How to pick the best motor for your quadcopter, now with PHYSICS!

In this video we're going deep into the fundamentals of what makes a good motor for our FPV quads. We're talking motor size, motor shape, KV, responsiveness, even throttle resolution and feel.
There are no bad questions only bad answers! So if you want to dive even deeper or want further clarification on anything get your questions into the comments.
/ chris_rosser
Slides: drive.google.com/drive/folder...
TIMESTAMPS
0:00 - Intro
1:45 - What governs motor torque
5:19 - Motor shape, and how it affects performance
6:50 - Motor responsiveness for low throttle stability
10:20 - Motor cooling
11:04 - Choosing the best motor shape
12:37 - Choosing the right motor size
13:53 - The effect of motor KV on performance
17:04 - Picking the right KV
20:32 - Getting the right throttle feel and resolution
22:28 - Outro
Song: Markvard - Life (Vlog No Copyright Music)
Video Link: • [1 Hour] - Markvard - ... ​
Music provided by 1 Hour Vlog No Copyright Music.
Channel: urlz.fr/9UQL

[@dishwashersafe222]

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.

[@ChrisRosser]

Glad you found this helpful! Thank you for your support.

[@aakashjana6225]

Been craving for this type of content for ages. What a blessing to have a man from Cambridge explain it to me for free.

[@ChrisRosser]

I'm glad you enjoyed it, more to come in the future!

[@verdi6092]

This type of content is what ive been looking for. 👍🏼👍🏼

[@ChrisRosser]

I'm glad you enjoyed the video. I'm super psyched that people like yourself are finding these deep dives useful.

[@winmarkesconde5651]

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.

[@breakflight]

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.

[@breakflight]

Could you do a deep dive into props?

[@ChrisRosser]

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.😁

[@ChrisRosser]

Glad it was helpful! I'm hoping it helps cut through some of the marketing fluff that we've all had to deal with.

[@lanxang173]

@@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.

[@JohnFSmitheugene]

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.

[@Bharat_Mata_Ki_Jai147]

Amazingly explained sir!!

[@RobertoCresto]

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!

[@dcdk1525]

Thanks 4 sharing your knowledge Chris, & happy flyin 2 U too

[@ZackLondres]

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.

[@tktktk17]

My man!!! This is finally some quality content. So many people in the community spread fake info on this topic!

[@camsurfpv4378]

You are one of those people that really put in the effort to share a large amount of knowledge towards the hobby. Thank you.

[@davet2563]

This is the content I am looking for! Thank you so much.

[@ChrisRosser]

Glad it was helpful!

[@alanhurdle3949]

Thank you! What an amazing video. It really helped me understand motors more

[@timothyphillips4801]

Seriously thank you Chris,that was well worth watching! Appreciate your time...subscribed!😊

[@vasiliyklx450r]

Great content! All the formulas are in the well explained manner, thank you, chief!

[@ChrisRosser]

Glad it was helpful!

[@stimmungsasdrohnautfpv3830]

Great work Chris. Thanks a lot for this input

[@ChrisRosser]

My pleasure!

[@allroads2454]

Amazing level of detail. Thank you.

[@yawnastyfpv6942]

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!

[@ChrisRosser]

My pleasure!

[@SOLARFPV]

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.

[@GuGuHBmX]

I'm so glad I found your channel! This is a treasure trove of analytical data!

[@ChrisRosser]

Welcome aboard!

[@isramv74]

Amazing content, thanks Chris

[@ChrisRosser]

My pleasure!

[@Caramellofellow]

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.

[@ChrisRosser]

Glad it was helpful! I'm going to keep making these kinds of videos going forward 😁

[@user-oe2nw1in2k]

Great content! This is what we've been missing on KZbin: 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.

[@ibnfpv]

Greate video! just love the details and the mathematical info you provide beyond the statements and the explanations. keep up SUB!

[@ChrisRosser]

Much appreciated!

[@KremerFPV]

Thanks a lot for the valuable information!

[@cccagley5276]

I really appreciate this video and have watched it several times to really understand brushless quadcopter motor selection. Your an FPV guru - "the professor"

[@starsstripesjacket]

Really interesting, this is deffinitely going in my drone info playlist :)

[@ChrisRosser]

Awesome, thank you! Glad you like the video 😁

[@poporbit2432]

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.

