higher KV will always take more current on 3S as a lower KV right? At least that is what i have seen in the specsheets of the motors. And if you see both motors the same power (like 800W), then the lower KV can only reach that with a higher voltage than the high KV one, wich would mean the power of a lower KV motor will be lower on the same voltage (what i meant with battery, like 3S). Or am i missing something. Isn't it so that a lower KV motor can only come to its fullest potential at a higher voltage than an High KV motor?
Sounds like you got it!
But you didn't speak to RPM. I suspect that the lower Kv motor would have higher torque at a lower RPM.
Why would you expect torque to be different at lower RPM? Can you show this mathematically?
@@RCexplained no, not all. But it seems intuitive that a higher rpm turning something would have greater force behind it than a slower rpm, assuming mass weight is the same.
Even if kv is different, the torque is the same when the voltage is the same, 0 rpm.
Hi Ryan, maybe a dumb question but I'm trying to replicate your table and the kt seems to be off by an order of magnitude, e.g. 1*1000/2830 = 0.35335689 mNm/A. Is this correct?
You need to convert kv to SI units - rad/s.
@@RCexplained thank you!
Great video, interesting insights! 👍🏼
I suspect discussing turns and resistance would be helpful to many.s
I think I may have a video on turns.
True, but it takes 3x the volts on a larger KV motor to produce the same torque as one with a much smaller KV value, no? So the conclusion seems to be what you stated in one of your other videos (Yes, I enjoy mostly all of them :)) is that you have to balance low kv with a ton more volts vs selecting a high kv motor with run on a lot less volts. Would the heat produced roughly be the same or would I select a higher kv with a lower voltage for less heat (since less stress on the motor)?
I'm trying to put together a basher setup where top speed isn't as important as torque for maneuvering the rc mostertruck while in the air off a ramp, pop wheelies and to more easily run through off road terrain like grass. Thoughts? I did watch you other video about selecting a KV based on RPM need and expected volts. I came to 50k RPM / 11.1 = 4500kv but wondering how to balance that with your topic in this video. My current motor's physical size is quite small at 2435 and not much room to make it much larger. 3900kv.
The kt constant multiplied by amps gives you the torque output. In general i prefer lower kv motors, however only if I am able to increase the cell count I run to them. This is where I am able to maximize the setup. Going with a larger motor also helps out as well. It generally provides a lower Rm value at the same kv and as you mentioned previously, there is more surface area for heat dissipation.
@@RCexplained Thanks. I'm not able to increase my cell count, so I used the formula you shared about RPM/V to determine the "ideal" kv. As you taught me, that'll maximize the RPM's while still staying within the range with use of the voltage I plan to equip my power system with. Thanks again. Keep up the good work. I'll be watching.
@@Funcentric sounds good Funcentric. Just make sure your Total RPM is realistic for your RC and you are good to go.
@@RCexplained A smaller physically sized motor with the same KV generally has a much lower amperage rating, meaning I can run it through a much smaller ESC and still achieve the same RPM.
Is there a reason I wouldn't select a 2435 4500kv motor running on 3S vs a 3650 4500kv also running on 3S? 3650 would get less hot b/c of the surface area? So advantage of 3650 is that it's less stressed than the smaller 2435 at 50,000 RPM?
@@Funcentric Keep in mind that if you load the motor to 200A it doesn't matter what the rating of the motor is. It's going to pull the 200A. The rating is a limitation and not an indication of how many amps your setup will pull.
The smaller motor has much less power potential. How many watts are you planning to pull from the motor?
After introducing Kt into explanation of brushless motors characteristics it get clear now. What about providing the same torque by motor with the higher Kv as provided by one with lower Kv - in theory yes, as I understood from your explanation, we can provide more current and thus get more torque. I.e. we can obtain the same torque from two motors with different Kv, but at cost of providing higher V/A for motor with higher Kv (and, probably, more heat on it). But, in practice we are usually bounded by ESC, which has some limit regarding max voltage/max current for two ones with lower and higher Kv (assuming that we use the same ESC model for each of two motors). In this case one with lower Kv will provide more torque than one with higher Kv. Is my understanding correct? I.e. if we choose motor with higher Kv, we obtain higher RPM, but lower torque, and vice versa for one with lower Kv.
