controling bldc using esc

Discussion in 'The Projects Forum' started by videh, Dec 3, 2014.

  1. videh

    Thread Starter New Member

    Nov 23, 2014
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    hi everyone,
    i want to control bldc with esc, for this i am using at89c51 microcontroller , i read previous blogs but still i am confused.....
    please help me
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Check out some of the RC sites where others have done it, RCgroups.com etc, it is just a 5v PWM signal, I do not recall the PWM freq.
    Max.
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    It is really quite simple. To make the motor move you need to know where it is. If you know where it is you can apply a pulse to the pole which exerts maximum torque on the rotor. As the rotor starts to move you wait until the rotor moves to the next pole and you kick it again with another pulse. As the rotor begins to move faster the time between pulses gets smaller and so the little kicks become more frequent. To slow down you just stop kicking the rotor with pulses and it will coast to a stop.

    Pretty simple...eh?
     
  4. videh

    Thread Starter New Member

    Nov 23, 2014
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    actually i don't know how to start movement in bldc, i read some post here and accordingly i applied low signal (0 volt) to the controlling pin in esc and waited for 5 seconds then i applied a pulse of 1 mili second duration with frequency around 5o hertz, i observed beeps, small jerk is also observed in motor but it was unable to move the motor continuously
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You said you were using a ESC so all the motor control is done, the ESC just needs a PWM signal?
    Max.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What does the ESC datasheet say about the input needed?
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    I guess I thought your question was how to move the motor without the ESC (Electronic Speed Control). Either you or the ESC must be able to sense the rotor position. You can't just apply pulses to the motor or the ESC and expect motion. There needs to be some method, and thus some wires that convey information, to determine the rotor position. Without that connection you're just spitting into the wind.


    You don't tug on superman's cape.
    You don't spit into the wind.
    You don't pull the mask off that ol' Lone Ranger
    ....
    -- Jim Croce
     
  8. videh

    Thread Starter New Member

    Nov 23, 2014
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    yes i am sending the pwm signal but i don't know the range of duty cycle and is it necessary to wait for around 5 second at start
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have not experimented with or monitored a RC ESC signal but apparently the PWM frequency is around 300Hz.
    Why the 5 sec start needed?
    If you set up a 300Hz PWM in to a off the shelf ESC, then I suggest experiment with the duty cycle and observe the results.
    Papabravo, RC motor ESC's do not have any feedback.
    Max.
     
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  10. videh

    Thread Starter New Member

    Nov 23, 2014
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    i brought it from local market and there was no any data sheet i just checked on internet and from that i started, i am just confused about duty cycle, i understand that it is just a pwm but i am unable to do that.
     
  11. videh

    Thread Starter New Member

    Nov 23, 2014
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    thanks.........
     
  12. MaxHeadRoom

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    Jul 18, 2013
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    Well first you need to use your Micro to produce a 5v PWM signal, I am only familiar with Picmicro's in this area, but this is the first thing, the duty cycle comes after.
    Most off the shelf ESC's abide by the general standard.
    Max.
     
  13. videh

    Thread Starter New Member

    Nov 23, 2014
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    ok can you tell me the way to get a pwm continuously, i mean with changing duty cycle
     
  14. MaxHeadRoom

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    Jul 18, 2013
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    Someone with knowledge of the at89c51 microcontroller can probably help.
    Max.
     
  15. videh

    Thread Starter New Member

    Nov 23, 2014
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    i mean the basic idea, actually i shall develope the code.
     
  16. videh

    Thread Starter New Member

    Nov 23, 2014
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    well, i am going to try, on facing problem i will again put some post here.
    thanks everyone for your valuable suggestions and precious time.
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you need basic idea of what PWM is there is way more out there than I can type in, one place as pertaining to micro's is the Picmicro site in the search app notes typing PWM should show a great deal of info on its own.
    The Processors that contain particular modules such as PWM have most of the work is already done for you.
    Max.
     
  18. Papabravo

    Expert

    Feb 24, 2006
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    OK, so running open loop means you get an approximate speed. How do you achieve reliable acceleration without feedback?

    PWM modules are not common in 8051 variants, but there are some out there. Try this one:

    https://sites.google.com/site/controlandelectronics/pwm-tutorial-using-8051
     
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  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I presume just running a prop on an aircraft and not used in such as a servo application there is no concern.
    All the 4,6 & 8 rotor drones use them also.(the position servo's DO have feeedback)
    The modern washing machines use a similar 3phase outrunner principle motor (Fisher-Paykel) with no feedback elements.
    http://www.fp.fisherpaykel.com/direct-drive-motors/common/pdf/4876_NZ_Motors_BRO_HR.pdf
    Max.
     
  20. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    This is a lengthy thread, and I did not see that issue addressed specifically. The advice to get a datasheet or operating manual is right on. Many, if not all ESC's today have a start-up and programming feature. They communicate by sending audio pulses to the motor's coils. Hence the beeps. Usually, it is some beeps, then you reduce throttle to "zero," then more beeps and you push throttle to max, etc. There may be other programming, such as for motor cut-off voltage.

    Try to get the manual fro your esc. If you cannot get a manual, get a manual for a Castle Creations or Turnigy (Hobby King, e.g., http://www.hobbyking.com/hobbyking/store/__452__182__Speed_Controllers-Under_20_Amp.html ). Turnigy is made in China and is very likely representative of most esc's made in China. That will help you see how it is done in general. Then, get a real RC transmitter (borrow, if necessary) and receiver. Program the esc and confirm working. Then you will be ready to use your microcntroller to manage the esc. Alternatively, many years ago, some "straight through" esc's were made. They didn't beep the motor's coils. They simply took a standard RC servo pulse of 1 mS to 2 mS and converted it to a % pwm or power. You may still be able to find one of those earlier designs.

    One other thing, when starting an esc, it will not have a way to know which direction to turn. You may see it flutter in both directions before actually starting consistently in one direction.

    John
     
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