[@maceliusfpv370]

Great presentation. I think this analysis just helped me finalize my mini-long range motor decision..

[@ChrisRosser]

Great to hear! I hope that it flies great for you.

[@registeronline588]

Very good video. Detailed and informative for beginners. Thank you.

[@thejdolby]

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!

[@ChrisRosser]

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 👍

[@reneseib6532]

this is such great content and so well exsplained. thankyou for your effort.

[@keysersoze6499]

Awesome video! Thank you

[@ChrisRosser]

Thanks for your support 👍

[@amitvadgama5014]

you are giving such a good information , thank you

[@lukasmohr97]

great video! i'm looking forward to see more

[@ChrisRosser]

More to come!

[@edouardmalot51]

Great content, big thanks for this work

[@ChrisRosser]

My pleasure!

[@armandrone9016]

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.

[@ScreamGreek]

This is phenomenal content!

[@peterfynn]

Brilliant - thank you. Extremely well explained.

[@CravenFPV]

This is a fantastic video!

[@ChrisRosser]

Thank you!

[@karanshah1406]

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 🙌👌.

[@ysforce]

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

[@arthurganz]

Verry nice video!!! Thanks!

[@JonasRech]

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!

[@ChrisRosser]

A lot of love right back at you from the UK!

[@otm646]

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.

[@daveopie1234]

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.

[@ChrisRosser]

Thanks for your comment and support!

[@thomasluesink]

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.

[@mpg500]

Engineering based content! Hooray!! Its been 20 years since I was at university. This takes me back and I like it.

[@AnomNOM]

i love your channel, please keep doing this.

[@ChrisRosser]

In the words of Jim Carrey in 'The Mask' "Somebody stop me!" I'm so pumped you're enjoying the videos. 😁

[@aakashjana6225]

Another fan of The Mask , imma say "Smoookinn!!"

[@ChrisRosser]

@@aakashjana6225 Appropriate for a motor video 😎

[@TheDeltatangowhiskey]

Awesome video

[@ThomasLa]

This was good. Thank you very much for all of those explanations.

[@ChrisRosser]

Glad you enjoyed it!

[@BonesFPV]

Great video. Thank you.

[@franciscomagalhaes7457]

This was very valuable for a newbie who needs to start looking at motors after a hard crash.

[@ChrisRosser]

Thanks! I'm glad it helped.

[@juliankulisev3279]

thank You! this information is gold :)

[@ChrisRosser]

Glad it was helpful!

[@gletschertroll]

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.

[@TTBROD12356]

Your a beast!! Love the Physics🎉

[@ChrisRosser]

Thanks 😁

[@butcher]

Wow, this is great content!

[@ChrisRosser]

Glad you think so!

[@aerialimagery3216]

Great, info! Thanks!!

[@ChrisRosser]

Glad it was helpful!

[@DopeyFPV]

Subbed and liked! Very informative. Wish i was this interested when I studied this in school. Keep em coming!

[@ChrisRosser]

Thanks for the sub! I've just finished a deep analysis of the FPVCycle Glide so that'll be uploaded soon.

[@DopeyFPV]

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.

[@jimpratt9520]

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.

[@AerialJohnny]

The detail in this is unreal, although so much of it goes right over my head because I'm simple minded!

[@k1ortia]

Wow, there is no better explanation then this anywhere.

[@DeeMenace]

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.

[@ChrisRosser]

You're welcome! Welcome to the rabbit hole 👍

[@mrclo2684]

You are a great teacher

[@ChrisRosser]

Thank you! 😃

[@kaptkrunchfpv]

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.

[@BluesMtn]

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.

[@ChrisRosser]

Glad it was helpful!

[@vladz1177]

Watched that from Russia. Very nice speech, easy to understand, material is interesting. Nice job.

[@flipfpv4539]

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 🤪

[@ChrisRosser]

Awesome, thank you!

[@user-ey9kt4fw7j]

WOW, thank you

[@_beacon.b.o.s.s]

The video is really helpful

[@charlesmarseille123]

fellow physicist enjoying them equations ;) keep those facts coming!

[@ChrisRosser]

More to come!

[@dingbatfpv]

Haven't finished watching yet but your videos are really good mate keep it up 👍

[@ChrisRosser]

Thanks, will do!

