Amazingly well explained! As a mechanical engineer, I really appreciate the math. If I were to make fpv quad content, it would be this, but you've already done it better than I could! Thank you. We need more of this in the community. There are so many people out there spewing nonsense.
3 YEARS ago you posted ... but i needed the answer literally today (okay this about week) ..... and boom sent from Heaven LOL Thank you for answering my exact question.... WITHOUT EVEN SEARCHING ... amazing LOL I guess the algotrithm and my intent crossed at the right time!! CHEERS
I can't compliment this enough. Wow. This is the most informative and clearest video I've ever seen on motors, props, and power. Until now, it's just been magic to me.
@@ChrisRosser So much this 😅 I barely trust FPV reviews now because everything seems to work perfectly for everyone, and every new drone is the best drone. Whereas I've had nothing but problems. Luckily I've found fixing drones is actually pretty fun and relaxing.
i screen shot every slides while listening thinking there's no way he would share the slide, after watching i checked the description to my surprised it actual has. thank you so much for sharing the materials.
Finally somebody who takes a more scientific approach than the usual "I-do-it-this-way-because-I-know-best". Glad to have discovered your channel. Subscribed, of course.
I agree with you.. 90%. There are too many "myths" and trends repeated over and over in forums Some like me are skeptical.. but no matter how much you try to disprove.. they get repeated over and over. HighKV - battery is the limit. No point of going even higher KV. Motor feel - its what rates and throttle expo is for. Can also be BLHeli ESC ramp up power. Pancake - Its not magic. The "smoothness" is bigger bearing and LACK of responsiveness.. ie lag. It IS great for slower cinematic flying with light props!! Diamater to height ratio. There is good reason why 2207/2306 is very common. It works. No "magic". Just result of trial and error. Now, we have lighter props. Lighter 2405.5 makes sense. Going above 4:1 or below 2.5:1 can lead to desync and bad experience.
i'm not new to the RC world but I bought my first quad 3 months ago and I can't tell you how much this has helped me as a newbie. Thanks Chris for making this kind of content.
The last time i got this feeling of physic enthusiasm was in school with the thematic electric motor. Oh wait, here we go again: Bring me the teacher i have to teach him about it! AGAIN xD Chris u made my day. A lot of love from germany!
Great content! This is what we've been missing on UA-cam: combining more engineering perspective with application. I have one suggestion on the next topic: Since the long range quads are getting more popular these days (especially 4" ones), I've been wondering which factor is the governing factor for long range cruising. Tilting your quad to 40 degrees while going 80kph obviously generates lots of drag, and on top of that, the prop drag, how much does it contributes to the overall efficiency? and so on, this could be expanded to a series of topic.
Much of motor selection for FPV seems to have been done via trial and error. Now you've added the theory to that. Great contribution. Thanks. I look forward to future work in this area to improve motors by combining practice and theory.
Thank you so much. You perfectly identified the source of overheating in my motor. I had exceeded the tip speed limit and was compressing air and heating the motor. Ive created a spread sheet to show max Kv for any prop size and battery voltage for future designs. Thanks again.
Thank you so much for doing this! I've been trying to get this across for years, but it's really hard to get this information through clearly in a hobby that is often governed by a lot of bro science. Some great stuff in here! I would point out one additional component in the width vs height debate. The stator isn't the only that is changing when the motor size changes. The magnets in the bell are also changing size, so there are some additional torque losses from the magnet size being smaller as well. This is particular problematic as you get to very flat motors as the thinner size of the magnets means that the magnet volume is decreasing at a greater rate than the stator volume as you go flatter and flatter on the stator size. Combined with the increased moment on the bell, and the overall lower torque from the stators, this is where you get into serious desync problems, and this is why some flat wide motors might need things like higher rampup power and lower timing in the ESCs to accommodate the torque problems.
I was hoping you might show up Ryan! Thanks for the really detailed comment. I hope you'll like my deep dive on props that will complete this two parter 😁
Awesome video, Chris! I'm so pleased that I found your channel. At last, some science and math to consider when listening to the anecdotal stories about why which pilot likes which motor/prop combination. A little theoretical consideration always helps to clarify data which can be interpreted in numerous ways depending on the rigor which is applied. Thanks... keep it up.
Heck yeah man! Thanks! People been throwing shade on my apex micro 4", saying the motors are to big, blah blah blah. I have 2004's on the corners and she flies like a screamin bat from hell.
Thanks for taking the time to make all this kinda stuff. Its exactly what i want when im gonna pick out moters and need help deciding. Thanks you my good sir, you have done us all a service.
I'm primarily selecting motors for model aircraft applications so they're bigger than what you're showing here but this lays the groundwork for me to calculate out what I need.l, thx.
Fantastic Data! A lot to absorb, but truly eye opening. Finding myself intrigued by the thought of field testing to these parameters. Please, keep this up!? This Hobby needs a Hero and this is just the information to kickstart something AMAZING!
Finally some deep dive in the inner workings of the motor! Loved it! I would like to understand more in depth how different KVs are made on the same stator dimensions and the mathematical interaction with the other laws and dimensions of the motor!
I really appreciate this video and have watched it several times to really understand brushless quadcopter motor selection. Your an FPV guru - "the professor"
I'm a proxy flier/duffer. Old guy stuff. Up until recently, I was an exclusively BNF flyer. I fly indoors using a 2S platform with 1103 7800kV motors and 1935 props. I managed to tame it by scaling the throttle back to 80% in Betaflight, and lots of expo using my transmitter's model profile software. I prefer setting my hover point to mid-throttle, as I don't use full throttle, ever. I've flown the same platform for three years and have accumulated almost 200 hours flying time on it. I started with BF 3.2, I think, with a PIKOBLX F3 FC, now I'm using a MAITEK 411 F4 running BF 4.2.6. After 3 years of contant poking and prodding, my numbers now make the thing fly ultra-smooth, with motors that are barely warm to the touch after a 2:30 flight. I've got parts on order for a new build using one of my spare 100mm frames for outside flying that will use the same FC, 12A ESC, and props as my indoor one, but I'll be using 1104 7500kV motors made by the same company as the 1103s. I expect I can go to 100% on the throttle scale and not worry about stressing the motors. If I understand this video correctly, I think I'm on the right track. Your content is great stuff, Chris. Super-detailed, uni-grade. Exactly the thing we bodgers need to help advance our understanding of this fascinating hobby.
