Page 1 of 4 123 ... LastLast
Results 1 to 10 of 31

Thread: RC motors, 3 phase..? Tell me about them.

  1. #1
    Join Date
    Jan 2003
    Posts
    3,793

    Default RC motors, 3 phase..? Tell me about them.

    Looking at my grandson's RC cars one of the motors has 3 leads which I assume is 3 phase.

    That same motor says max rpm is 100,000. That seems unrealistic, but what do I know about the current RC stuff.

    I see they still have the old standby, the RC10.

  2. #2
    Join Date
    May 2006
    Posts
    13,279

    Default

    I may be way off here - but JT or someone will correct me - it's DC so no reason for phases - one wire is the + the other the - and the other the signal (I forget the correct name) it's brushless and that's what the third wire is for... to tell the comp. where the motors at for the proper signal...

  3. #3
    Join Date
    Apr 2010
    Location
    Canada
    Posts
    2,597

    Default

    If three leads then they are are BLDC (brushless DC) motors they have a 3 conductors fed from a PWM controller.
    Only any two of the three windings are conducting at any given time, they represent a DC motor turned inside out.Hence BLDC.
    They are extremely high RPM.
    Most of the BLDC are out-runner motors.
    Max.

  4. #4
    Join Date
    Oct 2013
    Location
    Setubal, Portugal
    Posts
    361

    Default

    brushed motors have their days counted. Even electric fork lifts have three phase motors. With the improvement of power electronics its easy to convert DC to AC and three phase is the easy way to get a motor to turn. 100K rpm is obtainable by high frequency switching. BLDC motors include magnets so that they don't have to "induce" a magnetic field on the rotor and makes the motors more compact and efficient.
    Helder Ferreira
    Setúbal, Portugal

  5. #5
    Join Date
    Dec 2016
    Location
    Helsinki, Finland, Europe
    Posts
    2,056

    Default

    RC cars are stupidly powerful nowadays:
    https://www.youtube.com/watch?v=TyDvXA_0ZyA

  6. #6
    Join Date
    Mar 2015
    Posts
    2,150

    Default

    It is a three phase design, sensorless. 100,000 rpm is only attainable from an “in-runner” design. Poorly made ones will throw magnets, as the magnets spin on the shaft. Out-runner designs, the outside can rotates. It cannot throw magnets as centrifugal force holds them tighter to the can. Out-runners are now the most popular design for everything but cars. They have lower rpm’s but much more torque. They can spin bigger props for more efficiency. All of my airplanes and drones use them. I must have 15 of them.
    The electronic speed control is kind of like a VFD. It cycles the three legs in order to control rpm but with DC. They use back EMF to sense where the stator is. They have for the most part, along with LiPo battery packs, replaced IC engines in the hobby. They are simply amazing.

  7. #7
    Join Date
    May 2006
    Posts
    13,279

    Default

    Well there you have it sounds like RB knows exactly what it is - I thought i remember seeing ones that had two thick wires and one very thin one so did not think that would be used for power just a sensor wire for brushless control...

    RB my little fuego brushless has three wires all the same size - so is it a three phase ac or somehow alternating dc with a pulse?
    Last edited by A.K. Boomer; 03-12-2018 at 10:29 AM.

  8. #8
    Join Date
    Jan 2004
    Location
    Missouri
    Posts
    28,025

    Default

    Quote Originally Posted by A.K. Boomer View Post
    .....

    RB my little fuego brushless has three wires all the same size - so is it a three phase ac or somehow alternating dc with a pulse?
    Those are the same thing, really, so the answer to the question is "yes". The DC battery voltage is converted to pulses by the electronics.
    1601

    Keep eye on ball.
    Hashim Khan

  9. #9
    Join Date
    Apr 2010
    Location
    Canada
    Posts
    2,597

    Default

    There is no, or very little significant difference in the design of a BLDC RC or 3ph AC synchronous motor. Just the way it is commutated
    With BLDC there is only 2 windings energized at any given time, there are 3 pulses/ electrical rotation and the pulses are 120°
    apart, and PWM switched for varying RPM. The pole count decides how many electrical revolutions/mechanical revolutions there are.
    In the case of a VFD it produces a pseudo 3 phase signal with varying frequency and the sine waves itself is modulated.
    You will see RC motors rated in Kv this is not Killo-volts but RPM/volt, (thousand rpm/volt).
    Max.
    Last edited by MaxHeadRoom; 03-12-2018 at 11:14 AM.

  10. #10
    Join Date
    Dec 2008
    Location
    Luton,UK
    Posts
    1,983

    Default

    Almost all motors are AC, conventional brushed motors just use a mechanical inverter called a commutator.

    Pure DC motors and generators exist, but they're rare in application. Michael Faraday demonstrated the first electric motor in 1821 and it was of this pure DC or Homopolar type.

    Homopolar generators were used to produce very high currents at low voltages for refining metals and in electroplating.

    Various terms are used to describe brushless motors and many of them are more for marketing than anything else. Assuming a permenent magnet motor, then one definition is that AC means it's driven by a sinusoidal waveform and DC means a trapezoidal waveform.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •