How can I power my outrunner brushless motor?

Discussion in 'The Projects Forum' started by braindead, May 12, 2010.

  1. braindead

    Thread Starter New Member

    May 12, 2010
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    Hi, I bought this motor a while ago. It has a speed controller (i think?) rated at 30 A and the brushless motor is marked at 1550. I want to use it for a project, but I have no idea how to power it really. Do I really need to supply 30 Amps? The speed controller has 2 inputs for power, 3 inputs to the little engine, and 3 other inputs for PWM-steering I think.

    So looking in the store I can find a lab power source that can supply upwards 3 Amps, but 30? Forget it! What should I do? Do I need to use battery packs for this or what?

    Please help me explain how this works!
     
  2. retched

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    Dec 5, 2009
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    Do you have any other info on the make or model of the motor? Any data plate data?

    Is there a horsepower rating?

    Whats the brand of the speed controler? Model number?

    The speed controller is rated at 30 amps so it CAN handle up to 30 amps. This may be the amount it can handle on the initial amp draw of the motor when it starts, but your motor would be awful powerful to be 30A.

    Do you know if the motor is 12v? more? less?

    what is the size of the motor? 5 inches around? 8 inches long? this kind of thing. There may also be a NEMA size or rating on the name plate.
     
  3. braindead

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    May 12, 2010
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    The motor is marked with:

    Evo 1550
    RC Smart
    Outrunner Brushless Motor
    I would think it is about an inch in diamater.

    The speed controller is marked with
    30A4, 14NC, BEC, 30A, WK, WST
    X-Speed motor controller series No. 011607

    Does this give any clues? What were you saying in your post? Will I burn out my lab power source if I connect 12 V to the speed controller and motor?
     
  4. retched

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    No, maybe not. Does your lab supply have overcurrent protection? If so you should be ok.

    It definitely is NOT a 30A motor. I would start with a 9v battery and see what you get.

    Here is what I found on you motor:
    Idle current = 0.45 A
    Max Voltage = 8.4 V
    Max Current = 7 amp
    RPM @ 7.4 v 7.5X5 black slo-flyer prop (Static)
    5000 - 3A
    6500- 7A

    So I would stick to around 6v or 7v and a ps that can supply 3 or more amps will give you 5000R PM.

    Use the speed controller to vary the speed.

    The standard battery to run this is a 7.4v LiPo. This 1550 can apparently handle close to 12A with a serious helicopter prop blowing a lot of air across it.

    Be careful and watch your temperatures. These little motors use smaller that 30 gauge wire for the windings, so without some serious cooling, you will blow this quick.
     
    Last edited: May 12, 2010
  5. braindead

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    May 12, 2010
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    Well, I would really like to get all the power out of it. Power is really important for my application. How is it that the batteries can supply 30 Amps, but bringing that amount of juice out of a power supply at home is so difficult? Can I build some cheap current source to supply 30 Amps from the 230 VAC?
     
  6. retched

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    re-read my post. I edited it about the amperage. The amp draw on this motor is greatly exaggerated by the chinese manufacturer. 12A is your limit. This is a very specialized motor. If you are not using it water cooled, or in an aircraft for plenty of airflow, you will have a dead motor.

    What are you trying to do? Im sure I can help you get a better motor for the job.
    If you need strength and not speed, a geared motor will do. They can run off milliamps.
     
  7. braindead

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    May 12, 2010
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    As part of a project, I need to spin a wheel around. And it must be pretty powerful too. I want to spin it at around 60-300 rpm and with a force of maybe 5 kg at 10 cm, so that would be I guess 500 Ncm as the manufacturers rate it? Of course I did not think my small motor was going to pull this off, but I thought I would use it until I find something better.

    The other option at the moment are some small DC motors rated at 180 mA and 12 V. No idea what torque they provide. Perhaps you have some guess? Maybe 10 of those would get near the numbers I need?
     
  8. retched

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    You can get those numbers with a 1 geared motor. The thing is. you want reletivly low rpms, so standard high rpm motors use gearing to exchange speed for power.