[@justhackitfpv]

Finnaly a explanation which supports my theory

[@neilfpv]

Amazing! You are a great professor! Subd!

[@ChrisRosser]

Thanks for the sub!

[@AerialWaviator]

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.

[@ChrisRosser]

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.

[@TokeyFPV]

Awesome job..Thank you.

[@ChrisRosser]

Thanks for watching!

[@CarbonGlassMan]

This is all very interesting. There are so many variables. Change just one thing and everything else changed.

[@ChrisRosser]

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 :)

[@BMan_FPV]

Great content... super informative and well explained... I’ll prob go thru it a few times to get it down though!😊😀🤟🏻

[@ChrisRosser]

Glad you're finding it useful!

[@GregPless]

Well done 👍

[@QuadMcFlyFlies]

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.

[@ChrisRosser]

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 😁

[@QuadMcFlyFlies]

@@ChrisRosser Looking forward to it man!

[@slackerinmotion]

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.

[@ChrisRosser]

Propeller video is already in the works. I'm glad you enjoyed the video!

[@Niloc33567]

And yr videos are very informative bro

[@magmikefpv]

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

[@ChrisRosser]

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.

[@magmikefpv]

@@ChrisRosser Yes I'm going back to the F80s just wanted to see what these things were all about. Thanks again man .

[@hjvanderlinden]

Thanks!

[@mihavuk]

THANK YOU.!!! 👍

[@ChrisRosser]

You are welcome!

[@MarkKunoff]

Top notch! Now you need to do one like this for propellers

[@MarkKunoff]

Oh! Just saw you have one! Many thanks!

[@ChrisRosser]

😎 Thanks for your comment!

[@lavrin.]

*Chris Rosser* 💯 🏆 🥇 Щиро дякую за *просвітницьку* 🧑‍🔧🔬🧠✨ діяльність, дуже корисно!

[@DangoFPV]

I need to watch this a couple of times before it sink in ^_^

[@vincenthpl]

Thanks I was looking for a physic way of analysing motor performance and not just kv

[@ChrisRosser]

I'm glad this was useful to you! I'm doing a similar deep dive on props which you might find interesting also.

[@2oldfpv987]

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!!!

[@chibikaiju922]

Very interesting, thank you for bringing us this information Chris! I know your findings don't make everyone happy (me with a marmotte rig) but you always are backing up your information with actual principles of physics and objective math and I really appreciate that. I find this really useful information that goes beyond subjective flight feel. I am curious with people using motor and throttle scaling in betaflight to reproduce a 6s kv on 4s kv motors, will the efficiency losses be even greater with a 4s motor limited to 6s kvs?

[@ChrisRosser]

Using a throttle limit on a 2400KV motor with 6S to achieve the same performance as 1600KV will not be quite as efficient. But the efficiency penalty is likely to be moderate (

[@AarOnCoasters]

I'm only 5 minutes in and I'm craving more videos like this! Immediate like and sub.

[@phillipneyman9338]

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!!!!

[@ChrisRosser]

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!

[@Coachxray]

you are a legend

[@ChrisRosser]

Takes one to know one! 😎

[@CurlyFPV_MY]

Oh my god! Numbers & Maths makes me dizzier than doing a 10 pack continuous trippy. Now I wish I had study harder in school. Anyways Thanks much Chris!

[@wackywezfpv9335]

I really enjoyed this, Im learning, well done, I wondered if you could do a short explanation on the TPA (the throttle settings) and what it does, and how to tune it, thanks

[@ChrisRosser]

Coming up in the fine tuning video once we go over setting up rates.

[@JohnBrown-vn2qw]

good lord guys on another level

[@Rc_impulse]

It’s a pleasure watching your videos, subbed a few weeks ago and also recommend you to all my drone buddies. If I’m allowed to ask you What is a good motor for a 3” dead cat with the Dji AU running 450-850mAh the priority being throttle resolution also will updating to a newer version of betaflight help because it’s running onb3.5 and it’s working so didn’t mess around. Thanks a ton man!

[@Rc_impulse]

I watched the video again and will try changing throttle expo and others to see if it makes a difference. My motors are 1408 4000 KV with 3052 gemfans

[@dilbertmcfly5986]

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.