Thank you.
Not sure how to answer your question. If your ESC does not work for the higher Kv motor, the ESC was not selected correctly. Same thing with the lower Kv motor. If it does not allow the voltage you need to run the motor, efficiency is going to be effected and the resulting torque will not be accurate.
Best bet is to match the ESC for the setup you sre building. If the motor is going to pull more current, an adequately rated ESC is necessary.
@@RCexplained What do you mean for "ESC does not work"? Per my understanding, it works while amount of pulled by motor current doesn't exceed its limit.I'm not sure that understood point about voltage. Voltage is the same (at lease for those two motors) any time, irrespectively to load, and depends on battery we use. For example, 11,1V (3S LiPo).
You said "But, in practice we are usually bounded by ESC, which has some limit regarding max voltage/max current"
When selecting a power system you need to select the correct ESC to match your requirements.
To load 100 kg. How many kv required
Okay but speed runs we over amp the system. So shouldnt we multiply by a constant current instead of a decreasing current
Yeah I think this point is “moo” because of course the manufacturer do not want to have a bunch of claims or returns and is going to put low numbers yet subliminally advertise a lot of power. You should multiply by same amperage and that would have the lower kv equal more torque.
Oh nvm you say this point at the end anyways very quickly.
Your videos realy help me ☺️
Happy to help!
Good explanation, but I missed some rom torque curves.
Thanks for the comment Lazy Man. RPM / torque curves would be tough as with an electric motor I can give you what ever shape of a curve you want. Shape of the curve depends on the load and control settings put in place.
@@RCexplained I ment the calculated torque, is it from zero rpm available or in other words are the motors over the complete rpm band compareable.
@@RCexplained I think I'll have to learn more. But now I find you and will abo you to watch relaxed some old vids and of course the new ones.
Have to read more about the topics, I new start RC Hobby.
Finally someone speaks the truth!
Same basic principle applies to brushed motors too all else being equal. You might get an advantage in the brief transition between zero and a few RPM but that's it.
Thanks for the support and commenting Budget RC! You are very correct, this applies to brushed motors as well.
Thank you, now i will try to apply this to building my battle bot
No worries! That sounds like a lot of fun!
@@RCexplained yea ill post part of the build on my personal channel as i get parts, i have a very modest budget about $500 to build a 25-60lb
@@timmytheimpaler1750 Sounds good, I'll have to check it out.
What am I missing? Kt = 1/Kv. Kt = 1/790 = 0.00126582.
Unit conversions. kv uses RPM. Kt uses rad/s.
@@RCexplained Thanks for the reply - could explain this is another video perhaps - the maths of how to get to gearing from Kv, via Kt? Perhaps others, like me are intruiged as to how to choose the optimal gearing - I race 1/12 pan cars in stock 13.5 turn bsushless motors. 1s Lipo, 1s specific ESC (120amp). Each race is between 4 and 6 minutes so I want the best performance for that duration. I liked your video on designing/ choosing your power system - would be great to see a more in depth one for my case (although I don't have much choice), and perhaps specific examples of the other two? Great work - I've learnt a lot - I'm just missing a few details. Thanks
@@xaviertaylor759 the best way to further optimize gearing and other choices is by testing different combinations and measuring performance, power output and heat. The theoretical side will only get you so far.
Hey Xavier, just an update. The recently uploaded video shows the math on Kv vs Kt to answer your question here. Also the video planned for next week will look at gearing and kv selections to a degree.
@@RCexplained Do you have a link to this? I am curious to know how to convert Kv to Kt too. Came across this channel today, absolutely amazing. Liked and subscribed!
This series is the best explanation of the various motor parameters I've seen. Unfortunately, it's still not quite explaining what the advantage of bigger motors is (in my specific case, on fixed wing aircraft). Does more KV mean more speed? Why, if the total torque is always the same? Also how does motor size affect things, how is a larger motor better than a smaller one (I know it's more heat dissipation, but what does that mean in practice? More speed? More efficiency?).
I am hopelessly confused on this subject, alas.
Larger motors mean more power output potential. With more power output you can set your airplane up to go faster.
More kv can mean more speed if your motor and power system is able to deliver the increase in power output.
@@RCexplained I see, thank you, so basically what we care about is the wattage, not so much the size (except for heat dissipation, I guess), is that correct? Ie I can just look at the wattage to figure out how much power the motor can deliver and the amperage to figure out if it'll burn?
Also, why does more KV mean more speed, since power is constant? Wouldn't more KV with a smaller pitch prop be the same power as less KV with a larger pitch prop (since more KV = less torque for the same power/size motor)?
Sorry for all the questions, I'm just a bit confused because all the explanations I've seen tend to change more than one variable at a time, and not say "more KV means this, more power means this, more size means this, all else being equal". Thank you!
I thought v was for velocity?
The "v" in Kv is for velocity.
very good explanation, and professional talk! in the next video please explain how KV and torque will be affected by the gearing ! for example, a 2200kv will use a 16T pinion and a 1480kv will need a 19T pinion on the same car to achieve the same end speed
Hi stephane. Thank you for your comment. I have this topic included in my queue of video topics.
Whilst this is theoretically true I'd argue that in practice we don't scale everything appropriately, smaller than equivalent cells, same connectors and wiring etc. In practice I would argue that lower kv motors DO produce more torque because the system usually restricts the amp load for an equivalent high kv motor.
Hi Fraser, thanks for the comment. If we don't pick our power systems correctly and as a result restrict the amp load, that's on us. It's not the higher kv motors fault.
@@RCexplained 100% My point though is that it's rarely, if ever, done in practice. Even if you wanted to, there is so much that is standardised. Typically moving to higher voltage is something we do to prevent having to deal with huge current amounts that would be problematic. Often it is not really feasible to go the other way.
BTW your videos are spectacularly good. I'm somewhat honoured that you responded to a comment on a year old video.
@@RCexplained let me phrase the question slightly differently: In what practical rc application would you be able to halve the voltage/double the current and still have the same amount of torque?
I'm saying you practically can't because the requirements of the increased current dramatically change properties the system. If you don't change it, you suffer losses that will suck power out leading to lower torque. For example xt30->xt60.
Thanks for the comment Fraser. I respond to all new comments on the channel. It pops up in my feed as long as there arent too many all at the same time. I understand your point, and I guess it would really depend on the power system and the application.
Please lend some advice to a newb! Just got a limitless. It came with a 2650kv motor and mamba (something) esc! I just bought a hobby wing Max 6 combo with the 1650kv motor. What am i to expect? I'm running 6s (2 3s lipos) Thanks just subscribed!
Have you tried entering this combination on the radiocontrolinfo website? There is a calculator that will estimate the potential speed that you may be able to hit.
@@RCexplained I hadn't, but will now. Thanks!
no problem!
Love your channel. Very easy to understand. One suggestion...can you work on your background? Seems like you're in a Doctor's waiting room.
Hi Fritz, thanks for the comment. Once I move, I'll be able to focus on the background and completely change it. Until then, there's not much I can do.
@@RCexplained my #1 recommend rc doctor 👍
I have a 2000kv motor and a 70kv motor, weight is the same, but i get much more torque output out of the 2000kv with a 7:1 gear ration in comparison to the 70kv motor with no gear why is this? (Voltage is the same) and good video 😉
Hi Lukas, just curious how you know you are getting less torque?
What are the continuous wattage rating of both motors? What is the maximum RPM spec of each motor? What is the voltage you are operating on? What is the max continuous current spec of each motor?
