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

[@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.

[@wawifpv]

@@ChrisRosser I have I question which motor kv or propeller pitch is the best to use on 5inch 4s build for cinematic flying?

[@k1ortia]

Wow, there is no better explanation then this anywhere.

[@theronin48]

Good sanity check what with pancake motors being all the rage these days.

[@ChrisRosser]

If you NEED a very short motor they are great, but if you don't need the form factor than a 3:1 width to height ratio will probably serve you better. Glad you enjoyed the video.

[@theronin48]

@@ChrisRosser thats the question ... why would you really need them if torque is unaffected assuming same volume. And since the cool kids pancake motors are meant for ultralights why do you need the cooling? In addition the higher moi would not lend itself well to ultralight arms and gyro noise. Put another way is this just a marketing gimmick?

[@ChrisRosser]

@@theronin48 I really worry about people using pancake motors on ultralights particularly larger props like 5in with 2004 motors. You really need all the torque and responsiveness you can get and cooling is less of an issue because the motor is so lightly loaded. I would take an 1806 over a 2004 any day of the week!

[@theronin48]

@@ChrisRosser i am designing sub250 ultralight frames. My original intention was to use 2004s with 4 and 5 inch. The gyro noise with the 3mm arms were literallt fly away prone. 1404s work just fine for the use case so im wondering if we generally are using overpowered motors. Dont mean to beat this to death but when your focus is sub250, marketing gimmicks can really send you down a bad development path.

[@ChrisRosser]

@@theronin48 100% agree that marketing information for motors needs to be more accurate. That's the main reason I wanted to make this video! For Ultralight 5in I would say 1806 motors might have enough torque for a very light 5in prop like a 5x2.5x2.

[@John-qc6of]

Thank U for your valuable information. I am looking for a motor that resembles a pipe with a ID of approx 220mm and an OD of say 240mm. The center spins. Have you ever come across something of this nature? Thanks

[@fpv_9484]

Hello. Thank you so much for your video. Very interesting and informative. Now I have a different look at the choice of motors. Do you think it is necessary to subtract the volume inside the stator from the total volume, where there are bearings or a void (for example, in motors 4006-6006)? After all, the average radius of application of the magnetic field force will change with a change in the internal radius of the stator. I'm doing drones 13-21 inches and I'm really interested in motors like 3508,4006, 5006, 5010, 5210, 6006, 6215 is it for efficiency or is it just marketing. Sorry for my English and maybe not scientific formulations.

[@ChrisRosser]

No need to subtract any volume as the calculation is the curved surface area of the stator times the radius.

[@tktktk17]

Question: How would you extrapolate the graph of stator volume vs. Prop diameter for larger drones, for instance 10" props?

[@ChrisRosser]

It's a quadratic function as a rule of thumb if you double the prop diameter you need at least 4x the stator volume.

[@tktktk17]

@@ChrisRosser I assume this applies mostly for high performance stuff then? I think 2212 on 4s is a not an unfamiliar motor size for 10" props which is roughly only 2 times the volume of a normal 5" motor (saw some builds and I believe dji phantom motor sizes are also 2212, or 2312). Interested to hear your thoughts.

[@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.

[@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!

[@tiwidub8809]

Hi, Chris "Stator" Rosser ! (Stator because the fpv world is turning around you, even JB... 😂 What about the Flyfish Flash 2406 /1800 KV ? Nobody talks about this motor... If you could, it would be cool to compare more brands and volumes. Thanks for your scientific infos. Regards.

[@jamesmason7124]

What motos and props would you recommend for a 3/3.5 inch props on a freestyle cinewoop aka Rotor riot Skylite

[@strattonford2557]

Hey buddy what is your degree in/what's your line of work if you dont mind me asking??

[@ChrisRosser]

Aerothermal engineering and I am the principal system engineer for a start-up.

[@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 😎

[@nevillecreativitymentor]

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

[@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.

[@Fpvpilot928]

Title should have read: get juicy, with physics

[@tktktk17]

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

[@王抱恒-z1b]

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.

[@mouseFPV]

Confused: 05:27 "you will notice motor shape didn't feature on our torque calculations at all". Didn't they though? The radius of the motor is dependent on the motor shape....no?

[@ChrisRosser]

The way I looked at it shape would be represented by an r/h term. If you replaced pi*r2 with V for volume there would be no shape factor.

[@markhutchens]

Oh man, I have a set of 2604s I had planned for my next build. Anyone wanna buy 4off 2604 1690kV BNIB!? 🤷🏻‍♂️

[@ChrisRosser]

You could pair them with a lightweight lower pitch prop to offset the larger moment of inertia. 😁

[@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!

[@gus8378]

Shouldn't you remove the empty volume in the middle when calculating stator volume, including the volume of the bearings?

[@Gosuminer]

I was very surprised to see you claiming and physically substantiate exactly the opposite of what KabapFPV says. He claims that wider stator motors give better control in the low throttle range whereas you say that the speed of rpm change depends only on moment of inertia which is higher for wide stator motors. Is he feeling something that's not there or are there other effects not yet taken into account here, like efficiency of magnet commutations or aerodynamics of the motor bell. Also, 1407, 1408 and 1507 motors which I love to fly on 3" are missing in your chart :-).

[@ChrisRosser]

Researching this topic I watched this video from Bob: kzbin.info/www/bejne/iHmlc2l_eNKWgpY I think what I have found out matches with what he has found through experimentation and feel. There may be other factors that I have missed but I think that a smaller motor gives more low throttle feel because the throttle covers a smaller range of thrust. Sorry to miss off some motor sizes! I'll add them as well as a link to this chart on gdrive :)

[@LS-xb2fh]

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.

[@charlesmarseille123]

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

[@ChrisRosser]

More to come!

[@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!

[@eduardkhilenthusiast]

hi chris, does the aos5 fit the gemfan i love you props? thx :)

[@ChrisRosser]

Yes they do, but its a VERY tight fit I think. The AOS 5.5 would fit them easily.

[@MrShutterBug]

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?

[@ChrisRosser]

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!

[@JoshuaBardwell]

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]

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.

[@ChrisRosser]

@@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.

[@GuGuHBmX]

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

[@ChrisRosser]

Welcome aboard!

[@sewingmachinesindetail]

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.

[@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.

[@BuZZarDFPV]

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.

[@ChrisRosser]

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 😁

[@BuZZarDFPV]

@@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.

[@Switch180fpv]

The more I watch your videos the more I realize I have much to learn 🤦

[@ChrisRosser]

Do not worry about it. I get that feeling every single day! There is so much to learn about this hobby it keeps going forever, that's one of the reasons I love it 😁

[@rmhfpv9225]

Can we get this out there more " a wide motor does not make more torque than a narrow motor all else being equal"

[@ChrisRosser]

Did a livestream with JB on this 👍

[@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!

[@dronepilot260rc]

Is a high KV motor going to be faster with lower voltage? I have some 2206 2750kv motors that are blazing fast. But they do zap the battery super fast lol

[@vasiliyeah]

I don't believe we should obsess over KV as much. You can achieve any desired lower KV with a higher KV motor by limiting output power in FC firmware. You can not do the opposite with a lower KV motor. If you don't know what you prefer I would suggest buy high KV and play with output power over buy every KV your cell count and swap motors.

[@ChrisRosser]

To a certain extent I agree, the efficiency penalty is pretty small. As long as your battery can supply enough current to get the full motor torque you should be OK. If you have old batteries a lower KV will work better (even with throttle limit) as it will make more torque.

[@vasiliyeah]

@@ChrisRosser Thanks for sharing all this knowledge. Wish I had more time to digest your videos in more detail. I'm currently building a 2250KV 2206.5 machine that I intend to run on both 5s and 6s with different profiles with output limiting. Reason being I have a bunch of new unused 5s 120c batteries + a couple of 6s which I converted to 5s after a cell got punctured -- I know I have a degree in stupid. Really interested to see how this will run.

[@amitpaul6109]

can anyone tell me for 4kg and 2.5kg drone which should be the motor kv, and prop combination.