This is the video i was exactly looking for to explain why a new 6" build with 2604 motors has wobbles in low throttle, I had the wrong props . Thanks Chris
I graduated from aerospace & mechanical engineer , your information give us so much confidence about the science of fpv quad . thank you very much . Also will like to see some heavy loaded drone tuning case X8 thicc
Absolutely, hopefully the graph and my recommendations helped make it a little clearer. I will be doing a less technical take on this soon as well for people who don't have the time to go into all the detail :)
This is the video I really needed 🤩 Thank you so much sir. I am shopping for motors, and I am so happy I found this video just at the right time. Weight will obviously have a huge effect aswell.
This is a kind of content with which, learners like me are more than satisfied😌♥. I'm looking for more of such stuff, and people in my surrounding to chill with so that I can also improve myself as much as possible!! In short Great content 🙌👌.
Thank you for explaining this. I do not use drones, but I do know about electrical motors and electronics. I am just bit surprised, that there is a lack of responsiveness. I do understand the physics of it. But I tend to think, that the software and design of the ESC also might have some influence on the "reserve torque". Perhaps the ESC typically used got a limited bandwidth of the speed control loop. I guess that the ESC should be able to operate the motor in two quadrant mode. But if the ESC only can provide motor with torque in one direction (one quadrant), then that becomes a problem and will reduce responsiveness significantly. I did not do calculations on this, but I have worked with normal DC motors, and a speed control loop with bandwidth of about 40 Hz is not that difficult to do with two or four quadrant control, and it becomes very responsive. However it requires, that you got a good internal (ESC) signal for shaft speed, that is updated with a frequency of about 1-2 kHz.
This is brilliant content and such a valuable resource. Thank you, Chris. More science-based videos which we can all draw upon to make design decisions I'm sure will be most welcome, as not many people are making that sort of content.
Amazing video! But why do you think so many people prefer flat motors to tall ones? You mentioned that people go by motor feel (which can and should be tuned using throttle expo). Here is some speculation on more possible reasons: - A slower responding motor might be somewhat compensated by higher pids and therefore not that noticable. A higher motor time constant might even match the default pids better (specifically p i d ratios) - For some configurations the propeller's inertia might be dominant and the motor might not matter that much. - People compare different stator volumes: 2004 motors are slightly larger than 1408, 1507 and 1606. (And almost the same size as 1805) - Going from a 9s12p winding to 12s14p improves torque by about 7.5% (winding factor 0.933 vs 0.866) BetaFPV's 1805 motor seems to have a 9s12p configuration (like most narrower motors from all manufacturers), explaining the popularity of 2004 motors (which usually use 12s14p). - People compare motors with different (actual) kv. - Placebo effect when not doing blind testing.
Great video, tons of great info. Really explains the advantage of using a pancake motor style for a longer range cruising drone, and why not best choice for free-style, or racing. In LR, trading motor and throttle response for a larger moment of inertia, while having good torque with a lower kV. Picking the right motor really depends on what one is optimizing for: free-style, long-range, or racing. Moment of inertia also plays in prop size, and thus frame size, as having larger motors on long arms is not great for free-style, or a race-course with tight turns. Keep up the great content. Understanding the relationship in component specs and between components is invaluable knowledge.
Hi Aerial, thank you for the comment. Just to clarify, I don't think that pancake motors are necessarily good for long range. The only advantage larger diameter:height motors have is cooling which you don't need for long range cruising. In a long range application you want maximum torque in the lightest possible package with the smallest rotor MOI. I would target diameter:height of 3:1 e.g. 1806. For all quadcopters regardless of application we want the lowest motor MOI as possible.
Hi Chris, thank you for your "Master Class" on motor selection. You have demystified this selection process for the laymen and gained a subscriber. May I suggest you present another "Master Class" on propellers: their diameter, pitch, number of blades, and shape and their influence on motor selection. Or given a flight mission (free style, cruise, race), does one start the build with the props, match with motors, than match with the frame, etc. Sorry, too much to ask.
Thanks Chris for such relevant information, especially for me as I'm rewinding motors for pilots here in Brazil, both to keep the original specs and make changes to the KV factor when necessary.
So many people flying 2306 vs 2207 as we have been told for all these years that they have better low throttle torque and control. Yet your maths now show that is nonsense. 2306 vs 2207, all else the same, the 2207 will perform better, more torque, more response more top end. Dam.... Good work man.
A 2207 will have more torque yes. Throttle resolution could be better for the 2306 because it is a weaker motor and therefore a given movement of the throttle stick produces a smaller change in thrust. But this is no different than the 2207 with a 94% throttle limit or a bit of throttle expo. Glad you enjoyed the video 😁
@@ChrisRosser perfect, i was trying to tie up what we were feeling with what you were saying. This is great info thanks! I it the bullet and went2306 for the better low end feel. But grudgingly so as the narrower motors do tend to have better durability. Now I now how to make the narrower motors feel the same. I left a comment on the Apex video as well about some inconsistencies I found, really curious on what you think if you have the time to check it out.
Awesome content. Looking forward to seeing this channel grow. Love geeking out on this stuff and it's really the first time I've seen hard data from someone with relevant academics behind them.... not to say that people with experience don't also know what they're talking about though. I'm currently messing with some long range designs and would love to see some tips on selecting motors and props to maximize flight time and range on sub 250g designs! Keep up the great work Chris!