Thanks Ryan a lot! Shame on me I haven't learnt physics at school so now it takes so much time to understand all this things..... It's mindblowing for me right know but interesting at the same time....Like learning magic xD
Am I right with my current situation (my 1:10 truggy that has 3100 KV motor (size 3650), 60A Esc and 3s lipo battery) and I want this car to climb better at low speed (or rotate slightly larger and heavier wheels without noise and vibrations at the start), that swaping to 2400kv motor only(!) I will not reach my goal? I guess, I need a bigger motor (for example 3660 or 3665) with the kv matches my battery (already put a smalest pinion gear on my 3100kv motor). Is there a solution to reach my goal without changing (at least) my battery?))
Thanks in advance a lot! :] Keep it going!
P.S: I found the answer from two (or more) of your videos:
- it is better to use sensored brushless motor for this type of riding.....
Thaaaaanks!!)
Hello, if you are not looking to go faster a kv drop will help with more power for going up hills and accelerating. A sensored motor will help with extremely slow speeds.
You missed the most important aspect of this, which is the fact lower KV gives you better torque at lower rpm, and higher KV gives you better torque at higher rpm.
You fail to mention that the torque value max is reached much quicker at 790kv than 2830kv which is really the point in going lower kv, the way you've presented this is a little misleading.
You should give the simple answer first, and then get into the specific answer.
This is not realistic, the torque is at low and medium motor speed, where there is interest. Less Kv = More torque at low and medium engine speed.
What was described in the video occurs within the full RPM range.
@@RCexplained ; Ok , no problem ;-)
I'd say you'd need to look at the whole system to choose the correct motor. A low kV motor will require less amps but more voltage for the same power, while a high kV motor will require less voltage, but a lot more amps. Generally it's more difficult to get high amps delivered (need bigger wires, batteries with high C rating and beefier ESC), but you probably also don't want to use batteries with a lot of cells. To get the most torque and power out of the motor, you need to max out voltage and amps as best as you can with the space and money you have available.
Hi Razor Blade, that's very true. This video is specific to torque vs kv, if you are interested in how to choose a brushless motor there is a separate video for that on the channel. This video in no way covers how to select a brushless motor.
You say Kt is the "torque constant" of the motor, that is fine. You say (like 95% of the Internet) Kv is RPM/volt. Shouldn't that be Kv is the "voltage constant" of the motor? That is the relationship between rotational speed and back e.m.f. produced by the motor, it has nothing to do with the voltage applied to the motor. There is only an approximate relationship between this and RPM/V, close enough for our use I guess but this is just another example of inaccuracy being perpetuated across the internet.
Hi Don, thank you for your comment. I'm not exactly sure what you are after here as it seems you fully understand why Kv is used. But either way, please let me try to explain.
Similar to Kt, Kv has been defined for the sole purpose of providing us with a standard to determine a mechanical property we get out of the motor for an electrical input. Kv is known as the velocity constant (upper case V is voltage) and this is very important. Like the torque constant provides us with a means to understand mechanical output torque of a motor, the velocity constant provides us with a means to understand mechanical velocity. Translating between electrical and mechanical properties will never be "exact." This is for Kv and Kt.
Now if we were interested in back EMF produced per RPM of input we would use the back EMF constant also referred to as the voltage constant - Ke. Note that Kv and Ke are inverse to each other and setup for their intended use. Ke and Kt are equal to each other but use different units. Ke would be used in electrical motor calculations as standard practice. Kv would be used when relating mechanical output.
As for this video being another example of inaccuracy being perpetuated across the internet - There are many sources of information out there and I understand some may be inaccurate. It's not easy explaining this stuff to a world of opinions. But at the end of the day, we are all just trying to provide free information in order to bring the hobby to another level, allow hobbyists to reach their goals *successfully* and to be able to have the most fun possible.
@@RCexplained I'm trying to wrap my brain around all this R/C electrickery, I think I'm getting there but it is difficult as there's so many and differing explanations for things like this on the Internet. There are so may threads (and as you say, opinions) on so many forums on this subject. I must say your videos are proving to be the easiest way to learn this stuff, thanks for that. I hope you don't think I'm saying you or your video are wrong coz I'm not haha, apols if you got that impression. It's caused by my remaining but diminishing confusion, haha again.
Thanks Don