[@chiprobertson3094]

2208 1700kv to 1900kv 6s battery is all you need to know

[@abertheham]

While we're on the subject of challenging baseless dogma in the world of FPV hype, could you comment on the 'notchy motors make more vibrations and are therefore harder to tune' hypothesis please?? This one has driven me crazy for a couple years now because everyone takes it as fact, but a) that has not been my experience at all, and b) I can't think of a conceptual framework in physics for why it even would be true. When people talk about how 'notchy' a motor is, they're referring to the clicks they feel when they turn a motor bell with the quad powered OFF, i.e. the attraction between the static bell magnets and (I think) the metal posts holding the electromagnetic stators in place. I've been trying to help people understand that the magnetic attraction that they are describing ceases to exist entirely when the motor is on and current is running through the coils; the way the magnets interact in their off-state is a completely different system than when they are powered on. That rationale doesn't seem to rmean anything to many people though... I'm open to being wrong if I'm missing something - I almost hope I am wrong so that the people who have been making these claims publicly and influencing peoples' investments weren't doing so with bad information. But so far the only rebuttal I've received is "i don't know but I replaced the motors with some that aren't notchy and the problem disappeared" - attributing the improvement to the smoothness or notchiness, nevermind the fact that maybe the problem disappeared because the old, likely dinged /unbalanced motors were replaced with brand-new one. So, if there is indeed some truth behind the idea that notchiness of motors *when they're powered off* somehow translates to vibrations *when the electromagnets pulsing and the motors are spinning,* I'm at a loss for why that reason might be, from a physics perspective. Really appreciate your thoughtfulness and expertise in this area. Keep it up and thanks!

[@ChrisRosser]

I've added this question to my content list. I'll need to do some research but I'm sure we can answer this question!

[@richardheedfpv9626]

I'm with you. Rcinower and sunnysky are very notchy but I run many sets and they run smooth fast and powerful.

[@fotosaccion]

AWESOME VIDEO!! So will a 1203 5500kv be better than a 1404 4500kv?? I am looking for a quick for a 2" cinewhoop that's very age and fast.

[@danieldewindt3919]

Super awesome informative! I'll keep it short :)

[@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.

[@CurlyFPV]

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!

[@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.

[@p39483]

Please explain these differences in big motors. There are big low power motors like the X-NOVA 4812 and then higher powered ones like the comparatively smaller Xing 4214. Both are 400 KV, both spin similar props, but the big X-Nova weighs 161g and the Xing weighs 270g. The X-Nova has a coil resistance of 0.101 ohms and the Xing is 0.053 ohms. The smaller and heavier Xing is more powerful, though at similar power output the efficiencies are similar with the heavier Xing having the edge. These seem to be designed for completely different purposes despite their similar stator volume. There seem to be high and low copper motors, and if you want a light motor swinging a large prop at low speed then perhaps having less weight offsets the I^2×R losses for endurance. So copper mass seems to be an additional parameter. Some motors have a hollowed out stator like a ceiling fan. Others are heavy hand have high sustained power. Maybe you could elaborate on these tradeoffs.

[@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!

[@shamilrodrigo4265]

I have accidently bought rs2205 motors and i have a f405 v4 A55 stack and my motors are 40A max. Is it ok to use the motors with the stack or can any one recommend me a budjet motors pls 😊

[@lavrin.]

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

[@rmirov]

Fixed wing applications seem like they will have different priorities. I'm particularly interested in cruising for long-range efficient flight. But that could be a high wing loading very fast plane, or a big motor glider that just floats. For very small/lightweight models (like < 50g) may be running off a single cell, and I've had trouble getting enough thrust unless I go to a higher KV. But that's counter to most suggestions unfortunately to have a big prop and low KV.

[@sumoonice9610]

Hi everyone! I'm working on a drone that has a 23" frame and about 5lb (2.268kg). I'm trying to focus on power efficiency rather than speed because I just need it to travel farther distances. Does anyone know what motor would be more ideal for this?

[@niro_mtb_rc]

I LOVE YOUR CHANNEL!!! I am building my own quadrocopter I am a 16 year old german student and I hat if I build something that isn't perfectly adjusted! I watched every viedeo I could possibly need for my copter, but I have one final question. If I use your first method to determin the correct KV for my motors. It Does make more sence if I use the burst current and not the continually current the lipo is able to provide for the calculation right? I just want to make sure, otherwise I will buy more powerful Lipos. (I hope I didn't make a lot of grammar mistakes) I would be really happy if you take the time to answer my question! Greeting from Germany! Keep up the great work!

[@davet2563]

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

[@ChrisRosser]

Glad it was helpful!

[@Bigsybeast]

I’m looking at getting the aos 3.5 v2 with a mamba 20x20 stack what motors would you recommend for a 4s setup flowing freestyle, I’m new and not snappy at all atm 😂

[@PhanchaiSiam555]

05:31 I not understand nothing. What is a 2207 motor? What is a 2306 motor?

[@chaimaalebdaoui5759]

please how can I calculate the blade tip speed ?? i I found this formula (3,14 *D*rpm) with D: prop diameter but I'm not sure if it's the right formula or not?

[@HummingbirdUAV]

Would have been nice to have a section on actually picking a motor/prop combo for a given weight of a quadcopter. Where should one be on the thrust curve?

[@ChrisRosser]

I have another video on exactly that topic. 👍

[@HummingbirdUAV]

@@ChrisRosser Thanks, I'll give it a view.

[@HummingbirdUAV]

Well I watched kzbin.info/www/bejne/fnbSi4iLiMuKo6s (How to pick the right size motor for your build in 45 seconds) but it only showed which prop to use on a motor, didn't say anything about matching a motor/prop to a quad. I could have a 400 gram quad or a 1000 gram quad. These would surely need different motor/props. I am looking for a guide to show where on the motor/prop thrust curve should I be to get a well performing machine. i.e. hover at 1/4 , 1/3 or 1/2 way up the curve. The graph would be rpm for the motor/prop on y axis and thrust on the x axis.

[@Simofly]

Amazing video, I don’t know why I missed it ! So if I follow your rules about diameter:height proportion , I’m re-evaluating my 2806.5 1300kv motors in my AOS 7 build, I use triblades gemfan 7040 , maybe 2808 o even 3008 would be best ? My AUW it’s variable from 1.3kg with 6s1p 4000mah liion to 1.5kg 6s2p liion

[@MrJT270567]

so what you say about motor volume... can I use a 2212 motor for 7" cruising? the volume is much higher than the 2507 motor that I am currently using...🤔

[@AykutArgun]

Correct me if I am wrong. but the moment of inertia calculation seems wrong. It should be rho*h*2*pi* integrate( r^3dr) So it is indeed proportional to r^4 (not cubic dependence). Doesn't really change the point of anything you tell in the video though, if anything it makes the MOI argumentation stronger.

[@solarstrategy9967]

Chris .. Mate! Does your brain hurt with the weight of the vast knowledge and intelligence you carry in your head? Great information Chris.

[@pironiero]

between 2 same mostator sized motors- id pick higher KV one because you can actually limit you KV

[@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!

[@caffeinecreature]

It's been a pain finding recommendations on motors for endurance builds. I don't need a quick, zippy drone, I would love something that will give me more flight time and range given a smooth, flowy piloting style. Even this video only really talks about racing and freestyle.

[@ScottTomlinson]

Great video Chris! So calculating the stator volume on the entire cylinder is ok? Rather than the stator "donut" (Minus bearing, stator housing etc)

[@ChrisRosser]

Yes! Because it's not actually the volume of the windings. It's r* the ouside curved surface area. Just happens to come to pi*r2*h!

[@cwwisk]

What is the KV rating, and why is it called a KV rating? I'd love a deeper focus on this area. Maybe I just missed that part of the video?

[@WayneHunter1000]

Wondering if you could post a video on how to isolate any issue with a flight controller.

[@jaghook]

Can somebody please tell me the best sized motor for a 1045 prop, thanks.

[@oneoverboard]

How do I make juicy pancakes

[@ChrisRosser]

Pancake motors? I'm not sure it's possible. Pancake motors aren't that great for juicy flying.

[@dhanushsilveru7562]

what should be the thrust to weight of drone ratio in order to make a 2kg drone to fly at 15 meters altitude in a 10minutes flight

[@CamdenWallraff]

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

[@Bigbeardfpv]

So in theory, could you make a 2207 motor feel like a 2306 motor?? How would you do that ?