I think that if you combine this video with a future video I am working on on selecting props that should give you what you need. Pick the right prop for what you want to do and then the right motor for that prop 👍
Super helpful information, thanks! I'm building a 6" LR quad and there is very little info on such a beast beyond the generic iFlight frame recommendations. This let's me figure it out for myself and tailor it to my specifics.
Really interesting content, this video makes the theory more understandable! Also very useful as a 'cheatsheet' for choosing hardware :) Maybe it also would be helpful to give some extra suggestions at the end/conclusion of the video of setups that work really well in your opinion. For the people who don't want to dive into the theory but want a proper combination of hardware to go back in the field.
As a battlebots hobbyist, we have to use a different approach for these motors, which are typically seen in the 1 lb - 3lb weight classes of bot either as a weapon motor or drive motor. These motors need to swing effectively MASSIVE levels of intertia for a given size, and as such we need the lowest kv possible motors so they don't cook themselves or their speed controllers in the 3 minute or less fights, especially since airflow is basically 0. The motor has to heatsink all of its losses without demagnetizing. To this effect, a larger diameter pancake style rotor is vastly preferred, for example my 150 gram shell spinner has a 75 gram 4" diameter shell to which I need to fit all the torque I can in as flat a space as possible. I currently use a sunnysky V2302 1500kv at 2S for this. It has enough torque and heatsinking ability to maintain sub - 120C temps after a 2 minute match, and as it uses 3 x 9 x 3mm bearings is quite resilient to basically constant impacts. Check it out - my bot's name is Chakram
Another interesting factor is the mass of the permanent magnets. A tall narrow motor will have more volume of permanent magnets than a pancake motor of the same stator volume. The magnets contribute to the mass (and thus inertia) of motor bell. How do you think that factors into the responsiveness?
If we substitute constant stator volume and magnet thickness into the MOI equation I get a relationship where MOI increases linearly with stator diameter. However, due to edge effects a taller magnet may not need to be quite as thick to generate the same average field strength. Excellent question!
This is probably the most significant thing left out of the (excellent) video. As you move towards a pancake motor, you have smaller and smaller magnets, which affects performance. I wonder if there is an ideal ratio of magnet size to stator volume, which could change Chris's proposed 3:1 ratio.
@@sakfpv8444 Yep, so motors close to those sizes should be best for freestyle. If you have a cinewhoop or something heavier for its prop size then a flatter motor may be needed to stay cool.
Wow you da man!!! I've been drinking the pancake stator Kool-Aid, buying into the stator diameter increase is a plus for a given volume. What effects do motor heat have on efficiency and performance? Obviously heat can ultimately damage motors, but what effects does heat have during normal operation? Does a hot motor operate less effencitly and further generate more heat? I find it interesting you specifically mentioned the turbine cooling design. It seems to me that cooling is more a centrifugal fan function as the motor is operating against airflow/pressure. Another interesting topic would be propeller power requirements. As a corollary to KV selection it would be great to have some way to rate props as to power requirements or how to evaluate prop choices. Appreciate your efforts, you've raised the bar, please don't stop now!!!
The wrinkle in the KV selection problem - you can use higher KV to compensate for lighter loaded and lighter weight props, and end up with significantly more effective resolution, and be within a few percent of overall efficiency, with something that has inherently better responsiveness, and better transition characteristics from unloaded to loaded on props. That being said, I fly everything like it's a racer, so punishing batteries just is what it is.
You are spot on! The goal is to match the max current required by the motor at full throttle to the max current available from the battery. If you use a light pitch prop you will need a higher KV motor to make that happen.
Great video. Something I'd be interested to learn more about is the role of motor weight. For example, I might intentionally pick a motor with less stator volume because the motor will be significantly lighter. Good example is 1202.5/1303 being popular on 3" toothpicks rather than 1404 (the ideal motor according to your chart) since it will save 20g of weight (which is a lot for lightweight builds like that -- think TP3).
Similarly, I might go for different width/height because of weight. For example, according to your chart, 2004 and 1806 are similar stator volume, but from some quick Googling, it appears that many 2004 motors are quite a bit lighter than typical 1806 motors. Maybe that's why pancake motors are so popular with ultra-light builds?
I really like 1806 motors for 4in and even light 5in biblades. They are quite hard to find but they have a good amount of torque and aren't too heavy. 2004 is pretty good for 4in though.
Chris, Absolutely great video! Lots of information; I’ll watch it through again at least once to fully absorb everything. I’m becoming more and more interested in 6-7 inch long range “cruisers” such as the GEPRC Crocodile7, the Diatone F7 or the Iflight Chimera7. I’d very much like to see a deep dive into motor/prop/battery combinations that produce long flight times with the science and math behind it.
Great video. I've been experimenting with batteries recently. They are the limiting factor eg a 850 mah lipo can't provide the amps to run a 1408 at top speed.A1300 can but it's heavier. The balance is so hard to find even with the great info you provide.
so good!!!!!!!!!! I really hope your channel gains traction.. I LOVE it. However it's a tough sell to anyone who didn't pay too much attention in maths and physics (I'm gonna guess that's MOST of the YT audience)... That said, perhaps you can take some of this amazing data and manufacture some parts?. I would 100% consider a propeller designed by you, or a frame, or motors, or.... Im a fan. keep doing what you are doing. BRAVO!!!!
Hopefully the channel is accessible even for those who may not follow along with the formulas. I always try to give recommendations for that reason. Thank you for your support!
Would like to point out that also higher motors tend to last less - longer shaft bends easier than shorter one on lower height motors... Also after few years in fpv, i noticed that motors with weaker magnets - when they don't have that clicky feel when you spin them - tends to be more quite more efficient than clicky motors, but they also usually lack the power, so it is smart to go with bigger motor and weaker magnets if you are looking for something efficient rather than with lighter, more powerful motor :)
When talking about efficiency are you speaking of flight time or g/W. Less powerful motors will give a longer flight time because they make less thrust. The same effect can be achieved with a throttle limit.
