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Kv Ratings on Brushless motors

Discussion in 'Electric RC Talk' started by godale03, Apr 2, 2008.

  1. godale03

    godale03 Awesomer!! Supporter

    Hey Guys,

    I made a mistake earlier today by mistaking a 4300Kv motor for a 4.3 motor, therefore thinking that that motor was hotter than a 5300... of course which I mistook for a 5.3 motor. I have also found out that Novak, the brushless motors I am the most familiar with, used to classify there motors differently than they do now.... ie. a 4.5 motor is hotter than a 6.5 motor. So I guess my questions are... how do you find out how many Kv a motor is? What does this number mean?, and How do you use it to figure out if it is the right mill for your application? Thanks

    Tom
     
  2. flm_savage

    flm_savage Hardcore RCNT User Supporter Veteran

    lower motor number = higher torque and the ability to run higher voltages.
    higher motor number = lower torque but more rpm per volt. normally won't accept higher voltages.

    that said, i run a 6900kv in my firestorm. I would have gone with the 5700 but i only wanted to run a 7 cell pack and run time isn't crucial to me. So i got super fast with decent torque and average runtime.
     
    Last edited: Apr 2, 2008
  3. Lessen

    Lessen Super Awesome! Supporter

    I believe.... "believe" that the Kv rating is basically equal to RPM per Volt with no load. So your 4300 Kv motor would turn at 30,960 rpm (4300 x 7.2) at full throttle with a 7.2v pack under zero load
     
  4. godale03

    godale03 Awesomer!! Supporter

    Man... I have alot to learn. I thought the 4.5 would be the Kv rating. Thanks for the info guys. I will hit the books an try to educate myself with the proper information.
     
  5. Lessen

    Lessen Super Awesome! Supporter

    When it comes to the Novak motors I believe the number of the motor (in this case 4.5) is relative to the Kv rating. I think that motor has a Kv rating of 4500.

    I think what has you twisted is that you are used to knowing that less turns (lower number) = hotter motor. However, with brushless motors the higher number will give you more top speed.
     
  6. godale03

    godale03 Awesomer!! Supporter

    Yup... I am sure that is what I am confusing. Just going to take some time I suppose. I just appreciate you guys not hanging me for sounding like such a dumbass.

    Tom
     
  7. Lessen

    Lessen Super Awesome! Supporter

    Dont' sweat it man. For the past 3 years I thought you couldn't fast charge Nicd batteries. *buzzer*... wrong. Nobody knows everything.
     
  8. godale03

    godale03 Awesomer!! Supporter

    In my case sometimes I think I know nothing! Things change so damn fast these days. It's hard to keep up.
     
  9. Brushlessboy

    Brushlessboy RCNT Addict

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    The lower the number on the Novak systems, the faster the car will be. The 3.5 Velociti has a Kv rating of 10500 revs per volt, while the SS 8.5 Pro runs only 5000.
    You can get 2.5 turn motors but the quality of Novak sees no real difference in the REAL power results.
     
  10. Lessen

    Lessen Super Awesome! Supporter

    Dont' they realize that they are just confusing people with these stupid number ratings? Why can't they just call it Velociti 10.5?
     
  11. CharliesTheMan

    CharliesTheMan Gone - bye bye.

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    well it's kinda like a Chevy 350 small block having 350 cubic inches, 290 horsepower, and 325 lb/ft of torque. Different numbers for the size and power rating.
     
  12. Brushlessboy

    Brushlessboy RCNT Addict

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    Here Here Lessen! In both Nitro and Electric the numbers are confusing, and real outputs unknown unless you chase down manufacturers websites.
    I am SURE they could all give us a clue in the model name.
    Or maybe I'm just missing something!
    Just to confuse you even more. The Velenion system that comes with Traxxas VXL's has a rating of 10.5 turns, (according to Traxxas) but absolutely EATS my 8.5 turn Novak.
    GO FIGURE.......
     
  13. CharliesTheMan

    CharliesTheMan Gone - bye bye.

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    Well thats kinda like the os .21 that would eat the picco .26 isn't it?
     
