Diameter vs Length for Maximum Performance of a Brushless Motor
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- čas přidán 27. 09. 2020
- Motor Manufactures offer a lot of different sized motors that we can select for our RC Cars, Airplanes or Boats. But what is the performance difference of having a larger diameter motor vs a longer can length motor? What does a larger diameter and longer can length provide us with?
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Really like this channel that nails down the overall general relations between parameters/variable with the correct equations. But often the devil is in the details. If you really look at the stater copper coil loop shape, and think about the loop integral of Ampere or Faraday's laws, the same amount of copper generates more magnetic force with the larger diameter motors where the loop is roughly a square. The optimal shape is circle, but square is better than long, narrow rectangle. And as this channel said, the more void unfulfilled in the motor results in less efficiency, same goes with more work the copper is put to use results in high efficiency. So, go for the larger diameter if weight is the same for 2 different motors, if the craft allows the larger diameter.
The video I've been waiting for. Great thanks. I think if you do a video on 540 size 4 pole motor vs 550 size 2 pole motor. It would be great. Its a very common question most of the RC fans asks.
Great suggestion! Thanks for the comment Gehan Wijesundara.
This man will be a professor one day.
Excellent work!! This helped me out a lot being new to electric rc. Thank you sir!
A lot of information in this video. Good explanation. Really apprciate it. Thanks 👍🏻
Hi Kura2bulat Properties InC , thank you for your comment!
This is gold👍🏼😌 alot of usefull info,and very well explained. It helps us take the guesswork out of things,Keep it up😀
Hi Knut Roald, thank you for the comment!
Was thinking the exact same
Great video although one thing I noticed you didn't discuss in this video is the effects of rotational inertia, angular momentum and how the perpendicular distance to the specified axis may affect the motor's performance especially at high speed/rpm.
I was much excited to hear it being discussed because it's seldom talked about
From my understanding, given the same volume but different aspect ratios and all else being equal both will increase in torque with size in either dimension, however, maximum or initial torque should be higher in the motor with increased diameter, whilst the motor with a smaller diameter but longer can length although having a slightly less internal torque should be able to increase (and decrease) RPMs more rapidly as well as have less torque loss at higher RPMs and potentially produce more power as well as have a higher maximum rated voltage and rpm.
In short larger diameter is best for higher torque whilst smaller diameter and longer can length is best for high power and rotational speed.
Also its hard to compare motor aspect ratios when using the same power and kv as controls/baselines, as these are just product values that can be achieved from a variety of different variables. To make an even comparison you would need to compare the same or similar size/weight, number of poles, number of turns, same wind pattern, amateur, number of slots ect.. the motor with the longer can length will typically have more power, less ir, higher kV and less torque when used in its upper limits. Although if you match the kV the longer motor should still have a higher power output and maximum rpm too and i do see this trend when viewing motor specs too, also the same can also be said when comparing the specs on in-runner vs out-runner motors aswell.
A similar effect also occurs in gasoline engines too when increasing displacement. Increasing the stroke will result in the highest torque gain yet the trade off is lower rpm and less top end power compared to increasing bore which is less effective at increasing torque yet won't drop in torque so rapidly as motor rpm increases making for excellent top end power without any loss in rpm as well as being able to be more responsive to rev up or down rpm too.
Also, another difference is the centre of gravity as a longer can motor will have a lower cg than a short can larger diameter motor. This is also why alot of race boats option for such motors as a 2968 too.
If this is something you want to look into, would love to see a part 2 to this 👍🏻
Hey Andrew, I love your detailed analysis of the differences applicable to changing diameter and length parameters of a motor. Very Well thought out.
As much as I'd love to get in to some very deep details within the videos, this didn't seem to be what most viewers are interested in.
Really appreciate people like you for the extra info in your commentary as well as the owner of the channel for this video . Love the willingness to share the knowledge for people .👍
Another good video, thanks!
Thank you Remko!
Ahhh now I know why I didn't get mechanical engineering as my program :D
Good video, yes it does seem like best to choose based on the physical parameters, just like I chose a 4068 motor in my 1/8 serpent buggy because it simply doesn't have the space to fit something like a 3674 as 68mm is the maximum length.
Also I recently encountered a situation where two motors I was considering for my 1/12 buggy of different sizes had the exact same power output. A 2838 vs a 2445 both had a maximum of 500W at few different selections of KV/ maximum voltage and both had the same 2.3mm shaft (although most 2838 motors are 3.175mm shaft) I was after. I end up choosing the 2445 cause it was available in the KV value closet to what I was looking for since this vehicle has a fixed motor mount giving no option for larger or smaller pinions.