@@ChrisRosser I tested two motors of same size and KV. In both, crusing style flight and more agressive freestyle, motors with weaker magnets always flew longer (25-40%) but didn't have as much top end. Also compared 1106 and 1404 6000KV motors which have roughly the same volume. 1404s are more powerful while 1106s are bit more efficient - again, tested with several flight styles and 1106s always flew 15-25% longer.
@@ChrisRosser as i said, i tried to cruise for as long as possible, so throttle limit wouldn't make a difference in flight time... also I am using older, heavier components on build with weaker magnets, so even with extra weight it flew longer
@@flowrfpv 25-40% is an enormous discrepancy in flight time. Based on the information you have provided magnet strength would not account for this difference. I would look at differences in the battery, props and camera uptilt. If you have current sensing set up you can monitor your current draw during cruise. I would bet the quad with stronger magnets is cruising faster and using more current because you are requesting more thrust. Let me know what you find out!
beautiful! thanks. I would really like a video which explains what goes wrong on each "inapropriate usage" case scenario. For example, what happens when you use motors with lower kv than what you expect for that battery/propsize/payload. What happens when you do the contrary (for example use a "4s" motor with "6s" with the same prop size), and what are more or less tolerable margins. For example, Im buidling something like the terraplane (high power 3" cinwhoop) but I only have 2306 in 1900 kv. I'm wondering what would happen if use them. Props will spin slower than needed I guess. What will happen with the amps? If not, I have 1408 in 3500kv (typically though for 3" open prop). What will happen if I use them with 3" ducted hexablades? Will the motors be damaged? What happens with the amps on the esc. As you can see my questions respond to my "experimental" spirit in combination with the conservative one, as I dont want to breake everything... Thank you as always!!!
Iron losses are directly proportionate to operating voltage and a motor's idle current rating, and higher KV versions of motors can feature lower internal resistance ratings than do their lower KV ones. So, at sufficiently high cruising speeds, the 3400KV 2207.5 likely delivers 1.16 BHP more efficiently than its lower KV versions would.
I think the losses in the cables and stator windings are more important. Thrust tables clearly show higher KV motors are less efficient in terms of thrust per watt of power on the same props. The problem only gets worse when you take into account that more current drawn from the battery = more loss in its internal resistance.
@@ChrisRosser When pulling 45 A at 19.8 V, the combined iron and copper losses would total about 160 W in the 1750KV version of the 2208 Velox yet only about 120 W in the 2450KV one. Moreover, under those constraints, this 2450KV motor would deliver more of its brake horsepower in the form of angular velocity than would that 1750KV one - which is of benefit in maximizing cruising speed (albeit, to the detriment of acceleration and, thus, handling).
Amazingly well explained! As a mechanical engineer, I really appreciate the math. If I were to make fpv quad content, it would be this, but you've already done it better than I could! Thank you. We need more of this in the community. There are so many people out there spewing nonsense.
Glad you found this helpful! Thank you for your support.
@@ChrisRosser I have I question which motor kv or propeller pitch is the best to use on 5inch 4s build for cinematic flying?
Been craving for this type of content for ages. What a blessing to have a man from Cambridge explain it to me for free.
I'm glad you enjoyed it, more to come in the future!
This type of content is what ive been looking for. 👍🏼👍🏼
I'm glad you enjoyed the video. I'm super psyched that people like yourself are finding these deep dives useful.
3 YEARS ago you posted ... but i needed the answer literally today (okay this about week) ..... and boom sent from Heaven LOL
Thank you for answering my exact question.... WITHOUT EVEN SEARCHING ... amazing LOL
I guess the algotrithm and my intent crossed at the right time!! CHEERS
I can't compliment this enough. Wow. This is the most informative and clearest video I've ever seen on motors, props, and power. Until now, it's just been magic to me.
Could you do a deep dive into props?
Oh it's coming! Already started the research for the video, don't know yet when it'll be ready but I'm working hard on it.😁
Glad it was helpful! I'm hoping it helps cut through some of the marketing fluff that we've all had to deal with.
@@ChrisRosser So much this 😅 I barely trust FPV reviews now because everything seems to work perfectly for everyone, and every new drone is the best drone. Whereas I've had nothing but problems. Luckily I've found fixing drones is actually pretty fun and relaxing.
My man!!! This is finally some quality content. So many people in the community spread fake info on this topic!
i screen shot every slides while listening thinking there's no way he would share the slide, after watching i checked the description to my surprised it actual has. thank you so much for sharing the materials.
Engineering based content! Hooray!! Its been 20 years since I was at university. This takes me back and I like it.
I'm so glad I found your channel!
This is a treasure trove of analytical data!
Welcome aboard!
Finally somebody who takes a more scientific approach than the usual "I-do-it-this-way-because-I-know-best". Glad to have discovered your channel. Subscribed, of course.
I agree with you.. 90%. There are too many "myths" and trends repeated over and over in forums
Some like me are skeptical.. but no matter how much you try to disprove.. they get repeated over and over.
HighKV - battery is the limit. No point of going even higher KV.
Motor feel - its what rates and throttle expo is for. Can also be BLHeli ESC ramp up power.
Pancake - Its not magic. The "smoothness" is bigger bearing and LACK of responsiveness.. ie lag.
It IS great for slower cinematic flying with light props!!
Diamater to height ratio.
There is good reason why 2207/2306 is very common. It works. No "magic". Just result of trial and error.
Now, we have lighter props. Lighter 2405.5 makes sense. Going above 4:1 or below 2.5:1 can lead to desync and bad experience.
i'm not new to the RC world but I bought my first quad 3 months ago and I can't tell you how much this has helped me as a newbie. Thanks Chris for making this kind of content.
You're welcome! Welcome to the rabbit hole 👍
You are one of those people that really put in the effort to share a large amount of knowledge towards the hobby. Thank you.
The last time i got this feeling of physic enthusiasm was in school with the thematic electric motor. Oh wait, here we go again: Bring me the teacher i have to teach him about it! AGAIN xD Chris u made my day. A lot of love from germany!
A lot of love right back at you from the UK!
Great content! This is what we've been missing on UA-cam: combining more engineering perspective with application. I have one suggestion on the next topic: Since the long range quads are getting more popular these days (especially 4" ones), I've been wondering which factor is the governing factor for long range cruising. Tilting your quad to 40 degrees while going 80kph obviously generates lots of drag, and on top of that, the prop drag, how much does it contributes to the overall efficiency? and so on, this could be expanded to a series of topic.
Much of motor selection for FPV seems to have been done via trial and error. Now you've added the theory to that. Great contribution. Thanks. I look forward to future work in this area to improve motors by combining practice and theory.
Thanks for your comment and support!
Thank you so much. You perfectly identified the source of overheating in my motor. I had exceeded the tip speed limit and was compressing air and heating the motor. Ive created a spread sheet to show max Kv for any prop size and battery voltage for future designs. Thanks again.
Thank you so much for doing this! I've been trying to get this across for years, but it's really hard to get this information through clearly in a hobby that is often governed by a lot of bro science. Some great stuff in here!
I would point out one additional component in the width vs height debate. The stator isn't the only that is changing when the motor size changes. The magnets in the bell are also changing size, so there are some additional torque losses from the magnet size being smaller as well. This is particular problematic as you get to very flat motors as the thinner size of the magnets means that the magnet volume is decreasing at a greater rate than the stator volume as you go flatter and flatter on the stator size. Combined with the increased moment on the bell, and the overall lower torque from the stators, this is where you get into serious desync problems, and this is why some flat wide motors might need things like higher rampup power and lower timing in the ESCs to accommodate the torque problems.
I was hoping you might show up Ryan! Thanks for the really detailed comment. I hope you'll like my deep dive on props that will complete this two parter 😁
@@ChrisRosser Looking forward to it man!
This was very valuable for a newbie who needs to start looking at motors after a hard crash.
Thanks! I'm glad it helped.
Wow, there is no better explanation then this anywhere.
Awesome video, Chris! I'm so pleased that I found your channel. At last, some science and math to consider when listening to the anecdotal stories about why which pilot likes which motor/prop combination. A little theoretical consideration always helps to clarify data which can be interpreted in numerous ways depending on the rigor which is applied. Thanks... keep it up.
Heck yeah man! Thanks! People been throwing shade on my apex micro 4", saying the motors are to big, blah blah blah. I have 2004's on the corners and she flies like a screamin bat from hell.
Thanks for taking the time to make all this kinda stuff. Its exactly what i want when im gonna pick out moters and need help deciding. Thanks you my good sir, you have done us all a service.
I'm primarily selecting motors for model aircraft applications so they're bigger than what you're showing here but this lays the groundwork for me to calculate out what I need.l, thx.
*Chris Rosser* 💯 🏆 🥇
Щиро дякую за *просвітницьку* 🧑🔧🔬🧠✨ діяльність, дуже корисно!
Finnaly a explanation which supports my theory
i love your channel, please keep doing this.
In the words of Jim Carrey in 'The Mask' "Somebody stop me!" I'm so pumped you're enjoying the videos. 😁
Another fan of The Mask , imma say "Smoookinn!!"
@@aakashjana6225 Appropriate for a motor video 😎
The detail in this is unreal, although so much of it goes right over my head because I'm simple minded!
Fantastic Data! A lot to absorb, but truly eye opening. Finding myself intrigued by the thought of field testing to these parameters. Please, keep this up!? This Hobby needs a Hero and this is just the information to kickstart something AMAZING!
My pleasure!
Finally some deep dive in the inner workings of the motor! Loved it!
I would like to understand more in depth how different KVs are made on the same stator dimensions and the mathematical interaction with the other laws and dimensions of the motor!
This is the content I am looking for! Thank you so much.
Glad it was helpful!
I really appreciate this video and have watched it several times to really understand brushless quadcopter motor selection.
Your an FPV guru - "the professor"
fellow physicist enjoying them equations ;) keep those facts coming!
More to come!
I'm a proxy flier/duffer. Old guy stuff. Up until recently, I was an exclusively BNF flyer. I fly indoors using a 2S platform with 1103 7800kV motors and 1935 props. I managed to tame it by scaling the throttle back to 80% in Betaflight, and lots of expo using my transmitter's model profile software. I prefer setting my hover point to mid-throttle, as I don't use full throttle, ever.
I've flown the same platform for three years and have accumulated almost 200 hours flying time on it. I started with BF 3.2, I think, with a PIKOBLX F3 FC, now I'm using a MAITEK 411 F4 running BF 4.2.6. After 3 years of contant poking and prodding, my numbers now make the thing fly ultra-smooth, with motors that are barely warm to the touch after a 2:30 flight.
I've got parts on order for a new build using one of my spare 100mm frames for outside flying that will use the same FC, 12A ESC, and props as my indoor one, but I'll be using 1104 7500kV motors made by the same company as the 1103s. I expect I can go to 100% on the throttle scale and not worry about stressing the motors.
If I understand this video correctly, I think I'm on the right track. Your content is great stuff, Chris. Super-detailed, uni-grade. Exactly the thing we bodgers need to help advance our understanding of this fascinating hobby.
This is the video i was exactly looking for to explain why a new 6" build with 2604 motors has wobbles in low throttle, I had the wrong props . Thanks Chris
I'm glad the video helped. 2604 is a very flat motor also. Maybe a 2408 size for 6inch would also help with the wobbles.
@@ChrisRosser Yes I'm going back to the F80s just wanted to see what these things were all about. Thanks again man .