  14. Brushlessboy

    Brushlessboy RCNT Addict

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    Spot on again Charlie, but I've never understood how you can TUNE an electric motor.
    I though electric either worked or it didn't!!!!!
    (not real clever but I can lift heavy things)
     
  15. Lessen

    Lessen Super Awesome! Supporter

    yeah, there really aren't very many standards in the power world of r/c. Definitly when it comes to dyno there is no consistancy. One mag says one thing, one says another. I've read more than a couple articles on inconsistancy within the industry. :shrug:
     
  16. godale03

    godale03 Awesomer!! Supporter

    The only way I know to "tune" an electric motor is by either changing the pinion and/or spur gears to change the gear ratio. If you have a castle motor you can hook it up to your PC and fine tune it. The Novak speedos have profiles that you can change that will change some of the characteristics of the motor. That's about all I can tell you about tuning electric motors.

    SweetD is the man when it comes to electric motor questions.... I bet he would have the best answer as far as it comes to tuning electrics.

    Tom
     
  17. Brushlessboy

    Brushlessboy RCNT Addict

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    Of course for those that are really confused, go to the Novak website and they have ALL the info there.
    When I say ALL I have never seem a website with so much technical info....
    EXCELLENT
     
  18. abadk9420

    abadk9420 EEM Team Driver Supporter

    I know on brushed motors there is some degree of tweaking or tuning you can do such as different brush springs or brushes or changing the timing by turning the end bell a little but it seems that the only way to get more out of a brushless is by applying more voltage, like it has been stated what ever the kv is times what ever voltage you put into it is what you get and I think the modle numbers are just like cars they just identfy what model they are like Ford F150 or Chevy Suburban not whats under the hood for power..
     
  19. ohmygahitscoby

    ohmygahitscoby Hardcore RCNT User

    Can't you also change the magnets inside?
     
  20. CharliesTheMan

    CharliesTheMan Gone - bye bye.

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    yeap, but don't use refrigerator. I tried that and the tabasco jar magnet caught fire and made a weird grinding noise. From now on I'm sticking to electric motor magnets.
     
  21. sweetdiesel

    sweetdiesel aka SouRGassssssss Supporter

    At this time there is no consistent nomenclature for brushless motors. You can compare numbers within one manufacturer but it all gets thrown out the window when you compare two different manufacturers. I would look at the actual Kv rating, can size, efficiency, and how many cells are used to figure out which motor is right for your application. Unless you are a very good racer, a 3.5 or 4.5 Novak motor is better suited for bashing. I've gotten smoked by a guy running 19T brushed motor when I was running a LRP 4.5 in my Xray T2. Remember speed means nothing without control.

    Actually this is somewhat untrue. The lower the number on the Novak systems within the same series, the higher the maximum rpm the motor will spin with a given voltage. You can make your car have a higher top speed with a lower Kv rated motor with more voltage. Also if your batteries are insufficient in handling the amp load of the higher Kv motor your car will accelerate slower.

    Also with regards to a motor running "only 5000" rpms per volt, with a quality 2S battery you're looking at 35K rpms max which is pretty damn fast.

    Some brushless motors can be tuned, as some manufacturers will allow you to change the timing on the motor.

    Real power results are easily recorded by using a wattmeter. It would also be pretty easy to see the difference between a 2.5 turn motor and 3.5 turn motor from the same manufacturer given the same can size, batteries and gearing.
     
  22. CharliesTheMan

    CharliesTheMan Gone - bye bye.

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    Thanks SD, that cleared up several fuzzy issues all at one time.
     
  23. platgof

    platgof RCNT Qualifier

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    There needs to be a std for all motors, such as rpm, voltage draw, run time. I am sure more info could be added, but that would be a good start.
     
  24. gensace

    gensace RC Newbie

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    Check out this video to explain what is KV in a brushless motor

    [ame="http://www.youtube.com/watch?v=RmrtV8YHSFY"]YouTube - ‪Understanding KV in a Brushless Motor‬‏[/ame]
     

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