Hey Andrew, that's a very good example that you had written out. I like how you prioritized kv to truly match the power system you required rather than size differences between the motors.
Good explanation, good channel. Thanks
So nice of you!
Hi, what about the efficiency due to the lower percentage of wire making up the end turns in the winding for a longer but smaller diameter motor?
Great point. I'd expect the differences to be minimal and do not have any data to represent this.
As an engineer who tests electric motors and is starting with RC your explanations are fantastic 👍
Great to hear! Thanks for the comment Pedro!
Wow thanks for the info I was thinking about buying a TP motor but didn't know what size can I need but now I have a good idea the 4070
Glad the video could help, thanks for the comment!
I've been told buy multiple sources that my Diameter and Length is just right.
Hello? Georgia Tech admissions? How are you doing processing my application for the study of EE?
I’m sorry a bit confused.. the picture to the left shows motor A to be the long/thinner diameter one, but the picture in the middle show motor A to be the thicker one ?? Messed up my head when I tried to follow 😛
k man what you explained how many nm of torque a 36mm motor generate per mm, which is 12 , do you know the number that a 40mm can motor can generate per mm?
Good morning say I've studied and replayed this vid many times and even went to your website and now im even more confused.im trying to convert a gas powered 46 inch Prather deep vee to this new brushless technogiggle and im lost I can't seem to get figures to work right help
What figures do you have?
Informative video. Brushless motors do not live long at 60,000 even the ones that are supposedly rated for 60,000. Kv times volts equal rpm and DO NOT EXCEED 50,000.
I'm from Indonesia and don't really know English.. if I may know, in conclusion, which one is more recommended between the length and the size of the motorbike?
Guess I should have weighed my motors before installing them. I just replaced a 4092/1650kv with a 4985/1650kv. Was hoping the latter would allow me to gear a bit taller and not overheat.
You can see the one with larger diameter can have either lower Io or lower Rm, does it mean larger diameter is good for high efficiency setup? Will you make a video that explains why larger diameter can be more efficiency?
So if you have a 3650 motor vs a 3674 motor and they have the same KV at 3000. The 3674 motor would have more torque and produce the same RPMs?
Yes, both motors would have the same torque constant, however, the larger motor would be able to draw more continuous current. This would result in more torque potential.
Hi great video. How would I find the radius of the motor? Or how would I meshure it?
Spec sheet or measure it.
@@RCexplained ok and what would it be called? Rotor Length?
Length of the motor would typically be defined as length of motor can.
@@RCexplained oh ok I just thought the rotor was shorter that the motors can.
Yes if you want the rotor dimensions, (motor was in your original question) you'd have to measure this as manufactures don't specify always.
k what would you choose a 3674 2500kv 1900watts max vs 4268 2600kv 2200 watts max
If your goal is power, choose the one that makes more power if both motors fit in your rc.
you talk about the amount of copper which makes a lot of sense for me BUT...what about the longer arm/lever of the larger diameter-motor?
Hi Arcade Collectors Europe, there was a calculation running through this. It works out very similar to just lengthening the can size as you have more leverage occurring along the additional length.
So inshort, Longer motor more torque?
A larger motor, keeping all else equal, will always have the potential to develop more torque.
Generally the vehicle has space for a common size......
That is correct. In my case, almost every RC I own has an option to use multiple common sizes.
RCexplained so more turns and lower kv = more resistance, less heat? More low end power?
Lower current through a motor with higher resistance (lower kv) will produce less heat. Low RPM torque for any motor is based on the torque constant multiplied by the current being pulled.
I want to build a jet surfboard using 200a esc on 6s and a 4092-1520KV brushless motor that have 4300w will this system work i am 50Kg
NabiL: May I suggest you go to the CZcams channel: Youngsters Jets. Here you will find TONS of information and build experience!
Hi NabiL, this highly depends on the jet you are planning to run. First impression is that the 1520kv option is too high for 6s.
Remko Jerphanion yes i watch him i got the idea from him thanks for reply.
@@NabiL_Lam Cool!
These examples and assumptions appear too simplistic.
These motors would never weigh the same and would not have the same efficiency, etc. A longer can or a wider can will of course give more power but also will weigh proportionally more and use more amps. Those are critical factors I think.
Too many commercials sorry.
pls give conclusion sry bad English
Hi Tam, it really comes down to your specific RC vehicle. In general, a larger motor whether it's in diameter or length will provide you with more performance.
@@RCexplained I’m using a onroad 1:8 Rc what is the most ideal
check to see if a 40x82mm motor will fit. This size motor will be good for 140km/h.
TP 4070 is whats up