I graduated from aerospace & mechanical engineer , your information give us so much confidence about the science of fpv quad . thank you very much . Also will like to see some heavy loaded drone tuning case X8 thicc
Watched that from Russia. Very nice speech, easy to understand, material is interesting. Nice job.
This is all very interesting. There are so many variables. Change just one thing and everything else changed.
Absolutely, hopefully the graph and my recommendations helped make it a little clearer. I will be doing a less technical take on this soon as well for people who don't have the time to go into all the detail :)
This is the video I really needed 🤩 Thank you so much sir. I am shopping for motors, and I am so happy I found this video just at the right time. Weight will obviously have a huge effect aswell.
Great work Chris. Thanks a lot for this input
My pleasure!
This is exactly why I do taller rather than wider stator I'm my designs. Thanks for doing the math!
Glad to help! Thanks for the comment.
Really interesting, this is deffinitely going in my drone info playlist :)
Awesome, thank you! Glad you like the video 😁
This is a kind of content with which, learners like me are more than satisfied😌♥. I'm looking for more of such stuff, and people in my surrounding to chill with so that I can also improve myself as much as possible!!
In short Great content 🙌👌.
Thank you for explaining this. I do not use drones, but I do know about electrical motors and electronics. I am just bit surprised, that there is a lack of responsiveness. I do understand the physics of it. But I tend to think, that the software and design of the ESC also might have some influence on the "reserve torque". Perhaps the ESC typically used got a limited bandwidth of the speed control loop. I guess that the ESC should be able to operate the motor in two quadrant mode. But if the ESC only can provide motor with torque in one direction (one quadrant), then that becomes a problem and will reduce responsiveness significantly. I did not do calculations on this, but I have worked with normal DC motors, and a speed control loop with bandwidth of about 40 Hz is not that difficult to do with two or four quadrant control, and it becomes very responsive. However it requires, that you got a good internal (ESC) signal for shaft speed, that is updated with a frequency of about 1-2 kHz.
This is brilliant content and such a valuable resource. Thank you, Chris. More science-based videos which we can all draw upon to make design decisions I'm sure will be most welcome, as not many people are making that sort of content.
Glad it was helpful! I'm going to keep making these kinds of videos going forward 😁
Amazing video!
But why do you think so many people prefer flat motors to tall ones?
You mentioned that people go by motor feel (which can and should be tuned using throttle expo).
Here is some speculation on more possible reasons:
- A slower responding motor might be somewhat compensated by higher pids and therefore not that noticable. A higher motor time constant might even match the default pids better (specifically p i d ratios)
- For some configurations the propeller's inertia might be dominant and the motor might not matter that much.
- People compare different stator volumes: 2004 motors are slightly larger than 1408, 1507 and 1606. (And almost the same size as 1805)
- Going from a 9s12p winding to 12s14p improves torque by about 7.5% (winding factor 0.933 vs 0.866) BetaFPV's 1805 motor seems to have a 9s12p configuration (like most narrower motors from all manufacturers), explaining the popularity of 2004 motors (which usually use 12s14p).
- People compare motors with different (actual) kv.
- Placebo effect when not doing blind testing.
Greate video! just love the details and the mathematical info you provide beyond the statements and the explanations. keep up SUB!
Much appreciated!
Thanks a lot for the valuable information!
Great video, tons of great info.
Really explains the advantage of using a pancake motor style for a longer range cruising drone, and why not best choice for free-style, or racing. In LR, trading motor and throttle response for a larger moment of inertia, while having good torque with a lower kV.
Picking the right motor really depends on what one is optimizing for: free-style, long-range, or racing.
Moment of inertia also plays in prop size, and thus frame size, as having larger motors on long arms is not great for free-style, or a race-course with tight turns.
Keep up the great content. Understanding the relationship in component specs and between components is invaluable knowledge.
Hi Aerial, thank you for the comment. Just to clarify, I don't think that pancake motors are necessarily good for long range. The only advantage larger diameter:height motors have is cooling which you don't need for long range cruising. In a long range application you want maximum torque in the lightest possible package with the smallest rotor MOI. I would target diameter:height of 3:1 e.g. 1806.
For all quadcopters regardless of application we want the lowest motor MOI as possible.
Great presentation. I think this analysis just helped me finalize my mini-long range motor decision..
Great to hear! I hope that it flies great for you.
Hi Chris, thank you for your "Master Class" on motor selection. You have demystified this selection process for the laymen and gained a subscriber.
May I suggest you present another "Master Class" on propellers: their diameter, pitch, number of blades, and shape and their influence on motor selection. Or given a flight mission (free style, cruise, race), does one start the build with the props, match with motors, than match with the frame, etc. Sorry, too much to ask.
Propeller video is already in the works. I'm glad you enjoyed the video!
Thanks Chris for such relevant information, especially for me as I'm rewinding motors for pilots here in Brazil, both to keep the original specs and make changes to the KV factor when necessary.
Great content! All the formulas are in the well explained manner, thank you, chief!
Glad it was helpful!
So many people flying 2306 vs 2207 as we have been told for all these years that they have better low throttle torque and control. Yet your maths now show that is nonsense. 2306 vs 2207, all else the same, the 2207 will perform better, more torque, more response more top end. Dam.... Good work man.
A 2207 will have more torque yes. Throttle resolution could be better for the 2306 because it is a weaker motor and therefore a given movement of the throttle stick produces a smaller change in thrust. But this is no different than the 2207 with a 94% throttle limit or a bit of throttle expo. Glad you enjoyed the video 😁
@@ChrisRosser perfect, i was trying to tie up what we were feeling with what you were saying. This is great info thanks! I it the bullet and went2306 for the better low end feel. But grudgingly so as the narrower motors do tend to have better durability. Now I now how to make the narrower motors feel the same. I left a comment on the Apex video as well about some inconsistencies I found, really curious on what you think if you have the time to check it out.
Seriously thank you Chris,that was well worth watching!
