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Driving Phantom 2 2212 motor with Analog circuit

Discussion in 'General Discussion' started by fimbulvetr, Dec 2, 2014.

  1. fimbulvetr

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    Hi all,
    So I'm trying to build a simple quadcopter that uses an analog circuit to balance the copter in the air, as part of an analog electronics course. As part of this project we bought replacement motors for the Phantom 2, specifically the 2212 motors with 920 kv. While we have been able to generate the 3phase wave needed to drive the motor, it does not respond to our signal. My guess is we need to run more current through the motor, so we will be getting power opamps soon to supply up to 3 amps, but if anyone has specific details on what voltages or currents we need to drive the motor, I would really appreciate it. Thanks.
     
  2. noiseboy72

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    You will need closer to 6 amps with a 20 amp peak and stall. Frequency is crucial as well, but I assume you have some sort of PLL to power your inverter?

    Interesting project though, would love to hear more details.
     
  3. fimbulvetr

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  4. CityZen

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    Normally, the motor is powered by an electronic speed controller that actually has a little microprocessor on it. The ESC takes in the 11.1V (nominal) from the battery and provides a pulsed drive for the 3 motor coils. While driving 2 of the coils, it is looking for feedback on the 3rd coil to see how quickly the motor is turning. Together with the PWM signal from the flight controller, it uses this info to determine the timing of the drive pulses.

    You can drive the motor without this feedback, but it might not always behave as well as expected if you try to vary the speed too quickly.

    To see the circuit that's on the Phantom 2 ESC, see here http://www.rcgroups.com/forums/showthread.php?t=2264946

    Each ESC is spec-ed to drive up to 18A, I believe.
     
  5. noiseboy72

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    yeah....
    Not sure that will work for you. You need to monitor the motor speed by some method. I used to work on high speed tape duplicators (Showing my age!!) and we used a hall effect sensor and magnet to detect rpm. This was then part of the PLL to control rotational speed.

    I think your circuit will be too simplistic to give you the speed control that your require. The ESC on the Phantom applies braking as well as increase in motor speeds to give better control resolution. I think the best you will achieve will be getting the motors to run at the same speed.

    You will need at least 6A per motor, with a current capacity of 20A peak as a minimum.
     
  6. fimbulvetr

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    Thank you all so much for your feedback. It looks like the best course of action would be to buy a proper battery and ESC set, and then have it controlled by our analog circuit. What exactly is the throttle input for the ESC? Is it a voltage range? or a PWM signal? Or something else?
     
  7. CityZen

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    PWM. Look at the link I mentioned above; talks all about it.
     
  8. fimbulvetr

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    Ah yes sorry I did not read it fully. Thanks a lot!
     
  9. PhantomFanatic

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    I agree with what has been posted. In the 'old' days, everything was analog and varying voltage was used to control DC motors. But, in the digital age, pulsed voltage can control motor speed much more efficiently. The ESC accomplishes a lot of that, but even it is controlled digitally with Pulse Width Modulation.

    Welcome to the forum!!
     
  10. fimbulvetr

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    One last question, will I need some sort of control over the battery? Or will the ESC handle that, since they can be set to turn off below a certain voltage.
     
  11. noiseboy72

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    Using Lipos, you would be best to fit a low voltage detector - cheap to buy, easy to build, to give the pilot early warning of the battery life and allow them time to land. This is not a function of the ESC and in fact, most R/C aircraft have no warning at all, you just either fit your own or learn to tell when the power is dropping and it is time to land.

    Don't use the "smart" battery, just use ordinary 3S lipos. You will need the specific charger, unless your are very confident to build your own!. This will need to output about 12.5V @ 3A, with individual cell monitoring and balancing during charging.
     
  12. fimbulvetr

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  13. noiseboy72

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    Yep, that will work. Have a look online, as you can get higher capacity batteries for longer flight time.