    Where are you located in the world? I dont want to spend time finding you parts just to have you answer "Oh, sorry we cant get those in South Transylvania " ;)

    So we will figure on 10 lbs at 6 inches or 20lbs @ a foot (12 inches)

    This is 300 RPM at 12v .18 amp
    http://www.goldmine-elec-products.com/prodinfo.asp?number=G16819
     
  9. braindead

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  10. retched

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  11. braindead

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    Utterly amazing, 12 $ ?! I will take 2 just for the heck of it. Just gotta check the shipping!
     
  12. retched

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    7434gm*cm
    1 motor
    $20 us. International shipping. It is 23RPM at 6v
    http://www.solarbotics.com/products/gm21/
    So they are out there.
    You dont want to deal with three phase unless you REALLY have to.
    It will kill you quicker than a blink. And mistakes are easy to make.
     
  13. braindead

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    May 12, 2010
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    Oh, shipping was about 80$... darn. Perhaps something in the UK or Germany can be found cheaper.
     
  14. braindead

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    May 12, 2010
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    Really, why so deadly?
     
  15. retched

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    Shipping for batteryspace is $45 per box for international. So, fill the box ;)
     
  16. retched

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    You are dealing with very high potentials on each leg, and if you dont limit current, it can jump right through the small motor housing and "game over"

    You dont want to use 3 phase for a small motor if you dont have to. I dont even consider them until around 2 HP or more. And that is for industrial blower motors. Where there will be minimum human contact
     
  17. jpanhalt

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    Jan 18, 2008
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    This gives another perspective on brushless DC (BLDC) motors: http://en.wikipedia.org/wiki/Brushless_DC_electric_motor

    They are quite common, have high torque, and are very efficient even with power ratings of a few watts or less. It is also common practice to use a controller rated at more current than the motor, as the motor will draw what it needs. If the controller is rated at less current than the motor, then the controller burns up.

    The OP is correct about the two wires for power. Three wires, usually similar heavy gauge and color coded, go to the motor. Three other three lighter gauge wires go to the RC receiver or servo controller. They are normally black or brown (negative); red (positive), and yellow or white (signal). If it is a 3-wire ribbon, the center is usually the positive.

    John
     
  18. braindead

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    May 12, 2010
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    Correct me if I am wrong, been a while since I worked with elementary physics.

    But it is rather pointless to compare torques, right? What matters must be the radial power produced? I mean torque can always be increased using gears and such, but the radial power is what stays constant for a motor (not counting any speed control of the motor).

    So I assumed something like needing 50 N @ 8 cm @ 30-100 rpm.

    The 8 cm is the radius of my flywheel, and I need the force at the edge of it, so I get a rotation of (2*8)*pi about 0.5 m. And one revolution is as fast as about 0.5 seconds so it is in essence P = F*a/t = 50*0.5/0.5 = 50 Watts.

    Is this correct?
     
  19. jpanhalt

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    Going back to your original question, which I felt had not been answered, as the discussion seemed to be turning to something quite different from the small BLDC hobby motor you have:
    I addressed the controller inputs (power and servo) and outputs.

    As mentioned, that is the rating of the controller. Match your power source to the motor. Your motor apparently does not require anywhere near 30A. A power supply from a computer should be more than enough. Be sure the controller is rated for 12V input.

    I hope that has been accomplished. My comment about torque was used loosely in the sense that motors are often described as having good torque or poor torque at the low end of their controllable speed range.

    John
     
  20. braindead

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    May 12, 2010
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    Hi John, Yea the discussion has been steering away. I guess the focus must shift since obviously this small little BLDC is nowhere near what I require, operating even at its maximum, and furthermore with the heat-issues mentioned previously makes it utterly useless for anything but some low-end cheap helis.

    I am currently looking into more powerful motors, something in the range of 6-60 Watts I guess. I will correct my previous calculations of what kind of power I need.

    Somewhere around 20 cm about 60 to 180 times per minute. And I will down-spec the amount of force to say 40 N instead. So I get a maximum of 0.6 m/s and thus P = 0.6*40 = 24 Watt. So a motor rated with radial or axial power of 25 Watt should be ok right? Or is there something else I must consider?
     
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