Appreciate your time...subscribed!😊
Thanks 4 sharing your knowledge Chris, & happy flyin 2 U too
Fantastic stuff so needed in our hobbie please keep it up
Love your work now I’m going to watch again to get my head around it 🤪
Awesome, thank you!
Awesome content. Looking forward to seeing this channel grow. Love geeking out on this stuff and it's really the first time I've seen hard data from someone with relevant academics behind them.... not to say that people with experience don't also know what they're talking about though. I'm currently messing with some long range designs and would love to see some tips on selecting motors and props to maximize flight time and range on sub 250g designs! Keep up the great work Chris!
I think that if you combine this video with a future video I am working on on selecting props that should give you what you need. Pick the right prop for what you want to do and then the right motor for that prop 👍
👍🏻 FINALLY…. Someone introducing SCIENCE into the world of RC Flight !
Thank you Sir.
bardwell has a video for every troubleshooting question
rosser has a video for every technical question
Top notch! Now you need to do one like this for propellers
Oh! Just saw you have one! Many thanks!
😎 Thanks for your comment!
great video! i'm looking forward to see more
More to come!
This is a fantastic video!
Thank you!
Amazing content, thanks Chris
My pleasure!
Super helpful information, thanks! I'm building a 6" LR quad and there is very little info on such a beast beyond the generic iFlight frame recommendations. This let's me figure it out for myself and tailor it to my specifics.
Glad it was helpful!
Thank you! What an amazing video.
It really helped me understand motors more
This was good. Thank you very much for all of those explanations.
Glad you enjoyed it!
Very good video. Detailed and informative for beginners. Thank you.
Amazing level of detail. Thank you.
Really interesting content, this video makes the theory more understandable! Also very useful as a 'cheatsheet' for choosing hardware :) Maybe it also would be helpful to give some extra suggestions at the end/conclusion of the video of setups that work really well in your opinion. For the people who don't want to dive into the theory but want a proper combination of hardware to go back in the field.
Awesome video! Thank you
Thanks for your support 👍
As a battlebots hobbyist, we have to use a different approach for these motors, which are typically seen in the 1 lb - 3lb weight classes of bot either as a weapon motor or drive motor.
These motors need to swing effectively MASSIVE levels of intertia for a given size, and as such we need the lowest kv possible motors so they don't cook themselves or their speed controllers in the 3 minute or less fights, especially since airflow is basically 0. The motor has to heatsink all of its losses without demagnetizing.
To this effect, a larger diameter pancake style rotor is vastly preferred, for example my 150 gram shell spinner has a 75 gram 4" diameter shell to which I need to fit all the torque I can in as flat a space as possible. I currently use a sunnysky V2302 1500kv at 2S for this. It has enough torque and heatsinking ability to maintain sub - 120C temps after a 2 minute match, and as it uses 3 x 9 x 3mm bearings is quite resilient to basically constant impacts.
Check it out - my bot's name is Chakram
I'm only 5 minutes in and I'm craving more videos like this! Immediate like and sub.
Another interesting factor is the mass of the permanent magnets. A tall narrow motor will have more volume of permanent magnets than a pancake motor of the same stator volume. The magnets contribute to the mass (and thus inertia) of motor bell. How do you think that factors into the responsiveness?
If we substitute constant stator volume and magnet thickness into the MOI equation I get a relationship where MOI increases linearly with stator diameter. However, due to edge effects a taller magnet may not need to be quite as thick to generate the same average field strength. Excellent question!
This is probably the most significant thing left out of the (excellent) video. As you move towards a pancake motor, you have smaller and smaller magnets, which affects performance. I wonder if there is an ideal ratio of magnet size to stator volume, which could change Chris's proposed 3:1 ratio.
So the 3:1 ratio would be a 1204, 1806, 2608 size right? This is the kind of stuff I love about this hobby. Always a question looking for an answer.
@@sakfpv8444 Yep, so motors close to those sizes should be best for freestyle. If you have a cinewhoop or something heavier for its prop size then a flatter motor may be needed to stay cool.
Wow you da man!!!
I've been drinking the pancake stator Kool-Aid, buying into the stator diameter increase is a plus for a given volume.
What effects do motor heat have on efficiency and performance? Obviously heat can ultimately damage motors, but what effects does heat have during normal operation? Does a hot motor operate less effencitly and further generate more heat?
I find it interesting you specifically mentioned the turbine cooling design. It seems to me that cooling is more a centrifugal fan function as the motor is operating against airflow/pressure.
Another interesting topic would be propeller power requirements. As a corollary to KV selection it would be great to have some way to rate props as to power requirements or how to evaluate prop choices.
Appreciate your efforts, you've raised the bar, please don't stop now!!!
thank You! this information is gold :)
Glad it was helpful!
Great content, big thanks for this work
My pleasure!
Well done and high quality video
The wrinkle in the KV selection problem - you can use higher KV to compensate for lighter loaded and lighter weight props, and end up with significantly more effective resolution, and be within a few percent of overall efficiency, with something that has inherently better responsiveness, and better transition characteristics from unloaded to loaded on props. That being said, I fly everything like it's a racer, so punishing batteries just is what it is.
You are spot on! The goal is to match the max current required by the motor at full throttle to the max current available from the battery. If you use a light pitch prop you will need a higher KV motor to make that happen.
this is such great content and so well exsplained. thankyou for your effort.
Thanks I was looking for a physic way of analysing motor performance and not just kv
I'm glad this was useful to you! I'm doing a similar deep dive on props which you might find interesting also.
Brilliant - thank you. Extremely well explained.
This is phenomenal content!
Great video. Something I'd be interested to learn more about is the role of motor weight. For example, I might intentionally pick a motor with less stator volume because the motor will be significantly lighter. Good example is 1202.5/1303 being popular on 3" toothpicks rather than 1404 (the ideal motor according to your chart) since it will save 20g of weight (which is a lot for lightweight builds like that -- think TP3).
