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Brushless motor RPM/Volt rating

shai kon
Expert 1960 points

Hello,

When designing a direct drive brushless motor - what should I do to make the RPM/Volt rating lower?

In other words - how to increase tourqe and decrease speed (without a gearbox)...

 

For example - these 2 motors, have a different RPM/Volt rating:

http://www.modelmotors.cz/index.php?page=61&product=2212&serie=34&line=GOLD

vs

http://www.modelmotors.cz/index.php?page=61&product=2212&serie=26&line=GOLD

Being the same size, how do you think they differ internally?

  • 0
    TI__Mastermind 26065 points

    Hi Kon

    Higher magnetic flux density, higher inductance of the motor coils and higher Ampere-Turns will give you higher rating of RPM/Volt, which also gives you more tourqe but lower speed at related voltage.

    Usually the easiest way to make the RPM/Volt difference is to change the turns of the motor coils. if the motors are almost the same size and serial, it is probably they only have different turns on winding, also the diameter of the coil wires will be different to matching the Amperes rating and the slot space.

    Thanks.

    Wilson Zuo

    Motor Application Team

     

  • 0 in reply to Wilson Zuo
    Expert 1960 points

    1. Higher magnetic flux density is achieved by bigger magnets.

    2. Higher inductance of the motor coils can be achieved by more turns around the slots, use of longer wire, use of thinner wire

    Did I get 1,2 right?

    3. Also, what do you mean when you say: "higher Ampere-Turns" ?

  • 0 in reply to shai kon
    TI__Mastermind 26065 points

    Hi Kon

    1. Yes. By higher magnetic field intensity and less air gap.

    2. Yes.

    3. Ampere-Turns means  ( phase_current times phase_winding_turns ). The output torque will be proportion to this number when other conditions are constant.

    Thanks.

    Wilson Zuo

    Motor Application Team

  • 0 in reply to Wilson Zuo
    Expert 1960 points

    1. I heard of different types of winding schemes: LRK and DLRK. Is it of any significance when designing a high torque motor?

    2. Is using a square profiled magnet wire a good idea (to have less dead space in the windings)?

    3. When selecting a core material for the steel laminates - what is the most desirable property one should look for (is it magnetic permeability)? 

    4. What is the optimal "shoe" geometry?

     

     

  • 0 in reply to shai kon
    TI__Mastermind 26065 points

    Hi Kon

    I think your questions are more inside of motor design. I would recommend you to find answers on more professional sites or books for motor design and craft. Belows only are my personal comments.

    1. I think you can google LPK vs DLRK. I see lots of post related to the comparison.

    2. I think square profiled would help but more cost. Also the improvement is limited. If not for ultimate performance, I think it's not necessary in most cases.

    3. I think beside the magnetic permeability and high saturation level, soft ferromagnetic properties is also important to lower the core loss.

    4. This is beyond my scope. But I think no shape is optimal for all. It should depend on your needs, motor type and manufaturing.

    Thanks

    Wilson Zuo

    Motor Application Team

     

  • 0 in reply to Wilson Zuo
    Prodigy 10 points

    Thanks for your help.

    1. what do you mean by "soft ferromagnetic properties"?

    2. Can you suggest a forum for brushless motor design?

  • 0 in reply to Boris Gluzman
    TI__Mastermind 26065 points

    Hi Gluzman

    "Soft" means the material will not remain magnetised when the external magnetic field removed or the coil current not presented.

    The more soft, the less energy loss when re-magnetizing it with new direction.Also the material will have less "area" in its hysteresis loop inside its magnetizing curve. Found some links about those magnetic material knowledge.

    http://en.wikipedia.org/wiki/Magnetic_core

    http://en.wikipedia.org/wiki/Magnetic_hysteresis

    About the BLDC motor design forum, I think the first thing is to make clear what kind of BLDC you want to build. What is your final application? Single or MP for the production? It will lead to totally different focus aspects on design and manufacturing.

    And motor design really needs some basic mechanical and electromechanics backgrounds. If your major is not in that area, it will be difficult to dive into the field.

    I think if your purpose is to use motor for some application, in most of the cases, all your need it to choose a motor other than build or design a new type. Below link gives you a place to choose different kinds of motors.

    http://www.anaheimautomation.com/products/brushless/brushless-products.php

    Thanks

    Wilson Zuo

    Motor Application Team