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speed control problem for helicopter

Discussion in 'General Electronics Discussion' started by cathal, Dec 15, 2014.

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  1. cathal

    cathal

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    Nov 23, 2014
    Hi!
    For my masters thesis i have to develop a scaled helicopter test bench. The helicopter I use is a RC helicopter. It gets it's power from a power supply which produces a DC current. After the supply there's an electronic speed controller, which uses PWM to produce a current that produces a specific rotor speed.

    The problem I now have is that when i increase the angle of attack of the helicopter blades, so the load on the motor. The rotor speed decreases. I have to find a way to keep the correct rotor speed, but i have no clue how to do that.

    extra information: the esc is coupled to a servo system which should keep the rotor speed constant. But this servo obviously fails.

    Does anyone have an idea what I could do?

    thanks in advance

    Cathal
     
  2. BobK

    BobK

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    Jan 5, 2010
    You need feedback of the rotor speed to control the PWM signal. A rotary encoder of some kind or a hall effect sensor is typically used to do this. The sensor will produce N pulse per rotation. Then what you have to do is count these to get the speed (or more likely the time between pulses), and correct the PWM output to keep it constant.

    Bob
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    As you say, the servo system is failing to keep the motor speed constant. Do you have any information on the servo system?
     
  4. cathal

    cathal

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    Nov 23, 2014
    Hi!
    Thanks for the quick replies!
    First about the servo: I was wrong that the servo controlls the rotor speed. I was confused because the FBL (flybarlles control system) has 3 servo's to control the direction of the heli. The FBL system also controls the throttle (thus rotorspeed) but there's no feetback from the rotor, so it's not a servo system.

    second I understand the suggestion of bobk. would it work if I mount a magnet tot the rotor axis and install a hall sensor. I could then use an arduino to count the pulses. The only problem left, is adjusting the speed. Now the speed is controlled by the esc:
    [​IMG]

    how could I make the ESC adapt to the measured speed?

    edit: would it work if I use a servo motor and connect it to the esc?
     
    Last edited: Dec 15, 2014
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    When descrete components were used in electronics, it might have been possible to adapt different circuitry.
    These days with miniature circuitry, almost impossible to "tap into and change".
    Think you need to get a better understanding of what you are trying to achieve as it appears you are in way over your head.
     
  6. BobK

    BobK

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    Jan 5, 2010
    ESC (engine speed controller?)

    There must be some input to the ESC that determines the duty cycle of the PWM out. That is where you would intervene.

    Bob
     
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