Similarly, I might go for different width/height because of weight. For example, according to your chart, 2004 and 1806 are similar stator volume, but from some quick Googling, it appears that many 2004 motors are quite a bit lighter than typical 1806 motors. Maybe that's why pancake motors are so popular with ultra-light builds?
Nvm I think I misread the chart. 1806 is more volume.
I really like 1806 motors for 4in and even light 5in biblades. They are quite hard to find but they have a good amount of torque and aren't too heavy. 2004 is pretty good for 4in though.
Amazingly explained sir!!
Chris, Absolutely great video! Lots of information; I’ll watch it through again at least once to fully absorb everything.
I’m becoming more and more interested in 6-7 inch long range “cruisers” such as the GEPRC Crocodile7, the Diatone F7 or the Iflight Chimera7. I’d very much like to see a deep dive into motor/prop/battery combinations that produce long flight times with the science and math behind it.
you are giving such a good information , thank you
I need to watch this a couple of times before it sink in ^_^
Great video. I've been experimenting with batteries recently. They are the limiting factor eg a 850 mah lipo can't provide the amps to run a 1408 at top speed.A1300 can but it's heavier. The balance is so hard to find even with the great info you provide.
Great point! Hopefully as this information gets out into the hobby we'll see more options for batteries and motors better matched to each other.
good lord guys on another level
so good!!!!!!!!!!
I really hope your channel gains traction.. I LOVE it. However it's a tough sell to anyone who didn't pay too much attention in maths and physics (I'm gonna guess that's MOST of the YT audience)...
That said, perhaps you can take some of this amazing data and manufacture some parts?. I would 100% consider a propeller designed by you, or a frame, or motors, or.... Im a fan. keep doing what you are doing. BRAVO!!!!
Hopefully the channel is accessible even for those who may not follow along with the formulas. I always try to give recommendations for that reason. Thank you for your support!
Would like to point out that also higher motors tend to last less - longer shaft bends easier than shorter one on lower height motors...
Also after few years in fpv, i noticed that motors with weaker magnets - when they don't have that clicky feel when you spin them - tends to be more quite more efficient than clicky motors, but they also usually lack the power, so it is smart to go with bigger motor and weaker magnets if you are looking for something efficient rather than with lighter, more powerful motor :)
When talking about efficiency are you speaking of flight time or g/W. Less powerful motors will give a longer flight time because they make less thrust. The same effect can be achieved with a throttle limit.
@@ChrisRosser I tested two motors of same size and KV. In both, crusing style flight and more agressive freestyle, motors with weaker magnets always flew longer (25-40%) but didn't have as much top end. Also compared 1106 and 1404 6000KV motors which have roughly the same volume. 1404s are more powerful while 1106s are bit more efficient - again, tested with several flight styles and 1106s always flew 15-25% longer.
@@flowrfpv It would be interesting to compare the stronger magnet motors with a throttle limit to the weaker magnets without one.
@@ChrisRosser as i said, i tried to cruise for as long as possible, so throttle limit wouldn't make a difference in flight time... also I am using older, heavier components on build with weaker magnets, so even with extra weight it flew longer
@@flowrfpv 25-40% is an enormous discrepancy in flight time. Based on the information you have provided magnet strength would not account for this difference. I would look at differences in the battery, props and camera uptilt. If you have current sensing set up you can monitor your current draw during cruise. I would bet the quad with stronger magnets is cruising faster and using more current because you are requesting more thrust. Let me know what you find out!
You are a great teacher
Thank you! 😃
Subbed and liked! Very informative. Wish i was this interested when I studied this in school. Keep em coming!
Thanks for the sub! I've just finished a deep analysis of the FPVCycle Glide so that'll be uploaded soon.
Chris Rosser cant wait. Been eyeing that frame to go along with the fpvcycle imperial motors that is currently on two of my other quads.
Wow, this is great content!
Glad you think so!
beautiful! thanks. I would really like a video which explains what goes wrong on each "inapropriate usage" case scenario. For example, what happens when you use motors with lower kv than what you expect for that battery/propsize/payload. What happens when you do the contrary (for example use a "4s" motor with "6s" with the same prop size), and what are more or less tolerable margins.
For example, Im buidling something like the terraplane (high power 3" cinwhoop) but I only have 2306 in 1900 kv. I'm wondering what would happen if use them. Props will spin slower than needed I guess. What will happen with the amps? If not, I have 1408 in 3500kv (typically though for 3" open prop). What will happen if I use them with 3" ducted hexablades? Will the motors be damaged? What happens with the amps on the esc.
As you can see my questions respond to my "experimental" spirit in combination with the conservative one, as I dont want to breake everything...
Thank you as always!!!
Iron losses are directly proportionate to operating voltage and a motor's idle current rating, and higher KV versions of motors can feature lower internal resistance ratings than do their lower KV ones. So, at sufficiently high cruising speeds, the 3400KV 2207.5 likely delivers 1.16 BHP more efficiently than its lower KV versions would.
I think the losses in the cables and stator windings are more important. Thrust tables clearly show higher KV motors are less efficient in terms of thrust per watt of power on the same props. The problem only gets worse when you take into account that more current drawn from the battery = more loss in its internal resistance.
@@ChrisRosser When pulling 45 A at 19.8 V, the combined iron and copper losses would total about 160 W in the 1750KV version of the 2208 Velox yet only about 120 W in the 2450KV one. Moreover, under those constraints, this 2450KV motor would deliver more of its brake horsepower in the form of angular velocity than would that 1750KV one - which is of benefit in maximizing cruising speed (albeit, to the detriment of acceleration and, thus, handling).
Your a beast!! Love the Physics🎉
Thanks 😁
Great content... super informative and well explained... I’ll prob go thru it a few times to get it down though!😊😀🤟🏻
Glad you're finding it useful!
Amazing! You are a great professor! Subd!
Thanks for the sub!