[@ChrisRosser]

Try a 90% throttle limit and then add throttle expo until you get the feel you want.

[@Bigbeardfpv]

@@ChrisRosser ok thank you. By the way, I'm going to watch this over multiple times. It almost seems like you should be able to mimick the "feel" of any motor with any other motor.

[@user-otzlixr]

I avoid t motor direct sales. Bait and switch practices plus a return policy that makes it so it’s never worth a return explains all the product on eBay.

[@bobeshoz]

just wondering why in your chart the volume of the motor bearings is part of the calculated motor volume ? shouldn't the volume of the bearing be subtracted ?

[@ChrisRosser]

It's not actually the motor volume. Its the outside area of the stator (not including top and bottom)*r which comes to pi *r*r*h but isn't actually to do with the volume of the windings Vs bearings etc. The difference is very subtle. In general less volume of copper in the stator will reduce the maximum field strength and therefore torque so it does have an effect just in a different way.

[@bobeshoz]

@@ChrisRosser I see, but in that case the calculated numbers in your chart ("y" axis) reflect volume and not the outer cylinder area (minus top/bottom), you used "π*r*r*h" instead of "2*π*r*h"

[@ChrisRosser]

Outer cylinder area gives force so you multiply by radius to get torque. That gives 2*pi*r*h*r. Drop the 2 as a constant factor to get torque proportional to pi*r*h*r which can be calculated as stator envelope volume.

[@bobeshoz]

@@ChrisRosser alright, so now that you explained that, 2407 would be just about perfect for 6" ?

[@WayneHunter1000]

Would like a video on building a motor amp draw/load tester

[@starsstripesjacket]

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

[@ChrisRosser]

Awesome, thank you! Glad you like the video 😁

[@chriscflint]

Hi Chris, question. Does the Flight controller (via the ESC) know what the rotation speed is of the motor is does it work only on the Gyro giving it position and "encouraging" the slacking motor to spin up until the Gyro reads the FC as being in the position the pilot has selected i.e. parrallel to the ground.

[@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!!!

[@AarOnCoasters]

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

[@soumynonareverse7807]

I'm a bit confused with all the math that is involved in this video. I know this is an older video so do you have another video that covers the same info but just mentions in what situations you need a bigger motor for or higher KV instead of all the math that's been added that not every viewer will understand?

[@_burd]

It would be great if there was a calculator you could input the prop or motor specs to find a good match 🤔

[@jjenningsoh]

Thank God for science. Gonna be funny when it finally leads us to Him 😉

[@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 👍

[@mihavuk]

THANK YOU.!!! 👍

[@ChrisRosser]

You are welcome!

[@reneseib6532]

how do you know all this? your a absolute beast ahah, great atanchen to detail. truely helpfull thanks

[@mortonbeard2240]

I'm floundering at fpv. 🙃

[@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 (

[@llickmogan]

I had 2807 1700 eco 2 on my racer 5inch once,it was mint to fly

[@justhackitfpv]

Can you make a video telling difference between various winding method and cleanliness of winding

[@krapnijes9309]

what is the variable t in the MOI equation? is it thickness of the bell?

[@puel]

Can you make a video only about high efficiency and long flying.

[@justhackitfpv]

Finnaly a explanation which supports my theory

[@stimmungsasdrohnautfpv3830]

Great work Chris. Thanks a lot for this input

[@ChrisRosser]

My pleasure!

[@slaupen]

any quick tip for my 6inch build? 2604 or 2506 motors? 1350kv or 1650kv

[@ChrisRosser]

2408 1700KV 👍

[@slaupen]

@@ChrisRosser Thanks, there are not many of does motors around. And my vendors does not have any. Would 2506 1650 work good enough?

[@ChrisRosser]

@@slaupen As long as you use a light pitch it should be OK.

[@slaupen]

@@ChrisRosser Thank you very much for your help

[@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 :)

[@mpg500]

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

[@thommylue]

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.

[@kingromulus654]

That was awesome. I feel like I just got smarter.

[@neilfpv]

Amazing! You are a great professor! Subd!

[@ChrisRosser]

Thanks for the sub!

[@sakfpv8444]

I would love for you and Kababfpv to collaborate.